Science.gov

Sample records for atmospheric boundary layer

  1. The Atmospheric Boundary Layer

    ERIC Educational Resources Information Center

    Tennekes, Hendrik

    1974-01-01

    Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

  2. The atmospheric boundary layer

    SciTech Connect

    Garratt, J.R.

    1992-01-01

    This book is aimed at researchers in the atmospheric and associated sciences who require a moderately advanced text on the Atmospheric Boundary Layer (ABL) in which the many links between turbulence, air-surface transfer, boundary-layer structure and dynamics, and numerical modeling are discussed and elaborated upon. Chapter 1 serves as an introduction, with Chapters 2 and 3 dealing with the development of mean and turbulence equations, and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modelling of the ABL is crucially dependent for its realism on the surface boundary conditions, and Chapters 4 and 5 deal with aerodynamic and energy considerations, with attention to both dry and wet land surfaces and the sea. The structure of the clear-sky, thermally stratified ABL is treated in Chapter 6, including the convective and stable cases over homogeneous land, the marine ABL and the internal boundary layer at the coastline. Chapter 7 then extends the discussion to the cloudy ABL. This is seen as particularly relevant since the extensive stratocumulus regions over the sub-tropical oceans and stratus regions over the Arctic are now identified as key players in the climate system. Finally, Chapters 8 and 9 bring much of the book's material together in a discussion of appropriate ABL and surface parameterization schemes for the general circulation models of the atmosphere that are being used for climate simulation.

  3. Atmospheric boundary layer over steep surface waves

    NASA Astrophysics Data System (ADS)

    Troitskaya, Yuliya; Sergeev, Daniil A.; Druzhinin, Oleg; Kandaurov, Alexander A.; Ermakova, Olga S.; Ezhova, Ekaterina V.; Esau, Igor; Zilitinkevich, Sergej

    2014-08-01

    Turbulent air-sea interactions coupled with the surface wave dynamics remain a challenging problem. The needs to include this kind of interaction into the coupled environmental, weather and climate models motivate the development of a simplified approximation of the complex and strongly nonlinear interaction processes. This study proposes a quasi-linear model of wind-wave coupling. It formulates the approach and derives the model equations. The model is verified through a set of laboratory (direct measurements of an airflow by the particle image velocimetry (PIV) technique) and numerical (a direct numerical simulation (DNS) technique) experiments. The experiments support the central model assumption that the flow velocity field averaged over an ensemble of turbulent fluctuations is smooth and does not demonstrate flow separation from the crests of the waves. The proposed quasi-linear model correctly recovers the measured characteristics of the turbulent boundary layer over the waved water surface.

  4. Lower Atmospheric Boundary Layer Experiment (LABLE) Final Campaign Report

    SciTech Connect

    Klein, P; Bonin, TA; Newman, JF; Turner, DD; Chilson, P; Blumberg, WG; Mishra, S; Wainwright, CE; Carney, M; Jacobsen, EP; Wharton, S

    2015-11-01

    The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was designed as a multi-phase, low-cost collaboration among the University of Oklahoma, the National Severe Storms Laboratory, Lawrence Livermore National Laboratory, and the ARM program. A unique aspect was the role of graduate students in LABLE. They served as principal investigators and took the lead in designing and conducting experiments using different sampling strategies to best resolve boundary-layer phenomena.

  5. Turbulence and diffusion in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Baskett, Ronald L.

    1990-05-01

    This conference addressed recent theoretical advancements of turbulence and diffusion in the atmospheric boundary layer (ABL). Activities were centered on the technical sessions of the conference. Sessions addressed clouds and the marine atmospheric boundary layer, field experimental techniques, physical and numerical simulations, transport and diffusion, surface properties, general boundary layer, stratified turbulence and turbulence in complex terrain. A jointly authored poster on an evaluation of the ARAC emergency response models with and without on-site sound detection and ranging systems (sodars) which measure vertical wind profiles was presented. Several scientists commented on our work and some requested further information. In addition, there was a workshop on dispersion around groups of buildings and a tour of Riso National Laboratory. Developments relevant to our work included work on dispersion model evaluation, especially using Monte Carlo random walk techniques, parameterizations of mixing height and turbulence from remote sensing systems such as sodars and radars, and measurements and parameterizations of enhanced turbulence around groups of buildings.

  6. Atmospheric boundary layer processes during a total solar eclipse

    SciTech Connect

    SethuRaman, S.; Prabhu, A.; Narahari Rao, K.; Narasimha, R.

    1980-01-01

    The total solar eclipse that occurred over the southern part of India on February 16, 1980, gave a unique opportunity to study the earth's atmospheric boundary layer. The meteorological experiments during the 1980 solar eclipse were conducted at Raichur, India (16/sup 0/12'N, 77/sup 0/21'E) located in the state of Karnataka, approximately 400-m above sea level. The main objective was to determine the changes in the earth's atmosphere during and immediately after the eclipse. The goal was to study the changes in the momentum and heat fluxes in the boundary layer due to the eclipse. Measurements were made for 2 days prior to and 1 day after the day of the eclipse to determine background characteristics of the boundary layer which might be site-dependent.

  7. Atmospheric boundary layer evening transitions over West Texas

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A systemic analysis of the atmospheric boundary layer behavior during some evening transitions over West Texas was done using the data from an extensive array of instruments which included small and large aperture scintillometers, net radiometers, and meteorological stations. The analysis also comp...

  8. ATMOSPHERIC DISPERSION IN THE ARCTIC: WINTERTIME BOUNDARY-LAYER MEASUREMENTS

    EPA Science Inventory

    The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...

  9. Regional scale evaporation and the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Parlange, Marc B.; Eichinger, William E.; Albertson, John D.

    1995-01-01

    In this review we briefly summarize some current models of evaporation and the atmospheric boundary layer (ABL) and discuss new experimental and computational oppurtunities that may aid our understanding of evaporation at these larger scales. In particular, consideration is given to remote sensing of the atmosphere, computational fluid dynamics and the role numerical models can play in understanding land-atmosphere interactions. These powerful modeling and measurement tools are allowing us to visualize and study spatial and temporal scales previously untouched, thereby increasing the oppurtunities to improve our understanding of land-atmosphere interaction.

  10. Particle motion in atmospheric boundary layers of Mars and Earth

    NASA Technical Reports Server (NTRS)

    White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

    1975-01-01

    To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.

  11. Wind Tunnel Simulation of the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hohman, Tristen; Smits, Alexander; Martinelli, Luigi

    2013-11-01

    To simulate the interaction of large Vertical Axis Wind Turbines (VAWT) with the Atmospheric Boundary Layer (ABL) in the laboratory, we implement a variant of Counihan's technique [Counihan 1969] in which a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements is used to create an artificial ABL profile in a standard closed loop wind tunnel. To examine the development and formation of the artificial ABL hotwire and SPIV measurements were taken at various downstream locations with changes in wall roughness, wall type, and vortex generator arrangements. It was found possible to generate a boundary layer at Reθ ~106 , with a mean velocity that followed the 1/7 power law of a neutral ABL over rural terrain and longitudinal turbulence intensities and power spectra that compare well with the data obtained for high Reynolds number flat plate turbulent boundary layers [Hultmark et al. 2010]. Supported by Hopewell Wind Power Ltd., and the Princeton Grand Challenges Program.

  12. Wind Tunnel Simulation of the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hohman, Tristen; Smits, Alexander; Martinelli, Luigi

    2012-11-01

    To simulate the interaction of large Vertical Axis Wind Turbines (VAWT) with the Atmospheric Boundary Layer (ABL) in the laboratory, we implement a variant of Counihan's technique in which a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements is used to create an artificial ABL profile in a standard closed loop wind tunnel. We report hotwire measurements in a plane normal to the flow direction at various downstream positions and free stream velocities to examine the development and formation of the artificial ABL. It was found possible to generate a boundary layer at Reθ ~106 , with a mean velocity that followed the 1/7 power law of a neutral ABL over rural terrain and longitudinal turbulence intensities and power spectra that compare well with the data obtained by Hultmark in 2010 for high Reynolds number flat plate turbulent boundary layers. Supported by Hopewell Wind Power Ltd., and the Princeton Grand Challenges Program.

  13. Atmospheric Boundary-Layer Dynamics with Constant Bowen Ratio

    NASA Astrophysics Data System (ADS)

    Porporato, Amilcare

    2009-08-01

    Motivated by the observation that the diurnal evolution of sensible and latent heat fluxes tends to maintain a constant Bowen ratio, we derive approximate solutions of the ordinary differential equations of a simplified atmospheric boundary-layer (ABL) model. Neglecting the early morning transition, the potential temperature and specific humidity of the mixed layer are found to be linearly related to the ABL height. Similar behaviour is followed by the inversion strengths of temperature and humidity at the top of the ABL. The potential temperature of the mixed layer depends on the entrainment parameter and the free-atmosphere temperature lapse rate, while the specific humidity also depends on the free-atmosphere humidity lapse rate and the Bowen ratio. The temporal dynamics appear only implicitly in the evolution of the height of the boundary layer, which in turn depends on the time-integrated surface sensible heat flux. Studying the limiting behaviour of the Bowen ratio for very low and very large values of net available energy, we also show how the tendency to maintain constant Bowen ratio during midday hours stems from its relative insensitivity to the atmospheric conditions for large values of net available energy. The analytical expression for the diurnal evolution of the ABL obtained with constant Bowen ratio is simple and provides a benchmark for the results of more complex models.

  14. Finite-element numerical modeling of atmospheric turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Lee, H. N.; Kao, S. K.

    1979-01-01

    A dynamic turbulent boundary-layer model in the neutral atmosphere is constructed, using a dynamic turbulent equation of the eddy viscosity coefficient for momentum derived from the relationship among the turbulent dissipation rate, the turbulent kinetic energy and the eddy viscosity coefficient, with aid of the turbulent second-order closure scheme. A finite-element technique was used for the numerical integration. In preliminary results, the behavior of the neutral planetary boundary layer agrees well with the available data and with the existing elaborate turbulent models, using a finite-difference scheme. The proposed dynamic formulation of the eddy viscosity coefficient for momentum is particularly attractive and can provide a viable alternative approach to study atmospheric turbulence, diffusion and air pollution.

  15. Effects of mesoscale surface inhomogeneities on atmospheric boundary layer transfer

    SciTech Connect

    Shaw, W.J.; Doran, J.C.; Hubbe, J.M.

    1992-09-01

    Defining the nature of turbulent transfer over horizontally inhomogeneous surfaces remains one of the challenges in meteorology. Because the transfer of energy and momentum through the atmospheric boundary layer forms part of the lower boundary condition for global climate models (GCMs), the problem is important. Over the last two decades, advances in sensor and computer technology wave made good point measurements of turbulent fluxes fairly routine. A fundamental question with respect to climate models, however, is how such point measurements are related to average fluxes over the area of a GCM grid box. In this paper we will use data from the field program to depict the evolution of the boundary layer over adjacent, sharply contrasting surface types on two separate occasions. We will then use simple scaling based on the observations to argue that sub-gridscale motions would often be likely to significantly alter the estimates and resulting parameterizations of GCM-scale surface fluxes in the region.

  16. Behaviour of Atmospheric Boundary Layer Height at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Pietroni, I.; Argentini, S.

    2009-09-01

    The Antarctic Atmospheric Boundary Layer presents characteristics which are substantially different from the mid-latitudes ABLs. On the Antarctic plateau two different extreme situations are observed. During the summer a mixing height develops during the warmer hours of the day although the sensible heat flux is reduced compared to that at mid-latitudes. During the winter a long lived stable boundary layer is continuously present, the residual layer is never observed, consequently the inversion layer is connected at the free atmosphere. To understand the stable ABL process the STABLEDC (Study of the STAble Boundary Layer Environmental at Dome C) experimental field was held at Concordia, the French Italian plateau station at Dome C, during 2005. In the same period the RMO (Routine Measurements Observations) started. The data included turbulence data at the surface, temperature profiles by a microwave profiler (MTP-5P), a mini-sodar and radio-soundings. In this work we will show the results of a comparison of the ABL height at Concordia (3233 m a.s.l) during the summer and the winter using direct measurements and parameterization. The winter ABL height was estimated directly using experimental data (radio-soundings and radiometer temperature and wind velocity profiles) and different methods proposed in literature. The stable ABL height was also estimated using the formulation proposed by Zilitinkevich et al. (2007) for the long-lived stable boundary layer. The correlation of ABL height with the temperature and wind speed is also shown. The summer mixing height was instead estimated by mini-sodar data and compared with the height given by the model suggested by Batchvarova and Gryning (1991) which use as input the turbulence data.

  17. The Saharan atmospheric boundary layer: Turbulence, stratification and mixing

    NASA Astrophysics Data System (ADS)

    Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.

    2013-04-01

    High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (≤1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer

  18. Atmospheric surface and boundary layers of the Amazon Basin

    NASA Technical Reports Server (NTRS)

    Garstang, Michael

    1987-01-01

    Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.

  19. Problems in the simulation of atmospheric boundary layer flows. [natural wind environment in atmospheric boundary layer for aerospace and aeronautical applications

    NASA Technical Reports Server (NTRS)

    Fichtl, G. H.

    1973-01-01

    The realistic simulation of flow in the atmospheric boundary layers at heights greater than two kilometers is discussed. Information concerning horizontally homogeneous and statistically stationary atmospheric boundary layer flows is presented. The problems related to the incorporation of the information into atmospheric wind simulation programs are analyzed. The information which the meteorologist must acquire in order to provide a basis for improving the simulation of atmospheric boundary flows is explained.

  20. Methods for determining the height of the atmospheric boundary layer

    SciTech Connect

    Sugiyama, Gayle; Nasstrom, John S.

    1999-02-01

    The Atmospheric Release Advisory Capability (ARAC) is an operational emergency response program which provides real-time dose assessments of airborne pollutant releases. This report reviews methodologies for determining the height of the atmospheric boundary layer (ABL), which were investigated for use in the next generation of ARAC diagnostic and dispersion models. The ABL height, hABL, is an essential parameter in atmospheric dispersion modeling, controlling the extent of the vertical mixing of pollutants near the surface. Although eventually instrumentation (radiosonde, lidar, sodar, etc.) may provide accurate means for determining hABL, at present the availability of such data is too limited to provide a general capability for ARAC. The current operational ARAC diagnostic models use a fixed value of hABL for any given time. ARAC's new models support a horizontally-varying atmospheric boundary layer height, which is used to generate meteorological (mean wind, temperature, etc.) and turbulence fields. The purpose of the present work is to develop methods to derive the ABL height for all atmospheric stability regimes. One of our key requirements is to provide approaches which are applicable to routinely available data, which may be of limited temporal and spatial resolution. The final objective is to generate a consistent set of meteorological and turbulence or eddy diffusivity fields to drive the new ARAC dispersion model. A number of alternative definitions of the atmospheric boundary layer exist, leading to different approaches to deriving hABL. The definitions are based on either the turbulence characteristics of the atmosphere or the vertical structure of one or more meteorological variables. Most diagnostic analyses determine hABL from profiles of temperature or occasionally wind. A class of methods of considerable current interest are based on Richardson number criteria. Prognostic methods calculate the

  1. Interaction between the atmospheric and oceanic boundary layers

    NASA Technical Reports Server (NTRS)

    Yeh, G.-T.

    1974-01-01

    The two-layer system of an atmosphere over water bodies is reduced to a single-layer problem. Values of the interfacial quantities, such as the friction velocity, the surface velocity, the angles, alpha and beta, between the surface shear stress and the geostrophic wind velocity and the surface wind velocity, respectively, and the surface roughness, all of which depend upon external parameters, such as the geostrophic wind and stratifications, are obtained. The geostrophic drag coefficient, the geostrophic wind coefficient, and the angles alpha, and beta, of the turbulent flow at the sea-air interface are functions of a dimensionless number, mfG/kg, with S sub 1 and S sub 2 as two free stratification parameters. The surface roughness is uniquely determined from the geostrophic wind rather than from the wind profile in the boundary layer.

  2. Turbulent flux events in a nearly neutral atmospheric boundary layer.

    PubMed

    Narasimha, Roddam; Kumar, S Rudra; Prabhu, A; Kailas, S V

    2007-03-15

    We propose here a novel method of analysing turbulent momentum flux signals. The data for the analysis come from a nearly neutral atmospheric boundary layer and are taken at a height of 4m above ground corresponding to 1.1 x 10(5) wall units, within the log layer for the mean velocity. The method of analysis involves examining the instantaneous flux profiles that exceed a given threshold, for which an optimum value is found to be 1 s.d. of the flux signal. It is found feasible to identify normalized flux variation signatures separately for positive and negative 'flux events'-the sign being determined by that of the flux itself. Using these signatures, the flux signal is transformed to one of events characterized by the time of occurrence, duration and intensity. It is also found that both the average duration and the average time-interval between successive events are of order 1s, about four orders of magnitude higher than a wall unit in time. This episodic description of the turbulence flux in the time domain enables us to identify separately productive, counter-productive and idle periods (accounting, respectively, for 36, 15 and 49% of the time), taking as criterion the generation of the momentum flux. A 'burstiness' index of 0.72 is found for the data. Comparison with laboratory data indicates higher (/lower) ejection (/sweep) quadrant occupancy but lower (/higher) contributions to flux from the ejection (/sweep) quadrant at the high Reynolds numbers of the atmospheric boundary layer. Possible connections with the concept of active and passive motion in a turbulent boundary layer are briefly discussed. PMID:17244581

  3. Segregation in the Atmospheric Boundary Layer - A Discussion

    NASA Astrophysics Data System (ADS)

    Dlugi, Ralph; Berger, Martina; Zelger, Michael; Hofzumahaus, Andreas; Rohrer, Franz; Holland, Frank; Lu, Keding; Tsokankunku, Anywhere; Sörgel, Matthias; Kramm, Gerhard; Mölders, Nicole

    2016-04-01

    Segregation is a well known topic in technical chemistry and means an incomplete mixing of the reactants. Incomplete mixing reduces the rate of reaction which is of utmost importance in technical chemistry but has been payed less attention in atmospheric chemistry. Different observational and modelling studies on chemical reactions in the turbulent and convective atmospheric boundary layer are analysed for the influences of segregation in the systems NO ‑ NO2 ‑ O3 and OH + V OCs (with main focus on isoprene). Also some estimates on reactions like HO2 + NO (an important recycling mechanism for OH) will be given. Especially, different terms of the intensity of segregation IS (correlation coefficients, standard deviations of mixing ratios) are compared and are related to characteristics of the flow regimes, such as mixing conditions and Damköhler numbers. Also influences of fluctuations of actinic fluxes are discussed which influence the mostly photo chemically driven reactions that were investigated.

  4. Vegetation-atmosphere interactions and boundary layer cumulus clouds

    NASA Astrophysics Data System (ADS)

    Freedman, Jeffrey Michael

    2000-07-01

    A study of vegetation-atmosphere interactions and boundary layer cumulus clouds (``BLcu'') in terms of seasonal trends (i.e., heat and moisture tendencies) and short-term events (specifically the modification of in situ air masses) is presented. In the northeastern U.S., in response to increasing insolation and sensible heat flux, both the mixed layer height (zi) and lifting condensation level (LCL) peak (~1300 and 1700 m) just before the start of the growing season. With the commencement of transpiration, the Bowen ratio (β) falls abruptly (from greater than 3 to less than 1) as additional moisture is transpired into the boundary layer, and zi and the LCL decrease. By late spring, boundary layer cumulus cloud frequency increases sharply, as the mixed layer approaches a new equilibrium. At Harvard Forest during 1995, afternoon net carbon uptake (Fco2 ) was 52% greater on days with boundary layer cumulus clouds than clear days. For 1996-1998, afternoon Fco2 was also enhanced, especially during dry periods. The same enhancement, albeit reduced, was observed at a northern jack pine site during the BOREAS project, despite very different phenological, hydrological, and climatological regimes. Sixteen frontal sequences affecting the northeastern U.S. were analyzed in terms of local and regional contributions to the temperature and moisture tendency equations. A composite of sequences featuring the daily appearance of BLcu indicates a diminished role for entrainment and other external forcings due to the daily occurrence of a rapid growth phase in ML diurnal evolution subsequent to day 1. From the sequence minimum (day 2) in temperature and moisture, surface flux convergence accounts for about 50% of the overall net moistening and heating of the mixed layer. Model sensitivity tests show that changes in subsidence and γ θν affect ML processes most on day 1; dining subsequent days, the rapid growth phase dominates the ML growth equation, and reduces the impact of these

  5. Nonequilibrium Behavior of the Daytime Atmospheric Boundary Layer, from LES

    NASA Astrophysics Data System (ADS)

    Jayaraman, Balaji; Brasseur, James; McCandless, Tyler; Haupt, Sue

    2014-11-01

    LES of the daytime atmospheric boundary layer (ABL) over flat topography is universally developed as an equilibrium ABL with steady surface heat flux Q0 and steady unidirectional ``geostrophic'' wind vector Vg above a capping inversion, where Vg also defines a spatially uniform transverse mean pressure gradient. The LES approaches a quasiequilibrium state characterized statistically by the ratio of boundary layer depth to Obukhov length scale. In contrast, the true daytime ABL is driven by surface heat flux increases to peak mid-day and drops in the afternoon, and by mesoscale wind vectors Ug that change in magnitude and direction during the day. We study the consequences of mesoscale weather on ABL dynamics by forcing ABL LES with a WRF simulation of the Midwest during 3 days of frontal passage over Kansas. Assuming horizontal homogeneity, we derive the relationship between Ug and Vg and study ABL response with systematic variation in Q0 and the magnitude and direction of Ug. Interesting results include: (1) asymmetry nonequilibrium diurnal response of the ABL; (2) directional changes in surface layer winds relevant to wind turbine function; and (3) changes in ABL stability state arising solely from changes in the direction of Ug. Supported by DOE. Computer resources by NSF/XSEDE.

  6. Incorporation of the planetary boundary layer in atmospheric models

    NASA Technical Reports Server (NTRS)

    Moeng, Chin-Hoh; Wyngaard, John; Pielke, Roger; Krueger, Steve

    1993-01-01

    The topics discussed include the following: perspectives on planetary boundary layer (PBL) measurements; current problems of PBL parameterization in mesoscale models; and convective cloud-PBL interactions.

  7. Turbulence in a convective marine atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Chou, S.-H.; Atlas, D.; Yeh, E.-N.

    1986-01-01

    The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found during the Air Mass Transformation Experiment (AMTEX). This implies that for a given surface heating the present case is dynamically more active. The difference is mainly due to the greater importance of wind shear in the present case. This case is closer to the roll vortex regime, whereas AMTEX observed mesoscale cellular convection which is closer to free convection. Shear generation is found to provide a significant energy source, in addition to buoyancy production, to maintain a larger normalized turbulent kinetic energy and to balance a larger normalized dissipation. The interaction between turbulent pressure and divergence (i.e., pressure scrambling) is also found to transfer energy from the vertical to the horizontal components, and is expected to be stronger in roll vortices than in m esoscale cells. The sensible heat flux is found to fit well with a linear vertical profile in a clear or subcloud planetary boundary layer (PBL), in good agreement with the results of Lenschow et al., (1980). The heat flux ratio between the PBL top and the surface, derived from the linear fitted curve, is approximately -0.14, in good agreement with that derived from the lidar data for the same case. Near the PBL top, the heat flux profiles are consistent with those of Deardoff (1979) and Deardorff et al. (1980).

  8. Ground-based lidar for atmospheric boundary layer ozone measurements.

    PubMed

    Kuang, Shi; Newchurch, Michael J; Burris, John; Liu, Xiong

    2013-05-20

    Ground-based lidars are suitable for long-term ozone monitoring as a complement to satellite and ozonesonde measurements. However, current ground-based lidars are unable to consistently measure ozone below 500 m above ground level (AGL) due to both engineering issues and high retrieval sensitivity to various measurement errors. In this paper, we present our instrument design, retrieval techniques, and preliminary results that focus on the high-temporal profiling of ozone within the atmospheric boundary layer (ABL) achieved by the addition of an inexpensive and compact mini-receiver to the previous system. For the first time, to the best of our knowledge, the lowest, consistently achievable observation height has been extended down to 125 m AGL for a ground-based ozone lidar system. Both the analysis and preliminary measurements demonstrate that this lidar measures ozone with a precision generally better than ±10% at a temporal resolution of 10 min and a vertical resolution from 150 m at the bottom of the ABL to 550 m at the top. A measurement example from summertime shows that inhomogeneous ozone aloft was affected by both surface emissions and the evolution of ABL structures. PMID:23736241

  9. Urban atmospheric boundary layer height by aerosol lidar and ceilometer

    NASA Astrophysics Data System (ADS)

    Choi, M. H.; Park, M. S.; Park, S. H.

    2014-12-01

    The characteristics of urban atmospheric boundary layer (ABL) height on January, April, July and October 2014 using the gradient method by a ceilometer with a wavelength of 910 nm and an aerosol lidar with a wavelength of 532 and 1064 nm installed at two urban sites (Gwanghwamun and Jungnang) in Korea are analyzed. The Gwanghwamun site located at urban commercial area is 10 km apart from the Jungnang site located at urban residential area. The ABL height is determined by a height with a strong gradient of vertical backscatter intensity. It is found that the ABL height at both sites show a similar pattern and has a strong diurnal variation with a steep increase at 09-12 KST with a maximum in the late afternoon. And it is not determined clearly and the correlation between the ABL height by a ceilometer and that by an aerosol lidar is relatively low in case of high PM10 concentration such as Asian dust, haze and smog. Uncertainty of ABL height is also found to be strongly affected by the weather phenomena such as rain, haze or fog.

  10. Ground-Based Lidar for Atmospheric Boundary Layer Ozone Measurements

    NASA Technical Reports Server (NTRS)

    Kuang, Shi; Newchurch, Michael J.; Burris, John; Liu, Xiong

    2013-01-01

    Ground-based lidars are suitable for long-term ozone monitoring as a complement to satellite and ozonesonde measurements. However, current ground-based lidars are unable to consistently measure ozone below 500 m above ground level (AGL) due to both engineering issues and high retrieval sensitivity to various measurement errors. In this paper, we present our instrument design, retrieval techniques, and preliminary results that focus on the high-temporal profiling of ozone within the atmospheric boundary layer (ABL) achieved by the addition of an inexpensive and compact mini-receiver to the previous system. For the first time, to the best of our knowledge, the lowest, consistently achievable observation height has been extended down to 125 m AGL for a ground-based ozone lidar system. Both the analysis and preliminary measurements demonstrate that this lidar measures ozone with a precision generally better than 10% at a temporal resolution of 10 min and a vertical resolution from 150 m at the bottom of the ABL to 550 m at the top. A measurement example from summertime shows that inhomogeneous ozone aloft was affected by both surface emissions and the evolution of ABL structures.

  11. Simultaneous profiling of the Arctic Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Mayer, S.; Jonassen, M.; Reuder, J.

    2009-04-01

    The structure of the Arctic atmospheric boundary layer (AABL) and the heat and moisture fluxes between relatively warm water and cold air above non-sea-ice-covered water (such as fjords, leads and polynyas) are of great importance for the sensitive Arctic climate system. So far, such processes are not sufficiently resolved in numerical weather prediction (NWP) and climate models. Especially for regions with complex topography as the Svalbard mountains and fjords the state and diurnal evolution of the AABL is not well known yet. Knowledge can be gained by novel and flexible measurement techniques such as the use of an unmanned aerial vehicle (UAV). An UAV can perform vertical profiles as well as horizontal surveys of the mean meteorological parameters: temperature, relative humidity, pressure and wind. A corresponding UAV called Small Unmanned Meteorological Observer (SUMO) has been developed at the Geophysical Institute at the University of Bergen in cooperation with Müller Engineering (www.pfump.org) and the Paparazzi Project (http://paparazzi.enac.fr). SUMO will be used under Arctic conditions in March/April 2009. This time the special purpose will be to send two SUMOs simultaneously on mission; one over the ice and snow-covered land surface and the other one above the open water of Isfjorden. This will be the first step of future multiple UAV operations in so called "swarms" or "flocks". With this, corresponding measurements of the diurnal evolution of the AABL can be achieved with minimum technical efforts and costs.

  12. FLUID MODELING OF ATMOSPHERIC DISPERSION IN THE CONVECTIVE BOUNDARY LAYER

    EPA Science Inventory

    Study of convective boundary layer (CBL) processes has depended largely upon laboratory analogs for many years. The pioneering work of Willis and Deardorff (1974) and some 35 subsequent papers by the same authors showed that much useful research could be accomplished with a re...

  13. Coupled groundwater-atmosphere modeling: effects on atmospheric boundary layer development

    NASA Astrophysics Data System (ADS)

    Chow, F. K.; Maxwell, R. M.; Kollet, S. J.; Daniels, M. H.; Rihani, J. F.

    2007-12-01

    Newly-developed coupled land-atmosphere models which incorporate both subsurface and atmospheric moisture dynamics have the potential to change our understanding of the hydrologic cycle. This presentation describes the effects of coupled groundwater-atmosphere modeling on simulations of the atmospheric boundary layer. Both field observations and simulations indicate strong sensitivity of atmospheric dynamics to land-surface conditions, in particular surface soil moisture. Simulations of atmospheric flow in Owens Valley (California) and in the Riviera Valley (Switzerland) show strong sensitivity to land-surface conditions, thus motivating the need for more accurate representations of soil moisture. In addition to influences from weather and seasonal changes, soil moisture dynamics respond to diurnal heat fluxes on the land surface. Using our new fully-coupled groundwater-atmosphere model, we have demonstrated correlations of soil moisture and land-surface heat fluxes with groundwater fluctuations on short, diurnal time scales. By explicitly calculating groundwater dynamics for our domain of interest, we are able to produce realistic time- and space-varying soil moisture distributions that naturally correspond to variations in topography and surface evaporation. Simulations in idealized and real watersheds are shown to illustrate these effects. The observed variations in surface moisture distribution have large impacts on the moisture and temperature structure in the atmosphere, leading to changes in boundary layer depth and convective motions as compared to standard soil moisture representations. Our coupled model framework will allow detailed investigation of the complex cycle of land-atmosphere processes affecting moisture distributions in the subsurface and the atmosphere.

  14. Simultaneous profiling of the Arctic Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Mayer, S.; Jonassen, M.; Reuder, J.

    2009-09-01

    The structure of the Arctic atmospheric boundary layer (AABL) and the heat and moisture fluxes between relatively warm water and cold air above non-sea-ice-covered water (such as fjords, leads and polynyas) are of great importance for the sensitive Arctic climate system (e.g. Andreas and Cash, 1999). So far, such processes are not sufficiently resolved in numerical weather prediction (NWP) and climate models (e.g. Tjernström et al., 2005). Especially for regions with complex topography as the Svalbard mountains and fjords the state and diurnal evolution of the AABL is not well known yet. Knowledge can be gained by novel and flexible measurement techniques such as the use of an unmanned aerial vehicle (UAV). An UAV can perform vertical profiles as well as horizontal surveys of the mean meteorological parameters: temperature, relative humidity, pressure and wind. A corresponding UAV, called Small Unmanned Meteorological Observer (SUMO), has been developed at the Geophysical Institute at the University of Bergen in cooperation with Müller Engineering (www.pfump.org) and the Paparazzi Project (http://paparazzi.enac.fr). SUMO has been used under Arctic conditions at Longyear airport, Spitsbergen in March/April 2009. Besides vertical profiles up to 1500 m and horizontal surveys at flight levels of 100 and 200 m, SUMO could measure vertical profiles for the first time simultaneously in a horizontal distance of 1 km; one over the ice and snow-covered land surface and the other one above the open water of Isfjorden. This has been the first step of future multiple UAV operations in so called "swarms” or "flocks”. With this, corresponding measurements of the diurnal evolution of the AABL can be achieved with minimum technical efforts and costs. In addition, the Advanced Research Weather Forecasting model (AR-WRF version 3.1) has been run in high resolution (grid size: 1 km). First results of a sensitivity study where ABL schemes have been tested and compared with

  15. One-dimensional simulation of temperature and moisture in atmospheric and soil boundary layers

    NASA Technical Reports Server (NTRS)

    Bornstein, R. D.; Santhanam, K.

    1981-01-01

    Meteorologists are interested in modeling the vertical flow of heat and moisture through the soil in order to better simulate the vertical and temporal variations of the atmospheric boundary layer. The one dimensional planetary boundary layer model of is modified by the addition of transport equations to be solved by a finite difference technique to predict soil moisture.

  16. Wind farm performance in conventionally neutral atmospheric boundary layers with varying inversion strengths

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2014-06-01

    In this study we consider large wind farms in a conventionally neutral atmospheric boundary layer. In large wind farms the energy extracted by the turbines is dominated by downward vertical turbulent transport of kinetic energy from the airflow above the farm. However, atmospheric boundary layers are almost always capped by an inversion layer which slows down the entrainment rate and counteracts boundary layer growth. In a suite of large eddy simulations the effect of the strength of the capping inversion on the boundary layer and on the performance of a large wind farm is investigated. For simulations with and without wind turbines the results indicate that the boundary layer growth is effectively limited by the capping inversion and that the entrainment rate depends strongly on the inversion strength. The power output of wind farms is shown to decrease for increasing inversions.

  17. Atmospheric Boundary Layer Modeling for Combined Meteorology and Air Quality Systems

    EPA Science Inventory

    Atmospheric Eulerian grid models for mesoscale and larger applications require sub-grid models for turbulent vertical exchange processes, particularly within the Planetary Boundary Layer (PSL). In combined meteorology and air quality modeling systems consistent PSL modeling of wi...

  18. Wind sensing in an atmospheric boundary layer by means of micropulse coherent Doppler lidars

    NASA Astrophysics Data System (ADS)

    Banakh, V. A.; Smalikho, I. N.

    2016-07-01

    An algorithm is developed and computer simulation of wind sensing by means of micropulse coherent Doppler lidars (CDLs) in the atmospheric boundary layer is conducted for low values of the signalto- noise (SNR) ratio. The accuracy of lidar wind measurements is studied numerically for parameters of micropulse Stream Line CDLs. Optimal parameters of the measurements and processing data obtained at low SNR, which allow reconstructing vertical profiles of the wind velocity vector with required accuracy within an entire atmospheric boundary layer, are determined.

  19. Dynamics of the atmospheric boundary layer during the 1980 total solar eclipse

    SciTech Connect

    SethuRaman, S

    1981-01-01

    An atmospheric boundary layer experiment was conducted at Raichur, India to study the variations in the surface shear stress, heat flux and the meteorological processes that take place during a total solar eclipse. Interesting results were observed regarding the evolution of the planetary boundary layer. Changes in atmospheric stability from unstable to stable to unstable were observed during different phases of the eclipse. Downward propagation of negative heat flux associated with decreasing scales of convective eddies was also observed during the eclipse.

  20. Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions

    NASA Astrophysics Data System (ADS)

    Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

    2014-05-01

    Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

  1. BIOGENIC HYDROCARBONS IN THE ATMOSPHERIC BOUNDARY LAYER: A REVIEW

    EPA Science Inventory

    Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of hydrocarbons to the atmosphere. In this manuscript, the state of the science ...

  2. Analytical damped-oscillator models for unsteady atmospheric boundary layers

    NASA Astrophysics Data System (ADS)

    Momen, Mostafa; Bou-Zeid, Elie

    2015-11-01

    Geophysical flows are dynamical systems that are evolving nonlinearly with time. Non-stationary shear and buoyancy forces are the main sources that drive the unsteadiness of such flows. However, due to their inherent complexity, most previous studies focused on steady-state conditions. In these boundary layers, the pressure gradient, buoyancy, Coriolis, and friction forces interact. The mean PDEs governing the unsteady version of the problem, which emerges when these forces are not in equilibrium, are solvable only for a limited set of forcing variability modes, and the resulting solutions are intricate and difficult to interpret. Here we derive a simpler physical model that reduces the governing RANS equations into a first-order ODE with non-constant coefficients. The origin of the non-stationarity of turbulence can be buoyant stabilization/destabilization and/or unsteady pressure gradient. The reduced model is straightforward and solvable for arbitrary turbulent viscosity variability, and it captures LES results for linearly variable buoyancy and pressure gradient pretty well. The suggested model is thus general and will be useful for elucidating some features of the diurnal cycle, for short-term wind forecast, and in meteorological applications. NSF-PDM under AGS-10266362. Simulations performed at NCAR, and Della server at Princeton University. Cooperative Institute for Climate Science, NOAA-Princeton University under NA08OAR4320752.

  3. Boundary Layer

    NASA Technical Reports Server (NTRS)

    Loitsianskii. L. G.

    1956-01-01

    The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

  4. Horton, pipe hydraulics, and the atmospheric boundary layer (The Robert E. Horton Memorial Lecture)

    NASA Technical Reports Server (NTRS)

    Brutsaert, Wilfried

    1993-01-01

    The early stages of Horton's scientific career which provided the opportunity and stimulus to delve into the origins of some contemporary concepts on the atmospheric boundary layer are reviewed. The study of Saph and Schoder provided basis for the experimental verification and validation of similarity by Blasius, Staton and Pannel, and for the subsequent developments that led to the present understanding of the turbulent boundary layer. Particular attention is given to incorporation of similarity and scaling in the analysis of turbulent flow.

  5. Observations of Wind Profile of Marine Atmosphere Boundary Layer by Shipborne Coherent Doppler Lidar

    NASA Astrophysics Data System (ADS)

    Wu, Songhua; Yin, Jiaping; Liu, Bingyi; Liu, Jintao; Zhang, Hongwei; Song, Xiaoquan; Zhang, Kailin

    2016-06-01

    Pulsed Coherent Doppler Lidar (CDL) system is so good as to prove the feasibility of the marine atmosphere boundary layer detection. A ship-mounted Coherent Doppler lidar was used to measure the wind profile and vertical velocity in the boundary layer over the Yellow sea in 2014. Furthermore, for the purpose of reducing the impact of vibration during movement and correcting the LOS velocity, the paper introduces the attitude correction algorithm and comparison results.

  6. Modeling large wind farms in conventionally neutral atmospheric boundary layers under varying initial conditions

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2014-05-01

    Atmospheric boundary layers (ABL) are frequently capped by an inversion layer limiting the entrainment rate and boundary layer growth. Commonly used analytical models state that the entrainment rate is inversely proportional to the inversion strength. The height of the inversion turns out to be a second important parameter. Conventionally neutral atmospheric boundary layers (CNBL) are ABLs with zero surface heat flux developing against a stratified free atmosphere. In this regime the inversion-filling process is merely driven by the downward heat flux at the inversion base. As a result, CNBLs are strongly dependent on the heating history of the boundary layer and strong inversions will fail to erode during the course of the day. In case of large wind farms, the power output of the farm inside a CNBL will depend on the height and strength of the inversion above the boundary layer. On the other hand, increased turbulence levels induced by wind farms may partially undermine the rigid lid effect of the capping inversion, enhance vertical entrainment of air into the farm, and increase boundary layer growth. A suite of large eddy simulations (LES) is performed to investigate the effect of the capping inversion on the conventionally neutral atmospheric boundary layer and on the wind farm performance under varying initial conditions. For these simulations our in-house pseudo-spectral LES code SP-Wind is used. The wind turbines are modelled using a non-rotating actuator disk method. In the absence of wind farms, we find that a decrease in inversion strength corresponds to a decrease in the geostrophic angle and an increase in entrainment rate and geostrophic drag. Placing the initial inversion base at higher altitudes further reduces the effect of the capping inversion on the boundary layer. The inversion can be fully neglected once it is situated above the equilibrium height that a truly neutral boundary layer would attain under the same external conditions such as

  7. Measurements and Parametrizations of the Atmospheric Boundary-Layer Height at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Pietroni, Ilaria; Argentini, Stefania; Petenko, Igor; Sozzi, Roberto

    2012-04-01

    An experimental campaign, Study of the Atmospheric Boundary Layer Environmental at Dome C, was held during 2005 at the French-Italian station of Concordia at Dome C. Ground-based remote sensors, as well as in situ instrumentation, were used during the experimental campaign. The measurements allowed the direct estimation of the polar atmospheric boundary-layer height and the test of several parametrizations for the unstable and stable boundary layers. During the months of January and February, weak convection was observed while, during the polar night, a long-lived stable boundary layer occurred continuously. Under unstable stratification the mixing-layer height was determined using the sodar backscattered echoes and potential temperature profiles. The two estimations are highly correlated, with the mixing height ranging between 30 and 350 m. A simple prognostic one-dimensional model was used to estimate the convective mixing-layer height, with the correlation coefficient between observations and model results being 0.66. The boundary-layer height under stable conditions was estimated from radiosounding profiles as the height where the critical Richardson number is reached; values between 10 and 150 m were found. A visual inspection of potential temperature profiles was also used as further confirmation of the experimental height; the results of the two methods are in good agreement. Six parametrizations from the literature for the stable boundary-layer height were tested. Only the parametrization that considers the long-lived stable boundary layer and takes into account the interaction of the stable layer with the free atmosphere is in agreement with the observations.

  8. Experimental Investigation of Soil and Atmospheric Conditions on the Momentum, Mass, and Thermal Boundary Layers Above the Land Atmosphere Interface

    NASA Astrophysics Data System (ADS)

    Trautz, A.; Smits, K. M.; Illangasekare, T. H.; Schulte, P.

    2014-12-01

    The purpose of this study is to investigate the impacts of soil conditions (i.e. soil type, saturation) and atmospheric forcings (i.e. velocity, temperature, relative humidity) on the momentum, mass, and temperature boundary layers. The atmospheric conditions tested represent those typically found in semi-arid and arid climates and the soil conditions simulate the three stages of evaporation. The data generated will help identify the importance of different soil conditions and atmospheric forcings with respect to land-atmospheric interactions which will have direct implications on future numerical studies investigating the effects of turbulent air flow on evaporation. The experimental datasets generated for this study were performed using a unique climate controlled closed-circuit wind tunnel/porous media facility located at the Center for Experimental Study of Subsurface Environmental Processes (CESEP) at the Colorado School of Mines. The test apparatus consisting of a 7.3 m long porous media tank and wind tunnel, were outfitted with a sensor network to carefully measure wind velocity, air and soil temperature, relative humidity, soil moisture, and soil air pressure. Boundary layer measurements were made between the heights of 2 and 500 mm above the soil tank under constant conditions (i.e. wind velocity, temperature, relative humidity). The soil conditions (e.g. soil type, soil moisture) were varied between datasets to analyze their impact on the boundary layers. Experimental results show that the momentum boundary layer is very sensitive to the applied atmospheric conditions and soil conditions to a much less extent. Increases in velocity above porous media leads to momentum boundary layer thinning and closely reflect classical flat plate theory. The mass and thermal boundary layers are directly dependent on both atmospheric and soil conditions. Air pressure within the soil is independent of atmospheric temperature and relative humidity - wind velocity and soil

  9. Simulation of the Atmospheric Boundary Layer for Wind Energy Applications

    NASA Astrophysics Data System (ADS)

    Marjanovic, Nikola

    Energy production from wind is an increasingly important component of overall global power generation, and will likely continue to gain an even greater share of electricity production as world governments attempt to mitigate climate change and wind energy production costs decrease. Wind energy generation depends on wind speed, which is greatly influenced by local and synoptic environmental forcings. Synoptic forcing, such as a cold frontal passage, exists on a large spatial scale while local forcing manifests itself on a much smaller scale and could result from topographic effects or land-surface heat fluxes. Synoptic forcing, if strong enough, may suppress the effects of generally weaker local forcing. At the even smaller scale of a wind farm, upstream turbines generate wakes that decrease the wind speed and increase the atmospheric turbulence at the downwind turbines, thereby reducing power production and increasing fatigue loading that may damage turbine components, respectively. Simulation of atmospheric processes that span a considerable range of spatial and temporal scales is essential to improve wind energy forecasting, wind turbine siting, turbine maintenance scheduling, and wind turbine design. Mesoscale atmospheric models predict atmospheric conditions using observed data, for a wide range of meteorological applications across scales from thousands of kilometers to hundreds of meters. Mesoscale models include parameterizations for the major atmospheric physical processes that modulate wind speed and turbulence dynamics, such as cloud evolution and surface-atmosphere interactions. The Weather Research and Forecasting (WRF) model is used in this dissertation to investigate the effects of model parameters on wind energy forecasting. WRF is used for case study simulations at two West Coast North American wind farms, one with simple and one with complex terrain, during both synoptically and locally-driven weather events. The model's performance with different

  10. An Estimation of Turbulent Kinetic Energy and Energy Dissipation Rate Based on Atmospheric Boundary Layer Similarity Theory

    NASA Technical Reports Server (NTRS)

    Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)

    2000-01-01

    Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.

  11. Simulation of the Atmospheric Boundary Layer for Wind Energy Applications

    NASA Astrophysics Data System (ADS)

    Marjanovic, Nikola

    Energy production from wind is an increasingly important component of overall global power generation, and will likely continue to gain an even greater share of electricity production as world governments attempt to mitigate climate change and wind energy production costs decrease. Wind energy generation depends on wind speed, which is greatly influenced by local and synoptic environmental forcings. Synoptic forcing, such as a cold frontal passage, exists on a large spatial scale while local forcing manifests itself on a much smaller scale and could result from topographic effects or land-surface heat fluxes. Synoptic forcing, if strong enough, may suppress the effects of generally weaker local forcing. At the even smaller scale of a wind farm, upstream turbines generate wakes that decrease the wind speed and increase the atmospheric turbulence at the downwind turbines, thereby reducing power production and increasing fatigue loading that may damage turbine components, respectively. Simulation of atmospheric processes that span a considerable range of spatial and temporal scales is essential to improve wind energy forecasting, wind turbine siting, turbine maintenance scheduling, and wind turbine design. Mesoscale atmospheric models predict atmospheric conditions using observed data, for a wide range of meteorological applications across scales from thousands of kilometers to hundreds of meters. Mesoscale models include parameterizations for the major atmospheric physical processes that modulate wind speed and turbulence dynamics, such as cloud evolution and surface-atmosphere interactions. The Weather Research and Forecasting (WRF) model is used in this dissertation to investigate the effects of model parameters on wind energy forecasting. WRF is used for case study simulations at two West Coast North American wind farms, one with simple and one with complex terrain, during both synoptically and locally-driven weather events. The model's performance with different

  12. Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon boundary layer

    NASA Technical Reports Server (NTRS)

    Zimmerman, P. R.; Greenberg, J. P.; Westberg, C. E.

    1988-01-01

    Tropospheric mixing ratios of methane, C2-C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 micrograms/sq m per day and 5600 micrograms/sq m per day, respectively. This isoprene emission is equivalent to 2 percent of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8-13 ppb for carbon monoxide in the planetary boundary layer.

  13. Temporal Dynamics of Bacterial and Fungal Community Composition in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Emerson, J. B.; Perring, A. E.; Schwarz, J. P.; Fahey, D. W.; Fierer, N.

    2014-12-01

    There is increasing evidence for significant microbial influences on atmospheric chemistry, cloud condensation, and ice nuclei concentrations, with known health impacts, yet we have a limited understanding of the types, abundances, and spatiotemporal dynamics of bacteria and fungi in the atmosphere. Here we use culture-independent molecular approaches, including targeted gene sequencing and quantitative PCR, to characterize bacterial and fungal community composition and abundance in the atmospheric boundary layer. We present results from 32 air samples, collected via vacuum filtration at 10 m and 250 m on the Boulder Atmospheric Observatory tower (Erie, CO) between November 2013 and April 2014. Samples were collected at night, and each sample was integrated over consecutive nights for approximately two weeks. Significant temporal shifts in bacterial and fungal community composition were observed over the course of the study, corresponding to changing bacterial and fungal concentrations. Within the same sampling time periods, bacterial and fungal communities from the near-surface atmosphere (10 m) were generally similar to those aloft (250 m), although coupled temporal and altitudinal effects were observed in some cases, particularly for fungi. Overall, our results indicate that bacterial and fungal communities exhibit minimal vertical stratification throughout the nocturnal atmospheric boundary layer but show a high degree of variability on two-week timescales. This study paves the way for further research into the connections between boundary layer microbiology, atmospheric dynamics, emissions, and local meteorology.

  14. A Diagnostic Diagram to Understand the Marine Atmospheric Boundary Layer at High Wind Speeds

    NASA Astrophysics Data System (ADS)

    Kettle, Anthony

    2014-05-01

    Long time series of offshore meteorological measurements in the lower marine atmospheric boundary layer show dynamical regimes and variability that are forced partly by interaction with the underlying sea surface and partly by the passage of cloud systems overhead. At low wind speeds, the dynamics and stability structure of the surface layer depend mainly on the air-sea temperature difference and the measured wind speed at a standard height. The physical processes are mostly understood and the quantified through Monin-Obukhov (MO) similarity theory. At high wind speeds different dynamical regimes become dominant. Breaking waves contribute to the atmospheric loading of sea spray and water vapor and modify the character of air-sea interaction. Downdrafts and boundary layer rolls associated with clouds at the top of the boundary layer impact vertical heat and momentum fluxes. Data from offshore meteorological monitoring sites will typically show different behavior and the regime shifts depending on the local winds and synoptic conditions. However, the regular methods to interpret time series through spectral analysis give only a partial view of dynamics in the atmospheric boundary layer. Also, the spectral methods have limited use for boundary layer and mesoscale modellers whose geophysical diagnostics are mostly anchored in directly measurable quantities: wind speed, temperature, precipitation, pressure, and radiation. Of these, wind speed and the air-sea temperature difference are the most important factors that characterize the dynamics of the lower atmospheric boundary layer and they provide a dynamical and thermodynamic constraint to frame observed processes, especially at high wind speeds. This was recognized in the early interpretation of the Froya database of gale force coastal winds from mid-Norway (Andersen, O.J. and J. Lovseth, Gale force maritime wind. The Froya data base. Part 1: Sites and instrumentation. Review of the data base, Journal of Wind

  15. Dynamic Turbulence Modelling in Large-eddy Simulations of the Cloud-topped Atmospheric Boundary Layer

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, M. P.; Mansour, N. N.; Ackerman, A. S.; Stevens, D. E.

    2003-01-01

    The use of large eddy simulation, or LES, to study the atmospheric boundary layer dates back to the early 1970s when Deardor (1972) used a three-dimensional simulation to determine velocity and temperature scales in the convective boundary layer. In 1974 he applied LES to the problem of mixing layer entrainment (Deardor 1974) and in 1980 to the cloud-topped boundary layer (Deardor 1980b). Since that time the LES approach has been applied to atmospheric boundary layer problems by numerous authors. While LES has been shown to be relatively robust for simple cases such as a clear, convective boundary layer (Mason 1989), simulation of the cloud-topped boundary layer has proved more of a challenge. The combination of small length scales and anisotropic turbulence coupled with cloud microphysics and radiation effects places a heavy burden on the turbulence model, especially in the cloud-top region. Consequently, over the past few decades considerable effort has been devoted to developing turbulence models that are better able to parameterize these processes. Much of this work has involved taking parameterizations developed for neutral boundary layers and deriving corrections to account for buoyancy effects associated with the background stratification and local buoyancy sources due to radiative and latent heat transfer within the cloud (see Lilly 1962; Deardor 1980a; Mason 1989; MacVean & Mason 1990, for example). In this paper we hope to contribute to this effort by presenting a number of turbulence models in which the model coefficients are calculated dynamically during the simulation rather than being prescribed a priori.

  16. Wind Energy-Related Atmospheric Boundary Layer Large-Eddy Simulation Using OpenFOAM: Preprint

    SciTech Connect

    Churchfield, M.J.; Vijayakumar, G.; Brasseur, J.G.; Moriarty, P.J.

    2010-08-01

    This paper develops and evaluates the performance of a large-eddy simulation (LES) solver in computing the atmospheric boundary layer (ABL) over flat terrain under a variety of stability conditions, ranging from shear driven (neutral stratification) to moderately convective (unstable stratification).

  17. Pilot project of measuring and computing system for mesoscale monitoring of atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Korolkov, V. A.; Tikhomirov, A. A.; Telminov, A. E.; Komarov, A. I.; Kobzev, A. A.

    2015-11-01

    Conception of design of measuring and computing system for monitoring atmospheric boundary layer is proposed. The system includes: stationary measuring complex consisting of four multiple-elevation ultrasonic weather stations and mobile measuring complex consisting of transportable weather station, touch probing system of weather data profile based on unmanned aerial vehicle and also Raman scattering gas analyzer, and new modification mercury gas analyzer.

  18. Regional-scale evaluation of a land surface scheme from atmospheric boundary layer observations

    NASA Astrophysics Data System (ADS)

    Noilhan, J.; Donier, S.; LacarrèRe, P.; Sarrat, C.; Le Moigne, P.

    2011-01-01

    The study describes an evaluation of three configurations of the Interactions Soil-Biosphere-Atmosphere (ISBA) land surface scheme fully coupled with the Meso-NH mesoscale atmospheric model. The ability of the modeling system to correctly reproduce the screen-level variables as well as the boundary layer characteristics is examined for more than 30 clear convective days monitored during the CERES 2005 and 2007 field campaigns. For the horizontal resolution considered (8 km), this study shows that the boundary layer characteristics and the low-level variables are better simulated when the subgrid-scale surface process variability is simulated explicitly using the so-called "tiling method." An additional improvement is brought when the CO2 diurnal cycle is used interactively because of the physical link between the stomatal conductance used both for CO2 assimilation and plant transpiration. The parameterization of this link between CO2 and evaporation fluxes improves the simulation of the Bowen ratio and therefore of the atmospheric boundary layer. The last part of the paper discusses the realism of the simulated regional field of CO2 when the carbon configuration is activated in the mesoscale model. Large regional variability of CO2 within the atmospheric boundary layer is found in response to the spatial and seasonal variability of CO2 surface fluxes with respect to the three main land covers in the area: pine forest, extensive winter (wheat), and summer (maize) crops.

  19. Approximate analytical solution to diurnal atmospheric boundary-layer growth under well-watered conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The system of governing equations of a simplified slab model of the uniformly-mixed, purely convective, diurnal atmospheric boundary layer (ABL) is shown to allow immediate solutions for the potential temperature and specific humidity as functions of the ABL height and net radiation when expressed i...

  20. Physical modeling of the atmospheric boundary layer for wind energy and wind engineering studies

    NASA Astrophysics Data System (ADS)

    Taylor-Power, Gregory; Turner, John; Wosnik, Martin

    2015-11-01

    The Flow Physics Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPF's ability to experimentally simulate different types of the atmospheric boundary layer (ABL): the stable, unstable, and neutral ABL. The neutral ABL is characterized by a zero potential temperature gradient, which is readily achieved in the FPF by operating when air and floor temperatures are close to equal. The stable and unstable ABLs have positive and negative vertical temperature gradients, respectively, which are more difficult to simulate without direct control of air or test section floor temperature. The test section floor is a 10 inch thick concrete cement slab and has significant thermal mass. When combined with the diurnal temperature variation of the ambient air, it is possible to achieve vertical temperature gradients in the test section, and produce weakly stable or weakly unstable boundary layer. Achievable Richardson numbers and Obukhov lengths are estimated. The different boundary layer profiles were measured, and compared to theoretical atmospheric models. Supported by UNH Hamel Center for Undergraduate Research SURF.

  1. Effects of turbulent dispersion of atmospheric balance motions of planetary boundary layer

    NASA Astrophysics Data System (ADS)

    Liu, Shikuo; Huang, Wei; Rong, Pingping

    1992-06-01

    New Reynolds’ mean momentum equations including both turbulent viscosity and dispersion are used to analyze atmospheric balance motions of the planetary boundary layer. It is pointed out that turbulent dispersion with γ 0 will increase depth of Ekman layer, reduce wind velocity in Ekman layer and produce a more satisfactory Ekman spiral lines fit the observed wind hodograph. The wind profile in the surface layer including turbulent dispersion is still logarithmic but the von Karman constant k is replaced by k 1 = √ 1 — k/2, the wind increases a little more rapidly with height.

  2. LABLE: A multi-institutional, student-led, atmospheric boundary layer experiment

    SciTech Connect

    Klein, P.; Bonin, T. A.; Newman, J. F.; Turner, D. D.; Chilson, P. B.; Wainwright, C. E.; Blumberg, W. G.; Mishra, S.; Carney, M.; Jacobsen, E. P.; Wharton, Sonia; Newsom, Rob K.

    2015-10-23

    This paper presents an overview of the Lower Atmospheric Boundary Layer Experiment (LABLE), which included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was conducted as a collaborative effort between the University of Oklahoma (OU), the National Severe Storms Laboratory, Lawrence Livermore National Laboratory (LLNL), and the ARM program. LABLE can be considered unique in that it was designed as a multi-phase, low-cost, multi-agency collaboration. Graduate students served as principal investigators and took the lead in designing and conducting experiments aimed at examining boundary-layer processes. The main objective of LABLE was to study turbulent phenomena in the lowest 2 km of the atmosphere over heterogeneous terrain using a variety of novel atmospheric profiling techniques. Several instruments from OU and LLNL were deployed to augment the suite of in-situ and remote sensing instruments at the ARM site. The complementary nature of the deployed instruments with respect to resolution and height coverage provides a near-complete picture of the dynamic and thermodynamic structure of the atmospheric boundary layer. This paper provides an overview of the experiment including i) instruments deployed, ii) sampling strategies, iii) parameters observed, and iv) student involvement. To illustrate these components, the presented results focus on one particular aspect of LABLE, namely the study of the nocturnal boundary layer and the formation and structure of nocturnal low-level jets. During LABLE, low-level jets were frequently observed and they often interacted with mesoscale atmospheric disturbances such as frontal passages.

  3. The structure of the convective atmospheric boundary layer as revealed by lidar and Doppler radars

    NASA Astrophysics Data System (ADS)

    Eilts, M. D.; Sundara-Rajan, A.; Doviak, R. J.

    1985-02-01

    Results on the structure of the convective atmospheric boundary layer based on the analyses of data from the instrumented NSSL-KTVY tower, airborne Doppler lidar, and ground-based Doppler radars are presented. The vertically averaged wind over the boundary layer was found to be insensitive to baroclinicity, supporting the hypothesis of Arya and Wyngaard (1975). The computed momentum flux profiles were affected by baroclinicity. Horizontal wind spectra from lidar, radar, and tower data compared well with each other both in shape and magnitude. A consistent peak found near 4 km in all the computed spectra might have been caused by horizontally symmetric cells with horizontal wavelength 4 times the boundary-layer height as shown in Kuettner (1971) for the case of weak wind shear.

  4. The structure of the convective atmospheric boundary layer as revealed by lidar and Doppler radars

    NASA Technical Reports Server (NTRS)

    Eilts, M. D.; Sundara-Rajan, A.; Doviak, R. J.

    1985-01-01

    Results on the structure of the convective atmospheric boundary layer based on the analyses of data from the instrumented NSSL-KTVY tower, airborne Doppler lidar, and ground-based Doppler radars are presented. The vertically averaged wind over the boundary layer was found to be insensitive to baroclinicity, supporting the hypothesis of Arya and Wyngaard (1975). The computed momentum flux profiles were affected by baroclinicity. Horizontal wind spectra from lidar, radar, and tower data compared well with each other both in shape and magnitude. A consistent peak found near 4 km in all the computed spectra might have been caused by horizontally symmetric cells with horizontal wavelength 4 times the boundary-layer height as shown in Kuettner (1971) for the case of weak wind shear.

  5. Tracking atmospheric boundary layer dynamics with water vapor D-excess observations

    NASA Astrophysics Data System (ADS)

    Parkes, Stephen; McCabe, Matthew; Griffiths, Alan; Wang, Lixin

    2015-04-01

    Stable isotope water vapor observations present a history of hydrological processes that have impacted on an air mass. Consequently, there is scope to improve our knowledge of how different processes impact on humidity budgets by determining the isotopic end members of these processes and combining them with in-situ water vapor measurements. These in-situ datasets are still rare and cover a limited geographical expanse, so expanding the available data can improve our ability to define isotopic end members and knowledge about atmospheric humidity dynamics. Using data collected from an intensive field campaign across a semi-arid grassland site in eastern Australia, we combine multiple methods including in-situ stable isotope observations to study humidity dynamics associated with the growth and decay of the atmospheric boundary layer and the stable nocturnal boundary layer. The deuterium-excess (D-excess) in water vapor is traditionally thought to reflect the sea surface temperature and relative humidity at the point of evaporation over the oceans. However, a number of recent studies suggest that land-atmosphere interactions are also important in setting the D-excess of water vapor. These studies have shown a highly robust diurnal cycle for the D-excess over a range of sites that could be exploited to better understand variations in atmospheric humidity associated with boundary layer dynamics. In this study we use surface radon concentrations as a tracer of surface layer dynamics and combine these with the D-excess observations. The radon concentrations showed an overall trend that was inversely proportional to the D-excess, with early morning entrainment of air from the residual layer of the previous day both diluting the radon concentration and increasing the D-excess, followed by accumulation of radon at the surface and a decrease in the D-excess as the stable nocturnal layer developed in the late afternoon and early evening. The stable nocturnal boundary layer

  6. Modification of the Atmospheric Boundary Layer by a Small Island: Observations from Nauru

    SciTech Connect

    Matthews, Stuart; Hacker, Jorg M.; Cole, Jason N.; Hare, Jeffrey; Long, Charles N.; Reynolds, R. M.

    2007-03-01

    Nauru, a small island in the tropical pacific, generates plumes of clouds that may grow to several hundred km length. This study uses observations to examine the mesoscale disturbance of the marine atmospheric boundary layer by the island that produces these cloud streets. Observations of the surface layer were made from two ships in the vicinity of Nauru and from instruments on the island. The structure of the atmospheric boundary layer over the island was investigated using aircraft flights. Cloud production over Nauru was examined using remote sensing instruments. During the day the island surface layer was warmer than the marine surface layer and wind speed was lower than over the ocean. Surface heating forced the growth of a thermal internal boundary layer, above which a street of cumulus clouds formed. The production of clouds resulted in reduced downwelling shortwave irradiance at the island surface. A plume of warm-dry air was observed over the island which extended 15 – 20 km downwind.

  7. Implementation of a convective atmospheric boundary layer scheme in a tropospheric chemistry transport model

    NASA Astrophysics Data System (ADS)

    Wang, K.-Y.; Pyle, J. A.; Sanderson, M. G.; Bridgeman, C.

    1999-10-01

    A convective atmospheric boundary layer (ABL) scheme for the transport of trace gases in the lower troposphere has been implemented from the Community Climate Model, Version 2 [Hack et al., 1993] into a tropospheric chemistry transport model [Wang, 1998]. The atmospheric boundary layer scheme includes the calculation of atmospheric radiative transfer, surface energy balance, and land surface temperature and has a specified annual variation of sea surface temperature. The calculated diurnal variation of the height of the boundary layer is similar to the results of Troen and Mahrt [1986] and is in a good agreement with Holtslag and Boville [1993]. The modeled height of the boundary layer shows a seasonal shift between land and sea in the Northern Hemisphere. In summer (June-July-August), the height of the boundary layer is deeper over land (850-2250 m) and shallower over sea (50-850 m); while in winter (December-January-February), it is shallower over land (50-850 m) and deeper over sea (850-2850 m). The coupled ABL-chemical transport model is verified against measurements of radon 222 and methane. Comparison of the coupled model with a non-ABL model indicates significant differences between these model simulations and a better agreement between the coupled model and measurements. There is a significant effect on the trace gas distribution when the ABL model is compared with the non-ABL schemes. For example, the ABL scheme shows more O3 transported from the middle troposphere down to the surface, while more CO is pumped up from the surface into the middle troposphere. The seasonal cycle of modeled CH4 is significantly improved with the inclusion of the new ABL scheme, especially in regions which are not remote from methane sources.

  8. Sea ice edge position impact on the atmospheric boundary layer temperature structure

    NASA Astrophysics Data System (ADS)

    Khavina, Elena; Repina, Irina

    2016-04-01

    Processes happening in the Arctic region nowadays strongly influence global climate system; the polar amplification effect can be considered one of the main indicators of ongoing changes. Dramatic increase in amount of ice-free areas in the Arctic Ocean, which took place in 2000s, is one of the most significant examples of climate system dynamic in polar region. High amplitude of changes in Arctic climate, both observed and predicted, and existing inaccuracies of climate and weather forecasting models, enforce the development of a more accurate one. It is essential to understand the physics of the interaction between atmosphere and ocean in the Northern Polar area (particularly in boundary layer of the atmosphere) to improve the models. Ice conditions have a great influence on the atmospheric boundary layer in the Arctic. Sea ice inhibits the heat exchange between atmosphere and ocean water during the polar winter, while the heat exchange above the ice-free areas increases rapidly. Due to those significant temperature fluctuations, turbulence of heat fluxes grows greatly. The most intensive interaction takes place at marginal ice zones, especially in case of the cold outbreak - intrusion of cooled air mass from the ice to free water area. Still, thermal structure and dynamic of the atmosphere boundary layer are not researched and described thoroughly enough. Single radio sounding observations from the planes being done, bur they do not provide high-resolution data which is necessary for study. This research is based on continuous atmosphere boundary layer temperature and sea ice observation collected in the Arctic Ocean during the two NABOS expeditions in August and September in 2013 and 2015, as well as on ice conditions satellite data (NASA TEAM 2 and VASIA 2 data processing). Atmosphere temperature data has been obtained with Meteorological Temperature Profiler MTP-5 (ATTEX, Russia). It is a passive radiometer, which provides continuous data of atmospheric

  9. Atmospheric Boundary-Layer Dynamics and the Constancy of the Bowen Ratio (Invited)

    NASA Astrophysics Data System (ADS)

    Porporato, A.

    2009-12-01

    The diurnal evolution of sensible and latent heat fluxes tends to maintain a constant Bowen ratio, at least for the central part of the day. Using the solutions of the ordinary differential equations of a simplified atmospheric boundary-layer (ABL) model, we find that neglecting the early morning transition the potential temperature and specific humidity of the mixed layer tend to be linearly related to the ABL height. Similar behavior is followed by the inversion strengths of temperature and humidity at the top of the ABL. The potential temperature of the mixed layer depends on the entrainment parameter and the free-atmosphere temperature lapse rate, while the specific humidity also depends on the free-atmosphere humidity lapse rate and the Bowen ratio. The temporal dynamics appear only implicitly in the evolution of the height of the boundary layer, which in turn depends on the time-integrated surface sensible heat flux. Studying the limiting behavior of the Bowen ratio for very low and very large values of net available energy, we also show how the tendency to maintain constant Bowen ratio during midday hours stems from its relative insensitivity to the atmospheric conditions for large values of net available energy. The analytical expression for the diurnal evolution of the ABL obtained with constant Bowen ratio is simple and provides a benchmark for the results of more complex models.

  10. Observed Changes in Atmospheric Boundary Layer Properties at Memphis International Airport During August 1995

    NASA Technical Reports Server (NTRS)

    Zak, J. Allen; Rodgers, William G., Jr.

    1997-01-01

    As part of the NASA Terminal Area Productivity Program, Langley Research Center embarked on a series of field measurements of wake vortex characteristics and associated atmospheric boundary layer properties. One measurement period was at the Memphis International Airport in August 1995. Atmospheric temperature, humidity, winds, turbulence, radiation, and soil properties were measured from a variety of sensor systems and platforms including sodars, profilers, aircraft and towers. This research focused on: (1) changes that occurred in tower data during sunrise and sunset transitions, (2) vertical variation of temperature and cross-head winds at selected times utilizing combinations of sensors, and (3) changes measured by an OV-10 aircraft during approaches and level flights. Significant but not unusual changes are documented and discussed in terms of expected boundary layer behavior. Questions on measurement and prediction of these changes from existing and near-term capabilities are discussed in the context of a future Aircraft Vortex Spacing System.

  11. Study of the evening transition to the nocturnal atmospheric boundary layer: statistical analysis and case studies

    NASA Astrophysics Data System (ADS)

    Sastre, Mariano; Viana, Samuel; Maqueda, Gregorio; Yagüe, Carlos

    2010-05-01

    Turbulence is probably the most important feature dealing with the diffusion of contaminants in the planetary boundary layer. The main characteristics of turbulence are governed, apart from synoptic conditions, by the daily cycle of the Earth surface heating and cooling, so that, simplifying, two configurations are often found: convective and stable. The transition from a diurnal convective boundary layer to a typically stable nocturnal one is not still well understood (Edwards, 2009). Different micrometeorological conditions at sunset or a few hours previously may be critical for the establishment of a strong surface-based stability or a weak one, even for similar synoptic conditions. This work focuses on the characterization of the evening transition which takes place at the atmospheric boundary layer, considering the temporal interval 17.00-23.00 GMT. The methodology includes looking for some relations between meteorological variables, turbulent parameters and particulate matter (PM10, PM2.5 and PM1) concentrations measured by a GRIMM particle monitor (MODEL 365). Observational data (Summer 2009) is provided from permanent instrumentation at the Research Centre for the Lower Atmosphere (CIBA) in Valladolid (Spain), which is on a quite flat terrain (Cuxart et al., 2000). A 10m height mast equipped with temperature, wind speed and direction, and moisture sensors at several levels are available. Also two sonic anemometers (20 Hz sampling rate) at 1.5 and 10m were deployed in the mast. The database is complemented by a triangle of microbarometers installed next to the surface, and another three microbarometers placed in a 100m meteorological tower at 20, 50 and 100m respectively, which are ideal to study coherent structures present in the boundary layer. Statistical parameters of meteorological variables have been calculated and studied in order to find out connections with the most relevant physical processes. Moreover different cases studies will be analyzed

  12. Modelling the atmospheric boundary layer for remotely sensed estimates of daily evaporation

    NASA Technical Reports Server (NTRS)

    Gurney, R. J.; Blyth, K.; Camillo, P. J.

    1984-01-01

    An energy and moisture balance model of the soil surface was used to estimate daily evaporation from wheat and barley fields in West Germany. The model was calibrated using remotely sensed surface temperature estimates. Complete atmospheric boundary layer models are difficult to use because of the number of parameters involved and a simplified model was used here. The resultant evaporation estimates were compared to eddy correlation evaporation estimates and good agreement was found.

  13. Temporal variation of heat and moisture flux divergence in the FIFE atmospheric boundary layer during spring

    NASA Technical Reports Server (NTRS)

    Grossman, Robert L.

    1990-01-01

    A one-day investigation of the atmospheric boundary layer (ABL) is reported in which an aircraft monitors the temporal and spatial variations of heat and moisture turbulent-flux divergences. Incoming solar radiation is similar over natural prairie land and agriculturally developed land although the heat and moisture values show significant differences over the surfaces. Other temporal variations are noted which demonstrate that ABL transport of sensible and latent heat is affected by complex variables even under simple synoptic conditions.

  14. Amendment to "Analytical Solution for the Convectively-Mixed Atmospheric Boundary Layer": Inclusion of Subsidence

    NASA Astrophysics Data System (ADS)

    Ouwersloot, H. G.; de Arellano, J. Vilà-Guerau

    2013-09-01

    In Ouwersloot and Vilà-Guerau de Arellano (Boundary-Layer Meteorol. doi: 10.1007/s10546-013-9816-z , 2013, this issue), the analytical solutions for the boundary-layer height and scalar evolutions are derived for the convective boundary layer, based on the prognostic equations of mixed-layer slab models without taking subsidence into account. Here, we include and quantify the added effect of subsidence if the subsidence velocity scales linearly with height throughout the atmosphere. This enables analytical analyses for a wider range of observational cases. As a demonstration, the sensitivity of the boundary-layer height and the potential temperature jump to subsidence and the free tropospheric stability is graphically presented. The new relations show the importance of the temporal distribution of the surface buoyancy flux in determining the evolution if there is subsidence.

  15. On the Impact of Wind Farms on a Convective Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Lu, Hao; Porté-Agel, Fernando

    2015-10-01

    With the rapid growth in the number of wind turbines installed worldwide, a demand exists for a clear understanding of how wind farms modify land-atmosphere exchanges. Here, we conduct three-dimensional large-eddy simulations to investigate the impact of wind farms on a convective atmospheric boundary layer. Surface temperature and heat flux are determined using a surface thermal energy balance approach, coupled with the solution of a three-dimensional heat equation in the soil. We study several cases of aligned and staggered wind farms with different streamwise and spanwise spacings. The farms consist of Siemens SWT-2.3-93 wind turbines. Results reveal that, in the presence of wind turbines, the stability of the atmospheric boundary layer is modified, the boundary-layer height is increased, and the magnitude of the surface heat flux is slightly reduced. Results also show an increase in land-surface temperature, a slight reduction in the vertically-integrated temperature, and a heterogeneous spatial distribution of the surface heat flux.

  16. Large-eddy simulation of an infinitely large wind farm in a stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Lu, H.; Porté-Agel, F.

    2010-09-01

    When deployed as large arrays, wind turbines interact among themselves and with atmospheric boundary layer. To optimize their geometric arrangements, accurate knowledge of wind-turbine array boundary layer is of great importance. In this study, we integrated large eddy simulation with an actuator line technique, and used it to study the characteristics of wind-turbine wake in an idealized wind farm inside a stably stratified atmospheric boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were placed in a well-known SBL turbulent case that has a boundary layer height of approximately 180m. The super-geostrophic nocturnal jet near the top of the boundary layer was eliminated due to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric behavior of wake structure was observed in response to the non-uniform incoming turbulence, the Coriolis effects, and the rotational effects induced by blade motions. The turbulence intensity in the simulated turbine wakes was found to reach a maximum at the top-tip level and a downwind distance of approximately 3-5 rotor diameters from the turbines. The Coriolis effects caused a skewed spatial structure and drove certain amount of turbulent energy away from the center of the wake. The SBL height was increased, while the magnitudes of the surface momentum flux and the surface buoyancy flux were reduced by approximately 30%. The wind farm was also found to have a strong effect on area-averaged vertical turbulent fluxes of momentum and heat, which highlights the potential impact of wind farms on local meteorology.

  17. Modelled suppression of boundary-layer clouds by plants in a CO2-rich atmosphere

    NASA Astrophysics Data System (ADS)

    Vila-Guerau Arellano, J.; Vanheerwaarden, C.; Lelieveld, J.

    2013-12-01

    We will present and discuss a conceptual modelling framework that can facilitate the understanding of the interactions between land processes and atmospheric boundary layer dynamics/chemistry at diurnal scales. This framework has been successful applied to the interpretation of field experiments, but also to identify the non-linear relations that occur at larger spatial and temporal scales. We will then discuss in depth the link between shallow cumulus and vegetation exchange of water and carbon dioxide. Cumulus clouds in the atmospheric boundary layer play a key role in the hydrologic cycle, in the onset of severe weather by thunderstorms, and in modulating the Earth's reflectivity and climate. How these clouds respond to climate change, in particular over land, and how they interact with the carbon cycle is poorly understood. It is expected that as a consequence of rising atmospheric CO2 the plant stomata will close leading to lower latent heat fluxes and higher sensible heat fluxes. During the presentation, we will show that this causes a decline in boundary layer cloud formation in middle latitudes. This could be partly counteracted by the greater ability of a warmer atmosphere to take up water and by a growth in biomass due to CO2 fertilization. Our results are based on a new soil-water-atmosphere-plant model supported by comprehensive observational evidence, from which we identify the dominant atmospheric responses to plant physiological processes. They emphasize the intricate connection between biological and physical aspects of the climate system and the relevance of short-term and small-scale processes in establishing this connection

  18. The vertical turbulence structure of the coastal marine atmospheric boundary layer

    SciTech Connect

    Tjernstroem, M.; Smedman, A.S. )

    1993-03-15

    The vertical turbulence structure in the marine atmosphere along a shoreline has been investigated using data from tower and aircraft measurements performed along the Baltic coast in the southeast of Sweden. Two properties make the Baltic Sea particularly interesting. It is surrounded by land in all directions within moderate advection distances, and it features a significant annual lag in sea surface temperature as compared with inland surface temperature. The present data were collected mostly during spring or early summer, when the water is cool, i.e., with a stably or neutrally stratified marine boundary layer usually capped by an inversion. Substantial daytime heating over the land area results in a considerable horizontal thermal contrast. Measurements were made on a small island, on a tower with a good sea fetch, and with an airborne instrument package. The profile data from the aircraft is from 25 slant soundings performed in connection to low level boundary layer flights. The results from the profiles are extracted through filtering techniques on individual time (space) series (individual profiles), applying different normalization and finally averaging over all or over groups of profiles. The land-based data are from a low tower situated on the shoreline of a small island with a wide sector of unobstructed sea fetch. Several factors are found that add to the apparent complexity of the coastal marine environment: the state of the sea appears to have a major impact on the turbulence structure of the surface layer, jet-shaped wind speed profiles were very common at the top of the boundary layer (in about 50% of the cases) and distinct layers with increased turbulence were frequently found well above the boundary layer (in about 80% of the cases). The present paper will concentrate on a description of the experiment, the analysis methods, and a general description of the boundary layer turbulence structure over the Baltic Sea. 40 refs., 16 figs., 2 tabs.

  19. A Sensitivity Analysis of the Nocturnal Boundary-Layer Properties to Atmospheric Emissivity Formulations

    NASA Astrophysics Data System (ADS)

    Siqueira, Mario B.; Katul, Gabriel G.

    2010-02-01

    A one-dimensional model for the mean potential temperature within the nocturnal boundary layer (NBL) was used to assess the sensitivity of three NBL properties (height, thermal stratification strength, and near-surface cooling) to three widely used atmospheric emissivity formulations. The calculations revealed that the NBL height is robust to the choice of the emissivity function, though this is not the case for NBL Richardson number and near-surface cooling rate. Rather than endorse one formulation, our analysis highlights the importance of atmospheric emissivity in modelling the radiative properties of the NBL especially for clear-sky conditions.

  20. Complex measurements of aerosol and ion characteristics in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kikas, Iu. E.; Kolomiets, S. M.; Kornienko, V. I.; Mirme, A. A.; Sal'm, Ia. I.; Sergeev, I. Ia.; Tammet, Kh. F.

    Results of a comprehensive study of the characteristics of atmospheric ions and aerosols in the boundary layer during the summer season are reported. A study is also made of the kinetics of aerosol formation under conditions of high artificial ionization of the air by alpha and UV radiation. A high degree of correlation is shown to exist between atmospheric concentrations of medium ions and fine (less than 0.01 micron) aerosol. The results obtained support the radiation-chemical mechanism of aerosol formation.

  1. An equilibrium model for the coupled ocean-atmosphere boundary layer in the tropics

    NASA Technical Reports Server (NTRS)

    Sui, C.-H.; Lau, K.-M.; Betts, Alan K.

    1991-01-01

    An atmospheric convective boundary layer (CBL) model is coupled to an ocean mixed-layer (OML) model in order to study the equilibrium state of the coupled system in the tropics, particularly in the Pacific region. The equilibrium state of the coupled system is solved as a function of sea-surface temperature (SST) for a given surface wind and as a function of surface wind for a given SST. It is noted that in both cases, the depth of the CBL and OML increases and the upwelling below the OML decreases, corresponding to either increasing SST or increasing surface wind. The coupled ocean-atmosphere model is solved iteratively as a function of surface wind for a fixed upwelling and a fixed OML depth, and it is observed that SST falls with increasing wind in both cases. Realistic gradients of mixed-layer depth and upwelling are observed in experiments with surface wind and SST prescribed as a function of longitude.

  2. Impact of soil water property parameterization on atmospheric boundary layer simulation

    NASA Astrophysics Data System (ADS)

    Cuenca, Richard H.; Ek, Michael; Mahrt, Larry

    1996-03-01

    Both the form of functional relationships applied for soil water properties and the natural field-scale variability of such properties can significantly impact simulation of the soil-plant-atmosphere system on a diurnal timescale. Various input parameters for soil water properties including effective saturation, residual water content, anerobiosis point, field capacity, and permanent wilting point are incorporated into functions describing soil water retention, hydraulic conductivity, diffusivity, sorptivity, and the plant sink function. The perception of the meaning of these values and their variation within a natural environment often differs from the perspective of the soil physicist, plant physiologist, and atmospheric scientist. This article investigates the sensitivity of energy balance and boundary layer simulation to different soil water property functions using the Oregon State University coupled atmosphere-plant-soil (CAPS) simulation model under bare soil conditions. The soil parameterizations tested in the CAPS model include those of Clapp and Hornberger [1978], van Genuchten [1980], and Cosby et al. [1984] using initial atmospheric conditions from June 16, 1986 in Hydrologic Atmospheric Pilot Experiment-Modélisation du Bilan Hydrique (HAPEX-MOBILHY). For the bare soil case these results demonstrate unexpected model sensitivity to soil water property parameterization in partitioning all components of the diurnal energy balance and corresponding boundary layer development.

  3. Modelled suppression of boundary-layer clouds by plants in a CO2-rich atmosphere

    NASA Astrophysics Data System (ADS)

    de Arellano, Jordi Vilà-Guerau; van Heerwaarden, Chiel C.; Lelieveld, Jos

    2012-10-01

    Cumulus clouds in the atmospheric boundary layer play a key role in the hydrologic cycle, in the onset of severe weather by thunderstorms and in modulating Earth's reflectivity and climate. How these clouds respond to climate change, in particular over land, and how they interact with the carbon cycle are poorly understood. It is expected that as a consequence of rising atmospheric CO2 concentrations the plant stomata will close, leading to lower latent heat fluxes and higher sensible heat fluxes. Here we show that this causes a decline in boundary-layer cloud formation in middle latitudes. This could be partly counteracted by the greater ability of a warmer atmosphere to take up water and by a growth in biomass due to CO2 fertilization. Our results are based on a new soil-water-atmosphere-plant model supported by comprehensive observational evidence, from which we identify the dominant atmospheric responses to plant physiological processes. They emphasize the intricate connection between biological and physical aspects of the climate system and the relevance of short-term and small-scale processes in establishing this connection.

  4. How can a dusty cold pool change the diurnal evolution of the Saharan Atmospheric Boundary Layer ?

    NASA Astrophysics Data System (ADS)

    Kocha, Cécile; Flamant, Cyrille; Berckmans, Julie; Fink, Andreas; Garcia-Carreras, Luis; Knippertz, Peter; Lafore, Jean-Philippe; Marnas, Fabien; Marsham, John; Parker, Doug; Rosenberg, Philip; Ryder, Claire; Tulet, Pierre; Washington, Richard

    2013-04-01

    In the framework of the Fennec 2011 Special Observing period, a large and dusty density current (known as a haboob) was observed on the 21 June to cover half of the western part of the Sahara. Thanks to the AROME high resolution model used to forecast this event in real time, two research aircraft (the SAFIRE Falcon and the FAAM BAe 146) operated over Mauritania and Mali on that day, and we are able to document its characteristics in detail. Particularly large dust particles were observed in this haboob. These particles are known to absorb and scatter solar and thermal radiation. The comparison of AROME simulations with and without coupling with dust shows that the radiative impact of the dust induced a decrease of sensible heat fluxes by 200W/m²/AOD and an increase of the temperature in the atmospheric boundary layer by 1°C. Surface fluxes are one of the principal parameters controlling the growth of the boundary layer. However, during the day, the simulation coupled with dust shows a deeper boundary layer (reaching ~5km high) than the simulation without dust. Here, we explore the competition between surface heating and elevated heating in the boundary-layer development.

  5. Near-marine boundary layer atmospheric and turbulence measurement and modeling

    NASA Astrophysics Data System (ADS)

    Manzur, Tariq; Zeller, John; Magee, Eric

    2013-06-01

    Currently there are extensive modeling and measurement capabilities for the region extending from 100 ft above sea surface to space, but few such capabilities exist for the region extending up to 10 ft above the sea surface. By measuring and characterizing conditions in the marine boundary layer existing below 30 ft above the sea surface such as turbulence and extinction, the optical communication capabilities of maritime vessels when operating at or near the surface may be extended and enhanced. Key physical parameters such as absorption, scattering, and turbulence strength (Cn 2) along the propagation path have a degree of variability on meteorological conditions as well optical wavelength. Modeling of the atmospheric environment is thus critical in order to generate a good understanding of optical propagation through the atmosphere. NUWC is utilizing software provided by MZA to model Cn 2 and resultant beam propagation characteristics through the near-marine boundary layer. We are developing the capability of near-marine boundary layer atmospheric and turbulence measurements and modeling as well as optical laser link testing at outdoor test sites. Measurements are performed with optical laser links (e.g., bit rate error), scintillometer, and particle image velocimetry (PIV) cameras, while turbulence and propagation modeling is achieved using MODTRAN5, ATMTools, NSLOT, LEEDR, and WaveTrain modeling and simulation code. By better understanding the effects of turbulence on optical transmission in the near-marine boundary layer through modeling and experimental measurements, measures can be implemented to reduce the bit error rate and increase data throughput, enabling more efficient and accurate communication link capabilities.

  6. The impact of vegetation on the atmospheric boundary layer and convective storms

    NASA Astrophysics Data System (ADS)

    Lee, Tsengdar John

    1992-01-01

    The impact of vegetation on atmospheric boundary layer and convective storms is examined through the construction and testing of a soil-vegetation-atmosphere transfer (SVAT) model. The Land Ecosystem-Atmosphere (LEAF) model is developed using an elevated canopy structure, an above-canopy aerodynamic resistance, two in-canopy aerodynamic resistances, and one stomatal conductance functions. The air temperature and humidity are assumed to be constant in the canopy whereas the wind and radiation follow a specified vertical profile. A simple dump-bucket method is used to parameterize the interception of precipitation and a multi-layer soil model is utilized to handle the vertical transfer of soil water. Evaporation from soil and wet leaves and transpiration from dry leaves are evaluated separately. The solid water uptake is based on soil water potential rather than on the length of roots. Separate energy budgets for vegetation and for the soil are used in order to remove unnecessary assumptions on energy partition between the vegetation and the substrate. Primary parameters are LAI, maximum stomatal conductance, and albedo. Secondary parameters include displacement height and environmental controls on stomatal resistance function. Due to the complexity of the LEAF model, statistical methods are used to improve LEAF model performance. The Multi-response Randomized Bock Permutation (MRBP) procedure is used to guide the choice of model parameter values. The Fourier Amplitude Sensitivity Test (FAST) is applied to better understand the model behavior in response to the changes in model parameters. Finally, LEAF is used to study the growth of boundary layer and the local thermal circulations generated by surface inhomogeneities. Results show the atmospheric boundary layer is substantially cooler and more moist over unstressed vegetation than over bare dry soil. Thermally forced circulation can result from the juxtaposition of two vegetation types due to different biophysical

  7. The Impact of Vegetation on the Atmospheric Boundary Layer and Convective Storms

    NASA Astrophysics Data System (ADS)

    Lee, Tsengdar John

    The impact of vegetation on atmospheric boundary layer and convective storms is examined through the construction and testing of a soil-vegetation-atmosphere transfer (SVAT) model. The Land Ecosystem-Atmosphere (LEAF) model is developed using an elevated canopy structure, an above -canopy aerodynamic resistance, two in-canopy aerodynamic resistances, and one stomatal conductance functions. The air temperature and humidity are assumed to be constant in the canopy whereas the wind and radiation follow a specified vertical profile. A simple dump-bucket method is used to parameterize the interception of precipitation and a multi-layer soil model is utilized to handle the vertical transfer of soil water. Evaporation from soil and wet leaves and transpiration from dry leaves are evaluated separately. The solid water uptake is based on soil water potential rather than on the length of roots. Separate energy budgets for vegetation and for the soil are used in order to remove unnecessary assumptions on energy partition between the vegetation and the substrate. Primary parameters are LAI, maximum stomatal conductance, and albedo. Secondary parameters include displacement height and environmental controls on stomatal resistance function. Due to the complexity of the LEAF model, statistical methods are used to improve LEAF model performance. The Multi-response Randomized Bock Permutation (MRBP) procedure is used to guide the choice of model parameter values. The Fourier Amplitude Sensitivity Test (FAST) is applied to better understand the model behavior in response to the changes in model parameters. Finally, LEAF is used to study the growth of boundary layer and the local thermal circulations generated by surface inhomogeneities. Results show the atmospheric boundary layer is substantially cooler and more moist over unstressed vegetation than over bare dry soil. Thermally forced circulation can result from the juxtaposition of two vegetation types due to different biophysical

  8. Instability of wind turbine wakes immersed in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Viola, Francesco; Valerio Iungo, Giacomo; Camarri, Simone; Porté-Agel, Fernando; Gallaire, François

    2015-06-01

    In this work a technique capable to investigate the near-wake stability properties of a wind turbine immersed in the atmospheric boundary layer is presented. Specifically, a 2D local spatial stability analysis is developed in order to take into account typical flow features of real operating wind turbines, such as the presence of the atmospheric boundary layer and the turbulence heterogeneity of the oncoming wind. This stability analysis can be generally applied on either experimental measurements or numerical data. In this paper it was carried out on wind tunnel experiments, for which a downscaled wind turbine is immersed in a turbulent boundary layer. Through spatial stability analysis, the dominant mode in the near wake, i.e. the most amplified one, is characterized and its frequency matches the hub-vortex instability frequency measured in the wind tunnel. As in the case of [10], where an axisymmetric wake condition was investigated, the hub-vortex instability results in a single-helical mode.

  9. Effect of Large Finite-Size Wind Farms and Their Wakes on Atmospheric Boundary Layer Dynamics

    NASA Astrophysics Data System (ADS)

    Wu, Ka Ling; Porté-Agel, Fernando

    2016-04-01

    Through the use of large-eddy simulation, the effect of large finite-size wind farms and their wakes on conventionally-neutral atmospheric boundary layer (ABL) dynamics and power extraction is investigated. Specifically, this study focuses on a wind farm that comprises 25 rows of wind turbines, spanning a distance of 10 km. It is shown that large wind farms have a significant effect on internal boundary layer growth both inside and downwind of the wind farms. If the wind farm is large enough, the internal boundary layer interacts with the thermally-stratified free atmosphere above, leading to a modification of the ABL height and power extraction. In addition, it is shown that large wind farms create extensive wakes, which could have an effect on potential downwind wind farms. Specifically, for the case considered here, a power deficit as large as 8% is found at a distance of 10 km downwind from the wind farm. Furthermore, this study compares the wind farm wake dynamics for cases in which the conventionally neutral ABLs are driven by a unidirectional pressure gradient and Coriolis forces.

  10. LOTOS: A Proposed Lower Tropospheric Observing System from the Land Surface through the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Cohn, S. A.; Lee, W. C.; Carbone, R. E.; Oncley, S.; Brown, W. O. J.; Spuler, S.; Horst, T. W.

    2015-12-01

    Advances in sensor capabilities, but also in electronics, optics, RF communication, and off-the-grid power are enabling new measurement paradigms. NCAR's Earth Observing Laboratory (EOL) is considering new sensors, new deployment modes, and integrated observing strategies to address challenges in understanding within the atmospheric boundary layer and the underlying coupling to the land surface. Our vision is of a network of deployable observing sites, each with a suite of complementary instruments that measure surface-atmosphere exchange, and the state and evolution of the boundary layer. EOL has made good progress on distributed surface energy balance and flux stations, and on boundary layer remote sensing of wind and water vapor, all suitable for deployments of combined instruments and as network of such sites. We will present the status of the CentNet surface network development, the 449-MHz modular wind profiler, and a water vapor and temperature profiling differential absorption lidar (DIAL) under development. We will further present a concept for a test bed to better understand the value of these and other possible instruments in forming an instrument suite flexible for multiple research purposes.

  11. Study of Transitions in the Atmospheric Boundary Layer Using Explicit Algebraic Turbulence Models

    NASA Astrophysics Data System (ADS)

    Lazeroms, W. M. J.; Svensson, G.; Bazile, E.; Brethouwer, G.; Wallin, S.; Johansson, A. V.

    2016-08-01

    We test a recently developed engineering turbulence model, a so-called explicit algebraic Reynolds-stress (EARS) model, in the context of the atmospheric boundary layer. First of all, we consider a stable boundary layer used as the well-known first test case from the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study (GABLS1). The model is shown to agree well with data from large-eddy simulations (LES), and this agreement is significantly better than for a standard operational scheme with a prognostic equation for turbulent kinetic energy. Furthermore, we apply the model to a case with a (idealized) diurnal cycle and make a qualitative comparison with a simpler first-order model. Some interesting features of the model are highlighted, pertaining to its stronger foundation on physical principles. In particular, the use of more prognostic equations in the model is shown to give a more realistic dynamical behaviour. This qualitative study is the first step towards a more detailed comparison, for which additional LES data are needed.

  12. Intercomparison of Martian Lower Atmosphere Simulated Using Different Planetary Boundary Layer Parameterization Schemes

    NASA Technical Reports Server (NTRS)

    Natarajan, Murali; Fairlie, T. Duncan; Dwyer Cianciolo, Alicia; Smith, Michael D.

    2015-01-01

    We use the mesoscale modeling capability of Mars Weather Research and Forecasting (MarsWRF) model to study the sensitivity of the simulated Martian lower atmosphere to differences in the parameterization of the planetary boundary layer (PBL). Characterization of the Martian atmosphere and realistic representation of processes such as mixing of tracers like dust depend on how well the model reproduces the evolution of the PBL structure. MarsWRF is based on the NCAR WRF model and it retains some of the PBL schemes available in the earth version. Published studies have examined the performance of different PBL schemes in NCAR WRF with the help of observations. Currently such assessments are not feasible for Martian atmospheric models due to lack of observations. It is of interest though to study the sensitivity of the model to PBL parameterization. Typically, for standard Martian atmospheric simulations, we have used the Medium Range Forecast (MRF) PBL scheme, which considers a correction term to the vertical gradients to incorporate nonlocal effects. For this study, we have also used two other parameterizations, a non-local closure scheme called Yonsei University (YSU) PBL scheme and a turbulent kinetic energy closure scheme called Mellor- Yamada-Janjic (MYJ) PBL scheme. We will present intercomparisons of the near surface temperature profiles, boundary layer heights, and wind obtained from the different simulations. We plan to use available temperature observations from Mini TES instrument onboard the rovers Spirit and Opportunity in evaluating the model results.

  13. Investigating the Source, Transport, and Isotope Composition of Water in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Griffis, T. J.; Schultz, N. M.; Lee, X.

    2011-12-01

    The isotope composition of water (liquid and vapor phases) can provide important insights regarding the source of water used by plants, the origins of atmospheric water vapor, and the sources of carbon dioxide. In recent years there have been significant advances in the ability to quantify the isotope composition of water and water vapor using optical isotope techniques. We have used and helped develop some of these techniques to determine the isotope composition of soil and plant waters, to measure the isoflux of water vapor between the land surface and atmosphere, and to examine the isotope composition of water vapor and deuterium excess in the atmospheric boundary layer. In this presentation we will discuss three related issues: 1) Identification and correction of spectral contamination in soil and plant water samples using optical techniques; 2) The benefits and practical limitations of quantifying the isotope composition of evapotranspiration using the eddy covariance approach; and 3) The scientific value and feasibility of tracking the long-term (seasonal and interannual) behavior of the isotope composition of water vapor and deuterium excess in the atmospheric boundary layer. A few short stories will be provided from experiments conducted in the lab, at the field scale, and from a very tall tower at the University of Minnesota from 2008 to 2011.

  14. Large-eddy simulation of very-large-scale motions in atmospheric boundary-layer flows

    NASA Astrophysics Data System (ADS)

    Fang, Jiannong; Porté-Agel, Fernando

    2015-04-01

    In the last few decades, laboratory experiments and direct numerical simulations of turbulent boundary layers, performed at low to moderate Reynolds numbers, have found very-large-scale motions (VLSMs) in the logarithmic and outer regions. The size of VLSMs was found to be 10-20 times as large as the boundary-layer thickness. Recently, few studies based on field experiments examined the presence of VLSMs in neutral atmospheric boundary-layer flows, which are invariably at very high Reynolds numbers. Very large scale structures similar to those observed in laboratory-scale experiments have been found and characterized. However, it is known that field measurements are more challenging than laboratory-based measurements, and can lack resolution and statistical convergence. Such challenges have implications on the robustness of the analysis, which may be further adversely affected by the use of Taylor's hypothesis to convert time series to spatial data. We use large-eddy simulation (LES) to investigate VLSMs in atmospheric boundary-layer flows. In order to make sure that the largest flow structures are properly resolved, the horizontal domain size is chosen to be much larger than the standard domain size. It is shown that the contributions to the resolved turbulent kinetic energy and shear stress from VLSMs are significant. Therefore, the large computational domain adopted here is essential for the purpose of investigating VLSMs. The spatially coherent structures associated with VLSMs are characterized through flow visualization and statistical analysis. The instantaneous velocity fields in horizontal planes give evidence of streamwise-elongated flow structures of low-speed fluid with negative fluctuation of the streamwise velocity component, and which are flanked on either side by similarly elongated high-speed structures. The pre-multiplied power spectra and two-point correlations indicate that the scales of these streak-like structures are very large. These features

  15. Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth

    PubMed Central

    Davy, Richard; Esau, Igor

    2016-01-01

    The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response. PMID:27221757

  16. Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth

    NASA Astrophysics Data System (ADS)

    Davy, Richard; Esau, Igor

    2016-05-01

    The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response.

  17. Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth.

    PubMed

    Davy, Richard; Esau, Igor

    2016-01-01

    The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response. PMID:27221757

  18. Disturbance of the Boundary Layer at Summit Station, Greenland by an Atmospheric River

    NASA Astrophysics Data System (ADS)

    Neff, William; Shupe, Mathew; Ralph, Marty

    2014-05-01

    On 11 July 2012, a rare melt episode occurred at Summit Station Greenland. As described by Neff et al. 2014 (Submitted JGR), a major factor in this melt event was an Atmospheric River (AR), a narrow corridor of high water-vapor content. This AR transited the western Atlantic and theen moved up the west coast of Greenland and thence over Greenland. Back trajectories also indicated significant warm air advection from mid-North America during a major heat wave. We present here the boundary layer changes during this event using sodar to distinguish well-mixed from stable periods and relate these to changes in synoptic forcing and resulting changes in radiative forcing by low-level, shallow, warm clouds. A second near-melt episode also occurred on 29 July which provides an opportunity to compare and contrast boundary layer responses in the two cases.

  19. Ammonia Surface-Atmosphere Exchange in the Arctic Marine Boundary Layer

    NASA Astrophysics Data System (ADS)

    Murphy, J. G.; Wentworth, G.; Tremblay, J. E.; Gagnon, J.; Côté, J. S.; Courchesne, I.

    2014-12-01

    The net flux of ammonia between the ocean and the atmosphere is poorly known on global and regional scales. Data from high-latitude research cruises suggest that deposition from the atmosphere to the surface dominates, but the magnitude and drivers of this flux are not well understood. In the polar marine boundary layer, the surface may be composed of not only open ocean, but also first-year or multi-year sea ice which may be covered with meltponds. To characterize the air-sea exchange of ammonia in the polar marine boundary layer, data were collected aboard the Canadian Coast Guard Ship Amundsen between July 10 and Aug 14, 2014 in the Eastern Canadian Arctic. The Ambient Ion Monitor Ion Chromatograph was used to make hourly measurements of the mixing ratio of gas phase ammonia, and the water-soluble constituents of fine particle matter (PM2.5). Fluorometry was used to measure dissolved ammonium concentrations in the ocean between 0 and 20 m, and in low-salinity melt ponds encountered in regions of extensive sea ice. Observations indicate that the atmosphere contains higher levels of ammonia than are calculated to be in equilibrium with surface reservoirs, implying net deposition of ammonia from the atmosphere. While ammonium levels tended to be higher in melt ponds, the lower water temperatures still mean that these are unlikely to be sources of NH3 to the atmosphere. The disequilibrium between atmospheric and surface reservoirs of ammonia imply relatively large sources to the atmosphere (possibly nearby bird colonies) or high consumption rates in surface waters.

  20. Turbulent transport in the atmospheric boundary layer with application to wind farm dynamics

    NASA Astrophysics Data System (ADS)

    Waggy, Scott B.

    With the recent push for renewable energy sources, wind energy has emerged as a candidate to replace some of the power produced by traditional fossil fuels. Recent studies, however, have indicated that wind farms may have a direct effect on local meteorology by transporting water vapor away from the Earth's surface. Such turbulent transport could result in an increased drying of soil, and, in turn, negatively affect the productivity of land in the wind farm's immediate vicinity. This numerical study will analyze four scenarios with the goal of understanding turbulence transport in the wake of a turbine: the neutrally-stratified boundary layer with system rotation, the unstably-stratified atmospheric boundary layer, and wind turbine simulations of these previous two cases. For this work, the Ekman layer is used as an approximation of the atmospheric boundary layer and the governing equations are solved using a fully-parallelized direct numerical simulation (DNS). The in-depth studies of the neutrally and unstably-stratified boundary layers without introducing wind farm effects will act to provide a concrete background for the final study concerning turbulent transport due to turbine wakes. Although neutral stratification rarely occurs in the atmospheric boundary layer, it is useful to study the turbulent Ekman layer under such conditions as it provides a limiting case when unstable or stable stratification are weak. In this work, a thorough analysis was completed including turbulent statistics, velocity and pressure autocorrelations, and a calculation of the full turbulent energy budget. The unstably-stratified atmospheric boundary layer was studied under two levels of heating: moderate and vigorous. Under moderate stratification, both buoyancy and shearing contribute significantly to the turbulent dynamics. As the level of stratification increases, the role of shearing is shown to diminish and is confined to the near-wall region only. A recent, multi

  1. Influence of a high aerosol concentration on the thermal structure of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Khaikin, M. N.; Kuznetsova, I. N.; Kadygrov, E. N.

    2006-12-01

    The influence of increased concentrations of submicron aerosol produced by forest fires on thermal characteristics of the atmospheric boundary layer (ABL) in Moscow and its remote vicinity (the town of Zvenigorod) are analyzed on the basis of regular remote measurements of the ABL temperature profile with the use of MTP-5 profilers. In the air basin of a large city, additional aerosol and accompanying pollutants in early morning hours (at small heights of the Sun) most frequently did not cause substantial changes in the ABL thermal structure. In the locality remote from the megalopolis (Zvenigorod), the atmospheric pollution by aerosol led to noticeable changes in the ABL thermal characteristics. Especially strong changes were observed in the daytime, during the maximum supply of solar radiation. In morning hours, the heating rate of the lower 100-m layer of the polluted air exceeded the heating rate of a relatively pure air by more than one degree. In higher layers, the differences between the rates of temperature changes in a relatively clean atmosphere and in an atmosphere polluted by aerosol (in the suburb) were insignificant.

  2. Preliminary analysis of the Nocturnal Atmospheric Boundary Layer during the experimental campaign CIBA 2008

    NASA Astrophysics Data System (ADS)

    Yagüe, C.; Maqueda, G.; Ramos, D.; Sastre, M.; Viana, S.; Serrano, E.; Morales, G.; Ayarzagüena, B.; Viñas, C.; Sánchez, E.

    2009-04-01

    An Atmospheric Boundary Layer campaign was developed in Spain along June 2008 at the CIBA (Research Centre for the Lower Atmosphere) site which is placed on a fairly homogeneous terrain in the centre of an extensive plateau (41°49' N, 4°56' W). Different instrumentation at several levels was available on a new 10m meteorological mast, including temperature and humidity sensors, wind vanes and cup anemometers, as well as one sonic anemometer. Besides, two quartz-based microbarometers were installed at 50 and 100m on the main permanent 100m tower placed at CIBA. Three additional microbarometers were deployed on the surface on a triangular array of approximately 200 m side, and a tethered balloon was used in order to record vertical profiles of temperature, wind and humidity up to 1000m. Finally, a GRIMM particle monitor (MODEL 365), which can be used to continuously measure each six seconds simultaneously the PM10, PM2.5 and PM1 values, was deployed at 1.5m. This work will show some preliminary results from the campaign CIBA 2008, analysing the main physical processes present in the atmospheric Nocturnal Boundary Layer (NBL), the different stability periods observed and the corresponding turbulent parameters, as well as the coherent structures detected. The pressure perturbations measured from the surface and tower levels make possible to study the main wave parameters from wavelet transform, and compared the structures detected by the microbarometers with those detected in the wind and particles records.

  3. The atmospheric boundary layer evening transitions: an observational and numerical study from two different datasets

    NASA Astrophysics Data System (ADS)

    Sastre, Mariano; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio; Ander Arrillaga, Jon

    2015-04-01

    In this work we study the temporal evolution of the Atmospheric Boundary Layer (ABL) along the transition period from a diurnal typical convection to a nocturnal more frequently stable situation. This period is known as late afternoon or evening transition, depending on the specific definitions employed by different authors [1]. In order to obtain a proper characterization, we try to learn whether or not the behaviour of these transitional boundary layers is strongly dependent on local conditions. To do so, two sets of evening transitions are studied from data collected at two different experimental sites. These locations correspond to research facilities named CIBA (Spain) and CRA (France), which are the places where atmospheric field campaigns have been conducted during the last years, such as CIBA2008 and BLLAST 2011, respectively. In order to get comparable situations, we focus especially on transitions with weak synoptic forcing, and consider daily astronomical sunset as a reference time. A statistical analysis on main parameters related to the transition is carried out for both locations, and the average behaviour is shown as well as extreme values according to the timing. A similar pattern in the qualitative evolution of many variables is found. Nevertheless, several relevant differences in the progress of key variables are obtained too. Moisture, both from the soil and the air, is thought to have great relevance in explaining many of the differences found between the two sites. Some case studies are explored, focusing on the role played by the atmospheric turbulence. Complementary, numerical experiments are also performed using the Weather Research and Forecast (WRF) mesoscale model, in order to test the role of humidity, by artificially varying it in some of the simulations. [1] Lothon, M. and coauthors (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence. Atmos. Chem. Phys., 14, 10931-10960.

  4. The groundwater land-surface atmosphere connection: Soil moisture effects on the atmospheric boundary layer in fully-coupled simulations

    NASA Astrophysics Data System (ADS)

    Maxwell, Reed M.; Chow, Fotini Katopodes; Kollet, Stefan J.

    2007-12-01

    This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can simulate spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-h period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land-surface temperatures trigger shifts in wind behavior, such as during early morning surface heating.

  5. The groundwater-land-surface-atmosphere connection: soil moisture effects on the atmospheric boundary layer in fully-coupled simulations

    SciTech Connect

    Maxwell, R M; Chow, F K; Kollet, S J

    2007-02-02

    This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can represent spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-hour period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land surface temperatures trigger shifts in wind behavior, such as during early morning surface heating.

  6. Sodar observations of the atmospheric boundary layer over the ocean during ASTEX-91

    NASA Astrophysics Data System (ADS)

    Petenko, I. V.; Bedulin, A. N.; Shurygin, Ye. A.

    1996-10-01

    A complex marine experiment was conducted in autumn 1991 on the research vessel Dmitry Mendelev in association with the Atlantic Stratocumulus Transition Experiment (ASTEX). A three-axis Doppler sodar designed at the Institute of Atmospheric Physics, Moscow, was used in this experiment. Total observation time was about 770 hours from 6 October to 23 November. Besides facsimile records illustrating spatial and temporal structure of the turbulence distribution in the atmospheric boundary layer (ABL), routine quantitative measurements of profiles of wind and echo-signal strength were taken. Some main characteristics of the ABL behavior over the ocean were revealed through an analysis of these data as well as the results of other kinds of measurements. An important peculiarity of the ABL observed between the Canary Islands and the Azores was the presence of diurnal variation of convective turbulence strength having a maximum between 04:00 and 07:00 LT. A similar diurnal variation was observed for low-level cloud cover. Occurrence of various types of thermal stratification and their diurnal variation were obtained. Comparison of elevated stable layers and low-level cumulus showed that the lower boundary of clouds correlates well with the height of the bottom of elevated inversion layers (at heights of 200 600 m). Canary and Cabo Verde observations showed that islands strongly affect the ABL structure. The strong effect of a surface water temperature gradient on the ABL stability was observed when crossing the Canary, Azores, and Labrador currents and the Gulf Stream.

  7. Conditionally Averaged Large-Scale Motions in the Neutral Atmospheric Boundary Layer: Insights for Aeolian Processes

    NASA Astrophysics Data System (ADS)

    Jacob, Chinthaka; Anderson, William

    2016-06-01

    Aeolian erosion of flat, arid landscapes is induced (and sustained) by the aerodynamic surface stress imposed by flow in the atmospheric surface layer. Conceptual models typically indicate that sediment mass flux, Q (via saltation or drift), scales with imposed aerodynamic stress raised to some exponent, n, where n > 1 . This scaling demonstrates the importance of turbulent fluctuations in driving aeolian processes. In order to illustrate the importance of surface-stress intermittency in aeolian processes, and to elucidate the role of turbulence, conditional averaging predicated on aerodynamic surface stress has been used within large-eddy simulation of atmospheric boundary-layer flow over an arid, flat landscape. The conditional-sampling thresholds are defined based on probability distribution functions of surface stress. The simulations have been performed for a computational domain with ≈ 25 H streamwise extent, where H is the prescribed depth of the neutrally-stratified boundary layer. Thus, the full hierarchy of spatial scales are captured, from surface-layer turbulence to large- and very-large-scale outer-layer coherent motions. Spectrograms are used to support this argument, and also to illustrate how turbulent energy is distributed across wavelengths with elevation. Conditional averaging provides an ensemble-mean visualization of flow structures responsible for erosion `events'. Results indicate that surface-stress peaks are associated with the passage of inclined, high-momentum regions flanked by adjacent low-momentum regions. Fluid in the interfacial shear layers between these adjacent quasi-uniform momentum regions exhibits high streamwise and vertical vorticity.

  8. Atmospheric Boundary Layer Height Evolution with Lidar in Buenos Aires from 2008 to 2011

    NASA Astrophysics Data System (ADS)

    Pawelko, Ezequiel Eduardo; Salvador, Jacobo Omar; Ristori, Pablo Roberto; Pallotta, Juan Vicente; Otero, Lidia Ana; Quel, Eduardo Jaime

    2016-06-01

    The analysis of the atmospheric boundary layer top height evolution is obtained from 2008 to 2011 in Buenos Aires using the multiwavelength lidar located at CEILAP (CITEDEF-CONICET) (34°33' S; 58°30' W; 17 m asl). Algorithms recognition based on covariance wavelet transform are applied to obtain seasonal statistics. This method is being evaluated for use in the Lidar Network in Argentina and it is being deployed in Patagonia region currently. The technique operates in real time in both low and high aerosol loads and with almost no human supervision.

  9. The effect of the Asian Monsoon to the atmospheric boundary layer over the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Li, Maoshan; Su, Zhongbo; Chen, Xuelong; Zheng, Donghai; Sun, Fanglin; Ma, Yaoming; Hu, Zeyong

    2016-04-01

    Modulation of the diurnal variations in the convective activities associated with day-by-day changes of surface flux and soil moisture was observed in the beginning of the monsoon season on the central Tibetan plateau (Sugimoto et al., 2008) which indicates the importance of land-atmosphere interactions in determining convective activities over the Tibetan plateau. Detailed interaction processes need to be studied by experiments designed to evaluate a set of hypotheses on mechanisms and linkages of these interactions. A possible function of vegetation to increase precipitation in cases of Tibetan High type was suggested by Yamada and Uyeda (2006). Use of satellite derived plateau scale soil moisture (Wen et al., 2003) enables the verification of these hypotheses (e.g. Trier et al. 2004). To evaluate these feedbacks, the mesoscale WRF model will be used because several numerical experiments are being conducted to improve the soil physical parameterization in the Noah land surface scheme in WRF so that the extreme conditions on the Tibetan plateau could be adequately represented (Van der Velde et al., 2009) such that the impacts on the structure of the atmospheric boundary layer can be assessed and improved. The Tibetan Observational Research Platform (TORP) operated by the Institute of Tibetan Plateau (Ma et al., 2008) will be fully utilized to study the characteristics of the plateau climate and different aspects of the WRF model will be evaluated using this extensive observation platform (e.g. Su et al., 2012). Recently, advanced studies on energy budget have been done by combining field and satellite measurements over the Tibetan Plateau (e.g. Ma et al., 2005). Such studies, however, were based on a single satellite observation and for a few days over an annual cycle, which are insufficient to reveal the relation between the land surface energy budget and the Asian monsoon over the Tibetan plateau. Time series analysis of satellite observations will provide the

  10. The effect of the Asian Monsoon to the atmospheric boundary layer over the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Li, Maoshan; Su, Zhongbo; Chen, Xuelong; Zheng, Donghai; Sun, Fanglin; Ma, Yaoming; Hu, Zeyong

    2016-04-01

    Modulation of the diurnal variations in the convective activities associated with day-by-day changes of surface flux and soil moisture was observed in the beginning of the monsoon season on the central Tibetan plateau (Sugimoto et al., 2008) which indicates the importance of land-atmosphere interactions in determining convective activities over the Tibetan plateau. Detailed interaction processes need to be studied by experiments designed to evaluate a set of hypotheses on mechanisms and linkages of these interactions. A possible function of vegetation to increase precipitation in cases of Tibetan High type was suggested by Yamada and Uyeda (2006). Use of satellite derived plateau scale soil moisture (Wen et al., 2003) enables the verification of these hypotheses (e.g. Trier et al. 2004). To evaluate these feedbacks, the mesoscale WRF model will be used because several numerical experiments are being conducted to improve the soil physical parameterization in the Noah land surface scheme in WRF so that the extreme conditions on the Tibetan plateau could be adequately represented (Van der Velde et al., 2009) such that the impacts on the structure of the atmospheric boundary layer can be assessed and improved. The Tibetan Observational Research Platform (TORP) operated by the Institute of Tibetan Plateau (Ma et al., 2008) will be fully utilized to study the characteristics of the plateau climate and different aspects of the WRF model will be evaluated using this extensive observation platform (e.g. Su et al., 2012). Recently, advanced studies on energy budget have been done by combining field and satellite measurements over the Tibetan Plateau (e.g. Ma et al., 2005). Such studies, however, were based on a single satellite observation and for a few days over an annual cycle, which are insufficient to reveal the relation between the land surface energy budget and the Asian monsoon over the Tibetan plateau. Time series analysis of satellite observations will provide the

  11. Countergradient heat transfer in the atmospheric boundary layer over a rough surface

    NASA Astrophysics Data System (ADS)

    Kurbatskiy, A. F.

    2008-04-01

    The nonlocality of the mechanism of turbulent heat transfer in the atmospheric boundary layer over a rough surface manifests itself in the form of bounded areas of countergradient heat transfer, which are diagnosed from analysis of balance items in the transport equation for the variance of temperature fluctuations and from calculation of the coefficients of turbulent momentum and heat transfer invoking the model of “gradient diffusion.” It is shown that countergradient heat transfer in local regions is caused by turbulent diffusion or by the term of the divergence of triple correlation in the balance equation for the temperature variance.

  12. Structure and Optical Properties of the Atmospheric Boundary Layer over Dusty Hot Deserts

    NASA Astrophysics Data System (ADS)

    Chalermthai, B.; Al Marzooqi, M.; Basha, G.; Ouarda, T.; Armstrong, P.; Molini, A.

    2014-12-01

    Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature of the atmospheric boundary layer (ABL) over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main common features however, desert boundary layers present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as transport and deposition of dust and pollutants, local wind fields, turbulent fluxes and their impacts on the sustainable development, human health and solar energy harvesting in these regions. In this study, we explore the potential of the joint usage of Lidar Ceilometer backscattering profiles and sun-photometer optical depth retrievals to quantitatively determine the vertical aerosol profile over dusty hot desert regions. Toward this goal, we analyze a continuous record of observations of the atmospheric boundary layer height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4425N 54.6163E, Abu Dhabi, United Arab Emirates), starting March 2013, and the concurrent measurements of aerosol optical depth derived independently from the Masdar Institute AERONET sun-photometer. The main features of the desert ABL are obtained from the ceilometer range corrected backscattering profiles through bi-dimensional clustering technique we developed as a modification of the recently proposed single-profile clustering method, and therefore "directly" and "indirectly" calibrated to obtain a full diurnal cycle climatology of the aerosol optical depth and aerosol profiles. The challenges and the advantages of applying a similar methodology to the monitoring of aerosols and dust over hyper-arid regions are also discussed, together with the issues related to the sensitivity of commercial ceilometers to changes in the solar background.

  13. Numerical study of the anode boundary layer in atmospheric pressure arc discharges

    NASA Astrophysics Data System (ADS)

    Semenov, I. L.; Krivtsun, I. V.; Reisgen, U.

    2016-03-01

    The anode boundary layer in atmospheric pressure arc discharges is studied numerically on the basis of the hydrodynamic (diffusion) equations for plasma components. The governing equations are formulated in a unified manner without the assumptions of thermal equilibrium, ionization equilibrium or quasi-neutrality. For comparison, a quasi-neutral model of the anode layer is also considered. The numerical computations are performed for an argon arc at typical values of the current density in anode layers (500-2000 A cm-2). The results of numerical modelling show that the common collisionless model of the sheath fails to describe the sheath region for the problem under consideration. For this reason, a detailed analysis of the anode sheath is performed using the results of unified modelling. In addition, the distributions of plasma parameters in the anode layer are analysed and the basic characteristics of the layer (anode voltage drop, sheath voltage drop, anode layer thickness, sheath thickness, heat flux to the anode) are calculated. Our results are found to be in good agreement with the existing theoretical predictions and experimental data. The dependence of the anode layer characteristics on the current density is also discussed.

  14. Atmospheric Boundary Layer of a pasture site in Amazônia

    NASA Astrophysics Data System (ADS)

    Trindade de Araújo Tiburtino Neves, Theomar; Fisch, Gilberto; Raasch, Siegfried

    2013-04-01

    A great effort has been made by the community of micrometeorology and planetary boundary layer for a better description of the properties of the Atmospheric Boundary Layer (ABL), such as its height, thermodynamics characteristics and its time evolution. This work aims to give a review of the main characteristics of Atmospheric Boundary Layer over a pasture site in Amazonia. The measurements dataset was carried out from 3 different LBA field campaigns: RBLE 3 (during the dry season from 1993), RaCCI (during the dry-to-wet transition season from 2002) and WetAMC (during the wet season from 1999), collected with tethered balloon, radiosondes and eddy correlation method in a pasture site in the southwestern Amazonia. Different techniques and instruments were used to estimate the ABĹs properties. During the daytime, it was possible to observe that there is an abrupt growth of the Convective Boundary Layer (CBL) between 08 and 11 LT, with a stationary pattern between 14 and 17 LT. The maximum heights at late afternoon were around 1600 m during the dry season, whilst the wet season it only reached 1000 m. This is due to the lower surface turbulent sensible heat flux as the soil is wetter and the partition of energy is completely different between wet to the dry season. For the transition period (RaCCI 2002), it was possible to analyze and compare several estimates from different instruments and methods. It showed that the parcel method overestimates the heights of all measurements (mainly at 14 LT) due to the high incidence of solar radiation and superadiabatic gradients. The profile and Richardson number methods gave results very similar to estimate the height of the CBL. The onset of the Nocturnal Boundary Layer (NBL) occurs before the sunset (18 LT) and its height is reasonable stable during the night (typical values around 180-250 m). An alternative method (Vmax) which used the height of the maximum windspeed derived from a SODAR instrument during RaCCI 2002 was

  15. Immersed Boundary Methods for High-Resolution Simulation of Atmospheric Boundary-Layer Flow Over Complex Terrain

    SciTech Connect

    Lundquist, K A

    2010-05-12

    use of flux (non-zero) boundary conditions. This anabatic flow set-up is further coupled to atmospheric physics parameterizations, which calculate surface fluxes, demonstrating that the IBM can be coupled to various land-surface parameterizations in atmospheric models. Additionally, the IB method is extended to three dimensions, using both trilinear and inverse distance weighted interpolations. Results are presented for geostrophic flow over a three-dimensional hill. It is found that while the IB method using trilinear interpolation works well for simple three-dimensional geometries, a more flexible and robust method is needed for extremely complex geometries, as found in three-dimensional urban environments. A second, more flexible, immersed boundary method is devised using inverse distance weighting, and results are compared to the first IBM approach. Additionally, the functionality to nest a domain with resolved complex geometry inside of a parent domain without resolved complex geometry is described. The new IBM approach is used to model urban terrain from Oklahoma City in a one-way nested configuration, where lateral boundary conditions are provided by the parent domain. Finally, the IB method is extended to include wall model parameterizations for rough surfaces. Two possible implementations are presented, one which uses the log law to reconstruct velocities exterior to the solid domain, and one which reconstructs shear stress at the immersed boundary, rather than velocity. These methods are tested on the three-dimensional canonical case of neutral atmospheric boundary layer flow over flat terrain.

  16. Immersed boundary methods for high-resolution simulation of atmospheric boundary-layer flow over complex terrain

    NASA Astrophysics Data System (ADS)

    Lundquist, Katherine Ann

    use of flux (non-zero) boundary conditions. This anabatic flow set-up is further coupled to atmospheric physics parameterizations, which calculate surface fluxes, demonstrating that the IBM can be coupled to various land-surface parameterizations in atmospheric models. Additionally, the IB method is extended to three dimensions, using both trilinear and inverse distance weighted interpolations. Results are presented for geostrophic flow over a three-dimensional hill. It is found that while the IB method using trilinear interpolation works well for simple three-dimensional geometries, a more flexible and robust method is needed for extremely complex geometries, as found in three-dimensional urban environments. A second, more flexible, immersed boundary method is devised using inverse distance weighting, and results are compared to the first IBM approach. Additionally, the functionality to nest a domain with resolved complex geometry inside of a parent domain without resolved complex geometry is described. The new IBM approach is used to model urban terrain from Oklahoma City in a one-way nested configuration, where lateral boundary conditions are provided by the parent domain. Finally, the IB method is extended to include wall model parameterizations for rough surfaces. Two possible implementations are presented, one which uses the log law to reconstruct velocities exterior to the solid domain, and one which reconstructs shear stress at the immersed boundary, rather than velocity. These methods are tested on the three-dimensional canonical case of neutral atmospheric boundary layer flow over flat terrain.

  17. Experimental Study of the EM Transmission Properties of the Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hristov, T.; Friehe, C.; Anderson, K.

    2003-04-01

    The propagation of electro-magnetic signals over the ocean is primarily affected by atmospheric refraction and scattering from the rough ocean surface. Wave-guides (also known as refractive ducts) occurring in the first tens of meters above the sea surface have been modeled extensively, as they influence communications. However, discrepancies between models and measurements have been detected. Here we study experimentally the structure of the atmospheric refractive index and the ocean surface statistics, pertinent to EM signals scattering. The structure and the dynamics the marine atmospheric boundary layer is profoundly affected by the ocean surface waves, which deform the mean wind flow streamlines. In the presence of gradients of the atmospheric humidity and temperature, the deformation of the streamlines displaces the sheared profiles of these quantities and leads to wave-induced fluctuations of the atmospheric refractive index. As a result, radio and optical signals propagating over the ocean encounter a semi-periodic refractive structure, which along with the turbulence can degrade signal's energy. The wave-induced fluctuations of the refractive index are unique to the oceanic environment. Their structure function does not follow the power 2/3 scaling law, valid for turbulent fluctuations, and thus their influence should be studied separately. We analyze data of atmospheric turbulence, humidity, temperature, and sea surface temperature and waves from the Rough Evaporation Duct experiment, conducted in part from the instrument platform FLIP in the open ocean North of Oahu, Hawaii.

  18. Equilibrium Atmospheric Boundary-Layer Flow: Computational Fluid Dynamics Simulation with Balanced Forces

    NASA Astrophysics Data System (ADS)

    Cai, Xuhui; Huo, Qing; Kang, Ling; Song, Yu

    2014-09-01

    Forcing relationships in steady, neutrally stratified atmospheric boundary-layer (ABL) flow are thoroughly analyzed. The ABL flow can be viewed as balanced between a forcing and a drag term. The drag term results from turbulent stress divergence, and above the ABL, both the drag and the forcing terms vanish. In computational wind engineering applications, the ABL flow is simulated not by directly specifying a forcing term in the ABL but by specifying boundary conditions for the simulation domain. Usually, these include the inflow boundary and the top boundary conditions. This `boundary-driven' ABL flow is dynamically different from its real counterpart, and this is the major reason that the simulated boundary-driven ABL flow does not maintain horizontal homogeneity. Here, first a dynamical approach is proposed to develop a neutrally stratified equilibrium ABL flow. Computational fluid dynamics (CFD) software (Fluent 6.3) with the standard - turbulence model is employed, and by applying a driving force profile, steady equilibrium ABL flows are simulated by the model. Profiles of wind speed and turbulent kinetic energy (TKE) derived using this approach are reasonable in comparison with the conventional logarithmic law and with observational data respectively. Secondly, the equilibrium ABL profiles apply as inflow conditions to simulate the boundary-driven ABL flow. Simulated properties between the inlet and the outlet sections across a fetch of 10 km are compared. Although profiles of wind speed, TKE, and its dissipation rate are consistently satisfactory under higher wind conditions, a deviation of TKE and its dissipation rate between the inlet and outlet are apparent (7-8 %) under lower wind-speed conditions (2 m s at 10 m). Furthermore, the simulated surface stress systematically decreases in the downwind direction. A redistribution of the pressure field is also found in the simulation domain, which provides a different driving pattern from the realistic case in

  19. Short term variations of 7Be, 10Be concentrations in atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Yamagata, Takeyasu; Sugihara, Sinji; Morinaga, Ichiro; Matsuzaki, Hiroyuki; Nagai, Hisao

    2010-04-01

    To compare meteorological conditions, short term variations of atmospheric concentrations of 7Be ( T1/2 = 53.3 days) and 10Be ( T1/2 = 1.5 × 10 6 years) were investigated at Tokyo and Fukuoka, Japan, and Pacific Ocean nearby Japan. Atmospheric concentrations of 7Be and 10Be at anticyclone condition were higher than that at cyclone condition to a factor of 2-10. Because of being influenced by re-suspended components from soil ( 10Be/ 7Be > 1000), temporal variability of 10Be/ 7Be was high in daytime and low in nighttime. But when corrected for re-suspended component using Al concentration as an indicator of soil the 10Be/ 7Be ratio was constant. Comparing 7Be and 10Be concentrations with 212Pb concentration as soil-generated component, we make a conclusion that high 7Be and 10Be concentration air mass is brought into boundary layer by high convection at daytime. Those diurnal variations were not observed in marine boundary layer. When cyclone passed through Fukuoka to Tokyo, which is 12 h behind, 7Be and 10Be concentrations also decreased with 12 h lag between Fukuoka and Tokyo. The 10Be/ 7Be ratio was constant during anticyclone to cyclone condition, and between Tokyo and Fukuoka. We conclude that after stratospheric aerosols enter into the upper troposphere they reside there for a certain period and mix uniformly in horizontal strata; later they are transported down to lower troposphere by anticyclone and penetrate into ground level air at daytime by convective strong mixing of boundary layer.

  20. Boundary Layer Flow Control with a One Atmosphere Uniform Glow Discharge Surface Plasma

    NASA Technical Reports Server (NTRS)

    Roth, J. Reece; Sherman, Daniel M.; Wilkinson, Stephen P.

    1998-01-01

    Low speed wind tunnel data have been acquired for planar panels covered by a uniform, glow-discharge surface plasma in atmospheric pressure air known as the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). Streamwise and spanwise arrays of flush, plasma-generating surface electrodes have been studied in laminar, transitional, and fully turbulent boundary layer flow. Plasma between symmetric streamwise electrode strips caused large increases in panel drag, whereas asymmetric spanwise electrode configurations produced a significant thrust. Smoke wire flow visualization and mean velocity diagnostics show the primary cause of the phenomena to be a combination of mass transport and vortical structures induced by strong paraelectric ElectroHydroDynamic (EHD) body forces on the flow.

  1. Flow around new wind fence with multi-scale fractal structure in an atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    McClure, Sarah; Lee, Sang-Joon; Zhang, Wei

    2015-11-01

    Understanding and controlling atmospheric boundary-layer flows with engineered structures, such as porous wind fences or windbreaks, has been of great interest to the fluid mechanics and wind engineering community. Previous studies found that the regular mono-scale grid fence of 50% porosity and a bottom gap of 10% of the fence height are considered to be optimal over a flat surface. Significant differences in turbulent flow structure have recently been noted behind multi-scale fractal wind fences, even with the same porosity. In this study, wind-tunnel tests on the turbulent flow and the turbulence kinetic energy transport of 1D and 2D multi-scale fractal fences under atmospheric boundary-layer were conducted. Velocity fields around the fractal fences were systematically measured using Particle Image Velocimetry to uncover effects of key parameters on turbulent flows around the fences at a Reynolds number of approximately 3.6x104 based on the free-stream speed and fence height. The turbulent flow structures induced by specific 1D/2D multi-scale fractal wind fences were compared to those of a conventional grid fence. The present results would contribute to the design of new-generation wind fences to reduce snow/sand deposition on critical infrastructure such as roads and bridges.

  2. Numerical simulation of small-scale mixing processes in the upper ocean and atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Druzhinin, O.; Troitskaya, Yu; Zilitinkevich, S.

    2016-02-01

    The processes of turbulent mixing and momentum and heat exchange occur in the upper ocean at depths up to several dozens of meters and in the atmospheric boundary layer within interval of millimeters to dozens of meters and can not be resolved by known large- scale climate models. Thus small-scale processes need to be parameterized with respect to large scale fields. This parameterization involves the so-called bulk coefficients which relate turbulent fluxes with large-scale fields gradients. The bulk coefficients are dependent on the properties of the small-scale mixing processes which are affected by the upper-ocean stratification and characteristics of surface and internal waves. These dependencies are not well understood at present and need to be clarified. We employ Direct Numerical Simulation (DNS) as a research tool which resolves all relevant flow scales and does not require closure assumptions typical of Large-Eddy and Reynolds Averaged Navier-Stokes simulations (LES and RANS). Thus DNS provides a solid ground for correct parameterization of small-scale mixing processes and also can be used for improving LES and RANS closure models. In particular, we discuss the problems of the interaction between small-scale turbulence and internal gravity waves propagating in the pycnocline in the upper ocean as well as the impact of surface waves on the properties of atmospheric boundary layer over wavy water surface.

  3. THE SIMULATION OF FINE SCALE NOCTURNAL BOUNDARY LAYER MOTIONS WITH A MESO-SCALE ATMOSPHERIC MODEL

    SciTech Connect

    Werth, D.; Kurzeja, R.; Parker, M.

    2009-04-02

    A field project over the Atmospheric Radiation Measurement-Clouds and Radiation Testbed (ARM-CART) site during a period of several nights in September, 2007 was conducted to explore the evolution of the low-level jet (LLJ). Data was collected from a tower and a sodar and analyzed for turbulent behavior. To study the full range of nocturnal boundary layer (NBL) behavior, the Regional Atmospheric Modeling System (RAMS) was used to simulate the ARM-CART NBL field experiment and validated against the data collected from the site. This model was run at high resolution, and is ideal for calculating the interactions among the various motions within the boundary layer and their influence on the surface. The model reproduces adequately the synoptic situation and the formation and dissolution cycles of the low-level jet, although it suffers from insufficient cloud production and excessive nocturnal cooling. The authors suggest that observed heat flux data may further improve the realism of the simulations both in the cloud formation and in the jet characteristics. In a higher resolution simulation, the NBL experiences motion on a range of timescales as revealed by a wavelet analysis, and these are affected by the presence of the LLJ. The model can therefore be used to provide information on activity throughout the depth of the NBL.

  4. Retrieving 4-dimensional atmospheric boundary layer structure from surface observations and profiles over a single station

    SciTech Connect

    Pu, Zhaoxia

    2015-10-06

    Most routine measurements from climate study facilities, such as the Department of Energy’s ARM SGP site, come from individual sites over a long period of time. While single-station data are very useful for many studies, it is challenging to obtain 3-dimensional spatial structures of atmospheric boundary layers that include prominent signatures of deep convection from these data. The principal objective of this project is to create realistic estimates of high-resolution (~ 1km × 1km horizontal grids) atmospheric boundary layer structure and the characteristics of precipitating convection. These characteristics include updraft and downdraft cumulus mass fluxes and cold pool properties over a region the size of a GCM grid column from analyses that assimilate surface mesonet observations of wind, temperature, and water vapor mixing ratio and available profiling data from single or multiple surface stations. The ultimate goal of the project is to enhance our understanding of the properties of mesoscale convective systems and also to improve their representation in analysis and numerical simulations. During the proposed period (09/15/2011–09/14/2014) and the no-cost extension period (09/15/2014–09/14/2015), significant accomplishments have been achieved relating to the stated goals. Efforts have been extended to various research and applications. Results have been published in professional journals and presented in related science team meetings and conferences. These are summarized in the report.

  5. The Martian atmospheric planetary boundary layer stability, fluxes, spectra, and similarity

    NASA Technical Reports Server (NTRS)

    Tillman, James E.

    1994-01-01

    This is the first analysis of the high frequency data from the Viking lander and spectra of wind, in the Martian atmospheric surface layer, along with the diurnal variation of the height of the mixed surface layer, are calculated for the first time for Mars. Heat and momentum fluxes, stability, and z(sub O) are estimated for early spring, from a surface temperature model and from Viking Lander 2 temperatures and winds at 44 deg N, using Monin-Obukhov similarity theory. The afternoon maximum height of the mixed layer for these seasons and conditions is estimated to lie between 3.6 and 9.2 km. Estimations of this height is of primary importance to all models of the boundary layer and Martian General Circulation Models (GCM's). Model spectra for two measuring heights and three surface roughnesses are calculated using the depth of the mixed layer, and the surface layer parameters and flow distortion by the lander is also taken into account. These experiments indicate that z(sub O), probably lies between 1.0 and 3.0 cm, and most likely is closer to 1.0 cm. The spectra are adjusted to simulate aliasing and high frequency rolloff, the latter caused both by the sensor response and the large Kolmogorov length on Mars. Since the spectral models depend on the surface parameters, including the estimated surface temperature, their agreement with the calculated spectra indicates that the surface layer estimates are self consistent. This agreement is especially noteworthy in that the inertial subrange is virtually absent in the Martian atmosphere at this height, due to the large Kolmogorov length scale. These analyses extend the range of applicability of terrestrial results and demonstrate that it is possible to estimate the effects of severe aliasing of wind measurements, to produce a models which agree well with the measured spectra. The results show that similarity theory developed for Earth applies to Mars, and that the spectral models are universal.

  6. Response of the atmospheric boundary layer to changes in surfaces fluxes

    NASA Astrophysics Data System (ADS)

    Owinoh, A. Z.; Hunt, J. C.; Orr, A.; Clark, P.

    2003-04-01

    The response of the atmospheric boundary layer (ABL) to varying surface fluxes such as surface heat fluxes and roughness changes is a common element in several problems in mesoscale dynamics. We study some of these problems by reducing the complexity of the physical processes that are relevant to mechanism of interest so that analytical solutions can be obtained. Our presentation begins with the examination of the time dependent response and the influence of a 2-D low hill on the flow in a neutral boundary layer to a uniform surface heat flux switched at time, t=0. Analytical solutions for changes in temperature, mean wind and shear stress profiles in the ABL are sought. The modelled profiles are compared with those obtained from the UK Unified Model run on a idealised mode at 12km horizontal resolution. To understand the time and spatial dependence, perturbations are analysed of stratified ABL equations as they pass over areas where there is sharply differing surface heat flux and roughness; a situation freqently observed between rural and urban areas, or across coastline or across sea-ice boundaries. New estimates are derived for the transition distance and how the fluxes, temperature and velocity, vary in the transition distance zone. These simple estimates are compared with Rider et al. (1963) experimental data. Rider N. E., Philip J. R. &Bradley E. F. (1963), The horizontal transport of heat and moisture - A micrometeorological study. Q. J. R. Meteorol. Soc, 89, 507-531.

  7. The detection of clouds, aerosols and marine atmospheric boundary layer characteristics from simulated GLAS data

    NASA Technical Reports Server (NTRS)

    Palm, Stephen P.; Spinhirne, James D.

    1998-01-01

    Scheduled for launch in 2001 as part of NASA's Earth Observing System (EOS), the Geoscience Laser Altimeter System (GLAS) will provide continuous laser sounding of the earth's atmosphere from space for the first time. From its polar orbit about 600 km above the surface, GLAS will employ a 40 Hz solid state laser operating at 1064 nm to measure topography to an accuracy of 10 cm. Simultaneously, the atmospheric channels (1064 and 532 nm) of GLAS will provide profiles of atmospheric backscatter from 40 km to the ground with 75 meter vertical resolution (Spinhirne and Palm, 1996). These measurements will give scientists an unprecedented global data set on the vertical structure of clouds and aerosols which will greatly aid research efforts aimed at understanding their effects on climate and their role in climate change (Hartman, 1994). To better understand and predict the performance of the GLAS atmospheric channels, a computer model was developed to simulate the type of signal that the instrument would likely produce. The model uses aircraft lidar data and provides realistic simulated GLAS data sets over large areas spanning a wide range of atmospheric conditions. These simulated GLAS datasets are invaluable for designing and testing algorithms for the retrieval of parameters such as cloud and aerosol layer height, optical depth and extinction cross section. This work is currently proceeding and in this paper we will present results of the cloud and aerosol detection algorithm with emphasis on the detection of Marine Atmospheric Boundary Layer (MABL) aerosol. In addition, we use a recently developed technique to ascertain the feasability of estimating MABL moisture and temperature structure from spaceborne systems such as GLAS.

  8. 3-D water vapor field in the atmospheric boundary layer observed with scanning differential absorption lidar

    NASA Astrophysics Data System (ADS)

    Späth, Florian; Behrendt, Andreas; Muppa, Shravan Kumar; Metzendorf, Simon; Riede, Andrea; Wulfmeyer, Volker

    2016-04-01

    High-resolution three-dimensional (3-D) water vapor data of the atmospheric boundary layer (ABL) are required to improve our understanding of land-atmosphere exchange processes. For this purpose, the scanning differential absorption lidar (DIAL) of the University of Hohenheim (UHOH) was developed as well as new analysis tools and visualization methods. The instrument determines 3-D fields of the atmospheric water vapor number density with a temporal resolution of a few seconds and a spatial resolution of up to a few tens of meters. We present three case studies from two field campaigns. In spring 2013, the UHOH DIAL was operated within the scope of the HD(CP)2 Observational Prototype Experiment (HOPE) in western Germany. HD(CP)2 stands for High Definition of Clouds and Precipitation for advancing Climate Prediction and is a German research initiative. Range-height indicator (RHI) scans of the UHOH DIAL show the water vapor heterogeneity within a range of a few kilometers up to an altitude of 2 km and its impact on the formation of clouds at the top of the ABL. The uncertainty of the measured data was assessed for the first time by extending a technique to scanning data, which was formerly applied to vertical time series. Typically, the accuracy of the DIAL measurements is between 0.5 and 0.8 g m-3 (or < 6 %) within the ABL even during daytime. This allows for performing a RHI scan from the surface to an elevation angle of 90° within 10 min. In summer 2014, the UHOH DIAL participated in the Surface Atmosphere Boundary Layer Exchange (SABLE) campaign in southwestern Germany. Conical volume scans were made which reveal multiple water vapor layers in three dimensions. Differences in their heights in different directions can be attributed to different surface elevation. With low-elevation scans in the surface layer, the humidity profiles and gradients can be related to different land cover such as maize, grassland, and forest as well as different surface layer

  9. WRF simulations of the atmospheric boundary layer evening transitions during the BLLAST field campaign

    NASA Astrophysics Data System (ADS)

    Sastre Marugán, Mariano; Steeneveld, Gert-Jan; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio; van de Boer, Anneke

    2013-04-01

    The Planetary Boundary Layer (PBL) is mainly ruled by both mechanical and thermal turbulence, and shows an evident diurnal cycle. In the evening transitional period, decay in turbulent kinetic energy occurs, but all the mechanisms behind this decay are still not well understood. In this framework, the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) project aims to improve the knowledge on the physical processes taking place during the late afternoon and evening transition in the lower troposphere. The BLLAST field campaign was organized in Lannemezan (France) from 14th June to 8th July 2011 [1]. Both in situ measurements (i.e., with meteorological towers, surface based instruments, tethered balloons…) and remote sensors (i.e., SODAR, scintillometer…) were used for this purpose, and two different approaches were developed: vertical structure of the boundary layer and spatial heterogeneity. Besides, Numerical Weather Prediction (NWP) models have exhibited substantial difficulties to properly simulate the diurnal cycle in the atmosphere and also the PBL afternoon and evening transition. Typically, some errors are found in air temperature and wind speed close to the surface. Regarding this fact, the main goal of this work is to study how the mesoscale model WRF (Weather Research and Forecast) performs simulations of the evening transition during the BLLAST field campaign. In particular, it is tested for permutations of different PBL and Land Surface Model (LSM) schemes. We try to understand why some differences in model results appear. A comparison between observations and combinations of PBL and LSM parameterizations is shown, testing the sensitivity to these options. We specifically evaluate the surface radiation budget (out- and incoming long- and shortwave radiation), and the surface energy budget variables (latent and sensible heat fluxes, as well as soil heat flux). Furthermore, the vertical profiles of some key variables (such as potential

  10. Some Aspects of the Interaction of Blowing Snow with the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Déry, Stephen J.; Taylor, Peter A.

    1996-10-01

    Several possible effects of blowing snow on the atmospheric boundary layer are investigated, mostly within the general framework of the Prairie Blowing Snow Model (PBSM). The processes of snow saltation and suspension are first described. Variations to the drift density profile are tested and the effects of stratification and density variation calculations are evaluated. Despite high density gradients of blowing snow, stratification effects on turbulence and the velocity profiles can generally be neglected. However, with saltating or suspended snow in a constant shear stress layer, part of the shear stress is carried by the particles. A highly simplified, single-phase approach, based on the density variation of the air-snow mixture coupled to a simple turbulent stress-strain relationship, is used to illustrate this. Sublimation rates in a column of blowing snow are calculated using the PBSM and results are compared with those obtained with a modified formulation which incorporates a spectrum of sublimating particles of varying sizes at each height in a steady-state surface boundary layer and different specifications of the ventilation velocity.

  11. Large Eddy Simulation and Field Experiments of Pollen Transport in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Chamecki, M.; Meneveau, C.; Parlange, M. B.; van Hout, R.

    2006-12-01

    Dispersion of airborne pollen by the wind has been a subject of interest for botanists and allergists for a long time. More recently, the development of genetically modified crops and questions about cross-pollination and subsequent contamination of natural plant populations has brought even more interest to this field. A critical question is how far from the source field pollen grains will be advected. Clearly the answer depends on the aerodynamic properties of the pollen, geometrical properties of the field, topography, local vegetation, wind conditions, atmospheric stability, etc. As a consequence, field experiments are well suited to provide some information on pollen transport mechanisms but are limited to specific field and weather conditions. Numerical simulations do not have this drawback and can be a useful tool to study pollen dispersal in a variety of configurations. It is well known that the dispersion of particles in turbulent fields is strongly affected by the large scale coherent structures. Large Eddy Simulation (LES) is a technique that allows us to study the typical distances reached by pollen grains and, at the same time, resolve the larger coherent structures present in the atmospheric boundary layer. The main objective of this work is to simulate the dispersal of pollen grains in the atmospheric surface layer using LES. Pollen concentrations are simulated by an advection-diffusion equation including gravitational settling. Of extreme importance is the specification of the bottom boundary conditions characterizing the pollen source over the canopy and the deposition process everywhere else. In both cases we make use of the theoretical profile for suspended particles derived by Kind (1992). Field experiments were performed to study the applicability of the theoretical profile to pollen grains and the results are encouraging. Airborne concentrations as well as ground deposition from the simulations are compared to experimental data to validate the

  12. Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

    PubMed Central

    Savarino, Joel; Morin, Samuel; Erbland, Joseph; Grannec, Francis; Patey, Matthew D.; Vicars, William; Alexander, Becky; Achterberg, Eric P.

    2013-01-01

    Long-term observations of the reactive chemical composition of the tropical marine boundary layer (MBL) are rare, despite its crucial role for the chemical stability of the atmosphere. Recent observations of reactive bromine species in the tropical MBL showed unexpectedly high levels that could potentially have an impact on the ozone budget. Uncertainties in the ozone budget are amplified by our poor understanding of the fate of NOx (= NO + NO2), particularly the importance of nighttime chemical NOx sinks. Here, we present year-round observations of the multiisotopic composition of atmospheric nitrate in the tropical MBL at the Cape Verde Atmospheric Observatory. We show that the observed oxygen isotope ratios of nitrate are compatible with nitrate formation chemistry, which includes the BrNO3 sink at a level of ca. 20 ± 10% of nitrate formation pathways. The results also suggest that the N2O5 pathway is a negligible NOx sink in this environment. Observations further indicate a possible link between the NO2/NOx ratio and the nitrogen isotopic content of nitrate in this low NOx environment, possibly reflecting the seasonal change in the photochemical equilibrium among NOx species. This study demonstrates the relevance of using the stable isotopes of oxygen and nitrogen of atmospheric nitrate in association with concentration measurements to identify and constrain chemical processes occurring in the MBL. PMID:23431201

  13. Application of the Remotely Piloted Aircraft (RPA) 'MASC' in Atmospheric Boundary Layer Research

    NASA Astrophysics Data System (ADS)

    Wildmann, Norman; Bange, Jens

    2014-05-01

    The remotely piloted aircraft (RPA) MASC (Multipurpose Airborne Sensor Carrier) was developed at the University of Tübingen in cooperation with the University of Stuttgart, University of Applied Sciences Ostwestfalen-Lippe and 'ROKE-Modelle'. Its purpose is the investigation of thermodynamic processes in the atmospheric boundary layer (ABL), including observations of temperature, humidity and wind profiles, as well as the measurement of turbulent heat, moisture and momentum fluxes. The aircraft is electrically powered, has a maximum wingspan of 3.40 m and a total weight of 5-8 kg, depending on battery- and payload. The standard meteorological payload consists of temperature sensors, a humidity sensor, a flow probe, an inertial measurement unit and a GNSS. In normal operation, the aircraft is automatically controlled by the ROCS (Research Onboard Computer System) autopilot to be able to fly predefined paths at constant altitude and airspeed. Since 2010 the system has been tested and improved intensively. In September 2012 first comparative tests could successfully be performed at the Lindenberg observatory of Germany's National Meteorological Service (DWD). In 2013, several campaigns were done with the system, including fundamental boundary layer research, wind energy meteorology and assistive measurements to aerosol investigations. The results of a series of morning transition experiments in summer 2013 will be presented to demonstrate the capabilities of the measurement system. On several convective days between May and September, vertical soundings were done to record the evolution of the ABL in the early morning, from about one hour after sunrise, until noon. In between the soundings, flight legs of up to 1 km length were performed to measure turbulent statistics and fluxes at a constant altitude. With the help of surface flux measurements of a sonic anemometer, methods of similarity theory could be applied to the RPA flux measurements to compare them to

  14. Applications of the Remotely Piloted Aircraft (RPA) 'MASC' in Atmospheric Boundary Layer Research

    NASA Astrophysics Data System (ADS)

    Wildmann, Norman; Platis, Andreas; Tupman, David-James; Bange, Jens

    2015-04-01

    The remotely piloted aircraft (RPA) MASC (Multipurpose Airborne Sensor Carrier) was developed at the University of Tübingen in cooperation with the University of Stuttgart, University of Applied Sciences Ostwestfalen-Lippe and 'ROKE-Modelle'. Its purpose is the investigation of thermodynamic processes in the atmospheric boundary layer (ABL), including observations of temperature, humidity and wind profiles, as well as the measurement of turbulent heat, moisture and momentum fluxes. The aircraft is electrically powered, has a maximum wingspan of 3.40~m and a total weight of 5-8~kg, depending on the battery- and payload. The standard meteorological payload consists of two temperature sensors, a humidity sensor, a flow probe, an inertial measurement unit and a GNSS. The sensors were optimized for the resolution of small-scale turbulence down to length scales in the sub-meter range. In normal operation, the aircraft is automatically controlled by the ROCS (Research Onboard Computer System) autopilot to be able to fly predefined paths at constant altitude and airspeed. Only take-off and landing are carried out by a human RC pilot. Since 2012, the system is operational and has since then been deployed in more than ten measurement campaigns, with more than 100 measurement flights. The fields of research that were tackled in these campaigns include sensor validation, fundamental boundary-layer research and wind-energy research. In 2014, for the first time, two MASC have been operated at the same time within a distance of a few kilometres, in order to investigate the wind field over an escarpment in the Swabian Alb. Furthermore, MASC was first deployed off-shore in October 2014, starting from the German island Heligoland in the North Sea, for the purpose of characterization of the marine boundary layer for offshore wind parks. Detailed descriptions of the experimental setup and first preliminary results will be presented.

  15. Dynamics above a dense equatorial rain forest from the surface boundary layer to the free atmosphere

    NASA Astrophysics Data System (ADS)

    Lyra, R.; Druilhet, A.; Benech, B.; Biona, C. Bouka

    1992-08-01

    During the Dynamique et Chimie de l'Atmosphère en Forêt Equatoriale (DECAFE) campaign, dynamical and thermodynamical measurements were made at Impfondo (1°37'N, 18°04'W), over the dense rain forest of northern Congo during the dry season (February 1988). During the measurement period the experimental site was located south of the intertropical convergence zone ground track which manages the dynamics of the large scale. Above the experimental site, the atmospheric low layers are supplied by monsoon air coming from the Guinean gulf; the upper layers (>1500 m) are supplied by warm and dry air (trade winds) coming from the northern desert region and the savanna. Our experimental approach consists of analyzing the heat and moisture content in the low troposphere from vertical soundings made by a tethered balloon (0-400 m) and an aircraft (0-4000 m). The analysis of the evolution of the observed planetary boundary layer (PBL) is made with a mixed layer one-dimensional model which is forced to represent correctly the observed PBL height growth. The simulated and observed budgets of the heat and moisture in the PBL are balanced by adding dry air to the simulated PBL in the afternoon. This drying out can be maintained only by high levels of entrainment flux at the PBL top. An entrainment velocity of 3 cm s-1 enables the balancing of the moisture budget. This entrainment velocity seems compatible with physicochemical transfers as those of methane and ozone.

  16. Atmospheric Aerosol and Thermal Structure in the Boundary Layer Over the Los Angeles Basin

    NASA Technical Reports Server (NTRS)

    Johnson, Warren B.

    1973-01-01

    A field study using a mobile lidar was recently conducted in the L. A. Basin, California, to (1) examine the relationship between the vertical aerosol and the thermal structure, and (2) map the vertical aerosol structure in the atmospheric boundary layer over the basin. These data are needed for use in the development of a mixing-depth submodel required for photochemical air Quality simulation models. Toward these ends, a series of lidar aerosol measurements in conjunction with balloon and aircraft temperature soundings were taken at a site in El Monte, and in a mobile mode along a 90-mile freeway loop between El Monte, Santa Monica, and Long Beach. The lidar data are presented in the form of time-height and distance-height cross sections. The results indicate that, although aerosol concentrations are frequently present above the base of the marine inversion, these are generally in stratified layers in contrast to the more uniform nature of the lower convective layer, permitting the mixing depth to be distinguished on this basis. The lidar-derived mixing depths are well correlated (within 100 m) with daytime temperature inversions. Other significant features shown by the lidar data include large Basin-wide mixing-depth variations, waves with amplitudes of 200-300 m and wavelengths of 1000-1500 m on the lower aerosol layer, and apparent aerosol "chimneys" with overrunning in the vicinity of convergence zones.

  17. Interaction of the atmospheric boundary layer with large-scale processes over the Bay of Bengal during MONEX79

    SciTech Connect

    SethuRaman, S.

    1981-01-01

    This paper discusses the role of the atmospheric boundary layer in the Bay of Bengal cyclogenesis processes. The boundary layer experiment at Digha consisted of three main components: (1) a 10 m micrometeorological tower at the beach with instruments to observe turbulent fluxes of heat and momentum over the ocean; (2) a weather station that continuously recorded mean parameters; and (3) pilot balloon observations to a height of about 1000 m.

  18. Atmospheric Boundary Layer Sensors for Application in a Wake Vortex Advisory System

    NASA Technical Reports Server (NTRS)

    Zak, J. Allen; Rutishauser, David (Technical Monitor)

    2003-01-01

    Remote sensing of the atmospheric boundary layer has advanced in recent years with the development of commercial off-the-shelf (COTS) radar, sodar, and lidar wind profiling technology. Radio acoustic sounding systems for vertical temperature profiles of high temporal scales (when compared to routine balloon soundings- (radiosondes) have also become increasingly available as COTS capabilities. Aircraft observations during landing and departures are another source of available boundary layer data. This report provides an updated assessment of available sensors, their performance specifications and rough order of magnitude costs for a potential future aircraft Wake Vortex Avoidance System (WakeVAS). Future capabilities are also discussed. Vertical profiles of wind, temperature, and turbulence are anticipated to be needed at airports in any dynamic wake avoidance system. Temporal and spatial resolution are dependent on the selection of approach and departure corridors to be protected. Recommendations are made for potential configurations of near-term sensor technologies and for testing some of the sensor systems in order to validate performance in field environments with adequate groundtruth.

  19. Polarized light scattering by aerosols in the marine atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Quinby-Hunt, Mary S.; Erskine, Lael L.; Hunt, Arlon J.

    1997-07-01

    The intensity and polarization of light scattered from marine aerosols affect visibility and contrast in the marine atmospheric boundary layer (MABL). The polarization properties of scattered light in the MABL vary with size, refractive index, number distributions, and environmental conditions. Laboratory measurements were used to determine the characteristics and variability of the polarization of light scattered by aerosols similar to those in the MABL. Scattering from laboratory-generated sea-salt-containing (SSC) NaCl, (NH 4 ) 2 SO 4 , and seawater components of marine aerosols was measured with a scanning polarization-modulated nephelometer. Mie theory with Gaussian and log normal size distributions of spheres was used to calculate the polarized light scattering from various aerosol composition models and from experimentally determined distributions of aerosols in the marine boundary layer. The modeling was verified by comparison with scattering from distilled water aerosols. The study suggests that polarimetric techniques can be used to enhance techniques for improving visibility and remote imaging for various aerosol types, Sun angles, and viewing conditions.

  20. Improved Atmospheric Boundary Layer Observations of Tropical Cyclones with the Imaging Wind and Rain Airborne Profiler

    NASA Technical Reports Server (NTRS)

    Fernandez, D. Esteban; Chang, P.; Carswel, J.; Contreras, R.; Chu, T.; Asuzu, P.; Black, P.; Marks, F.

    2006-01-01

    The Imaging Wind and Rain Arborne Profilers (IWRAP) is a dual-frequency, conically-scanning Doppler radar that measures high-resolution, dual-polarized, multi-beam C- and Ku-band reflectivity and Doppler velocity profiles of the atmospheric boundary layer (ABL) within the inner core of hurricanes.From the datasets acquired during the 2002 through 20O5 hurricane seasons as part of the ONR Coupled Boundary Layer Air-Sea Transfer (CBLAST) program and the NOAA/NESDIS Ocean Winds and Rain experiments, very high resolution radar observations of hurricanes have been acquired and made available to the CBLAST community. Of particular interest am the ABL wind fields and 3-D structures found within the inner core of hurricanes. As a result of these analysis, a limitation in the ability to retrieve the ABL wind field at very low altitudes was identified. This paper shows how this limitation has been removed and presents initial results demonstrating its new capabilities to derive the ABL wind field within the inner are of hurricanes to much lower altitudes than the ones the original system was capable of.

  1. Characteristics of Spatiotemporally Homogenized Boundary Layers at Atmospheric Reentry-like Conditions

    NASA Astrophysics Data System (ADS)

    Ulerich, Rhys; Moser, Robert

    2014-11-01

    Turbulent boundary layers approximating those found on the NASA Orion Multi-Purpose Crew Vehicle thermal protection system during atmospheric reentry from the International Space Station have been studied by direct numerical simulation using a ``slow growth'' spatiotemporal homogenization approach recently developed by Topalian et al. The two data sets generated were Mae ~ 0 . 9 and 1 . 15 homogenized boundary layers possessing Reθ ~ 382 and 531, respectively. Edge-to-wall temperature ratios were approximately 4.15 and wall blowing velocities, vw+ =vw /uτ , were roughly 8 ×10-3 . The favorable pressure gradients had Pohlhausen parameters between 25 and 42. Nusselt numbers under 22 were observed. Small or negative displacement effects are evident. Near-wall vorticity fluctuations show qualitatively different profiles than observed by Spalart [J. Fluid Mech. 187 (1988)] or Guarini et al. [J. Fluid Mech. 414 (2000)] suggesting that the simulations have atypical structures perhaps as a consequence of wall blowing or the homogenization. This material is based in part upon work supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615].

  2. Influence of the characteristics of atmospheric boundary layer on the vertical distribution of air pollutant in China's Yangtze River Delta

    NASA Astrophysics Data System (ADS)

    Wang, Chenggang; Cao, Le

    2016-04-01

    Air pollution occurring in the atmospheric boundary layer is a kind of weather phenomenon which decreases the visibility of the atmosphere and results in poor air quality. Recently, the occurrence of the heavy air pollution events has become more frequent all over Asia, especially in Mid-Eastern China. In December 2015, the most severe air pollution in recorded history of China occurred in the regions of Yangtze River Delta and Beijing-Tianjin-Hebei. More than 10 days of severe air pollution (Air Quality Index, AQI>200) appeared in many large cities of China such as Beijing, Tianjin, Shijiazhuang and Baoding. Thus, the research and the management of the air pollution has attracted most attentions in China. In order to investigate the formation, development and dissipation of the air pollutions in China, a field campaign has been conducted between January 1, 2015 and January 28, 2015 in Yangtze River Delta of China, aiming at a intensive observation of the vertical structure of the air pollutants in the atmospheric boundary layer during the time period with heavy pollution. In this study, the observation data obtained in the field campaign mentioned above is analyzed. The characteristics of the atmospheric boundary layer and the vertical distribution of air pollutants in the city Dongshan located in the center of Lake Taihu are shown and discussed in great detail. It is indicated that the stability of the boundary layer is the strongest during the nighttime and the early morning of Dongshan. Meanwhile, the major air pollutants, PM2.5 and PM10 in the boundary layer, reach their maximum values, 177.1μg m-3 and 285μg m-3 respectively. The convective boundary layer height in the observations ranges from approximately 700m to 1100m. It is found that the major air pollutants tend to be confined in a relatively shallow boundary layer, which represents that the boundary layer height is the dominant factor for controlling the vertical distribution of the air pollutants. In

  3. Surface ozone-aerosol behaviour and atmospheric boundary layer structure in Saharan dusty scenario

    NASA Astrophysics Data System (ADS)

    Adame, Jose; Córdoba-Jabonero, Carmen; Sorrribas, Mar; Gil-Ojeda, Manuel; Toledo, Daniel; Yela, Margarita

    2016-04-01

    A research campaign was performed for the AMISOC (Atmospheric Minor Species relevant to the Ozone Chemistry) project at El Arenosillo observatory (southwest Spain) in May-June 2012. The campaign focused on the impact of Saharan dust intrusions at the Atmospheric Boundary Layer (ABL) and ozone-aerosol interactions. In-situ and remote-sensing techniques for gases and aerosols were used moreover to modelling analyses. Meteorology features, ABL structures and evolution, aerosol profiling distributions and aerosol-ozone interactions on the surface were analysed. Two four-day periods were selected according to non-dusty (clean conditions) and dusty (Saharan dust) situations. In both scenarios, sea-land breezes developed in the lower atmosphere, but differences were found in the upper levels. Results show that surface temperatures were greater than 3°C and humidity values were lower during dusty conditions than non-dusty conditions. Thermal structures on the surface layer (estimated using an instrument on a 100 m tower) show differences, mainly during nocturnal periods with less intense inversions under dusty conditions. The mixing layer during dusty days was 400-800 m thick, less than observed on non-dusty days. Dust also disturbed the typical daily ABL evolution. Stable conditions were observed during the early evening during intrusions. Aerosol extinction on dusty days was 2-3 times higher, and the dust was confined between 1500 and 5500 m. Back trajectory analyses confirmed that the dust had an African origin. On the surface, the particle concentration was approximately 3.5 times higher during dusty events, but the local ozone did not exhibit any change. The arrival of Saharan dust in the upper levels impacted the meteorological surface, inhibited the daily evolution of the ABL and caused an increase in aerosol loading on the surface and at higher altitudes; however, no dust influence was observed on surface ozone.

  4. An Experimental Study of the Statistical Scaling of Turbulent Surface Pressure in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Lyons, G. W.; Murray, N. E.

    2015-12-01

    Turbulence in the atmospheric boundary layer (ABL) produces fluctuations in the static pressure. The instantaneous pressure at a point depends on an integral over the entire flow; therefore, the effects from turbulence far aloft may be felt at the earth's surface. The statistics of fluctuating pressure at the surface have been studied extensively in the context of wall-bounded engineering-type flows. At best, these neutral flows are a special case of the thermally-stratified ABL, but relatively few experimental studies have considered pressure at the ground under various stability conditions. Here the scaling of pressure statistics at the surface, particularly the spectral density, is reported over a range of convective and stable conditions for both inner and outer turbulence parameters. Measurements of turbulent surface pressure were made using low-frequency microphones buried flush to the ground in a field near Laramie, Wyoming. Simultaneous measurements from three near-surface sonic anemometers and a 50-meter wind tower give estimates of the mean surface-layer parameters. The normalization of the pressure spectrum with the inner scales collapses the spectra along the high-frequency viscous power-law band. The wall shear stress, Obukhov length, L, and horizontal integral scale, λ, are identified as outer scaling parameters for the surface pressure spectrum from an integral solution employing a Monin-Obukhov-similar profile and a simple model of inhomogeneous surface-layer turbulence. Normalization with the outer scales collapses the spectra at low frequencies. Spectral scaling also reveals trends with λ/L in the low-frequency region for both convective and stable boundary layers.

  5. Aerosols in the Convective Boundary Layer: Radiation Effects on the Coupled Land-Atmosphere System

    NASA Astrophysics Data System (ADS)

    Barbaro, E.; Vila-Guerau Arellano, J.; Ouwersloot, H. G.; Schroter, J.; Donovan, D. P.; Krol, M. C.

    2013-12-01

    We investigate the responses of the surface energy budget and the convective boundary-layer (CBL) dynamics to the presence of aerosols using a combination of observations and numerical simulations. A detailed observational dataset containing (thermo)dynamic variables observed at CESAR (Cabauw Experimental Site for Atmospheric Research) and aerosol information from the European Integrated Project on Aerosol, Cloud, Climate, and Air Quality Interactions (IMPACT/EUCAARI) campaign is employed to design numerical experiments reproducing two prototype clear-sky days characterized by: (i) a well-mixed residual layer above a ground inversion and (ii) a continuously growing CBL. A large-eddy simulation (LES) model and a mixed-layer (MXL) model, both coupled to a broadband radiative transfer code and a land-surface model, are used to study the impacts of aerosol scattering and absorption of shortwave radiation on the land-atmosphere system. We successfully validate our model results using the measurements of (thermo)dynamic variables and aerosol properties for the two different CBL prototypes studied here. Our findings indicate that in order to reproduce the observed surface energy budget and CBL dynamics, information of the vertical structure and temporal evolution of the aerosols is necessary. Given the good agreement between the LES and the MXL model results, we use the MXL model to explore the aerosol effect on the land-atmosphere system for a wide range of optical depths and single scattering albedos. Our results show that higher loads of aerosols decrease irradiance, imposing an energy restriction at the surface. Over the studied well-watered grassland, aerosols reduce the sensible heat flux more than the latent heat flux. As a result, aerosols increase the evaporative fraction. Moreover, aerosols also delay the CBL morning onset and anticipate its afternoon collapse. If also present above the CBL during the morning transition, aerosols maintain a persistent near

  6. On Lamb wave propagation from small surface explosions in the atmospheric boundary layer

    SciTech Connect

    ReVelle, D.O.; Kulichkov, S.N.

    1998-12-31

    The problem of Lamb waves propagation from small explosions in the atmospheric boundary layer are discussed. The results of lamb waves registrations from surface explosions with yields varied from 3 tons up to a few hundred tons (TNT equivalent) are presented. The source-receiver distances varied from 20 km up to 310 km. Most of the explosions were conducted during the evening and early morning hours when strong near-surface temperature and wind inversions existed. The corresponding profiles of effective sound velocity are presented. Some of the explosions had been realized with 15 minute intervals between them when morning inversion being destroyed. Corresponding transformation of Lamb waves was observed. The Korteveg-de Vrize equation to explain experimental data on Lamb waves propagation along earth surface is used.

  7. The influence of Nunataks on atmospheric boundary layer convection during summer in Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Stenmark, Aurora; Hole, Lars Robert; Voss, Paul; Reuder, Joachim; Jonassen, Marius O.

    2014-06-01

    The effects of nunataks on temperature profiles and wind patterns are studied using simulations from the Weather Research and Forecasting model. Simulations are compared to hourly observations from an automatic weather station located at the Troll Research Station in Dronning Maud Land. Areas of bare ground have been implemented in the model, and the simulations correspond well with meteorological measurements acquired during the 4 day simulation period. The nunataks are radiatively heated during daytime, and free convection occurs in the overlying atmospheric boundary layer. The inflow below the updraft forces strong horizontal convergence at the surface, whereas weaker divergence appears aloft. In a control run with a completely ice-covered surface, the convection is absent. In situ observations carried out by a remotely controlled balloon and a small model airplane compare well with model temperature profiles, but these are only available over the ice field upwind to the nunatak.

  8. Interaction of Atmospheric Boundary Layer Flow With Permeable Tapered Forest Edges

    NASA Astrophysics Data System (ADS)

    Ruck, B.; Frank, C.; Tischmacher, M.

    2010-05-01

    Experimental investigations in an atmospheric boundary layer wind tunnel were carried out in order to study the influence of the windward forest edge structure on the flow characteristics above the canopy. Two different types of forest edges were used: abstracted edges, made of highly porous foam, and more realistic edges, consisting of individual model trees. The taper angle of the edge was varied three times for both edge types and all edges were combined with both dense and sparse forest stands. Time-averaged mean and turbulent flow quantities were measured by means of a two-dimensional laser Doppler anemometer system (LDA) and are presented in form of horizontal profiles near the canopy top.

  9. Isotope discrimination and partitioning exercises at the scale of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Berry, J.; Helliker, B.; Bakwin, P.; Davis, K.; Torn, M.

    2003-12-01

    During the daytime the atmospheric boundary layer (ABL) is typically well mixed by convection up to about 1.5 km and moves across the land about 500 km per day. Underlying ecosystems modify carbon dioxide in the ABL through photosynthesis and respiration, and ABL air is ultimately replaced by air from the overlying free troposphere. Hence, measurements of carbon dioxide and isotopes in the ABL and the free troposphere offer the potential for regionally integrated estimates of isotope discrimination. We use tall-tower and airplane measurements of carbon dioxide and carbon and oxygen isotopes to develop estimates of ABL-scale isotope discrimination. We then utilize ecosystem-level measurements of the isotope ratio of respiration and land surface model estimates of photosynthetic discrimination to deconvolve net carbon dioxide fluxes into the gross components of photosynthesis and respiration at the regional scale.

  10. Acid–base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer

    PubMed Central

    Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L.; Eisele, Fred L.; Siepmann, J. Ilja; Hanson, David R.; Zhao, Jun; McMurry, Peter H.

    2012-01-01

    Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid–base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta. PMID:23091030

  11. Large Eddy Simulation of Pollen Transport in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Chamecki, Marcelo; Meneveau, Charles; Parlange, Marc B.

    2007-11-01

    The development of genetically modified crops and questions about cross-pollination and contamination of natural plant populations enhanced the importance of understanding wind dispersion of airborne pollen. The main objective of this work is to simulate the dispersal of pollen grains in the atmospheric surface layer using large eddy simulation. Pollen concentrations are simulated by an advection-diffusion equation including gravitational settling. Of great importance is the specification of the bottom boundary conditions characterizing the pollen source over the canopy and the deposition process everywhere else. The velocity field is discretized using a pseudospectral approach. However the application of the same discretization scheme to the pollen equation generates unphysical solutions (i.e. negative concentrations). The finite-volume bounded scheme SMART is used for the pollen equation. A conservative interpolation scheme to determine the velocity field on the finite volume surfaces was developed. The implementation is validated against field experiments of point source and area field releases of pollen.

  12. Atmospheric new particle formation as source of CCN in the Eastern Mediterranean marine boundary layer

    NASA Astrophysics Data System (ADS)

    Kalivitis, N.; Kerminen, V.-M.; Kouvarakis, G.; Stavroulas, I.; Bougiatioti, A.; Nenes, A.; Manninen, H. E.; Petäjä, T.; Kulmala, M.; Mihalopoulos, N.

    2015-04-01

    While Cloud Condensation Nuclei (CCN) production associated with atmospheric new particle formation (NPF) is thought to be frequent throughout the continental boundary layers, few studies on this phenomenon in marine air exist. Here, based on simultaneous measurement of particle number size distributions, CCN properties and aerosol chemical composition, we present the first direct evidence on CCN production resulting from NPF in the Eastern Mediterranean atmosphere. We show that condensation of both gaseous sulfuric acid and organic compounds from multiple sources leads to the rapid growth of nucleated particles to CCN sizes in this environment during the summertime. Sub-100 nm particles were found to be substantially less hygroscopic than larger particles during the period with active NPF and growth (0.2-0.4 lower κ between the 60 and 120 nm particles), probably due to enrichment of organic material in the sub-100 nm size range. The aerosol hygroscopicity tended to be at minimum just before the noon and at maximum in afternoon, which was very likely due to the higher sulfate to organic ratios and higher degree of oxidation of the organic material during the afternoon. Simultaneously to the formation of new particles during daytime, particles formed in the previous day or even earlier were growing into the size range relevant to cloud droplet activation, and the particles formed in the atmosphere were possibly mixed with long-range transported particles.

  13. Atmospheric new particle formation as a source of CCN in the eastern Mediterranean marine boundary layer

    NASA Astrophysics Data System (ADS)

    Kalivitis, N.; Kerminen, V.-M.; Kouvarakis, G.; Stavroulas, I.; Bougiatioti, A.; Nenes, A.; Manninen, H. E.; Petäjä, T.; Kulmala, M.; Mihalopoulos, N.

    2015-08-01

    While cloud condensation nuclei (CCN) production associated with atmospheric new particle formation (NPF) is thought to be frequent throughout the continental boundary layers, few studies on this phenomenon in marine air exist. Here, based on simultaneous measurement of particle number size distributions, CCN properties and aerosol chemical composition, we present the first direct evidence on CCN production resulting from NPF in the eastern Mediterranean atmosphere. We show that condensation of both gaseous sulfuric acid and organic compounds from multiple sources leads to the rapid growth of nucleated particles to CCN sizes in this environment during the summertime. Sub-100 nm particles were found to be substantially less hygroscopic than larger particles during the period with active NPF and growth (the value of κ was lower by 0.2-0.4 for 60 nm particles compared with 120 nm particles), probably due to enrichment of organic material in the sub-100 nm size range. The aerosol hygroscopicity tended to be at minimum just before the noon and at maximum in the afternoon, which was very likely due to the higher sulfate-to-organic ratios and higher degree of oxidation of the organic material during the afternoon. Simultaneous with the formation of new particles during daytime, particles formed during the previous day or even earlier were growing into the size range relevant to cloud droplet activation, and the particles formed in the atmosphere were possibly mixed with long-range-transported particles.

  14. Large eddy simulations and reduced models of the Unsteady Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Momen, M.; Bou-Zeid, E.

    2013-12-01

    Most studies of the dynamics of Atmospheric Boundary Layers (ABLs) have focused on steady geostrophic conditions, such as the classic Ekman boundary layer problem. However, real-world ABLs are driven by a time-dependent geostrophic forcing that changes at sub-diurnal scales. Hence, to advance our understanding of the dynamics of atmospheric flows, and to improve their modeling, the unsteady cases have to be analyzed and understood. This is particularly relevant to new applications related to wind energy (e.g. short-term forecast of wind power changes) and pollutant dispersion (forecasting of rapid changes in wind velocity and direction after an accidental spill), as well as to classic weather prediction and hydrometeorological applications. The present study aims to investigate the ABL behavior under variable forcing and to derive a simple model to predict the ABL response under these forcing fluctuations. Simplifications of the governing Navier-Stokes equations, with the Coriolis force, are tested using LES and then applied to derive a physical model of the unsteady ABL. LES is then exploited again to validate the analogy and the output of the simpler model. Results from the analytical model, as well as LES outputs, open the way for inertial oscillations to play an important role in the dynamics. Several simulations with different variable forcing patterns are then conducted to investigate some of the characteristics of the unsteady ABL such as resonant frequency, ABL response time, equilibrium states, etc. The variability of wind velocity profiles and hodographs, turbulent kinetic energy, and vertical profiles of the total stress and potential temperature are also examined. Wind Hodograph of the Unsteady ABL at Different Heights - This figure shows fluctuations in the mean u and v components of the velocity as time passes due to variable geostrophic forcing

  15. Radical product yields from the ozonolysis of short chain alkenes under atmospheric boundary layer conditions.

    PubMed

    Alam, Mohammed S; Rickard, Andrew R; Camredon, Marie; Wyche, Kevin P; Carr, Timo; Hornsby, Karen E; Monks, Paul S; Bloss, William J

    2013-11-27

    The gas-phase reaction of ozone with unsaturated volatile organic compounds (VOCs), alkenes, is an important source of the critical atmospheric oxidant OH, especially at night when other photolytic radical initiation routes cannot occur. Alkene ozonolysis is also known to directly form HO2 radicals, which may be readily converted to OH through reaction with NO, but whose formation is poorly understood. We report a study of the radical (OH, HO2, and RO2) production from a series of small alkenes (propene, 1-butene, cis-2-butene, trans-2-butene, 2-methylpropene, 2,3-dimethyl-2-butene (tetramethyl ethene, TME), and isoprene). Experiments were performed in the European Photoreactor (EUPHORE) atmospheric simulation chamber, with OH and HO2 levels directly measured by laser-induced fluorescence (LIF) and HO2 + ΣRO2 levels measured by peroxy-radical chemical amplification (PERCA). OH yields were found to be in good agreement with the majority of previous studies performed under comparable conditions (atmospheric pressure, long time scales) using tracer and scavenger approaches. HO2 yields ranged from 4% (trans-2-butene) to 34% (2-methylpropene), lower than previous experimental determinations. Increasing humidity further reduced the HO2 yields obtained, by typically 50% for an RH increase from 0.5 to 30%, suggesting that HOx production from alkene ozonolysis may be lower than current models suggest under (humid) ambient atmospheric boundary layer conditions. The mechanistic origin of the OH and HO2 production observed is discussed in the context of previous experimental and theoretical studies. PMID:24171583

  16. Large eddy simulation of a large wind-turbine array in a conventionally neutral atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2015-06-01

    Under conventionally neutral conditions, the boundary layer is frequently capped by an inversion layer, which counteracts vertical entrainment of kinetic energy. Very large wind farms are known to depend on vertical entrainment to transport energy from above the farm towards the turbines. In this study, large eddy simulations of an infinite wind-turbine array in a conventionally neutral atmospheric boundary layer are performed. By carefully selecting the initial potential-temperature profile, the influence of the height and the strength of a capping inversion on the power output of a wind farm is investigated. Results indicate that both the height and the strength have a significant effect on the boundary layer flow, and that the height of the neutral boundary layer is effectively controlled by the capping inversion. In addition, it is shown that the vertical entrainment rate decreases for increasing inversion strength or height. In our infinite wind-farm simulations, varying the inversion characteristics leads to differences in power extraction on the order of 13% ± 0.2% (for increasing the strength from 2.5 to 10 K), and 31% ± 0.4% (for increasing the height from 500 to 1500 m). A detailed analysis of the mean kinetic-energy equation is included, showing that the variation in power extraction originates from the work done by the driving pressure gradient related to the boundary layer height and the geostrophic angle, while entrainment of kinetic energy from the free atmosphere does not play a significant role. Also, the effect of inversion strength on power extraction is energetically not related to different amounts of energy entrained, but explained by a difference in boundary layer growth, leading to higher boundary layers for lower inversion strengths. We further present a simple analytical model that allows to obtain wind-farm power output and driving power for the fully developed regime as function of Rossby number and boundary layer height.

  17. Multiyear measurements of the oceanic and atmospheric boundary layers at the Brazil-Malvinas confluence region

    NASA Astrophysics Data System (ADS)

    Pezzi, Luciano Ponzi; de Souza, Ronald Buss; Acevedo, OtáVio; Wainer, Ilana; Mata, Mauricio M.; Garcia, Carlos A. E.; de Camargo, Ricardo

    2009-10-01

    This study analyzes and discusses data taken from oceanic and atmospheric measurements performed simultaneously at the Brazil-Malvinas Confluence (BMC) region in the southwestern Atlantic Ocean. This area is one of the most dynamical frontal regions of the world ocean. Data were collected during four research cruises in the region once a year in consecutive years between 2004 and 2007. Very few studies have addressed the importance of studying the air-sea coupling at the BMC region. Lateral temperature gradients at the study region were as high as 0.3°C km-1 at the surface and subsurface. In the oceanic boundary layer, the vertical temperature gradient reached 0.08°C m-1 at 500 m depth. Our results show that the marine atmospheric boundary layer (MABL) at the BMC region is modulated by the strong sea surface temperature (SST) gradients present at the sea surface. The mean MABL structure is thicker over the warmside of the BMC where Brazil Current (BC) waters predominate. The opposite occurs over the coldside of the confluence where waters from the Malvinas (Falkland) Current (MC) are found. The warmside of the confluence presented systematically higher MABL top height compared to the coldside. This type of modulation at the synoptic scale is consistent to what happens in other frontal regions of the world ocean, where the MABL adjusts itself to modifications along the SST gradients. Over warm waters at the BMC region, the MABL static instability and turbulence were increased while winds at the lower portion of the MABL were strong. Over the coldside of the BC/MC front an opposite behavior is found: the MABL is thinner and more stable. Our results suggest that the sea-level pressure (SLP) was also modulated locally, together with static stability vertical mixing mechanism, by the surface condition during all cruises. SST gradients at the BMC region modulate the synoptic atmospheric pressure gradient. Postfrontal and prefrontal conditions produce opposite thermal

  18. Stability and Turbulence in the Atmospheric Boundary Layer: A Comparison of Remote Sensing and Tower Observations

    SciTech Connect

    Friedrich, K.; Lundquist, J. K.; Aitken, M.; Kalina, E. A.; Marshall, R. F.

    2012-01-01

    When monitoring winds and atmospheric stability for wind energy applications, remote sensing instruments present some advantages to in-situ instrumentation such as larger vertical extent, in some cases easy installation and maintenance, measurements of vertical humidity profiles throughout the boundary layer, and no restrictions on prevailing wind directions. In this study, we compare remote sensing devices, Windcube lidar and microwave radiometer, to meteorological in-situ tower measurements to demonstrate the accuracy of these measurements and to assess the utility of the remote sensing instruments in overcoming tower limitations. We compare temperature and wind observations, as well as calculations of Brunt-Vaisala frequency and Richardson numbers for the instrument deployment period in May-June 2011 at the U.S. Department of Energy National Renewable Energy Laboratory's National Wind Technology Center near Boulder, Colorado. The study reveals that a lidar and radiometer measure wind and temperature with the same accuracy as tower instruments, while also providing advantages for monitoring stability and turbulence. We demonstrate that the atmospheric stability is determined more accurately when the liquid-water mixing ratio derived from the vertical humidity profile is considered under moist-adiabatic conditions.

  19. Internal gravity-shear waves in the atmospheric boundary layer from acoustic remote sensing data

    NASA Astrophysics Data System (ADS)

    Lyulyukin, V. S.; Kallistratova, M. A.; Kouznetsov, R. D.; Kuznetsov, D. D.; Chunchuzov, I. P.; Chirokova, G. Yu.

    2015-03-01

    The year-round continuous remote sounding of the atmospheric boundary layer (ABL) by means of the Doppler acoustic radar (sodar) LATAN-3 has been performed at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, since 2008. A visual analysis of sodar echograms for four years revealed a large number of wavelike patterns in the intensity field of a scattered sound signal. Similar patterns were occasionally identified before in sodar, radar, and lidar sounding data. These patterns in the form of quasi-periodic inclined stripes, or cat's eyes, arise under stable stratification and significant vertical wind shears and result from the loss of the dynamic stability of the flow. In the foreign literature, these patterns, which we call internal gravity-shear waves, are often associated with Kelvin-Helmholtz waves. In the present paper, sodar echograms are classified according to the presence or absence of wavelike patterns, and a statistical analysis of the frequency of their occurrence by the year and season was performed. A relationship between the occurrence of the patterns and wind shear and between the wave length and amplitude was investigated. The criteria for the identification of gravity-shear waves, meteorological conditions of their excitation, and issues related to their observations were discussed.

  20. Stability and turbulence in the atmospheric boundary layer: A comparison of remote sensing and tower observations

    NASA Astrophysics Data System (ADS)

    Friedrich, Katja; Lundquist, Julie K.; Aitken, Matthew; Kalina, Evan A.; Marshall, Robert F.

    2012-02-01

    When monitoring winds and atmospheric stability for wind energy applications, remote sensing instruments present some advantages to in-situ instrumentation such as larger vertical extent, in some cases easy installation and maintenance, measurements of vertical humidity profiles throughout the boundary layer, and no restrictions on prevailing wind directions. In this study, we compare remote sensing devices, Windcube lidar and microwave radiometer, to meteorological in-situ tower measurements to demonstrate the accuracy of these measurements and to assess the utility of the remote sensing instruments in overcoming tower limitations. We compare temperature and wind observations, as well as calculations of Brunt-Väisälä frequency and Richardson numbers for the instrument deployment period in May-June 2011 at the U.S. Department of Energy National Renewable Energy Laboratory's National Wind Technology Center near Boulder, Colorado. The study reveals that a lidar and radiometer measure wind and temperature with the same accuracy as tower instruments, while also providing advantages for monitoring stability and turbulence. We demonstrate that the atmospheric stability is determined more accurately when the liquid-water mixing ratio derived from the vertical humidity profile is considered under moist-adiabatic conditions.

  1. The Relation Between Wind Speed and Air-Sea Temperature Difference in the Marine Atmospheric Boundary Layer off Northwest Europe

    NASA Astrophysics Data System (ADS)

    Kettle, A. J.

    2014-12-01

    Wind speed and atmospheric stability have an important role in determining the turbulence in the marine atmospheric boundary layer (MABL) as well as the surface wave field. The understanding of MABL dynamics in northwest Europe is complicated by fetch effects, the proximity of coastlines, shallow topography, and larger scale circulation patterns (e.g., cold air outbreaks). Numerical models have difficulty simulating the marine atmospheric boundary layer in coastal areas and partially enclosed seas, and this is partly due to spatial resolution problems at coastlines. In these offshore environments, the boundary layer processes are often best understood directly from time series measurements from fixed platforms or buoys, in spite of potential difficulties from platform flow distortion as well as the spatial sparseness of the data sets. This contribution presents the results of time series measurements from offshore platforms in the North Sea and Norwegian Sea in terms of a summary diagnostic - wind speed versus air-sea temperature difference (U-ΔT) - with important implications for understanding atmospheric boundary layer processes. The U-ΔT diagram was introduced in earlier surveys of data from coastal (Sletringen; O.J. Andersen and J. Løvseth, J. Wind Eng. Ind. Aerodyn., 57, 97-109, 1995) and offshore (Statfjord A; K.J. Eidsvik, Boundary-Layer Meteorol., 32, 103-132, 1985) sites in northwest Europe to summarize boundary layer conditions at a given location. Additional information from a series of measurement purpose-built offshore measurement and oil/gas production platforms from the southern North Sea to the Norwegian Sea illustrates how the wind characteristics vary spatially over large distances, highlighting the influence of cold air outbreaks, in particular. The results are important for the offshore wind industry because of the way that wind turbines accrue fatigue damage in different conditions of atmospheric stability and wind speed.

  2. Nonequilibrium Response of the Daytime Atmospheric Boundary Layer to Mesoscale Forcing

    NASA Astrophysics Data System (ADS)

    Brasseur, James; Jayaraman, Bajali; Haupt, Sue; Lee, Jared

    2015-11-01

    The essential turbulence structure of the daytime atmospheric boundary layer (ABL) is driven by interactions between shear and buoyancy. A relatively strong inversion layer ``lid'' typically confines the ABL turbulence, whose height grows during the day with increasing surface heat flux (Q0) to ~ 1-2 km before collapsing with Q0 towards the day's end. The 3D ``microscale'' ABL turbulence is forced largely in the horizontal by winds above the capping inversion at the ``mesoscale'' at the O(100) km scale. Whereas the ``canonical'' ABL is in equilibrium and quasi-stationary, quasi-2D weather dynamics at the mesoscale is typically nonstationary at sub-diurnal time scales. We study the consequences of nonstationarity in the quasi-2D mesoscale forcing in horizontal winds and solar heating on the dynamics of ABL turbulence and especially on the potential for significant deviations from the canonical equilibrium state. We apply high-fidelity LES of the dry cloudless ABL over Kansas in July forced at the mesoscale (WRF) with statistical homogeneity in the horizontal. We find significant deviations from equilibrium that appear in a variety of interesting ways. One of the more interesting results is that the changes in mesoscale wind direction at the diurnal time scale can destabilize the ABL and sometimes cause a transition in ABL eddy structure that are normally associated with increased surface heating. Supported by DOE. Computer resources by the Penn State ICS.

  3. Dust aerosol radiative effect and influence on urban atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Chen, M.; Li, L.

    2007-11-01

    An 1.5-level-closure and 3-D non-stationary atmospheric boundary layer (ABL) model and a radiation transfer model with the output of Weather Research and Forecast (WRF) Model and lidar AML-1 are employed to simulate the dust aerosol radiative effect and its influence on ABL in Beijing for the period of 23-26 January 2002 when a dust storm occurred. The simulation shows that daytime dust aerosol radiative effect heats up the ABL at the mean rate of about 0.68 K/h. The horizontal wind speed from ground to 900 m layer is also overall increased, and the value changes about 0.01 m/s at 14:00 LT near the ground. At night, the dust aerosol radiative effect cools the ABL at the mean rate of -0.21 K/h and the wind speed lowers down at about -0.19 m/s at 02:00 LT near the ground.

  4. A Study On Atmospheric Boundary-Layer Characteristics At Anand, India Using Lsp Experimental Data Sets

    NASA Astrophysics Data System (ADS)

    Satyanarayana, A. N. V.; Lykossov, V. N.; Mohanty, U. C.

    An attempt is made to study the planetary boundary layer (PBL) characteristics during the winter period at Anand (22.4°N, 72.6°E), a semi-arid region, which is located in the western part of India. A one-dimensional turbulent kinetic energy (TKE) closure model is used for the study. The structure of the PBL,which consists of profiles of zonal and meridional components of wind,potential temperature and specific humidity, is simulated. A one-dimensional soil heat and moisture transport parameterization scheme is incorporated for the accurate representation of the energy exchange processes at the soil-atmosphere interface. The diurnal variation of fluxes of sensible heat, latent heat, shortwave radiation, net radiation and soil flux, soil temperature at different depths, Richardson number and TKE at the height of the constant flux layer is studied. The model predictions are compared with the available observations obtained from a special Land Surface Processes (LSP) experiment.

  5. Atmospheric Feedback of Urban Boundary Layer with Implications for Climate Adaptation.

    PubMed

    Liang, Marissa S; Keener, Timothy C

    2015-09-01

    Atmospheric structure changes in response to the urban form, land use, and the type of land cover (LULC). This interaction controls thermal and air pollutant transport and distribution. The interrelationships among LULC, ambient temperature, and air quality were analyzed and found to be significant in a case study in Cincinnati, Ohio, U.S.A. Within the urban canopy layer (UCL), traffic-origin PM2.5 and black carbon followed Gaussian dispersion in the near road area in the daytime, while higher concentrations, over 1 order of magnitude, were correlated to the lapse rate under nocturnal inversions. In the overlying urban boundary layer (UBL), ambient temperature and PM2.5 variations were correlated among urban-wide locations indicating effective thermal and mass communications. Beyond the spatial correlation, LULC-related local urban heat island effects are noteworthy. The high-density urbanized zone along a narrow highway-following corridor is marked by higher nighttime temperature by ∼1.6 °C with a long-term increase by 2.0 °C/decade, and by a higher PM2.5 concentration, than in the low-density residential LULC. These results indicate that the urban LULC may have contributed to the nocturnal thermal inversion affecting urban air circulation and air quality in UCL and UBL. Such relationships point to the potentials of climate adaptation through urban planning. PMID:26237246

  6. Comparing modeled isoprene with aircraft-based measurements in the atmospheric boundary layer.

    SciTech Connect

    Doskey, P.; Gao, W.

    1997-12-12

    Nonmethane hydrocarbons (NMHCs) are involved in a complex series of reactions that regulate the levels of oxidants in the troposphere. Isoprene (C{sub 5}H{sub 8}), the primary NMHC emitted from deciduous trees, is one of the most important reactive hydrocarbons in the troposphere. The amount of isoprene entering the free troposphere is regulated by the compound's rate of emission from leaves and by chemical and physical processes in the forest canopy and the atmospheric boundary layer (ABL). This study uses a coupled canopy-ABL model to simulate these complex processes and compares calculated isoprene concentration profiles with those measured during aircraft flights above a forested region in the northeastern US. Land use information is coupled with satellite remote sensing data to describe spatial changes in canopy density during the field measurements. The high-resolution transport-chemistry model of Gao et al. (1993) for the ABL and the forest canopy layer is used to simulate vertical changes in isoprene concentration due to turbulent mixing and chemical reactions. The one-dimensional (1-D) ABL model includes detailed radiation transfer, turbulent diffusion, biogenic emissions, dry deposition, and chemical processes within the forest canopy and the ABL. The measured profiles are compared with the model simulations to investigate the biological, physical, and chemical processes that regulate the levels of isoprene within the ABL.

  7. Pollutant Plume Dispersion in the Atmospheric Boundary Layer over Idealized Urban Roughness

    NASA Astrophysics Data System (ADS)

    Wong, Colman C. C.; Liu, Chun-Ho

    2013-05-01

    The Gaussian model of plume dispersion is commonly used for pollutant concentration estimates. However, its major parameters, dispersion coefficients, barely account for terrain configuration and surface roughness. Large-scale roughness elements (e.g. buildings in urban areas) can substantially modify the ground features together with the pollutant transport in the atmospheric boundary layer over urban roughness (also known as the urban boundary layer, UBL). This study is thus conceived to investigate how urban roughness affects the flow structure and vertical dispersion coefficient in the UBL. Large-eddy simulation (LES) is carried out to examine the plume dispersion from a ground-level pollutant (area) source over idealized street canyons for cross flows in neutral stratification. A range of building-height-to-street-width (aspect) ratios, covering the regimes of skimming flow, wake interference, and isolated roughness, is employed to control the surface roughness. Apart from the widely used aerodynamic resistance or roughness function, the friction factor is another suitable parameter that measures the drag imposed by urban roughness quantitatively. Previous results from laboratory experiments and mathematical modelling also support the aforementioned approach for both two- and three-dimensional roughness elements. Comparing the UBL plume behaviour, the LES results show that the pollutant dispersion strongly depends on the friction factor. Empirical studies reveal that the vertical dispersion coefficient increases with increasing friction factor in the skimming flow regime (lower resistance) but is more uniform in the regimes of wake interference and isolated roughness (higher resistance). Hence, it is proposed that the friction factor and flow regimes could be adopted concurrently for pollutant concentration estimate in the UBL over urban street canyons of different roughness.

  8. Global pollution aerosol monitoring (GPAM) in the atmospheric boundary layer using future earth observing satellite remote sensing

    NASA Astrophysics Data System (ADS)

    Qu, Jianhe; Kafatos, Menas; Yang, Ruixin; Chiu, Long S.; Riebau, Allen R.

    2003-04-01

    Global pollution aerosol monitoring is a very important climatic and environmental problem. It affects not only human health but also ecological systems. Because most pollution aerosols are concentrated in the atmospheric boundary layer where human, animal and vegetation live, global pollution aerosol stuides have been an important topic since about a decade ago. Recently, many new chemistry remote sensing satellite systems, such as NASA's Aura (EOS-CHEM), have been established. However, pollution aerosols in the atmospheric boundary layer cannot be detected using current remote sensing technologies. George Mason University (GMU) proposes to design scientific algorithms and technologies to monitor the atmospheric boundary layer pollution aerosols, using both satellite remote sensing measurements and ground measurements, collaborating with NASA and the United States Department of Agriculture (USDA)/Forest Services (FS). Boundary layer pollution aerosols result from industrial pollution, desert dust storms, smoke from wildfires and biomass burning, volcanic eruptions, and from other trace gases. The current and next generation satellite instruments, such as The Ozone Mapping and Profiler Suite (OMPS), Ozone Monitoring Instrument (OMI), Thermal Emission Spectrometer (TES), and High Resolution Dynamics Limb Sounder (HIRDLS) can be used for this study. Some surface measurements from USDA/FS and other agencies may also be used in this study. We will discuss critical issues for GPAM in the boundary layer using Earth observing satellite remote sensing in detail in this paper.

  9. An Evaluation of Land-Surface Heterogeneity Effects on Atmospheric Boundary Layer Processes at Various Scales

    NASA Astrophysics Data System (ADS)

    Bolch, M. A.; Avissar, R.

    2010-12-01

    Land-surface heterogeneity (LSH) at different scales has significant influence on atmospheric boundary layer (ABL) buoyant and shear turbulence generation and transfers of water, carbon and heat. The extent of proliferation of this influence into larger-scale circulations and atmospheric structures is a topic continually investigated in experimental and numerical studies, in many cases with the hopes of improving land-atmosphere parameterizations for modeling purposes. The blending height is a potential measure for the vertical propagation of LSH effects into the ABL, and has been the subject of study for several decades. Its potential as a powerful metric and the lack of combined efforts of modeling and observations are the motivations for this study. The central goal of this project is to assess how blending height estimates compare with observed and modeled vertical propagation of heterogeneity. To accomplish this, a Helicopter Observation Platform (HOP) will provide in-situ atmospheric observations at a range of different altitudes, especially in the lower ABL, where the effects of LSH are expected to be the strongest. Empirical Mode Decomposition (EMD) will be used to filter noise and unwanted trends from the HOP data and to assess possible LSH correlations. An Ocean-Land-Atmosphere-Model (OLAM), a state-of-the-art numerical model will provide high horizontal resolution mesh refinement to resolve large-eddy scale turbulence throughout the observation area. And the modeling and observations are linked through the Cloud and Land Surface Interaction Campaign (CLASIC) field campaign sites, which supply a host of additional data as well as sites with varying LSH regimes. The patchwork of different crops at the Central Facility (CF) provides a relatively small LSH scale, the forest site at Okmulgee (FS) has vegetated, bare and water areas aggregated at a larger LSH scale, and the Fort Cobb watershed (FC) is dominated by the Fort Cobb Lake, giving the largest scale

  10. The NOx dependence of bromine chemistry in the Arctic atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Custard, K. D.; Thompson, C. R.; Pratt, K. A.; Shepson, P. B.; Liao, J.; Huey, L. G.; Orlando, J. J.; Weinheimer, A. J.; Apel, E.; Hall, S. R.; Flocke, F.; Mauldin, L.; Hornbrook, R. S.; Pöhler, D.; S., General; Zielcke, J.; Simpson, W. R.; Platt, U.; Fried, A.; Weibring, P.; Sive, B. C.; Ullmann, K.; Cantrell, C.; Knapp, D. J.; Montzka, D. D.

    2015-09-01

    Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean - Atmosphere - Sea Ice - Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

  11. The NOx dependence of bromine chemistry in the Arctic atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Custard, K. D.; Thompson, C. R.; Pratt, K. A.; Shepson, P. B.; Liao, J.; Huey, L. G.; Orlando, J. J.; Weinheimer, A. J.; Apel, E.; Hall, S. R.; Flocke, F.; Mauldin, L.; Hornbrook, R. S.; Pöhler, D.; General, S.; Zielcke, J.; Simpson, W. R.; Platt, U.; Fried, A.; Weibring, P.; Sive, B. C.; Ullmann, K.; Cantrell, C.; Knapp, D. J.; Montzka, D. D.

    2015-03-01

    Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean-Atmosphere-Sea Ice-Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase radical chemistry, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr, with a concomitant, decreased net O3 loss rate. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

  12. Atmospheric boundary layer characteristics and land-atmosphere energy transfer in the Third Pole area

    NASA Astrophysics Data System (ADS)

    Ma, Y.; Zhu, Z.; Amatya, P. M.; Chen, X.; Hu, Z.; Zhang, L.; Li, M.; Ma, W.

    2015-05-01

    The Tibetan Plateau and nearby surrounding area (the Third Pole area) dramatically impacts the world's environment and especially controls climatic and environmental changes in China, Asia and even in the Northern Hemisphere. Supported by the Chinese Academy of Sciences (CAS) and some international organizations, the Third Pole Environment (TPE) Programme is now under way. First, the background of the establishment of the TPE, the establishment and monitoring plans on long-term for the TPE and six comprehensive observation and study stations are introduced. Then the preliminary observational analysis results on atmosphere-land interaction are presented. The study on the regional distribution of land surface heat fluxes is of paramount importance over the heterogeneous landscape of the Third Pole area. A parameterization methodology based on satellite and in situ data is described and tested for deriving the regional surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) over the heterogeneous landscape. As a case study, the methodology was applied to the whole Tibetan Plateau area. Eight images of MODIS data and four images of AVHRR data were used for the comparison among winter, spring, summer and autumn, and the annual variation analyses. The derived results were also validated by using the ``ground truth'' measured in the stations of the TPE. The results show that the derived surface heat fluxes in the four different seasons over the Tibetan Plateau area are in good agreement with the ground measurements. The results from AVHRR were also in agreement with MODIS. It is therefore concluded that the proposed methodology is successful for the retrieval of surface heat fluxes using the MODIS data, AVHRR data and in situ data over the Tibetan Plateau area.

  13. Isolating Effects of Water Table Dynamics, Terrain, and Soil Moisture Heterogeneity on the Atmospheric Boundary Layer Using Coupled Models

    NASA Astrophysics Data System (ADS)

    Rihani, Jehan Fouad

    Previous observational and modeling studies have demonstrated the sensitivity of atmospheric processes to land surface and subsurface conditions. The extent of the connection between these processes, however, is not yet fully understood. A sufficient understanding is needed of the circumstances under which these coupled processes might play a more significant role and when they might be simplified into the decoupled systems so frequently modeled in practice. This work focuses on the effects of terrain and soil moisture heterogeneity in changing water table depth and energy fluxes at the land surface, and how this might impact the development and structure of the atmospheric boundary layer. A three-dimensional, variably saturated groundwater model coupled to a three dimensional mesoscale atmospheric model (PF.ARPS) is used here to study the two-way feedback between the subsurface, land-surface, and atmosphere for both idealized cases and a real watershed. This is done by addressing the following key questions: How do terrain, soil moisture heterogeneity, and subsurface properties affect the planetary boundary layer? What are the effects of water table depth on land surface fluxes and boundary layer development and depth? What times of the diurnal cycle and which locations within a watershed demonstrate stronger feedbacks between the subsurface and the atmosphere? These questions are first addressed for idealized simulations designed to illustrate subsurface-surface feedbacks on one hand, and land-atmosphere feedbacks on the other hand. The coupled hydrologic model is then used to simulate real conditions over the Little Washita watershed in Oklahoma with the goal of addressing the above questions for a real watershed, and exploring the two-way feedback between the atmospheric boundary layer and the water table. The coupled simulations are compared to non-coupled atmospheric simulations initialized with simplified and realistic soil moisture profiles. Effects of a

  14. The Influence of High Aerosol Concentration on Atmospheric Boundary Layer Temperature Stratification

    SciTech Connect

    Khaykin, M.N.; Kadygrove, E.N.; Golitsyn, G.S.

    2005-03-18

    Investigations of the changing in the atmospheric boundary layer (ABL) radiation balance as cased by natural and anthropogenic reasons is an important topic of the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program. The influence of aerosol on temperature stratification of ABL while its concentration was extremely high within a long period of time was studied experimentally. The case was observed in Moscow region (Russia) with the transport of combustion products from peat-bog and forest fires in July-September, 2002. At this time the visibility was some times at about 100-300 m. Aerosol concentration measured by Moscow University Observatory and A.M. Obukhov Institute of Atmospheric Physics field station in Zvenigorod (55.7 N; 36.6 E) for several days was in 50-100 times more than background one (Gorchakov at al 2003). The high aerosol concentration can change the radiation balance at ABL, and so to change thermal stratification in ABL above the mega lopolis. For the analysis the data were used of synchronous measurements by MTP-5 (Microwave Temperature Profiler operating at wavelength 5 mm) in two locations, namely: downtown Moscow and country-side which is 50 km apart to the West (Zvenigorod station). (Kadygrov and Pick 1998; Westwater at al 1999; Kadygrov at al 2002). Zvenigorod station is located in strongly continental climate zone which is in between of the climates of ARM sites (NSANorth Slope of Alaska and SGP-Southern Great Plains). The town of Zvenigorod has little industry, small traffic volume and topography conductive to a good air ventilation of the town. For these reasons Zvenigorod can be considered as an undisturbed rural site. For the analysis some days were chosen with close meteorological parameters (average temperature, humidity, wind, pressure and cloud form) but strongly differing in aerosol concentration level.

  15. Speciated atmospheric mercury in the marine boundary layer of the Bohai Sea and Yellow Sea

    NASA Astrophysics Data System (ADS)

    Wang, Chunjie; Ci, Zhijia; Wang, Zhangwei; Zhang, Xiaoshan; Guo, Jia

    2016-04-01

    The objectives of this study are to identify the spatial and temporal distributions of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and fine particulate mercury (HgP2.5) in the marine boundary layer (MBL) of the Bohai Sea (BS) and Yellow Sea (YS), and to investigate the relationships between mercury species and meteorological parameters. The mean concentrations of GEM, RGM, and HgP2.5 were 2.03 ng m-3, 2.5 pg m-3, and 8.2 pg m-3 in spring, and 2.09 ng m-3, 4.3 pg m-3, and 8.3 pg m-3 in fall. Reactive mercury (RGM + HgP2.5) represented < 1% of total atmospheric mercury (GEM + RGM + HgP2.5), which indicated that most mercury export in the MBL was GEM and the direct outflow of reactive mercury was very small. Moreover, GEM concentrations over the BS were generally higher than those over the YS both in spring and fall. Although RGM showed a homogeneous distribution over the BS and YS both in spring and fall, the mean RGM concentration in fall was significantly higher than that in spring. In contrast, the spatial distribution of HgP2.5 generally reflected a gradient with high levels near the coast of China and low levels in the open sea, suggesting the significant atmospheric mercury outflow from China. Interestingly, the mean RGM concentrations during daytime were significantly higher than those during nighttime both in spring and fall, while the opposite results were observed for HgP2.5. Additionally, RGM positively correlates with air temperature while negatively correlates with relative humidity. In conclusion, the elevated atmospheric mercury levels in the BS and YS compared to other open seas suggested that the human activities had a significant influence on the oceanic mercury cycle downwind of China.

  16. Rotational Raman lidar with a multispectral detector for temperature profiling in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Yoshikawa, K.; Yabuki, M.; Tsuda, T.

    2013-12-01

    Temperature profiling in the atmospheric boundary layer is essential for studying atmospheric processes such as dynamics, thermodynamics, and cloud physics. The rotational Raman (RR) lidar has the ability to conduct continuous observation of the spatial distributions of atmospheric temperature. In this study, a combination of the temperature lidar with a multispectral detector is proposed, in order to construct a system that is compact, robust, and easy to align for the detection of RR signals. The multispectral detector enables simultaneous acquisition of multi-channel photon counts and provides spectral and range-resolved data by applying lidar techniques. Conventional temperature lidar detects the ratio of two RR lidar signals of opposite temperature dependence in combination with several edge- and interference-filters. Conversely, the multispectral detector can define the shape of the RR spectrum. Therefore, the proposed system with a multispectral detector detects the variation of the lidar signals by temperature as well as that of the wavelength shift of the emitted laser. It is suggested that this technique can reduce uncertainties in the optical alignment of the polychromator and in the stability of laser wavelength. The statistical temperature-error derived from the proposed method depends on both the spectral resolution and the spectral range of the multispectral detector. The ideal settings for multispectral observation were estimated by the theoretical simulation of the effect of both spectral resolution and spectral range on the accuracy of temperature estimation. Further, we construct the temperature lidar by employing the multispectral detector with the ideal spectral resolution derived from the simulation. In this presentation, we introduce our proposed system and the preliminary results of the temperature observation from RR lidar with a multi spectral detector.

  17. Ocean front-atmosphere interactions in the marine boundary layer and beyond

    NASA Astrophysics Data System (ADS)

    Xie, S.; Xu, H.; Minobe, S.; Zhang, S.; Liu, J.

    2012-12-01

    A bottle neck for extratropical climate prediction is insufficient understanding of how the atmosphere responds to oceanic changes. On the basin scale, interannual variability tends to be negatively correlated between sea surface temperature (SST) and wind speed, indicative of the atmosphere forcing ocean. Recent satellite observations reveal ubiquitous positive correlations between SST and wind on the ocean mesoscale (1,000km or less), indicating that ocean forces the atmosphere near SST fronts and over ocean eddies. Such ocean frontal effects are recorded in high-wind (>20 m/s) occurrence along the Gulf Stream and Southern Ocean circumpolar current. The SST effect is also evident in low cloud occurrence and type (fog vs. stratocumulus) across ocean fronts. An important question is whether such ocean frontal effects are confined to the marine boundary layer (MBL) or extend into the troposphere. Deep response has been observed along the Gulf Stream, Kuroshio and its extension. The second half of the paper focuses on the East China Sea, which the Kuroshio flows through. Meiyu-Baiu is an elongated rain band that extends from eastern China through Japan. Bringing much needed rain to the region, it is the single most important climate phenomenon of East Asia. Evidence is emerging that the warm Kuroshio anchors active convection and heavy rainfall during late spring to summer, presumably through surface wind convergence and locally enhanced evaporation. Fog frequents the East China Sea and its coasts during the Meiyu-Baiu season as the broad southerly monsoon embrace East Asia. Sea fog visualizes suppressed surface evaporation, which in turn modulates the regional rainfall distribution. Several field experiments are ongoing/planned to explore the rich interactions between the Kuroshio, MBL, and troposphere.

  18. Investigation of chemical properties and transport phenomena associated with pollutants in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Holmes, Heather A.

    Under the Clean Air Act, the U.S. Environmental Protection Agency is required to determine which air pollutants are harmful to human health, then regulate, monitor and establish criteria levels for these pollutants. To accomplish this and for scientific advancement, integration of knowledge from several disciplines is required including: engineering, atmospheric science, chemistry and public health. Recently, a shift has been made to establish interdisciplinary research groups to better understand the atmospheric processes that govern the transport of pollutants and chemical reactions of species in the atmospheric boundary layer (ABL). The primary reason for interdisciplinary collaboration is the need for atmospheric processes to be treated as a coupled system, and to design experiments that measure meteorological, chemical and physical variables simultaneously so forecasting models can be improved (i.e., meteorological and chemical process models). This dissertation focuses on integrating research disciplines to provide a more complete framework to study pollutants in the ABL. For example, chemical characterization of particulate matter (PM) and the physical processes governing PM distribution and mixing are combined to provide more comprehensive data for source apportionment. Data from three field experiments were utilized to study turbulence, meteorological and chemical parameters in the ABL. Two air quality field studies were conducted on the U.S./Mexico border. The first was located in Yuma, AZ to investigate the spatial and temporal variability of PM in an urban environment and relate chemical properties of ambient aerosols to physical findings. The second border air quality study was conducted in Nogales, Sonora, Mexico to investigate the relationship between indoor and outdoor air quality in order to better correlate cooking fuel types and home activities to elevated indoor PM concentrations. The final study was executed in southern Idaho and focused on

  19. The Morning NO x maximum in the forest atmosphere boundary layer

    NASA Astrophysics Data System (ADS)

    Alaghmand, M.; Shepson, P. B.; Starn, T. K.; Jobson, B. T.; Wallace, H. W.; Carroll, M. A.; Bertman, S. B.; Lamb, B.; Edburg, S. L.; Zhou, X.; Apel, E.; Riemer, D.; Stevens, P.; Keutsch, F.

    2011-10-01

    During the 1998, 2000, 2001, 2008, and 2009 summer intensives of the Program for Research on Oxidants: PHotochemistry, Emissions and Transport (PROPHET), ambient measurement of nitrogen oxides (NO + NO2 = NOx) were conducted. NO and NOx mole fractions displayed a diurnal pattern with NOx frequently highest in early morning. This pattern has often been observed in other rural areas. In this paper, we discuss the potential sources and contributing factors of the frequently observed morning pulse of NOx. Of the possible potential contributing factors to the observed morning pulse of NO and NOx, we find that surface-layer transport and slow upward mixing from soil emissions, related to the thermodynamic stability in the nocturnal boundary layer (NBL) before its morning breakup are the largest contributors. The morning NOx peak can significantly impact boundary layer chemistry, e.g. through production of HONO on surfaces, and by increasing the importance of NO3 chemistry in the morning boundary layer.

  20. Isolating Effects of Water Table Dynamics, Terrain, and Soil Moisture Heterogeneity on the Atmospheric Boundary Layer Using Coupled Models

    NASA Astrophysics Data System (ADS)

    Rihani, J. F.; Maxwell, R. M.; Katopodes Chow, F.

    2008-12-01

    There is a growing body of literature recognizing the connection between atmospheric boundary layer processes and surface and subsurface heterogeneity and flow, but much remains unknown about the nature of these hydrologic feedbacks. In recent work, the three-dimensional, variably saturated groundwater model ParFlow (PF) was coupled to the three-dimensional mesoscale atmospheric model ARPS (Advanced Regional Prediction System). The coupled model, PF.ARPS, was used to demonstrate atmosphere-land surface-subsurface interactions for a watershed in Oklahoma. In the current work, this coupled model is used to study effects of water table dynamics and soil moisture heterogeneity on the development and behavior of the atmospheric boundary layer for a set of idealized test cases. Numerical experiments that isolate the effects of subsurface heterogeneity, terrain, soil moisture initialization, and atmospheric conditions are performed. Detailed soil moisture distributions from offline spinups using ParFlow coupled to the Common Land Model (PF.CLM) are used to initialize idealized PF.ARPS runs. Results indicate that the water table becomes more dynamic as subsurface heterogeneity increases. This is reflected in soil moisture profiles and thus energy fluxes and evaporation at the land surface. Our results also illustrate the role of terrain in inducing differential land surface heating and cooling which stimulates the development of convective circulations in addition to those induced from heterogeneous soil moisture. Subsequent effects on atmospheric boundary layer development are discussed.

  1. On the characterization of coherent structures within a neutrally-stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Rosi, Giuseppe; Le Bastide, Benen; Gaebler, Julia; Kinzel, Matias; Rival, David

    2012-11-01

    Up to this point, a clear characterization of wind turbulence and extreme gust events through experimentation has frustrated countless researchers. The statistical analysis of fluctuating components has been exhausted while the conditional analysis of extreme events, though insightful, often results in constricted conclusions that cannot be bridged from study to study. Thus the current study shifts towards an understanding of the fundamental turbulent flow structures within a neutrally-stratified atmospheric boundary layer. Two approaches to characterize coherent wind structures are presented. The first approach identifies hairpin-vortex heads by correlating three-dimensional, fluctuating data from two high-speed anemometers situated at 40m and 50m heights on a wind mast. The model assumes that a hairpin-vortex head can be approximated as a transverse vortex with a Vatistas viscous core of assumed radius when the hairpin-vortex head impinges onto the two anemometers. The second approach employs large-scale particle tracking velocimetry to follow seeded bubbles next to the wind mast. The results obtained with both approaches are then compared, and the advantages and shortcomings of each method are discussed.

  2. Near-wake instability and sensitivity analysis of wind turbines immersed in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Viola, Francesco; Iungo, Giacomo Valerio; Camarri, Simone; Porté-Agel, Fernando; Gallaire, François

    2014-11-01

    In wind farms, the separation distance among wind turbines is mainly determined by the downstream recovery of wind turbine wakes, which affects in turn power production and fatigue loads of downstream turbines. Thus, the optimization of a wind farm relies on the understanding of the single wake dynamics and a better characterization of their interactions within the atmospheric boundary layer (ABL). This work is focused on the stability analysis of vorticity structures present in wind turbine wakes. In order to take into account the effects of a non-uniform incoming wind investing the turbine, a 3D local stability analysis is performed on the non-axisymmetric swirling wake prevailing at different downstream stations. Different wind shear and veer of the incoming wind can now be investigated, together with a 3D non-isotropic turbulent velocity field. This procedure enables to perform stability analysis of wind turbine wakes for wind conditions very similar to the ones experienced in reality. The present analysis is carried out on wind tunnel data acquired in the wake of a down-scaled three-bladed wind turbine. The Reynolds stresses are taken into account via eddy-viscosity models calibrated on the experimental data. Furthermore, the effect of an external perturbation in the wake flow is investigated through linear sensitivity. This analysis represents a preliminary step for control of wind turbine wakes, and optimization of wake interactions and power harvesting.

  3. Adjustment of the summertime marine atmospheric boundary layer to the western Iberia coastal morphology

    NASA Astrophysics Data System (ADS)

    Monteiro, Isabel T.; Santos, Aires J.; Belo-Pereira, Margarida; Oliveira, Paulo B.

    2016-04-01

    During summer (June, July, and August), northerly winds driven by the Azores anticyclone are prevalent over western Iberia. The Quick Scatterometer Satellite 2000 to 2009 summertime estimates reveal a broad high wind speed (≥7 ms-1) area extending about 300 km from shore and along the entire Iberian west coast. Nested in this large high-speed region, preferred maximum regions anchored in the Iberian major capes, Finisterre, Roca, and S. Vicente, are found. Composite analyses of wind maxima were performed to diagnose the typical summertime synoptic-scale pressure distribution associated with these smaller size high-speed regions. The flow low-level structure was further studied with a mesoscale numerical prediction model for three northerly events characterized by typical summertime synoptic conditions. A low-level coastal jet, setting the background conditions to the marine atmospheric boundary layer (MABL) response to topography, was found in the three cases. The causes for wind maximum downwind capes were investigated, focusing on the hypothesis that western Iberia MABL responds to hydraulic forcing. For the three events supercritical and transcritical flow conditions were identified and expansion fan signatures were found downwind each cape. Aircraft measurements, performed during one of the events, gave additional evidence of the expansion fan leeward Cape Roca. The importance of other forcing mechanisms was also assessed by considering the hypothesis of downslope wind acceleration and found to be in direct conflict with soundings and surface observations.

  4. Simulations of Vertical Axis Wind Turbine Farms in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hezaveh, Seyed Hossein; Bou-Zeid, Elie; Lohry, Mark; Martinelli, Luigi

    2014-11-01

    Wind power is an abundant and clean source of energy that is increasingly being tapped to reduce the environmental footprint of anthropogenic activities. The vertical axis wind turbine (VAWT) technology is now being revisited due to some important advantages over horizontal axis wind turbines (HAWTS) that are particularly important for farms deployed offshore or in complex terrain. In this talk, we will present the implementation and testing of an actuator line model (ALM) for VAWTs in a large eddy simulation (LES) code for the atmospheric boundary layer, with the aim of optimizing large VAWT wind farm configurations. The force coefficients needed for the ALM are here obtained from blade resolving RANS simulations of individual turbines for each configuration. Comparison to various experimental results show that the model can very successfully reproduce observed wake characteristic. The influence of VAWT design parameters such as solidity, height to radius ratio, and tip speed ratio (TSR) on these wake characteristics, particularly the velocity deficit profile, is then investigated.

  5. Scaling laws of turbulence intermittency in the atmospheric boundary layer: the role of stability

    NASA Astrophysics Data System (ADS)

    Paradisi, Paolo; Cesari, Rita; Allegrini, Paolo

    2015-09-01

    Bursting and intermittent behavior is a fundamental feature of turbulence, especially in the vicinity of solid obstacles. This is associated with the dynamics of turbulent energy production and dissipation, which can be described in terms of coherent motion structures. These structures are generated at random times and remain stable for long times, after which they become suddenly unstable and undergo a rapid decay event. This intermittent behavior is described as a birth-death point process of self-organization, i.e., a sequence of critical events. The Inter-Event Time (IET) distribution, associated with intermittent self-organization, is typically a power-law decay, whose power exponent is known as complexity index and characterizes the complexity of the system, i.e., the ability to develop self-organized, metastable motion structures. We use a method, based on diffusion scaling, for the estimation of system's complexity. The method is applied to turbulence velocity data in the atmospheric boundary layer. A neutral condition is compared with a stable one, finding that the complexity index is lower in the neutral case with respect to the stable one. As a consequence, the crucial birth-death events are more rare in the stable case, and this could be associated with a less efficient transport dynamics.

  6. Reduced-order FSI simulation of NREL 5 MW wind turbine in atmospheric boundary layer turbulence

    NASA Astrophysics Data System (ADS)

    Motta-Mena, Javier; Campbell, Robert; Lavely, Adam; Jha, Pankaj

    2015-11-01

    A partitioned fluid-structure interaction (FSI) solver based on an actuator-line method solver and a finite-element modal-dynamic structural solver is used to evaluate the effect of blade deformation in the presence of a day-time, moderately convective atmospheric boundary layer (ABL). The solver components were validated separately and the integrated solver was partially validated against FAST. An overview of the solver is provided in addition to results of the validation study. A finite element model of the NREL 5 MW rotor was developed for use in the present simulations. The effect of blade pitching moment and the inherent bend/twist coupling of the rotor blades are assessed for both uniform inflow and the ABL turbulence cases. The results suggest that blade twisting in response to pitching moment and the bend/twist coupling can have a significant impact on rotor out-of-plane bending moment and power generated for both the uniform inflow and the ABL turbulence cases.

  7. Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Salizzoni, Pietro; Marro, Massimo; Soulhac, Lionel; Grosjean, Nathalie; Perkins, Richard J.

    2011-12-01

    The turbulent exchange of momentum between a two-dimensional cavity and the overlying boundary layer has been studied experimentally, using hot-wire anemometry and particle image velocimetry (PIV). Conditions within the boundary layer were varied by changing the width of the canyons upstream of the test canyon, whilst maintaining the square geometry of the test canyon. The results show that turbulent transfer is due to the coupling between the instabilities generated in the shear layer above the canyons and the turbulent structures in the oncoming boundary layer. As a result, there is no single, unique velocity scale that correctly characterizes all the processes involved in the turbulent exchange of momentum across the boundary layer. Similarly, there is no single velocity scale that can characterize the different properties of the turbulent flow within the canyon, which depends strongly on the way in which turbulence from the outer flow is entrained into the cavity and carried round by the mean flow. The results from this study will be useful in developing simple parametrizations for momentum exchange in the urban canopy, in situations where the street geometry consists principally of relatively long, uniform streets arranged in grid-like patterns; they are unlikely to be applicable to sparse geometries composed of isolated three-dimensional obstacles.

  8. Effects on the atmospheric boundary layer of a solar eclipse in the Arctic

    NASA Astrophysics Data System (ADS)

    Sjöblom, Anna

    2010-05-01

    On 1 August 2008, a total solar eclipse took place in the Arctic and in Longyearbyen, the main settlement in the High Arctic archipelago of Svalbard (78° 13' N, 15° 37' E), the maximum solar coverage was 93%. The eclipse had a large impact on the atmospheric boundary layer and the local weather in general around Longyearbyen triggering a fog that lasted for three days. This fog grounded all air traffic to and from Svalbard and so in addition to the change in local weather, the eclipse also had economic and social consequences. Approximately 60% of Svalbard is covered with permanent ice and snow. Permafrost underlies most of the surface. In Longyearbyen, the midnight sun is present between 19 April and 23 August and so on the day of the eclipse the sun was about 30 degrees above the horizon at noon and 6 degrees above at midnight. A rare opportunity therefore occurred to study what happens when the sunlight is suddenly decreased after several months with no dark night. The maximum solar coverage at Longyearbyen took place at 10.41 Local Standard Time. The incoming shortwave radiation had then decreased from approximately 300 W m-2 before the start of the eclipse to 20 W m-2, i.e. less radiation than during a normal cloud free night at the same location at the same time of the year. Observations of turbulence and mean meteorological parameters were taken both over land and over a large fjord in the vicinity of Longyearbyen. In addition, cloud observations were recorded. Data have been analysed in detail from 31 July to 2 August, i.e., from one day before to one day after the eclipse. The simultaneous observations over land and over water showed that the atmospheric response was much faster and stronger over land than over water. Over land, the air temperature sank by 0.3-1.5°C, wind speed decreased, turbulent fluctuations were significantly reduced and the atmospheric stability changed from unstable to stable. Over the fjord, no clear minima in these parameters

  9. Interactions between soil moisture and Atmospheric Boundary Layer at the Brazilian savana-type vegetation Cerrado

    NASA Astrophysics Data System (ADS)

    Pinheiro, L. R.; Siqueira, M. B.

    2013-05-01

    Before the large people influx and development of the central part of Brazil in the sixties, due to new capital Brasília, Cerrado, a typical Brazilian savanna-type vegetation, used to occupy about 2 million km2, going all the way from the Amazon tropical forest, in the north of the country, to the edges of what used to be of the Atlantic forest in the southeast. Today, somewhat 50% of this area has given place to agriculture, pasture and managed forests. It is forecasted that, at the current rate of this vegetation displacement, Cerrado will be gone by 2030. Understanding how Cerrado interacts with the atmosphere and how this interaction will be modified with this land-use change is a crucial step towards improving predictions of future climate-change scenarios. Cerrado is a vegetation adapted to a climate characterized by two very distinct seasons, a wet season (Nov-Mar) and dry season (May-Ago), with April and October being transitions between seasons. Typically, based on measurements in a weather station located in Brasilia, 75% of precipitation happens in the wet-season months and only 5% during dry-season. Under these circumstances, it is clear that the vegetation will have to cope with long periods of water stress. In this work we studied using numerical simulations, the interactions between soil-moisture, responsible for the water stress, with the Atmospheric Boundary Layer (ABL). The numerical model comprises of a Soil-Vegetation-Atmosphere model where the biophysical processes are represented with a big-leaf approach. Soil water is estimated with a simple logistic model and with water-stress effects on stomatal conductance are parameterized from local measurements of simultaneous latent-heat fluxes and soil moisture. ABL evolution is calculate with a slab model that considers independently surface and entrainment fluxes of sensible- and latent- heat. Temperature tropospheric lapse-rate is taken from soundings at local airport. Simulations of 30-day dry

  10. Large-eddy Simulation of the Nighttime Stable Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Zhou, Bowen

    A stable atmospheric boundary layer (ABL) develops over land at night due to radiative surface cooling. The state of turbulence in the stable boundary layer (SBL) is determined by the competing forcings of shear production and buoyancy destruction. When both forcings are comparable in strength, the SBL falls into an intermittently turbulent state, where intense turbulent bursts emerge sporadically from an overall quiescent background. This usually occurs on clear nights with weak winds when the SBL is strongly stable. Although turbulent bursts are generally short-lived (half an hour or less), their impact on the SBL is significant since they are responsible for most of the turbulent mixing. The nighttime SBL can be modeled with large-eddy simulation (LES). LES is a turbulence-resolving numerical approach which separates the large-scale energy-containing eddies from the smaller ones based on application of a spatial filter. While the large eddies are explicitly resolved, the small ones are represented by a subfilter-scale (SFS) stress model. Simulation of the SBL is more challenging than the daytime convective boundary layer (CBL) because nighttime turbulent motions are limited by buoyancy stratification, thus requiring fine grid resolution at the cost of immense computational resources. The intermittently turbulent SBL adds additional levels of complexity, requiring the model to not only sustain resolved turbulence during quiescent periods, but also to transition into a turbulent state under appropriate conditions. As a result, LES of the strongly stable SBL potentially requires even finer grid resolution, and has seldom been attempted. This dissertation takes a different approach. By improving the SFS representation of turbulence with a more sophisticated model, intermittently turbulent SBL is simulated, to our knowledge, for the first time in the LES literature. The turbulence closure is the dynamic reconstruction model (DRM), applied under an explicit filtering

  11. Radiative effects of tropospheric aerosols on the evolution of the atmospheric boundary layer and its feedback on the haze formation

    NASA Astrophysics Data System (ADS)

    Wei, Chao; Su, Hang; Cheng, Yafang

    2016-04-01

    Planetary boundary layer (PBL) plays a key role in air pollution dispersion and influences day-to-day air quality. Some studies suggest that high aerosol loadings during severe haze events may modify PBL dynamics by radiative effects and hence enhance the development of haze. This study mainly investigates the radiative effects of tropospheric aerosols on the evolution of the atmospheric boundary layer by conducting simulations with Weather Research and Forecasting single-column model (WRF-SCM). We find that high aerosol loading in PBL depressed boundary layer height (PBLH). But the magnitude of the changes of PBLH after adding aerosol loadings in our simulations are small and can't explain extreme high aerosol concentrations observed. We also investigate the impacts of the initial temperature and moisture profiles on the evolution of PBL. Our studies show that the impact of the vertical profile of moisture is comparable with aerosol effects.

  12. Representation of the grey zone of turbulence in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Honnert, Rachel

    2016-04-01

    Numerical weather prediction model forecasts at horizontal grid lengths in the range of 100 to 1 km are now possible. This range of scales is the "grey zone of turbulence". Previous studies, based on large-eddy simulation (LES) analysis from the MésoNH model, showed that some assumptions of some turbulence schemes on boundary-layer structures are not valid. Indeed, boundary-layer thermals are now partly resolved, and the subgrid remaining part of the thermals is possibly largely or completely absent from the model columns. First, some modifications of the equations of the shallow convection scheme have been tested in the MésoNH model and in an idealized version of the operational AROME model at resolutions coarser than 500 m. Secondly, although the turbulence is mainly vertical at mesoscale (> 2 km resolution), it is isotropic in LES (< 100 m resolution). It has been proved by LES analysis that, in convective boundary layers, the horizontal production of turbulence cannot be neglected at resolutions finer than half of the boundary-layer height. Thus, in the grey zone, fully unidirectional turbulence scheme should become tridirectional around 500 m resolution. At Météo-France, the dynamical turbulence is modelled by a K-gradient in LES as well as at mesoscale in both MésoNH and AROME, which needs mixing lengths in the formulation. Vertical and horizontal mixing lengths have been calculated from LES of neutral and convective cases at resolutions in the grey zone.

  13. Nocturnal Low-Level-Jet-Dominated Atmospheric Boundary Layer Observed by a Doppler Lidar Over Oklahoma City during JU2003

    SciTech Connect

    Wang, Yansen; Klipp, Cheryl L.; Garvey, Dennis M.; Ligon, David; Williamson, Chatt C.; Chang, Sam S.; Newsom, Rob K.; Calhoun, Ron

    2007-12-01

    Boundary layer wind data observed by a Doppler lidar and sonic anemometers during the mornings of three intensive observational periods (IOP2, IOP3, and IOP7) of the Joint Urban 2003 (JU2003) field experiment are analyzed to extract the mean and turbulent characteristics of airflow over Oklahoma City, Oklahoma. A strong nocturnal low-level jet (LLJ) dominated the flow in the boundary layer over the measurement domain from midnight to the morning hours. Lidar scans through the LLJ taken after sunrise indicate that the LLJ elevation shows a gradual increase of 25-100 m over the urban area relative to that over the upstream suburban area. The mean wind speed beneath the jet over the urban area is about 10%-15% slower than that over the suburban area. Sonic anemometer observations combined with Doppler lidar observations in the urban and suburban areas are also analyzed to investigate the boundary layer turbulence production in the LLJ-dominated atmospheric boundary layer. The turbulence kinetic energy was higher over the urban domain mainly because of the shear production of building surfaces and building wakes. Direct transport of turbulent momentum flux from the LLJ to the urban street level was very small because of the relatively high elevation of the jet. However, since the LLJ dominated the mean wind in the boundary layer, the turbulence kinetic energy in the urban domain is correlated directly with the LLJ maximum speed and inversely with its height. The results indicate that the jet Richardson number is a reasonably good indicator for turbulent kinetic energy over the urban domain in the LLJ-dominated atmospheric boundary layer.

  14. Estimations of atmospheric boundary layer fluxes and other turbulence parameters from Doppler lidar data

    NASA Astrophysics Data System (ADS)

    Eberhard, Wynn L.

    1992-11-01

    Techniques for extraction of boundary layer parameters from measurements of a short pulse (~0.4 μs) CO2 Doppler lidar (λ=10.6 μm) are described. The lidar is operated by the National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL). The measurements are those collected during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). The recorded radial velocity measurements have a range resolution of 150 m. With a pulse repetition rate of 20 Hz it is possible to perform scannings in two perpendicular vertical planes (x-z and y-z) in approximately 72 s. By continuously operating the lidar for about an hour, one can extract stable statistics of the radial velocities. Assuming that the turbulence is horizontally homogeneous, we have estimated the mean wind, its standard deviations, and the momentum fluxes. We have estimated the first, second, and, third moments of the vertically velocity from the vertical pointing beam. Spectral analysis of the radial velocities is also performed, from which (by examining the amplitude of the power spectrum at the inertial range) we have deduced the kinetic energy dissipation. Finally, using the statistical form of the Navier-Stokes equations, the surface heat flux is derived as the residual balance between the vertical gradient of the third moment of the vertical velocity and the kinetic energy dissipation. With the exception of the vertically pointing beam an individual radial velocity estimate is accurate only to +/-0.7 ms-1. Combining many measurements would normally reduce the error, provided that it is unbiased and uncorrelated. The nature of some of the algorithms, however, is such that biased and correlated errors may be generated even though the ``raw'' measurements are not. We have developed data processing procedures that eliminate bias and minimize error correlation. Once bias and error correlations are accounted for, the large sample size is

  15. Estimations of atmospheric boundary layer fluxes and other turbulence parameters from Doppler lidar data

    NASA Astrophysics Data System (ADS)

    Gal-Chen, Tzvi; Xu, Mei; Eberhard, Wynn L.

    1992-11-01

    Techniques for extraction of boundary layer parameters from measurements of a short pulse (≈0.4 μs) CO2 Doppler lidar (λ = 10.6 μm) are described. The lidar is operated by the National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL). The measurements are those collected during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). The recorded radial velocity measurements have a range resolution of 150 m. With a pulse repetition rate of 20 Hz it is possible to perform scannings in two perpendicular vertical planes (x-z and y-z) in approximately 72 s. By continuously operating the lidar for about an hour, one can extract stable statistics of the radial velocities. Assuming that the turbulence is horizontally homogeneous, we have estimated the mean wind, its standard deviations, and the momentum fluxes. We have estimated the first, second, and, third moments of the vertical velocity from the vertically pointing beam. Spectral analysis of the radial velocities is also performed, from which (by examining the amplitude of the power spectrum at the inertial range) we have deduced the kinetic energy dissipation. Finally, using the statistical form of the Navier-Stokes equations, the surface heat flux is derived as the residual balance between the vertical gradient of the third moment of the vertical velocity and the kinetic energy dissipation. With the exception of the vertically pointing beam an individual radial velocity estimate is accurate only to ±0.7 m s-1. Combining many measurements would normally reduce the error, provided that it is unbiased and uncorrelated. The nature of some of the algorithms, however, is such that biased and correlated errors may be generated even though the "raw" measurements are not. We have developed data processing procedures that eliminate bias and minimize error correlation. Once bias and error correlations are accounted for, the large sample size is

  16. Two-phase measurements of wind and saltating sand in an atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Wang, Yuan; Lee, Sang-Joon

    2007-07-01

    Wind-blown sand movement is a particle-laden two-phase flow related to wind erosion in which the velocity distributions of both wind and sand are of particular interest. In the present study, two types of natural sand, one collected from the Pohang beach (diameter d = 200-300 μm) in South Korea and the other from the Taklimakan desert ( d = 100-125 μm) in China, were tested in a simulated atmospheric boundary layer. A high-speed digital camera system was used to capture images of the saltating sand particles at 2000 fps with an exposure time of 1/3000 s. Instantaneous velocity fields of the saltating sand particles were obtained using a particle tracking velocimetry (PTV) method. From these data, the particle resultant velocity, volume concentration, and streamwise mass flux were estimated as a function of height. The results reveal that the resultant particle velocity has an approximate log-linear profile with vertical height. Both the particle concentration and streamwise mass flux decay dramatically in the near surface region ( z < 20 mm for the beach sand, and z < 15 mm for the desert sand), then decline mildly beyond this region. To investigate the modification of the surrounding wind by the saltating sand particles, a hot-wire anemometry with a robust hot-film probe was employed to measure the wind velocity profiles with and without saltation. The present experimental data on both the saltating sand and wind provide useful information that enhances our understanding of saltation transport and further development of control techniques of wind erosion.

  17. Modelling of atmospheric boundary-layer flow in complex terrain with different forest parameterizations

    NASA Astrophysics Data System (ADS)

    Chávez Arroyo, R.; Sanz Rodrigo, J.; Gankarski, P.

    2014-06-01

    This work explores the accuracy of two approaches that account for the effects of the forest canopy on the wind flow by using a RANS-based model. The first approach implements additional terms in the RANS equations (canopy model), whilst the second one uses large values of roughness length and a zero-plane displacement height. The model uses a limited-length-scale k-epsilon turbulence closure that considers processes occurring in the Atmospheric Boundary-Layer (ABL) such as the Coriolis effects. Both the forest and the ABL implementations are compared with experimental data obtained from 118 m high met masts installed in a large mountain- range site with mixed forest characteristics for neutral stability cases. In order to perform a meaningful comparison at multiple mast locations, a novel methodology is presented which allows the selection of a velocity bin for a given wind direction and a stability class that minimizes the error of using short-term measurement periods at some masts compared to long-term wind statistics from a reference mast. Based on the outcome of the model validation it is possible to conclude that more consistent results are obtained by the canopy model since it reduces the uncertainty in the selection of correct input parameters in the large-roughness approach. The errors in the vertical profiles of velocity and turbulence intensity are reduced by the forest model by almost 63% and 11%, respectively, compared to the standard configuration (no forest). The large-roughness method reduces the error in the velocity profiles by 54% while the predictions of turbulence intensity are barely improved.

  18. Urban Heat Island and Its Influence on Atmospheric Boundary Layer Temperature Field

    NASA Astrophysics Data System (ADS)

    Kadygrov, N.; Kruchenitsky, G.; Lykov, A.

    2006-12-01

    The effect of megacity on atmospheric boundary layer (ABL) temperature is a well known phenomenon called "Urban Heat Island" revealed in increasing temperature over megacity relative to its suburb. Until recently the only way to investigate and gather the data about its vertical distribution was to observe temperature on the meteorological, TV towers and by radiosonde. The available information appears to be irregular in time and space. The situation has changed in recent years since the advent of temperature profiler based on microwave radiometer, which can produce the vertical distribution of ABL temperature up to 600 meters ASL with 5 minute sampling period. The station in the center of Moscow megacity and 2 observation sites near Moscow (20 km and 50 km away from city center) were equipped by MTP-5 radiometer in order to get quantitative estimations of the Heat Island Effect on ABL temperature field. Three sites were selected in order to look at transition from megacity to suburb. The main aim was not to get the climatological averages but to get the differences between Heat Island and its background (suburb). The period of observation was from beginning of 2000 till the middle of 2004. The ABL temperature model was developed separately for each station in the multiplicative manner as the product of seasonal and diurnal variations of ABL temperature in order to obtain the differences between Urban Heat Island and suburb ABL temperatures. As the result of data analysis, the amplitudes and phases of seasonal and diurnal harmonics, average annual noon temperature value, average temperature gradients and daily altitude-time crossection of ABL temperature were obtained. The analysis performed in this work has given us a better insight into the mechanism of Urban Heat Island influence on ABL temperature field with quantitative estimations of such influence.

  19. Atmospheric controls on soil moisture-boundary layer interactions: Three-dimensional wind effects

    NASA Astrophysics Data System (ADS)

    Findell, Kirsten L.; Eltahir, Elfatih A. B.

    2003-04-01

    This paper expands the one-dimensionally based CTP-HIlow framework for describing atmospheric controls on soil moisture-boundary layer interactions [, 2003] to three dimensions by including low-level wind effects in the analysis. The framework is based on two measures of atmospheric thermodynamic properties: the convective triggering potential (CTP), a measure of the temperature lapse rate between approximately 1 and 3 km above the ground surface, and a low-level humidity index, HIlow. These two measures are used to distinguish between three types of early morning soundings: those favoring rainfall over dry soils, those favoring rainfall over wet soils, and those whose convective potential is unaffected by the partitioning of fluxes at the surface. The focus of this paper is the additional information gained by incorporating information about low-level winds into the CTP-HIlow framework. Three-dimensional simulations using MM5 and an analysis of observations from the FIFE experiment within this framework highlight the importance of the winds in determining the sensitivity of convection to fluxes from the land surface. A very important impact of the 3D winds is the potential for low-level backing or unidirectional winds with great shear to suppress convective potential. Because of this suppression of convection in certain wind conditions, far fewer simulations produced rain than would be anticipated based solely on the 1D framework of understanding. However, when the winds allowed, convection occurred in a manner consistent with the 1D-based expectations. Generally speaking, in the regime where dry soils were expected to have an advantage, convection was triggered over dry soils more often than over wet; in the regime where wet soils were expected to have an advantage, convection was more frequently triggered over wet soils than over dry. Additionally, when rainfall occurred in both simulations with wet soils and simulations with dry soils for a given day, rainfall

  20. Atmospheric boundary layer top height in South Africa: measurements with lidar and radiosonde compared to three atmospheric models

    NASA Astrophysics Data System (ADS)

    Korhonen, K.; Giannakaki, E.; Mielonen, T.; Pfüller, A.; Laakso, L.; Vakkari, V.; Baars, H.; Engelmann, R.; Beukes, J. P.; Van Zyl, P. G.; Ramandh, A.; Ntsangwane, L.; Josipovic, M.; Tiitta, P.; Fourie, G.; Ngwana, I.; Chiloane, K.; Komppula, M.

    2014-04-01

    Atmospheric lidar measurements were carried out at Elandsfontein measurement station, on the eastern Highveld approximately 150 km east of Johannesburg in South Africa throughout 2010. The height of the planetary boundary layer (PBL) top was continuously measured using a Raman lidar, PollyXT (POrtabLe Lidar sYstem eXTended). High atmospheric variability together with a large surface temperature range and significant seasonal changes in precipitation were observed, which had an impact on the vertical mixing of particulate matter, and hence, on the PBL evolution. The results were compared to radiosondes, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) space-borne lidar measurements and three atmospheric models that followed different approaches to determine the PBL top height. These models included two weather forecast models operated by ECMWF (European Centre for Medium-range Weather Forecasts) and SAWS (South African Weather Service), and one mesoscale prognostic meteorological and air pollution regulatory model TAPM (The Air Pollution Model). The ground-based lidar used in this study was operational for 4935 h during 2010 (49% of the time). The PBL top height was detected 86% of the total measurement time (42% of the total time). Large seasonal and diurnal variations were observed between the different methods utilised. High variation was found when lidar measurements were compared to radiosonde measurements. This could be partially due to the distance between the lidar measurements and the radiosondes, which were 120 km apart. Comparison of lidar measurements to the models indicated that the ECMWF model agreed the best with mean relative difference of 15.4%, while the second best correlation was with the SAWS model with corresponding difference of 20.1%. TAPM was found to have a tendency to underestimate the PBL top height. The wind speeds in the SAWS and TAPM models were strongly underestimated which probably led to underestimation of the vertical wind

  1. Visualization of the flow field around a generic destroyer model in a simulated turbulent atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Bolinger, William K.

    1987-06-01

    An experimental flow visualization study was performed on a rectangular block and other elements that could be assembled in the form of a generic destroyer ship model. The purpose of the study was to visually analyze the flow field around the model in a simulated open ocean atmospheric boundary layer. To ensure correct simulation of the atmospheric boundary layer, both velocity profile and longitudinal turbulence intensities were matched. For the actual flow visualization studies, two techniques were used. During the on-body portion of the study, the ultraviolet lighting/fluorescent minituft technique was used. For the off-body portion, helium bubble system, with a neutral density centrifuge, was utilized. Both techniques produced excellent photographic results and allowed for direct comparison of the flow fields using the two flow visualization techniques.

  2. The Small Unmanned Meteorological Observer SUMO: Recent developments and applications of a micro-UAS for atmospheric boundary layer research

    NASA Astrophysics Data System (ADS)

    Reuder, Joachim; Jonassen, Marius; Ólafsson, Haraldur

    2012-10-01

    During the last 5 years, the Small Unmanned Meteorological Observer SUMO has been developed as a flexible tool for atmospheric boundary layer (ABL) research to be operated as sounding system for the lowest 4 km of the atmosphere. Recently two main technical improvements have been accomplished. The integration of an inertial measurement unit (IMU) into the Paparazzi autopilot system has expanded the environmental conditions for SUMO operation. The implementation of a 5-hole probe for determining the 3D flow vector with 100 Hz resolution and a faster temperature sensor has enhanced the measurement capabilities. Results from two recent field campaigns are presented. During the first one, in Denmark, the potential of the system to study the effects of wind turbines on ABL turbulence was shown. During the second one, the BLLAST field campaign at the foothills of the Pyrenees, SUMO data proved to be highly valuable for studying the processes of the afternoon transition of the convective boundary layer.

  3. Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

    NASA Technical Reports Server (NTRS)

    Rasmussen, R. A.; Khalil, M. A. K.

    1981-01-01

    Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH3I, CHCl3, CO and CH4 which are largely natural in origin, and C2Cl4, CCl4, CH3CCl3, (F-11), CCl2F2, (F-12), CHClF, (F-22) and C2F3Cl3 (F-113), which are due to anthropogenic (CCl3F) etc. activities. It was found that all these gases are significantly (alpha is equal to or less than 0.05) more abundant in the boundary layer than above it.

  4. Quantitative estimates of disturbances contributed by a megalopolis to the temperature field of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kadygrov, N. E.; Kruchenitskii, G. M.; Lykov, A. D.

    2007-02-01

    Seasonal and diurnal variations in the temperature of the atmospheric boundary layer (ABL) are analyzed, and the features of spatial and temporal variations in ABL temperature that are caused by the influence of a megalopolis are revealed. The gradients of air temperature for the megalopolis, its vicinity, and background conditions are compared. A multiplicative model of the seasonal diurnal variability of ABL temperature is constructed, and the relative frequencies of unstable ABL-temperature stratification are studied.

  5. Atmospheric marine boundary layer mixing rates in the California coastal region. Technical report

    SciTech Connect

    Schacher, G.E.; Fairall, C.W.; Davidson, K.L.

    1980-05-01

    The Naval Postgraduate School has conducted five research cruises in California coastal waters for which sufficient data was obtained to allow boundary layer mixing rates to be determined. These data have been processed to determine the mixing rates. The rates have been correlated with meteorological conditions and geographical location and average values for use in air pollution models have been determined. A simplified method for calculating the mixing rate from mean meteorological parameters is presented.

  6. Western Pacific Warm Pool Region Sensitivity to Convective Triggering byBoundary Layer Thermals in the NOGAPS Atmospheric GCM.

    NASA Astrophysics Data System (ADS)

    Ridout, James A.; Reynolds, Carolyn A.

    1998-07-01

    The sensitivity of the atmospheric general circulation model of the Navy Operational Global Atmospheric Prediction System to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated. The study focuses on the western Pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987/88. A parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer. Surface-based deep convection is allowed only for boundary layer regimes associated with the presence of thermals. The regime classification is expressed in terms of a Richardson number that reflects the relative significance of buoyancy and shear in the boundary layer. By constraining deep convection to conditions consistent with the occurrence of thermals (high buoyancy to shear ratios), there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical Pacific and along the ITCZ. This decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the Pacific warm pool. Improvements in the simulated distribution of precipitation, precipitable water, and low-level winds in the tropical Pacific are demonstrated. Over the western Pacific, the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed. Low-level winds thus play the major role in regulating the ability of thermals to initiate deep convection. The lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard.

  7. Characterization of wake turbulence in a wind turbine array submerged in atmospheric boundary layer flow

    NASA Astrophysics Data System (ADS)

    Jha, Pankaj Kumar

    Wind energy is becoming one of the most significant sources of renewable energy. With its growing use, and social and political awareness, efforts are being made to harness it in the most efficient manner. However, a number of challenges preclude efficient and optimum operation of wind farms. Wind resource forecasting over a long operation window of a wind farm, development of wind farms over a complex terrain on-shore, and air/wave interaction off-shore all pose difficulties in materializing the goal of the efficient harnessing of wind energy. These difficulties are further amplified when wind turbine wakes interact directly with turbines located downstream and in adjacent rows in a turbulent atmospheric boundary layer (ABL). In the present study, an ABL solver is used to simulate different atmospheric stability states over a diurnal cycle. The effect of the turbines is modeled by using actuator methods, in particular the state-of-the-art actuator line method (ALM) and an improved ALM are used for the simulation of the turbine arrays. The two ALM approaches are used either with uniform inflow or are coupled with the ABL solver. In the latter case, a precursor simulation is first obtained and data saved at the inflow planes for the duration the turbines are anticipated to be simulated. The coupled ABL-ALM solver is then used to simulate the turbine arrays operating in atmospheric turbulence. A detailed accuracy assessment of the state-of-the-art ALM is performed by applying it to different rotors. A discrepancy regarding over-prediction of tip loads and an artificial tip correction is identified. A new proposed ALM* is developed and validated for the NREL Phase VI rotor. This is also applied to the NREL 5-MW turbine, and guidelines to obtain consistent results with ALM* are developed. Both the ALM approaches are then applied to study a turbine-turbine interaction problem consisting of two NREL 5-MW turbines. The simulations are performed for two ABL stability

  8. Advances and Limitations of Atmospheric Boundary Layer Observations with GPS Occultation over Southeast Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Xie, F.; Wu, D. L.; Ao, C. O.; Mannucci, A. J.; Kursinski, E. R.

    2012-01-01

    The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific Ocean is featured with a strong temperature inversion and a sharp moisture gradient across the ABL top. The strong moisture and temperature gradients result in a sharp refractivity gradient that can be precisely detected by the Global Positioning System (GPS) radio occultation (RO) measurements. In this paper, the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect a wide range of ABL height variations (1-2 kilometer) as observed from the radiosondes. However, the ECMWF analysis systematically underestimates the ABL heights. The sharp refractivity gradient at the ABL top frequently exceeds the critical refraction (e.g., -157 N-unit per kilometer) and becomes the so-called ducting condition, which results in a systematic RO refractivity bias (or called N-bias) inside the ABL. Simulation study based on radiosonde profiles reveals the magnitudes of the N-biases are vertical resolution dependent. The N-bias is also the primary cause of the systematically smaller refractivity gradient (rarely exceeding -110 N-unit per kilometer) at the ABL top from RO measurement. However, the N-bias seems not affect the ABL height detection. Instead, the very large RO bending angle and the sharp refractivity gradient due to ducting allow reliable detection of the ABL height from GPS RO. The seasonal mean climatology of ABL heights derived from a nine-month composite of COSMIC RO soundings over the SE Pacific reveals significant differences from the ECMWF analysis. Both show an increase of ABL height from the shallow stratocumulus near the coast to a much higher trade wind inversion further off the coast. However, COSMIC RO shows an overall deeper ABL and reveals different locations of the minimum and maximum ABL heights as compared to the ECMWF analysis

  9. A comprehensive investigation on afternoon transition of the atmospheric boundary layer over a tropical rural site

    NASA Astrophysics Data System (ADS)

    Sandeep, A.; Rao, T. N.; Rao, S. V. B.

    2015-07-01

    The transitory nature of the atmospheric boundary layer (ABL) a few hours before and after the time of sunset has been studied comprehensively over a tropical station, Gadanki (13.45° N, 79.18° E), using a suite of in situ and remote sensing devices. This study addresses the following fundamental and important issues related to the afternoon transition (AT): which state variable first identifies the AT? Which variable best identifies the AT? Does the start time of the AT vary with season and height? If so, which physical mechanism is responsible for the observed height variation in the start time of the transition? At the surface, the transition is first seen in temperature (T) and wind variance (σ2WS), ~ 100 min prior to the time of local sunset, then in the vertical temperature gradient and finally in water vapor mixing ratio variations. Aloft, both signal-to-noise ratio (SNR) and spectral width (σ) show the AT nearly at the same time. The T at the surface and SNR aloft are found to be the best indicators of transition. Their distributions for the start time of the AT with reference to time of sunset are narrow and consistent in both total and seasonal plots. The start time of the transition shows some seasonal variation, with delayed transitions occurring mostly in the rainy and humid season of the northeast monsoon. Interestingly, in contrast to the general perception, the signature of the transition is first seen in the profiler data, then in the sodar data, and finally in the surface data. This suggests that the transition follows a top-to-bottom evolution. It indicates that other processes, like entrainment, could also play a role in altering the structure of the ABL during the AT, when the sensible heat flux decreases progressively. These mechanisms are quantified using a unique high-resolution data set to understand their variation in light of the intriguing height dependency of the start time of the AT.

  10. Isolating effects of terrain and soil moisture heterogeneity on the atmospheric boundary layer: Idealized simulations to diagnose land-atmosphere feedbacks

    NASA Astrophysics Data System (ADS)

    Rihani, Jehan F.; Chow, Fotini K.; Maxwell, Reed M.

    2015-06-01

    The effects of terrain, soil moisture heterogeneity, subsurface properties, and water table dynamics on the development and behavior of the atmospheric boundary layer are studied through a set of idealized numerical experiments. The mesoscale atmospheric model Advanced Regional Prediction System (ARPS) is used to isolate the effects of subsurface heterogeneity, terrain, and soil moisture initialization. The simulations are initialized with detailed soil moisture distributions obtained from offline spin-ups using a coupled surface-subsurface model (ParFlow-CLM). In these idealized simulations, we observe that terrain effects dominate the planetary boundary layer (PBL) development during early morning hours, while the soil moisture signature overcomes that of terrain during the afternoon. Water table and subsurface properties produce a similar effect as that of soil moisture as their signatures (reflected in soil moisture profiles, energy fluxes, and evaporation at the land surface) can also overcome that of terrain during afternoon hours. This is mostly clear for land surface energy fluxes and evaporation at the land surface. We also observe the coupling between water table depth and planetary boundary layer depth in our cases is strongest within wet-to-dry transition zones. This extends the findings of previous studies which demonstrate the subsurface connection to surface energy fluxes is strongest in such transition zones. We investigate how this connection extends into the atmosphere and can affect the structure and development of the convective boundary layer.

  11. Estimation of the ozone formation rate in the atmospheric boundary layer over a background region of Western Siberia

    NASA Astrophysics Data System (ADS)

    Antokhin, P. N.; Antokhina, O. Y.; Belan, B. D.

    2015-11-01

    The ozone formation rate in the atmospheric boundary layer (ABL) and the ozone inflow from the free atmosphere have been studied experimentally. The obtained estimates are based on the data of airborne sounding carried out over a background region of Western Siberia. As a result, it is obtained that the rate of ozone inflow from the upper atmospheric layers is only 20% of the rate of photochemical formation of ozone inside ABL. The vertical profiles of ozone flows in ABL have been additionally calculated based on the k-theory with the approach proposed by Troen and Mahrt. It has been shown in the calculations that the maximum of the ozone concentration in ABL is formed due to photochemical reactions from precursor gases.

  12. Lidar Applications in Atmospheric Dynamics: Measurements of Wind, Moisture and Boundary Layer Evolution

    NASA Technical Reports Server (NTRS)

    Demoz, Belay; Whiteman, David; Gentry, Bruce; Schwemmer, Geary; Evans, Keith; DiGirolamo, Paolo; Comer, Joseph

    2005-01-01

    A large array of state-of-the-art ground-based and airborne remote and in-situ sensors were deployed during the International H2O Project (THOP), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. These instruments provided extensive measurements of water vapor mixing ratio in order to better understand the influence of its variability on convection and on the skill of quantitative precipitation prediction (Weckwerth et all, 2004). Among the instrument deployed were ground based lidars from NASA/GSFC that included the Scanning Raman Lidar (SRL), the Goddard Laboratory for Observing Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). A brief description of the three lidars is given below. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars during MOP at the MOP ground profiling site in the Oklahoma Panhandle (hereafter referred as Homestead). This presentation will focus on the evolution and variability of moisture and wind in the boundary layer when frontal and/or convergence boundaries (e.g. bores, dry lines, thunderstorm outflows etc) were observed.

  13. Heat transport in the marine atmospheric boundary layer during an intense cold air outbreak

    NASA Technical Reports Server (NTRS)

    Chou, Shu-Hsien; Zimmerman, Jeffrey

    1988-01-01

    The generation of the virtual heat flux in the convective MABL associated with the January 28, 1986 intense cold air airbreak offshore of the Carolinas is studied. A technique based on the joint frequency distribution of the virtual potential temperature and vertical motion (Mahrt and Paumier, 1984) is used. The results suggest that, if buoyancy is mainly driven by the temperature flux, the physical processes for generating buoyancy flux are about the same for boundary layers over land and ocean, even with different convective regimes.

  14. Non-steady dynamics of atmospheric turbulence interaction with wind turbine loadings through blade-boundary-layer-resolved CFD

    NASA Astrophysics Data System (ADS)

    Vijayakumar, Ganesh

    Modern commercial megawatt-scale wind turbines occupy the lower 15-20% of the atmospheric boundary layer (ABL), the atmospheric surface layer (ASL). The current trend of increasing wind turbine diameter and hub height increases the interaction of the wind turbines with the upper ASL which contains spatio-temporal velocity variations over a wide range of length and time scales. Our interest is the interaction of the wind turbine with the energetic integral-scale eddies, since these cause the largest temporal variations in blade loadings. The rotation of a wind turbine blade through the ABL causes fluctuations in the local velocity magnitude and angle of attack at different sections along the blade. The blade boundary layer responds to these fluctuations and in turn causes temporal transients in local sectional loads and integrated blade and shaft bending moments. While the integral scales of the atmospheric boundary layer are ˜ O(10--100m) in the horizontal with advection time scales of order tens of seconds, the viscous surface layer of the blade boundary layer is ˜ O(10 -- 100 mum) with time scales of order milliseconds. Thus, the response of wind turbine blade loadings to atmospheric turbulence is the result of the interaction between two turbulence dynamical systems at extremely disparate ranges of length and time scales. A deeper understanding of this interaction can impact future approaches to improve the reliability of wind turbines in wind farms, and can underlie future improvements. My thesis centers on the development of a computational framework to simulate the interaction between the atmospheric and wind turbine blade turbulence dynamical systems using a two step one-way coupled approach. Pseudo-spectral large eddy simulation (LES) is used to generate a true (equilibrium) atmospheric boundary layer over a flat land with specified surface roughness and heating consistent with the stability state of the daytime lower troposphere. Using the data from the

  15. Detecting surface roughness effects on the atmospheric boundary layer via AIRSAR data: A field experiment in Death Valley, California

    NASA Technical Reports Server (NTRS)

    Blumberg, Dan G.; Greeley, Ronald

    1992-01-01

    The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.

  16. DIFFUSION IN THE VICINITY OF STANDARD-DESIGN NUCLEAR POWER PLANTS-I. WIND-TUNNEL EVALUATION OF DIFFUSIVE CHARACTERISTICS OF A SIMULATED SUBURBAN NEUTRAL ATMOSPHERIC BOUNDARY LAYER

    EPA Science Inventory

    A large meteorological wind tunnel was used to simulate a suburban atmospheric boundary layer. The model-prototype scale was 1:300 and the roughness length was approximately 1.0 m full scale. The model boundary layer simulated full scale dispersion from ground-level and elevated ...

  17. The Small Unmanned Meteorological Observer SUMO: Recent developments and applications of a Micro-UAS for atmospheric boundary layer research

    NASA Astrophysics Data System (ADS)

    Reuder, J.; Jonassen, M. O.; Ólafsson, H.

    2012-04-01

    During the last 5 years, the Small Unmanned Meteorological Observer SUMO has been developed as a new and flexible tool for atmospheric boundary layer (ABL) research to be operated as controllable and recoverable atmospheric sounding system for the lowest 4 km above the Earth's surface. In the year 2011 two main technical improvements of the system have been accomplished. The integration of an inertial measurement unit (IMU) into the Paparazzi autopilot system has expanded the environmental conditions for SUMO operation to now even allowing incloud flights. In the field of sensor technology the implementation of a 5-hole probe for the determination of the 3 dimensional flow vector impinging the aircraft with a 100 Hz resolution and of a faster Pt1000 based temperature sensor have distinctly enhanced the meteorological measurement capabilities. The extended SUMO version has recently been operated during two field campaigns. The first one in a wind farm close to Vindeby on Lolland, Denmark, was dedicated to the investigation of the effects of wind turbines on boundary layer turbulence. In spite of a few pitfalls related to configuration and synchronisation of the corresponding data logging systems, this campaign provided promising results indicating the capability and future potential of small UAS for turbulence characterization in and around wind farms. The second one, the international BLLAST (Boundary Layer Late Afternoon and Sunset Transition) field campaign at the foothills of the Pyrenees in Lannemezan, France was focussing on processes related to the afternoon transition of the convective boundary layer. On a calm sunny day during this experiment, the SUMO soundings revealed an unexpected 2°C cooling in the ABL during morning hours. By a comparison with model simulations this cooling can be associated with thermally-driven upslope winds and the subsequent advection of relatively cool air from the lowlands north of the Pyrenees.

  18. An Observational Case Study on the Influence of Atmospheric Boundary-Layer Dynamics on New Particle Formation

    NASA Astrophysics Data System (ADS)

    Platis, Andreas; Altstädter, Barbara; Wehner, Birgit; Wildmann, Norman; Lampert, Astrid; Hermann, Markus; Birmili, Wolfram; Bange, Jens

    2016-01-01

    We analyze the influence of atmospheric boundary-layer development on new particle formation (NPF) during the morning transition. Continuous in-situ measurements of vertical profiles of temperature, humidity and aerosol number concentrations were quasi-continously measured near Melpitz, Germany, by unmanned aerial systems to investigate the potential connection between NPF and boundary-layer dynamics in the context of turbulence, temperature and humidity fluctuations. On 3 April 2014 high number concentrations of nucleation mode particles up to 6.0 × 10^4 cm^{-3} were observed in an inversion layer located about 450 m above ground level. The inversion layer exhibited a spatial temperature structure parameter C_T^2 15 times higher and a spatial humidity structure parameter C_q^2 5 times higher than in the remaining part of the vertical profile. The study provides hints that the inversion layer is responsible for creating favorable thermodynamic conditions for a NPF event. In addition, this layer showed a strong anti-correlation of humidity and temperature fluctuations. Using estimates of the turbulent mixing and dissipation rates, it is concluded that the downward transport of particles by convective mixing was also the reason of the sudden increase of nucleation mode particles measured on ground. This work supports the hypothesis that many of the NPF events that are frequently observed near the ground may, in fact, originate at elevated altitude, with newly formed particles subsequently being mixed down to the ground.

  19. Boundary-Layer & health

    NASA Astrophysics Data System (ADS)

    Costigliola, V.

    2010-09-01

    It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate

  20. Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface.

    PubMed

    Smits, Kathleen; Eagen, Victoria; Trautz, Andrew

    2015-01-01

    Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study evaporation under various surface boundary conditions to improve our current understanding and characterization of this multiphase phenomenon as well as to validate numerical heat and mass transfer theories that couple Navier-Stokes flow in the atmosphere and Darcian flow in the porous media. Experimental data were collected using a unique soil tank apparatus interfaced with a small climate controlled wind tunnel. The experimental apparatus was instrumented with a suite of state of the art sensor technologies for the continuous and autonomous collection of soil moisture, soil thermal properties, soil and air temperature, relative humidity, and wind speed. This experimental apparatus can be used to generate data under well controlled boundary conditions, allowing for better control and gathering of accurate data at scales of interest not feasible in the field. Induced airflow at several distinct wind speeds over the soil surface resulted in unique behavior of heat and mass transfer during the different evaporative stages. PMID:26131928

  1. Meteorological responses in the atmospheric boundary layer over southern England to the deep partial eclipse of 20 March 2015.

    PubMed

    Burt, Stephen

    2016-09-28

    A wide range of surface and near-surface meteorological observations were made at the University of Reading's Atmospheric Observatory in central southern England (latitude 51.441° N, longitude 0.938° W, altitude 66 m above mean sea level) during the deep partial eclipse on the morning of 20 March 2015. Observations of temperature, humidity, radiation, wind speed and direction, and atmospheric pressure were made by computerized logging equipment at 1 Hz, supplemented by an automated cloud base recorder sampling at 1 min intervals and a high-resolution (approx. 10 m vertical interval) atmospheric sounding by radiosonde launched from the same location during the eclipse. Sources and details of each instrumental measurement are described briefly, followed by a summary of observed and derived measurements by meteorological parameter. Atmospheric boundary layer responses to the solar eclipse were muted owing to the heavily overcast conditions which prevailed at the observing location, but instrumental records of the event documented a large (approx. 80%) reduction in global solar radiation, a fall in air temperature of around 0.6°C, a decrease in cloud base height, and a slight increase in atmospheric stability during the eclipse. Changes in surface atmospheric moisture content and barometric pressure were largely insignificant during the event.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'. PMID:27550762

  2. An Experimental Study of the Statistics of Temperature Fluctuations in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Costa Frola, Elena; Mazzino, Andrea; Cassola, Federico; Mortarini, Luca; Ferrero, Enrico

    2014-01-01

    A statistical characterization for two-point temperature fluctuations in the planetary boundary layer (PBL) is analyzed and its implications on the long-standing closure problem discussed. Despite the non-triviality of the dynamics of temperature fluctuations, our analysis supports the idea that the most relevant statistical properties can be captured solely in terms of two scaling exponents. They turned out to be weakly dependent on the stability properties of the PBL. Its statistics have been investigated by collecting data from a field experiment carried out in the urban area of Turin (Italy) from January 2007 to March 2008. Our results confirm those from a large-eddy simulation (LES) analysis carried out for the convective PBL with different level of convection. We extend the scenario to the stable PBL, a regime much more difficult to simulate when exploiting LES.

  3. The Deep Atmospheric Boundary Layer and Its Significance to the Stratosphere and Troposphere Exchange over the Tibetan Plateau

    PubMed Central

    Chen, Xuelong; Añel, Juan A.; Su, Zhongbo; de la Torre, Laura; Kelder, Hennie; van Peet, Jacob; Ma, Yaoming

    2013-01-01

    In this study the depth of the atmospheric boundary layer (ABL) over the Tibetan Plateau was measured during a regional radiosonde observation campaign in 2008 and found to be deeper than indicated by previously measurements. Results indicate that during fair weather conditions on winter days, the top of the mixed layers can be up to 5 km above the ground (9.4 km above sea level). Measurements also show that the depth of the ABL is quite distinct for three different periods (winter, monsoon-onset, and monsoon seasons). Turbulence at the top of a deep mixing layer can rise up to the upper troposphere. As a consequence, as confirmed by trajectory analysis, interaction occurs between deep ABLs and the low tropopause during winter over the Tibetan Plateau. PMID:23451108

  4. Atmospheric Boundary-Layer Evening Transitions: A Comparison Between Two Different Experimental Sites

    NASA Astrophysics Data System (ADS)

    Sastre, Mariano; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio

    2015-12-01

    The planetary boundary-layer (PBL) afternoon and evening transition is investigated with measurements from two-month datasets, gathered at two experimental sites significantly different regarding heterogeneity, the degree of terrain wetness, and proximity to mountains. The period of 4 h prior to and after astronomical sunset is extensively analyzed. We show the mean evolution, average, maximum and minimum values of PBL variables, including wind speed, turbulent kinetic energy and potential temperature vertical gradient. Characteristic events, such as the wind minimum around sunset and a common pattern in the evolution of other variables, are identified. Results suggest that, for the establishment of the nocturnal stable boundary layer, moisture plays a more decisive role than turbulence. We also look into the occurrence of katabatic flows, finding more intense but less frequent events at the driest site. In contrast, at that location the crossover of the sensible heat flux takes place later. Time-scale evolution is investigated through case studies, and air humidity and soil moisture are found to have crucial importance explaining most of the site-to-site differences. Therefore, a humidity sensitivity experiment with the Weather Research and Forecasting model is performed, evaluating the role of moisture during the transition by increasing the soil humidity at the driest site and reducing it at the other location. The simulations reveal that humidity effects are more important until 1 h before sunset, both near the surface and at upper levels in the PBL. Furthermore, the moisture change is more relevant at the less humid and more homogeneous site, with intense and long-lasting effects after sunset.

  5. A bulk similarity approach in the atmospheric boundary layer using radiometric skin temperature to determine regional surface fluxes

    NASA Technical Reports Server (NTRS)

    Brutsaert, Wilfried; Sugita, Michiaki

    1991-01-01

    Profiles of wind velocity and temperature in the outer region of the atmospheric boundary layer (ABL) were used together with surface temperature measurements, to determine regional shear stress and sensible heat flux by means of transfer parameterizations on the basis of bulk similarity. The profiles were measured by means of radiosondes and the surface temperatures by infrared radiation thermometry over hilly prairie terrain in northeastern Kansas during the First ISLSCP Field Experiment (FIFE). In the analysis, the needed similarity functions were determined and tested.

  6. Large-eddy Simulation of Stratocumulus-topped Atmospheric Boundary Layers with Dynamic Subgrid-scale Models

    NASA Technical Reports Server (NTRS)

    Senocak, Inane

    2003-01-01

    The objective of the present study is to evaluate the dynamic procedure in LES of stratocumulus topped atmospheric boundary layer and assess the relative importance of subgrid-scale modeling, cloud microphysics and radiation modeling on the predictions. The simulations will also be used to gain insight into the processes leading to cloud top entrainment instability and cloud breakup. In this report we document the governing equations, numerical schemes and physical models that are employed in the Goddard Cumulus Ensemble model (GCEM3D). We also present the subgrid-scale dynamic procedures that have been implemented in the GCEM3D code for the purpose of the present study.

  7. Lagrangian stochastic modeling of pollutant dispersion in the turbulent atmospheric boundary layer - application to an urban area over complex terrain

    NASA Astrophysics Data System (ADS)

    Fattal, Eyal; Gavze, Ehud

    2014-05-01

    The modeling of pollutant dispersion in the atmospheric boundary layer depends on an adequate description of the turbulent processes. Since turbulence is a multi-scale phenomenon characterized by a high degree of disorder, a statistical approach is needed. Among the statistical approaches, Lagrangian stochastic particle models provide a well established theoretical framework for the description of pollutant dispersion in different atmospheric boundary layer scenarios. Usually turbulent structure in the surface layer is described in terms of Monin-Obukhov similarity theory (MOST) using universal relationships between scaling parameters. These relationships have been shown to be valid in the case of horizontal homogeneity for stationary turbulence. The description of the turbulent processes above rough surfaces, such as over canopies, is a more complex case. For the urban canopy it was found that under developed stationary turbulence conditions MOST relations are approximately valid (in some cases, with extensions). An even more complex case is that of rough surfaces over topography, as no similarity theory has been established to properly describe the turbulence exchange over heterogeneous surfaces in complex terrain. We show Lagrangian stochastic model simulations based on MOST against measurements in urban canopy over complex terrain. Comparison gives good agreement with direct tracer measurements, in cases of neutral and convective stratifications. It is shown that in conditions of developed stationary turbulence, at most areas, there is in an agreement with MOST predictions. However, in very low wind conditions the turbulent nocturnal boundary layer is not necessarily stationary and is spatially non-homogeneous. This results in larger horizontal velocity standard deviation than expected in regular stable regime, as manifested in the pollutant pattern.

  8. The thermal structure of the atmospheric surface boundary layer on Mars as modified by the radiative effect of aeolian dust

    NASA Technical Reports Server (NTRS)

    Pallmann, A. J.

    1983-01-01

    A computational simulation, based on Mariner 9 data, was performed for the thermal characteristics of the Martian atmospheric surface boundary layer in clear and dust-filled conditions. A radiative transfer model consisting of the atmospheric enthalpy rate equation, the radiative flux integrated over the 0.2-50 microns, the solid angle interval, and 0.50 km altitudes, broken into 52 levels. Mariner 9 IR data for CO2 absorption lines were included in the form of a temperture-dependent equation, while the line-widths were interpreted in terms of the pressure dependene as well as temperature. The lines covered the regions from 1-50 microns and varying conditions of dust content in the atmosphere. Attention was given to the thermal coupling between the ground and the atmosphere. It was found that convective heat exchange develops quickly due to radiative heating of the Martian desert surface, but does not cool the surface because of the attenuated atmosphere. The model predictd the 100 K temperature variations in the dusty atmosphere, as observed by the Viking thermal mapper. It is suggested that radiative flux convergence is as important as convection at equivalent efficiencies.

  9. On determination of formaldehyde content in atmospheric boundary layer for overcast using DOAS technique

    NASA Astrophysics Data System (ADS)

    Postylyakov, Oleg; Borovski, Alexander; Ivanov, Victor

    2015-11-01

    Formaldehyde (HCHO) is involved in a lot of chemical reactions in the atmosphere. Taking into account that HCHO basically undergo by photolysis and reaction with hydroxyl radical within a few hours, short-lived VOCs and direct HCHO emissions can cause local HCHO enhancement over certain areas, and, hence, exceeding background level of HCHO can be examined as a local pollution of the atmosphere by VOCs or existence of a local HCHO source. Several retrieval algorithms applicable for DOAS measurements in cloudless were previously developed. A new algorithm applicable for overcast and cloudless sky and its error analysis is briefly introduced by this paper. Analysis of our HCHO VCD retrieval for overcast shows that when one know the cloud base height, but doesn't know cloud optical depth, the typical errors of HCHO total content retrieval are less than 10% for snow season, less than 5% for snow-free seasons, and reaches 40-45% for season with non-stable snow cover. In case one knows both the cloud base height and the cloud optical depth, the typical errors are about 5% for snow season, less than 2.5% for snow-free seasons, and are within about 10-30% for season with non-stable snow cover. Given above error estimations are valid if the HCHO layer is below the cloud base. The errors dramatically increase when HCHO layer penetrates into clouds in both cases. The first preliminary results of HCHO VCD retrieval for overcast are shown. The average difference of the HCHO VCDs for wind from Moscow megapolis and wind from few urbanized areas is about 0.8×1016 mol×cm-2 and approximately corresponds to estimates of influence of Moscow megapolis observed in clear-sky conditions.

  10. The influence of the atmospheric boundary layer on nocturnal layers of noctuids and other moths migrating over southern Britain.

    PubMed

    Wood, Curtis R; Chapman, Jason W; Reynolds, Donald R; Barlow, Janet F; Smith, Alan D; Woiwod, Ian P

    2006-03-01

    Insects migrating at high altitude over southern Britain have been continuously monitored by automatically operating, vertical-looking radars over a period of several years. During some occasions in the summer months, the migrants were observed to form well-defined layer concentrations, typically at heights of 200-400 m, in the stable night-time atmosphere. Under these conditions, insects are likely to have control over their vertical movements and are selecting flight heights that are favourable for long-range migration. We therefore investigated the factors influencing the formation of these insect layers by comparing radar measurements of the vertical distribution of insect density with meteorological profiles generated by the UK Meteorological Office's (UKMO) Unified Model (UM). Radar-derived measurements of mass and displacement speed, along with data from Rothamsted Insect Survey light traps, provided information on the identity of the migrants. We present here three case studies where noctuid and pyralid moths contributed substantially to the observed layers. The major meteorological factors influencing the layer concentrations appeared to be: (a) the altitude of the warmest air, (b) heights corresponding to temperature preferences or thresholds for sustained migration and (c) on nights when air temperatures are relatively high, wind-speed maxima associated with the nocturnal jet. Back-trajectories indicated that layer duration may have been determined by the distance to the coast. Overall, the unique combination of meteorological data from the UM and insect data from entomological radar described here show considerable promise for systematic studies of high-altitude insect layering. PMID:16432728

  11. ALADINA - an unmanned research aircraft for observing vertical and horizontal distributions of ultrafine particles within the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Altstädter, B.; Platis, A.; Wehner, B.; Scholtz, A.; Wildmann, N.; Hermann, M.; Käthner, R.; Baars, H.; Bange, J.; Lampert, A.

    2015-04-01

    This paper presents the unmanned research aircraft Carolo P360 "ALADINA" (Application of Light-weight Aircraft for Detecting IN situ Aerosol) for investigating the horizontal and vertical distribution of ultrafine particles in the atmospheric boundary layer (ABL). It has a wingspan of 3.6 m, a maximum take-off weight of 25 kg and is equipped with aerosol instrumentation and meteorological sensors. A first application of the system, together with the unmanned research aircraft MASC (Multi-Purpose Airborne Carrier) of the Eberhard Karls University of Tübingen (EKUT), is described. As small payload for ALADINA, two condensation particle counters (CPC) and one optical particle counter (OPC) were miniaturised by re-arranging the vital parts and composing them in a space-saving way in the front compartment of the airframe. The CPCs are improved concerning the lower detection threshold and the response time to less than 1.3 s. Each system was characterised in the laboratory and calibrated with test aerosols. The CPCs are operated in this study with two different lower detection threshold diameters of 11 and 18 nm. The amount of ultrafine particles, which is an indicator for new particle formation, is derived from the difference in number concentrations of the two CPCs (ΔN). Turbulence and thermodynamic structure of the boundary layer are described by measurements of fast meteorological sensors that are mounted at the aircraft nose. A first demonstration of ALADINA and a feasibility study were conducted in Melpitz near Leipzig, Germany, at the Global Atmosphere Watch (GAW) station of the Leibniz Institute for Tropospheric Research (TROPOS) on 2 days in October 2013. There, various ground-based instruments are installed for long-term atmospheric monitoring. The ground-based infrastructure provides valuable additional background information to embed the flights in the continuous atmospheric context and is used for validation of the airborne results. The development of the

  12. Atmospheric conditions associated with high and low summertime ozone levels in the boundary layer over some eastern Mediterranean airports

    NASA Astrophysics Data System (ADS)

    Kalabokas, Pavlos D.; Thouret, Valerie; Cammas, Jean-Pierre; Volz-Thomas, Andreas; Boulanger, Damien; Repapis, Christos C.

    2013-04-01

    Thanks to the vertical atmospheric measurements of the MOZAIC program, enhanced ozone mixing ratios in the lower troposphere over the Eastern Mediterranean have been found, frequently exceeding the 60 ppb, 8-h EU air quality standard, whereas ozone between 700 hPa and 400 hPa was only slightly (3-5 ppb, 5-10%) higher than over Central Europe. Also, the examination of the highest and lowest ozone levels in the lower troposphere (1.5-5 km) over some airports in the Eastern Mediterranean area showed the lower-tropospheric ozone variability over there is controlled mainly by the synoptic meteorological conditions, combined with local topographical and meteorological features. In particular, the highest ozone concentrations in the lower troposphere and subsequently in the boundary layer in the area are associated with large scale subsidence of ozone rich air masses from the upper troposphere under anticyclonic conditions while the lowest ozone concentrations are associated with low pressure conditions inducing uplifting of boundary layer air, poor in ozone and rich in relative humidity, to the lower troposphere. In order to further evaluate the observed high rural ozone levels during summertime, vertical summer ozone profiles measured by MOZAIC in the period 1994-2008 over the Eastern Mediterranean basin (Cairo, Tel-Aviv, Heraklion, Rhodes, Antalya) are analyzed, focusing in the boundary layer (0-1.5 km). First, vertical profiles collected during extreme days with very high or very low tropospheric ozone mixing ratios are examined. Also, the average profiles of ozone, relative humidity, carbon monoxide, vertical temperature gradient and wind speed corresponding to the 7% highest and the 7% lowest ozone mixing ratios for the height layers of 0-500m, 500-1000m and 1000-1500m for Cairo and Tel-Aviv are examined along with the corresponding composite maps of geopotential heights at 850 hPa and 925 hPa. In addition, analyses of backward trajectories, using the FLEXPART model

  13. Study of Near-Surface Models in Large-Eddy Simulations of a Neutrally Stratified Atmospheric Boundary Layer

    NASA Technical Reports Server (NTRS)

    Senocak, I.; Ackerman, A. S.; Kirkpatrick, M. P.; Stevens, D. E.; Mansour, N. N.

    2004-01-01

    Large-eddy simulation (LES) is a widely used technique in armospheric modeling research. In LES, large, unsteady, three dimensional structures are resolved and small structures that are not resolved on the computational grid are modeled. A filtering operation is applied to distinguish between resolved and unresolved scales. We present two near-surface models that have found use in atmospheric modeling. We also suggest a simpler eddy viscosity model that adopts Prandtl's mixing length model (Prandtl 1925) in the vicinity of the surface and blends with the dynamic Smagotinsky model (Germano et al, 1991) away from the surface. We evaluate the performance of these surface models by simulating a neutraly stratified atmospheric boundary layer.

  14. Structure of the Entrainment Zone Capping the Convective Atmospheric Boundary Layer.

    NASA Astrophysics Data System (ADS)

    Sullivan, Peter P.; Moeng, Chin-Hoh; Stevens, Bjorn; Lenschow, Donald H.; Mayor, Shane D.

    1998-10-01

    The authors use large-eddy simulation (LES) to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer (PBL) over a range of bulk Richardson numbers, Ri. The LES code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer.Extensive flow visualization is used to examine the structure of the inversion layer and to illustrate the temporal and spatial interaction of a thermal plume and the overlying inversion. It is found that coherent structures in the convective PBL, that is, thermal plumes, are primary instigators of entrainment in the Ri range 13.6 Ri 43.8. At Ri = 13.6, strong horizontal and downward velocities are generated near the inversion layer because of the plume-interface interaction. This leads to folding of the interface and hence entrainment of warm inversion air at the plume's edge. At Ri = 34.5, the inversion's strong stability prevents folding of the interface but strong horizontal and downward motions near the plume's edge pull down pockets of warm air below the nominal inversion height. These pockets of warm air are then scoured off by turbulent motions and entrained into the PBL. The structure of the inversion interface from LES is in good visual agreement with lidar measurements in the PBL obtained during the Lidars in Flat Terrain field experiment.A quadrant analysis of the buoyancy flux shows that net entrainment flux (or average minimum buoyancy flux min) is identified with quadrant IV + < 0 motions, that is, warm air moving downward. Plumes generate both large negative quadrant II + < 0 and positive quadrant III > 0 buoyancy fluxes that tend to cancel.The maximum vertical gradient in potential temperature at every (x, y) grid point is used to define a local PBL height, zi(x, y). A statistical analysis of zi shows that skewness of zi depends on the inversion strength. Spectra of zi exhibit a sensitivity to grid resolution. The

  15. A Large-eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Shamsoddin, Sina; Porté-Agel, Fernando

    2016-04-01

    Vertical axis wind turbines (VAWTs) offer some advantages over their horizontal axis counterparts, and are being considered as a viable alternative to conventional horizontal axis wind turbines (HAWTs). Nevertheless, a relative shortage of scientific, academic and technical investigations of VAWTs is observed in the wind energy community with respect to HAWTs. Having this in mind, in this work, we aim to study the wake of a single VAWT, placed in the atmospheric boundary layer, using large-eddy simulation (LES) coupled with actuator line model (ALM). It is noteworthy that this is the first time that such a study is being performed. To do this, for a typical 1 MW VAWT design, first, the variation of power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed using LES-ALM, and an optimum combination of chord length and tip-speed ratio is obtained. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulent wake flow statistics. Keywords: vertical axis wind turbine (VAWT); VAWT wake; Atmospheric Boundary Layer (ABL); large eddy simulation (LES); actuator line model (ALM); turbulence.

  16. An Experimental Investigation on the Interference of the Multiple Wind Turbines with Different Layout Patterns in Atmospheric Boundary Layer Winds

    NASA Astrophysics Data System (ADS)

    Hu, Hui; Tian, Wei; Ozbay, Ahmet

    2012-11-01

    We report an experimental study to investigate the wake interferences of multiple wind turbines in atmospheric boundary layer (ABL) winds. The experimental study is conducted by taking advantages of the large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University to quantify the performances of an array of wind turbine models with aligned and staggered arrangement patterns. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the wind turbine models, advanced flow diagnostic techniques such as digital Particle Image Velocimetry (PIV) is used to conduct detailed flow field measurements to quantify the flow characteristics of the surface winds and wake interferences among the multiple wind turbines with different layout patterns. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics for the optimal design of the wind turbine array layout with the ultimate goal of higher total power yield and better durability of the wind turbines operating in more realistic environments. The reserach work is funded by IAWIND and NSF with Award # CBET-1133751.

  17. Observations of the atmospheric boundary layer height under marine upstream flow conditions at a coastal site

    NASA Astrophysics Data System (ADS)

    PeñA, A.; Gryning, S.-E.; Hahmann, A. N.

    2013-02-01

    AbstractWe investigate several lidar-type instruments and methodologies for <span class="hlt">boundary</span> <span class="hlt">layer</span> height (BLH) estimation during 2 days at a coastal site for winds that experience marine upstream flow conditions. Wavelet and profile fitting procedures on the aerosol backscatter signals from a ceilometer and an aerosol lidar reveal similar BLHs, but their agreement depends on the presence of clouds and the instrument signal, among others. BLHs derived by a threshold on the carrier-to-noise profiles of a wind lidar agree well with those derived by using a threshold on the backscatter profile of the ceilometer and are used as reference for a 10 day BLH intercomparison. Furthermore, the BLHs from the aerosol analysis are comparable to those derived from wind speed and direction profiles from combined mast/wind lidar measurements. The BLH derived from simulations performed with the Weather Research and Forecasting (WRF) model shows similar behavior compared to the lidar observations. The seasonal diurnal variation of the BLH for 2010, derived from the wind lidar and ceilometer thresholds, shows similar BLHs but generally higher values compared to that from WRF. No clear BLH diurnal variation is observed neither from the observations nor from the WRF model outputs, except in summer for the latter. Both observations and WRF model simulations reveal higher BLHs during autumn compared to spring time. These BLHs are used to evaluate the intra-annual variation and show high peaks in September, November, and February.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AeoRe..20..147K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AeoRe..20..147K"><span id="translatedtitle">Modeling of particulate matter transport in <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> following dust emission from source areas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Katra, Itzhak; Elperin, Tov; Fominykh, Andrew; Krasovitov, Boris; Yizhaq, Hezi</p> <p>2016-03-01</p> <p>A two-dimensional model for particulate matter (PM) dispersion due to dust emission from soils is presented. Field experiments were performed at a dust source site (Negev loess soil) with a portable <span class="hlt">boundary</span> <span class="hlt">layer</span> wind tunnel to determine the emitted PM fluxes for different wind speeds and varying soil conditions. The numerical model is formulated using parameterizations based on the aeolian experiments. The wind velocity profiles used in the simulations were fitted from data obtained in field measurements. Size distribution of the emitted dust particles in the numerical simulations was taken into account using a Monte Carlo method. The PM concentration distributions at a distance of several kilometers from the dust source under specific shear velocities and PM fluxes from the soil were determined numerically by solving advection-diffusion equation. The obtained PM10 concentrations under typical wind and soil conditions are supported by PM data recorded over time in a standard environmental monitoring station. The model enhances our capacity of quantification of dust processes to support climate models as well as health risk assessment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713717C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713717C"><span id="translatedtitle">Large-eddy simulation of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> flow and passive scalar dispersion over idealized urban surfaces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cheng, Wai Chi; Porté-Agel, Fernando</p> <p>2015-04-01</p> <p>Accurate prediction of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) flow and its interaction with urban surfaces is critical for understanding the transport of momentum and scalars within and above cities. This, in turn, is essential for predicting the local climate and pollutant dispersion patterns in urban areas. Large-eddy simulation (LES) explicitly resolves the large-scale turbulent eddy motions and, therefore, can potentially provide improved understanding and prediction of flows and scalar transport inside and above urban canopies. In this study, LES is used to simulate the dispersion of passive scalar over idealized urban surfaces represented by uniform arrays of cubes. A modulated gradient subgird-scale (SGS) model is used to parametrize the SGS fluxes of momentum and scalar, and an immersed <span class="hlt">boundary</span> method is used to model the presence of cubes. A similar LES framework for flow was validated in our previous studies in simulations of turbulent <span class="hlt">boundary-layer</span> flow past a 2D block and a uniform array of cubes. Here, the LES framework is further validated with wind tunnel experimental data of passive scalar dispersion within and above a staggered array of cubes with a localized scalar source at ground level. Good agreement between the simulation results and experimental data are found in the vertical and horizontal profiles of scalar concentration in different streamwise locations. After the validation, the LES framework is used to simulate the scalar transport at rural-to-urban flow transition region and the results obtained are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JESS..123.1233C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JESS..123.1233C"><span id="translatedtitle">Characterization of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> from radiosonde observations along eastern end of monsoon trough of India</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chandra, Sagarika; Dwivedi, Arun K.; Kumar, Manoj</p> <p>2014-08-01</p> <p>In this paper, a comparison of two methods for the calculation of the height of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature ( 𝜃 v ) profile for the determination of mixed <span class="hlt">layer</span> heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number ( R i B ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JESS..tmp...86C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JESS..tmp...86C"><span id="translatedtitle">Characterization of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> from radiosonde observations along eastern end of monsoon trough of India</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chandra, Sagarika; Dwivedi, Arun K.; Kumar, Manoj</p> <p>2014-08-01</p> <p>In this paper, a comparison of two methods for the calculation of the height of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature (𝜃 v ) profile for the determination of mixed <span class="hlt">layer</span> heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number (R i B ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AMTD....712283A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AMTD....712283A"><span id="translatedtitle">ALADINA - an unmanned research aircraft for observing vertical and horizontal distributions of ultrafine particles within the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Altstädter, B.; Platis, A.; Wehner, B.; Scholtz, A.; Lampert, A.; Wildmann, N.; Hermann, M.; Käthner, R.; Bange, J.; Baars, H.</p> <p>2014-12-01</p> <p>This paper presents the unmanned research aircraft Carolo P360 "ALADINA" (Application of Light-weight Aircraft for Detecting IN-situ Aerosol) for investigating the horizontal and vertical distribution of ultrafine particles in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL). It has a wingspan of 3.6 m, a maximum take-off weight of 25 kg and is equipped with aerosol instrumentation and meteorological sensors. A first application of the system, together with the unmanned research aircraft MASC (Multi-Purpose Airborne Carrier) of the Eberhard-Karls University of Tübingen (EKUT), is described. As small payload for ALADINA, two condensation particle counters (CPC) and one optical particle counter (OPC) were miniaturized by re-arranging the vital parts and composing them in a space saving way in the front compartment of the airframe. The CPCs are improved concerning the lower detection threshold and the response time. Each system was characterized in the laboratory and calibrated with test aerosols. The CPCs are operated with two different lower detection threshold diameters of 6 and 18 nm. The amount of ultrafine particles, which is an indicator for new particle formation, is derived from the difference in number concentrations of the two CPCs. Turbulence and thermodynamic structure of the <span class="hlt">boundary</span> <span class="hlt">layer</span> are described by measurements of fast meteorological sensors that are mounted at the aircraft nose. A first demonstration of ALADINA and a feasibility study were conducted in Melpitz near Leipzig, Germany, at the Global <span class="hlt">Atmosphere</span> Watch (GAW) station of the Leibniz Institute for Tropospheric Research (TROPOS) on two days in October 2013. There, various ground-based instruments are installed for long-term <span class="hlt">atmospheric</span> monitoring. The ground-based infrastructure provides valuable additional background information to embed the flights in the continuous <span class="hlt">atmospheric</span> context and is used for validation of the airborne results. The development of the <span class="hlt">boundary</span> <span class="hlt">layer</span>, derived from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGC31B1180R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGC31B1180R"><span id="translatedtitle">The Tturbulent Structure of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> over Small Northern Lakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Repina, I.; Stepanenko, V.; Artamonov, A.; Barskov, K.; Polukhov, A.</p> <p>2015-12-01</p> <p>Wetland and freshwater ecosystems of the Northern Europe are an important natural source of <span class="hlt">atmospheric</span> methane. Adequate calculation of gas emission from the northern territories requires calculation of balances of heat, moisture, and gases at the surface of water bodies on the sub-grid scale in the climate models. We carried out measurements in North Karelia on the lake Verkhneye (White Sea Biological Station of Moscow State University). The purpose of the study is evaluation of turbulent transport in the system "lake water- near-surface air - surrounding forest" in the winter season. We used an array of acoustic anemometers mounted at different distances from the lake shore. Measurements were taken at two heights in the center of the lake. It was revealed that the intensity of the turbulent transfer essentially depends on the height and location of sensors, and the wind direction. Stratification in the near-to-surface air probably does not play significant role. Besides, there is no constant-flux <span class="hlt">layer</span>. The later makes Monin and Obukhov similarity theory (which is used in most of the parameterizations for calculating turbulent flows) inapplicable in this case. The work was sponsored by RFBR 14-05-91752, 14-05-91764, 15-35-20958.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3884S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3884S"><span id="translatedtitle">Turbulence Generation in the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> and Limitations of the Monin-Obukhov Similarity Theory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Jielun; Lenschow, Donald; LeMone, Margaret; Mahrt, Larry</p> <p>2015-04-01</p> <p>Turbulent fluxes from the Cooperative <span class="hlt">Atmosphere</span>-Surface Exchange Study in 1999 (CASES-99) field experiment are further analyzed for both day- and nighttime as a follow-on to the investigation of the nighttime turbulence in Sun et al. (2012). The behavior of momentum and heat fluxes is investigated as functions of wind speed and the bulk temperature difference between observation heights and the surface. Vertical variations of momentum and heat flux at a given height z are correlated and are explained in terms of the energy and heat balance in a <span class="hlt">layer</span> above the ground surface in which the surface heating/cooling and momentum sink need to be included. In addition, the surface also plays an important role in constraining the size of the dominant turbulent eddies, which is directly related to turbulence strength and the length scale of turbulence generation. The turbulence generation is not related to local vertical gradients especially under neutral condition as assumed in Monin-Obukhov similarity theory. Based on the observed relationships between momentum and heat fluxes, a new bulk formula for turbulence parameterization is developed to mainly examine the above-mentioned surface effects on vertical variation of turbulent momentum and heat fluxes. The new understanding of the observed relationships between these turbulent variables and mean variables explains the observed nighttime turbulence regime change observed in Sun et al. (2012) as well as the daytime momentum and heat flux variations with height up to the maximum observation height of 55 m.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ACPD...1527539R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ACPD...1527539R"><span id="translatedtitle">Controlled meteorological (CMET) balloon profiling of the Arctic <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> around Spitsbergen compared to a mesoscale model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, T. J.; Dütsch, M.; Hole, L. R.; Voss, P. B.</p> <p>2015-10-01</p> <p>Observations from CMET (Controlled Meteorological) balloons are analyzed in combination with mesoscale model simulations to provide insights into tropospheric meteorological conditions (temperature, humidity, wind-speed) around Svalbard, European High Arctic. Five Controlled Meteorological (CMET) balloons were launched from Ny-Ålesund in Svalbard over 5-12 May 2011, and measured vertical <span class="hlt">atmospheric</span> profiles above Spitsbergen Island and over coastal areas to both the east and west. One notable CMET flight achieved a suite of 18 continuous soundings that probed the Arctic marine <span class="hlt">boundary</span> <span class="hlt">layer</span> over a period of more than 10 h. The CMET profiles are compared to simulations using the Weather Research and Forecasting (WRF) model using nested grids and three different <span class="hlt">boundary</span> <span class="hlt">layer</span> schemes. Variability between the three model schemes was typically smaller than the discrepancies between the model runs and the observations. Over Spitsbergen, the CMET flights identified temperature inversions and low-level jets (LLJ) that were not captured by the model. Nevertheless, the model largely reproduced time-series obtained from the Ny-Ålesund meteorological station, with exception of surface winds during the LLJ. Over sea-ice east of Svalbard the model underestimated potential temperature and overestimated wind-speed compared to the CMET observations. This is most likely due to the full sea-ice coverage assumed by the model, and consequent underestimation of ocean-<span class="hlt">atmosphere</span> exchange in the presence of leads or fractional coverage. The suite of continuous CMET soundings over a sea-ice free region to the northwest of Svalbard are analysed spatially and temporally, and compared to the model. The observed along-flight daytime increase in relative humidity is interpreted in terms of the diurnal cycle, and in the context of marine and terrestrial air-mass influences. Analysis of the balloon trajectory during the CMET soundings identifies strong wind-shear, with a low-level channeled</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SPIE.9299E..0LL','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SPIE.9299E..0LL"><span id="translatedtitle">Observations of <span class="hlt">atmospheric</span> trace gases by MAX-DOAS in the coastal <span class="hlt">boundary</span> <span class="hlt">layer</span> over Jiaozhou Bay</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Xianxin; Wang, Zhangjun; Meng, Xiangqian; Zhou, Haijin; Du, Libin; Qu, Junle; Chen, Chao; An, Quan; Wu, Chengxuan; Wang, Xiufen</p> <p>2014-11-01</p> <p><span class="hlt">Atmospheric</span> trace gases exist in the <span class="hlt">atmosphere</span> of the earth rarely. But the <span class="hlt">atmospheric</span> trace gases play an important role in the global <span class="hlt">atmospheric</span> environment and ecological balance by participating in the global <span class="hlt">atmospheric</span> cycle. And many environmental problems are caused by the <span class="hlt">atmospheric</span> trace gases such as photochemical smog, acid rain, greenhouse effect, ozone depletion, etc. So observations of <span class="hlt">atmospheric</span> trace gases become very important. Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) developed recently is a kind of promising passive remote sensing technology which can utilize scattered sunlight received from multiple viewing directions to derive vertical column density of lower tropospheric trace gases like ozone, sulfur dioxide and nitrogen dioxide. It has advantages of simple structure, stable running, passive remote sensing and real-time online monitoring automatically. A MAX-DOAS has been developed at Shandong Academy of Sciences Institute of Oceanographic Instrumentation (SDIOI) for remote measurements of lower tropospheric trace gases (NO2, SO2, and O3). In this paper, we mainly introduce the stucture of the instrument, calibration and results. Detailed performance analysis and calibration of the instrument were made at Qingdao. We present the results of NO2, SO2 and O3 vertical column density measured in the coastal <span class="hlt">boundary</span> <span class="hlt">layer</span> over Jiaozhou Bay. The diurnal variation and the daily average value comparison of vertical column density during a long-trem observation are presented. The vertical column density of NO2 and SO2 measured during Qingdao oil pipeline explosion on November 22, 2013 by MAX-DOAS is also presented. The vertical column density of NO2 reached to a high value after the explosion. Finally, the following job and the outlook for future possible improvements are given. Experimental calibration and results show that the developed MAX-DOAS system is reliable and credible.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3700011','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3700011"><span id="translatedtitle">Some Observational and Modeling Studies of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> at Mississippi Gulf Coast for Air Pollution Dispersion Assessment</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Yerramilli, Anjaneyulu; Challa, Venkata Srinivas; Indracanti, Jayakumar; Dasari, Hariprasad; Baham, Julius; Patrick, Chuck; Young, John; Hughes, Robert; White, Lorren D.; Hardy, Mark G.; Swanier, Shelton</p> <p>2008-01-01</p> <p>Coastal <span class="hlt">atmospheric</span> conditions widely vary from those over inland due to the land-sea interface, temperature contrast and the consequent development of local circulations. In this study a field meteorological experiment was conducted to measure vertical structure of <span class="hlt">boundary</span> <span class="hlt">layer</span> during the period 25–29 June, 2007 at three locations Seabee base, Harrison and Wiggins sites in the Mississippi coast. A GPS Sonde along with slow ascent helium balloon and automated weather stations equipped with slow and fast response sensors were used in the experiment. GPS sonde were launched at three specific times (0700 LT, 1300 LT and 1800 LT) during the experiment days. The observations indicate shallow <span class="hlt">boundary</span> <span class="hlt">layer</span> near the coast which gradually develops inland. The weather research and forecasting (WRF) meso-scale <span class="hlt">atmospheric</span> model and a Lagrangian particle dispersion model (HYSPLIT) are used to simulate the lower <span class="hlt">atmospheric</span> flow and dispersion in a range of 100 km from the coast for 28–30 June, 2007. The simulated meteorological parameters were compared with the experimental observations. The meso-scale model results show significant temporal and spatial variations in the meteorological fields as a result of development of sea breeze flow, its coupling with the large scale flow field and the ensuing alteration in the mixing depth across the coast. Simulated ground-level concentrations of SO2 from four elevated point sources located along the coast indicate diurnal variation and impact of the local sea-land breeze on the direction of the plume. Model concentration levels were highest during the stable morning condition and during the sea-breeze time in the afternoon. The highest concentrations were found up to 40 km inland during sea breeze time. The study illustrates the application of field meteorological observations for the validation of WRF which is coupled to HYSPLIT for dispersion assessment in the coastal region. PMID:19151446</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.A23F0392J&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.A23F0392J&link_type=ABSTRACT"><span id="translatedtitle">Massive-scale aircraft observations of giant sea-salt aerosol particle size distributions in <span class="hlt">atmospheric</span> marine <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jensen, J. B.</p> <p>2015-12-01</p> <p>iant sea-salt aerosol particles (dry radius, rd > 0.5 μm) occur nearly everywhere in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> and frequently above. This study presents observations of <span class="hlt">atmospheric</span> sea-salt size distributions in the range 0.7 < rd < 14 μm based on external impaction of sea-spray aerosol particles onto microscope polycarbonate microscope slides. The slides have very large sample volumes, typically about 250 L over a 10-second sampling period. This provides unprecedented sampling of giant sea-salt particles for flights in marine <span class="hlt">boundary</span> <span class="hlt">layer</span> air. The slides were subsequently analyzed in a humidified chamber using dual optical digital microscopy. At a relative humidity of 90% the sea-salt aerosol particles form spherical cap drops. Based on measurement the volume of the spherical cap drop and assuming NaCl composition, the Kohler equation is used to derive the dry salt mass of tens of thousands of individual aerosol particles on each slide. Size distributions are given with a 0.2 μm resolution. The slides were exposed from the NSF/NCAR C-130 research aircraft during the 2008 VOCALS project off the coast of northern Chile and the 2011 ICE-T in the Caribbean. In each deployment, size distributions using hundreds of slides are used to relate fitted log-normal size distributions parameters to wind speed, altitude and other <span class="hlt">atmospheric</span> conditions. The size distributions provide a unique observational set for initializing cloud models with coarse-mode aerosol particle observations for marine <span class="hlt">atmospheres</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.A43A0206V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.A43A0206V"><span id="translatedtitle">Investigating the intermittency of turbulence in the stable <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> - a field data and stochastic modeling approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vercauteren, N.; Von Larcher, T. G.; Bou-Zeid, E.; Klein, R.; Parlange, M. B.</p> <p>2013-12-01</p> <p>Intermittent turbulence is a common feature of stably stratified <span class="hlt">atmospheric</span> flows, yet its modeling is still problematic. Mesoscale motions such as gravity waves, Kelvin Helmholtz instabilities or density currents may trigger intermittent turbulence and greatly complicate the modeling and measurements of the stable <span class="hlt">boundary</span> <span class="hlt">layer</span> (SBL). In this study we investigate the intermittency of turbulence in very stable conditions by applying new statistical analysis tools to the existing SnoHATS dataset, collected in Switzerland over the Glacier de la Plaine Morte in 2006. These tools could then be used to develop stochastic parameterization for the SBL for use in weather or climate models. The SnoHATS dataset includes measurements of <span class="hlt">atmospheric</span> turbulence collected by horizontal arrays of sonic anemometers. This study applies timeseries analysis tools developed for meteorological data to analyze the SnoHATS dataset with a new perspective. Turbulence in very stable conditions exhibits intermittency, and there is interplay between larger scale <span class="hlt">atmospheric</span> flow features (at the so-called submesoscales) and onset of turbulence. We investigate the use of statistical tools such as hidden Markov models (HMM) and nonstationary multivariate autoregressive factor models (VARX) as a way to define the interactions between lower frequency modes and turbulence modes. The statistical techniques allow for separation of the data according to metastable states, such as quiet and turbulent periods in the stratified <span class="hlt">atmosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1810802P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1810802P&link_type=ABSTRACT"><span id="translatedtitle">Description of the <span class="hlt">atmospheric</span> circulation in the <span class="hlt">boundary</span> <span class="hlt">layer</span> over a tropical island: Case study of Guadeloupe Archipelago</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Plocoste, Thomas; Dorville, Jean-François; Jacoby-Koaly, Sandra; Roussas, André</p> <p>2016-04-01</p> <p>Over past two decades the use of <span class="hlt">atmospheric</span> sounding methods as Sodars, Lidar equipped drones increased sharply. Compare to weather balloon, these modern methods allow measure of profile at constant heights during long period. There are few studies using this type of equipment in tropical climates and lesser on small island. Wind regime on island of diameter less than 50 km are mostly considered as oceanic. Many author consider that thermal effect are negligible in land. But recent observations and simulations show importance of the thermal circulation at small- and meso- scales particularly in <span class="hlt">atmospheric</span> pollution process. Up to 2009 no wind profile data were available continuously to study <span class="hlt">atmospheric</span> circulation in Guadeloupe Archipelago (GA) which is one of the islands of the Lesser Antilles Arc. In first approximation wind was evaluated based on measures done at the most upwind island of the GA for many application as wind power and <span class="hlt">atmospheric</span> pollution. From 2009 to 2012 a measurement campaign of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (ABL) have been performed by the University of Antilles (UA) in GA. To assess effects of dynamic of ABL on air quality in sub urban area, particularly during the sunset and sunrise, UA monitored two sites with a weather station and a doppler sodar (REMTECH PAO). Both sites are close to the sea with one in a coastal area and the other in an open landfill surrounded by densely populated building and a mangrove swamp. Thermal and chemical measurements with a portable mass spectrometer were made in the vicinity of the landfill and showed the existence of urban heat islands. This study presents the first Doppler Sodar long measurements campaign in GA. Statistical analysis of the three year of doppler sodar data (i.e. wind components and its fluctuations) allow to identified and characterized the complex circulations on the two sites in the ABL between 25 and 500m above the sea level. Orographic and thermal effects due to urban area were</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...55H&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...55H&link_type=ABSTRACT"><span id="translatedtitle">A Numerical Study of Sea Breeze and Spatiotemporal Variation in the Coastal <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> at Hainan Island, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, Qian-Qian; Cai, Xu-Hui; Song, Yu; Kang, Ling</p> <p>2016-06-01</p> <p>Numerical simulations of sea breezes and the coastal <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) at Hainan Island, China during summer and winter are discussed. The different behaviour of sea breezes and the ABL on the leeward and windward sides of the island are examined, and it is found that offshore flows are more likely to create a strong sea-breeze signature, whereas the process of sea-breeze development under onshore flows is difficult to capture. At the location where the sea-breeze signal is remarkable, the height of the coastal ABL displays an abnormal decrease, corresponding to a transitional point from a continental ABL to a thermal internal <span class="hlt">boundary</span> <span class="hlt">layer</span> (TIBL) formed under sea-breeze conditions. This is corroborated by the sudden increase in the water vapour mixing ratio and/or wind speed, indicating the arrival of the sea breeze. Regarding the spatial distribution, the TIBL height decreases abruptly just ahead of the sea-breeze front, and above the cold air mass. When the sea-breeze front occurs with a raised head, a cold air mass is separated from the sea-breeze flow and penetrates inland. This separation is attributed to the interaction between the sea breeze and valley breeze, while the dry airflow entraining to the sea-breeze flow may also partially contribute to this air mass separation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713746S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713746S"><span id="translatedtitle">Large-eddy Simulation of <span class="hlt">Atmospheric</span> <span class="hlt">Boundary-layer</span> Flow through a Wind Farm Sited on Complex Terrain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shamsoddin, Sina; Porté-Agel, Fernando</p> <p>2015-04-01</p> <p>In this work, the performance of a wind farm situated on a hilly terrain is studied using large-eddy simulation and especial attention is paid to the effect of the topography on the wake flow characteristics. To this end, first, <span class="hlt">boundary-layer</span> flow is simulated over a two-dimensional hill and the corresponding mean and instantaneous flow-field is captured. Subsequently, flow simulation through a wind farm, consisting of five horizontal-axis wind turbines, sited over the same hill in an aligned layout is performed and the resulting flow characteristics are compared with the former case, i.e., the case without wind turbines. To assess the validity of the simulations, the calculated results are compared with the measurements carried out by Tian et al. (2013) in the aerodynamic/<span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> wind tunnel of Iowa State University. The agreement between the simulation and experimental results is good in terms of mean velocity and turbulence intensity profiles at different streamwise positions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910014899','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910014899"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> simulator improvement</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.</p> <p>1989-01-01</p> <p><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous <span class="hlt">boundary</span> <span class="hlt">layer</span> program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick <span class="hlt">boundary</span> <span class="hlt">layers</span> by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996JAtS...53.2054C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996JAtS...53.2054C"><span id="translatedtitle">High-Resolution Properties of the Equatorial Pacific Marine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> from Lidar and Radiosonde Observations.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cooper, D. I.; Eichinger, W. E.; Barr, S.; Cottingame, W.; Hynes, M. V.; Keller, C. F.; Lebeda, C. F.; Poling, D. A.</p> <p>1996-07-01</p> <p>A `thermostat' mechanism for cooling the Equatorial pacific is being tested with data collected during the Central Equatorial Pacific Experiment. The Los Alamos National Laboratory participated by fielding two shipboard lidars that collected nearly continuous data over the Pacific from 10 to 21 March 1993 as the ship sailed from Guadalcanal to Christmas Island. A Raman lidar measured water vapor mixing ratio in the lower troposphere, especially in the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL), and an aerosol backscatter lidar measured height and thickness of clouds to an altitude of 20 km. The data collected from these two lidars were used to determine ocean-<span class="hlt">atmosphere</span> phenomenology, which in turn, affects the climatology of the Central Pacific.Agreement between coincident radiosonde and the Raman water vapor lidar measurements was typically within ±0.25 g kg1 of water. Divergence between the two instruments occurred at transitions between distinct <span class="hlt">layers</span> in the lower marine <span class="hlt">atmosphere</span>. Reasons for this divergence will be discussed. Above the ABL the lidar and radiosonde are in excellent agreement. A wealth of detail is apparent in the lidar-derived profiles. For example, there are large variations in water vapor mixing ratio-the expression of the inherent low-frequency, intermittent, <span class="hlt">atmospheric</span> turbulence that produces spatially discrete features such as convective plumes. These features define the structure and extent of the ABL. Using the ABL structural characteristics, an analysis of the relationship between entrainment zone (EZ) height and observed sea surface temperature (SST) revealed counterintuitive behavior-that the height of the EZ decreases as SST increases in the range between 27° and 3°C.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1047098','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1047098"><span id="translatedtitle">Ice at the Interface: <span class="hlt">Atmosphere</span>-Ice-Ocean <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Processes and Their Role in Polar Change---Workshop Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hunke, Elizabeth C.</p> <p>2012-07-23</p> <p>The <span class="hlt">atmosphere</span>-ocean <span class="hlt">boundary</span> <span class="hlt">layer</span> in which sea ice resides includes many complex processes that require a more realistic treatment in GCMs, particularly as models move toward full earth system descriptions. The primary purpose of the workshop was to define and discuss such coupled processes from observational and modeling points of view, including insight from both the Arctic and Antarctic systems. The workshop met each of its overarching goals, including fostering collaboration among experimentalists, theorists and modelers, proposing modeling strategies, and ascertaining data availability and needs. Several scientific themes emerged from the workshop, such as the importance of episodic or extreme events, precipitation, stratification above and below the ice, and the marginal ice zone, whose seasonal Arctic migrations now traverse more territory than in the past.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ACPD...1428973H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ACPD...1428973H"><span id="translatedtitle">Temperature profiling of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> with rotational Raman lidar during the HD(CP)2 observational prototype experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hammann, E.; Behrendt, A.; Le Mounier, F.; Wulfmeyer, V.</p> <p>2014-11-01</p> <p>The temperature measurements of the Rotational Raman Lidar of the University of Hohenheim (UHOH RRL) during the High Definition of Clouds and Precipitation for advancing Climate Prediction (HD(CP)2 Prototype Experiment (HOPE) in April and May 2013 are discussed. The lidar consists of a frequency-tripled Nd:YAG laser at 355 nm with 10 W average power at 50 Hz, a two-mirror scanner, a 40 cm receiving telescope and a highly efficient polychromator with cascading interference filters for separating four signals: the elastic backscatter signal, two rotational Raman signals with different temperature dependence, and the vibrational Raman signal of water vapor. The main measurement variable of the UHOH RRL is temperature. For the HOPE campaign, the lidar receiver was optimized for high and low background levels, respectively, with a novel switch for the passband of the second rotational Raman channel. The instrument delivers <span class="hlt">atmospheric</span> profiles of water vapor mixing ratio as well as particle backscatter coefficient and particle extinction coefficient as further products. As examples for the measurement performance, measurements of the temperature gradient and water vapor mixing ratio revealing the development of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> within 25 h are presented. As expected from simulations, a significant advance during nighttime was achieved with the new low-background setting. A two-mirror scanner allows for measurements in different directions. When pointing the scanner to low elevation, measurements close to the ground become possible which are otherwise impossible due to the non-total overlap of laser beam and receiving telescope field-of-view in the near range. We present an example of a low-level temperature measurement which resolves the temperature gradient at the top of the stable nighttime <span class="hlt">boundary</span> <span class="hlt">layer</span> a hundred meters above the ground.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ACP....15.2867H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ACP....15.2867H"><span id="translatedtitle">Temperature profiling of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> with rotational Raman lidar during the HD(CP)2 Observational Prototype Experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hammann, E.; Behrendt, A.; Le Mounier, F.; Wulfmeyer, V.</p> <p>2015-03-01</p> <p>The temperature measurements of the rotational Raman lidar of the University of Hohenheim (UHOH RRL) during the High Definition of Clouds and Precipitation for advancing Climate Prediction (HD(CP)2) Observation Prototype Experiment (HOPE) in April and May 2013 are discussed. The lidar consists of a frequency-tripled Nd:YAG laser at 355 nm with 10 W average power at 50 Hz, a two-mirror scanner, a 40 cm receiving telescope, and a highly efficient polychromator with cascading interference filters for separating four signals: the elastic backscatter signal, two rotational Raman signals with different temperature dependence, and the vibrational Raman signal of water vapor. The main measurement variable of the UHOH RRL is temperature. For the HOPE campaign, the lidar receiver was optimized for high and low background levels, with a novel switch for the passband of the second rotational Raman channel. The instrument delivers <span class="hlt">atmospheric</span> profiles of water vapor mixing ratio as well as particle backscatter coefficient and particle extinction coefficient as further products. As examples for the measurement performance, measurements of the temperature gradient and water vapor mixing ratio revealing the development of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> within 25 h are presented. As expected from simulations, a reduction of the measurement uncertainty of 70% during nighttime was achieved with the new low-background setting. A two-mirror scanner allows for measurements in different directions. When pointing the scanner to low elevation, measurements close to the ground become possible which are otherwise impossible due to the non-total overlap of laser beam and receiving telescope field of view in the near range. An example of a low-level temperature measurement is presented which resolves the temperature gradient at the top of the stable nighttime <span class="hlt">boundary</span> <span class="hlt">layer</span> 100 m above the ground.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007ACPD....715105P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007ACPD....715105P"><span id="translatedtitle">Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and <span class="hlt">atmospheric</span> lifetime in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petzold, A.; Hasselbach, J.; Lauer, P.; Baumann, R.; Franke, K.; Gurk, C.; Schlager, H.; Weingartner, E.</p> <p>2007-10-01</p> <p>Particle emissions from ship engines and their <span class="hlt">atmospheric</span> transformation in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> (MBL) were investigated in engine test bed studies and in airborne measurements of expanding ship plumes. During the test rig studies, detailed aerosol microphysical and chemical properties were measured in the exhaust gas of a serial MAN B&W seven-cylinder four-stroke marine diesel engine under various load conditions. The emission studies were complemented by airborne aerosol transformation studies in the plume of a large container ship in the English Channel using the DLR aircraft Falcon 20 E-5. Observations from emission studies and plume studies combined with a Gaussian plume dispersion model yield a consistent picture of particle transformation processes from emission to <span class="hlt">atmospheric</span> processing during plume expansion. Particulate matter emission indices obtained from plume measurements are 8.8±1.0×1015(kg fuel)-1 by number for non-volatile particles and 174±43 mg (kg fuel)-1 by mass for Black Carbon (BC). Values determined for test rig conditions between 85 and 110% engine load are of similar magnitude. For the total particle number including volatile compounds no emission index can be derived since the volatile aerosol fraction is subject to rapid transformation processes in the plume. Ship exhaust particles occur in the size range Dp<0.3 μm, showing a bi-modal structure. The combustion particle mode is centred at modal diameters of 0.05 μm for raw emissions to 0.10 μm at a plume age of 1 h. The smaller-sized volatile particle mode is centred at Dp≤0.02 μm. From the decay of ship exhaust particle number concentrations in an expanding plume, a maximum plume life time of approx. 24 h is estimated for a well-mixed marine <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008ACP.....8.2387P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008ACP.....8.2387P"><span id="translatedtitle">Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and <span class="hlt">atmospheric</span> lifetime in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petzold, A.; Hasselbach, J.; Lauer, P.; Baumann, R.; Franke, K.; Gurk, C.; Schlager, H.; Weingartner, E.</p> <p>2008-05-01</p> <p>Particle emissions from ship engines and their <span class="hlt">atmospheric</span> transformation in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> (MBL) were investigated in engine test bed studies and in airborne measurements of expanding ship plumes. During the test rig studies, detailed aerosol microphysical and chemical properties were measured in the exhaust gas of a serial MAN B&W seven-cylinder four-stroke marine diesel engine under various load conditions. The emission studies were complemented by airborne aerosol transformation studies in the plume of a large container ship in the English Channel using the DLR aircraft Falcon 20 E-5. Observations from emission studies and plume studies combined with a Gaussian plume dispersion model yield a consistent picture of particle transformation processes from emission to <span class="hlt">atmospheric</span> processing during plume expansion. Particulate matter emission indices obtained from plume measurements are 8.8±1.0×1015(kg fuel)-1 by number for non-volatile particles and 174±43 mg (kg fuel)-1 by mass for Black Carbon (BC). Values determined for test rig conditions between 85 and 110% engine load are of similar magnitude. For the total particle number including volatile compounds no emission index can be derived since the volatile aerosol fraction is subject to rapid transformation processes in the plume. Ship exhaust particles occur in the size range Dp<0.3 μm, showing a bi-modal structure. The combustion particle mode is centred at modal diameters of 0.05 μm for raw emissions to 0.10 μm at a plume age of 1 h. The smaller-sized volatile particle mode is centred at Dp≤0.02 μm. From the decay of ship exhaust particle number concentrations in an expanding plume, a maximum plume life time of approx. 24 h is estimated for a well-mixed marine <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/14740719','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/14740719"><span id="translatedtitle">Chasing quicksilver: modeling the <span class="hlt">atmospheric</span> lifetime of Hg(0)(g) in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> at various latitudes.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hedgecock, Ian M; Pirrone, Nicola</p> <p>2004-01-01</p> <p>The lifetime of elemental mercury in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span>(MBL) has been studied using AMCOTS (<span class="hlt">Atmospheric</span> Mercury Chemistry Over The Sea), a box model of MBL photochemistry including aerosols and detailed mercury chemistry. Recently measured Hg(0)(g) oxidation reactions have been included, and the studies were performed as a function of latitude, time of year, <span class="hlt">boundary</span> <span class="hlt">layer</span> liquid water content (LWC) and cloud optical depth. The results show that Hg has the shortest lifetime when air temperatures are low and sunlight and deliquescent aerosol particles are plentiful. Thus the modeled lifetime for clear-sky conditions is actually shorter at mid-latitudes and high latitudes than near the equator, and for a given latitude and time of year, cooler temperatures enhance the rate of Hg oxidation. Under typical summer conditions (for a given latitude) of temperature and cloudiness, the lifetime (tau) of Hg(0)(g) in the MBL is calculated to be around 10 days at all latitudes between the equator and 60 degrees N. This is much shorter than the generally accepted <span class="hlt">atmospheric</span> residence time for Hg(0)(g) of a year or more. Given the relatively stable background concentrations of Hg(0)(g) which have been measured, continual replenishment of Hg(0)(g) must take place, suggesting a "multihop" mechanism for the distribution of Hg, rather than solely aeolian transport with little or no chemical transformation between source and receptor. Inclusion of an empirical Hg(0)(g) emission factor related to insolation was used to stabilize the Hg(0)(g) concentration in the model, and the emission rates necessarily agree well with estimated emission fluxes for the open ocean. PMID:14740719</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6961A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6961A"><span id="translatedtitle">Forcing of global ocean models using an <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> model: assessing consequences for the simulation of the AMOC</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abel, Rafael; Boening, Claus</p> <p>2015-04-01</p> <p>Current practice in the <span class="hlt">atmospheric</span> forcing of ocean model simulations can lead to unphysical behaviours. The problem lies in the bulk formulation of the turbulent air-sea fluxes in conjunction with a prescribed, and unresponsive, <span class="hlt">atmospheric</span> state as given, e.g., by reanalysis products. This forcing formulation corresponds to assuming an <span class="hlt">atmosphere</span> with infinite heat capacity, and effectively damps SST anomalies even on basin scales. It thus curtails an important negative feedback between meridional ocean heat transport and SST in the North Atlantic, rendering simulations of the AMOC in such models excessively sensitive to details in the freshwater fluxes. As a consequence, such simulations are known for spurious drift behaviors which can only partially controlled by introducing some (and sometimes strong) unphysical restoring of sea surface salinity. There have been several suggestions during the last 20 years for at least partially alleviating the problem by including some simplified model of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (AML) which allows a feedback of SST anomalies on the near-surface air temperature and humidity needed to calculate the surface fluxes. We here present simulations with a simple, only thermally active AML formulation (based on the 'CheapAML' proposed by Deremble et al., 2013) implemented in a global model configuration based on NEMO (ORCA05). In a suite of experiments building on the CORE-bulk forcing methodology, we examine some general features of the AML-solutions (in which only the winds are prescribed) in comparison to solutions with a prescribed atmosperic state. The focus is on the North Atlantic, where we find that the adaptation of the <span class="hlt">atmospheric</span> temperature the simulated ocean state can lead to strong local modifications in the surface heat fluxes in frontal regions (e.g., the 'Northwest Corner'). We particularly assess the potential of the AML-forcing concept for obtaining AMOC-simulations with reduced spurious drift, without</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64572&keyword=Turnover+AND+Rates&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=65035328&CFTOKEN=59790290','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64572&keyword=Turnover+AND+Rates&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=65035328&CFTOKEN=59790290"><span id="translatedtitle">TETHERED BALLOON MEASUREMENTS OF BIOGENIC VOCS IN THE <span class="hlt">ATMOSPHERIC</span> <span class="hlt">BOUNDARY</span> <span class="hlt">LAYER</span></span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>Measurements of biogenic volatile organic compounds (BVOCs) have been made on a tethered balloon platform in eleven field deployments between 1985 and 1996. A series of balloon sampling packages have been developed for these campaigns and they have been used to describe <span class="hlt">boundary</span> ...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.8067S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.8067S"><span id="translatedtitle">Seasonal variations in stable isotope ratios of <span class="hlt">atmospheric</span> nitrate in a tropical <span class="hlt">boundary</span> <span class="hlt">layer</span> environment (Cape Verde Observatory).</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Savarino, Joël.; Morin, Samuel; Erbland, Joseph; Grannec, Francis; Patey, Matthew; Achterberg, Eric</p> <p>2010-05-01</p> <p> seasonal cycle of the nitrate isotope systematic at the Cap Verde (lat. 16° 85'N, lon. 24° 87' W) characteristic of a tropical oceanic <span class="hlt">boundary</span> <span class="hlt">layer</span>. Both ?17O and δ15N display a marked seasonal cycle in opposing phase. ?17O values are maximum in winter (≠ƒ 30 permil) and minimal in summer (≠ƒ 26 permil) while δ15N display the opposite trend with maximum in summer (-2.9 permil) and minimum in winter (-8.8 permil). No correlation is found with the nitrate <span class="hlt">atmospheric</span> loading for any of the isotope ratio. ?17O seasonal variations correlate with the monthly averaged daytime depletion of ozone whose seasonal variation have been attributed mainly to halogen oxides. This observation suggests that part of the maximum nitrate oxygen anomaly (?17O) could result from halogen chemistry in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> via probably the strong NOx oxidant BrO. For δ15N, a broad correlation is found with the <span class="hlt">atmospheric</span> concentration of NO and solar radiation intensity, confirming that δ15N of nitrate retranscribes principally a source and/or a photochemical equilibrium effect between NO and NO2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT.......101H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT.......101H"><span id="translatedtitle">The Characterization of <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Depth and Turbulence in a Mixed Rural and Urban Convective Environment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hicks, Micheal M.</p> <p></p> <p>A comprehensive analysis of surface-<span class="hlt">atmosphere</span> flux exchanges over a mixed rural and urban convective environment is conducted at Howard University Beltsville, MD Research Campus. This heterogeneous site consists of rural, suburban and industrial surface covers to its south, east and west, within a 2 km radius of a flux sensor. The eddy covariance method is utilized to estimate surface-<span class="hlt">atmosphere</span> flux exchanges of momentum, heat and moisture. The attributes of these surface flux exchanges are contrasted to those of classical homogeneous sites and assessed for accuracy, to evaluate the following: (I) their similarity to conventional convective <span class="hlt">boundary</span> <span class="hlt">layer</span> (CBL) processes and (II) their representativeness of the surrounding environment's turbulent properties. Both evaluations are performed as a function of upwind surface conditions. In particular, the flux estimates' obedience to spectrum power laws and similarity theory relationships is used for performing the first evaluation, and their ability to close the surface energy balance and accurately model CBL heights is used for the latter. An algorithm that estimates <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> heights from observed lidar extinction backscatter was developed, tested and applied in this study. The derived lidar based CBL heights compared well with those derived from balloon borne soundings, with an overall Pearson correlation coefficient and standard deviation of 0.85 and 223 m, respectively. This algorithm assisted in the evaluation of the response of CBL processes to surface heterogeneity, by deriving high temporal CBL heights and using them as independent references of the surrounding area averaged sensible heat fluxes. This study found that the heterogeneous site under evaluation was rougher than classical homogeneous sites, with slower dissipation rates of turbulent kinetic energy. Flux measurements downwind of the industrial complexes exhibited enhanced efficiency in surface-<span class="hlt">atmosphere</span> momentum, heat, and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUSM.A22B..12H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUSM.A22B..12H"><span id="translatedtitle">EM Propagation in Marine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span>: Analysis of RED Experiment Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hristov, T.; Friehe, C. A.</p> <p>2002-05-01</p> <p>The pattern of propagation for EM signals over the ocean is a combined result of the <span class="hlt">atmospheric</span> refraction and scattering from the rough ocean surface. Here we study experimentally the structure of the <span class="hlt">atmospheric</span> refractive index and the ocean surface statistics, pertinent to scattering. We are also interested in fluctuations of the refractive index induced by the ocean surface waves, which along with the turbulence contribute to the random refraction. However, these fluctuations exhibit behavior different from turbulence (e.g. their structure function does not follow the 2/3 scaling valid for the turbulent fluctuations) and require to be studied separately. We analyze data of <span class="hlt">atmospheric</span> turbulence, humidity, temperature, and sea surface temperature and waves from the Rough Evaporation Duct experiment, conducted in part from the instrument platform FLIP in the open ocean north of Oahu, Hawaii.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999JGR...10421263D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JGR...10421263D"><span id="translatedtitle">Vertical mixing and chemistry of isoprene in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>: Aircraft-based measurements and numerical modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doskey, Paul V.; Gao, Weigang</p> <p>1999-09-01</p> <p>Vertical profiles of isoprene, methanol, and ozone (O3) concentrations were measured between the middle and upper <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) from a research aircraft and were numerically simulated for the ABL and a deciduous forest canopy with a one-dimensional model coupling turbulence diffusion and <span class="hlt">atmospheric</span> chemistry. Isoprene emissions from the deciduous forest canopy were estimated by coupling an existing biogenic emission algorithm with estimates of canopy leaf density inferred from satellite remote sensing observations. Numerical simulations predicted low isoprene concentrations in the middle and upper ABL; however, the agreement between the simulations and the measured values was poor for two of the three profiles, indicating that a three-dimensional transport model might be necessary in future simulations. Chemical oxidation of isoprene by O3 and hydroxyl radical (OH), particularly in the middle and upper ABL, tends to reduce the isoprene concentrations and influences the vertical fluxes in that <span class="hlt">layer</span>; however, chemical reactions have little effect on fluxes of isoprene near the emission source, where turbulent mixing is much faster than chemical reactions and where the emission process controls the vertical flux. The isoprene flux decreases rapidly with increasing height, with little isoprene escaping from the ABL. Vertical profiles of methanol concentrations were simulated with the biogenic emission algorithm used for isoprene; these vertical profiles were similar to the measured values for the well-mixed ABL but were much lower than the measured concentrations in the lower <span class="hlt">layers</span> of the growing ABL because of weaker calculated mixing in the upper ABL during the morning. The results of this investigation indicate that chemical oxidation of isoprene is rapid enough to allow O3 and other oxidants to accumulate in the ABL on a regional scale if sufficient levels of nitrogen oxides are present; however, methanol is much more stable, and biogenic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.B41D0461P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.B41D0461P&link_type=ABSTRACT"><span id="translatedtitle">UAS and DTS: Using Drones and Fiber Optics to Measure High Resolution Temperature of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Predosa, R. A.; Darricau, B.; Higgins, C. W.</p> <p>2015-12-01</p> <p>The <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) is the lowest part of the <span class="hlt">atmosphere</span> that directly interacts with the planet's surface. The development of the ABL plays a vital role, as it affects the transport of <span class="hlt">atmospheric</span> constituents such as air pollutants, water vapor, and greenhouse gases. Measurements of the processes in the ABL have been difficult due to the limitations in the spatial and temporal resolutions of the equipment as well as the height of the traditional flux tower. Recent advances in the unmanned aerial vehicle (UAV) and distributed temperature sensing (DTS) technologies have provided us with new tools to study the complex processes in ABL. We conducted a series of pioneering experiments in Eastern Oregon using a platform that combines UAV and DTS to collect data during morning and evening transitions in the ABL. The major components of this platform consists of a quad-copter, a DTS computer unit, and a set of customized fiber optic cables. A total of 75 flights were completed to investigate: (1) the capability of a duplexed fiber optic cable to reduce noise in the high spatial and temporal temperature measurements taken during the morning transition; (2) the possibility of using fiber optic cable as "wet bulb" thermometer to calculate relative humidity in the ABL at high spatial and temporal resolution. The preliminary results showed that using a fiber optic cable in a duplexed configuration with the UAV-DTS platform can effectively reduce noise level during the morning transition data collection. The customized "wet bulb" fiber optic cable is capable of providing information for the calculation of relative humidity in the ABL at unprecedented spatial and temporal resolutions. From this study, the UAV-DTS platform demonstrated great potential in collecting temperature data in the ABL and with the development of <span class="hlt">atmospheric</span> sensor technologies, it will have more applications in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19880051586&hterms=upwelling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dupwelling','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19880051586&hterms=upwelling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dupwelling"><span id="translatedtitle">The profile of upwelling 11-micron radiance through the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> overlying the ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hagen, Denise E.</p> <p>1988-01-01</p> <p>Measurements of the gradient of 11-micron radiance from the ocean surface were made with spaceborne AVHRR and with radiometers carried on research vessels in California and east Florida waters. The results obtained for the radiance gradient at a variety of <span class="hlt">atmospheric</span> conditions are in good agreement with radiative transfer calculations, suggesting that there was no significant error in the water vapor absorption parameters used in the calculations. The results confirm earlier predictions that, for a typical viewing factor (i.e., zenith angle 60 deg) and for mid-latitude standard water vapor conditions, the 11-micron radiant flux measured by a spaceborne sensor will be dominated by the <span class="hlt">atmospheric</span> contribution to the total outgoing radiation in this 'window' region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.8026E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.8026E"><span id="translatedtitle">RAMS sensitivity to mesh resolution in large eddy simulation of the neutral and convective <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ercolani, Giulia; Gorlé, Catherine; Corbari, Chiara; Mancini, Marco</p> <p>2014-05-01</p> <p>Large Eddy Simulation (LES) is a computational fluid dynamic technique that has been extensively used to reproduce turbulence in the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (ABL). Most LES applications to ABL modelling deal with idealized regimes, particularly suited for the verification of simulation results and consisting in homogeneous surface properties, prescribed fluxes at the surface and periodic lateral <span class="hlt">boundary</span> conditions. In recent years interest has grown around the possibility of using LES as a tool to study ABL turbulence in more realistic situations, i.e. avoiding periodic lateral <span class="hlt">boundary</span> conditions and coupling LES with a land surface model that dynamically computes heat and moisture fluxes at the surface. One appealing alternative to periodic lateral <span class="hlt">boundary</span> conditions seems to be grid nesting, that should make LES a suitable tool to reproduce real meteorological flows over complex terrain at the microscale. In this framework Numerical Weather Prediction Limited Area Models (NWP-LAMs) appear to be particularly suitable to perform LES of the ABL in realistic conditions because of both i) their capability of nesting, ii) the presence of one or more land surface model coupled with the equations of motion. The use of NWP-LAMs at the microscale is increasing, but the fact that NWP-LAMs are built to work at the mesoscale has to be taken into account. Consequently the evaluation of their performances at the microscale in idealized regimes should be the first step for their use in more complex simulations. The Regional <span class="hlt">Atmospheric</span> Modelling System (RAMS) is one of the most popular and used NWP-LAMs, and its performances in LES of a ABL in both real and idealized conditions have been evaluated in several studies. This work aims at assessing the impact of mesh resolution on the performances of RAMS-LES in the two opposite idealized regimes of neutral and convective <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>, for which the turbulent statistics and flow structures are well known. For</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003RaSc...38.8048K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003RaSc...38.8048K"><span id="translatedtitle">Investigation of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> temperature, turbulence, and wind parameters on the basis of passive microwave remote sensing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kadygrov, Evgeny N.; Shur, Genrih N.; Viazankin, Anton S.</p> <p>2003-06-01</p> <p>The MTP-5, a microwave temperature profiler, has been widely used since 1991 for investigation of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL). The MTP-5 is an angular scanning single-channel instrument with a central frequency of about 60 GHz, designed to provide continuous, unattended observations. It can measure the thermal emission of the <span class="hlt">atmosphere</span> with high sensitivity (0.03 K at 1 s integration time) from different zenith angles. On the basis of this measurement, it is possible to retrieve temperature profiles at the altitude range up to 600 m, to calculate wind speed and wind direction at the lowest 250 m, and to get information about some parameters of <span class="hlt">atmospheric</span> turbulence. This report presents some applications of the MTP-5 instrument data collected in 1998-2001 within a number of international field projects: the dynamics of ABL temperature inversion in a mountain valley (Mesoscale Alpine Program (MAP)), as well as along an island coast (north part of Sakhalin Island, Russia-Japan Project); continuous measurements of the ABL temperature profile provided from a special scientific train that crossed the territory of Russia (the Transcontinental Observations of the Chemistry of the <span class="hlt">Atmosphere</span> Project (TROICA)); and simultaneous measurements of the ABL temperature profile provided over the central and northern part of Moscow in a continuous mode (the Global Urban Research Meteorology and Environment Project (GURME)). In 1999, two MTP-5 instruments were installed on a platform that was rotating in the azimuth direction at the 310 m Obninsk Meteorological Research Tower (Meteo Tower) to validate the method and microwave equipment for measurement of wind speed and wind direction and investigation of <span class="hlt">atmospheric</span> turbulence. Spectral analyses of the integrated signal provided an opportunity to estimate the inertial subrange low-frequency limit and its height dependence for thermal turbulence at the lowest 200 m <span class="hlt">layer</span>. Wavelet analysis of the signal made it possible to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990radr.conf..370S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990radr.conf..370S"><span id="translatedtitle">Radar coverage predictions through time- and range-dependent refractive <span class="hlt">atmospheres</span> with planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> and electromagnetic parabolic equation models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Skura, J. P.; Schemm, C. E.; Ko, H. W.; Manzi, L. P.</p> <p></p> <p>The enhancement of the capability of electromagnetic parabolic equation (EMPE) and other propagation codes by using predictions from an <span class="hlt">atmospheric</span> forecast model to provide refractivity data for range-dependent and time-varying situations is demonstrated. Starting from measured temperature and humidity data at one location and time, the JHU/APL planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) model is used to obtained predictions for a 24-h forecast period. Predicted fields of temperature, humidity, and refractivity after 12 and 24 h are compared with measured data to verify the forecast, and vertical profiles of refractivity for each hour are provided, along with appropriate radar parameters, as input to EMPE. The EMPE calculations of expected radiation patterns as functions of height and range at selected times demonstrate the effects of hourly changes in the structure of the lower <span class="hlt">atmosphere</span> on radar propagation. The radar propagation calculations have been repeated using the IREPS code to illustrate the similarities and differences between the two models when applied to this somewhat idealized, horizontally homogeneous situation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014EGUGA..1612424H&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014EGUGA..1612424H&link_type=ABSTRACT"><span id="translatedtitle">Zeppelin NT - Measurement Platform for the Exploration of <span class="hlt">Atmospheric</span> Chemistry and Dynamics in the Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hofzumahaus, Andreas; Holland, Frank; Oebel, Andreas; Rohrer, Franz; Mentel, Thomas; Kiendler-Scharr, Astrid; Wahner, Andreas; Brauchle, Artur; Steinlein, Klaus; Gritzbach, Robert</p> <p>2014-05-01</p> <p>The planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) is the chemically most active and complex part of the <span class="hlt">atmosphere</span> where freshly emitted reactive trace gases, tropospheric radicals, <span class="hlt">atmospheric</span> oxidation products and aerosols exhibit a large variability and spatial gradients. In order to investigate the chemical degradation of trace gases and the formation of secondary pollutants in the PBL, a commercial Zeppelin NT was modified to be used as an airborne measurement platform for chemical and physical observations with high spatial resolution. The Zeppelin NT was developed by Zeppelin Luftschifftechnik (ZLT) and is operated by Deutsche Zeppelin Reederei (DZR) in Friedrichshafen, Germany. The modification was performed in cooperation between Forschungszentrum Jülich and ZLT. The airship has a length of 75 m, can lift about 1 ton of scientific payload and can be manoeuvered with high precision by propeller engines. The modified Zeppelin can carry measurement instruments mounted on a platform on top of the Zeppelin, or inside the gondola beneath the airship. Three different instrument packages were developed to investigate a. gas-phase oxidation processes involving free radicals (OH, HO2) b. formation of secondary organic aerosols (SOA) c. new particle formation (nucleation) The presentation will describe the modified airship and provide an overview of its technical performance. Examples of its application during the recent PEGASOS flight campaigns in Europe will be given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15381321','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15381321"><span id="translatedtitle">Seasonal variations of aerosol residence time in the lower <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ahmed, A A; Mohamed, A; Ali, A E; Barakat, A; Abd El-Hady, M; El-Hussein, A</p> <p>2004-01-01</p> <p>During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the <span class="hlt">atmospheric</span> air activity concentrations of short- and long-lived (222Rn) decay products 214Pb and 210Pb. The samples were taken by using a single-filter technique and gamma-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of 214Pb and 210Pb in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of 214Pb and 210Pb within the whole year was found to be 1.4+/-0.27 Bq m(-3) and 1.2+/-0.15 mBq m(-3), respectively. Different 210Pb:214Pb activity ratios during the year varied between 1.78 x 10(-4) and 1.6 x 10(-3) with a mean value of 8.9 x 10(-4) +/- 7.6 x 10(-5). From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time (MRT) of aerosol particles in the <span class="hlt">atmosphere</span> of about 10.5+/-0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the <span class="hlt">atmospheric</span> air. PMID:15381321</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.A53O..06W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.A53O..06W"><span id="translatedtitle">Near-Surface Wind Predictions in Complex Terrain with a CFD Approach Optimized for <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagenbrenner, N. S.; Forthofer, J.; Butler, B.; Shannon, K.</p> <p>2014-12-01</p> <p>Near-surface wind predictions are important for a number of applications, including transport and dispersion, wind energy forecasting, and wildfire behavior. Researchers and forecasters would benefit from a wind model that could be readily applied to complex terrain for use in these various disciplines. Unfortunately, near-surface winds in complex terrain are not handled well by traditional modeling approaches. Numerical weather prediction models employ coarse horizontal resolutions which do not adequately resolve sub-grid terrain features important to the surface flow. Computational fluid dynamics (CFD) models are increasingly being applied to simulate <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) flows, especially in wind energy applications; however, the standard functionality provided in commercial CFD models is not suitable for ABL flows. Appropriate CFD modeling in the ABL requires modification of empirically-derived wall function parameters and <span class="hlt">boundary</span> conditions to avoid erroneous streamwise gradients due to inconsistences between inlet profiles and specified <span class="hlt">boundary</span> conditions. This work presents a new version of a near-surface wind model for complex terrain called WindNinja. The new version of WindNinja offers two options for flow simulations: 1) the native, fast-running mass-consistent method available in previous model versions and 2) a CFD approach based on the OpenFOAM modeling framework and optimized for ABL flows. The model is described and evaluations of predictions with surface wind data collected from two recent field campaigns in complex terrain are presented. A comparison of predictions from the native mass-consistent method and the new CFD method is also provided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850005493','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850005493"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> simulator improvement</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.</p> <p>1984-01-01</p> <p>High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick <span class="hlt">boundary</span> <span class="hlt">layers</span> is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002JApMe..41..447D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002JApMe..41..447D"><span id="translatedtitle">Spatial and Structural Variation of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> during Summer in Israel--Profiler and Rawinsonde Measurements.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dayan, Uri; Lifshitz-Goldreich, Batia; Pick, Karel</p> <p>2002-04-01</p> <p>An opportunity to improve understanding related to the structure of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) in Israel along the coastal region environs emerged in April 1997 when the Israel Electric Corporation, Ltd. (IEC), installed and began the operation of a 1290-MHz radar profiler and radio acoustic sounding system (RASS) midway between Haifa and Tel Aviv. This instrument is, in addition to the upper-air measurements carried out routinely by the Israel Meteorological Service (IMS) in Beit-Dagan, at the central coastal plain of Israel. In order to better characterize the spatial variation of the turbulent mixed <span class="hlt">layer</span> and the stable <span class="hlt">layer</span> capping it within the ABL, the upper-air measurements from the profiler were compared with the concurrent rawinsonde data from the permanent sounding site in Beit-Dagan. The analysis and simultaneous comparison of both instruments was done for noontime of two consecutive summers (1997-98) and included the following ABL parameters: depth and lapse rate of the mixed <span class="hlt">layer</span>, depth and virtual temperature gradient of the inversion <span class="hlt">layer</span>, wind speed and direction at base and top of the inversion <span class="hlt">layer</span>, and wind speed and direction shears within the inversion. All the sampling days were classified into three modes of the predominant synoptic situation typifying most of the summer days in Israel (i.e., the `Persian trough' synoptic system). Means, standard deviation, and relative standard deviation were calculated and compared between both sites for each of the assigned synoptic category. The analysis shows that (a) a consistently deeper and less unstable mixed <span class="hlt">layer</span> is observed in the northern coastal site; (b) the interface separating the mixed <span class="hlt">layer</span> and its capping inversion is sharper at the farther southern and inland site-a feature caused by stronger subsiding conditions above this site; (c) variation in the depth of the mixed <span class="hlt">layer</span> for the different mode of the Persian trough is more pronounced at the northern site because of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4133707','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4133707"><span id="translatedtitle">High variability of <span class="hlt">atmospheric</span> mercury in the summertime <span class="hlt">boundary</span> <span class="hlt">layer</span> through the central Arctic Ocean</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Yu, Juan; Xie, Zhouqing; Kang, Hui; Li, Zheng; Sun, Chen; Bian, Lingen; Zhang, Pengfei</p> <p>2014-01-01</p> <p>The biogeochemical cycles of mercury in the Arctic springtime have been intensively investigated due to mercury being rapidly removed from the <span class="hlt">atmosphere</span>. However, the behavior of mercury in the Arctic summertime is still poorly understood. Here we report the characteristics of total gaseous mercury (TGM) concentrations through the central Arctic Ocean from July to September, 2012. The TGM concentrations varied considerably (from 0.15 ng/m3 to 4.58 ng/m3), and displayed a normal distribution with an average of 1.23 ± 0.61 ng/m3. The highest frequency range was 1.0–1.5 ng/m3, lower than previously reported background values in the Northern Hemisphere. Inhomogeneous distributions were observed over the Arctic Ocean due to the effect of sea ice melt and/or runoff. A lower level of TGM was found in July than in September, potentially because ocean emission was outweighed by chemical loss. PMID:25125264</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013DPS....4540503K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013DPS....4540503K"><span id="translatedtitle">Remotely Measured <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Temperature and Carbon Dioxide Isotopes in Mars <span class="hlt">Atmosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kostiuk, Theodor; Smith, R.; Hewagama, T.; Livengood, T.; Annen, J.</p> <p>2013-10-01</p> <p>Retrieving accurate abundances for trace species and isotopic ratios from remote spectroscopic measurements requires knowledge of the temperature-pressure profile in the region measured. Temperature profiles on Mars have been measured from orbiting spacecraft such as MGS/TES, but not at the Mars local time or location of subsequent studies. We present results from fully resolved spectroscopic measurements near 10.6 micron of both the normal and singly substituted oxygen-18 CO2 lines, taken with the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds And Composition (HIPWAC) at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Measurements with spectral resolving power R=10,000,000 were obtained in October 2007 with an instantaneous field-of-view on the planet of 1 arcsec near mid-day on the planet. The normal isotope of CO2 is near uniformly mixed in the <span class="hlt">atmosphere</span> and its strong absorption line is used to retrieve temperature information. Surface pressure is constrained by the altitude relief of the surface in regions probed. Surface temperature is constrained using the calibrated continuum radiance between the measured line profiles. Using these constraints and a MGS/TES profile for a comparable Mars location, a thermal profile at the time and location of the 18OCO2 line can be retrieved. The retrieved profile can be used in turn to extract a more accurate 18OC16O/16OC16O ratio at the time and location of the ground-based measurements or to accurately retrieve other trace constituents, such as ozone or water. A description of the analytic process and results of the temperature and isotopic ratio retrievals will be described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/686860','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/686860"><span id="translatedtitle">Vertical mixing and chemistry of isoprene in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>: Aircraft-based measurements and numerical modeling</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Doskey, P.V.; Gao, W.</p> <p>1999-09-01</p> <p>Vertical profiles of isoprene, methanol, and ozone (O{sub 3}) concentrations were measured between the middle and upper <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) from a research aircraft and were numerically simulated for the ABL and a deciduous forest canopy with a one-dimensional model coupling turbulence diffusion and <span class="hlt">atmospheric</span> chemistry. Isoprene emissions from the deciduous forest canopy were estimated by coupling an existing biogenic emission algorithm with estimates of canopy leaf density inferred from satellite remote sensing observations. Numerical simulations predicted low isoprene concentrations in the middle and upper ABL; however, the agreement between the simulations and the measured values was poor for two of the three profiles, indicating that a three-dimensional transport model might be necessary in future simulations. Chemical oxidation of isoprene by O{sub 3} and hydroxyl radical (OH), particularly in the middle and upper ABL, tends to reduce the isoprene concentrations and influences the vertical fluxes in that <span class="hlt">layer</span>; however, chemical reactions have little effect on fluxes of isoprene near the emission source, where turbulent mixing is much faster than chemical reactions and where the emission process controls the vertical flux. The isoprene flux decreases rapidly with increasing height, with little isoprene escaping from the ABL. Vertical profiles of methanol concentrations were simulated with the biogenic emission algorithm used for isoprene; these vertical profiles were similar to the measured values for the well-mixed ABL but were much lower than the measured concentrations in the lower <span class="hlt">layers</span> of the growing ABL because of weaker calculated mixing in the upper ABL during the morning. The results of this investigation indicate that chemical oxidation of isoprene is rapid enough to allow O{sub 3} and other oxidants to accumulate in the ABL on a regional scale if sufficient levels of nitrogen oxides are present; however, methanol is much more stable</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ThApC.109..577B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ThApC.109..577B"><span id="translatedtitle">Sensitivity of MM5-simulated planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> height to soil dataset: comparison of soil and <span class="hlt">atmospheric</span> effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breuer, Hajnalka; Ács, Ferenc; Laza, Borbála; Horváth, Ákos; Matyasovszky, István; Rajkai, Kálmán</p> <p>2012-08-01</p> <p>The effects of two soil datasets on planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) height are analyzed, using model simulations. Simulations are performed with the MM5 weather prediction system over the Carpathian Basin, with 6 km horizontal resolution, investigating three summer days, two autumn, and one winter day of similar synoptic conditions. Two soil datasets include that of the United States Department of Agriculture, which is globally used, and a regional Hungarian called Hungarian unsaturated soil database. It is shown that some hydraulic parameter values between the two datasets can differ up to 5-50%. These differences resulted in 10% deviations in the space-time-averaged PBL height (averaged over Hungary and over 12 h in the daytime period). Over smaller areas, these relative deviations could reach 25%. Daytime course changes in the PBL height for reference run conditions were significant ( p < 0.01) in ≈70% of the grid points covering Hungary. Ensemble runs using different <span class="hlt">atmospheric</span> parameterizations and soil moisture initialization setups are also performed to analyze the sensitivity under changed conditions. In these cases, the sensitivity test showed that irrespective of the radiation and PBL scheme, the effect of different soil datasets on PBL height is roughly the same. PBL height is also sensitive to field capacity (Θf) and wilting point (Θw) changes. Θf changes seem to be more important for loamy sand, while Θw changes for the clay soil textural class.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010067777','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010067777"><span id="translatedtitle">The Estimation of Surface Latent Heat Flux over the Ocean and its Relationship to Marine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (MABL) Structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Palm, Stephen P.; Schwemmer, Geary K.; Vandemark, Doug; Evans, Keith; Miller, David O.; Demoz, Belay B.; Starr, David OC. (Technical Monitor)</p> <p>2001-01-01</p> <p>A new technique combining active and passive remote sensing instruments for the estimation of surface latent heat flux over the ocean is presented. This synergistic method utilizes aerosol lidar backscatter data, multi-channel infrared radiometer data, and microwave scatterometer data acquired onboard the NASA P-313 research aircraft during an extended field campaign over the Atlantic ocean in support of the Lidar In-space Technology Experiment (LITE) in September of 1994. The 10 meter wind speed derived from scatterometers and lidar-radiometer inferred near-surface moisture are used to obtain an estimate of the surface flux of moisture via a bulk aerodynamic formula. The results are compared with the Special Sensor Microwave Imager (SSM/I) daily average latent heat flux and show reasonable agreement. However, the SSM/I values are biased low by about 15 W/sq m. In addition, the Marine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (MABL) height, entrainment zone thickness and integrated lidar backscatter intensity are computed from the lidar data and compared with the magnitude of the surface fluxes. The results show that the surface latent heat flux is most strongly correlated with entrainment zone depth, MABL height and the integrated MABL lidar backscatter, with corresponding correlation coefficients of 0.39, 0.43 and 0.71, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......196S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......196S"><span id="translatedtitle">Passive Effluent Diffusion in a Convective <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span>: An Airborne Approach to Locating Sources and Estimating Their Emission Rates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Suard, Maxime</p> <p></p> <p>We studied the near field dispersion of natural gas plumes leaking from transmission lines and diffusing in a convective <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (ABL), with the intent of providing an aerial system of leak detection and pinpointing, as well as quantitative leak rate estimation. We used high frequency measurements of methane and ethane concentrations on a fixed wing aircraft using high rate spectroscopic gas concentration measurements. We looked for characteristics of the effluent concentration field which can be related to the distance from the effluent source, and developed an empirical approach to effluent source position estimation from airborne effluent concentration measurements. From a mass-balance approach we developed a practical method of effluent leak rate estimation based on airborne effluent concentration measurements. Since gathering experimental data was costly and time-expensive, Large Eddy Simulation (LES) results were also investigated. Results showed that analysis of effluent concentration variability is likely to provide information about the position of the effluent source. The developed leak rate estimation method provided encouraging results showing that such an approach is able to yield relatively accurate leak rate estimates. LES results proved to be very useful as they helped to provide guidelines for experiments as well as to deepen our understanding of the diffusion dynamics of turbulent effluent plumes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25305325','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25305325"><span id="translatedtitle">The impacts of summer monsoons on the ozone budget of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> of the Asia-Pacific region.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hou, Xuewei; Zhu, Bin; Fei, Dongdong; Wang, Dongdong</p> <p>2015-01-01</p> <p>The seasonal and inter-annual variations of ozone (O3) in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> of the Asia-Pacific Ocean were investigated using model simulations (2001-2007) from the Model of Ozone and Related chemical Tracers, version 4 (MOZART-4). The simulated O3 and diagnostic precipitation are in good agreement with the observations. Model results suggest that the Asia-Pacific monsoon significantly influences the seasonal and inter-annual variations of ozone. The differences of anthropogenic emissions and zonal winds in meridional directions cause a pollutants' transition zone at approximately 20°-30°N. The onset of summer monsoons with a northward migration of the rain belt leads the transition zone to drift north, eventually causing a summer minimum of ozone to the north of 30°N. In years with an early onset of summer monsoons, strong inflows of clean oceanic air lead to low ozone at polluted oceanic sites near the continent, while strong outflows from the continent exist, resulting in high levels of O3 over remote portions of the Asia-Pacific Ocean. The reverse is true in years when the summer monsoon onset is late. PMID:25305325</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15296321','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15296321"><span id="translatedtitle">Tedlar bag sampling technique for vertical profiling of carbon dioxide through the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> with high precision and accuracy.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schulz, Kristen; Jensen, Michael L; Balsley, Ben B; Davis, Kenneth; Birks, John W</p> <p>2004-07-01</p> <p>Carbon dioxide is the most important greenhouse gas other than water vapor, and its modulation by the biosphere is of fundamental importance to our understanding of global climate change. We have developed a new technique for vertical profiling of CO2 and meteorological parameters through the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and well into the free troposphere. Vertical profiling of CO2 mixing ratios allows estimates of landscape-scale fluxes characteristic of approximately100 km2 of an ecosystem. The method makes use of a powered parachute as a platform and a new Tedlar bag air sampling technique. Air samples are returned to the ground where measurements of CO2 mixing ratios are made with high precision (< or =0.1%) and accuracy (< or =0.1%) using a conventional nondispersive infrared analyzer. Laboratory studies are described that characterize the accuracy and precision of the bag sampling technique and that measure the diffusion coefficient of CO2 through the Tedlar bag wall. The technique has been applied in field studies in the proximity of two AmeriFlux sites, and results are compared with tower measurements of CO2. PMID:15296321</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JPhCS.555a2087S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JPhCS.555a2087S"><span id="translatedtitle">Large Eddy Simulation of Wind Turbine Wakes in Prescribed Neutral and Non-Neutral <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sarlak Chivaee, Hamid; Sørensen, Jens N.</p> <p>2014-12-01</p> <p>Large eddy simulation (LES) of an infinitely long wind farm in a fully developed flow is carried out based on solution of the incompressible Navier-Stokes equations. The wind turbines are modeled as equivalent rotating actuator disks by applying aerodynamic loads on the flow field using tabulated aerodynamic lift and drag coefficients to save computational time. As a substitute to standard wall modeling LES, a ''prescribed mean shear" profile (hereafter called PMS) approach has been implemented and analysed for generating the desired turbulent shear flow. It is applied on Neutral, Stable and Convective <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layers</span> in presence of the -actuator disc represented- wind turbines and qualitatively meaningful results of mean and fluctuating velocity field is obtained. The effect of four different sub-grid scale (SGS) models on the flow structure is investigated and it is seen that subgrid scale modeling (in particular, the Mix-O and Smagorinsky models) improves the accuracy of the simulations. An optimal grid resolution is also proposed for this kind of simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2761K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2761K"><span id="translatedtitle">A diagram of wind speed versus air-sea temperature difference to understand the dynamics of the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> off northwest Europe</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kettle, Anthony</p> <p>2015-04-01</p> <p>Wind speed and <span class="hlt">atmospheric</span> stability have an important role in determining the turbulence in the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (MABL) as well as the surface wave field. The understanding of MABL dynamics in northwest Europe is complicated by fetch effects, the proximity of coastlines, shallow topography, and larger scale circulation patterns (e.g., cold air outbreaks). Numerical models have difficulty simulating the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> in coastal areas and partially enclosed seas, and this is partly due to spatial resolution problems at land-sea coastline discontinuities. In these offshore environments, the <span class="hlt">boundary</span> <span class="hlt">layer</span> processes are often best understood directly from time series measurements from measurement platforms or buoys, in spite of potential difficulties from platform flow distortion as well as the spatial sparseness of the data sets. This contribution presents updated results of measurements from offshore platforms in the North Sea and Norwegian Sea in terms of a summary diagnostic - wind speed versus air-sea temperature difference (U-ΔT) - with important implications for understanding <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> processes. The U-ΔT diagram was introduced in earlier surveys of data from coastal and offshore sites in northwest Europe to summarize <span class="hlt">boundary</span> <span class="hlt">layer</span> conditions at a given location. Additional information from a series of measurement purpose-built offshore measurement and oil/gas production platforms from the North Sea illustrates how the wind characteristics vary spatially over large distances. The results are important for the offshore wind industry because of the way that wind turbines accrue fatigue damage in different conditions of <span class="hlt">atmospheric</span> stability and wind speed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950026033','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950026033"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> transition studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Watmuff, Jonathan H.</p> <p>1995-01-01</p> <p>A small-scale wind tunnel previously used for turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> experiments was modified for two sets of <span class="hlt">boundary</span> <span class="hlt">layer</span> transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar <span class="hlt">layer</span> asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the <span class="hlt">layer</span> to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the <span class="hlt">layer</span> remains attached, i.e. the <span class="hlt">layer</span> is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear <span class="hlt">layer</span>, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.A33A3150G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.A33A3150G"><span id="translatedtitle">Application and Limitations of GPS Radio Occultation (GPS-RO) Data for <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Height Detection over the Arctic.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ganeshan, M.; Wu, D. L.</p> <p>2014-12-01</p> <p>Due to recent changes in the Arctic environment, it is important to monitor the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) properties over the Arctic Ocean, especially to explore the variability in ABL clouds (such as sensitivity and feedback to sea ice loss). For example, radiosonde and satellite observations of the Arctic ABL height (and low-cloud cover) have recently suggested a positive response to sea ice loss during October that may not occur during the melt season (June-September). Owing to its high vertical and spatiotemporal resolution, an independent ABL height detection algorithm using GPS Radio Occultation (GPS-RO) refractivity in the Arctic is explored. Similar GPS-RO algorithms developed previously typically define the level of the most negative moisture gradient as the ABL height. This definition is favorable for subtropical oceans where a stratocumulus-topped ABL is often capped by a <span class="hlt">layer</span> of sharp moisture lapse rate (coincident with the temperature inversion). The Arctic Ocean is also characterized by stratocumulus cloud cover, however, the specific humidity does not frequently decrease in the ABL capping inversion. The use of GPS-RO refractivity for ABL height retrieval therefore becomes more complex. During winter months (December-February), when the total precipitable water in the troposphere is a minimum, a fairly straightforward algorithm for ABL height retrieval is developed. The applicability and limitations of this method for other seasons (Spring, Summer, Fall) is determined. The seasonal, interannual and spatial variability in the GPS-derived ABL height over the Arctic Ocean, as well as its relation to the underlying surface (ice vs. water), is investigated. The GPS-RO profiles are also explored for the evidence of low-level moisture transport in the cold Arctic environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AtmRe..89..330C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AtmRe..89..330C"><span id="translatedtitle">Concentrations of PM 10, PM 2.5, and PM 1 influenced by <span class="hlt">atmospheric</span> circulation and <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> in the Korean mountainous coast during a duststorm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Choi, Hyo; Choi, Doo Sun</p> <p>2008-09-01</p> <p>Particle size concentrations of 100 ng m - 3 to 203" in the main text were changed to "100 ng m- 3". Please check if appropriate.--> μg m - 3 were measured at two sampling points over the eastern coastal region of Korea by two GRIMM aerosol samplers from March 7-17, 2004. One sampling point was located on the western upwind side of the mountains, and the other sampling point was located in the city of Kangnung in the coastal basin downwind and adjacent to the East Sea. Concentrations of PM 10, PM 2.5, and PM 1 were measured near the ground in Kangnung on March 8, 2004, until 1200 LST before the passage of a duststorm. Values of about 40, 35, and 30 μg m - 3 , respectively, were detected indicating little variation among sample concentrations. Before the duststorm, maximum concentrations for PM 10 occurred around 0800 and 1700 LST due to increased fuel combustion from road vehicles. From the afternoon of March 10-16 when the largest amount of dust from China had passed over Kangnung under the influence of a westerly wind, PM 10 concentration reached 340 μg m - 3 , and PM 2.5 and PM 1 concentrations reached 105 μg m - 3 and 60 μg m - 3 , respectively, indicating double the PM 10 concentration as compared to PM 2.5. Most of the dust transported from China consisted of particle sizes larger than PM 2.5 and PM 1. Dust transported from the western, upwind side of the mountains combined with the particulates emitted from road vehicles and industrial and residential boilers in the city after sunrise under the influence of westerly winds resulted in a high particulate concentration at 0900 LST. However, a low concentration of particulates in the city was detected near 1200 LST due to changes in the structure of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>, while a high concentration over the mountains occurred due to a stable <span class="hlt">layer</span>. High-particulate concentrations in the city occurred again after 1700 LST owing to increased fuel combustion from road vehicles and residential boilers</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010AGUFM.H21J..05S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010AGUFM.H21J..05S&link_type=ABSTRACT"><span id="translatedtitle">A large-eddy simulation study of the impact of different land-<span class="hlt">atmosphere</span> coupling schemes on the dynamics of the nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stoll, J. R.; Shingleton, N. D.; Bosveld, F.</p> <p>2010-12-01</p> <p>Accurately reproducing the dynamic two-way interaction between the land surface and the <span class="hlt">atmosphere</span> in the stable <span class="hlt">boundary</span> <span class="hlt">layer</span> (SBL) requires detailed treatment of the governing physical processes. Increasingly, large-eddy simulation (LES) is used for this purpose. In many studies, the dominant treatment of surface <span class="hlt">boundary</span> conditions is to specify a known state or flux. This results in one-way or weak two-way coupling between the land surface and the <span class="hlt">boundary</span> <span class="hlt">layer</span>. The impact of how this coupling is modeled on <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) dynamics is still not fully understood, especially under transitional and weakly turbulent conditions. Here, LES that is fully coupled to a land-surface model (LSM) is used to investigate the nocturnal and the transitional periods of the diurnal cycle. The LSM explicitly solves for the transport of heat and water in a one-dimensional column of the upper soil and is coupled to the <span class="hlt">atmosphere</span> through a surface energy budget. The fully coupled LES-LSM is used to simulate the third GEWEX (Global Energy and Water Cycle Experiment) ABL (GABLS3) LES intercomparison case. Turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> profiles and surface fluxes are compared to field data and results from simulations using three different levels of physical description as lower <span class="hlt">boundary</span> conditions. These include simulations with prescribed temperature and moisture state, with a LSM that uses a bare-soil approximation and a LSM that include a skin <span class="hlt">layer</span>. Overall, simulations with all three types of <span class="hlt">boundary</span> conditions compare fairly well with the general trends observed in the field data for surface fluxes and <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence statistical profiles during the intercomparison time period (night to early morning) with a few differences. The LES-LSM model under-predicts the latent heat flux during the night and over-predicts the ground heat and moisture fluxes. The addition of a skin <span class="hlt">layer</span> improves flux predictions during the night and early morning. Surface fluxes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=311697&keyword=meteorology&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=65343270&CFTOKEN=68114189','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=311697&keyword=meteorology&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=65343270&CFTOKEN=68114189"><span id="translatedtitle">Recent Advances in Modeling of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> and Land Surface in the Coupled WRF-CMAQ Model</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>Advances in the land surface model (LSM) and planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) components of the WRF-CMAQ coupled meteorology and air quality modeling system are described. The aim of these modifications was primarily to improve the modeling of ground level concentrations of trace c...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016cosp...41E1707S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016cosp...41E1707S"><span id="translatedtitle">Variability of <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> height over the tropical oceans - A study using <span class="hlt">atmospheric</span> refractivity profiles from multi campaign in-situ and satellite radio occultation data.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Santosh, M.</p> <p>2016-07-01</p> <p><span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (ABL) over the tropical oceans controls and regulates the influx of water vapour into the free <span class="hlt">atmosphere</span> due to evaporation. The availability of in situ data for determining the ABL characteristics over tropical oceans are limited to different ship based campaigns and hence restricted in spatial and temporal coverage. For ABL studies the Radio Occultation (RO) based satellite data over tropical oceans have good temporal and spatial coverage but limited in temporal and spatial resolution. <span class="hlt">Atmospheric</span> refractivity profiles are extensively used in many studies to determine the ABL height from both platforms. The present study attempts to use the advantages in both in-situ and satellite (RO) based data to quantify the variability in the ABL height over the tropical oceans. All studies done so far to identify the ABL height from RO derived refractivity profiles rely extensively on the detection of the minimum refractivity gradient (MRG) below ~6 km along with additional threshold criteria. This leads to an over estimation of ABL heights especially in presence of strong subsidence inversion caused by local/ mesoscale/ synoptic scale processes where the MRG lies significantly above the ABL. The present study attempts to quantify this over estimation using <span class="hlt">atmospheric</span> refractivity profiles derived from thermo-dynamical parameters from radiosonde ascents over the tropical ocean, suggests an improved method of ABL detection and quantifies the variability so deduced. Over 1000 radiosonde ascents from four ship cruises conducted during DYNAMO 2011 field campaign over the tropical Indian Ocean are used for the purpose. ABL heights determined from radiosonde data using traditional methods (using virtual potential temperature and specific humidity) are compared with those identified from simulated <span class="hlt">atmospheric</span> refractivity profiles from same data (using prevalent methods for RO) to quantify the over estimation. A new method of ABL detection from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013EGUGA..15.2576T&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013EGUGA..15.2576T&link_type=ABSTRACT"><span id="translatedtitle">Wind-wave coupling in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over a reservoir: field measurements and verification of the model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Troitskaya, Yuliya; Papko, Vladislav; Baidakov, Georgy; Vdovin, Maxim; Kandaurov, Alexander; Sergeev, Daniil</p> <p>2013-04-01</p> <p>This paper presents the results of field experiments conducted at the Gorky Reservoir to test a quasi-linear model of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> [1]. In the course of the experiment we simultaneously measured profiles of wind speed and surface wave spectra using instruments placed on the Froude buoy, which measures the following parameters: i) the module and the direction of the wind speed using ultrasonic wind sensor WindSonic Gill instruments, located on the 4 - levels from 0.1 x 5 m long; ii) profile of the surface waves with 3-channel string wave-gauge with a base of 5 cm, iii) the temperature of the water and air with a resistive sensor. From the measured profiles of wind speed, we calculated basic parameters of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>: the friction velocity u*, the wind speed at the standard height of 10 m U10 and the drag coefficient CD. Data on CD(U10), obtained at the Gorky Reservoir, were compared with similar data obtained on Lake George in Australia during the Australian Shallow Water Experiment (AUSWEX) conducted in 1997 - 1999 [2,3]. A good agreement was obtained between measured data at two different on the parameters of inland waters: deep Gorky reservoir and shallow Lake George.To elucidate the reasons for this coincidence of the drag coefficients under strongly different conditions an analysis of surface waves was conducted.Measurements have shown that in both water bodies the surface wave spectra have almost the same asymptotics (spatial spectrum - k-3, the frequency spectrum -5), corresponding to the Phillips saturation spectrum.These spectra are typically observed for the steep surface waves, for which the basic dissipation mechanism is wave breaking. The similarity of the short-wave parts of the spectra can be regarded as a probable cause of coincidence of dependency of drag coefficient of the water surface on wind speed. Quantitative verification of this hypothesis was carried out in the framework of quasi-linear model of the wind</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ACPD...1431483S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ACPD...1431483S"><span id="translatedtitle">A comprehensive investigation on afternoon-evening transition of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over a tropical rural site</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sandeep, A.; Narayana Rao, T.; Rao, S. V. B.</p> <p>2014-12-01</p> <p>The transitory nature of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> few hours before and after the time of sunset has been studied comprehensively over a tropical station, Gadanki (13.45° N, 79.18° E), using a suite of in-situ and remote sensing devices. This study addresses the following fundamental and important issues related to the afternoon-to-evening transition (AET). Which state variable first identifies it? Which variable best identifies it? Does the start time of AET varies with season and height? If so, which physical mechanism is responsible for the observed height variation in the start time of transition? The transition is seen first in temperature (T) and wind variance (σ2ws) variations at the surface, ∼ 100 min prior to the time of sunset, then in vertical temperature gradient and finally in water vapour mixing ratio variation. Aloft, the AET is observed nearly at the same time in signal to noise ratio (SNR) and spectral width (σ) measurements of wind profiler and sodar. TheT at the surface and SNR aloft identify the signature of transition unambiguously. Also, their distributions for start time of AET with reference to the time of sunset are narrow and consistent in total and seasonal plots. The start time of transition shows some seasonal variation with delayed transitions occurring mostly in the rainy and humid season of northeast monsoon. Interestingly, in contrast to the general perception, the signature of the transition is first seen in the profiler data then in sodar data and finally in the surface data, suggesting that the transition follows top-to-bottom evolution. It indicates that other forcings, like entrainment, play a major role in altering the structure of ABL during the AET, when the sensible heat flux decreases progressively. These forcing terms are quantified using a unique high-resolution dataset to understand their variation in light of the intriguing height dependency of the start time of AET.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.158..429A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.158..429A&link_type=ABSTRACT"><span id="translatedtitle">The Impact of Upstream Flow on the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> in a Valley on a Mountainous Island</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adler, Bianca; Kalthoff, Norbert</p> <p>2016-03-01</p> <p>Comprehensive measurements on the mountainous island of Corsica were used to investigate how the mountain <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (mountain ABL) in a valley downstream of the main mountain ridge was influenced by the upstream flow. The data used were mainly collected with the mobile observation platform KITcube during the first special observation period of the Hydrological cycle in the Mediterranean Experiment (HyMeX) in 2012 and were based on various in situ, remote sensing and aircraft measurements. Two days in autumn 2012 were analyzed in detail. On these days the mountain ABL evolution was a result of convection and thermally-driven circulations as well as terrain-induced dynamically-driven flows. During periods when dynamically-driven flows were dominant, warm and dry air from aloft with a large-scale westerly wind component was transported downwards into the valley. On one day, these flows controlled the mountain ABL characteristics in a large section of the valley for several hours, while on the other day their impact was observed in a smaller section of the valley for about 1 h only. To explain the observations we considered a theoretical concept based on uniform upstream stratification and wind speed, and calculated the non-dimensional mountain height and the horizontal aspect ratio of the barrier to relate the existing conditions to diagnosed regimes of stratified flow past a ridge. On both days, wave breaking, flow splitting and lee vortices were likely to occur. Besides the upstream conditions, a reduction of stability in the valley seemed to be important for the downward transport to reach the ground. The spatio-temporal structure of such a mountain ABL over complex terrain, which was affected by various interacting flows, differed a lot from that of the classical ABL over homogeneous, flat terrain and it is stressed that the traditional ABL definitions need to be revised when applying them to complex terrain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=20120009941&hterms=loco&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dloco','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=20120009941&hterms=loco&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dloco"><span id="translatedtitle">Diagnosing the Sensitivity of Local Land-<span class="hlt">Atmosphere</span> Coupling via the Soil Moisture-<span class="hlt">Boundary</span> <span class="hlt">Layer</span> Interaction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Santanello, Joseph A., Jr.; Peters-Lidard, Christa D.; Kumar, Sujay V.</p> <p>2011-01-01</p> <p>The inherent coupled nature of earth s energy and water cycles places significant importance on the proper representation and diagnosis of land <span class="hlt">atmosphere</span> (LA) interactions in hydrometeorological prediction models. However, the precise nature of the soil moisture precipitation relationship at the local scale is largely determined by a series of nonlinear processes and feedbacks that are difficult to quantify. To quantify the strength of the local LA coupling (LoCo), this process chain must be considered both in full and as individual components through their relationships and sensitivities. To address this, recent modeling and diagnostic studies have been extended to 1) quantify the processes governing LoCo utilizing the thermodynamic properties of mixing diagrams, and 2) diagnose the sensitivity of coupled systems, including clouds and moist processes, to perturbations in soil moisture. This work employs NASA s Land Information System (LIS) coupled to the Weather Research and Forecasting (WRF) mesoscale model and simulations performed over the U.S. Southern Great Plains. The behavior of different planetary <span class="hlt">boundary</span> <span class="hlt">layers</span> (PBL) and land surface scheme couplings in LIS WRF are examined in the context of the evolution of thermodynamic quantities that link the surface soil moisture condition to the PBL regime, clouds, and precipitation. Specifically, the tendency toward saturation in the PBL is quantified by the lifting condensation level (LCL) deficit and addressed as a function of time and space. The sensitivity of the LCL deficit to the soil moisture condition is indicative of the strength of LoCo, where both positive and negative feedbacks can be identified. Overall, this methodology can be applied to any model or observations and is a crucial step toward improved evaluation and quantification of LoCo within models, particularly given the advent of next-generation satellite measurements of PBL and land surface properties along with advances in data assimilation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015APS..DFDL12011A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015APS..DFDL12011A&link_type=ABSTRACT"><span id="translatedtitle">Outer <span class="hlt">layer</span> effects in wind-farm <span class="hlt">boundary</span> <span class="hlt">layers</span>: Coriolis forces and <span class="hlt">boundary</span> <span class="hlt">layer</span> height</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Allaerts, Dries; Meyers, Johan</p> <p>2015-11-01</p> <p>In LES studies of wind-farm <span class="hlt">boundary</span> <span class="hlt">layers</span>, scale separation between the inner and outer region of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner <span class="hlt">layer</span> and are not affected by outer <span class="hlt">layer</span> effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer <span class="hlt">layer</span> effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer <span class="hlt">layer</span> effects on wind-farm <span class="hlt">boundary</span> <span class="hlt">layers</span>. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal <span class="hlt">boundary</span> <span class="hlt">layer</span> (IBL), which is limited in cases with low inversion <span class="hlt">layers</span>. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing <span class="hlt">boundary</span> <span class="hlt">layer</span> height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960017580','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960017580"><span id="translatedtitle">Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Simulation Using TASS</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael</p> <p>1996-01-01</p> <p><span class="hlt">Boundary</span> conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. Several options are now available, including the use of a surface energy balance. In addition, we compare convective <span class="hlt">boundary</span> <span class="hlt">layer</span> simulations with the Wangara and Minnesota field experiments as well as with other model results. We find excellent agreement of modelled mean profiles of wind and temperature with observations and good agreement for velocity variances. Neutral <span class="hlt">boundary</span> simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......164W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......164W"><span id="translatedtitle">An evaluation and parameterization of stably stratified turbulence: Insights on the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and implications for wind energy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wilson, Jordan M.</p> <p></p> <p>This research focuses on the dynamics of turbulent mixing under stably stratified flow conditions. Velocity fluctuations and instabilities are suppressed by buoyancy forces limiting mixing as stability increases and turbulence decreases until the flow relaminarizes. Theories that ubiquitously assume turbulence collapse above a critical value of the gradient Richardson number (e.g. Ri > Ric) are common in meteorological and oceanographic communities. However, most theories were developed from results of small-scale laboratory and numerical experiments with energetic levels several orders of magnitude less than geophysical flows. Geophysical flows exhibit strong turbulence that enhances the transport of momentum and scalars. The mixing length for the turbulent momentum field, L M, serves as a key parameter in assessing large-scale, energy-containing motions. For a stably stratified turbulent shear flow, the shear production of turbulent kinetic energy, P, is here considered to be of greater relevance than the dissipation rate of turbulent kinetic energy, epsilon. Thus, the turbulent Reynolds number can be recast as Re ≡ k2/(nuP) where k is the turbulent kinetic energy, allowing for a new perspective on flow energetics. Using an ensemble data set of high quality direct numerical simulation (DNS) results, large-eddy simulation (LES) results, laboratory experiments, and observational field data of the stable <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (SABL), the dichotomy of data becomes apparent. High mixing rates persist to strong stability (e.g. Ri ≈ 10) in the SABL whereas numerical and laboratory results confirm turbulence collapse for Ri ˜ O(1). While this behavior has been alluded to in literature, this direct comparison of data elucidates the disparity in universal theories of stably stratified turbulence. From this theoretical perspective, a Reynolds-averaged framework is employed to develop and evaluate parameterizations of turbulent mixing based on the competing forces</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1110541B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1110541B"><span id="translatedtitle"><span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> and Clouds wind speed profile measurements with the new compact long range wind Lidar WindCube(TM) WLS70</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boquet, M.; Cariou, J. P.; Sauvage, L.; Lolli, S.; Parmentier, R.; Loaec, S.</p> <p>2009-04-01</p> <p>To fully understand <span class="hlt">atmospheric</span> dynamics, climate studies, energy transfer, and weather prediction the wind field is one of the most important <span class="hlt">atmospheric</span> state variables. Small scales variability and low <span class="hlt">atmospheric</span> <span class="hlt">layers</span> are not described with sufficient resolution up to now. To answer these needs, the WLS70 long-range wind Lidar is a new generation of wind Lidars developed by LEOSPHERE, derived from the commercial WindCube™ Lidar widely used by the wind power industry and well-known for its great accuracy and data availability. The WLS70 retrieves the horizontal and vertical wind speed profiles as well as the wind direction at various heights simultaneously inside the <span class="hlt">boundary</span> <span class="hlt">layer</span> and cloud <span class="hlt">layers</span>. The amplitude and spectral content of the backscattering signal are also available. From raw data, the embedded signal processing software performs the computation of the aerosol Doppler shift and backscattering coefficient. Higher values of normalized relative backscattering (NRB) are proportional to higher aerosol concentration. At 1540 nm, molecular scattering being negligible, it is then possible to directly retrieve the <span class="hlt">Boundary</span> <span class="hlt">Layer</span> height evolution observing the height at which the WindCube NRB drops drastically. In this work are presented the results of the measurements obtained during the LUAMI campaign that took place in Lindenberg, at the DWD (Deutscher WetterDienst) meteorological observatory, from November 2008 to January 2009. The WLS70 Lidar instrument was placed close together with an EZ Lidar™ ALS450, a rugged and compact eye safe aerosol Lidar that provides a real time measurement of backscattering and extinction coefficients, aerosol optical depth (AOD), automatic detection of the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) height and clouds base and top from 100m up to more than 20km. First results put in evidence wind shear and veer phenomena as well as strong convective effects during the raise of the mixing <span class="hlt">layer</span> or before rain periods. Wind speed</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760010652','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760010652"><span id="translatedtitle">Modeling the urban <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bergstrom, R. W., Jr.</p> <p>1976-01-01</p> <p>A summary and evaluation is given of the Workshop on Modeling the Urban <span class="hlt">Boundary</span> <span class="hlt">Layer</span>; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and <span class="hlt">boundary</span> problems, (5) nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span>, and (6) verification of models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...50W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...50W&link_type=ABSTRACT"><span id="translatedtitle">The Variability of Refractivity in the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> of a Tropical Island Volcano Measured by Ground-Based Interferometric Radar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wadge, G.; Costa, A.; Pascal, K.; Werner, C.; Webb, T.</p> <p>2016-06-01</p> <p>For 24 h we measured continuously the variability of <span class="hlt">atmospheric</span> refractivity over a volcano on the tropical island of Montserrat using a ground-based radar interferometer. We observed variations in phase that we interpret as due to changing water vapour on the propagation path between the radar and the volcano and we present them here in the context of the behaviour of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over the island. The water vapour behaviour was forced by diurnal processes, the passage of a synoptic-scale system and the presence of a plume of volcanic gas. The interferometer collected images of amplitude and phase every minute. From pairs of phase images, interferograms were calculated and analyzed every minute and averaged hourly, together with contemporaneous measurements of zenith delays estimated from a network of 14 GPS receivers. The standard deviation of phase at two sites on the volcano surface spanned a range of about 1-5 radians, the lowest values occurring at night on the lower slopes and the highest values during the day on the upper slopes. This was also reflected in spatial patterns of variability. Two-dimensional profiles of radar-measured delays were modelled using an <span class="hlt">atmosphere</span> with water vapour content decreasing upwards and water vapour variability increasing upwards. Estimates of the effect of changing water vapour flux from the volcanic plume indicate that it should contribute only a few percent to this <span class="hlt">atmospheric</span> variability. A diurnal cycle within the lower <span class="hlt">boundary</span> <span class="hlt">layer</span> producing a turbulence-dominated mixed <span class="hlt">layer</span> during the day and stable <span class="hlt">layers</span> at night is consistent with the observed refractivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25192929','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25192929"><span id="translatedtitle">Impact of the Loess Plateau on the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> structure and air quality in the North China Plain: a case study.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hu, Xiao-Ming; Ma, ZhiQiang; Lin, Weili; Zhang, Hongliang; Hu, Jianlin; Wang, Ying; Xu, Xiaobin; Fuentes, Jose D; Xue, Ming</p> <p>2014-11-15</p> <p>The North China Plain (NCP), to the east of the Loess Plateau, experiences severe regional air pollution. During the daytime in the summer, the Loess Plateau acts as an elevated heat source. The impacts of such a thermal effect on meteorological phenomena (e.g., waves, precipitation) in this region have been discussed. However, its impacts on the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the <span class="hlt">boundary</span> <span class="hlt">layer</span> structure and ambient concentrations of pollutants over the NCP under certain meteorological conditions. Thus, this study investigates such effect and its impacts using measurements and three-dimensional model simulations. It is found that in the presence of daytime westerly wind in the lower troposphere (~1 km above the NCP), warmer air above the Loess Plateau was transported over the NCP and imposed a thermal inversion above the mixed <span class="hlt">boundary</span> <span class="hlt">layer</span>, which acted as a lid and suppressed the mixed <span class="hlt">layer</span> growth. As a result, pollutants accumulated in the shallow mixed <span class="hlt">layer</span> and ozone was efficiently produced. The downward branch of the thermally-induced Mountain-Plains Solenoid circulation over the NCP contributed to enhancing the capping inversion and exacerbating air pollution. Previous studies have reported that low mixed <span class="hlt">layer</span>, a factor for elevated pollution in the NCP, may be caused by aerosol scattering and absorption of solar radiation, frontal inversion, and large scale subsidence. The present study revealed a different mechanism (i.e., westerly warm advection) for the suppression of the mixed <span class="hlt">layer</span> in summer NCP, which caused severe O3 pollution. This study has important implications for understanding the essential meteorological factors for pollution episodes in this region and forecasting these severe events. PMID:25192929</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFDL35005M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFDL35005M"><span id="translatedtitle">A concurrent precursor inflow method for LES of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> flows with variable inflow direction for coupling with meso-scale models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Munters, Wim; Meneveau, Charles; Meyers, Johan</p> <p>2014-11-01</p> <p>In order to incorporate multiple scales of meteorological phenomena in <span class="hlt">atmospheric</span> simulations, subsequent nesting of meso-scale models is often used. However, the spatial and temporal resolution in such models is too coarse to resolve the three-dimensional turbulent eddies that are characteristic for <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> flows. This motivates the development of tools to couple meso-scale models to Large-Eddy Simulations (LES), in which turbulent fluctuations are explicitly resolved. A major challenge in this area is the spin-up region near the inlet of the LES in which the flow has to evolve from a RANS-like inflow, originating from the meso-scale model, to a fully turbulent velocity field. We propose a generalized concurrent precursor inflow method capable of imposing <span class="hlt">boundary</span> conditions for time-varying inflow directions. The method is based on a periodic fully-developed precursor <span class="hlt">boundary-layer</span> simulation that is dynamically rotated with the wind direction that drives the main LES. In this way realistic turbulent inflow conditions are applied while still retaining flexibility to dynamically adapt to meso-scale variations in wind directions. Applications to wind simulations with varying inflow directions, and comparisons to conventional coupling methods are shown. Work supported by ERC (ActiveWindFarms, Grant No: 306471). CM is supported by NSF (Grant No. 1243482).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987bpnl.rept.....W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987bpnl.rept.....W&link_type=ABSTRACT"><span id="translatedtitle">Minnesota 1973 <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> experiment: Micrometeorological and tracer data archive. Set 1 (revision 2) documentation report</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Woodruff, R. K.; Droppo, J. G.; Glantz, C. S.</p> <p>1987-03-01</p> <p>An archive for micrometeorological and tracer dispersion data was developed by Battelle, Pacific Northwest Labs. for the U.S. Environmental Protection Agency. The archive was designed to make the results of extensive field tests readily accessible to EPA for model testing, development, and verification efforts. Documentation was provided for one of the archived data sets, The Minnesota 1973 <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Experiment. The aim of the effort was to archive invaluable data sets in a timely fashion before the necessary supporting information about the data becomes lost forever. The entries are as follows: data set fact summary, a narrative description of experimental and data, special information, references, a description of archive data files, contacts (names, addresses, and phone numbers) and standard experiment summary table. Revision 2 includes previously unpublished rawinsonde profile data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=aerodynamics&pg=5&id=EJ445026','ERIC'); return false;" href="http://eric.ed.gov/?q=aerodynamics&pg=5&id=EJ445026"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Control on Airfoils.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Gerhab, George; Eastlake, Charles</p> <p>1991-01-01</p> <p>A phenomena, <span class="hlt">boundary</span> <span class="hlt">layer</span> control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/263507','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/263507"><span id="translatedtitle">Modeling the summertime Arctic cloudy <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Curry, J.A.; Pinto, J.O.; McInnes, K.L.</p> <p>1996-04-01</p> <p>Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic <span class="hlt">boundary</span> <span class="hlt">layer</span>. The presence of multiple cloud <span class="hlt">layers</span>, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud <span class="hlt">layers</span> in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the <span class="hlt">layered</span> structure of the Arctic summertime <span class="hlt">boundary-layer</span> clouds and in particular, the representation of the more complex <span class="hlt">boundary</span> <span class="hlt">layer</span> type consisting of a stable foggy surface <span class="hlt">layer</span> surmounted by a cloud-topped mixed <span class="hlt">layer</span>. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate <span class="hlt">layers</span> in the Arctic summertime <span class="hlt">boundary</span> <span class="hlt">layer</span>. A three-dimensional mesoscale <span class="hlt">atmospheric</span> model is then used to simulate the interaction of this cloud deck with the large-scale <span class="hlt">atmospheric</span> dynamics. An assessment of the improvements needed to the parameterizations of the <span class="hlt">boundary</span> <span class="hlt">layer</span>, cloud microphysics, and radiation in the 3-D model is made.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930090758','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930090758"><span id="translatedtitle">Removing <span class="hlt">Boundary</span> <span class="hlt">Layer</span> by Suction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ackeret, J</p> <p>1927-01-01</p> <p>Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl <span class="hlt">boundary-layer</span> theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the <span class="hlt">boundary</span> <span class="hlt">layer</span> into the inside of a body through a slot or slots in its surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1612522B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1612522B"><span id="translatedtitle">First simultaneous space measurements of <span class="hlt">atmospheric</span> pollutants in the <span class="hlt">boundary</span> <span class="hlt">layer</span> from IASI: a case study in the North China Plain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boynard, Anne; Clerbaux, Cathy; Clarisse, Lieven; Safieddine, Sarah; Pommier, Matthieu; Van Damme, Martin; Bauduin, Sophie; Oudot, Charlotte; Hadji-Lazaro, Juliette; Hurtmans, Daniel; Coheur, Pierre-François</p> <p>2014-05-01</p> <p>An extremely severe and persistent smog episode occurred in January 2013 over China. The levels of air pollution have been dangerously high, reaching 40 times recommended safety levels and have affected health of millions of people. China faced one of the worst periods of air quality in recent history and drew worldwide attention. This pollution episode was caused by the combination of anthropogenic emissions and stable meteorological conditions (absence of wind and temperature inversion) that trapped pollutants in the <span class="hlt">boundary</span> <span class="hlt">layer</span>. To characterize this episode, we used the IASI (Infrared <span class="hlt">Atmospheric</span> Sounding Interferometer) instrument onboard the MetOp-A platform. IASI observations show high concentrations of key trace gases such as carbon monoxide (CO), sulfur dioxide (SO2) and ammonia (NH3) along with ammonium sulfate aerosol. We show that IASI is able to detect <span class="hlt">boundary</span> <span class="hlt">layer</span> pollution in case of large negative thermal contrast combined with high levels of pollution. Our findings demonstrate the ability of thermal infrared instrument such as IASI to monitor <span class="hlt">boundary</span> <span class="hlt">layer</span> pollutants, which can support air quality evaluation and management.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012AGUFM.H31D1136S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012AGUFM.H31D1136S&link_type=ABSTRACT"><span id="translatedtitle">Study of the Effect of Wind Speed on Evaporation from Soil Through Integrated Modeling of <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> and Shallow Subsurface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smits, K. M.; Davarzani, H.; Illangasekare, T. H.</p> <p>2012-12-01</p> <p>The study of the interaction between the land and <span class="hlt">atmosphere</span> is paramount to our understanding of many emerging problems to include climate change and the movement of green house gases such as possible leaking of sequestered CO2. Soil moisture distribution in the shallow subsurface becomes a critical factor in these problems. The heat and mass flux in the form of soil evaporation across the land surface couples the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> to the shallow subsurface. The coupling between land and the <span class="hlt">atmosphere</span> leads to highly dynamic interactions between the porous media properties, transport processes and <span class="hlt">boundary</span> conditions, resulting in dynamic evaporative behavior. However, the coupling at the land-<span class="hlt">atmospheric</span> interface is rarely considered in most current models and their validation for practical applications. This is due to the complexity of the problem in field scenarios and the scarcity of field or laboratory data capable of testing and refining coupled energy and mass transfer theories. In most efforts to compute evaporation from soil, only indirect coupling is provided to characterize the interaction between non-isothermal multiphase flows under realistic <span class="hlt">atmospheric</span> conditions even though heat and mass flux are controlled by the coupled dynamics of the land and the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. In earlier drying modeling concepts, imposing evaporation flux (kinetic of relative humidity) and temperature as surface <span class="hlt">boundary</span> condition is often needed. With the goal of improving our understanding of the land/<span class="hlt">atmospheric</span> coupling, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model consists of the coupled equations of mass conservation for the liquid phase (water) and gas phase (water vapor and air) in porous medium with gas phase (water vapor and air) in free flow domain under non-isothermal, non-equilibrium conditions. The <span class="hlt">boundary</span> conditions at the porous medium-free flow medium interface include</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013EGUGA..1511431D&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013EGUGA..1511431D&link_type=ABSTRACT"><span id="translatedtitle">Study of the effect of wind speed on evaporation from soil through integrated modeling of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and shallow subsurface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan; Illangasekare, Tissa</p> <p>2013-04-01</p> <p>The study of the interaction between the land and <span class="hlt">atmosphere</span> is paramount to our understanding of many emerging problems to include climate change, the movement of green house gases such as possible leaking of sequestered CO2 and the accurate detection of buried objects such as landmines. Soil moisture distribution in the shallow subsurface becomes a critical factor in all these problems. The heat and mass flux in the form of soil evaporation across the land surface couples the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> to the shallow subsurface. The coupling between land and the <span class="hlt">atmosphere</span> leads to highly dynamic interactions between the porous media properties, transport processes and <span class="hlt">boundary</span> conditions, resulting in dynamic evaporative behavior. However, the coupling at the land-<span class="hlt">atmospheric</span> interface is rarely considered in most current models and their validation for practical applications. This is due to the complexity of the problem in field scenarios and the scarcity of field or laboratory data capable of testing and refining coupled energy and mass transfer theories. In most efforts to compute evaporation from soil, only indirect coupling is provided to characterize the interaction between non-isothermal multiphase flows under realistic <span class="hlt">atmospheric</span> conditions even though heat and mass flux are controlled by the coupled dynamics of the land and the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. In earlier drying modeling concepts, imposing evaporation flux (kinetic of relative humidity) and temperature as surface <span class="hlt">boundary</span> condition is often needed. With the goal of improving our understanding of the land/<span class="hlt">atmospheric</span> coupling, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model consists of the coupled equations of mass conservation for the liquid phase (water) and gas phase (water vapor and air) in porous medium with gas phase (water vapor and air) in free flow domain under non-isothermal, non-equilibrium conditions. The <span class="hlt">boundary</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996JGR...101.6899Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996JGR...101.6899Y"><span id="translatedtitle"><span class="hlt">Atmospheric</span> sulfur cycling in the tropical Pacific marine <span class="hlt">boundary</span> <span class="hlt">layer</span> (12°S, 135°W): A comparison of field data and model results: 1. Dimethylsulfide</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yvon, S. A.; Saltzman, E. S.; Cooper, D. J.; Bates, T. S.; Thompson, A. M.</p> <p>1996-03-01</p> <p>Shipboard measurements of <span class="hlt">atmospheric</span> and seawater DMS were made at 12°S, 135°W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 ± 0.45 nM (1σ, n = 260) and the mean <span class="hlt">atmospheric</span> DMS mole fraction was 453 ± 93 pmol mol-1 (1σ, n = 843). Consistent <span class="hlt">atmospheric</span> diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol-1. Photochemical box model calculations were made to test the sensitivity of <span class="hlt">atmospheric</span> DMS concentrations to the following parameters: 1) sea-to-air flux, 2) <span class="hlt">boundary</span> <span class="hlt">layer</span> height, 3) oxidation rate, and 4) vertical entrainment velocities. The observed relationship between the mean oceanic and <span class="hlt">atmospheric</span> DMS levels require the use of an air-sea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in <span class="hlt">atmospheric</span> DMS is significantly larger than that predicted by a photochemical model. This suggests that the sea-to-air DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.C54A..02O&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.C54A..02O&link_type=ABSTRACT"><span id="translatedtitle">Southern Hemisphere Sea Ice and the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> in a High-Resolution Simulation of the Community Earth System Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ordóñez, A.; Bitz, C. M.</p> <p>2015-12-01</p> <p>Increasing the horizontal resolution of the sea ice and ocean components in a global climate model has been shown to affect the extent of sea ice and the strength of <span class="hlt">atmosphere</span>/ocean fluxes. Since existing high-resolution (0.1°) coupled simulations include a dynamical ocean, it is difficult to pinpoint how these results are influenced by the resolution of the sea ice. This project takes a closer look at the impact of sea ice resolution on ocean/<span class="hlt">atmosphere</span> interactions in the Southern Hemisphere using the Community Earth System Model (CESM1-CAM5) in a slab ocean configuration. In this set-up, sea ice and mixed <span class="hlt">layer</span> ocean models on a 0.1° grid (high resolution) or 1° grid (standard resolution) are coupled with <span class="hlt">atmosphere</span> and land models run at the same 0.5° resolution. The high resolution model can produce fine scale, open water areas within the ice pack that facilitate air/sea flux exchanges and reduce the stability of the lower <span class="hlt">atmosphere</span> in the model. Correlations between sea ice concentration and <span class="hlt">boundary</span> <span class="hlt">layer</span> variables will be described at different spatial scales to understand the effects of resolving small scale features. Finally, a kernel feedback analysis will be shown on a 0.1°, double CO2 run to look at the impact of sea ice resolution on the regional lapse rate feedback.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17641195','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17641195"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> halogens in coastal Antarctica.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Saiz-Lopez, Alfonso; Mahajan, Anoop S; Salmon, Rhian A; Bauguitte, Stephane J-B; Jones, Anna E; Roscoe, Howard K; Plane, John M C</p> <p>2007-07-20</p> <p>Halogens influence the oxidizing capacity of Earth's troposphere, and iodine oxides form ultrafine aerosols, which may have an impact on climate. We report year-round measurements of <span class="hlt">boundary</span> <span class="hlt">layer</span> iodine oxide and bromine oxide at the near-coastal site of Halley Station, Antarctica. Surprisingly, both species are present throughout the sunlit period and exhibit similar seasonal cycles and concentrations. The springtime peak of iodine oxide (20 parts per trillion) is the highest concentration recorded anywhere in the <span class="hlt">atmosphere</span>. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic <span class="hlt">boundary</span> <span class="hlt">layer</span>. PMID:17641195</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/15014318','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/15014318"><span id="translatedtitle">Influences on the Height of the Stable <span class="hlt">Boundary</span> <span class="hlt">Layer</span> as seen in LES</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kosovic, B; Lundquist, J</p> <p>2004-06-15</p> <p>Climate models, numerical weather prediction (NWP) models, and <span class="hlt">atmospheric</span> dispersion models often rely on parameterizations of planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> height. In the case of a stable <span class="hlt">boundary</span> <span class="hlt">layer</span>, errors in <span class="hlt">boundary</span> <span class="hlt">layer</span> height estimation can result in gross errors in <span class="hlt">boundary-layer</span> evolution and in prediction of turbulent mixing within the <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...71S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016BoLMe.tmp...71S&link_type=ABSTRACT"><span id="translatedtitle">Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Due to an Extensive Wind Farm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, V.; Parlange, M. B.; Calaf, M.</p> <p>2016-08-01</p> <p>The effect of extensive terrestrial wind farms on the spatio-temporal structure of the diurnally-evolving <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> is explored. High-resolution large-eddy simulations of a realistic diurnal cycle with an embedded wind farm are performed. Simulations are forced by a constant geostrophic velocity with time-varying surface <span class="hlt">boundary</span> conditions derived from a selected period of the CASES-99 field campaign. Through analysis of the bulk statistics of the flow as a function of height and time, it is shown that extensive wind farms shift the inertial oscillations and the associated nocturnal low-level jet vertically upwards by approximately 200 m; cause a three times stronger stratification between the surface and the rotor-disk region, and as a consequence, delay the formation and growth of the convective <span class="hlt">boundary</span> <span class="hlt">layer</span> (CBL) by approximately 2 h. These perturbations are shown to have a direct impact on the potential power output of an extensive wind farm with the displacement of the low-level jet causing lower power output during the night as compared to the day. The low-power regime at night is shown to persist for almost 2 h beyond the morning transition due to the reduced growth of the CBL. It is shown that the wind farm induces a deeper entrainment region with greater entrainment fluxes. Finally, it is found that the diurnally-averaged effective roughness length for wind farms is much lower than the reference value computed theoretically for neutral conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012cosp...39.1927A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012cosp...39.1927A"><span id="translatedtitle">An Investigation on the role of Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Parameterization scheme on the performance of a hydrostatic <span class="hlt">atmospheric</span> model over a Coastal Region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anurose, J. T.; Subrahamanyam, Bala D.</p> <p>2012-07-01</p> <p>As part of the ocean/land-<span class="hlt">atmosphere</span> interaction, more than half of the total kinetic energy is lost within the lowest part of <span class="hlt">atmosphere</span>, often referred to as the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL). A comprehensive understanding of the energetics of this <span class="hlt">layer</span> and turbulent processes responsible for dissipation of kinetic energy within the PBL require accurate estimation of sensible and latent heat flux and momentum flux. In numerical weather prediction (NWP) models, these quantities are estimated through different surface-<span class="hlt">layer</span> and PBL parameterization schemes. This research article investigates different factors influencing the accuracy of a surface-<span class="hlt">layer</span> parameterization scheme used in a hydrostatic high-resolution regional model (HRM) in the estimation of surface-<span class="hlt">layer</span> turbulent fluxes of heat, moisture and momentum over the coastal regions of the Indian sub-continent. Results obtained from this sensitivity study of a parameterization scheme in HRM revealed the role of surface roughness length (z_{0}) in conjunction with the temperature difference between the underlying ground surface and <span class="hlt">atmosphere</span> above (ΔT = T_{G} - T_{A}) in the estimated values of fluxes. For grid points over the land surface where z_{0} is treated as a constant throughout the model integration time, ΔT showed relative dominance in the estimation of sensible heat flux. In contrast to this, estimation of sensible and latent heat flux over ocean were found to be equally sensitive on the method adopted for assigning the values of z_{0} and also on the magnitudes of ΔT.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2273M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2273M"><span id="translatedtitle">Stable isotopes of water vapor during the Strasse cruise in the sub-tropical North Atlantic; <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> composition in relation to local evaporation.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marion, Benetti; Gilles, Reverdin; Catherine, Pierre; Jerome, Demange; Camille, Risi</p> <p>2013-04-01</p> <p>During the Strasse cruise, a PICARRO L2130-i equipment was installed on the top deck of RV Thalassa with air pumped at an altitude of 20m above the sea surface. With this installation, the isotopic composition of water vapor was continuously measured from mid-August 2012 to mid-Septembre 2012 in the North Atlantic subtropical gyre, mostly around 26°N/36°W. The sea surface water was also regularly collected as well as rain water during a few showers during the cruise. The isotopic composition of these water samples was measured after the cruise at LOCEAN. Two weather packages were continuously measuring relative humidity, air temperature, strength and direction of wind, which provide data close to where the air was pumped, and allow to estimate net evaporation. Radiosondes were also launched during part of the survey in the morning and evening to get information on the lower <span class="hlt">atmosphere</span> vertical structure. These measurements allow a better understanding of the budget of the <span class="hlt">atmospheric</span> mixed <span class="hlt">layer</span> during the cruise in this region of high excess evaporation. In particular, we will comment a two-day event of large deviation in water vapor isotopic composition. We will also discuss to which extent the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> acquires its isotopic composition during exchanges with the surface ocean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950016851','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950016851"><span id="translatedtitle">Physics of magnetospheric <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cairns, Iver H.</p> <p>1995-01-01</p> <p>This final report was concerned with the ideas that: (1) magnetospheric <span class="hlt">boundary</span> <span class="hlt">layers</span> link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its <span class="hlt">boundary</span> <span class="hlt">layers</span>, which included the bow shock, the magnetosheath, the plasma sheet <span class="hlt">boundary</span> <span class="hlt">layer</span>, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730010570','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730010570"><span id="translatedtitle">Unsteady turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> analysis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.</p> <p>1973-01-01</p> <p>The governing equations for an unsteady turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span>. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760007940','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760007940"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> control for airships</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pake, F. A.; Pipitone, S. J.</p> <p>1975-01-01</p> <p>An investigation is summarized of the aerodynamic principle of <span class="hlt">boundary</span> <span class="hlt">layer</span> control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the <span class="hlt">boundary</span> <span class="hlt">layer</span> development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing <span class="hlt">boundary-layer</span> control to nonrigid airships.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......167R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......167R"><span id="translatedtitle">Design, testing and demonstration of a small unmanned aircraft system (sUAS) and payload for measuring wind speed and particulate matter in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Riddell, Kevin Donald Alexander</p> <p></p> <p>The <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) is the <span class="hlt">layer</span> of air directly influenced by the Earth's surface and is the <span class="hlt">layer</span> of the <span class="hlt">atmosphere</span> most important to humans as this is the air we live in. Methods for measuring the properties of the ABL include three general approaches: satellite based, ground based and airborne. A major research challenge is that many contemporary methods provide a restricted spatial resolution or coverage of variations of ABL properties such as how wind speed varies across a landscape with complex topography. To enhance our capacity to measure the properties of the ABL, this thesis presents a new technique that involves a small unmanned aircraft system (sUAS) equipped with a customized payload for measuring wind speed and particulate matter. The research presented herein outlines two key phases in establishing the proof of concept of the payload and its integration on the sUAS: (1) design and testing and (2) field demonstration. The first project focuses on measuring wind speed, which has been measured with fixed wing sUASs in previous research. but not with a helicopter sUAS. The second project focuses on the measurement of particulate matter, which is a major air pollutant typically measured with ground-based sensors. Results from both proof of concept projects suggest that ABL research could benefit from the proposed techniques. .</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900003198','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900003198"><span id="translatedtitle">Nonparallel stability of <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nayfeh, Ali H.</p> <p>1987-01-01</p> <p>The asymptotic formulations of the nonparallel linear stability of incompressible growing <span class="hlt">boundary</span> <span class="hlt">layers</span> are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing <span class="hlt">boundary</span> <span class="hlt">layers</span> is explained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1514159P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1514159P"><span id="translatedtitle">Particulate plumes in <span class="hlt">boundary</span> <span class="hlt">layers</span> with obstacles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petrosyan, Arakel; Karelsky, Kirill</p> <p>2013-04-01</p> <p>This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary <span class="hlt">boundaries</span>. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex <span class="hlt">boundary</span>. In viscous <span class="hlt">atmosphere</span> with as small as one likes coefficient of molecular viscosity, the non-slip <span class="hlt">boundary</span> condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring <span class="hlt">layers</span> energy dissipation of <span class="hlt">atmosphere</span> flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in <span class="hlt">atmosphere</span> movement characterizing by a high Reynolds number the <span class="hlt">boundary</span> <span class="hlt">layer</span> is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external <span class="hlt">boundary</span> of the <span class="hlt">layer</span> that are quite close to ones in ideal <span class="hlt">atmosphere</span> flow. In that <span class="hlt">layer</span> fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid <span class="hlt">boundary</span> caused not only by non-slip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of big wind gradients in the <span class="hlt">boundary</span> <span class="hlt">layer</span> and on the other hand disregard of molecular viscosity in two-phase <span class="hlt">atmosphere</span> equations.We deal with describing big field</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3500F&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3500F&link_type=ABSTRACT"><span id="translatedtitle">Observation studies on the influence of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> characteristics associate with air quality in dry season over the Pearl River Delta, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fan, Shaojia; Wu, Meng; Li, Haowen; Liao, Zhiheng; Fan, Qi; Zhu, Wei</p> <p>2016-04-01</p> <p>The characteristics of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) is the very important factors influence on air quality in dry season over the Pearl River Delta (PRD), China. Based on the sounding data at six stations (Xinken,Dongguan, Sanshui, Nanhai, Shunde, and Heshan) which obtained from three times ABL experiments carried in dry season over PRD, the influence of wind and temperature vertical structure to the air quality over PRD has been studied with wind and temperature profiles, inversion <span class="hlt">layer</span>, recirculation factor (RF), <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> height (ABLH) and ventilation index (VI). It was found that the vertical wind of PRD could be divided in typical three <span class="hlt">layers</span> according two wind shears appeared in 800 m and 1300 m. The thickness of calm or lower wind speed <span class="hlt">layer</span> in pollution days was 500-1000m thicker than that of clean days, and its last time also much longer than that of clean days. The frequency of surface inversion in pollution days was about 35%,the mean thickness was about 100 m. With the influence of sea breeze, the frequency and thickness of surface inversion <span class="hlt">layer</span> at Xinken station was a little lower than that in inland. Influenced by sea-land breezes and urban heat-island circulation, the RF of pollution days in coastal and urban area was quite smaller than that of clean days. During sea-land breezes days, the pollutants would be transported back to inland in nighttime with the influence of sea breeze, and resulted in 72.7% sea-land breezes was pollution days. The evolution of ABL was very typical in PRD during dry season. In pollution days, daily ABLH in PRD was lower than 500 m, daily VI was about 500-1500 m2/s. In clean days, daily VI was much larger than 2500 m2/s. An improved conceptual model of ABL influence on poor air quality and the parameters of the ABL characteristics associate with poor air quality in dry season over PRD had been summarized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987MsT..........5W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987MsT..........5W"><span id="translatedtitle">The spatial and temporal variability of the arctic <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and its effect on electromagnetic (EM) propagation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Willis, Zdenka S.</p> <p>1987-12-01</p> <p>Gradients of temperature, pressure and moisture affect the propagation of electromagnetic (EM) waves. Navy systems which are dependent on EM propagation can be either enhanced or degraded due to <span class="hlt">atmospheric</span> conditions which affect <span class="hlt">atmospheric</span> refractive index profiles. The Navy's model for predicting the refractive index is the Integrated Refractive Effects Prediction System (IREPS) version 2.2, developed by the Naval Ocean Systems Center (NOSC). <span class="hlt">Atmospheric</span> parameters of temperature, vapor pressure and relative humidity - with relative humidity being the most critical - are used by IREPS to predict the <span class="hlt">atmospheric</span> refractivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940017363','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940017363"><span id="translatedtitle">Physics of magnetospheric <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cairns, I. H.</p> <p>1993-01-01</p> <p>The central ideas of this grant are that the magnetospheric <span class="hlt">boundary</span> <span class="hlt">layers</span> link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its <span class="hlt">boundary</span> <span class="hlt">layers</span>. These <span class="hlt">boundary</span> <span class="hlt">layers</span> include the bow shock, magnetosheath, the plasma sheet <span class="hlt">boundary</span> <span class="hlt">layer</span>, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000117694','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000117694"><span id="translatedtitle">BOREAS AFM-6 <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Height Data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)</p> <p>2000-01-01</p> <p>The Boreal Ecosystem-<span class="hlt">Atmosphere</span> Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and <span class="hlt">Atmospheric</span> Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides <span class="hlt">boundary</span> <span class="hlt">layer</span> height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The <span class="hlt">boundary</span> <span class="hlt">layer</span> height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760024363','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760024363"><span id="translatedtitle">Turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> over nonstationary plane <span class="hlt">boundaries</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Roper, A. T.</p> <p>1976-01-01</p> <p>Methods of predicting integral parameters and skin-friction coefficients of turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> developing over moving-ground-planes are evaluated using test information from three different wind tunnel facilities at the NASA Langley Research Center. These data include test information from the VSTOL tunnel which is presented for the first time. The three methods evaluated were: (1) relative integral parameter method, (2) relative power law method, and (3) modified law of the wall method. Methods (1) and (2) can be used to predict moving-ground-plane shape factors with an expected accuracy of + or - 10%. They may also be used to predict moving-ground-plane displacement and momentum thicknesses with lower expected accuracy. This decrease in accuracy can be traced to the failure of approximations upon which these methods are based to prove universal when compared with VSTOL tunnel test results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JGRD..11511109V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JGRD..11511109V"><span id="translatedtitle">Persistent unstable <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> enhances sensible and latent heat loss in a tropical great lake: Lake Tanganyika</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Verburg, Piet; Antenucci, Jason P.</p> <p>2010-06-01</p> <p>Energy fluxes across the surface of lakes regulate heat storage and affect the water balance. Sensible and latent heat fluxes are affected by <span class="hlt">atmospheric</span> stability, especially for large lakes. We examined the effect of <span class="hlt">atmospheric</span> stability on the heat fluxes on seasonal time scales at Lake Tanganyika, East Africa, by estimating hourly sensible and latent heat fluxes and net radiation using thermistor chains and meteorological stations. The <span class="hlt">atmosphere</span> was almost always unstable, in contrast to the <span class="hlt">atmosphere</span> above North American Great Lakes which is unstable in winter and stable in summer. Persistent <span class="hlt">atmospheric</span> instability resulted in a 13% and 18% increase in the annual mean heat loss by latent and sensible heat fluxes, respectively, relative to conditions of neutral stability. The persistent unstable <span class="hlt">atmosphere</span> is caused by a higher water surface temperature compared with air temperature, which we argue is the case in general in (sub)tropical lakes. Low humidity further enhanced the frequency of unstable conditions and enhanced the exchange of heat and vapor from the lake to the <span class="hlt">atmosphere</span>. The estimated heat fluxes were sensitive to the temporal scale of data inputs and to the local values of parameters such as air density. To our knowledge this is the first paper that demonstrates and quantifies the effect of <span class="hlt">atmospheric</span> stability on latent and sensible heat fluxes from a lake on an annual basis, using data collected from the lake surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GMD.....8..453J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GMD.....8..453J"><span id="translatedtitle">Description and implementation of a MiXed <span class="hlt">Layer</span> model (MXL, v1.0) for the dynamics of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> in the Modular Earth Submodel System (MESSy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Janssen, R. H. H.; Pozzer, A.</p> <p>2015-03-01</p> <p>We present a new submodel for the Modular Earth Submodel System (MESSy): the MiXed <span class="hlt">Layer</span> (MXL) model for the diurnal dynamics of the convective <span class="hlt">boundary</span> <span class="hlt">layer</span>, including explicit representations of entrainment and surface fluxes. This submodel is embedded in a new MESSy base model (VERTICO), which represents a single <span class="hlt">atmospheric</span> column. With the implementation of MXL in MESSy, MXL can be used in combination with other MESSy submodels that represent processes related to <span class="hlt">atmospheric</span> chemistry. For instance, the coupling of MXL with more advanced modules for gas-phase chemistry (such as the Mainz Isoprene Mechanism 2 (MIM2)), emissions, dry deposition and organic aerosol formation than in previous versions of the MXL code is possible. Since MXL is now integrated in the MESSy framework, it can take advantage of future developments of this framework, such as the inclusion of new process submodels. The coupling of MXL with submodels that represent other processes relevant to chemistry in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) yields a computationally inexpensive tool that is ideally suited for the analysis of field data, for evaluating new parametrizations for 3-D models, and for performing systematic sensitivity analyses. A case study for the DOMINO campaign in southern Spain is shown to demonstrate the use and performance of MXL/MESSy in reproducing and analysing field observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.A31H3112H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.A31H3112H"><span id="translatedtitle">Ground-Based Cloud and <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Observations for the Project: High Definition Clouds and Precipitation for Advancing Climate Prediction, HD(CP)2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hirsikko, A.; Ebell, K.; Ulrich, U.; Schween, J. H.; Bohn, B.; Görsdorf, U.; Leinweber, R.; Päschke, E.; Baars, H.; Seifert, P.; Klein Baltink, H.</p> <p>2014-12-01</p> <p>The German research initiative ''High Definition Clouds and Precipitation for advancing Climate Prediction, HD(CP)2'' aims for an improved representation of clouds and precipitation in climate models. Model development and its evaluation require comprehensive observational datasets. A specific work package was established to create uniform and documented observational datasets for the HD(CP)2 data base. Datasets included ground-based remote-sensing (Doppler lidars, ceilometers, microwave radiometers, and cloud radars) and in-situ (meteorological and radiation sensors) measurements. Four supersites (Jülich ObservatorY for Cloud Evolution (JOYCE), Lindenberg Meteorological Observatory - Richard Assmann Observatory (RAO), and Leipzig Aerosol and Cloud Remote Observations System (LACROS) in Germany, and Cabauw experimental site for <span class="hlt">atmospheric</span> research (Cesar) in the Netherlands) are finalizing the operational procedures to provide quality controlled (and calibrated if possible) remote-sensing and in-situ observations, retrievals on <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> state (e.g. winds, mixing <span class="hlt">layer</span> height, humidity and temperature), and cloud macro and micro physical properties with uncertainty estimations or at least quality flags. During the project new processing and retrieval methods were developed if no commonly agreed or satisfying methods were available. Especially, large progress was made concerning uncertainty estimation and automated quality control. Additionally, the data from JOYCE are used in a radiative closure studies under cloudy conditions to evaluate retrievals of cloud properties. The current status of work progress will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100018561','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100018561"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layers</span>, Transitions and Separation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2010-01-01</p> <p>Effects of roughness in <span class="hlt">boundary</span> <span class="hlt">layers</span> have to be addressed. Until adverse pressure gradient effects are understood, roughness will not significantly drive design. Mechanisms responsible for separation not understood. Effects on Zero Pressure Gradient <span class="hlt">boundary</span> <span class="hlt">layers</span> (shear stress). Effects on separation in pressure gradient (prediction of separation). Effect on scalar transport (heat transfer) not understood. Model for skin friction needed in simulations - first grid point likely to be in buffer <span class="hlt">layer</span>. Definition of roughness important for useful experiments. A lot of validation experiments will be needed. How to get to ks for roughness of engineering interest? - depends on wavelength height, etc. for engineering interest? Re-discovering the wheel should be avoided: existing knowledge (theoretical and experimental) should find its way into the engineering models. It is a task of the industry to filter out the existing information in the literature for results relevant to its application, being external or internal.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011SPIE.8182E..10S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011SPIE.8182E..10S"><span id="translatedtitle">Experimental evaluation of a model for the influence of coherent wind lidars on their remote measurements of <span class="hlt">atmospheric</span> <span class="hlt">boundary-layer</span> turbulence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sjöholm, Mikael; Kapp, Stefan; Kristensen, Leif; Mikkelsen, Torben</p> <p>2011-11-01</p> <p>Affordable coherent wind lidars based on modern telecom components have recently emerged on the wind energy market spurred by high demand of the industry for compact and accurate remote sensing wind and turbulence profilers. Today, hundreds of ground based wind lidars that achieve the range resolution by either focusing a continuous-wave laser beam or by gating a pulsed laser beam are used for measuring mean wind and turbulence profiles in the lower <span class="hlt">atmospheric</span> <span class="hlt">boundary-layer</span>. However, detailed understanding of the influence of the spatial filtering of the lidars on their precise assessment of turbulence is still a challenge. For assessment of the fine structure turbulence, and in particular for the easy and fast assessment of the dissipation rate of turbulent kinetic energy from measurements in the Kolmogorov inertial subrange, we havemodeled the <span class="hlt">atmospheric</span> velocity structure functions and spectra obtainable from fixed-orientation along-beam wind measurements by these lidars. The dissipation rate retrieval model is experimentally evaluated with data obtained with a pulsed lidar pointing horizontally into horizontally homogeneous turbulence encountered at the top level of a 125 m tall meteorological tower, equipped with an in-situ turbulence measurement device (a three-dimensional sonic anemometer) for intercomparison. Our experimental study has revealed that the easily manageable analytical model accounts well for the observed fine structure turbulent spectra and their dependence on the pointing direction of the lidar beam relative to the mean wind direction. The results demonstrate that turbulence dissipation rates, and hence <span class="hlt">boundary-layer</span> turbulence, can easily be obtained from wind lidar-based fine structure measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25105753','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25105753"><span id="translatedtitle">Impact of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> depth variability and wind reversal on the diurnal variability of aerosol concentration at a valley site.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pal, S; Lee, T R; Phelps, S; De Wekker, S F J</p> <p>2014-10-15</p> <p>The development of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) plays a key role in affecting the variability of <span class="hlt">atmospheric</span> constituents such as aerosols, greenhouse gases, water vapor, and ozone. In general, the concentration of any tracers within the ABL varies due to the changes in the mixing volume (i.e. ABL depth). In this study, we investigate the impact on the near-surface aerosol concentration in a valley site of 1) the <span class="hlt">boundary</span> <span class="hlt">layer</span> dilution due to vertical mixing and 2) changes in the wind patterns. We use a data set obtained during a 10-day field campaign in which a number of remote sensing and in-situ instruments were deployed, including a ground-based aerosol lidar system for monitoring of the ABL top height (zi), a particle counter to determine the number concentration of aerosol particles at eight different size ranges, and tower-based standard meteorological instruments. Results show a clearly visible decreasing trend of the mean daytime zi from 2900 m AGL (above ground level) to 2200 m AGL during a three-day period which resulted in increased near-surface pollutant concentrations. An inverse relationship exists between the zi and the fine fraction (0.3-0.7 μm) accumulation mode particles (AMP) on some days due to the dilution effect in a well-mixed ABL. These days are characterized by the absence of daytime upvalley winds and the presence of northwesterly synoptic-driven winds. In contrast, on the days with an onset of an upvalley wind circulation after the morning transition, the wind-driven local transport mechanism outweighs the ABL-dilution effect in determining the variability of AMP concentration. The interplay between the ABL depth evolution and the onset of the upvalley wind during the morning transition period significantly governs the air quality in a valley and could be an important component in the studies of mountain meteorology and air quality. PMID:25105753</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.6375K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.6375K&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Atmospheric</span> conditions and transport patterns associated with high and low summer ozone levels in the lower troposphere and the <span class="hlt">boundary</span> <span class="hlt">layer</span> over the eastern Mediterranean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalabokas, Pavlos; Cammas, Jean-Pierre; Thouret, Valerie; Volz-Thomas, Andreas; Boulanger, Damien; Repapis, Christos</p> <p>2016-04-01</p> <p> <span class="hlt">layer</span>, there are extended regions of strong subsidence in the eastern Mediterranean but also in eastern and northern Europe and over these regions the <span class="hlt">atmosphere</span> is dryer than average. The results of this study will be used within the framework of the MACC project. References Kalabokas, P. D., Cammas, J.-P., Thouret, V., Volz-Thomas, A., Boulanger, D. and Repapis C.C. 2013. Examination of the <span class="hlt">atmospheric</span> conditions associated with high and low summer ozone levels in the lower troposphere over the eastern Mediterranean. Atmos. Chem. Phys. 13, 10339-10352. DOI: http://dx.doi.org/10.5194/acp-13-10339-2013 Kalabokas P. D., Thouret V., Cammas J.-P., Volz-thomas A., Boulanger D., Repapis C.C., 2015. The geographical distribution of meteorological parameters associated with high and low summer ozone levels in the lower troposphere and the <span class="hlt">boundary</span> <span class="hlt">layer</span> over the eastern Mediterranean (Cairo case), Tellus B, 67, 27853, http://dx.doi.org/10.3402/tellusb.v67.27853.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890011582','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890011582"><span id="translatedtitle">Stability of compressible <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nayfeh, Ali H.</p> <p>1989-01-01</p> <p>The stability of compressible 2-D and 3-D <span class="hlt">boundary</span> <span class="hlt">layers</span> is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar <span class="hlt">boundary</span> <span class="hlt">layers</span> and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3695G&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3695G&link_type=ABSTRACT"><span id="translatedtitle">Modeling the feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> during a severe fog-haze event over the North China Plain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gao, Yi; Zhang, Meigen; Liu, Zirui; Wang, Lili; Wang, Pucai; Xia, Xiangao; Tao, Minghui; Zhu, Lingyun</p> <p>2016-04-01</p> <p>The feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over the North China Plain (NCP) is analyzed by conducting numerical experiments with and without the aerosol direct and indirect effects via a coupled meteorology and aerosol/chemistry model(WRF-Chem). The numerical experiments are performed for the period of 2-26 January 2013, during which a severe fog-haze event (10-15 January 2013) occurred, with the simulated maximum hourly surface PM2.5 concentration of ~600 μg m-3, minimum <span class="hlt">atmospheric</span> visibility of ~0.3 km, and 10-100 hours of simulated hourly surface PM2.5 concentration above 300 μg m-3 over NCP. A comparison of model results with aerosol feedback against observations indicates that the model can reproduce the spatial and temporal characteristics of temperature, relative humidity (RH), wind, surface PM2.5 concentration, <span class="hlt">atmospheric</span> visibility, and aerosol optical depth reasonably well. Analysis of model results with and without aerosol feedback shows that during the fog-haze event aerosols lead to a significant negative radiative forcing of ~20 to ~140 W m-2 at the surface and a large positive radiative forcing of 20-120 W m-2 in the <span class="hlt">atmosphere</span> and induce significant changes in meteorological variables with maximum changes during 09:00-18:00 local time (LT) over urban Beijing and Tianjin and south Hebei: the temperature decreases by 0.8-2.8 °C at the surface and increases by 0.1-0.5 °C at around 925 hPa, while RH increases by about 4-12% at the surface and decreases by 1-6% at around 925 hPa. As a result, the aerosol-induced equivalent potential temperature profile change shows that the <span class="hlt">atmosphere</span> is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10 %) and the <span class="hlt">atmosphere</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> height decreases by 40-200 m (5-30 %) during the daytime of this severe fog-haze event. Owing to this more stable <span class="hlt">atmosphere</span> during 09:00-18:00, 10-15 January, compared to the surface PM2</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015ACP....15.4279G&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015ACP....15.4279G&link_type=ABSTRACT"><span id="translatedtitle">Modeling the feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> during a severe fog-haze event over the North China Plain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gao, Y.; Zhang, M.; Liu, Z.; Wang, L.; Wang, P.; Xia, X.; Tao, M.; Zhu, L.</p> <p>2015-04-01</p> <p>The feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over the North China Plain (NCP) is analyzed by conducting numerical experiments with and without the aerosol direct and indirect effects via a coupled meteorology and aerosol/chemistry model (WRF-Chem). The numerical experiments are performed for the period of 2-26 January 2013, during which a severe fog-haze event (10-15 January 2013) occurred, with the simulated maximum hourly surface PM2.5 concentration of ~600 ug m-3, minimum <span class="hlt">atmospheric</span> visibility of ~0.3 km, and 10-100 hours of simulated hourly surface PM2.5 concentration above 300 ug m-3 over NCP. A comparison of model results with aerosol feedback against observations indicates that the model can reproduce the spatial and temporal characteristics of temperature, relative humidity (RH), wind, surface PM2.5 concentration, <span class="hlt">atmospheric</span> visibility, and aerosol optical depth reasonably well. Analysis of model results with and without aerosol feedback shows that during the fog-haze event aerosols lead to a significant negative radiative forcing of -20 to -140 W m-2 at the surface and a large positive radiative forcing of 20-120 W m-2 in the <span class="hlt">atmosphere</span> and induce significant changes in meteorological variables with maximum changes during 09:00-18:00 local time (LT) over urban Beijing and Tianjin and south Hebei: the temperature decreases by 0.8-2.8 °C at the surface and increases by 0.1-0.5 °C at around 925 hPa, while RH increases by about 4-12% at the surface and decreases by 1-6% at around 925 hPa. As a result, the aerosol-induced equivalent potential temperature profile change shows that the <span class="hlt">atmosphere</span> is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10%) and the <span class="hlt">atmosphere</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> height decreases by 40-200 m (5-30%) during the daytime of this severe fog-haze event. Owing to this more stable <span class="hlt">atmosphere</span> during 09:00-18:00, 10-15~January, compared to the surface PM2</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015P%26SS..111..116N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015P%26SS..111..116N"><span id="translatedtitle">Jupiter's deep magnetotail <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.</p> <p>2015-06-01</p> <p>In 2007 the New Horizons (NH) spacecraft flew by Jupiter for a gravity assist en route to Pluto. After closest approach on day of year (DOY) 58, 2007, NH followed a tailward trajectory that provided a unique opportunity to explore the deep jovian magnetotail and the surrounding magnetosheath. After DOY 132, 16 magnetopause crossings were observed between 1654 and 2429 Jupiter radii (Rj) along the dusk flank tailward of the planet. In some cases the crossings were identified as rapid transitions from the magnetotail to the magnetosheath and vice versa. In other cases a <span class="hlt">boundary</span> <span class="hlt">layer</span> was observed just inside the magnetopause. Solar Wind Around Pluto (SWAP) is an instrument on board NH that obtained spectra of low energy ions during the flyby period. We use a forward model including the SWAP instrument response to derive plasma parameters (density, temperature and velocity) which best reproduce the observations. We also vary the plasma parameters in our model in order to fit the observations more accurately on occasions where the measurements exhibit significant variability. We compare the properties of the plasma in the <span class="hlt">boundary</span> <span class="hlt">layer</span> with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the <span class="hlt">boundary</span> <span class="hlt">layer</span> assuming pressure balance between it and the magnetosheath. Finally, we investigate several possible scenarios to assess if magnetopause movement and structure could cause the variations seen in the data.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015EGUGA..17.7701P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015EGUGA..17.7701P&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Atmosphere</span>-Ice-Ocean Interactions During Early Autumn Freeze-up: <span class="hlt">Boundary-Layer</span> and Surface Observations from the ACSE Field Program</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Persson, Ola; Brooks, Barbara; Tjernström, Michael; Sedlar, Joseph; Brooks, Ian; Shupe, Matthew; Björck, Göran; Prytherch, John; Salisbury, Dominic; Achtert, Peggy; Sotiropoulou, Georgia; Johnston, Paul; Wolfe, Daniel</p> <p>2015-04-01</p> <p>Surface energy fluxes are key to the annual summer melt and autumn freeze-up of Arctic sea ice, but are strongly modulated by <span class="hlt">atmospheric</span>, ocean, and sea-ice processes. This paper will examine direct observations of energy fluxes during the onset of autumn freeze-up from the Arctic Clouds in Summer Experiment (ACSE), and place them in context of those from other observational campaigns. The ACSE field program obtained measurements of surface energy fluxes, <span class="hlt">boundary-layer</span> structure, cloud macro- and microphysical structure, and upper-ocean thermal and salinity structure from pack-ice and open-water regions in the eastern Arctic from early July to early October 2014. Late August and September measurements showed periods of energy flux deficits, leading to freeze-up of sea ice and the ocean surface. The surface albedo and processes impacting the energy content of the upper ocean appear key to producing a temporal difference between the freeze-up of the sea ice and adjacent open water. While synoptic conditions, <span class="hlt">atmospheric</span> advection, and the annual solar cycle have primary influence determining when energy fluxes are conducive for melt or freeze, mesoscale <span class="hlt">atmospheric</span> phenomena unique to the ice edge region appear to also play a role. For instance, low-level jets were often observed near the ice edge during the latter part of ACSE, and may have enhanced the turbulent energy loss. In conjunction with observations of summer melt, these observations of the onset of freeze-up suggest scenarios of key <span class="hlt">atmospheric</span> processes, including thermal advection on various scales, that are important for the annual evolution of melt and freeze-up.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940019668','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940019668"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> receptivity and control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hill, D. C.</p> <p>1993-01-01</p> <p>Receptivity processes initiate natural instabilities in a <span class="hlt">boundary</span> <span class="hlt">layer</span>. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel <span class="hlt">boundary</span> <span class="hlt">layer</span> is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius <span class="hlt">boundary</span> <span class="hlt">layer</span> responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1036067','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1036067"><span id="translatedtitle">Large Amplitude Spatial and Temporal Gradients in <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> CO2 Mole Fractions Detected With a Tower-Based Network in the U.S. Upper Midwest</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Miles, Natasha; Richardson, S. J.; Davis, Kenneth J.; Lauvaux, Thomas; Andrews, A.; West, Tristram O.; Bandaru, Varaprasad; Crosson, Eric R.</p> <p>2012-02-21</p> <p>This study presents observations of <span class="hlt">atmospheric</span> CO{sub 2} mole fraction from a nine-tower, regional network deployed during the North American Carbon Program's Mid-Continent Intensive during 2007-2009. Within this network in a largely agricultural area, mean <span class="hlt">atmospheric</span> CO{sub 2} gradients were strongly correlated with both ground-based inventory data and estimates from satellite remote sensing. The average seasonal drawdown for corn-dominated sites (35 ppm) is significantly larger than has been observed at other continental <span class="hlt">boundary</span> <span class="hlt">layer</span> sites. Observed growing-season median CO{sub 2} gradients are strongly dependent on local flux. The gradients between cross-vegetation site-pairs, for example, average 2.0 ppm/100 km, four times larger than the similar-vegetation site-pair average. Daily-timescale gradients are as large as 5.5 ppm/100 km, but dominated by advection rather than local flux. Flooding in 2008 led to a region-wide 23 week delay in growing-season minima. The observations show that regional-scale CO{sub 2} mole fraction networks yield large, coherent signals governed largely by regional sources and sinks of CO{sub 2}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3397S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.3397S&link_type=ABSTRACT"><span id="translatedtitle">The distribution of <span class="hlt">atmospheric</span> black carbon in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> over the North Atlantic and the Russian Arctic Seas in July - October 2015</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shevchenko, Vladimir P.; Kopeikin, Vladimir M.; Evangeliou, Nikolaos; Novigatsky, Alexander N.; Pankratova, Natalia V.; Starodymova, Dina P.; Stohl, Andreas; Thompson, Rona</p> <p>2016-04-01</p> <p>Black carbon (BC) particles are highly efficient at absorbing visible light, which has a large potential impact on Arctic climate. However, measurement data on the distribution of BC in the <span class="hlt">atmosphere</span> over the North Atlantic and the Russian Arctic Seas are scarce. We present measurement data on the distribution of <span class="hlt">atmospheric</span> BC in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> of the North Atlantic and Baltic, North, Norwegian, Barents, White, Kara and Laptev Seas from research cruises during July 23 to October 6, 2015. During the 62nd and 63rd cruises of the RV "Akademik Mstislav Keldysh" air was filtered through Hahnemuhle fineart quarz-microfibre filters. The mass of BC on the filter was determined by measurement of the attenuation of a beam of light transmitted through the filter. Source areas were estimated by backwards trajectories of air masses calculated using NOAA's HYSPLIT model (http://www.arl.noaa.gov/ready.html) and FLEXPART model (http://www.flexpart.eu). During some parts of the cruises, air masses arrived from background areas of high latitudes, and the measured BC concentrations were low. During other parts of the cruise, air masses arrived from industrially developed areas with strong BC sources, and this led to substantially enhanced measured BC concentrations. Model-supported analyses are currently performed to use the measurement data for constraining the emission strength in these areas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015ACPD...15.1093G&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015ACPD...15.1093G&link_type=ABSTRACT"><span id="translatedtitle">Modeling the feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> during a severe fog-haze event over the North China Plain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gao, Y.; Zhang, M.; Liu, Z.; Wang, L.; Wang, P.; Xia, X.; Tao, M.</p> <p>2015-01-01</p> <p>The feedback between aerosol and meteorological variables in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> over the North China Plain is analyzed by conducting numerical experiments with and without the aerosol direct and indirect effects via a coupled meteorology and aerosol/chemistry model (WRF-Chem). The numerical experiments are performed for the period 2-26 January 2013, during which a severe fog-haze event (10-15 January 2013) occurred. Comparison of the model results with aerosol feedback against observations indicates that the model can reproduce the spatial and temporal characteristics of temperature, relative humidity (RH), wind, surface PM2.5 concentration, <span class="hlt">atmospheric</span> visibility, and aerosol optical depth. Comparison of modeling results in the presence and absence of aerosol feedback during the fog-haze event shows that aerosols lead to a significant negative radiative forcing of -20 to -140 W m-2 at the surface and a large positive radiative forcing of 20-120 W m-2 in the <span class="hlt">atmosphere</span> and induce significant changes in meteorological variables of which the maximum changes occur during 09:00-18:00 LT over urban Beijing and Tianjin, and south Hebei Province: the temperature decreases by 0.8-2.8 °C at the surface and increases by 0.1-0.5 °C at around 925 hPa while the RH increases by about 4-12% at the surface and decreases by 1-6% at around 925 hPa. As a result, the aerosol-induced equivalent potential temperature profile change shows that the <span class="hlt">atmosphere</span> is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10%) and the <span class="hlt">atmosphere</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> height decreases by 40-200 m (5-30%) during the daytime of this severe fog-haze event. Owing to this more stable <span class="hlt">atmosphere</span>, during 09:00-18:00, 10-15 January, compared to the surface PM2.5 concentration from the model results without aerosol feedback, the average surface PM2.5 concentration increases by 10-50 μg m-3 (2-30%) over Beijing, Tianjin, and south Hebei province and the maximum increase of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19790059404&hterms=boundary+descriptions&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dboundary%2Bdescriptions','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19790059404&hterms=boundary+descriptions&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dboundary%2Bdescriptions"><span id="translatedtitle">The entraining moist <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Randall, D. A.</p> <p>1978-01-01</p> <p>A unified theory of entrainment into the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> is presented. It is assumed that the rates of buoyant and shear production of turbulence kinetic energy can be determined in terms of the entrainment mass flux. An expression is derived from the conservation law for turbulence kinetic energy, which, with the introduction of an empirical parameter, can be used together with a second relation between turbulence kinetic energy and the turbulence velocity scale to obtain the mass entrainment flux. The theory provides descriptions of storage-limited entrainment, buoyancy-limited entrainment into a clear mixed <span class="hlt">layer</span>, and shallowing. It has been incorporated into a simulation of Day 33 of the Wangara experiment using a simple mixed <span class="hlt">layer</span> model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/885125','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/885125"><span id="translatedtitle">Consequences of the Large-Scale Subsidence Rate on the Stably Stratified <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Over the Arctic Ocean, as seen in Large-Eddy Simulations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mirocha, J D; Kosovic, B</p> <p>2006-01-19</p> <p>The analysis of surface heat fluxes and sounding profiles from SHEBA indicated possible significant effects of subsidence on the structure of stably-stratified ABLs (Mirocha et al. 2005). In this study the influence of the large-scale subsidence rate on the stably stratified <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) over the Arctic Ocean during clear sky, winter conditions is investigated using a large-eddy simulation model. Simulations are conducted while varying the subsidence rate between 0, 0.001 and 0.002 ms{sup -1}, and the resulting quasi-equilibrium ABL structure and evolution are examined. Simulations conducted without subsidence yield ABLs that are deeper, more strongly mixed, and cool much more rapidly than were observed. The addition of a small subsidence rate significantly improves agreement between the simulations and observations regarding the ABL height, potential temperature profiles and bulk heating rates. Subsidence likewise alters the shapes of the surface-<span class="hlt">layer</span> flux, stress and shear profiles, resulting in increased vertical transport of heat while decreasing vertical momentum transport. A brief discussion of the relevance of these results to parameterization of the stable ABL under subsiding conditions in large-scale numerical weather and climate prediction models is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009ems..confE..64B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009ems..confE..64B"><span id="translatedtitle">Measuring Vertical Profiles of Wind, Temperature and Humidity within the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> using the Research UAVs 'M2AV Carolo'</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bange, J.; Martin, S.</p> <p>2009-09-01</p> <p>The measurement of vertical profiles is important to characterise the vertical structure of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL). For instance, the dependence of the potential temperature on altitude defines the thermal stratification. The mechanical shear (i.e. the variation of wind speed and direction) produces turbulence and turbulent fluxes. The top of the ABL is required for scaling approaches (e.g. Deardorff scaling in the convective <span class="hlt">boundary</span> <span class="hlt">layer</span>, local scaling in the stable <span class="hlt">boundary</span> <span class="hlt">layer</span>). The Meteorological Mini Aerial Vehicles (M²AV) are self-constructed, automatically operating research aircraft of 6 kg in weight (including 1.5 kg scientific payload) and 2 m wingspan. These systems are capable of performing turbulence measurements (wind vector, temperature and humidity) and are used as a new instrument for measuring vertical profiles of the lower troposphere. Compared to a radiosonde, the spatial resolution of the M²AV is significantly higher. Especially the wind measurement is significantly more accurate compared to radiosonde data when using an aircraft that is equipped with a proper flow sensor (mainly a five-hole probe). It is important to maintain flow angles (sideslip and angle of attack) within the calibration range (typically 10 to 20 degree). This limits the vertical speed (the rate of climb and descent) of the research aircraft. In general there are two approaches to measure vertical profiles with research aircraft. Instantaneous profiles (slant flight pattern) are suitable if only little time is available, if the ABL is very in-stationary (or the aircraft is slow), if the dependence of the profile on time is requested (repeated slant flight patterns over one location) or if the dependence of the profile on the location is requested (saw-tooth pattern). For mean profiles (horizontal straight and level flights 'legs' at several altitudes within the ABL) it is necessary to use fast sensors. If the response time is too large, the vertical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.A43C0319W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.A43C0319W"><span id="translatedtitle">Using satellite and in-situ observations to evaluate short-term forecasts of cloud-topped <span class="hlt">boundary</span> <span class="hlt">layers</span> with the Community <span class="hlt">Atmospheric</span> Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williamson, D.; Hannay, C.; Olson, J.; Bretherton, C.; Park, S.; Koehler, M.</p> <p>2008-12-01</p> <p>The South East Pacific (SEP) has the most persistent stratocumulus deck in the world. Until recently, only sparse observations of the SEP were available. In the last few years, new satellite observations, research cruise data and buoy measurements have become available and give new prospects to improve our understanding and modeling of <span class="hlt">boundary</span> <span class="hlt">layer</span> clouds over the SEP. Stratocumulus are among the worst-simulated tropical clouds in climate models. However, it is difficult to take advantage of in-situ observations to understand the causes of the stratocumulus bias in climate simulations because limited observation periods are difficult to compare with model climatological statistics. Applying climate model in short-term forecasts can be extremely valuable to evaluate parameterizations against a limited-period observation. If the model is started from realistic conditions, the systematic errors in short forecasts are predominantly due to parameterization errors. This is because the large-scale circulation stays close to the observed state in these short-range runs. Therefore, it is possible to gain insight into the parameterization deficiencies and to diagnose the processes behind the drift away from reality. Here we evaluate short-term forecasts of the SEP with the Community <span class="hlt">Atmospheric</span> Model (CAM) against a set of satellite and in-situ observations. The forecasts are analyzed from ECWMF analysis. The simulated period is October 2006, which corresponds to the SEP stratocumulus maximum. The set of observations was gathered for the Pre-VOCALS Model assessment* and includes a week of in-situ data (sounding, ship remote sensing and aerosols) and satellite observations (GOES, MODIS, ISCCP, AMSR-E, SSMI, Quikscat, CloudSat, CALIPSO, AIRS and COSMIC/GPS) We use this testbed to examine the forecast errors in CAM3 and to assess new parameterizations for the next generation model, CAM4. In particular, we evaluate the performance of a new moist turbulence/shallow cumulus</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AtmEn..63..261P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AtmEn..63..261P"><span id="translatedtitle">Spatio-temporal variability of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> depth over the Paris agglomeration: An assessment of the impact of the urban heat island intensity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pal, S.; Xueref-Remy, I.; Ammoura, L.; Chazette, P.; Gibert, F.; Royer, P.; Dieudonné, E.; Dupont, J.-C.; Haeffelin, M.; Lac, C.; Lopez, M.; Morille, Y.; Ravetta, F.</p> <p>2012-12-01</p> <p>Within the framework of a French nationally funded project (CO2-MEGAPARIS) for quantifying the CO2 emissions of the Paris area, a lidar-based experimental investigation of the variability of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) depths was performed over four days in March 2011 under clear sky conditions. The prevailing synoptic settings were mainly characterized by anti-cyclonic situations with low wind. The key aim of this paper is to assess the impact of the urban heat island intensity (UHII) on the spatio-temporal variability of the ABL depths over the Paris megacity. A network of fixed aerosol lidars was deployed inside the city and in the vicinity of sub-urban and rural areas. Additionally, the spatial heterogeneity of the nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span> (NBL) depths over greater Paris area is addressed, thanks in particular, to the deployment of a 355-nm elastic lidar in a mobile van to measure the aerosol distributions. Radiosonde-derived profiles (twice a day) of thermodynamic variables over the sub-urban site helped investigate the temperature inversion above ground and hence to compare the lidar-derived ABL depths. Comparing these two results, an excellent concordance was found with a correlation coefficient of 0.994. Five important factors closely related to the ABL circulation, namely, spatio-temporal variability of the ABL depths, growth rate of the ABL depths, entrainment zone thickness, and near-surface temperature fields including resultant UHII were considered to infer the urban-rural contrasts. The mean NBL depth over the urban area was on average 63 m (45%) higher than its adjacent sub-urban area which was, on occasion, as much as (74 m) 58% higher mainly due to the effect of UHII. Daytime well-mixed convective <span class="hlt">boundary</span> <span class="hlt">layer</span> and associated strong turbulent mixing near its top over the urban area showed higher entrainment zone thickness (326 m) than over sub-urban (234 m) and rural (200 m) areas. Temperature growth rates during sunrise increased up to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AtmEn..44.1815X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AtmEn..44.1815X"><span id="translatedtitle"><span class="hlt">Atmospheric</span> mercury in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> along a cruise path from Shanghai, China to Prydz Bay, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xia, Chonghuan; Xie, Zhouqing; Sun, Liguang</p> <p>2010-05-01</p> <p>The total gaseous mercury (TGM) measurements were performed using an automatic Mercury Vapor Analyze (model 2537B) aboard the Chinese research vessel (R/V) XueLong during the 24th China Antarctic Research Expedition from Shanghai, China to Prydz Bay, Antarctica in 2007. TGM ranged between 0.302 and 4.496 ng m -3 with an average of 1.536 ± 0.785 ng m -3 over the entire period. Geographically, TGM in the Northern Hemisphere and the Southern Hemisphere along the cruise path were 1.746 ± 0.513 and 1.471 ± 0.842 ng m -3 in average, respectively. Higher TGM concentrations were observed in the coastal regions outside the polar region due primarily to air masses transported from the adjacent mainland reflecting the contribution from anthropogenic sources. The pronounced episode was recorded when ship passed through Sunda straits, which should be ascribed to the volcano plume and/or biomass burning contamination. In the maritime Antarctic TGM level was in agreement with the values by land-based observation, presenting a diurnal cycle with the maximum around midday and minimum at night. <span class="hlt">Atmospheric</span> mercury destruction events dominated by the oxidation of <span class="hlt">atmospheric</span> Hg 0 were apparently observed in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10155459','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10155459"><span id="translatedtitle">Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.</p> <p>1993-03-01</p> <p>A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through <span class="hlt">atmospheric</span> depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating <span class="hlt">atmospheric</span> radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform`s operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6473490','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6473490"><span id="translatedtitle">Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.</p> <p>1993-03-01</p> <p>A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through <span class="hlt">atmospheric</span> depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating <span class="hlt">atmospheric</span> radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform's operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, rather than ascending in discrete steps with halts at set altitudes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15504507','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15504507"><span id="translatedtitle">The <span class="hlt">boundary</span> <span class="hlt">layer</span> growth in an urban area.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pino, D; Vilà-Guerau de Arellano, J; Comerón, A; Rocadenbosch, F</p> <p>2004-12-01</p> <p>The development and maintenance of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) plays a key role in the distribution of <span class="hlt">atmospheric</span> constituents, especially in a polluted urban area. In particular, the ABL has a direct impact on the concentration and transformation of pollutants. In this work, in order to analyze the different mechanisms which control the <span class="hlt">boundary</span> <span class="hlt">layer</span> growth, we have simulated by means of the non-hydrostatic model MM5 several <span class="hlt">boundary</span> <span class="hlt">layer</span> observed in the city of Barcelona (Spain). Sensitivity analysis of the modelled ABL is carried out by using various descriptions of the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL). Direct and continuous measurements of the <span class="hlt">boundary</span> <span class="hlt">layer</span> depth taken by a lidar are used to evaluate the results obtained by the model. PMID:15504507</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JGRD..114.5303M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JGRD..114.5303M"><span id="translatedtitle">Comprehensive isotopic composition of <span class="hlt">atmospheric</span> nitrate in the Atlantic Ocean <span class="hlt">boundary</span> <span class="hlt">layer</span> from 65°S to 79°N</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morin, S.; Savarino, J.; Frey, M. M.; Domine, F.; Jacobi, H.-W.; Kaleschke, L.; Martins, J. M. F.</p> <p>2009-03-01</p> <p>The comprehensive isotopic composition of <span class="hlt">atmospheric</span> nitrate (i.e., the simultaneous measurement of all its stable isotope ratios: 15N/14N, 17O/16O and 18O/16O) has been determined for aerosol samples collected in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> (MBL) over the Atlantic Ocean from 65°S (Weddell Sea) to 79°N (Svalbard), along a ship-borne latitudinal transect. In nonpolar areas, the δ15N of nitrate mostly deriving from anthropogenically emitted NOx is found to be significantly different (from 0 to 6‰) from nitrate sampled in locations influenced by natural NOx sources (-4 ± 2)‰. The effects on δ15N(NO3-) of different NOx sources and nitrate removal processes associated with its <span class="hlt">atmospheric</span> transport are discussed. Measurements of the oxygen isotope anomaly (Δ17O = δ17O - 0.52 × δ18O) of nitrate suggest that nocturnal processes involving the nitrate radical play a major role in terms of NOx sinks. Different Δ17O between aerosol size fractions indicate different proportions between nitrate formation pathways as a function of the size and composition of the particles. Extremely low δ15N values (down to -40‰) are found in air masses exposed to snow-covered areas, showing that snowpack emissions of NOx from upwind regions can have a significant impact on the local surface budget of reactive nitrogen, in conjunction with interactions with active halogen chemistry. The implications of the results are discussed in light of the potential use of the stable isotopic composition of nitrate to infer <span class="hlt">atmospherically</span> relevant information from nitrate preserved in ice cores.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ClDy...46.2179X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ClDy...46.2179X"><span id="translatedtitle">A case study of effects of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence, wind speed, and stability on wind farm induced temperature changes using observations from a field campaign</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xia, Geng; Zhou, Liming; Freedman, Jeffrey M.; Roy, Somnath Baidya; Harris, Ronald A.; Cervarich, Matthew Charles</p> <p>2016-04-01</p> <p>Recent studies using satellite observations show that operational wind farms in west-central Texas increase local nighttime land surface temperature (LST) by 0.31-0.70 °C, but no noticeable impact is detected during daytime, and that the diurnal and seasonal variations in the magnitude of this warming are likely determined by those in the magnitude of wind speed. This paper further explores these findings by using the data from a year-long field campaign and nearby radiosonde observations to investigate how thermodynamic profiles and surface-<span class="hlt">atmosphere</span> exchange processes work in tandem with the presence of wind farms to affect the local climate. Combined with satellite data analyses, we find that wind farm impacts on LST are predominantly determined by the relative ratio of turbulence kinetic energy (TKE) induced by the wind turbines compared to the background TKE. This ratio explains not only the day-night contrast of the wind farm impact and the warming magnitude of nighttime LST over the wind farms, but also most of the seasonal variations in the nighttime LST changes. These results indicate that the diurnal and seasonal variations in the turbine-induced turbulence relative to the background TKE play an essential role in determining those in the magnitude of LST changes over the wind farms. In addition, <span class="hlt">atmospheric</span> stability determines the sign and strength of the net downward heat transport as well as the magnitude of the background TKE. The study highlights the need for better understanding of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and wind farm interactions, and for better parameterizations of sub-grid scale turbulent mixing in numerical weather prediction and climate models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ClDy...46.1699P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ClDy...46.1699P"><span id="translatedtitle">Influence of small-scale North Atlantic sea surface temperature patterns on the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> and free troposphere: a study using the <span class="hlt">atmospheric</span> ARPEGE model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Piazza, Marie; Terray, Laurent; Boé, Julien; Maisonnave, Eric; Sanchez-Gomez, Emilia</p> <p>2016-03-01</p> <p>A high-resolution global <span class="hlt">atmospheric</span> model is used to investigate the influence of the representation of small-scale North Atlantic sea surface temperature (SST) patterns on the <span class="hlt">atmosphere</span> during boreal winter. Two ensembles of forced simulations are performed and compared. In the first ensemble (HRES), the full spatial resolution of the SST is maintained while small-scale features are smoothed out in the Gulf Stream region for the second ensemble (SMTH). The model shows a reasonable climatology in term of large-scale circulation and air-sea interaction coefficient when compared to reanalyses and satellite observations, respectively. The impact of small-scale SST patterns as depicted by differences between HRES and SMTH shows a strong meso-scale local mean response in terms of surface heat fluxes, convective precipitation, and to a lesser extent cloudiness. The main mechanism behind these statistical differences is that of a simple hydrostatic pressure adjustment related to increased SST and marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> temperature gradient along the North Atlantic SST front. The model response to small-scale SST patterns also includes remote large-scale effects: upper tropospheric winds show a decrease downstream of the eddy-driven jet maxima over the central North Atlantic, while the subtropical jet exhibits a significant northward shift in particular over the eastern Mediterranean region. Significant changes are simulated in regard to the North Atlantic storm track, such as a southward shift of the storm density off the coast of North America towards the maximum SST gradient. A storm density decrease is also depicted over Greenland and the Nordic seas while a significant increase is seen over the northern part of the Mediterranean basin. Changes in Rossby wave breaking frequencies and weather regimes spatial patterns are shown to be associated to the jets and storm track changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.5966S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.5966S"><span id="translatedtitle">The distribution of <span class="hlt">atmospheric</span> black carbon in marine <span class="hlt">boundary</span> <span class="hlt">layer</span> over the seas of the western part of the Russian Arctic in September - October 2011</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shevchenko, V. P.; Novigatsky, A. N.; Kopeikin, V. M.; Starodymova, D. P.</p> <p>2012-04-01</p> <p>Black carbon (BC) is the most efficient <span class="hlt">atmospheric</span> particulate species at absorbing visible light, it could have the large potential impact on Arctic climate. The data on the distribution of the BC in <span class="hlt">atmosphere</span> over the seas of the Russian Arctic are scarce. New data are presented in this work. The distribution of black carbon in the <span class="hlt">atmosphere</span> in marine <span class="hlt">boundary</span> <span class="hlt">layer</span> in the White, Barents and Kara seas has been measured from September 12 to October 7, 2011 during the 59-th cruise of the RV "Akademik Mstislav Keldysh". The method of aethalometry was used. Backwards trajectories of air masses were calculated using NOAA HYSPLIT model (http://www.arl.noaa.gov/ready.html). The highest values of BC concentrations were recorded near port of Arkhangelsk (600-830 ng/cub.m). In the background areas the BC concentrations varied from 10 to 470 ng/cub.m (120 ng/cub.m in average, standard deviation is 110 ng/cub.m, n=45 measurements). These values are at the level of background values for the Russian Arctic seas. The lowest values were recorded after rains and when air masses came from the Central Arctic. Relatively high BC concentrations in the Kara Sea were in air massed arrived from the NW Siberia and in the Barents Sea in air masses arrived from the Arkhangelsk industrial area. Our studies were supported by the Department of the Earth Sciences of the Russian Academy of Sciences (project "Nanoparticles"), Russian-German Otto Schmidt Laboratory and grant NSh-3714.2010.5. The authors are indebted to crew of the RV "Akademik Mstislav Keldysh" for help in the expedition and to Academician A.P. Lisitzin for valuable recommendations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BoLMe.tmp...27S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BoLMe.tmp...27S"><span id="translatedtitle">Quantitative Interpretation of Air Radon Progeny Fluctuations in Terms of Stability Conditions in the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salzano, Roberto; Pasini, Antonello; Casasanta, Giampietro; Cacciani, Marco; Perrino, Cinzia</p> <p>2016-03-01</p> <p>Determining the mixing height using a tracer can improve the information obtained using traditional techniques. Here we provide an improved box model based on radon progeny measurements, which considers the vertical entrainment of residual <span class="hlt">layers</span> and the variability in the soil radon exhalation rate. The potential issues in using progeny instead of radon have been solved from both a theoretical and experimental perspective; furthermore, the instrumental efficiency and the counting scheme have been included in the model. The applicability range of the box model has been defined by comparing radon-derived estimates with sodar and lidar data. Three intervals have been analyzed ("near-stable", "transition" and "turbulent"), and different processes have been characterized. We describe a preliminary application case performed in Rome, Italy, while case studies will be required to determine the range limits that can be applied in any circumstances.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JMetR..29..747M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JMetR..29..747M"><span id="translatedtitle">Characteristics and mechanisms of the sudden warming events in the nocturnal <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>: A case study using WRF</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Yuanyuan; Yang, Yi; Hu, Xiao-Ming; Gan, Ruhui</p> <p>2015-10-01</p> <p>Although sudden nocturnal warming events near the earth's surface in Australia and the United States have been examined in previous studies, similar events observed occasionally over the Loess Plateau of Northwest China have not yet been investigated. The factors that lead to these warming events in such areas with their unique topography and climate remain not clear. To understand the formation mechanisms and associated thermal and dynamical features, a nocturnal warming event recorded in Gansu Province (northwest of the Loess Plateau) in June 2007 was investigated by using observations and model simulations with the Weather Research and Forecasting (WRF) model. Observations showed that this near-surface warming event lasted for 4 h and the temperature increased by 2.5°C. During this event, a decrease in humidity occurred simultaneously with the increase of temperature. The model simulation showed that the nocturnal warming was caused mainly by the transport of warmer and drier air aloft downward to the surface through enhanced vertical mixing. Wind shear played an important role in inducing the elevated vertical mixing, and it was enhanced by the continuous development of the <span class="hlt">atmospheric</span> baroclinicity, which converted more potential energy to kinetic energy.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930094594','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930094594"><span id="translatedtitle">Turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> of an airfoil</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fediaevsky, K</p> <p>1937-01-01</p> <p>A need has arisen for a new determination of the velocity profiles in the <span class="hlt">boundary</span> <span class="hlt">layer</span>. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the <span class="hlt">boundary</span> <span class="hlt">layer</span>, we shall consider the nature of the shear distribution for a <span class="hlt">boundary</span> <span class="hlt">layer</span> with a pressure gradient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22403216','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22403216"><span id="translatedtitle">A stochastic perturbation method to generate inflow turbulence in large-eddy simulation models: Application to neutrally stratified <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Muñoz-Esparza, D.; Kosović, B.; Beeck, J. van; Mirocha, J.</p> <p>2015-03-15</p> <p>Despite the variety of existing methods, efficient generation of turbulent inflow conditions for large-eddy simulation (LES) models remains a challenging and active research area. Herein, we extend our previous research on the cell perturbation method, which uses a novel stochastic approach based upon finite amplitude perturbations of the potential temperature field applied within a region near the inflow <span class="hlt">boundaries</span> of the LES domain [Muñoz-Esparza et al., “Bridging the transition from mesoscale to microscale turbulence in numerical weather prediction models,” <span class="hlt">Boundary-Layer</span> Meteorol., 153, 409–440 (2014)]. The objective was twofold: (i) to identify the governing parameters of the method and their optimum values and (ii) to generalize the results over a broad range of <span class="hlt">atmospheric</span> large-scale forcing conditions, U{sub g} = 5 − 25 m s{sup −1}, where U{sub g} is the geostrophic wind. We identified the perturbation Eckert number, Ec=U{sub g}{sup 2}/ρc{sub p}θ{sup ~}{sub pm}, to be the parameter governing the flow transition to turbulence in neutrally stratified <span class="hlt">boundary</span> <span class="hlt">layers</span>. Here, θ{sup ~}{sub pm} is the maximum perturbation amplitude applied, c{sub p} is the specific heat capacity at constant pressure, and ρ is the density. The optimal Eckert number was found for nonlinear perturbations allowed by Ec ≈ 0.16, which instigate formation of hairpin-like vortices that most rapidly transition to a developed turbulent state. Larger Ec numbers (linear small-amplitude perturbations) result in streaky structures requiring larger fetches to reach the quasi-equilibrium solution, while smaller Ec numbers lead to buoyancy dominated perturbations exhibiting difficulties for hairpin-like vortices to emerge. Cell perturbations with wavelengths within the inertial range of three-dimensional turbulence achieved identical quasi-equilibrium values of resolved turbulent kinetic energy, q, and Reynolds-shear stress, <w′u′>. In contrast, large-scale perturbations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910006682','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910006682"><span id="translatedtitle">Modelling the transitional <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Narasimha, R.</p> <p>1990-01-01</p> <p>Recent developments in the modelling of the transition zone in the <span class="hlt">boundary</span> <span class="hlt">layer</span> are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.A53G0213K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.A53G0213K"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Heights from CALIOP</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kuehn, R.; Ackerman, S. A.; Holz, R.; Roubert, L.</p> <p>2012-12-01</p> <p>This work is focused on the development of a planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL) height retrieval algorithm for CALIOP and validation studies. Our current approach uses a wavelet covariance transform analysis technique to find the top of the <span class="hlt">boundary</span> <span class="hlt">layer</span>. We use the methodology similar to that found in Davis et. al. 2000, ours has been developed to work with the lower SNR data provided by CALIOP, and is intended to work autonomously. Concurrently developed with the CALIOP algorithm we will show results from a PBL height retrieval algorithm from profiles of potential temperature, these are derived from Aircraft Meteorological DAta Relay (AMDAR) observations. Results from 5 years of collocated AMDAR - CALIOP retrievals near O'Hare airport demonstrate good agreement between the CALIOP - AMDAR retrievals. In addition, because we are able to make daily retrievals from the AMDAR measurements, we are able to observe the seasonal and annual variation in the PBL height at airports that have sufficient instrumented-aircraft traffic. Also, a comparison has been done between the CALIOP retrievals and the NASA Langley airborne High Spectral Resolution Lidar (HSRL) PBL height retrievals acquired during the GoMACCS experiment. Results of this comparison, like the AMDAR comparison are favorable. Our current work also involves the analysis and verification of the CALIOP PBL height retrieval from the 6 year CALIOP global data set. Results from this analysis will also be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/243437','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/243437"><span id="translatedtitle">The minisodar and planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> studies</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Coulter, R.L.</p> <p>1996-06-01</p> <p>The minisodar, in addition to being smaller than conventional sodar, operates at higher frequencies, obtains usable signal returns closer to the surface, and can use smaller range gates. Because the max range is generally limited to the lower 200 m above the surface, the minisodar is not able to interrogate the entire daytime <span class="hlt">atmospheric</span> Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span> (PBL); however it can be a very useful tool for understanding the PBL. In concert with other instruments, the minisodar can add significant new insights to our understanding of the PBL. This paper gives examples of past and potential uses of minisodars in such situations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMOS44A..03R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMOS44A..03R"><span id="translatedtitle">Observations of Marine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Processes and High-Frequency Internal Waves from Ship-Launched UAVs and Ship-based Instrumentation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reineman, B. D.; Lenain, L.; Melville, W. K.</p> <p>2014-12-01</p> <p>We present measurements obtained during the October 2012 EquatorMix experiment (0N, 140W), in which we deployed ship-launched and recovered Boeing-Insitu ScanEagle unmanned aerial vehicles (UAVs) to measure momentum and energy fluxes, ocean surface processes, and the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (MABL). The UAV dataset is complemented by measurements from a suite of ship-based instrumentation, including a foremast MABL eddy covariance system, scanning and point lidar altimeters, a laser Doppler wind profiler, and a digitized X-band radar system (WaMoS). The combination of the unmanned aircraft and the ship instrumentation provides a novel and valuable dataset of many air-sea interaction phenomena, extending from 100s of meters below the surface to 1500 m above. Ocean surface displacements observed with the UAV lidar altimeter (coupled with a GPS/IMU) give evidence of high-frequency equatorial internal waves, with measurements consistent and coherent with those from ship-based X-band radar, the Hydrographic Doppler Sonar System (HDSS), and a theoretical model. UAV-based flux measurements at low altitudes (down to 30 meters) are consistent with ship-based eddy covariance measurements, but reveal differences between along- and crosswind sampling flight legs associated with longitudinal roll structures that are not captured by the ship measurements from tracks mainly in the upwind-downwind directions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JGRG..117.1019M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JGRG..117.1019M"><span id="translatedtitle">Large amplitude spatial and temporal gradients in <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> CO2 mole fractions detected with a tower-based network in the U.S. upper Midwest</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miles, Natasha L.; Richardson, Scott J.; Davis, Kenneth J.; Lauvaux, Thomas; Andrews, Arlyn E.; West, Tristram O.; Bandaru, Varaprasad; Crosson, Eric R.</p> <p>2012-03-01</p> <p>This study presents observations of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> CO2mole fraction from a nine-tower regional network deployed during the North American Carbon Program's Mid-Continent Intensive (MCI) during 2007-2009. The MCI region is largely agricultural, with well-documented carbon exchange available via agricultural inventories. By combining vegetation maps and tower footprints, we show the fractional influence of corn, soy, grass, and forest biomes varies widely across the MCI. Differences in the magnitude of CO2 flux from each of these biomes lead to large spatial gradients in the monthly averaged CO2mole fraction observed in the MCI. In other words, the monthly averaged gradients are tied to regional patterns in net ecosystem exchange (NEE). The daily scale gradients are more weakly connected to regional NEE, instead being governed by local weather and large-scale weather patterns. With this network of tower-based mole fraction measurements, we detect climate-driven interannual changes in crop growth that are confirmed by satellite and inventory methods. These observations show that regional-scale CO2 mole fraction networks yield large, coherent signals governed largely by regional sources and sinks of CO2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010037384','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010037384"><span id="translatedtitle">Operational Performance of Sensor Systems Used to Determine <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Properties as Part of the NASA Aircraft Vortex Spacing System Project</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zak, J. Allen; Rodgers, William G., Jr.; Nolf, Scott; McKissick, Burnell T. (Technical Monitor)</p> <p>2001-01-01</p> <p>There has been a renewed interest in the application of remote sensor technology to operational aviation and airport-related activities such as Aircraft Vortex Spacing System (AVOSS). Radio Acoustic Sounding Systems (RASS), Doppler-acoustic sodars, Ultrahigh Frequencies (UHF) profilers and lidars have many advantages in measuring wind and temperature profiles in the lower <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> since they can operate more or less continuously and unattended; however, there are limitations in their operational use at airports. For example, profilers deteriorate (limited altitude coverage or missing) in moderate or greater rain and can be affected by airplane targets in their field of view. Sodars can handle precipitation better but are affected by the high noise environments of airports and strong winds. Morning temperature inversions typically limit performance of RASS, sodars and profilers. Fog affects sonic anemometers. Lidars can have difficulties in clouds, fog or heavy precipitation. Despite their limitations these sensors have proven useful to provide wind and temperature profiles for AVOSS. Capabilities and limitations of these and other sensors used in the AVOSS program are discussed, parameter settings for the sensor systems are documented, and recommendations are made for the most cost-effective group of sensors for the future. The potential use of specially tuned dynamic forecast models and measurements from landing and departing aircraft are addressed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000094364','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000094364"><span id="translatedtitle"><span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Wind Data During the Period January 1, 1998 Through January 31, 1999 at the Dallas-Fort Worth Airport. Volume 1; Quality Assessment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zak, J. Allen; Rodgers, William G., Jr.</p> <p>2000-01-01</p> <p>The quality of the Aircraft Vortex Spacing System (AVOSS) is critically dependent on representative wind profiles in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. These winds observed from a number of sensor systems around the Dallas-Fort Worth airport were combined into single vertical wind profiles by an algorithm developed and implemented by MIT Lincoln Laboratory. This process, called the AVOSS Winds Analysis System (AWAS), is used by AVOSS for wake corridor predictions. During times when AWAS solutions were available, the quality of the resultant wind profiles and variance was judged from a series of plots combining all sensor observations and AWAS profiles during the period 1200 to 0400 UTC daily. First, input data was evaluated for continuity and consistency from criteria established. Next, the degree of agreement among all wind sensor systems was noted and cases of disagreement identified. Finally, the resultant AWAS solution was compared to the quality-assessed input data. When profiles differed by a specified amount from valid sensor consensus winds, times and altitudes were flagged. Volume one documents the process and quality of input sensor data. Volume two documents the data processing/sorting process and provides the resultant flagged files.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.A33B0138O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.A33B0138O"><span id="translatedtitle">Improved Large-Eddy Simulation Using a Stochastic Backscatter Model: Application to the Neutral <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> and Urban Street Canyon Flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Neill, J. J.; Cai, X.; Kinnersley, R.</p> <p>2015-12-01</p> <p>Large-eddy simulation (LES) provides a powerful tool for developing our understanding of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) dynamics, which in turn can be used to improve the parameterisations of simpler operational models. However, LES modelling is not without its own limitations - most notably, the need to parameterise the effects of all subgrid-scale (SGS) turbulence. Here, we employ a stochastic backscatter SGS model, which explicitly handles the effects of both forward and reverse energy transfer to/from the subgrid scales, to simulate the neutrally stratified ABL as well as flow within an idealised urban street canyon. In both cases, a clear improvement in LES output statistics is observed when compared with the performance of a SGS model that handles forward energy transfer only. In the neutral ABL case, the near-surface velocity profile is brought significantly closer towards its expected logarithmic form. In the street canyon case, the strength of the primary vortex that forms within the canyon is more accurately reproduced when compared to wind tunnel measurements. Our results indicate that grid-scale backscatter plays an important role in both these modelled situations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFDE24001S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFDE24001S"><span id="translatedtitle">Coupled wake <span class="hlt">boundary</span> <span class="hlt">layer</span> model of windfarms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stevens, Richard; Gayme, Dennice; Meneveau, Charles</p> <p>2014-11-01</p> <p>We present a coupled wake <span class="hlt">boundary</span> <span class="hlt">layer</span> (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm <span class="hlt">boundary</span> <span class="hlt">layer</span> structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1511593C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1511593C"><span id="translatedtitle">Seasonal, synoptic and diurnal variation of <span class="hlt">atmospheric</span> water-isotopologues in the <span class="hlt">boundary</span> <span class="hlt">layer</span> of Southwestern Germany caused by plant transpiration, cold-front passages and dewfall.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Christner, Emanuel; Dyroff, Christoph; Kohler, Martin; Zahn, Andreas; Gonzales, Yenny; Schneider, Matthias</p> <p>2013-04-01</p> <p><span class="hlt">Atmospheric</span> water is an enormously crucial trace gas. It is responsible for ~70 % of the natural greenhouse effect (Schmidt et al., JGR, 2010) and carries huge amounts of latent heat. The isotopic composition of water vapor is an elegant tracer for a better understanding and quantification of the extremely complex and variable hydrological cycle in Earth's <span class="hlt">atmosphere</span> (evaporation, cloud condensation, rainout, re-evaporation, snow), which in turn is a prerequisite to improve climate modeling and predictions. As H216O, H218O and HDO differ in vapor pressure and mass, isotope fractionation occurs due to condensation, evaporation and diffusion processes. In contrast to that, plants are able to transpire water with almost no isotope fractionation. For that reason the ratio of isotopologue concentrations in the <span class="hlt">boundary</span> <span class="hlt">layer</span> (BL) provides, compared to humidity measurements alone, independent and additional constraints for quantifying the strength of evaporation and transpiration. Furthermore the isotope ratios contain information about transport history of an air mass and microphysical processes, that is not accessible by humidity measurements. Within the project MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of <span class="hlt">Atmospheric</span> water) a commercial Picarro Analyzer L2120-i is operated at Karlsruhe in Southwestern Germany, which is continuously measuring the isotopologues H216O, HDO and H218O of <span class="hlt">atmospheric</span> water vapor since January 2012. A one year record of H216O, HDO and H218O shows clear seasonal, synoptic and diurnal characteristics and reveals the main driving processes affecting the isotopic composition of water vapor in the Middle European BL. Changes in continental plant transpiration and evaporation throughout the year lead to a slow seasonal HDO/H216O-variation, that cannot be explained by pure Rayleigh condensation. Furthermore, cold-front passages from NW lead to fast and pronounced depletion of the HDO/H216O-ratio within</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMOS51E1937R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMOS51E1937R"><span id="translatedtitle">Development and testing of instrumentation for ship-based UAV measurements of ocean surface processes and the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reineman, B. D.; Lenain, L.; Statom, N.; Melville, W. K.</p> <p>2012-12-01</p> <p>We have developed instrumentation packages for unmanned aerial vehicles (UAVs) to measure ocean surface processes along with momentum fluxes and latent, sensible, and radiative heat fluxes in the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (MABL). The packages have been flown over land on BAE Manta C1s and over water on Boeing-Insitu ScanEagles. The low altitude required for accurate surface flux measurements (< 30 m) is below the typical safety limit of manned research aircraft; however, with advances in laser altimeters, small-aircraft flight control, and real-time kinematic differential GPS, low-altitude flight is now within the capability of small UAV platforms. Fast-response turbulence, hygrometer, and temperature probes permit turbulent flux measurements, and short- and long-wave radiometers allow the determination of net radiation, surface temperature, and albedo. Onboard laser altimetry and high-resolution visible and infrared video permit observations of surface waves and fine-scale (O(10) cm) ocean surface temperature structure. Flight tests of payloads aboard ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center Dahlgren Division (Dahlgren, VA), where measurements of water vapor, heat, and momentum fluxes were made from low-altitude (31-m) UAV flights over water (Potomac River). ScanEagles are capable of ship-based launch and recovery, which can extend the reach of research vessels and enable scientific measurements out to ranges of O(10-100) km and altitudes up to 5 km. UAV-based <span class="hlt">atmospheric</span> and surface observations can complement observations of surface and subsurface phenomena made from a research vessel and avoid the well-known problems of vessel interference in MABL measurements. We present a description of the instrumentation, summarize results from flight tests, and discuss potential applications of these UAVs for ship-based MABL studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.A43B0297D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.A43B0297D"><span id="translatedtitle">An Investigation of Biogenic Trace Gas Emissions from the Southern Ocean: Impact on <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Marine Composition and on the Distant Antarctic Plateau <span class="hlt">Atmosphere</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davis, D. D.; Neff, W.; Wang, Y.; Zeng, T.; Slusher, D.; Bradshaw, J.; Stickel, R.; Nicovitch, M.</p> <p>2008-12-01</p> <p>During the last ten years chemical measurements at the South Pole as well as over extended regions of the larger plateau have revealed the presences of a chemically unique <span class="hlt">boundary</span> <span class="hlt">layer</span> (BL) <span class="hlt">atmosphere</span>. Unique in that it has been shown to have a very large chemical oxidizing capacity. This has been reflected in summertime concentration measurements of the hydroxyl radical that average between 2 to 3 x 10(6) molec/cm(3). These new findings make quite evident that the Antarctic plateau (geographically the size of continental USA) must now be viewed as much more than a chemical graveyard where species transported to its surface from a multitude of SH sources are simply buried in ice. In fact, during the Austral spring, summer, and fall months, chemical elements arriving at the plateau may in many cases be further oxidized before burial and in still other cases oxidized even after burial. To be presented are several previously unreported observations of biogenic gases measured both over the Southern Ocean and on the plateau, some of which span all seasons of the year. Of particular significance will be regional modeling results that suggest that the concentration levels and chemical forms that these biogenic gases appear upon reaching the plateau depend not only on the productivity of the Southern Ocean and the seas surrounding Antarctica, but also on at least two additional factors. These include the efficiency of the transport process (e.g., as influenced by the sea ice extent) and the chemical oxidizing capacity of the Antarctic plateau's BL <span class="hlt">atmosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1711915B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1711915B"><span id="translatedtitle">The marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> during the HyMeX-ASICS-MED campaign: characterization of coherent structures and impact on turbulent flux estimates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brilouet, Pierre-Etienne; Canut, Guylaine; Durand, Pierre</p> <p>2015-04-01</p> <p>During winter, the North Western Mediterranean Sea is characterised by intense air-sea exchanges linked to regional strong winds (Mistral or Tramontana) which bring cold and dry continental air over a warmer sea. The HyMeX-ASICS-MED field campaign, devoted to intense sea-<span class="hlt">atmosphere</span> exchange and deep oceanic convection analysis took place in the Gulf of Lion during winter 2013. The French ATR42 aircraft was operated to document the mean and turbulent structure of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) during strong wind conditions. The aircraft was equipped to measure turbulence fluctuations, thus allowing the computation of turbulence parameters. The flight strategy consisted of stacked horizontal legs oriented along and across the wind direction, in order to obtain information about the isotropy of the turbulent field and about coherent structures. Strong wind events were documented with 11 flights during which latent heat flux up to 600 W.m-2 were observed. The structure of the turbulent field is analysed through the integral length scale and the wavelength of the spectrum peak of the vertical velocity which represent the size of the large and the most energetic eddies, respectively. It reveals a stretching of turbulent eddies along the mean wind. This kind of organized structures plays a major role by modulating the transfers inside the ABL. In particular, this non-isotropic behaviour alters the flux estimates from along-wind samples. This last point is critical because surface and entrainment fluxes, deduced from extrapolation of the flux profiles, are essential parameters to characterise the coupling between air-sea exchanges and the ABL structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730023103','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730023103"><span id="translatedtitle">Nonequilibrium chemistry <span class="hlt">boundary</span> <span class="hlt">layer</span> integral matrix procedure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tong, H.; Buckingham, A. C.; Morse, H. L.</p> <p>1973-01-01</p> <p>The development of an analytic procedure for the calculation of nonequilibrium <span class="hlt">boundary</span> <span class="hlt">layer</span> flows over surfaces of arbitrary catalycities is described. An existing equilibrium <span class="hlt">boundary</span> <span class="hlt">layer</span> integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general <span class="hlt">boundary</span> condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010ffcd.confE.107Z&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010ffcd.confE.107Z&link_type=ABSTRACT"><span id="translatedtitle">The structures of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> in the Yellow Sea summer fog-a comparison study with the spring fog</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, S.-P.; Ren, Z.-P.; Yang, Y.-Q.; Wang, X.-G.; Xu, X.-L.</p> <p>2010-07-01</p> <p>The Yellow Sea is a highly foggy area in spring-summer (April to July) seasons. A Yellow Sea fog case occurred on July 7-11, 2008 is investigated by the data from the sea buoy stations, high-resolution digital sounding instruments and other observations and from a three-dimensional mesoscale model (WRF). Espcially, the <span class="hlt">boundary</span> <span class="hlt">layer</span> structure are analyzed and simulated, and the comparison is made between the summer fog case and a spring fog case in May 2-3, 2008. The results are as follows (1) In summer fog, the marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (MABL) is less stable (almost no temperature inversion)than that in spring fog and the summer fog is thicker in elevation due to the development of turbulence and plenty of moisture supply advected by the East Asian summer monsoon in the low level of the MABL; whereas in spring fog the MABL is very stable with pronounced temperature inversion and the moisture is mainly transported by a shallow local anticyclone in the Yellow Sea surface and traped close to a very low level, thus leading to thin fog. (2) In summer, the southerly air column in the MABL is of similar physical features since it comes from the southern ocean, producing the less vertical gradient both in temperature and in humidity (no obvious dry <span class="hlt">layer</span>). In contrast, in spring the southerly sea surface air is cooling gradualy as it passes the cold Yellow Sea, but the air at about 950 hPa is westerly from inland that is dry and warm by the increased solar radiation, thus forming temerature inversion and evident dry <span class="hlt">layer</span> over the sea. (3) The surface air temperature (SAT) is obviously higher than the sea surface temperature (SST) in the process of the summer fog, and the SAT does not derease or even increase in the fog, which is related to the weaker long wave radiation at the fog top and the huge amount of latent heat; while in spring sea fog the SAT decreases rapidly and is even lower than the SST in the peak phase of the fog due to strong long wave radiation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997PhDT........42A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997PhDT........42A"><span id="translatedtitle">Measurements of Pb-212 and Pb-214 in surface air around Lake Michigan and their implications for <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aquino, Nadja Wackerling</p> <p>1997-10-01</p> <p>The dynamics of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> are a result of turbulence generated at the Earth's surface. The extent of mixing in the <span class="hlt">boundary</span> <span class="hlt">layer</span> is studied by using radionuclides as tracers under different conditions such as: wind direction dependent on passing synoptic systems, upwind and downwind lake shore sites, urban versus rural setting, and urban setting at two different altitudes. Data were collected by high volume air samplers at each site, which filtered air for day and night intervals several days in a row. The filters were placed in a GeLe detector and gamma rays of 212Pb and 214Pb decays were counted. From these measurements, the concentrations of 212Pb and 214Pb in the sampled air were determined. Among the types of radionuclide behavior are diurnal variation in activities, synoptic-scale variation, variation due to different surface roughness characteristics and position with respect to the wind at the lake shore, and limited variation in activity at high altitude at the urban site. A series of one dimensional models were developed to interpret the data. The horizontal advection model predicted the effect on 212Pb and 214Pb activities of advecting air over a 100 km zero source region at constant velocity. 212Pb activities decrease substantially for velocities greater than 1 m/s, whereas 214Pb does not decrease much until velocities reach 100 m/s. The vertical diffusion model predicted 212Pb and 214Pb vertical profiles for different vertical diffusivities, κ z. A one order of magnitude change in κ z produces a /sqrt[10] change in activity in surface air. The results of both models are equivalent for 212Pb activities. Comparing 212Pb and 214Pb, vertical mixing affects both radionuclides similarly, but horizontal advection fractionates the two radionuclides. The diurnal box models predict activities an order of magnitude lower than the steady state models, in close agreement with observations. Furthermore, an order of magnitude increase can</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AtmEn..40..856O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AtmEn..40..856O"><span id="translatedtitle">Estimation of Hg 0 exchange between ecosystems and the <span class="hlt">atmosphere</span> using 222Rn and Hg 0 concentration changes in the stable nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obrist, Daniel; Conen, Franz; Vogt, Roland; Siegwolf, Rolf; Alewell, Christine</p> <p></p> <p>The goal of this study was to test a 222Rn/Hg 0 method to measure exchange fluxes of Hg 0 between ecosystems and the <span class="hlt">atmosphere</span> complementing gradient-based micrometeorological methods which are difficult to apply when exchange fluxes are very low, during calm nights, and over heterogeneous surfaces. The method is based on absolute concentration changes of Hg 0 and of the trace gas 222Rn over several hours in the stable nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span> (NBL) when absolute gas concentrations change according to the source or sink strength of the underlying landscape. 222Rn accumulations were observed in 28 of 66 measured nights in an urban area and in 14 of the 40 nights at a subalpine grassland. Concurrent and significant increases in <span class="hlt">atmospheric</span> Hg 0 concentrations were observed 22 times in the urban area and calculated Hg 0 emissions—for the first time measured over a city area—averaged 6.4±0.9 ng m -2 h -1. Concurrent changes in Hg 0 in the stable NBLs at the subalpine site were very small and significant only nine times with calculated Hg 0 fluxes averaging -0.2±0.3 ng m -2 h -1, indicating that the flux of Hg 0 in the grassland was a very small net deposition of <span class="hlt">atmospheric</span> Hg 0 to the ecosystem. At the subalpine grassland the 222Rn/Hg 0 method compared reasonably well to a modified Bowen ratio (MBR) method applied during turbulent conditions (-1.9±0.2 ng m -2 h -1 [or -1.7±0.4 ng m -2 h -1 during nights only]). The MBR, however, was not applicable in the urban area due to high surface roughness. We conclude that the 222Rn/Hg 0 method—although limited to nighttime periods in our study—can complement gradient-based methods during stable NBL periods and can be used over heterogeneous surfaces when conventional micrometeorological approaches are not applicable.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.B13I0322L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.B13I0322L"><span id="translatedtitle">Seasonal variations in δ13C and δ18O of <span class="hlt">atmospheric</span> CO2 measured in the urban <span class="hlt">boundary</span> <span class="hlt">layer</span> over Vancouver, Canada in relation to fuel emissions.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, J.; Christen, A.; Ketler, R.; Nesic, Z.; Schwendenmann, L.; Semmens, C.</p> <p>2014-12-01</p> <p>Recent advances in techniques to measure carbon dioxide (CO2) in urban plumes show potential for validating and monitoring emission inventories at regional to urban scale. A major challenge remains the attribution of elevated CO2 in urban plumes to different fuel and biogenic sources. Stable isotopes are a promising source of additional information. Here, we report a full year of measurements of CO2 mixing ratios, δ13C and δ18O in CO2 in the urban <span class="hlt">boundary</span> <span class="hlt">layer</span> over Vancouver, Canada. The goal of the work is to link seasonally changing isotopic composition to dominant fuel sources and put the urban enhancement into the context of regional background concentrations. <span class="hlt">Atmospheric</span> composition in the urban <span class="hlt">atmosphere</span> was measured continuously using a tunable diode laser absorption system (TGA 200, Campbell Scientific, Logan, UT, USA). In addition, end member signatures were determined by means of bag samples from representative fuel emission sources (gasoline, diesel, natural gas). While δ13C depends on the fuel type and origin (for Vancouver in 2013/14: δ13C gasoline 27.2‰; diesel -28.8‰; natural gas -41.6‰), δ18O is fractionated in catalytic converters (d18O gasoline vehicles -12.5‰; diesel -18.6‰; natural gas -22.7‰) and exhibits higher variability between samples. Additional signatures were determined for human, soil and plant respiration. During the study year, monthly mean mixing ratios in the urban <span class="hlt">atmosphere</span> ranged between 410.5 (Jul) and 425.7 ppm (Dec), which was on average 18 ppm elevated above the regional background. As expected, mean monthly δ13C was lower in winter than summer with seasonally changing intercepts between -33.6‰ (JJF) and -27.7‰ (MJJ). Making the simple assumption that natural gas and gasoline are the only major fuel sources, natural gas would contribute ~45% to emissions in winter and ~3% in early summer, which is lower than the downscaled Local Emissions Inventory (57% in winter and 20% in summer). Mean δ18O showed</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050217285','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050217285"><span id="translatedtitle">Microgravity Effects on Plant <span class="hlt">Boundary</span> <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stutte, Gary; Monje, Oscar</p> <p>2005-01-01</p> <p>The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental <span class="hlt">boundary</span> <span class="hlt">layers</span> in roots and leaves and to determine the effects of air flow on <span class="hlt">boundary</span> <span class="hlt">layer</span> development. It is hypothesized that microgravity induces larger <span class="hlt">boundary</span> <span class="hlt">layers</span> around plant organs because of the absence of buoyancy-driven convection. These larger <span class="hlt">boundary</span> <span class="hlt">layers</span> may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in <span class="hlt">boundary</span> <span class="hlt">layer</span> associated with microgravity, quantify the change if it exists, and determine influence of air velocity on <span class="hlt">boundary</span> <span class="hlt">layer</span> thickness under different gravity conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860018365','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860018365"><span id="translatedtitle">A model for the estimation of the surface fluxes of momentum, heat and moisture of the cloud topped marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> from satellite measurable parameters. M.S. Thesis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allison, D. E.</p> <p>1984-01-01</p> <p>A model is developed for the estimation of the surface fluxes of momentum, heat, and moisture of the cloud topped marine <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> by use of satellite remotely sensed parameters. The parameters chosen for the problem are the integrated liquid water content, q sub li, the integrated water vapor content, q sub vi, the cloud top temperature, and either a measure of the 10 meter neutral wind speed or the friction velocity at the surface. Under the assumption of a horizontally homogeneous, well-mixed <span class="hlt">boundary</span> <span class="hlt">layer</span>, the model calculates the equivalent potential temperature and total water profiles of the <span class="hlt">boundary</span> <span class="hlt">layer</span> along with the <span class="hlt">boundary</span> <span class="hlt">layer</span> height from inputs of q sub li, q sub vi, and cloud top temperature. These values, along with the 10m neutral wind speed or friction velocity and the sea surface temperature are then used to estimate the surface fluxes. The development of a scheme to parameterize the integrated water vapor outside of the <span class="hlt">boundary</span> <span class="hlt">layer</span> for the cases of cold air outbreak and California coastal stratus is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAMES...7.1602M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAMES...7.1602M"><span id="translatedtitle">Seasonal variation of local <span class="hlt">atmospheric</span> circulations and <span class="hlt">boundary</span> <span class="hlt">layer</span> structure in the Beijing-Tianjin-Hebei region and implications for air quality</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miao, Yucong; Hu, Xiao-Ming; Liu, Shuhua; Qian, Tingting; Xue, Ming; Zheng, Yijia; Wang, Shu</p> <p>2015-12-01</p> <p>The Beijing-Tianjin-Hebei (BTH) region experiences frequent heavy haze pollution in fall and winter. Pollution was often exacerbated by unfavorable <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (BL) conditions. The topography in this region impacts the BL processes in complex ways. Such impacts and implications on air quality are not yet clearly understood. The BL processes in all four seasons in BTH are thus investigated in this study using idealized simulations with the WRF-Chem model. Results suggest that seasonal variation of thermal conditions and synoptic patterns significantly modulates BL processes. In fall, with a relatively weak northwesterly synoptic forcing, thermal contrast between the mountains and the plain leads to a prominent mountain-plain breeze circulation (MPC). In the afternoon, the downward branch of the MPC, in addition to northwesterly warm advection, suppresses BL development over the western side of BTH. In the eastern coastal area, a sea-breeze circulation develops late in the morning and intensifies during the afternoon. In summer, southeasterly BL winds allow the see-breeze front to penetrate farther inland (˜150 km from the coast), and the MPC is less prominent. In spring and winter, with strong northwesterly synoptic winds, the sea-breeze circulation is confined in the coastal area, and the MPC is suppressed. The BL height is low in winter due to strong near-surface stability, while BL heights are large in spring due to strong mechanical forcing. The relatively low BL height in fall and winter may have exacerbated the air pollution, thus contributing to the frequent severe haze events in the BTH region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRC..121..861Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRC..121..861Z"><span id="translatedtitle">Impact of storm-induced cooling of sea surface temperature on large turbulent eddies and vertical turbulent transport in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> of Hurricane Isaac</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhu, Ping; Wang, Yuting; Chen, Shuyi S.; Curcic, Milan; Gao, Cen</p> <p>2016-01-01</p> <p>Roll vortices in the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) are important to oil operation and oil spill transport. This study investigates the impact of storm-induced sea surface temperature (SST) cooling on the roll vortices generated by the convective and dynamic instability in the ABL of Hurricane Isaac (2012) and the roll induced transport using hindcasting large eddy simulations (LESs) configured from the multiply nested Weather Research & Forecasting model. Two experiments are performed: one forced by the Unified Wave INterface - Coupled Model and the other with the SST replaced by the NCEP FNL analysis that does not include the storm-induced SST cooling. The simulations show that the roll vortices are the prevalent eddy circulations in the ABL of Isaac. The storm-induced SST cooling causes the ABL stability falls in a range that satisfies the empirical criterion of roll generation by dynamic instability, whereas the ABL stability without considering the storm-induced SST cooling meets the criterion of roll generation by convective instability. The ABL roll is skewed and the increase of convective instability enhances the skewness. Large convective instability leads to large vertical transport of heat and moisture; whereas the dominant dynamic instability results in large turbulent kinetic energy but relatively weak heat and moisture transport. This study suggests that failure to consider roll vortices or incorrect initiation of dynamic and convective instability of rolls in simulations may substantially affect the transport of momentum, energy, and pollutants in the ABL and the dispersion/advection of oil spill fume at the ocean surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015BoLMe.157..421X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015BoLMe.157..421X"><span id="translatedtitle">Sensitivity Issues in Finite-Difference Large-Eddy Simulations of the <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> with Dynamic Subgrid-Scale Models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, Shengbai; Ghaisas, Niranjan; Archer, Cristina L.</p> <p>2015-12-01</p> <p>The neutral <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) is simulated by finite-difference large-eddy simulations (LES) with various dynamic subgrid-scale (SGS) models. The goal is to understand the sensitivity of the results to several aspects of the simulation set-up: SGS model, numerical scheme for the convective term, resolution, and filter type. Three dynamic SGS models are tested: two scale-invariant models and the Lagrangian-averaged scale-dependent (LASD) model. The results show that the LASD model has the best performance in capturing the law-of-the-wall, because the scale invariance hypothesis is violated in finite-difference LES. Two forms of the convective term are tested, the skew-symmetric and the divergence forms. The choice of the convective term is more important when the LASD model is used and the skew-symmetric scheme leads to better simulations in general. However, at fine resolutions both in space and time, the sensitivity to the convective scheme is reduced. Increasing the resolution improves the performance in general, but does not better capture the law of the wall. The box and Gaussian filters are tested and it is found that, combined with the LASD model, the Gaussian filter is not sufficient to dissipate the small numerical noises, which in turn affects the large-scale motions. In conclusion, to get the most benefits of the LASD model within the finite-difference framework, the simulations need to be set up properly by choosing the right combination of numerical scheme, resolution, and filter type.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4171757','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4171757"><span id="translatedtitle">Study of the effect of wind speed on evaporation from soil through integrated modeling of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and shallow subsurface</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa</p> <p>2014-01-01</p> <p>In an effort to develop methods based on integrating the subsurface to the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account. PMID:25309005</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19840065340&hterms=Jeddah&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DJeddah','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19840065340&hterms=Jeddah&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DJeddah"><span id="translatedtitle">Goertler instability of compressible <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>El-Hady, N. M.; Verma, A. K.</p> <p>1984-01-01</p> <p>The instability of the laminar compressible <span class="hlt">boundary-layer</span> flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating, longitudinal-type vortices in two-dimensional <span class="hlt">boundary</span> <span class="hlt">layers</span> are presented in an orthogonal curvilinear system of coordinates. The basic approximation of the disturbance equations, which includes the effect of the growth of the <span class="hlt">boundary</span> <span class="hlt">layer</span>, is considered and solved numerically.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850004868','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850004868"><span id="translatedtitle">Turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> with secondary flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grushwitz, E.</p> <p>1984-01-01</p> <p>An experimental analysis of the <span class="hlt">boundary</span> <span class="hlt">layer</span> on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to <span class="hlt">boundary</span> <span class="hlt">layers</span> in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for <span class="hlt">boundary</span> <span class="hlt">layers</span> with spatial flow. The wall shear stresses were calculated with this equation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770003414','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770003414"><span id="translatedtitle">Three-dimensional <span class="hlt">boundary</span> <span class="hlt">layers</span> approaching separation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Williams, J. C., III</p> <p>1976-01-01</p> <p>The theory of semi-similar solutions of the laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> equations is applied to several flows in which the <span class="hlt">boundary</span> <span class="hlt">layer</span> approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910033011&hterms=finite-time&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dfinite-time','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910033011&hterms=finite-time&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dfinite-time"><span id="translatedtitle">Interactions in <span class="hlt">boundary-layer</span> transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Frank T.</p> <p>1989-01-01</p> <p>Certain theoretical studies of <span class="hlt">boundary-layer</span> transition are described, based on high Reynolds numbers and with attention drawn to the various nonlinear interactions and scales present. The article concentrates in particular on theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent-<span class="hlt">boundary-layer</span> structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive <span class="hlt">boundary</span> <span class="hlt">layers</span>; strong vortex/wave interactions; and prediction of turbulent <span class="hlt">boundary-layer</span> displacement- and stress sublayer-thicknesses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910055283&hterms=finite-time&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfinite-time','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910055283&hterms=finite-time&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfinite-time"><span id="translatedtitle">Nonlinear breakdowns in <span class="hlt">boundary</span> <span class="hlt">layer</span> transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Frank T.</p> <p>1990-01-01</p> <p>Theoretical studies of <span class="hlt">boundary-layer</span> transition are described, based on high Reynolds numbers and with attention drawn to nonlinear interactions, breakdowns and scales. The article notes in particular truly nonlinear theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent <span class="hlt">boundary-layer</span> structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive <span class="hlt">boundary</span> <span class="hlt">layers</span>; strong vortex/wave interactions; and prediction of turbulent <span class="hlt">boundary-layer</span> displacement- and stress sublayer-thicknesses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860012322','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860012322"><span id="translatedtitle">Development of perturbations in the <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.</p> <p>1986-01-01</p> <p>The transition of laminar flows into turbulent flows in a <span class="hlt">boundary</span> <span class="hlt">layer</span> is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the <span class="hlt">boundary</span> <span class="hlt">layer</span>, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the <span class="hlt">boundary</span> <span class="hlt">layer</span>; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed <span class="hlt">boundary</span> <span class="hlt">layer</span> by means of a focused effect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810012109','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810012109"><span id="translatedtitle">Structure of the low latitude <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.</p> <p>1980-01-01</p> <p>Observations at high temporal resolution of the frontside magnetopause and plasma <span class="hlt">boundary</span> <span class="hlt">layer</span>, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed <span class="hlt">boundary</span> <span class="hlt">layers</span>. A cool tailward streaming <span class="hlt">boundary</span> <span class="hlt">layer</span> plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the <span class="hlt">boundary</span> <span class="hlt">layer</span> plasma last only a few minutes, the total observation time may extend over one hour or more.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUSM...B41A03D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUSM...B41A03D"><span id="translatedtitle">Multiple Flux Footprints, Flux Divergences and <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Mixing Ratios: Studies of Ecosystem-<span class="hlt">Atmosphere</span> CO2 Exchange Using the WLEF Tall Tower.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davis, K. J.; Bakwin, P. S.; Yi, C.; Cook, B. D.; Wang, W.; Denning, A. S.; Teclaw, R.; Isebrands, J. G.</p> <p>2001-05-01</p> <p> Willow Creek site. The WLEF tower also allows us to study the potential for monitoring continental CO2 mixing ratios from tower sites. Despite concerns about the proximity to ecosystem sources and sinks, it is clear that <span class="hlt">boundary</span> <span class="hlt">layer</span> CO2 mixing ratios can be monitored using typical surface <span class="hlt">layer</span> towers. Seasonal and annual land-ocean mixing ratio gradients are readily detectable, providing the motivation for a flux-tower based mixing ratio observation network that could greatly improve the accuracy of inversion-based estimates of NEE of CO2, and enable inversions to be applied on smaller temporal and spatial scales. Results from the WLEF tower illustrate the degree to which local flux measurements represent interannual, seasonal and synoptic CO2 mixing ratio trends. This coherence between fluxes and mixing ratios serves to "regionalize" the eddy-covariance based local NEE observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.H14B..05F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.H14B..05F"><span id="translatedtitle">Organised Coherent Motion in <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Flow in the Proximity to Tall Plant Canopies as Detected in Acoustic Doppler Profiler and Tower-based Observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Foken, T.; Thomas, C. K.</p> <p>2007-12-01</p> <p>We investigated coherent structures above and in a tall plant canopy during a field campaign at a mountainous site in Germany (WALDATEM-2003). Data from a remote sensing acoustic Doppler system in concert with in-situ point measurements of turbulence in flow velocity and scalars deployed on towers yielded continuous observations from the forest ground to 200 m above the ground with a vertical resolution of 10 m at a sampling frequency of 0.4 and 20 Hz respectively. Coherent structures were extracted from time series utilizing wavelet transform techniques allowing for single structure analysis and averaged statistics of detected events. In addition to their spatiotemporal scales, we focused on the identification of generating mechanisms and surface parameters affecting coherent structures. Time scales were on the order of 20 to 36 s depending on the upstream topography and canopy morphology. Lateral transport dominated scalar coherent exchange. Vertical profiles of time scales in longitudinal and vertical velocities were mirror images showing an increase/ decrease, respectively, with height. Time scales in scalars were nearly height-constant. The ratio of the contribution of coherent structures to total vertical exchange was 0.2 for momentum and 0.25 to 0.4 for sensible heat. Analysis of power spectra confirmed an interaction between inactive eddies of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> scale and the horizontal flow in 4 % of all studied cases only, mainly under near-neutral stratification. Evaluation of the Mixing-<span class="hlt">Layer</span> Analogy suggested that vertical shear caused by the immense canopy drag was the dominant generating mechanism. However, daytime coherent structures were found to be a superposition of shear generated events and convectional eddies. The latter led to an increase of vertical coherency in the flow around noon. At night, terrain induced linear gravity waves showed similar time scales as coherent structures emphasizing the need to differentiate between these two</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850061377&hterms=layers+earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlayers%2Bearth','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850061377&hterms=layers+earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlayers%2Bearth"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layers</span> of the earth's outer magnetosphere</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Eastman, T. E.; Frank, L. A.</p> <p>1984-01-01</p> <p>The magnetospheric <span class="hlt">boundary</span> <span class="hlt">layer</span> and the plasma-sheet <span class="hlt">boundary</span> <span class="hlt">layer</span> are the primary <span class="hlt">boundary</span> <span class="hlt">layers</span> of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric <span class="hlt">boundary</span> <span class="hlt">layer</span> is predominantly deenergized whereas plasma in the plasma-sheet <span class="hlt">boundary</span> <span class="hlt">layer</span> has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the <span class="hlt">boundaries</span> have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.A54B..07V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.A54B..07V"><span id="translatedtitle">Scaling the heterogeneously heated convective <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Van Heerwaarden, C.; Mellado, J.; De Lozar, A.</p> <p>2013-12-01</p> <p>We have studied the heterogeneously heated convective <span class="hlt">boundary</span> <span class="hlt">layer</span> (CBL) by means of large-eddy simulations (LES) and direct numerical simulations (DNS). What makes our study different from previous studies on this subject are our very long simulations in which the system travels through multiple states and that from there we have derived scaling laws. In our setup, a stratified <span class="hlt">atmosphere</span> is heated from below by square patches with a high surface buoyancy flux, surrounded by regions with no or little flux. By letting a <span class="hlt">boundary</span> <span class="hlt">layer</span> grow in time we let the system evolve from the so-called meso-scale to the micro-scale regime. In the former the heterogeneity is large and strong circulations can develop, while in the latter the heterogeneity is small and does no longer influence the <span class="hlt">boundary</span> <span class="hlt">layer</span> structure. Within each simulation we can now observe the formation of a peak in kinetic energy, which represents the 'optimal' heterogeneity size in the meso-scale, and the subsequent decay of the peak and the development towards the transition to the micro-scale. We have created a non-dimensional parameter space that describes all properties of this system. By studying the previously described evolution for different combinations of parameters, we have derived three important conclusions. First, there exists a horizontal length scale of the heterogeneity (L) that is a function of the <span class="hlt">boundary</span> <span class="hlt">layer</span> height (h) and the Richardson (Ri) number of the inversion at the top of the <span class="hlt">boundary</span> <span class="hlt">layer</span>. This relationship has the form L = h Ri^(3/8). Second, this horizontal length scale L allows for expressing the time evolution, and thus the state of the system, as a ratio of this length scale and the distance between two patches Xp. This ratio thus describes to which extent the circulation fills up the space that exists between two patch centers. The timings of the transition from the meso- to the micro-scale collapse under this scaling for all simulations sharing the same flux</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/160132','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/160132"><span id="translatedtitle">Toward evaluation of heat fluxes in the convective <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sorbjan, Z.</p> <p>1995-05-01</p> <p>This article demonstrates that vertical profiles of the heat flux in the convective <span class="hlt">boundary</span> <span class="hlt">layer</span> can be diagnosed through an integration over height of the time change rates of observed potential temperature profiles. Moreover, the basic characteristics of the convective <span class="hlt">boundary</span> <span class="hlt">layer</span>, such as the mixed-<span class="hlt">layer</span> height z{sub t}, the depth of the interfacial (entrainment) <span class="hlt">layer</span>, and the heat flux zero-crossing height h{sub 0} can be uniquely evaluated based on a time evolution of potential temperature profiles in the lower <span class="hlt">atmosphere</span>. 12 refs., 12 figs., 1 tab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/865424','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/865424"><span id="translatedtitle">Cyclone separator having <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence control</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Krishna, Coimbatore R.; Milau, Julius S.</p> <p>1985-01-01</p> <p>A cyclone separator including <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the <span class="hlt">boundary</span> <span class="hlt">layer</span> of the vortical fluid flow through the separator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=541526','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=541526"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layers</span> of Air Adjacent to Cylinders</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Nobel, Park S.</p> <p>1974-01-01</p> <p>Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the <span class="hlt">boundary</span> <span class="hlt">layer</span> of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated <span class="hlt">boundary-layer</span> thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the <span class="hlt">boundary</span> <span class="hlt">layers</span> adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The <span class="hlt">boundary-layer</span> thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective <span class="hlt">boundary-layer</span> thickness in centimeters was equal to [Formula: see text]. PMID:16658855</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFDG27004R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFDG27004R"><span id="translatedtitle">Structure of relaminarizing turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramesh, O.; Patwardhan, Saurabh</p> <p>2014-11-01</p> <p>Relaminarization of a turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> in a strongly accelerated flow has received a great attention in recent times. It has been found that such relaminarization is a general and regularly occurring phenomenon in the leading-edge region of a swept wing of an airplane (van Dam et al., 1993). In this work, we investigate the effect of initial Reynolds number on the process of relaminarization in turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span>. The experimental and numerical investigation of relaminarizing turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> undergoing same history reveals that the <span class="hlt">boundary</span> <span class="hlt">layer</span> with higher initial Reynolds number relaminarizes at a lower pressure gradient value compared to the one with lower Reynolds number. This effect can be explained on the inviscid theory proposed earlier in the literature. Further, various parameter criteria proposed to predict relaminarization, are assessed and the structure of relaminarizing <span class="hlt">boundary</span> <span class="hlt">layers</span> is investigated. A mechanism for stabilization of near-wall low speed streaks is proposed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008SPIE.6834E..38Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008SPIE.6834E..38Z"><span id="translatedtitle">Simulation of <span class="hlt">atmospheric</span> turbulence <span class="hlt">layers</span> with phase screens by JAVA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Xiaofang; Chen, Wenqin; Yu, Xin; Yan, Jixiang</p> <p>2008-03-01</p> <p>In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate <span class="hlt">atmospheric</span> turbulence <span class="hlt">layers</span> to study the optimal turbulence delamination and the determination of <span class="hlt">layer</span> <span class="hlt">boundary</span> position. In this paper, the method of power spectrum inversion and sub-harmonic compensation were used to simulate <span class="hlt">atmospheric</span> turbulence <span class="hlt">layers</span> and results can be shown by grey map. The simulation results showed that, with the increase of turbulence <span class="hlt">layers</span>, the RMS of adaptive system decreased, but the amplitude diminished. So the <span class="hlt">atmospheric</span> turbulence can be split into 2-3 <span class="hlt">layers</span> and be modeled by phase screens. Otherwise, a small simulation <span class="hlt">atmospheric</span> turbulence delamination system was realized by JAVA.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.4421P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.4421P"><span id="translatedtitle">Halogen chemistry in the marine <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.</p> <p>2009-04-01</p> <p>Important <span class="hlt">atmospheric</span> sources of iodine include the air-sea exchange of biogenic iodocarbons, and the emission of I2 from macro-algae. The major source of bromine is the release of bromide ions from sea-salt aerosol. The subsequent <span class="hlt">atmospheric</span> chemistry of these halogens (1), changes the oxidizing capacity of the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> by destroying ozone and changing the hydroxyl radical concentration; (2), reacts efficiently with dimethyl sulphide and mercury (in the polar regions); and (3), leads to the formation of ultra-fine particles which may contribute to cloud condensation nuclei (CCN) and hence affect climate. This paper will report observations of IO, BrO, OIO and I2 made by the technique of differential optical absorption spectroscopy, in several contrasting marine environments: the equatorial mid-Atlantic (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar marine <span class="hlt">boundary</span> <span class="hlt">layer</span> (Hudson Bay, Canada). Both IO and BrO are observed in all these locations at significant concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. To complement the field campaigns we have also carried out wide-ranging laboratory investigation. A new study of OIO photochemistry shows that absorption in the visible bands between 490 and 630 nm leads to I atom production with a quantum yield of unity, which now means that iodine is a particularly powerful ozone-depleting agent. We have also studied the formation and growth kinetics of iodine oxide nano-particles, and their uptake of water, sulphuric acid and di-carboxylic organic acids, in order to model their growth to a size where they can act as CCN. Their ice-nucleating properties will also be reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10192039','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10192039"><span id="translatedtitle">LDV measurements of turbulent baroclinic <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Neuwald, P.; Reichenbach, H.; Kuhl, A.L.</p> <p>1993-07-01</p> <p>Described here are shock tube experiments of nonsteady, turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> with large density variations. A dense-gas <span class="hlt">layer</span> was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the <span class="hlt">layer</span>, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic <span class="hlt">boundary</span> <span class="hlt">layer</span>. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the <span class="hlt">boundary</span> <span class="hlt">layer</span> profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty <span class="hlt">boundary</span> <span class="hlt">layer</span> value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19760056441&hterms=1234&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3D1234','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19760056441&hterms=1234&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3D1234"><span id="translatedtitle">Viscous <span class="hlt">boundary</span> <span class="hlt">layers</span> in rotating fluids driven by periodic flows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bergstrom, R. W.; Cogley, A. C.</p> <p>1976-01-01</p> <p>The paper analyzes the <span class="hlt">boundary</span> <span class="hlt">layers</span> formed in a rotating fluid by an oscillating flow over an infinite half plate, with particular attention paid to the effects of unsteadiness, the critical latitude effect and the structure of the solution to the <span class="hlt">boundary</span> <span class="hlt">layer</span> equations at resonance. The Navier-Stokes <span class="hlt">boundary</span> <span class="hlt">layer</span> equations are obtained through an asymptotic expansion with the incorporation of the Rossby and Ekman numbers and are analyzed as the sum of a nonlinear steady solution and a linearized unsteady solution. The solution is predominantly composed of two inertial wave vector components, one circularly polarized to the left and the other circularly polarized to the right. The problem considered here has relevance in oceanography and meteorology, with special reference to the unsteady <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983STIA...8316682M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983STIA...8316682M"><span id="translatedtitle">Longitudinal vortices imbedded in turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mehta, R. D.; Shabaka, I. M. M.; Shibl, A.; Bradshaw, P.</p> <p>1983-01-01</p> <p>The attenuation of skew-induced longitudinal vortices by turbulent or viscous stresses is studied for the case of pure, artificially-generated longitudinal vortices entrained into initially two-dimensional <span class="hlt">boundary</span> <span class="hlt">layers</span> in nominally zero pressure gradients. Three types of vortex-<span class="hlt">boundary</span> interactions are studied in detail: (1) an isolated vortex in a two-dimensional <span class="hlt">boundary</span> <span class="hlt">layer</span>; (2) a vortex pair in a turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> with the common flow between the vortices moving away from the surface; (3) a vortex pair in a <span class="hlt">boundary</span> <span class="hlt">layer</span> with the common flow moving towards the surface. Detailed mean flow and turbulence measurements are made, showing that the eddy viscosities defined for the different shear-stress components behave in different and complicated ways. Terms in the Reynolds stress transport equations, notably the triple products that effect turbulent diffusion of Reynolds stress, also fail to obey simple rules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AtmEn.131...97T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AtmEn.131...97T"><span id="translatedtitle">Highly buoyant bent-over plumes in a <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tohidi, Ali; Kaye, Nigel B.</p> <p>2016-04-01</p> <p>Highly buoyant plumes, such as wildfire plumes, in low to moderate wind speeds have initial trajectories that are steeper than many industrial waste plumes. They will rise further into the <span class="hlt">atmosphere</span> before bending significantly. In such cases the plume's trajectory will be influenced by the vertical variation in horizontal velocity of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. This paper examined the behavior of a plume in an unstratified environment with a power-law ambient velocity profile. Examination of previously published experimental measurements of plume trajectory show that inclusion of the <span class="hlt">boundary</span> <span class="hlt">layer</span> velocity profile in the plume model often provides better predictions of the plume trajectory compared to algebraic expressions developed for uniform flow plumes. However, there are many cases in which uniform velocity profile algebraic expressions are as good as <span class="hlt">boundary</span> <span class="hlt">layer</span> models. It is shown that it is only important to model the role of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> velocity profile in cases where either the momentum length (square root of source momentum flux divided by the reference wind speed) or buoyancy length (buoyancy flux divided by the reference wind speed cubed) is significantly greater than the plume release height within the <span class="hlt">boundary</span> <span class="hlt">layer</span>. This criteria is rarely met with industrial waste plumes, but it is important in modeling wildfire plumes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/792807','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/792807"><span id="translatedtitle">An Evaluation of <span class="hlt">Boundary</span> Conditions for Modeling Urban <span class="hlt">Boundary</span> <span class="hlt">Layers</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Calhoun, R.J.; Chan, S.T.; Lee, R.L.</p> <p>2000-05-18</p> <p>Numerical modeling of the urban <span class="hlt">boundary</span> <span class="hlt">layer</span> is complicated by the need to describe airflow patterns outside of the computational domain. These patterns have an impact on how successfully the simulation is able to model the turbulence associated with the urban <span class="hlt">boundary</span> <span class="hlt">layer</span>. This talk presents experiments with the model <span class="hlt">boundary</span> conditions for simulations that were done to support two Department of Energy observational programs involving the Salt Lake City basin. The Chemical/Biological Non-proliferation Program (CBNP) is concerned with the effects of buildings on influencing dispersion patterns in urban environments. The Vertical Transport and Mixing Program (VTMX) investigating mixing mechanisms in the stable <span class="hlt">boundary</span> <span class="hlt">layer</span> and how they are influenced by the channeling caused by drainage flows or by obstacles such as building complexes. Both of these programs are investigating the turbulent mixing caused by building complexes and other urban obstacles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19840025688&hterms=digital+suction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Ddigital%2Bsuction','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19840025688&hterms=digital+suction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Ddigital%2Bsuction"><span id="translatedtitle"><span class="hlt">Boundary-layer</span> linear stability theory</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mack, L. M.</p> <p>1984-01-01</p> <p>Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of <span class="hlt">boundary</span> <span class="hlt">layer</span> instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius <span class="hlt">boundary</span> <span class="hlt">layer</span>, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a <span class="hlt">boundary</span> <span class="hlt">layer</span>, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to <span class="hlt">boundary</span> <span class="hlt">layers</span> with pressure gradients and suction was applied. The only large body of numerical results for exact <span class="hlt">boundary</span> <span class="hlt">layer</span> solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984scst.agar.....M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984scst.agar.....M"><span id="translatedtitle"><span class="hlt">Boundary-layer</span> linear stability theory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mack, L. M.</p> <p>1984-06-01</p> <p>Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of <span class="hlt">boundary</span> <span class="hlt">layer</span> instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius <span class="hlt">boundary</span> <span class="hlt">layer</span>, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a <span class="hlt">boundary</span> <span class="hlt">layer</span>, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to <span class="hlt">boundary</span> <span class="hlt">layers</span> with pressure gradients and suction was applied. The only large body of numerical results for exact <span class="hlt">boundary</span> <span class="hlt">layer</span> solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19790010770&hterms=caries&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dcaries','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19790010770&hterms=caries&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dcaries"><span id="translatedtitle">Calculation methods for compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.</p> <p>1976-01-01</p> <p>Calculation procedures for non-reacting compressible two- and three-dimensional turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete <span class="hlt">boundary</span> <span class="hlt">layer</span> equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880014358','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880014358"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> flow visualization for flight testing</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Obara, Clifford J.</p> <p>1986-01-01</p> <p>Flow visualization is used extensively in flight testing to determine aerodynamic characteristics such as surface flow direction and <span class="hlt">boundary</span> <span class="hlt">layer</span> state. Several visualization techniques are available to the aerodynamicist. Two of the most popular are oil flows and sublimating chemicals. Oil is used to visualize <span class="hlt">boundary</span> <span class="hlt">layer</span> transition, shock wave location, regions of separated flow, and surface flow direction. <span class="hlt">Boundary</span> <span class="hlt">layer</span> transition can also be visualized with sublimating chemicals. A summary of these two techniques is discussed, and the use of sublimating chemicals is examined in some detail. The different modes of <span class="hlt">boundary</span> <span class="hlt">layer</span> transition are characterized by different patterns in the sublimating chemical coating. The discussion includes interpretation of these chemical patterns and the temperature and velocity operating limitations of the chemical substances. Information for selection of appropriate chemicals for a desired set of flight conditions is provided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970003073','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970003073"><span id="translatedtitle">Dynamic Acoustic Detection of <span class="hlt">Boundary</span> <span class="hlt">Layer</span> transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grohs, Jonathan R.</p> <p>1995-01-01</p> <p>The wind tunnel investigation into the acoustic nature of <span class="hlt">boundary</span> <span class="hlt">layer</span> transition using miniature microphones. This research is the groundwork for entry into the National Transonic Facility (NTF) at the NASA Langley Research Center (LaRC). Due to the extreme environmental conditions of NTF testing, low temperatures and high pressures, traditional <span class="hlt">boundary</span> <span class="hlt">layer</span> detection methods are not available. The emphasis of this project and further studies is acoustical sampling of a typical <span class="hlt">boundary</span> <span class="hlt">layer</span> and environmental durability of the miniature microphones. The research was conducted with the 14 by 22 Foot Subsonic Tunnel, concurrent with another wind tunnel test. Using the resources of LaRC, a full inquiry into the feasibility of using Knowles Electronics, Inc. EM-3086 microphones to detect the surface <span class="hlt">boundary</span> <span class="hlt">layer</span>, under differing conditions, was completed. This report shall discuss the difficulties encountered, product performance and observations, and future research adaptability of this method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19890023280&hterms=Harvey+William&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2528Harvey%2BWilliam%2529','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19890023280&hterms=Harvey+William&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2528Harvey%2BWilliam%2529"><span id="translatedtitle"><span class="hlt">Boundary-layer</span> control for drag reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Harvey, William D.</p> <p>1988-01-01</p> <p>Although the number of possible applications of <span class="hlt">boundary-layer</span> control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, <span class="hlt">boundary</span> <span class="hlt">layer</span> stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19780000255&hterms=tunnel+detection&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dtunnel%2Bdetection','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19780000255&hterms=tunnel+detection&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dtunnel%2Bdetection"><span id="translatedtitle">Detection of <span class="hlt">boundary-layer</span> transitions in wind tunnels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wood, W. R.; Somers, D. M.</p> <p>1978-01-01</p> <p>Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent <span class="hlt">boundary-layer</span> transitions on wind-tunnel models. Technique allows measurements above or below <span class="hlt">atmospheric</span> pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740015049','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740015049"><span id="translatedtitle">Acoustic sounding in the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kelly, E. H.</p> <p>1974-01-01</p> <p>Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the <span class="hlt">boundary</span> between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion <span class="hlt">layer</span>. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion <span class="hlt">layer</span> as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower <span class="hlt">atmosphere</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910001208','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910001208"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> roll circulations during FIRE</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shirer, Hampton N.; Haack, Tracy</p> <p>1990-01-01</p> <p>The probable mechanism underlying the development of <span class="hlt">boundary</span> <span class="hlt">layer</span> roll circulations are studied using wind and temperature profiles measured by the National Center for <span class="hlt">Atmospheric</span> Research (NCAR) Electra during the stratocumulus phase of the First ISCCP Regional Experiment (FIRE). The expected, or preferred, roll orientations, horizontal wavelengths, and propagation periods are determined by finding the minimum values of the dynamic and thermodynamic forcing parameters, which here are the eddy Reynolds number (Re) and moist Rayleigh number (Ra sub m). These minimum values depend on the height z sub T of the capping temperature inversion and on the values of the Fourier coefficients of the background height-dependent vector wind profile. As input to our nonlinear spectral model, descent and ascent runs by the Electra provide for initial estimates of the inversion height and the wind profiles. In the first phase of the investigation presented here, a mechanism is said to be a probable contributor to the development of roll circulations within the stratocumulus-topped <span class="hlt">boundary</span> <span class="hlt">layer</span> if the modeled roll orientation and wavelengths agree with their observed values. Preliminary results using the 14-coefficient model of Haack-Hirschberg (1988) are discussed for the 7 July 1987 Electra Mission 188-A (Flight 5). This mission was flown across a sharp cloud <span class="hlt">boundary</span> that was within a LANDSAT/SPOT scene. The stratocumulus deck was relatively solid in the eastern part of the scene, while there was a rapid decrease in cloud cover to scattered cumulus clouds aligned in streets to the west. These cloud streets were oriented nearly parallel to the mean wind direction in the <span class="hlt">layer</span>, which was approximately 340 degrees. The hypothesis that roll circulations occurred in both the relatively clear and the cloudy regions is investigated using as model input a descent profile obtained in the relatively clear air and an ascent profile obtained in the cloudy air. Initial results for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880014354','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880014354"><span id="translatedtitle"><span class="hlt">Boundary-layer</span> stability and airfoil design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Viken, Jeffrey K.</p> <p>1986-01-01</p> <p>Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the <span class="hlt">boundary</span> <span class="hlt">layer</span> laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850006060&hterms=marine+structure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dmarine%2Bstructure','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850006060&hterms=marine+structure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dmarine%2Bstructure"><span id="translatedtitle">Structure and Growth of the Marine <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mccumber, M.</p> <p>1984-01-01</p> <p>LANDSAT visible imagery and a one-dimensional Lagrangian <span class="hlt">boundary</span> <span class="hlt">layer</span> model were used to hypothesize the nature and the development of the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> during a winter episode of strong seaward cold air advection. Over-water heating and moistening of the cold, dry continental air is estimable from linear relations involving horizontal gradients of the near-surface air temperature and humidity. A line of enhanced convection paralleling the Atlantic U.S. coast from south of New York Bay to the vicinity of Virginia Beach, VA was attributed to stronger convergence at low levels. This feature was characterized as a mesoscale front. With the assistance of a three-dimensional mesoscale <span class="hlt">boundary</span> <span class="hlt">layer</span> model, initialized with data obtained from the MASEX, the marine <span class="hlt">boundary</span> <span class="hlt">layer</span> can be mapped over the entire Atlantic coastal domain and the evolution of the <span class="hlt">boundary</span> <span class="hlt">layer</span> can be studied as a function of different characteristics of important surface level forcings. The effects on <span class="hlt">boundary</span> <span class="hlt">layer</span> growth due to the magnitude and pattern of sea surface temperature, to the shape of the coastline, and to <span class="hlt">atmospheric</span> conditions, such as the orientation of the prevailing wind are examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvL.112l4301D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvL.112l4301D"><span id="translatedtitle">Turbulent <span class="hlt">Boundary</span> <span class="hlt">Layer</span> in High Rayleigh Number Convection in Air</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian</p> <p>2014-03-01</p> <p>Flow visualizations and particle image velocimetry measurements in the <span class="hlt">boundary</span> <span class="hlt">layer</span> of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra =1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span>. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the <span class="hlt">boundary</span> <span class="hlt">layer</span> thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layers</span>. From our observations, we conclude that the convective <span class="hlt">boundary</span> <span class="hlt">layer</span> becomes turbulent locally and temporarily although its Reynolds number Re ≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the <span class="hlt">boundary</span> <span class="hlt">layer</span> towards turbulence depends on subtle details of the flow field and is therefore not universal.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.6259S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.6259S"><span id="translatedtitle">Dependence of <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Mixing On Lateral <span class="hlt">Boundary</span> Conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Straub, D.</p> <p></p> <p>Ocean circulation models often show strong mixing in association with lateral bound- ary <span class="hlt">layers</span>. Such mixing is generally considered to be artifactual rather than real. Fur- thermore, the severity of the problem is <span class="hlt">boundary</span> condition dependent. For example, an inconsistency between geostrophy and insulating <span class="hlt">boundary</span> conditions on tempera- ture and salinity cause many modelers to opt for the no slip, rather than slip <span class="hlt">boundary</span> condtion on the tangential component of momentum. As modellers increasingly move into the eddy revealing regime, biharmonic, rather than harmonic dissipative operators are likely to become more common. Biharmonic operators, however, require specifi- cation of additional <span class="hlt">boundary</span> conditions. For example, there are several `natural ex- tensions' to each of the slip and no slip conditions. Here, these various possiblities are considered in the context of a simple model. Particular attention is payed to how mixing (and the associated overturning cell) is affected by the choice of <span class="hlt">boundary</span> condition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015EGUGA..1713651Z&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015EGUGA..1713651Z&link_type=ABSTRACT"><span id="translatedtitle">Nature, theory and modelling of geophysical convective planetary <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zilitinkevich, Sergej</p> <p>2015-04-01</p> <p>Geophysical convective planetary <span class="hlt">boundary</span> <span class="hlt">layers</span> (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the <span class="hlt">boundary</span> <span class="hlt">layer</span> remains unstable. Penetration of the mixed <span class="hlt">layer</span> into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer <span class="hlt">boundary</span>. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer <span class="hlt">boundaries</span> (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface <span class="hlt">layer</span> and entrainment <span class="hlt">layer</span> (at the CPBL inner and outer <span class="hlt">boundaries</span>) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-<span class="hlt">layer</span> turbulence in <span class="hlt">atmospheric</span> and marine CPBLs is strongly enhanced by the velocity shears in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720018582','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720018582"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> loss sensitivity study using a modified ICRPG turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> computer program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Omori, S.; Krebsbach, A.; Gross, K. W.</p> <p>1972-01-01</p> <p>Modifications of the turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> (TBL) computer program refer to a more accurate representation of <span class="hlt">boundary</span> <span class="hlt">layer</span> edge conditions, internal calculation of the Prandtl number, a changed friction coefficient relationship, and computation of the performance degradation. Important input parameters of the modified TBL program such as wall temperature distribution, Prandtl number, Stanton number, and velocity profile exponent were changed and the individual effects on significant <span class="hlt">boundary</span> <span class="hlt">layer</span> parameters, heat transfer, and performance degradation are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFMGC53E1253A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFMGC53E1253A&link_type=ABSTRACT"><span id="translatedtitle">Effect of Derating and Shutting Down of Turbines on the Extracted Power of Large Wind Farms in Thermally-Stratified <span class="hlt">Atmospheric</span> <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adkins, K. A.</p> <p>2015-12-01</p> <p>Wind power is being increasingly employed to help meet an increasing energy demand in a more environmentally friendly manner and, consequently, large wind farms consisting of thousands of turbines have been constructed and deployed in various areas. Due to a multitude of factors, the layout of these multi-turbine arrays is not always optimized for maximum wind farm power extraction. Additionally, the shutting down or derating of certain wind turbines may impact the efficiency of large wind farms. In this study, a large eddy simulation (LES) of a fully developed wind turbine array <span class="hlt">boundary</span> <span class="hlt">layer</span> is performed in thermally stratified conditions. The impact on the overall plant performance, quantified by the collective extracted power of the turbines, is explored using a systematic shut down and derating of selected turbines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800017105','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800017105"><span id="translatedtitle">Lear jet <span class="hlt">boundary</span> <span class="hlt">layer</span>/shear <span class="hlt">layer</span> laser propagation experiments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gilbert, K.</p> <p>1980-01-01</p> <p>Optical degradations of aircraft turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> with shear <span class="hlt">layers</span> generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft <span class="hlt">boundary</span> <span class="hlt">layer</span> in double pass via a reflective airfoil. In addition, several flights examined shear <span class="hlt">layer</span>-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the <span class="hlt">boundary</span> <span class="hlt">layer</span>. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920001586','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001586"><span id="translatedtitle">Characteristics of the Martian <span class="hlt">atmosphere</span> surface <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clow, G. D.; Haberle, R. M.</p> <p>1991-01-01</p> <p>Researchers extend elements of various terrestrial <span class="hlt">boundary</span> <span class="hlt">layer</span> models to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian <span class="hlt">atmospheric</span> surface <span class="hlt">layer</span>. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed. Parameterizations for specific heat and and binary diffusivity were also determined. The Prandtl and Schmidt numbers derived from these thermophysical properties were found to range from 0.78 - 1.0 and 0.47 - 0.70, respectively, for Mars. Brutsaert's model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the researchers modified the definition of the Monin-Obukhov length to properly account for the buoyancy forces arising from water vapor gradients in the Martian <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. This length scale was then utilized with similarity theory turbulent flux profiles with the same form as those used by Businger et al. and others. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013AGUFM.A11F0124P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013AGUFM.A11F0124P&link_type=ABSTRACT"><span id="translatedtitle">Investigation of the spatio-temporal variability of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> depths over mountainous terrain observed with a suite of ground-based and airborne instruments during the MATERHORN field experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pal, S.; De Wekker, S.; Emmitt, G. D.</p> <p>2013-12-01</p> <p>We present first results of the spatio-temporal variability of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> depths obtained with a suite of ground-based and airborne instruments deployed during the first field phase of The Mountain Terrain <span class="hlt">Atmospheric</span> Modeling and Observations (MATERHORN) Program (http://www3.nd.edu/~dynamics/materhorn/index.php) at Dugway Proving Ground (DPG, Utah, USA) in Fall 2012. We mainly use high-resolution data collected on selected intensive observation periods obtained by Doppler lidars, ceilometer, and in-situ measurements from an unmanned aerial vehicle for the measurements of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) depths. In particular, a Navy Twin Otter aircraft flew 6 missions of about 5 hours each during the daytime, collecting remotely sensed (Doppler lidar, TODWL) wind data in addition to in-situ turbulence measurements which allowed a detailed investigation of the spatial heterogeneity of the convective <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence features over a steep isolated mountain of a horizontal and vertical scale of about 10 km and 1 km, respectively. Additionally, we use data collected by (1) radiosonde systems at two sites of Granite Mountain area in DPG (Playa and Sagebrush), (2) sonic anemometers (CSAT-3D) for high resolution turbulence flux measurements near ground, (3) Pyranometer for incoming solar radiation, and (4) standard meteorological measurements (PTU) obtained near the surface. In this contribution, we discuss and address (1) composites obtained with lidar, ceilometer, micro-meteorological measurements, and radiosonde observations to determine the quasi-continuous regime of ABL depths, growth rates, maximum convective <span class="hlt">boundary</span> <span class="hlt">layer</span> (CBL) depths, etc., (2) the temporal variability in the ABL depths during entire diurnal cycle and the spatial heterogeneity in the daytime ABL depths triggered by the underlying orography in the experimental area to investigate the most possible mechanisms (e.g. combined effect of diurnal cycle and orographic trigger</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1414376K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1414376K"><span id="translatedtitle">Modeling of particulate plumes transportation in <span class="hlt">boundary</span> <span class="hlt">layers</span> with obstacles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karelsky, K. V.; Petrosyan, A. S.</p> <p>2012-04-01</p> <p>This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary <span class="hlt">boundaries</span>. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex <span class="hlt">boundary</span>. In viscous <span class="hlt">atmosphere</span> with as small as one likes coefficient of molecular viscosity, the non-slip <span class="hlt">boundary</span> condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring <span class="hlt">layers</span> energy dissipation of <span class="hlt">atmosphere</span> flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in <span class="hlt">atmosphere</span> movement characterizing by a high Reynolds number the <span class="hlt">boundary</span> <span class="hlt">layer</span> is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external <span class="hlt">boundary</span> of the <span class="hlt">layer</span> that are quite close to ones in ideal <span class="hlt">atmosphere</span> flow. In that <span class="hlt">layer</span> fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid <span class="hlt">boundary</span> caused not only by nonslip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of high wind gradients in the <span class="hlt">boundary</span> <span class="hlt">layer</span> and on the other hand disregard of molecular viscosity in two-phase <span class="hlt">atmosphere</span> equations. We deal with describing high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616905K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616905K"><span id="translatedtitle">Transport of Particulates in <span class="hlt">Boundary</span> <span class="hlt">Layer</span> with Obstacles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karelsky, Kirill; Petrosyan, Arakel</p> <p>2014-05-01</p> <p>This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary <span class="hlt">boundaries</span>. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex <span class="hlt">boundary</span>. In viscous <span class="hlt">atmosphere</span> with as small as one likes coefficient of molecular viscosity, the non-slip <span class="hlt">boundary</span> condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring <span class="hlt">layers</span> energy dissipation of <span class="hlt">atmosphere</span> flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in <span class="hlt">atmosphere</span> movement characterizing by a high Reynolds number the <span class="hlt">boundary</span> <span class="hlt">layer</span> is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external <span class="hlt">boundary</span> of the <span class="hlt">layer</span> that are quite close to ones in ideal <span class="hlt">atmosphere</span> flow. In that <span class="hlt">layer</span> fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid <span class="hlt">boundary</span> caused not only by nonslip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of high wind gradients in the <span class="hlt">boundary</span> <span class="hlt">layer</span> and on the other hand disregard of molecular viscosity in two-phase <span class="hlt">atmosphere</span> equations. We deal with describing high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730023455','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730023455"><span id="translatedtitle">High enthalpy hypersonic <span class="hlt">boundary</span> <span class="hlt">layer</span> flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yanow, G.</p> <p>1972-01-01</p> <p>A theoretical and experimental study of an ionizing laminar <span class="hlt">boundary</span> <span class="hlt">layer</span> formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium <span class="hlt">boundary</span> <span class="hlt">layer</span> equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen <span class="hlt">boundary</span> <span class="hlt">layer</span> solution than in an equilibrium <span class="hlt">boundary</span> <span class="hlt">layer</span> calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen <span class="hlt">boundary</span> <span class="hlt">layer</span> will adequately predict surface heat transfer rate in very high enthalpy flows.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080037569','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080037569"><span id="translatedtitle"><span class="hlt">Boundary-Layer</span>-Ingesting Inlet Flow Control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.</p> <p>2008-01-01</p> <p>An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant <span class="hlt">boundary-layer</span>-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a <span class="hlt">boundary-layer</span>-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large <span class="hlt">boundary</span> <span class="hlt">layer</span> with a <span class="hlt">boundary-layer</span>-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset <span class="hlt">boundary</span> <span class="hlt">layer</span>, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/830034','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/830034"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Cloudiness Parameterizations Using ARM Observations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bruce Albrecht</p> <p>2004-09-15</p> <p>This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of <span class="hlt">boundary</span> <span class="hlt">layer</span> clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of <span class="hlt">boundary</span> <span class="hlt">layer</span> clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in <span class="hlt">boundary</span> <span class="hlt">layer</span> clouds and estimate the limitations of using current and past MMCR data for <span class="hlt">boundary</span> <span class="hlt">layer</span> cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of <span class="hlt">boundary</span> <span class="hlt">layer</span> clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910017151','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910017151"><span id="translatedtitle">The Kinematics of Turbulent <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Robinson, Stephen Kern</p> <p>1991-01-01</p> <p>The long history of research into the internal structure of turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of <span class="hlt">boundary</span> <span class="hlt">layer</span> structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of <span class="hlt">boundary</span> <span class="hlt">layer</span> structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the <span class="hlt">boundary</span> <span class="hlt">layer</span>. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813245H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813245H"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Flow Over a Moving Wavy Surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hendin, Gali; Toledo, Yaron</p> <p>2016-04-01</p> <p><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Flow Over a Moving Wavy Surface Gali Hendin(1), Yaron Toledo(1) January 13, 2016 (1)School of Mechanical Engineering, Tel-Aviv University, Israel Understanding the <span class="hlt">boundary</span> <span class="hlt">layer</span> flow over surface gravity waves is of great importance as various <span class="hlt">atmosphere</span>-ocean processes are essentially coupled through these waves. Nevertheless, there are still significant gaps in our understanding of this complex flow behaviour. The present work investigates the fundamentals of the <span class="hlt">boundary</span> <span class="hlt">layer</span> air flow over progressive, small-amplitude waves. It aims to extend the well-known Blasius solution for a <span class="hlt">boundary</span> <span class="hlt">layer</span> over a flat plate to one over a moving wavy surface. The current analysis pro- claims the importance of the small curvature and the time-dependency as second order effects, with a meaningful impact on the similarity pattern in the first order. The air flow over the ocean surface is modelled using an outer, inviscid half-infinite flow, overlaying the viscous <span class="hlt">boundary</span> <span class="hlt">layer</span> above the wavy surface. The assumption of a uniform flow in the outer <span class="hlt">layer</span>, used in former studies, is now replaced with a precise analytical solution of the potential flow over a moving wavy surface with a known celerity, wavelength and amplitude. This results in a conceptual change from former models as it shows that the pressure variations within the <span class="hlt">boundary</span> <span class="hlt">layer</span> cannot be neglected. In the <span class="hlt">boundary</span> <span class="hlt">layer</span>, time-dependent Navier-Stokes equations are formulated in a curvilinear, orthogonal coordinate system. The formulation is done in an elaborate way that presents additional, formerly neglected first-order effects, resulting from the time-varying coordinate system. The suggested time-dependent curvilinear orthogonal coordinate system introduces a platform that can also support the formulation of turbulent problems for any surface shape. In order to produce a self-similar Blasius-type solution, a small wave-steepness is assumed and a perturbation method is applied. Consequently, a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910013675','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910013675"><span id="translatedtitle">Characteristics of the Martian <span class="hlt">atmosphere</span> surface <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clow, G. D.; Haberle, R. M.</p> <p>1990-01-01</p> <p>Elements of various terrestrial <span class="hlt">boundary</span> <span class="hlt">layer</span> models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian <span class="hlt">atmospheric</span> surface ('constant flux') <span class="hlt">layer</span>. The <span class="hlt">atmospheric</span> surface <span class="hlt">layer</span> consists of an interfacial sublayer immediately adjacent to the ground and an overlying fully turbulent surface sublayer where wind-shear production of turbulence dominates buoyancy production. Within the interfacial sublayer, sensible and latent heat are transported by non-steady molecular diffusion into small-scale eddies which intermittently burst through this zone. Both the thickness of the interfacial sublayer and the characteristics of the turbulent eddies penetrating through it depend on whether airflow is aerodynamically smooth or aerodynamically rough, as determined by the Roughness Reynold's number. Within the overlying surface sublayer, similarity theory can be used to express the mean vertical windspeed, temperature, and water vapor profiles in terms of a single parameter, the Monin-Obukhov stability parameter. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed using data from the TPRC Data Series and the first-order Chapman-Cowling expressions; the required collision integrals were approximated using the Lenard-Jones potential. Parameterizations for specific heat and binary diffusivity were also determined. The Brutsart model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the definition of the Monin-Obukhov length was modified to properly account for the buoyancy forces arising from water vapor gradients in the Martian <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span>. It was found that under most Martian conditions, the interfacial and surface</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19950014657&hterms=raumfahrt&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Draumfahrt','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19950014657&hterms=raumfahrt&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Draumfahrt"><span id="translatedtitle">Numerical simulation of supersonic <span class="hlt">boundary</span> <span class="hlt">layer</span> transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.</p> <p>1994-01-01</p> <p>The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible <span class="hlt">boundary</span> <span class="hlt">layer</span> transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate <span class="hlt">boundary</span> <span class="hlt">layers</span> in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing <span class="hlt">boundary</span> <span class="hlt">layer</span>. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790022341','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790022341"><span id="translatedtitle">Mechanics of <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Transition. Part 5: <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Stability theory in incompressible and compressible flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mack, L. M.</p> <p>1967-01-01</p> <p>The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar <span class="hlt">boundary</span> determines whether a small disturbance introduced into the <span class="hlt">boundary</span> <span class="hlt">layer</span> will amplify or damp. If the disturbance damps, the <span class="hlt">boundary</span> <span class="hlt">layer</span> remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the <span class="hlt">boundary</span> <span class="hlt">layer</span> which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.A54B..06K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.A54B..06K"><span id="translatedtitle">Aerosol buffering of marine <span class="hlt">boundary</span> <span class="hlt">layer</span> cloudiness</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kazil, J.; Feingold, G.; Wang, H.</p> <p>2010-12-01</p> <p>The role of aerosol particles in maintaining a cloudy <span class="hlt">boundary</span> <span class="hlt">layer</span> in the remote marine environment is explored. It has previously been shown that precipitation can result in the transition from a closed- to open-cellular state but that the <span class="hlt">boundary</span> <span class="hlt">layer</span> cannot maintain this open-cell state without a resupply of particles. Potential sources include wind-driven production of sea salt particles from the ocean, nucleation from the gas phase, and entrainment from the free troposphere. Here we investigate with model simulations how the interplay of cloud properties, aerosol production, and <span class="hlt">boundary</span> <span class="hlt">layer</span> dynamics results in aerosol sources acting as a buffer against processes that destabilize cloudiness and the dynamic state of the marine <span class="hlt">boundary</span> <span class="hlt">layer</span>. For example, at nighttime, cloud liquid water increases in the absence of solar heating, resulting in increased precipitation, stronger cloud top cooling, accelerated <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence, and faster surface wind speeds. Faster surface wind speeds drive an enhanced flux of sea salt aerosol, at a time when aerosol particles are scavenged more readily by enhanced precipitation. In contrast, absorption of solar radiation during daytime reduces cloud water, decelerates <span class="hlt">boundary</span> <span class="hlt">layer</span> turbulence, reduces surface wind speeds, and therefore slows surface emissions. This is compensated by nucleation of small aerosol particles from the gas phase in response to the nigh complete removal of cloud condensation nuclei in precipitating open cell walls. These newly formed particles need to grow to larger sizes before they can serve as cloud condensation nuclei (CCN), but will likely contribute to the CCN population during the nighttime and, together with ocean emissions, buffer the system against precipitation removal.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850015927','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850015927"><span id="translatedtitle">Stability of an oscillating <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Levchenko, V. Y.; Solovyev, A. S.</p> <p>1985-01-01</p> <p>Levchenko and Solov'ev (1972, 1974) have developed a stability theory for space periodic flows, assuming that the Floquet theory is applicable to partial differential equations. In the present paper, this approach is extended to unsteady periodic flows. A complete unsteady formulation of the stability problem is obtained, and the stability characteristics over an oscillating period are determined from the solution of the problem. Calculations carried out for an oscillating incompressible <span class="hlt">boundary</span> <span class="hlt">layer</span> on a plate showed that the <span class="hlt">boundary</span> <span class="hlt">layer</span> flow may be regarded as a locally parallel flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985STIN...8524238L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985STIN...8524238L"><span id="translatedtitle">Stability of an oscillating <span class="hlt">boundary</span> <span class="hlt">layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Levchenko, V. Y.; Solovyev, A. S.</p> <p>1985-03-01</p> <p>Levchenko and Solov'ev (1972, 1974) have developed a stability theory for space periodic flows, assuming that the Floquet theory is applicable to partial differential equations. In the present paper, this approach is extended to unsteady periodic flows. A complete unsteady formulation of the stability problem is obtained, and the stability characteristics over an oscillating period are determined from the solution of the problem. Calculations carried out for an oscillating incompressible <span class="hlt">boundary</span> <span class="hlt">layer</span> on a plate showed that the <span class="hlt">boundary</span> <span class="hlt">layer</span> flow may be regarded as a locally parallel flow.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19940000264&hterms=fortran+code&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfortran%2Bcode','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19940000264&hterms=fortran+code&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfortran%2Bcode"><span id="translatedtitle"><span class="hlt">Boundary-Layer</span> Code For Supersonic Combustion</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pinckney, S. Z.; Walton, J. T.</p> <p>1994-01-01</p> <p>HUD is integral computer code based on Spaulding-Chi method for predicting development of <span class="hlt">boundary</span> <span class="hlt">layers</span> in laminar, transitional, and turbulent regions of flows on two-dimensional or axisymmetric bodies. Approximates nonequilibrium velocity profiles as well as local surface friction in presence of pressure gradient. Predicts transfer of heat in turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> in presence of high axial presure gradient. Provides for pressure gradients both normal and lateral to surfaces. Also used to estimate requirements for cooling scramjet engines. Because of this capability, HUD program incorporated into several scramjet-cycle-performance-analysis codes, including SCRAM (ARC-12338) and SRGULL (LEW-15093). Written in FORTRAN 77.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhFl...27b5108E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhFl...27b5108E"><span id="translatedtitle">Hairpin vortices in turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eitel-Amor, G.; Örlü, R.; Schlatter, P.; Flores, O.</p> <p>2015-02-01</p> <p>The present work presents a number of parallel and spatially developing simulations of <span class="hlt">boundary</span> <span class="hlt">layers</span> to address the question of whether hairpin vortices are a dominant feature of near-wall turbulence, and which role they play during transition. In the first part, the parent-offspring regeneration mechanism is investigated in parallel (temporal) simulations of a single hairpin vortex introduced in a mean shear flow corresponding to either turbulent channels or <span class="hlt">boundary</span> <span class="hlt">layers</span> (Reτ ≲ 590). The effect of a turbulent background superimposed on the mean flow is considered by using an eddy viscosity computed from resolved simulations. Tracking the vortical structure downstream, it is found that secondary hairpins are only created shortly after initialization, with all rotational structures decaying for later times. For hairpins in a clean (laminar) environment, the decay is relatively slow, while hairpins in weak turbulent environments (10% of νt) dissipate after a couple of eddy turnover times. In the second part, the role of hairpin vortices in laminar-turbulent transition is studied using simulations of spatial <span class="hlt">boundary</span> <span class="hlt">layers</span> tripped by hairpin vortices. These vortices are generated by means of specific volumetric forces representing an ejection event, creating a synthetic turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span> initially dominated by hairpin-like vortices. These hairpins are advected towards the wake region of the <span class="hlt">boundary</span> <span class="hlt">layer</span>, while a sinusoidal instability of the streaks near the wall results in rapid development of a turbulent <span class="hlt">boundary</span> <span class="hlt">layer</span>. For Reθ > 400, the <span class="hlt">boundary</span> <span class="hlt">layer</span> is fully developed, with no evidence of hairpin vortices reaching into the wall region. The results from both the parallel and spatial simulations strongly suggest that the regeneration process is rather short-lived and may not sustain once a turbulent background is developed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former direct numerical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.H13C1116T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.H13C1116T"><span id="translatedtitle">Study of the effect of soil disturbance on vapor transport through integrated modeling of the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> and shallow subsurface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Trautz, A.; Smits, K. M.; Cihan, A.; Wallen, B.</p> <p>2014-12-01</p> <p>Soil-water evaporation is one of the governing processes responsible for controlling water and energy exchanges between the land and <span class="hlt">atmosphere</span>. Despite its wide relevance and application in many natural and manmade environments (e.g. soil tillage practices, wheel-track compaction, fire burn environments, textural <span class="hlt">layering</span> and buried ordinances), there are very few studies of evaporation from disturbed soil profiles. The purpose of this study was to explore the effect of soil disturbance and capillary coupling on water distribution and fluxes. We modified a theory previously developed by the authors that allows for coupling single-phase (gas), two-component (air and water vapor) transfer in the <span class="hlt">atmosphere</span> and two-phase (gas, liquid), two-component (air and water vapor) flow in porous media at the REV scale under non-isothermal, non-equilibrium conditions to better account for the hydraulic and thermal interactions within the media. Modeling results were validated and compared using precision data generated in a two-dimensional soil tank consisting of a loosely packed soil surrounded by a tightly packed soil. The soil tank was outfitted with an array of sensors for the measurement of wind velocity, soil and air temperature, relative humidity, soil moisture, and weight. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process in heterogeneous soils with good accuracy. Evaporation from a heterogeneous soil consisting of a loose and tight packing condition is larger than the homogeneous equivalent systems. Liquid water is supplied from the loosely packed soil region to the tightly packed soil regions, sustaining a longer Stage I evaporation in the tightly packed regions with overall greater evaporation rate than uniform homogeneous packing. In contrast, lower evaporation rates from the loosely packed regions are observed due to a limited liquid water supply resulting from capillary flow to the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19750063131&hterms=blast+wave&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dblast%2Bwave','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19750063131&hterms=blast+wave&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dblast%2Bwave"><span id="translatedtitle"><span class="hlt">Boundary-layer</span> theory for blast waves</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.</p> <p>1975-01-01</p> <p>It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a <span class="hlt">boundary</span> <span class="hlt">layer</span>. Reported here is an analytical method developed for the study of such <span class="hlt">layers</span>, based on the matched asymptotic expansion technique combined with patched solutions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780005428','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780005428"><span id="translatedtitle">Calculation methods for compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span>, 1976</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.</p> <p>1977-01-01</p> <p>Equations and closure methods for compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> are discussed. Flow phenomena peculiar to calculation of these <span class="hlt">boundary</span> <span class="hlt">layers</span> were considered, along with calculations of three dimensional compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span>. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent <span class="hlt">boundary</span> <span class="hlt">layers</span> were appended, including finite difference, finite element, and mass-weighted residual methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JESS..118..281A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JESS..118..281A"><span id="translatedtitle">A case study of <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> features during winter over a tropical inland station — Kharagpur (22.32°N, 87.32°E)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alappattu, Denny P.; Kunhikrishnan, P. K.; Aloysius, Marina; Mohan, M.</p> <p>2009-08-01</p> <p>The local weather and air quality over a region are greatly influenced by the <span class="hlt">atmospheric</span> <span class="hlt">boundary</span> <span class="hlt">layer</span> (ABL) structure and dynamics. ABL characteristics were measured using a tethered balloon-sonde system over Kharagpur (22.32°N, 87.32°E, 40m above MSL), India, for the period 7 December 2004 to 30 December 2004, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP) Aerosol Land Campaign II. High-resolution data of pressure, temperature, humidity, wind speed and wind direction were archived along with surface <span class="hlt">layer</span> measurements using an automatic weather station. This paper presents the features of ABL, like ABL depth and nocturnal <span class="hlt">boundary</span> <span class="hlt">layer</span> (NBL) depth. The sea surface winds from Quikscat over the oceanic regions near the experiment site were analyzed along with the NCEP/NCAR reanalysis winds over Kharagpur to estimate the convergence of wind, moisture and vorticity to understand the observed variations in wind speed and relative humidity, and also the increased aerosol concentrations. The variation of ventilation coefficient ( V C), a factor determining the air pollution potential over a region, is also discussed in detail.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160010024','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160010024"><span id="translatedtitle">Nonlinear Transient Growth and <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Paredes, Pedro; Choudhari, Meelan M.; Li, Fei</p> <p>2016-01-01</p> <p>Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate <span class="hlt">boundary</span> <span class="hlt">layer</span> and a Mach 6 circular cone <span class="hlt">boundary</span> <span class="hlt">layer</span>. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the <span class="hlt">boundary</span> <span class="hlt">layer</span> flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed <span class="hlt">boundary</span> <span class="hlt">layer</span> without any streaks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900015241','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900015241"><span id="translatedtitle">Flow unsteadiness effects on <span class="hlt">boundary</span> <span class="hlt">layers</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Murthy, Sreedhara V.</p> <p>1989-01-01</p> <p>The development of <span class="hlt">boundary</span> <span class="hlt">layers</span> at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on <span class="hlt">boundary</span> <span class="hlt">layer</span> growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire <span class="hlt">boundary</span> <span class="hlt">layer</span> for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080023459','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080023459"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">Layer</span> Transition on X-43A</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert</p> <p>2008-01-01</p> <p>The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote <span class="hlt">boundary</span> <span class="hlt">layer</span> transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of <span class="hlt">boundary</span> <span class="hlt">layer</span> transition, for both Mach 7 and 10 flight conditions, suggested that forebody <span class="hlt">boundary</span> <span class="hlt">layer</span> trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the <span class="hlt">boundary</span> <span class="hlt">layer</span> trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100003043','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100003043"><span id="translatedtitle">Orbiter <span class="hlt">Boundary</span> <span class="hlt">Layer</span> Transition Prediction Tool Enhancements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.</p> <p>2010-01-01</p> <p>Updates to an analytic tool developed for Shuttle support to predict the onset of <span class="hlt">boundary</span> <span class="hlt">layer</span> transition resulting from thermal protection system damage or repair are presented. The <span class="hlt">boundary</span> <span class="hlt">layer</span> transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The <span class="hlt">boundary</span> <span class="hlt">layer</span> transition criteria utilized within the tool were updated based on new local <span class="hlt">boundary</span> <span class="hlt">layer</span> properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1171944','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1171944"><span id="translatedtitle">Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span> from AERI and MPL</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sawyer, Virginia</p> <p>2014-02-13</p> <p>The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> (PBL), which limits the dilution of pollutants and influences <span class="hlt">boundary-layer</span> convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed <span class="hlt">boundary-layer</span> air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of <span class="hlt">boundary-layer</span> processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016HEAD...1511901B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016HEAD...1511901B"><span id="translatedtitle">Astrophysical <span class="hlt">Boundary</span> <span class="hlt">Layers</span>: A New Picture</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Belyaev, Mikhail; Rafikov, Roman R.; Mclellan Stone, James</p> <p>2016-04-01</p> <p>Accretion is a ubiquitous process in astrophysics. In cases when the magnetic field is not too strong and a disk is formed, accretion can proceed through the mid plane all the way to the surface of the central compact object. Unless that compact object is a black hole, a <span class="hlt">boundary</span> <span class="hlt">layer</span> will be formed where the accretion disk touches its surfaces. The <span class="hlt">boundary</span> <span class="hlt">layer</span> is both dynamically and observationally significant as up to half of the accretion energy is dissipated there.Using a combination of analytical theory and computer simulations we show that angular momentum transport and accretion in the <span class="hlt">boundary</span> <span class="hlt">layer</span> is mediated by waves. This breaks with the standard astrophysical paradigm of an anomalous turbulent viscosity that drives accretion. However, wave-mediated angular momentum transport is a natural consequence of "sonic instability." The sonic instability, which we describe analytically and observe in our simulations, is a close cousin of the Papaloizou-Pringle instability. However, it is very vigorous in the <span class="hlt">boundary</span> <span class="hlt">layer</span> due to the immense radial velocity shear present at the equator.Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940024859','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940024859"><span id="translatedtitle"><span class="hlt">Boundary</span> <span class="hlt">layer</span> control device for duct silencers</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schmitz, Fredric H. (Inventor); Soderman, Paul T. (Inventor)</p> <p>1993-01-01</p> <p>A <span class="hlt">boundary</span> <span class="hlt">layer</span> control device includes a porous cover plate, an acoustic absorber disposed under the porous cover plate, and a porous flow resistive membrane interposed between the porous cover plate and the acoustic absorber. The porous flow resistive membrane has a flow resistance low enough to permit sound to enter the acoustic absorber and high enough to damp unsteady flow oscillations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EOSTr..91..253L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EOSTr..91..253L"><span id="translatedtitle">Studying the Afternoon Transition of the Planetary <span class="hlt">Boundary</span> <span class="hlt">Layer</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lothon, Marie; Lenschow, Donald H.</p> <p>2010-07-01</p> <p>The planetary <span class="hlt">boundary</span> <span class="hlt">layer</span> is the part of the <span class="hlt">atmosphere</span> that interacts directly with the Earth's surface on a time scale of a few hours or less. In daytime, solar heating of the surface can generate buoyant turbulent eddies that efficiently mix the air through a depth of more than a kilometer. This convective <span class="hlt">boundary</span> <span class="hlt">layer</span> (CBL) is a conduit for trace gases such as water vapor and carbon dioxide that are emitted or absorbed by the surface (and surface vegetation) to be transported into or out of the <span class="hlt">layer</span> nearest the surface. The CBL has been extensively observed and relatively successfully modeled. But the early morning transition—when the CBL emerges from the nocturnal <span class="hlt">boundary</span> layer—and the late afternoon transition—when the CBL decays to an intermittently turbulent “residual layer” overlying a shallower, stably stratified <span class="hlt">boundary</span> layer—are difficult to observe and model due to turbulence intermittency and anisotropy, horizontal heterogeneity, and rapid time changes. Even the definition of the <span class="hlt">boundary</span> <span class="hlt">layer</span> during these transitional periods is fuzzy; there is no consensus on what criteria to use and no simple scaling laws, as there are for the CBL, that apply during these transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989AtmEn..23.1465L&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989AtmEn..23.1465L&link_type=ABSTRACT"><span id="translatedtitle">Simulation of chemical processes occurring in an <span class="hlt">atmospheric</span> <span class="hlt">boun