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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. Temperature structure in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Smedman, Ann-Sofi

    2010-05-01

    Temperature structure in the atmospheric boundary layer It is well established from experimental and theoretical studies that the temperature structure in the atmospheric boundary layer is depends on stability. During free convection conditions the flow is dominated by circular thermals but when stratification is becoming slightly unstable longitudinal roll structures that extend vertically throughout the entire boundary layer will be present. In close to neutral conditions on the unstable side (the UVCN regime) when the Obukhov length is much greater than the surface layer depth, it is observed that the structure of the surface layer turbulence does not accord with standard similarity theory. In particular the efficiency of the turbulent exchange of sensible and latent heat is observed to be more strongly enhanced than is consistent with the standard model. Also the profiles of dissipation of turbulent kinetic energy and temperature fluctuation variance are found to depend on the structure of the whole boundary layer (i.e. are non-local), indicating that a large-scale transport process is at work. At the same time, co-spectral analysis shows how the large scale eddy motions that determine the heat transport process near the surface are typically 1/5 of the surface layer depth. All these features are found to be similar in measurements at two marine sites, in the Baltic Sea and in Lake Ontario respectively and at several flat land sites ( around Uppsala and at the Island of Gotland), indicating that they are determined by the dynamics of the whole boundary layer rather than being simply dependent on the surface boundary conditions. The observed structures can also be interpreted as possible manifestations of a bifurcation of the large scale eddy structure towards a state in which there are quasi-steady longitudinal rolls and, on a smaller scale, unsteady detached eddies. Our interpretation of the results from the measurements is that, in the UVCN regime, the latter

  3. 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.

  4. 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.

  5. 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.

  6. Atmospheric tides on Venus. III - The planetary boundary layer

    NASA Astrophysics Data System (ADS)

    Dobrovolskis, A. R.

    1983-10-01

    Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.

  7. 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.

  8. 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.

  9. On Parameterizing Turbulence in the Stably Stratified Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Wilson, Jordan M.; Venayagamoorthy, Subhas K.

    2014-11-01

    Parameterizing turbulent mixing in the stably stratified atmospheric boundary layer remains an active area of research connecting available field measurements with appropriate model parameters. The research presented studies the pertinent mixing lengths for shear- and buoyancy-dominated (or weakly stable and very stable) regimes in the stable atmospheric boundary layer (SABL). Incorporating shear and buoyancy effects, two length scales can be constructed, LkS =k 1 / 2 / S and LkN =k 1 / 2 / N , respectively. Extending the conceptual framework of Mater & Venayagamoorthy (2014), LkS and LkN are shown to be accurate representations of large-scale motions from which relevant model parameters are developed using observations from three field campaigns. An a priori analysis of large-eddy simulation (LES) data evaluates the efficacy of parameterizations applied to the vertical structure of the SABL. The results of this study provide a thorough evaluation of the pertinent mixing lengths in stably stratified turbulence through applications to atmospheric observations and numerical models for the boundary layer extendable to larger-scale weather prediction or global circulation models. S.K.V. gratefully acknowledges the support of the National Science Foundation under Grant No. OCE-1151838.

  10. Study of the morning transition of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Sastre, M.; Yagüe, C.; Maqueda, G.; Viana, S.

    2009-04-01

    In this work it will be analyzed the main physical processes related to the transition of the Atmospheric Boundary Layer (ABL) that takes place from the last hours of the night until the first hours of the morning. In order to achieve that, it will be used data from field campaigns which took place in the Research Centre for the Lower Atmosphere (CIBA), especially those gathered in the campaign carried out in June, 2008 where information was obtained from a 10m height mast provided with temperature, wind speed and direction, and moisture sensors at several levels. Also a sonic anemometer (20 Hz sampling rate) at 10m was available. The database is complemented by a triangle of microbarometers installed next to the surface, and another two microbarometers placed in a 100m meteorological tower at 50 and 100m respectively. 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 also available to evaluate the degree of mixing taking place near the surface. The thermodynamic characteristics of the first hundreds of meters remain registered from information obtained with a tethered balloon and with a RASS-SODAR. The main turbulent and stability parameters, as well as coherent structures present in the Nocturnal Boundary Layer are studied in connection to their influence in the developing of the next Convective Boundary Layer.

  11. 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.

  12. 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.

  13. Wake Dynamics in the Atmospheric Boundary Layer Over Complex Terrain

    NASA Astrophysics Data System (ADS)

    Markfort, Corey D.

    The goal of this research is to advance our understanding of atmospheric boundary layer processes over heterogeneous landscapes and complex terrain. The atmospheric boundary layer (ABL) is a relatively thin (˜ 1 km) turbulent layer of air near the earth's surface, in which most human activities and engineered systems are concentrated. Its dynamics are crucially important for biosphere-atmosphere couplings and for global atmospheric dynamics, with significant implications on our ability to predict and mitigate adverse impacts of land use and climate change. In models of the ABL, land surface heterogeneity is typically represented, in the context of Monin-Obukhov similarity theory, as changes in aerodynamic roughness length and surface heat and moisture fluxes. However, many real landscapes are more complex, often leading to massive boundary layer separation and wake turbulence, for which standard models fail. Trees, building clusters, and steep topography produce extensive wake regions currently not accounted for in models of the ABL. Wind turbines and wind farms also generate wakes that combine in complex ways to modify the ABL. Wind farms are covering an increasingly significant area of the globe and the effects of large wind farms must be included in regional and global scale models. Research presented in this thesis demonstrates that wakes caused by landscape heterogeneity must be included in flux parameterizations for momentum, heat, and mass (water vapor and trace gases, e.g. CO2 and CH4) in ABL simulation and prediction models in order to accurately represent land-atmosphere interactions. Accurate representation of these processes is crucial for the predictions of weather, air quality, lake processes, and ecosystems response to climate change. Objectives of the research reported in this thesis are: 1) to investigate turbulent boundary layer adjustment, turbulent transport and scalar flux in wind farms of varying configurations and develop an improved

  14. 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.

  15. 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.

  16. Non-linear processes in the Earth atmosphere boundary layer

    NASA Astrophysics Data System (ADS)

    Grunskaya, Lubov; Valery, Isakevich; Dmitry, Rubay

    2013-04-01

    The work is connected with studying electromagnetic fields in the resonator Earth-Ionosphere. There is studied the interconnection of tide processes of geophysical and astrophysical origin with the Earth electromagnetic fields. On account of non-linear property of the resonator Earth-Ionosphere the tides (moon and astrophysical tides) in the electromagnetic Earth fields are kinds of polyharmonic nature. It is impossible to detect such non-linear processes with the help of the classical spectral analysis. Therefore to extract tide processes in the electromagnetic fields, the method of covariance matrix eigen vectors is used. Experimental investigations of electromagnetic fields in the atmosphere boundary layer are done at the distance spaced stations, situated on Vladimir State University test ground, at Main Geophysical Observatory (St. Petersburg), on Kamchatka pen., on Lake Baikal. In 2012 there was continued to operate the multichannel synchronic monitoring system of electrical and geomagnetic fields at the spaced apart stations: VSU physical experimental proving ground; the station of the Institute of Solar and Terrestrial Physics of Russian Academy of Science (RAS) at Lake Baikal; the station of the Institute of volcanology and seismology of RAS in Paratunka; the station in Obninsk on the base of the scientific and production society "Typhoon". Such investigations turned out to be possible after developing the method of scanning experimental signal of electromagnetic field into non- correlated components. There was used a method of the analysis of the eigen vectors ofthe time series covariance matrix for exposing influence of the moon tides on Ez. The method allows to distribute an experimental signal into non-correlated periodicities. The present method is effective just in the situation when energetical deposit because of possible influence of moon tides upon the electromagnetic fields is little. There have been developed and realized in program components

  17. Atmospheric boundary layers in storms: advanced theory and modelling applications

    NASA Astrophysics Data System (ADS)

    Zilitinkevich, S. S.; Esau, I. N.; Baklanov, A.

    2005-03-01

    Turbulent planetary boundary layers (PBLs) control the exchange processes between the atmosphere and the ocean/land. The key problems of PBL physics are to determine the PBL height, the momentum, energy and matter fluxes at the surface and the mean wind and scalar profiles throughout the layer in a range of regimes from stable and neutral to convective. Until present, the PBLs typical of stormy weather were always considered as neutrally stratified. Recent works have disclosed that such PBLs are in fact very strongly affected by the static stability of the free atmosphere and must be treated as factually stable (we call this type of the PBL "conventionally neutral" in contract to the "truly neutral" PBLs developed against the neutrally stratified free flow). It is common knowledge that basic features of PBLs exhibit a noticeable dependence on the free-flow static stability and baroclinicity. However, the concern of the traditional theory of neural and stable PBLs was almost without exception the barotropic nocturnal PBL, which develops at mid latitudes during a few hours in the night, on the background of a neutral or slightly stable residual layer. The latter separates this type of the PBL from the free atmosphere. It is not surprising that the nature of turbulence in such regimes is basically local and does not depend on the properties of the free atmosphere. Alternatively, long-lived neutral (in fact only conditionally neutral) or stable PBLs, which have much more time to grow up, are placed immediately below the stably stratified free flow. Under these conditions, the turbulent transports of momentum and scalars even in the surface layer - far away from the PBL outer boundary - depend on the free-flow Brunt-Väisälä frequency, N. Furthermore, integral measures of the long-lived PBLs (their depths and the resistance law functions) depend on N and also on the baroclinic shear, S. In the traditional PBL models both non-local parameters N and S were overlooked

  18. High resolution properties of the marine atmospheric boundary layer

    SciTech Connect

    Cooper, D.; Cottingame, W.; Eichinger, W.; Forman, P.; Lebeda, C.; Poling, D.; Thorton, R.

    1994-02-01

    Los Alamos National Laboratory (LANL) participated in the Central Equatorial Pacific Experiment (CEPEX) by fielding a water-vapor Raman lidar on board the Research Vessel Vickers. The lidar measured water vapor concentration from the surface to lower tropospheric altitudes in order to support the CEPEX goal of evaluating a hypothesis regarding feedback mechanisms for global circulation models. This report describes some of the features observed within the marine Atmospheric Boundary Layer (ABL) and the lower troposphere. Data was collected continuously 24 hours per day over the equatorial Pacific from March 8th to March 2 1st of 1993 while in route between Guadalcanal and Christmas Island (the transect was at approximately 2{degree} south latitude). The lidar collected vertical transects of water vapor concentration up to 10 km during night operations and 4 km in the day. The vertical lidar profiles of water vapor were produced by summing the data over a period up to 600 seconds. The water-vapor Raman lidar measured the properties of the marine ABL as well as the lower and mid-troposphere. From the lidar water vapor profiles, ``images`` of water vapor concentration versus altitude and date or sea surface temperature will be produced along with other products such as latent heat fluxes. The Raman water vapor lidar data will be used to better understand the role of transport and exchange at the ocean-atmosphere interface and throughout the marine atmosphere.

  19. The Atmospheric Boundary Layer Over Baltic Sea Ice

    NASA Astrophysics Data System (ADS)

    Brümmer, Burghard; Kirchgäßner, Amèlie; Müller, Gerd

    2005-10-01

    The temporal and spatial variability of the atmospheric boundary layer (ABL) over Baltic Sea ice is presented. The focus is on the properties of the underlying surface (temperature and albedo), the heat fluxes at the air ice/water interface and the vertical ABL structure (inversion layer and low-level jet). The study uses data from two field campaigns, BASIS 1998 and BASIS 2001, applying ice stations, a ship and aircraft over various surface types (land-fast ice, drift ice, and open water). Sensible heat flux ranges from -100 W m-2 under warm-air advection conditions to 300 W m-2 under cold-air advection conditions. On average, it is negative over land-fast ice and positive over open water. An ABL inversion is almost permanently present. It is surface-based 2/3 of the time and extends to 165 m on average. The average base of the elevated inversion is 343 m. The mean temperature increase across all inversions is 2.1 K and is clearly smaller than for Arctic sea-ice inversions. A low-level jet occurs about 86% of the time with an average height of 245 m and speed of 13.3 m s-1, which is 7 m s-1 higher than the surface-layer wind. On average, the low-level jet is located near the top of the surface-based inversion or near the base of the elevated inversion.

  20. 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).

  1. Heavy-Particle Deposition in the Atmospheric Boundary Layer.

    NASA Astrophysics Data System (ADS)

    Liao, Yingcheng

    A set of experiments of heavy-particle deposition on the ground in a wind-tunnel simulated atmospheric boundary layer has been conducted. Different particle fall velocities and different wind speeds were used. In order to analyze inertial, continuity, and crossing-trajectories effects of heavy particles, a new random-walk model has been developed in which vertical velocity variance is a function of height. For calibration of the numerical model, a set of tracer-gas concentration measurements was also carried out. The analysis of experimental results reveals that, in the atmospheric surface layer, for most of the practical situations, the crossing-trajectories and the inertia of heavy particles have a very limited effect on heavy-particle dispersion and deposition. However, the continuity effect greatly affects the lateral dispersion and deposition of heavy particles. The continuity effect is strongly height dependent. Influences of different factors on heavy-particle deposition are discussed. This includes the fall-velocity distribution of heavy particles, the integral-time scales of turbulent flow, longitudinal turbulent velocity components, release height, etc. Comparisons between the theoretical prediction and the calculated results from both the model used in this study and the model of Legg and Raupach (1982) support the author's approach in which vertical velocity variance is taken to be height dependent. For practical purposes, the new random-walk model has greatly improved the accuracy of predicting longitudinal deposition of heavy particles compared to that of the traditional Gaussian model. Experiments with more release heights and larger differences of particle fall velocity are suggested in order to further confirm the findings of this dissertation.

  2. Heavy-particle deposition in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Liao, Yingcheng

    A set of experiments of heavy-particle deposition on the ground in a wind-tunnel simulated atmospheric boundary layer was conducted. Different particle fall velocities and different wind speeds were used. In order to analyze inertial, continuity, and crossing-trajectories effects of heavy particles, a new random-walk model was developed in which vertical velocity variance is a function of height. For calibration of the numerical model, a set of tracer-gas concentration measurements was also carried out. The analysis of experimental results reveals that, in the atmospheric surface layer, for most of the practical situations, the crossing-trajectories and the inertia of heavy particles have a very limited effect on heavy-particle dispersion and deposition. However, the continuity effect greatly affects the lateral dispersion and deposition of heavy particles. The continuity effect is strongly height dependent. Influences of different factors on heavy-particle deposition are discussed. This includes the fall-velocity distribution of heavy particles, the integral-time scales of turbulent flow, longitudinal turbulent velocity components, release height, etc. Comparisons between the theoretical prediction and the calculated results from both the model used in this study and the model of Legg and Raupach (1982) support the author's approach in which vertical velocity variance is taken to be height dependent. For practical purposes, the new random-walk model has greatly improved the accuracy of predicting longitudinal deposition of heavy particles compared to that of the traditional Gaussian model. Experiments with more release heights and larger differences of particle fall velocity are suggested in order to further confirm the findings.

  3. 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.

  4. 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.

  5. 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.

  6. 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...

  7. Spectral Gap Energy Transfer in Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Bhushan, S.; Walters, K.; Barros, A. P.; Nogueira, M.

    2012-12-01

    Experimental measurements of atmospheric turbulence energy spectra show E(k) ~ k-3 slopes at synoptic scales (~ 600 km - 2000 km) and k-5/3 slopes at the mesoscales (< 400 km). The -5/3 spectra is presumably related to 3D turbulence which is dominated by the classical Kolmogrov energy cascade. The -3 spectra is related to 2D turbulence, which is dominated by strong forward scatter of enstrophy and weak forward scatter of energy. In classical 2D turbulence theory, it is expected that a strong backward energy cascade would develop at the synoptic scale, and that circulation would grow infinitely. To limit this backward transfer, energy arrest at macroscales must be introduced. The most commonly used turbulence models developed to mimic the above energy transfer include the energy backscatter model for 2D turbulence in the horizontal plane via Large Eddy Simulation (LES) models, dissipative URANS models in the vertical plane, and Ekman friction for the energy arrest. One of the controversial issues surrounding the atmospheric turbulence spectra is the explanation of the generation of the 2D and 3D spectra and transition between them, for energy injection at the synoptic scales. Lilly (1989) proposed that the existence of 2D and 3D spectra can only be explained by the presence of an additional energy injection in the meso-scale region. A second issue is related to the observations of dual peak spectra with small variance in meso-scale, suggesting that the energy transfer occurs across a spectral gap (Van Der Hoven, 1957). Several studies have confirmed the spectral gap for the meso-scale circulations, and have suggested that they are enhanced by smaller scale vertical convection rather than by the synoptic scales. Further, the widely accepted energy arrest mechanism by boundary layer friction is closely related to the spectral gap transfer. This study proposes an energy transfer mechanism for atmospheric turbulence with synoptic scale injection, wherein the generation

  8. Large eddy simultations of the atmospheric boundary layer east of the Colorado Rockies

    SciTech Connect

    Costigan, K.R.; Cotton, W.R.

    1992-10-22

    Large eddy simulation, LES, has often been carried out for the idealized situation of a simple convective boundary layer. Studies of dual Doppler radar and aircraft data from the Phoenix II experiment indicate that the boundary layer of the Colorado High Plains is not a purely convective boundary layer and it is influenced by the mountains to the west. The purpose of this study is to investigate the atmospheric boundary layer on one particular day on the Colorado High Plains. This research applies a LES nested within larger grids, which contain realistic topography and can simulate the larger-scale circulations initiated by the presence of the mountain barrier. How and to what extent the atmospheric boundary layer of the Colorado High Plains is influenced by larger scale circulations and other phenomena associated with the mountain barrier to the west is investigated. The nested grid LES reproduces the characteristics of the atmosphere for the case study day reasonably well. The mountains influence the atmospheric boundary layer over the plains to the east in several ways. The mountains contribute to the vertical shear of the horizontal winds through the thermally-induced mountain-plains circulation. As a consequence of the wind shear, the boundary layer that develops over the mountains is advected eastward over the top of the plains boundary layer, which is developing separately. This layer is marked by a mixture of gravity waves and turbulence and is atypical of a purely convective boundary layer. Just below this layer, the capping inversion of the plains boundary layer is weak and poorly defined compared to the inversions capping purely convective boundary layers. Gravity waves, triggered by the obstacle of the Rocky Mountains and by convection in the mountain boundary layer, also influence the atmosphere above the Colorado High Plains. These influences are found to have significant effects on the turbulence statistics and the energy spectra.

  9. Total Solar Eclipses and Atmospheric Boundary Layer Response

    NASA Astrophysics Data System (ADS)

    Stoev, A.; Stoeva, P.; Kuzin, S.

    2012-11-01

    The effect of three total solar eclipses on meteorological parameters is discussed in the paper. Measurements were conducted at the village of Ravnets,General Toshevo municipality, Bulgaria, 1999,in Manavgat, near Antalya, Turkey, 2006 and in Tian Huang Ping, China, 2009. The observed decrease of the sky illumination (incoming solar radiation) during the eclipses was proportional to the percentage of solar coverage. The after eclipse sky illumination level is due to the effect of the natural change of the solar elevation angle. For the 1999 TSE it did not regain its pre eclipse value, it has exactly the same value for the 2006 TSE, and, It is three times larger than the pre eclipse value for the 2009 TSE. This fact can be easily explained by the Local Time of the maximum of the eclipses: LT 13:12, LT 12:58, and LT 09:34, respectively. Measurements showed significant changes in the surface air temperature. The minimum of the air temperature during the 2009 TSE (Tmin=4.5°C) was measured 6 min after the end of the total phase. This minimal temperature drop and larger time lag can be explained with the huge artificial lake near the place of observation, which minimizes the temperature response due to its larger heat capacity. During the 1999 TSE, minimal temperature (Tmin=6.4°C) is measured 7 min 30 s after the total phase, and for the 2006 TSE (Tmin=5°C) - 5 min. It is in accordance with the fact that the temperature minima at residential/commercial stations occurred in general, before the minima at stations in agricultural terrains. In 2006 we were at the yard of the hotel, and in 1999 in the countryside. The wind velocity drops during the total phase as a result of the cooling and stabilization of the atmospheric boundary layer. The wind direction during the total phase changes and the wind begins to blow in the same direction as the direction of motion of the lunar shadow on the earth. Cirrus and cirrostratus clouds were observed during the 2006 total solar

  10. 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

  11. 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.

  12. 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.

  13. 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...

  14. Estimation of Atmospheric Boundary Layer Parameters for Diffusion Applications.

    NASA Astrophysics Data System (ADS)

    van Ulden, A. P.; Holtslag, A. A. M.

    1985-11-01

    This paper gives the outline of a `meteorological preprocessor' for air pollution modeling. It is shown how significantly more information can be extracted from routinely available measurements than the traditional Pasquil stability classes and power law wind speed profiles. Also it is shown how additional special measurements-if available-can be accommodated. The methods are primarily intended for application in generally level, but not necessarily homogeneous terrain. The improved characterization of the state of the planetary boundary layer allows a more modern and probably more accurate description of diffusion. The paper is an extended version of an introductory paper presented during the `Workshop on Updating Applied Diffusion Models' Clearwater, Florida, January 1984.

  15. 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.

  16. 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.

  17. 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 ...

  18. 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.

  19. Turbulence structure of the marine atmospheric boundary layer observed during the SEMAPHORE experiment

    SciTech Connect

    Durand, P.; Benech, B.; Druilhet, A.; Ferret, B.

    1994-12-31

    The SEMAPHORE experiment was conducted in the Azores region in 1993 and was devoted to mesoscale studies of oceanic and atmospheric circulations, as well as interactions between oceanic and atmospheric boundary layers. From October 4 to November 17, two instrumented aircraft gathered data. One of the major objectives of SEMAPHORE was to study the coupling between the atmospheric and oceanic boundary layers in the vicinity of an oceanic temperature front. This front, associated with the Azores current, was located south of the Santa Maria Island where the aircraft were based. The aim of this paper is to document the turbulent structure of the atmospheric boundary layer, analyzed from aircraft measurements, for two different meteorological situations.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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...

  11. 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).

  12. 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.

  13. Efficiency of eddy mixing in a stable stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kurbatskiy, A. F.; Kurbatskaya, L. I.

    2011-12-01

    Based on a mesoscale RANS model of turbulence, the behavior of turbulent eddy mixing parameters is found to agree with the latest data of laboratory and atmospheric measurements. Some problems of the description of turbulent eddy mixing in the atmospheric boundary layer are studied. When the flow transforms to an extremely stable state, in particular, it is found the flux Richardson number Ri f can change nonmonotonically: it increases with increasing gradient Richardson number Rig until the state of saturation is reached at Ri g ≃ 1 and then decreases. The behavior of the coefficients of eddy diffusion of momentum and heat agrees with the concept of momentum (but not heat) transfer by internal waves propagating in an extremely stable atmospheric boundary layer.

  14. Laser beam propagation through an atmospheric transitional and turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Katz, Richard A.; Manzur, Tariq

    2015-05-01

    This study investigates laser beam propagation through an atmospheric boundary layer near the ocean surface. Objectives of this research are to ascertain feasibility limits for achieving maximum energy efficiency at extended ranges in the face of atmospheric and other distortions as the laser beam penetrates through transitional (anisotropic) and turbulent (isotropic) boundary layer regimes. Various aspects of turbulence modeling of laser beam propagation near the ocean surface are discussed including: Kolmogorov's model of atmospheric turbulence, parameterized structure functions (e.g., velocity and temperature gradients, gradients in refractive index) and other important factors affecting near surface propagation such as humidity, aerosols, and wave slap. Various preliminary modeled propagation results are shown, and a new methodology is proposed for improving existing model estimates with new time domain measurement procedures.

  15. 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.

  16. 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.

  17. Internal boundary-layer height formulae — A comparison with atmospheric data

    NASA Astrophysics Data System (ADS)

    Walmsley, John L.

    1989-04-01

    The height of the internal boundary layer (IBL) downwind of a step change in surface roughness is computed using formulae of Elliott (1958), Jackson (1976) and Panofsky and Dutton (1984). The results are compared with neutral-stratification atmospheric data extracted from the set of wind-tunnel and atmospheric data summarized by Jackson (1976) as well as neutral-stratification data presented by Peterson et al. (1979) and new data measured at Cherrywood, Ontario. It is found that the Panofsky-Dutton formulation gives the least root-mean-square (RMS) absolute errors for atmospheric applications.

  18. 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.

  19. Model simulations of the Arctic atmospheric boundary-layer from the SHEBA year.

    PubMed

    Tjernström, Michael; Zagar, Mark; Svensson, Gunilla

    2004-06-01

    We present Arctic atmospheric boundary-layer modeling with a regional model COAMPS, for the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. Model results are compared to soundings, near-surface measurements and forecasts from the ECMWF model. The near-surface temperature is often too high in winter, except in shorter periods when the boundary layer was cloud-capped and well-mixed due to cloud-top cooling. Temperatures are slightly too high also during the summer melt season. Effects are too high boundary-layer moisture and formation of too dense stratocumulus, generating a too deep well-mixed boundary layer with a cold bias at the simulated boundary-layer top. Errors in temperature and therefore moisture are responsible for large errors in heat flux, in particular in solar radiation, by forming these clouds. We conclude that the main problems lie in the surface energy balance and the treatment of the heat conduction through the ice and snow and in how low-level clouds are treated.

  20. 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.

  1. Study of the Mechanism of Nucleation in the Polluted Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Chen, Modi

    Atmospheric aerosols can affect human health and earth's radiation balance. The formation of these aerosols has been shown to cast high uncertainty in current global climate modeling. Most observed nucleation events in the boundary layers are correlated with high sulfuric acid concentration. Nucleation rates are usually proportional to sulfuric acid concentration up to the third power. After atmospheric aerosol particles are formed, they often grow at a speed faster than can be explained by sulfuric acid condensation, suggesting that other chemical species also participate in this process. The detailed mechanisms of how these particles are formed and their subsequent growth are still unclear. This work is focused on furthering our understanding of atmospheric nucleation. My contribution is mainly on the following three topics: (1) characterizing condensation particle counters (CPCs) for accurate particle measurements down to 1 nm, the size close to the smallest stable sulfuric acid clusters; (2) developing a method of estimating time and size resolved particle growth rates and atmospheric nucleation rates based on data from both atmospheric and laboratory studies; (3) deriving of a simple semi-empirical acid-base reaction model for atmospheric nucleation in the polluted atmospheric boundary layer.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. Towards Improved Turbulence Model Parameterizations of the Stably Stratified Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Wilson, J.; Venayagamoorthy, S. K.

    2014-12-01

    Connecting available field measurements with appropriate model parameters of turbulent mixing in the stably stratified atmospheric boundary layer remains an active research area. The research presented in this study extends the theoretical framework of Mater & Venayagamoorthy (textit{Phys. Fluids}, vol. 26, no. 3, 2014, 036601) on shear- and buoyancy-dominated regimes to the stable atmospheric boundary layer (SABL). Two pertinent length scales can be constructed to directly include the effects of shear and buoyancy, LkS=k1/2/SL_{kS} = k^{1/2} /S and LkN=k1/2/NL_{kN} = k^{1/2}/N, respectively, that are representative of large-scale motions in these two regimes. Model parameters are developed using observations from three field campaigns and further evaluated with an textit{a priori} analysis of large-eddy simulation (LES) data of the SABL vertical structure. Results of this study thoroughly evaluate the pertinent mixing lengths applied to stably stratified turbulence in atmospheric observations and boundary layer models extendable to large-scale numerical weather prediction or global circulation models. *S.K.V. gratefully acknowledges the support of the National Science Foundation under Grant No. OCE-1151838

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

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

    SciTech Connect

    Lee, T.J.

    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-atmospheric transfer (SVAT) model. The Land Ecosystem-Atmospheric (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 length of roots. Separate energy budgets for vegetation and for 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. The Multi-response Randomized Bock Permutation (MRBP) procedure is used to help choose the model parameter values. The Fourier Amplitude Sensitivity Test (FAST) is applied to understand the model behavior in response to changes in model parameters. LEAF is used to study growth of boundary layer and local thermal circulations generated by surface inhomogeneities. Results show that atmospheric boundary layer is 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 characteristics. Simulations show that the surface spatial heterogeneities made by vegetation play an important role in generating local convective storms.

  15. A Lagrangian Stochastic Model for Sea-Spray Evaporation in the Atmospheric Marine Boundary Layer

    NASA Astrophysics Data System (ADS)

    Mueller, James; Veron, Fabrice

    2010-10-01

    The dispersion of heavy particles subjected to a turbulent forcing is often simulated with Lagrangian stochastic models. Although these models have been employed successfully over land, the implementation of traditional LS models in the marine boundary layer is significantly more challenging. We present an adaptation of traditional Lagrangian stochastic models to the atmospheric marine boundary layer with a particular focus on the representation of the scalar turbulence for temperature and humidity. In this new model, the atmosphere can be stratified and the bottom boundary is represented by a realistic wavy surface that moves and deforms. Hence, the correlation function for the turbulent flow following a particle is extended to the inhomogenous, anisotropic case. The results reproduce behaviour for scalar Lagrangian turbulence in a stratified airflow that departs only slightly from the expected behaviour in isotropic turbulence. When solving for the surface temperature and the radius of evaporating heavy water droplets in the airflow, the modelled turbulent forcing on the particle also behaves remarkably well. We anticipate that this model will prove especially useful in the context of sea-spray dispersion and its associated sensible heat, latent heat, and gas fluxes between spray droplets and the atmosphere.

  16. 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.

    2016-10-01

    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.

  17. 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.

  18. 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.

  19. 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.

  20. [Analysis on concentration variety characteristics of atmospheric ozone under the boundary layer in Beijing].

    PubMed

    Zong, Xue-Mei; Wang, Geng-Chen; Chen, Hong-Bin; Wang, Pu-Cai; Xuan, Yue-Jian

    2007-11-01

    Based on the atmospheric ozone sounding data, the average monthly and seasonal variety principles of atmospheric ozone concentration during six years are analyzed under the boundary layer in Beijing. The results show that the monthly variation of atmospheric ozone are obvious that the minimum values appear in January from less than 10 x 10(-9) on ground to less than 50 x 10(-9) on upper layer (2 km), but the maximum values appear in June from 85 x 10(-9) on ground to more than 90 x 10(-9) on upper layer. The seasonal variation is also clear that the least atmospheric ozone concentration is in winter and the most is in summer, but variety from ground to upper layer is largest in winter and least in summer. According to the type of outline, the outline of ozone concentration is composite of three types which are winter type, summer type and spring-autumn type. The monthly ozone concentration in different heights is quite different. After analyzing the relationship between ozone concentration and meteorological factors, such as temperature and humidity, we find ozone concentration on ground is linear with temperature and the correlation coefficient is more than 85 percent.

  1. [Measurement of atmospheric boundary layer pollutants by mobile lidar in Beijing].

    PubMed

    Wang, Shao-Lin; Xie, Pin-Hua; Hu, Shun-Xing; Wei, He-Li; Hu, Huan-Ling; Xie, Jun; Cao, Kai-Fa; Fang, Xin

    2008-03-01

    The parameters of AML-2 mobile lidar were introduced, which was based on differential absorption principle and designed by our institute. In Yufa of Beijing, the pollutants including O3, NO2, SO2 in atmospheric boundary layer were monitored in August and September of 2006 under different weather conditions. Vertical profile and diurnal variation of concentrations of these pollutants were analyzed. If without the influence of pollution air transport from south region, the concentrations of these pollutants are low under the overcast weather condition. The concentrations of O3 and NO2 decrease with altitude, and this characteristic is not obvious for SO2, but there is a high concentration layer of SO2 near ground (about 0.6km). The quality of atmosphere Beijing is influenced significantly by air transportation from south region, and the altitude of the severe pollution air transport is about 1km to 1.5km in August 23rd to 25th. As a result, the characteristics of vertical profile and daily variation of the pollutants are changed, and the concentrations of O3, NO2, SO2 in atmospheric boundary layer of Yufa area increased obviously.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. Observation of the atmospheric boundary layer in the Western and Central Gulf of Mexico. First annual report

    SciTech Connect

    1998-12-01

    For the Gulf of Mexico, present data sets poorly represent how temperature, winds, and mixing height vary vertically over the atmospheric boundary layer and free troposphere. Under this project, the MMS shall obtain field observations describing the vertical structure of the marine boundary layer over the Western and Central Gulf of Mexico for ongoing and future applications. The agency will accomplish this goal by establishing two (2) boundary layer profiler systems on offshore platforms for approximately three (3) years of data collection. This project will provide a valuable source of information to the National Weather Service (NWS) operations as the boundary layer observations are collected in real time and distributed.

  10. Effects of artificial sea film slick upon the atmospheric boundary layer structure

    NASA Astrophysics Data System (ADS)

    Repina, Irina; Artamonov, Arseniy; Malinovsky, Vladimir; Chechin, Dmitriy

    2010-05-01

    Organic surface-active compounds accumulate at the ocean-atmosphere boundary, influencing several air-sea interaction processes. In coastal areas with high biological activity this accumulation frequently becomes visible as mirrorlike patches ("slicks") on the sea surface. The artificial surface films of oleyl alcohol and vegetable oil were produced in the Black Sea coastal zone (one site was located near Gelendjik and another was near Crimea coast) to investigate its influence on energy and gas exchange between atmosphere and sea surface under different meteorological conditions. The atmospheric turbulence measurements during the passage of an artificial sea slick are compared with similar measurements without a sea slick. The effects of the slick are modifications of roughness length z0, and a possible increase in mean wind speed. In the mean, during the passage of the slick, the roughness length decreased while the mean wind speed appeared to increase. For the spectral comparison we compared the wind field over the sea during the time the film slick was in the vicinity of the measurement site with the wind field observed after the slick had passed. The cross-spectral density was computed between horizontal velocity and vertical velocity (Reynolds stress) and between atmospheric temperature and vertical velocity (heat flux). The introduction of the sea film slick, with its damping and suppression of capillary waves, appears to completely destroy the atmospheric turbulence generation. When a slick is present, the U-W phase angle and Reynolds stress spectrum for the atmosphere appear to be completely unaffected by undulating sea surface directly below the sensors. Spectral and wavelet analysis of the atmospheric surface layer characteristics showed a significant correlation between the processes on the sea surface and the atmospheric boundary layer. An intensification of change processes in the vicinity of the windward slick boundary are detected. It may be

  11. 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.

  12. 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.

  13. Spectral and cospectral characteristics of atmospheric turbulence in the marine boundary layer

    SciTech Connect

    Volkov, Yu.A.; Grachev, A.A.; Elagina, L.G.; Matveev, D.T.

    1994-12-31

    The behavior of frequency spectra and cospectra of atmospheric turbulence over the sea surface is described through analysis of data obtained from shipboard in a number of marine expeditions in Atlantic. These data sets have a wide variety of weather conditions. Many cases have demonstrated similarity between spectra of velocity, temperature and humidity fluctuations as well as momentum, heat and water vapor flux cospectra. These cases are characterized by strongly unstable stratification of surface layer, which observed during expedition in winter/spring 1988 in North Atlantic near Newfoundland Island. However, in weak unstable conditions typical for Subtropical (Pre-ASTEX-91 experiment) and Equatorial Atlantic, spectra of temperature and humidity and heat and moisture flux cospectra were often dissimilar. Spectral dissimilarity of turbulent quantities are also related with unsteady cases. For these cases heat flux cospectra often change sign at low frequency and the net sensible heat flux may be close to zero. The turbulent measurements are accompanied by simultaneous remote sensing of sea surface temperature and cloud low boundary. The obtained results indicate that the anomalous behavior of low-frequency cospectra is related to large-scale circulations (coherent structures) in the atmospheric boundary layer (ABL) and oceanic subsurface layer.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Atmospheric dispersion in the Arctic: Winter-time boundary-layer measurements

    SciTech Connect

    Guenther, A.; Lamb, B.

    1989-01-01

    In the paper, the authors present measurements of turbulence and boundary-layer structure over open winter-time tundra with an emphasis upon the implications of these observations for pollutant dispersion modeling. Vertical profiles of mean wind speed, wind direction and temperature are described, in addition to fluctuations in these quantities. Dispersion coefficients are estimated and compared with the open terrain tracer plume measurements. The work is part of an arctic dispersion modeling program supported by the EPA Cold Climate Research Program. In other aspects of the program, they have investigated plume downwash and dispersion at an arctic industrial site using wind-tunnel model studies and atmospheric tracer field studies.

  19. 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

  20. Comparison between the atmospheric boundary layer in Paris and its rural suburbs during the ECLAP experiment

    NASA Astrophysics Data System (ADS)

    Dupont, E.; Menut, L.; Carissimo, B.; Pelon, J.; Flamant, P.

    The ECLAP experiment has been performed during the winter of 1995 in order to study the influence of the urban area of Paris on the vertical structure and diurnal evolution of the atmospheric boundary layer, in situations favourable to intense urban heat island and pollution increase. One urban site and one rural site have been instrumented with sodars, lidars and surface measurements. Additional radiosondes, 100 m masts and Eiffel Tower data were also collected. This paper gives a general overview of this experiment, and presents results of the analysis of four selected days, characterized by various wind directions and temperature inversion strengths. This analysis, which consists in a comparison between data obtained in the two sites, has been focused on three parameters of importance to the ABL dynamics: the standard deviation of vertical velocity, the surface sensible heat flux, and the boundary layer height. The vertical component of turbulence is shown to be enhanced by the urban area, the amplitude of this effect strongly depending on the meteorological situation. The sensible heat flux in Paris is generally found larger than in the rural suburbs. The most frequent differences range from 25-65 W m -2, corresponding to relative differences of 20-60%. The difference of unstable boundary layer height between both sites are most of the time less than 100 m. However, sodar and temperature data show that the urban influence is enhanced during night-time and transitions between stable and unstable regimes.

  1. Complex turbulent flow in the atmospheric boundary layer: Lab and field measurements of embedded canopy wakes

    NASA Astrophysics Data System (ADS)

    Markfort, C. D.; Carbajo Fuertes, F.; Porte-Agel, F.

    2015-12-01

    Natural and anthropogenic fragmented landscapes are pervasive and this complexity significantly affects the structure of the atmospheric boundary layer, causing classic similarity theories to break down. This is especially true in areas affected by wake turbulence. Steep topography and canopy patches can lead to separation of the boundary layer and delay in the adjustment of turbulence to an adjacent underlying surface. Canopy wakes have been shown, in controlled wind tunnel experiments, to significantly affect the mean and turbulence profiles compared to classic rough to smooth transitions (Markfort et al. 2014, Env. Fluid Mech.). The added turbulence due to wakes delay the development of a new boundary layer and turbulent flux measurements and models that rely on similarity theory to determine surface fluxes exhibit significant errors. Here we compare lab-scale experimental measurements using PIV to field-scale measurements using scanning Doppler wind LiDARs. The measurements provide information on how the wake evolves in space and varies over time. Results from the lab and field show a time-varying recirculation zone downwind of the canopy, enhanced turbulence extending far downwind of the transition and reduced surface fluxes in the wake region. The field measurements show that the open trunk space near the base of the canopy results in a surface jet that can be detected just downwind of the canopy and farther downwind dissipates as it mixes with the wake flow above. The implications of canopy wakes for measurements and modeling of surface fluxes will be discussed.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hancock, P. E.; Zhang, S.; Hayden, P.

    2013-12-01

    A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by `standard forms' in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases.

  13. 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

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

    PubMed

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

    2013-10-29

    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.

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

    PubMed

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

    2013-10-29

    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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  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. Modified shape of the Eiffel Tower determined for an atmospheric boundary-layer wind profile

    NASA Astrophysics Data System (ADS)

    Weidman, P. D.

    2009-06-01

    The design and construction of the Eiffel Tower was based, in part, on a uniform horizontal wind model giving 300 kg m-2 kinematic pressure acting on the surface of the tower. Eiffel received a patent for his method of construction that eliminates the need for diagonal trellis bars used to resist the moment of an oncoming wind. At the end of the 19th century boundary-layer theory, laminar or turbulent, was nonexistent. Now, however, models for atmospheric flow over rough landscapes are available, the simplest being a power-law distribution of velocity with height. In this paper we deduce the shape of the tower had Eiffel incorporated this information into the design and construction of his world famous tower. Moreover, we prove Eiffel's observation that the tower profile conforms to the moment distribution wrought by the wind.

  5. Turbulence structure of a cloud-capped marine atmospheric boundary layer analyzed from ASTEX field data

    SciTech Connect

    Tjernstroem, M.

    1994-12-31

    The cloud-capped marine atmospheric boundary layer has gained attention for several reasons, one being the impact marine stratocumulus is believed to have on the climate system. To really understand the sensitivity of the climate system to marine low level clouds, let alone to predict their effect on climate for decades to come, require numerical modeling. Furthermore, in addition to there being several other important processes, e.g., radiative transfer, turbulent mixing and transport, etc., many of these interact in a way not fully understood. Parameterization of such processes in models on all scales is fundamental and cannot be performed without sound knowledge of important scaling and structures. Concerning in-cloud turbulence, such knowledge can today essentially only be gained from analysis of in-situ experimental data. Furthermore, if model parameterizations are successful, models can also be used to increase the understanding of the physics behind observed motion systems and how they interact with the PBL dynamics.

  6. Acid-base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer.

    PubMed

    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

    2012-11-13

    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

  7. Radiation Exchanges at the Atmosphere-Vegetation Canopy Boundary Layer Based on Unmanned Aerial Vehicle Observations

    NASA Astrophysics Data System (ADS)

    Dim, J. R.; Kajiwara, K.; Honda, Y.

    2007-12-01

    Radiation exchanges at the vegetation boundary layer, regulating the amount of energy received by the vegetation canopy are examined through remote sensing observations carried out by an unmanned helicopter, flying according to pre-programmed plans, above a forested area. Information obtained from the laser scanning system, radiometric measurements and aerial photographs are combined to ambient meteorological parameters in order to examine interactions between leaf characteristics, elements of vegetation structure, and the surrounding atmosphere. A vegetation mass transfer model showing variable dependencies of leaf water content, leaf temperature, leaf-air vapor-pressure differences and solar radiation intensity as well as canopy structure is used to discuss transpiration mechanisms of the studied forest.

  8. 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.

  9. Acid-base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer.

    PubMed

    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

    2012-11-13

    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.

  10. 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.

  11. Non-equilibrium model of spray-stratified atmospheric boundary layer under high wind conditions

    NASA Astrophysics Data System (ADS)

    Rastigejev, Yevgenii; Suslov, Sergey

    2014-11-01

    Tropical cyclone is a complex meteorological phenomenon which dynamics is defined by a wide variety of factors including exchange of momentum, heat and moisture between the atmosphere and the ocean. Ocean spray plays an important role in this air-sea interaction. Here we developed a two-temperature non-equilibrium variable density (non-Bousinessq) turbulence closure model to describe the ocean spray-stratified hurricane boundary layer structure and dynamics. The model consistently describes a two-way coupling between mechanical and thermodynamic influences of the ocean spray. The obtained results confirm that the impact of non-equilibrium effects is significant over the complete range of possible spray concentration values, therefore has to be included into a consistent parameterization of moisture, heat and momentum transfer process over the ocean under high wind condition of a hurricane. NSF HRD-1036563.

  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 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.

  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.

  16. 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.

  17. 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.

  18. The atmospheric boundary layer and its effect on NO concentrations during ANTCI-2003

    NASA Astrophysics Data System (ADS)

    Neff, W.; Helmig, D.; Davis, D.; Buhr, M.; Gottas, D.; Grachev, A.; Oncley, S.; Warshawsky, M.

    2004-12-01

    The Antarctic Tropospheric Chemistry Investigation (ANTCI) field program, during November and December 2003 at the South Pole, deployed a number of measurement systems to document the behavior of the atmospheric boundary layer (ABL) and the associated chemical processes that lead to high values of NO. These measurements included an acoustic sounder to provide continuous measurements of the ABL through the entire experimental period. During a special observing period from December 13 to 30, a sonic anemometer was used to measure the surface fluxes of momentum and heat together with a tethered balloon that profiled NO, O3 and meteorological variables (see Helmig et al., this conference). Our analysis has focused on developing a comprehensive picture of the ABL and the meteorological processes that control its behavior. We used both meteorological and chemical data to trace the evolution of the ABL through transitions between well-mixed states (deeper than 200m) and ones with very shallow mixing layers (20 to 30 m) characterized by strongly suppressed turbulence and low-level jets (30 to 40 m above the surface).

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. A Climatology of Atmospheric Rivers Potentially Impacting the Boundary Layer over Greenland: 1871-2012

    NASA Astrophysics Data System (ADS)

    Neff, William; Compo, Gilbert P.

    2016-04-01

    Recently, (Neff et al. 2014) examined the 2012 Greenland melt episode and compared it to the last episode in 1889 using the Twentieth Century Reanalysis (Compo et al. 2011), finding similar factors at work. A key factor in 2012 was the presence of an Atmospheric River (AR) that transported warm air from a mid-continent heat wave over the Atlantic Ocean and thence to the west coast of Greenland and then over the Greenland ice sheet (GIS) with a confirming water vapor isotopic signature (Bonne et al. 2015). ARs are thin filaments of high-moisture air occurring at frontal boundaries and represent an efficient poleward transport mechanism for warm moist air (Newell et al. 1992) to the Arctic (Bonne et al. 2015; Neff et al. 2014) and the Antarctic (Gorodetskaya et al. 2014). Some common characteristics of the events in 1889 and 2012, in addition to the expression of poleward transport as an AR, included continental heat anomalies in the trajectory source regions as well as a trough-ridge pattern that focused transport along the west coast of Greenland. The latter consisted of a trough of low-pressure situated to the west, generally over Baffin Island, and a high-pressure ridge to the southeast of Greenland. This type trough-ridge pattern was also implicated in a major rain event in 2011 along the western margin of the Greenland ice sheet in late summer that accelerated the flow of ice into the ocean (Doyle et al. 2015). Although the events of 2012 and 1889 were extreme, the question remains of how frequent are the near-misses of ARs that are likely to have affected lower elevations and/or included increases in moisture over the GIS that would have modified the boundary layer over the high elevations of the GIS. In this presentation we will show an example of the boundary layer modification lifecycle during the 2012 event and then the climatology of events that reveal an increase in such AR events along the west coast of Greenland over the last three decades.

  8. 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

  9. Characterization of the 222Rn family turbulent transport in the convective atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Vinuesa, J.-F.; Galmarini, S.

    2006-09-01

    The combined effect of turbulent transport and radioactive decay on the distribution of 222Rn and its progeny in convective atmospheric boundary layers (CBL) is investigated. Large eddy simulation is used to simulate their dispersion in steady state CBL and in unsteady conditions represented by the growth of a CBL within a pre-existing reservoir layer. The exact decomposition of the concentration and flux budget equations under steady state conditions allowed us to determine which processes are responsible for the vertical distribution of 222Rn and its progeny. Their mean concentrations are directly correlated with their half-life, e.g. 222Rn and 210Pb are the most abundant whereas 218Po show the lowest concentrations. 222Rn flux decreases linearly with height and its flux budget is similar to the one of inert emitted scalar, i.e., a balance between on the one hand the gradient and the buoyancy production terms, and on the other hand the pressure and dissipation at smaller scales which tends to destroy the fluxes. While 222Rn exhibits the typical bottom-up behavior, the maximum flux location of the daughters is moving upwards while their rank in the 222Rn progeny is increasing leading to a typical top-down behavior for 210Pb. We also found that 222Rn short-lived daughters, e.g. 218Po and 214Pb, have relevant radioactive decaying contributions acting as flux sources leading to deviations from the linear flux shape. In addition, while analyzing the vertical distribution of the radioactive decay contributions to the concentrations, e.g. the decaying zone, we found a discrepancy in height of 222Rn daughters' radioactive transformations. Under unsteady conditions, the same behaviors reported under steady state conditions are found: deviation of the fluxes from the linear shape for 218Po, enhanced discrepancy in height of the radioactive transformation contributions for all the daughters. In addition, 222Rn and its progeny concentrations collapse due to the rapid growth

  10. Characterization of the 222Rn family turbulent transport in the convective atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Vinuesa, J.-F.; Galmarini, S.

    2007-02-01

    The combined effect of turbulent transport and radioactive decay on the distribution of 222Rn and its progeny in convective atmospheric boundary layers (CBL) is investigated. Large eddy simulation is used to simulate their dispersion in steady state CBL and in unsteady conditions represented by the growth of a CBL within a pre-existing reservoir layer. The exact decomposition of the concentration and flux budget equations under steady state conditions allowed us to determine which processes are responsible for the vertical distribution of 222Rn and its progeny. Their mean concentrations are directly correlated with their half-life, e.g. 222Rn and 210Pb are the most abundant whereas 218Po show the lowest concentrations. 222Rn flux decreases linearly with height and its flux budget is similar to the one of inert emitted scalar, i.e., a balance between on the one hand the gradient and the buoyancy production terms, and on the other hand the pressure and dissipation at smaller scales which tends to destroy the fluxes. While 222Rn exhibits the typical bottom-up behavior, the maximum flux location of the daughters is moving upwards while their rank in the 222Rn progeny is increasing leading to a typical top-down behavior for 210Pb. We also found that the relevant radioactive decaying contributions of 222Rn short-lived daughters (218Po and 214Pb) act as flux sources leading to deviations from the linear flux shape. In addition, while analyzing the vertical distribution of the radioactive decay contributions to the concentrations, e.g. the decaying zone, we found a variation in height of 222Rn daughters' radioactive transformations. Under unsteady conditions, the same behaviors reported under steady state conditions are found: deviation of the fluxes from the linear shape for 218Po, enhanced discrepancy in height of the radioactive transformation contributions for all the daughters. In addition, 222Rn and its progeny concentrations decrease due to the rapid growth of the

  11. Atmospheric mercury over the marine boundary layer observed during the third China Arctic Research Expedition.

    PubMed

    Kang, Hui; Xie, Zhouqing

    2011-01-01

    TGM measurements on board ships have proved to provide valuable complementary information to measurements by a ground based monitoring network. During the third China Arctic Research Expedition (from July 11 to September 24, 2008), TGM concentrations over the marine boundary layer along the cruise path were in-situ measured using an automatic mercury vapor analyzer. Here we firstly reported the results in Japan Sea, North Western Pacific Ocean and Bering Sea, where there are rare reports. The value ranged between 0.30 and 6.02 ng/m3 with an average of (1.52 +/- 0.68) ng/m3, being slightly lower than the background value of Northern Hemisphere (1.7 ng/m3). Notably TGM showed considerably spatial and temporal variation. Geographically, the average value of TGM in Bering Sea was higher than those observed in Japan Sea and North Western Pacific Ocean. In the north of Japan Sea TGM levels were found to be lower than 0.5 ng/m3 during forward cruise and displayed obviously diurnal cycle, indicating potential oxidation of gaseous mercury in the atmosphere. The pronounced episode was recorded as well. Enhanced levels of TGM were observed in the coastal regions of southern Japan Sea during backward cruise due primarily to air masses transported from the adjacent mainland reflecting the contribution from anthropogenic sources. When ship returned back and passed through Kamchatka Peninsula TGM increased by the potential contamination from volcano emissions.

  12. Flux measurements in the surface Marine Atmospheric Boundary Layer over the Aegean Sea, Greece.

    PubMed

    Kostopoulos, V E; Helmis, C G

    2014-10-01

    Micro-meteorological measurements within the surface Marine Atmospheric Boundary Layer took place at the shoreline of two islands at northern and south-eastern Aegean Sea of Greece. The primary goal of these experimental campaigns was to study the momentum, heat and humidity fluxes over this part of the north-eastern Mediterranean Sea, characterized by limited spatial and temporal scales which could affect these exchanges at the air-sea interface. The great majority of the obtained records from both sites gave higher values up to factor of two, compared with the estimations from the most widely used parametric formulas that came mostly from measurements over open seas and oceans. Friction velocity values from both campaigns varied within the same range and presented strong correlation with the wind speed at 10 m height while the calculated drag coefficient values at the same height for both sites were found to be constant in relation with the wind speed. Using eddy correlation analysis, the heat flux values were calculated (virtual heat fluxes varied from -60 to 40 W/m(2)) and it was found that they are affected by the limited spatial and temporal scales of the responding air-sea interaction mechanism. Similarly, the humidity fluxes appeared to be strongly influenced by the observed intense spatial heterogeneity of the sea surface temperature.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Atmospheric mercury over the marine boundary layer observed during the third China Arctic Research Expedition.

    PubMed

    Kang, Hui; Xie, Zhouqing

    2011-01-01

    TGM measurements on board ships have proved to provide valuable complementary information to measurements by a ground based monitoring network. During the third China Arctic Research Expedition (from July 11 to September 24, 2008), TGM concentrations over the marine boundary layer along the cruise path were in-situ measured using an automatic mercury vapor analyzer. Here we firstly reported the results in Japan Sea, North Western Pacific Ocean and Bering Sea, where there are rare reports. The value ranged between 0.30 and 6.02 ng/m3 with an average of (1.52 +/- 0.68) ng/m3, being slightly lower than the background value of Northern Hemisphere (1.7 ng/m3). Notably TGM showed considerably spatial and temporal variation. Geographically, the average value of TGM in Bering Sea was higher than those observed in Japan Sea and North Western Pacific Ocean. In the north of Japan Sea TGM levels were found to be lower than 0.5 ng/m3 during forward cruise and displayed obviously diurnal cycle, indicating potential oxidation of gaseous mercury in the atmosphere. The pronounced episode was recorded as well. Enhanced levels of TGM were observed in the coastal regions of southern Japan Sea during backward cruise due primarily to air masses transported from the adjacent mainland reflecting the contribution from anthropogenic sources. When ship returned back and passed through Kamchatka Peninsula TGM increased by the potential contamination from volcano emissions. PMID:22432276

  18. [Measurements of atmospheric boundary layer O3, NOx and CO in summer with Beijing 325 m meteorological tower].

    PubMed

    An, Junlin; Li, Xin; Wang, Yuesi; Shi, Liqing; Hu, Fei; Xu, Yongfu

    2003-11-01

    Based on the Beijing 325 m meteorological tower, O3, NOx and CO concentrations and meteorological parameters in urban atmospheric boundary layer were measured in July 2002. The variations of O3 concentration were remarkably different among the five levels. Contrasted with the higher levels, the daily variations were clear and the difference values between day and night were large in the lower levels. It was also found that the photochemistry reaction was an important source in boundary layer in daytime and precipitation process could arouse marked change of O3 concentration.

  19. 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

  20. Analysis of temporal variability in land-atmosphere interactions, boundary layer dynamics and chemistry during the 2012 PEGASOS field campaigns

    NASA Astrophysics Data System (ADS)

    Ganzeveld, Laurens; Krol, Maarten; Bosveld, Fred; Hofzumahaus, Andreas; Kiendler-Scharr, Astrid; Rohrer, Franz; Wahner, Andreas; Descari, Stefano

    2014-05-01

    Surface and airborne measurements collected during the 2012 PEGASOS intensive field campaign over the Netherlands and the Po valley, Italy, offer an optimal source of information to further improve our knowledge on the role boundary layer exchange processes in atmospheric chemistry. The use of a zeppelin, sampling close to the surface ( ~50m) up to ~600m altitude and measuring in the early morning, provided detailed measurements of vertical gradients as well as the temporal evolution in chemical composition and relevant meteorological parameters. This allows more detailed analysis of the role of the morning transition and entrainment of residual air masses previously being identified to be essential to daytime chemical processing in the boundary layer. Analysis of these measurements is supported by the use of a number of modelling systems including a selection of 1-D model approaches. In addition, these 1-D models are applied to directly link the observations to the representation of these processes in the 3-D atmospheric chemistry models used to address the overall PEGASOS research goals. In this presentation, results of simulations with an 1-D chemistry-climate model system covering the full measurement period will be presented. Assimilation of meteorological and chemical composition re-analysis data as well as a detailed representation of atmosphere-biosphere and boundary layer exchange processes in this 1-D system allow to assess the role of local scale land-atmosphere interactions versus long-range transport during the PESOSAS field campaigns. In this presentation we will focus on an assessment to what extent daytime boundary layer dynamics and chemistry depends on the short- and more long-term history of the system, e.g., residual layer processing and the role of changes in soil moisture status on land-atmosphere interactions.

  1. 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.

  2. Analysis of the correlations between atmospheric boundary-layer and free-tropospheric temperatures in the tropics

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Dessler, Andrew E.; North, Gerald R.

    2006-10-01

    We investigate the vertical correlations between temperature variations at 925 hPa, in the atmospheric boundary layer, and temperature variations in the free troposphere and lower stratosphere in the Tropics in daily and monthly averaged satellite and radiosonde measurements and in six General Circulation Models (GCMs). The results show generally positive correlations between the boundary layer temperatures and temperatures in the rest of the troposphere, with negative correlations occurring around the tropopause and in the lower stratosphere. In typically non-convective regions, the variations at the surface show little connection to mid and upper tropospheric temperature variations. In the convective Western Pacific, the correlations are low in the mid troposphere and much larger around 200 hPa. GCMs generally capture the temperature correlations, although as a group they tend to overpredict the coupling between the boundary layer and the rest of the troposphere. The basic correlation patterns of monthly temperature are found similar to the daily results.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  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. The Boundary Layer Radiometer

    NASA Astrophysics Data System (ADS)

    Irshad, Ranah; Bowles, N. E.; Calcutt, S. B.; Hurley, J.

    2010-10-01

    The Boundary Layer Radiometer is a small, low mass (<1kg) radiometer with only a single moving part - a scan/calibration mirror. The instrument consists of a three mirror telescope system incorporating an intermediate focus for use with miniature infrared and visible filters. It also has an integrated low power blackbody calibration target to provide long-term calibration stability The instrument may be used as an upward looking boundary layer radiometer for both the terrestrial and Martian atmospheres with appropriate filters for the mid-infrared carbon dioxide band, as well as a visible channel for the detection of aerosol components such as dust. The scan mirror may be used to step through different positions from the local horizon to the zenith, allowing the vertical temperature profile of the atmosphere to be retrieved. The radiometer uses miniature infrared filter assemblies developed for previous space-based instruments by Oxford, Cardiff and Reading Universities. The intermediate focus allows for the use of upstream blocking filters and baffles, which not only simplifies the design of the filters and focal plane assembly, but also reduces the risk of problems due to stray light. Combined with the calibration target this means it has significant advantages over previous generations of small radiometers.

  9. 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

  10. Very-Large-Scale Motions in the Atmospheric Boundary Layer Educed by Snapshot Proper Orthogonal Decomposition

    NASA Astrophysics Data System (ADS)

    Shah, Stimit; Bou-Zeid, Elie

    2014-12-01

    Large-eddy simulations of the atmospheric boundary layer (ABL) under a wide range of stabilities are conducted to educe very-large-scale motions and then to study their dynamics and how they are influenced by buoyancy. Preliminary flow visualizations suggest that smaller-scale motions that resemble hairpins are embedded in much larger scale streamwise meandering rolls. Using simulations that represent more than 150 h of physical time, many snapshots in the -, - and -planes are then collected to perform snapshot proper orthogonal decomposition and further investigate the large structures. These analyses confirm that large streamwise rolls that share several features with the very-large-scale motions observed in laboratory studies arise as the dominant modes under most stabilities, but the effect of the surface kinematic buoyancy flux on the energy content of these dominant modes is very significant. The first two modes in the -plane in the neutral case contain up to 3 % of the total turbulent kinetic energy; they also have a vertical tilt angle in the -plane of about 0 to 30 due to the turning effect associated with the Coriolis force. Unstable cases also feature streamwise rolls, but in the convective ABL they are strengthened by rising plumes in between them, with two to four rolls spanning the whole domain in the first few modes; the Coriolis effect is much weaker in the unstable ABL. These rolls are no longer the dominant modes under stable conditions where the first mode is observed to contain sheet-like motions with high turbulent kinetic energy. Using these proper orthogonal decomposition modes, we are also able to extract the vertical velocity fields corresponding to individual modes and then to correlate them with the horizontal velocity or temperature fields to obtain the momentum and heat flux carried by individual modes. Structurally, the fluxes are explained by the topology of their corresponding modes. However, the fraction of the fluxes produced by

  11. 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.

  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. Simulation of the atmospheric boundary layer in the wind tunnel for modeling of wind loads on low-rise structures

    NASA Technical Reports Server (NTRS)

    Tieleman, H. W.; Reinhold, T. A.; Marshall, R. D.

    1976-01-01

    The lower part of the atmospheric boundary layer (strong wind conditions) was simulated in low speed wind tunnel for the modeling of wind loads on low-rise structures. The turbulence characteristics of the turbulent boundary layer in the wind tunnel are compared with full scale measurements and with measurements made at NASA Wallops Flight Center. Wind pressures measured on roofs of a 1:70 scale model of a small single family dwelling were compared with results obtained from full scale measurements. The results indicate a favorable comparison between full scale and model pressure data as far as mean, r.m.s. and peak pressures are concerned. In addition, results also indicate that proper modeling of the turbulence is essential for proper simulation of the wind pressures.

  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. 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

  19. 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'.

  20. 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

  1. Turbulent measurements in the stable atmospheric boundary layer during SHEBA: ten years after

    NASA Astrophysics Data System (ADS)

    Grachev, Andrey; Andreas, Edgar; Fairall, Christopher; Guest, Peter; Persson, P.

    2008-03-01

    This paper surveys results of the comprehensive turbulent measurements in the stable boundary layer (SBL) made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) in the Beaufort Gyre from October 1997 through September 1998. Turbulent fluxes and mean meteorological data were continuously measured and reported hourly at five levels on a 20-m main SHEBA tower. Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime to very stable stratification, and allow studying the SBL in detail. A brief overview of the SBL regimes, the flux-profile relationships, the turbulent Prandtl number, and other parameters obtained during SHEBA is given. The traditional Monin—Obukhov approach, z-less scaling, and gradient-based scaling are evaluated and discussed based on the data from SHEBA.

  2. A study of turbulence in an evolving stable atmospheric boundary layer using large-eddy simulation

    SciTech Connect

    Cederwall, R; Street, R L

    1999-05-01

    A study is made of the effects of stable stratification on the fine-scale features of the flow in an evolving stable boundary layer (SBL). Large-eddy simulation (LES) techniques are used so that spatially and temporally varying and intermittent features of the turbulence can be resolved; traditional Reynolds-averaging approaches are not well suited to this. The LES model employs a subgrid turbulence model that allows upscale energy transfer (backscatter) and incorporates the effects of buoyancy. The afternoon, evening transition, and nighttime periods are simulated. Highly anisotropic turbulence is found in the developed SBL, with occasional periods of enhanced turbulence. Energy backscatter occurs in a fashion similar to that found in DNS, and is an important capability in LES of the SBL. Coherent structures are dominant in the SBL, as the damping of turbulent energy occurs more at the smaller, less organized scales.

  3. Long-term measurements of refractive index structure constant in atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Jicha, Otakar; Pechac, Pavel; Zvanovec, Stanislav; Grabner, Martin; Kvicera, Vaclav

    2012-10-01

    Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C2n, allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.

  4. Standard deviation of vertical two-point longitudinal velocity differences in the atmospheric boundary layer.

    NASA Technical Reports Server (NTRS)

    Fichtl, G. H.

    1971-01-01

    Statistical estimates of wind shear in the planetary boundary layer are important in the design of V/STOL aircraft, and for the design of the Space Shuttle. The data analyzed in this study consist of eleven sets of longitudinal turbulent velocity fluctuation time histories digitized at 0.2 sec intervals with approximately 18,000 data points per time history. The longitudinal velocity fluctuations were calculated with horizontal wind and direction data collected at the 18-, 30-, 60-, 90-, 120-, and 150-m levels. The data obtained confirm the result that Eulerian time spectra transformed to wave-number spectra with Taylor's frozen eddy hypothesis possess inertial-like behavior at wave-numbers well out of the inertial subrange.

  5. Turbulence and Coherent Structure in the Atmospheric Boundary Layer near the Eyewall of Hurricane Hugo (1989)

    NASA Astrophysics Data System (ADS)

    Zhang, J. A.; Marks, F. D.; Montgomery, M. T.; Black, P. G.

    2008-12-01

    In this talk we present an analysis of observational data collected from NOAA'S WP-3D research aircraft during the eyewall penetration of category five Hurricane Hugo (1989). The 1 Hz flight level data near 450m above the sea surface comprising wind velocity, temperature, pressure and relative humidity are used to estimate the turbulence intensity and fluxes. In the turbulent flux calculation, the universal shape spectra and co-spectra derived using the 40 Hz data collected during the Coupled Boundary Layer Air-sea Transfer (CBLAST) Hurricane experiment are applied to correct the high frequency part of the data collected in Hurricane Hugo. Since the stationarity assumption required for standard eddy correlations is not always satisfied, different methods are summarized for computing the turbulence parameters. In addition, a wavelet analysis is conducted to investigate the time and special scales of roll vortices or coherent structures that are believed important elements of the eye/eyewall mixing processes that support intense storms.

  6. 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

  7. Satellite remote sounding of atmospheric boundary layer temperature inversions over the subtropical eastern Pacific

    NASA Astrophysics Data System (ADS)

    Fetzer, Eric J.; Teixeira, Joao; Olsen, Edward T.; Fishbein, Evan F.

    2004-09-01

    We describe atmospheric temperature inversions and height-resolved water vapor fields over the wintertime subtropical northeastern Pacific Ocean in observations by the satellite-borne Atmospheric Infrared Sounder (AIRS) experiment. A comparison with model analyses shows good agreement in temperature. Water vapor comparisons with operational radiosondes at four sites in California and Hawaii during December 2002-January 2003 have low biases in the 1000-700 and 700-500 hPa layers. Maps of inversion frequency, and, water vapor at 1000-700 and 700-500 hPa over the subtropical northeast Pacific during 1-16 January 2003-when high pressure and clear conditions prevail-show inversions occurring at a local minimum in water vapor at 1000-700 hPa. Water vapor at 700-500 hPa has a broad minimum extending from Baja California to Hawaii, with inversions found on its eastern half. These observations illustrate the potential of the AIRS data for describing a climatology of temperature and water vapor in subtropical oceanic regions.

  8. Boundary Layer Relaminarization Device

    NASA Technical Reports Server (NTRS)

    Creel, Theodore R. (Inventor)

    1993-01-01

    Relamination of a boundary layer formed in supersonic flow over the leading edge of a swept airfoil is accomplished using at least one band, especially a quadrangular band, and most preferably a square band. Each band conforms to the leading edge and the upper and lower surfaces of the airfoil as an integral part thereof and extends perpendicularly from the leading edge. Each band has a height of about two times the thickness of the maximum expected boundary layer.

  9. 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.

  10. Retrieval of structure functions of air temperature and refractive index from large eddy simulations of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Wilson, Chris; van Eijk, Alexander M.; Fedorovich, Evgeni

    2013-09-01

    A methodology is presented to infer the refractive-index structure function parameter and the structure parameters for temperature and humidity from numerical simulations of the turbulent atmospheric convective boundary layer (CBL). The method employs spatial and temporal averaging of multiple realizations of the CBL flow field reproduced by a large-eddy simulation (LES) of the atmosphere. The Cn2 values yielded by LES-based approach agree fairly well with Cn2 values predicted by the Monin-Obukhov similarity theory. In this respect, the Cn2 retrieval from the LES data is promising for evaluating the vertical profile of Cn2 throughout the entire CBL. Under the considered CBL conditions and for the selected optical wavelength of 0.55 μm the value of Cn2 was found to be dominated by the CT2 contribution in the first few hundred meters above the surface, whereas the CTq contribution became significant aloft.

  11. 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.

  12. The Interactive Evolution of the Oceanic and Atmospheric Boundary Layers in the Source Regions of the Trades.

    NASA Astrophysics Data System (ADS)

    Kraus, Eric B.; Leslie, Lynn D.

    1982-12-01

    Subtropical status tends to form over relatively cold water, its presence then keeps the water cold. We have investigated the resultant downstream development in the framework of an interactive, two-dimensional, steady-state model of the oceanic and atmospheric mixed layers. Upstream boundary and interior conditions in both media, and irradiance and advection velocities are specified; mixed-layer temperature salinity, heat and moisture content are evolving dependent variables. The integration is continued downstream until convective instability develops or, failing that, for a distance of 2000 km.Sensitivity tests show this development to be strongly affected by the upstream boundary conditions, implying an effect of coastal upwelling processes upon oceanic and atmospheric temperature profiles for a long distance downstream. The dependence on the advection velocity is very nonlinear. The amplitude of temperature changes is of the same order in both media, despite the greater oceanic heat capacity. This is due to the unequal advection rate, which causes a water column to remain in the affected area some fifty times longer than the air above.

  13. On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

    NASA Astrophysics Data System (ADS)

    Archer, Cristina L.; Colle, Brian A.; Veron, Dana L.; Veron, Fabrice; Sienkiewicz, Matthew J.

    2016-08-01

    The marine boundary layer of the northeastern U.S. is studied with focus on wind speed, atmospheric stability, and turbulent kinetic energy (TKE), the three most relevant properties in the context of offshore wind power development. Two long-term observational data sets are analyzed. The first one consists of multilevel meteorological variables measured up to 60 m during 2003-2011 at the offshore Cape Wind tower, located near the center of the Nantucket Sound. The second data set comes from the 2013-2014 IMPOWR campaign (Improving the Modeling and Prediction of Offshore Wind Resources), in which wind and wave data were collected with new instruments on the Cape Wind platform, in addition to meteorological data measured during 19 flight missions offshore of New York, Connecticut, Rhode Island, and Massachusetts. It is found that, in this region: (1) the offshore wind resource is remarkable, with monthly average wind speeds at 60 m exceeding 7 m s-1 all year round, highest winds in winter (10.1 m s-1) and lowest in summer (7.1 m s-1), and a distinct diurnal modulation, especially in summer; (2) the marine boundary layer is predominantly unstable (61% unstable vs. 21% neutral vs. 18% stable), meaning that mixing is strong, heat fluxes are positive, and the wind speed profile is often nonlogarithmic (~40% of the time); and (3) the shape of the wind speed profile (log versus nonlog) is an effective qualitative proxy for atmospheric stability, whereas TKE alone is not.

  14. Atmospheric boundary layer effects induced by the 20 March 2015 solar eclipse

    NASA Astrophysics Data System (ADS)

    Gray, Suzanne L.; Harrison, R. Giles

    2016-04-01

    The British Isles benefits from dense meteorological observation networks, enabling insights into the still-unresolved effects of solar eclipse events on the near-surface wind field. The near-surface effects of the solar eclipse of 20 March 2015 are derived through comparison of output from the Met Office's operational weather forecast model (which is ignorant of the eclipse) with data from two meteorological networks: the Met Office's land surface station (MIDAS) network and a roadside measurement network operated by Vaisala. Synoptic-evolution relative calculations reveal the cooling and increase in relative humidity almost universally attributed to eclipse events. In addition, a slackening of wind speeds by up to about 2 knots in already weak winds and backing in wind direction of about 20 degrees under clear skies across middle England are attributed to the eclipse event. The slackening of wind speed is consistent with the previously reported boundary layer stabilisation during eclipse events. Wind direction changes have previously been attributed to a large-scale `eclipse-induced cold-cored cyclone', mountain slope flows, and changes in the strength of sea breezes. A new explanation is proposed here by analogy with nocturnal wind changes at sunset and shown to predict direction changes consistent with those observed.

  15. Multiscale aeroelastic simulations of large wind farms in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Vitsas, Athanasios; Meyers, Johan

    2016-09-01

    In large wind farms, the turbulence induced by each turbine results in high overall turbulence levels that can be detrimental for downstream wind turbine components. In the current study, we scrutinize structural loads and dynamics, and their correlation to turbulent flow structures by conducting aeroelastic simulations in wind farms. To this end, a pseudospectral large-eddy simulation solver is coupled with a multibody dynamics module in a multiscale framework. The multirate approach leads us naturally to the development of an aeroelastic actuator sector model that represents the wind turbine forces on the flow. This makes it computationally feasible to simulate long time horizons of the two-way coupled aeroelastic system. Hence, it allows us to look at the interaction of the turbine structure with the turbulent boundary layer and the wakes of multiple turbine arrays, and to get estimates of damage equivalent loads and structural loading statistics, as longer time series are available. Results are shown for two typical wind farm layouts, i.e. aligned and staggered, for above-rated flow regimes.

  16. Atmospheric boundary layer observation by ground-based lidar at KMITL, Thailand 13 deg N, 100 deg E

    NASA Astrophysics Data System (ADS)

    Lerkvaranyu, Somkiat; Dejhan, Kobchai; Cheevasuvit, Fusak; Itabe, Toshikasu; Mizutani, Kohei; Aoki, Tetsuo; Yasui, Motoaki

    2001-02-01

    Tropospheric aerosols effects on climate in directly through various cloud formation, the lidar has been used to study the composition of many particles mixing in the atmosphere including to study the aerosol and cloud. Currently, it has many types of lidar systems depending on the purpose of measurements. In this report, the ground-based lidar system was established at King Mongkut's Institute of Technology Ladkrabang (KMITL), THAILAND to study and measure the aerosol in boundary layer and cirrus clouds in the tropopause region. The aerosol measurement is in the form of scattering ratio whereas the signal depolarization has been applied to identify layers of cirrus clouds. The lidar system consists of laser source (Nd:YAG) with second harmonic wavelength, 28 cm Schmidt-Cassegrain telescope, photomultiplier tube (PMT) and data acquisition system.

  17. Turbulence Variance Characteristics in the Unstable Atmospheric Boundary Layer above Flat Pine Forest

    NASA Astrophysics Data System (ADS)

    Asanuma, Jun

    Variances of the velocity components and scalars are important as indicators of the turbulence intensity. They also can be utilized to estimate surface fluxes in several types of "variance methods", and the estimated fluxes can be regional values if the variances from which they are calculated are regionally representative measurements. On these motivations, variances measured by an aircraft in the unstable ABL over a flat pine forest during HAPEX-Mobilhy were analyzed within the context of the similarity scaling arguments. The variances of temperature and vertical velocity within the atmospheric surface layer were found to follow closely the Monin-Obukhov similarity theory, and to yield reasonable estimates of the surface sensible heat fluxes when they are used in variance methods. This gives a validation to the variance methods with aircraft measurements. On the other hand, the specific humidity variances were influenced by the surface heterogeneity and clearly fail to obey MOS. A simple analysis based on the similarity law for free convection produced a comprehensible and quantitative picture regarding the effect of the surface flux heterogeneity on the statistical moments, and revealed that variances of the active and passive scalars become dissimilar because of their different roles in turbulence. The analysis also indicated that the mean quantities are also affected by the heterogeneity but to a less extent than the variances. The temperature variances in the mixed layer (ML) were examined by using a generalized top-down bottom-up diffusion model with some combinations of velocity scales and inversion flux models. The results showed that the surface shear stress exerts considerable influence on the lower ML. Also with the temperature and vertical velocity variances ML variance methods were tested, and their feasibility was investigated. Finally, the variances in the ML were analyzed in terms of the local similarity concept; the results confirmed the original

  18. 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.; Lampert, A.; Wildmann, N.; Hermann, M.; Käthner, R.; Bange, J.; Baars, H.

    2014-12-01

    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 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 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 two 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 boundary layer, derived from

  19. Modeling the atmospheric convective boundary layer within a zero-order jump approach: An extended theoretical framework

    SciTech Connect

    Fedorovich, E.

    1995-09-01

    The paper presents an extended theoretical background for applied modeling of the atmospheric convective boundary layer within the so-called zero-order jump approach, which implies vertical homogeneity of meteorological fields in the bulk of convective boundary layer (CBL) and zero-order discontinuities of variables at the interfaces of the layer. The zero-order jump model equations for the most typical cases of CBL are derived. The models of nonsteady, horizontally homogeneous CBL with and without shear, extensively studied in the past with the aid of zero-order jump models, are shown to be particular cases of the general zero-order jump theoretical framework. The integral budgets of momentum and heat are considered for different types of dry CBL. The profiles of vertical turbulent fluxes are presented and analyzed. The general version of the equation of CBL depth growth rate (entrainment rate equation) is obtained by the integration of the turbulence kinetic energy balance equation, invoking basic assumptions of the zero-order parameterizations of the CBL vertical structure. The problems of parameterizing the turbulence vertical structure and closure of the entrainment rate equation for specific cases of CBL are discussed. A parameterization scheme for the horizontal turbulent exchange in zero-order jump models of CBL is proposed. The developed theory is generalized for the case of CBL over irregular terrain. 28 refs., 2 figs.

  20. The Tturbulent Structure of the Atmospheric Boundary Layer over Small Northern Lakes

    NASA Astrophysics Data System (ADS)

    Repina, I.; Stepanenko, V.; Artamonov, A.; Barskov, K.; Polukhov, A.

    2015-12-01

    Wetland and freshwater ecosystems of the Northern Europe are an important natural source of atmospheric 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 layer. 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.

  1. Controlled meteorological (CMET) balloon profiling of the Arctic atmospheric boundary layer around Spitsbergen compared to a mesoscale model

    NASA Astrophysics Data System (ADS)

    Roberts, T. J.; Dütsch, M.; Hole, L. R.; Voss, P. B.

    2015-10-01

    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 atmospheric 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 boundary layer 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 boundary layer 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-atmosphere 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

  2. Observations of atmospheric trace gases by MAX-DOAS in the coastal boundary layer over Jiaozhou Bay

    NASA Astrophysics Data System (ADS)

    Li, Xianxin; Wang, Zhangjun; Meng, Xiangqian; Zhou, Haijin; Du, Libin; Qu, Junle; Chen, Chao; An, Quan; Wu, Chengxuan; Wang, Xiufen

    2014-11-01

    Atmospheric trace gases exist in the atmosphere of the earth rarely. But the atmospheric trace gases play an important role in the global atmospheric environment and ecological balance by participating in the global atmospheric cycle. And many environmental problems are caused by the atmospheric trace gases such as photochemical smog, acid rain, greenhouse effect, ozone depletion, etc. So observations of atmospheric 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 boundary layer 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.

  3. Massive-scale aircraft observations of giant sea-salt aerosol particle size distributions in atmospheric marine boundary layers

    NASA Astrophysics Data System (ADS)

    Jensen, J. B.

    2015-12-01

    iant sea-salt aerosol particles (dry radius, rd > 0.5 μm) occur nearly everywhere in the marine boundary layer and frequently above. This study presents observations of atmospheric 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 boundary layer 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 atmospheric conditions. The size distributions provide a unique observational set for initializing cloud models with coarse-mode aerosol particle observations for marine atmospheres.

  4. Some Observational and Modeling Studies of the Atmospheric Boundary Layer at Mississippi Gulf Coast for Air Pollution Dispersion Assessment

    PubMed Central

    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

    2008-01-01

    Coastal atmospheric 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 boundary layer 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 boundary layer near the coast which gradually develops inland. The weather research and forecasting (WRF) meso-scale atmospheric model and a Lagrangian particle dispersion model (HYSPLIT) are used to simulate the lower atmospheric 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

  5. Some observational and modeling studies of the atmospheric boundary layer at Mississippi gulf coast for air pollution dispersion assessment.

    PubMed

    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

    2008-12-01

    Coastal atmospheric 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 boundary layer 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 boundary layer near the coast which gradually develops inland. The weather research and forecasting (WRF) meso-scale atmospheric model and a Lagrangian particle dispersion model (HYSPLIT) are used to simulate the lower atmospheric 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.

  6. Description of the atmospheric circulation in the boundary layer over a tropical island: Case study of Guadeloupe Archipelago

    NASA Astrophysics Data System (ADS)

    Plocoste, Thomas; Dorville, Jean-François; Jacoby-Koaly, Sandra; Roussas, André

    2016-04-01

    Over past two decades the use of atmospheric 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 atmospheric pollution process. Up to 2009 no wind profile data were available continuously to study atmospheric 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 atmospheric pollution. From 2009 to 2012 a measurement campaign of the Atmospheric Boundary Layer (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

  7. Large-Eddy Simulation of Very-Large-Scale Motions in the Neutrally Stratified Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Fang, Jiannong; Porté-Agel, Fernando

    2015-06-01

    Large-eddy simulation is used to investigate very-large-scale motions (VLSMs) in the neutrally stratified atmospheric boundary layer at a very high friction Reynolds number, . The vertical height of the computational domain is m, which corresponds to the thickness of the boundary layer. In order to make sure that the largest flow structures are properly resolved, the horizontal domain size is chosen to be and , which is much larger than the standard domain size, especially in the streamwise direction (i.e., the direction of elongation of the flow structures). It is shown that the contributions to the resolved turbulent kinetic energy and the resolved shear stress from streamwise wavelengths larger than are up to 27 and 31 % respectively. 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, up to in the streamwise direction and in the spanwise direction. These features are similar to those found in the logarithmic and outer regions of laboratory-scale boundary layers by direct numerical simulation and experiments conducted at low to moderate Reynolds numbers. The three-dimensional correlation map and conditional average of the three components of velocity further indicate that the low-speed and high-speed regions possess the same elongated ellipsoid-like structure, which is inclined upward along the streamwise direction, and they are accompanied by counter-rotating roll modes in the

  8. A Numerical Study of Sea Breeze and Spatiotemporal Variation in the Coastal Atmospheric Boundary Layer at Hainan Island, China

    NASA Astrophysics Data System (ADS)

    Huang, Qian-Qian; Cai, Xu-Hui; Song, Yu; Kang, Ling

    2016-06-01

    Numerical simulations of sea breezes and the coastal atmospheric boundary layer (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 boundary layer (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.

  9. Large-eddy Simulation of Atmospheric Boundary-layer Flow through a Wind Farm Sited on Complex Terrain

    NASA Astrophysics Data System (ADS)

    Shamsoddin, Sina; Porté-Agel, Fernando

    2015-04-01

    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, boundary-layer 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/atmospheric boundary layer 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.

  10. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

    1989-01-01

    Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer 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 boundary layers 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.

  11. High-resolution properties of the Equatorial Pacific marine atmospheric boundary layer from lidar and radiosonde observations

    SciTech Connect

    Cooper, D.I.; Eichinger, W.E.; Barr, S.

    1996-07-15

    A {open_quotes}thermostat{close_quotes} 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 atmosphere boundary layer (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-atmosphere phenomonology, which in turn, affects the climatology of the Central Pacific. Agreement between coincident radiosonde and the Raman water vapor lidar measurements was typically within {plus_minus} 0.25 g kg{sup {minus}1} of water. Divergence between the two instruments occurred at transitions between distinct layers in the lower marine atmosphere. 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, atmospheric 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{degrees} and 30{degrees}C. 56 refs., 14 figs.

  12. Ice at the Interface: Atmosphere-Ice-Ocean Boundary Layer Processes and Their Role in Polar Change---Workshop Report

    SciTech Connect

    Hunke, Elizabeth C.

    2012-07-23

    The atmosphere-ocean boundary layer 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.

  13. Investigation and validation of wake model combinations for large wind farm modelling in neutral atmospheric boundary layers

    NASA Astrophysics Data System (ADS)

    Tromeur, E.; Puygrenier, S.; Sanquer, S.

    2016-09-01

    This study is focused on assessing the ability of two refined large wind farm models to describe the disturbance of the neutral atmospheric flow caused by large offshore wind farms. Sensitivity studies of internal boundary layer parameters are carried out. An optimum large wind farm correction is then proposed and combined with two different standard single wake models, the Park and EVM models. The large wind farm wake effect is evaluated and validated against measurements of two offshore wind farms at Horns Rev and Nysted and four standard wake models by computing velocity deficit and normalized power. All large wind farm models proposed were able to capture wake width to some degree and the decrease of power output moving through the wind farm. Despite some uncertainties, this very promising model combinations allows us to take into account the slowdown in large wind farms.

  14. Temperature profiling of the atmospheric boundary layer with rotational Raman lidar during the HD(CP)2 Observational Prototype Experiment

    NASA Astrophysics Data System (ADS)

    Hammann, E.; Behrendt, A.; Le Mounier, F.; Wulfmeyer, V.

    2015-03-01

    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 atmospheric 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 atmospheric boundary layer 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 boundary layer 100 m above the ground.

  15. Temperature profiling of the atmospheric boundary layer with rotational Raman lidar during the HD(CP)2 observational prototype experiment

    NASA Astrophysics Data System (ADS)

    Hammann, E.; Behrendt, A.; Le Mounier, F.; Wulfmeyer, V.

    2014-11-01

    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 atmospheric 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 atmospheric boundary layer 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 boundary layer a hundred meters above the ground.

  16. Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and atmospheric lifetime in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Petzold, A.; Hasselbach, J.; Lauer, P.; Baumann, R.; Franke, K.; Gurk, C.; Schlager, H.; Weingartner, E.

    2007-10-01

    Particle emissions from ship engines and their atmospheric transformation in the marine boundary layer (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 atmospheric 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 boundary layer.

  17. Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and atmospheric lifetime in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Petzold, A.; Hasselbach, J.; Lauer, P.; Baumann, R.; Franke, K.; Gurk, C.; Schlager, H.; Weingartner, E.

    2008-05-01

    Particle emissions from ship engines and their atmospheric transformation in the marine boundary layer (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 atmospheric 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 boundary layer.

  18. TETHERED BALLOON MEASUREMENTS OF BIOGENIC VOCS IN THE ATMOSPHERIC BOUNDARY LAYER

    EPA Science Inventory

    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 boundary ...

  19. Simulation of CO2 dispersion in the atmospheric boundary layer using a mesoscale model

    NASA Astrophysics Data System (ADS)

    Granvold, P. W.; Chow, F. K.; Oldenburg, C. M.

    2007-12-01

    The consequences of unexpected releases of CO2 from underground carbon sequestration sites must be understood before large-scale carbon capture and storage projects are implemented. Carbon dioxide gas can migrate through faults, fractures, or abandoned wells that penetrate the subsurface storage site and provide a pathway to the ground surface. Though such leakage is typically slow and in small amounts, CO2 can accumulate at the ground surface because it is denser than the surrounding atmosphere. Such accumulation presents health risks for humans and animals in the vicinity, and can cause damage to crops, trees, and other vegetation. Because atmospheric dispersion of CO2 is driven by gravity and ambient wind conditions, the danger from CO2 is greatest in regions with topographic depressions where the dense gas can pool, or under stably- stratified background atmospheric conditions which further inhibit mixing and dilution of the gas. We are developing a simulation tool for predictions of CO2 releases from underground storage sites in a mesoscale atmospheric model. The model solves the compressible fluid flow equations, and has been modified to account for transport of dense gases. Example simulations from sources of different release strengths over various topography and background atmospheric conditions illustrate the behavior of the model and its utility for risk assessment and certification of carbon sequestration sites.

  20. UAS and DTS: Using Drones and Fiber Optics to Measure High Resolution Temperature of the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Predosa, R. A.; Darricau, B.; Higgins, C. W.

    2015-12-01

    The atmospheric boundary layer (ABL) is the lowest part of the atmosphere that directly interacts with the planet's surface. The development of the ABL plays a vital role, as it affects the transport of atmospheric 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 atmospheric sensor technologies, it will have more applications in the future.

  1. RAMS sensitivity to mesh resolution in large eddy simulation of the neutral and convective atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Ercolani, Giulia; Gorlé, Catherine; Corbari, Chiara; Mancini, Marco

    2014-05-01

    Large Eddy Simulation (LES) is a computational fluid dynamic technique that has been extensively used to reproduce turbulence in the Atmospheric Boundary Layer (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 boundary 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 boundary 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 boundary 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 Atmospheric 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 atmospheric boundary layer, for which the turbulent statistics and flow structures are well known. For

  2. Evaluation of the atmospheric boundary layer schemes in the mesoscale models WRF and RAMS using scintillometry and in situ observations at Cabauw

    NASA Astrophysics Data System (ADS)

    Steeneveld, Gj; Tolk, Lf

    2009-09-01

    Limited area models are widely used for high resolution weather forecasting and atmospheric research. These models also provide the meteorological input for air quality forecasting and for inverse modeling studies, e.g. for identification of CO2 sources and sinks. The success of these applications depends on the accuracy of the provided meteorology, especially in the atmospheric boundary layer and close to the surface. We evaluate the atmospheric boundary layer schemes in the mesoscale models WRF and RAMS for two contrasting apparent golden days (i.e. calm and windy) in The Netherlands, for both grassland and forest sites. The windy case is exclusive because of a large humidity jump between the boundary layer and the free atmosphere, and is therefore particularly interesting to study the representation of entrainment. Also, the influence of different boundary conditions will be assessed. The model intercomparison reveals that radiation components are estimated reasonably well by both models. Both models forecast the latent heat flux correctly, but relatively large differences occur for sensible heat flux and boundary layer height. Observations of the PBL potential temperature and humidity suggest other optimal settings for the energy flux model than the surface flux observations. Standard RAMS energy fluxes return a cold bias in the PBL. WRF and RAMS with increased Bowen ratios, capture the atmospheric temperature correctly but overestimate the Bowen ratio. The uncertainty in the surface energy fluxes is reflected in height of the PBL, which also differs substantially between the two models. Note that our model results appear insensitive to the choice of the initial and boundary conditions (ECMWF or NCEP). Thus, we find that the observed surface sensible heat flux cannot explain the boundary layer growth and energy content during the day. Therefore, a further discussion of both the observed and modeled terms of the heat budget equation is required to understand the

  3. Zeppelin NT - Measurement Platform for the Exploration of Atmospheric Chemistry and Dynamics in the Planetary Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hofzumahaus, Andreas; Holland, Frank; Oebel, Andreas; Rohrer, Franz; Mentel, Thomas; Kiendler-Scharr, Astrid; Wahner, Andreas; Brauchle, Artur; Steinlein, Klaus; Gritzbach, Robert

    2014-05-01

    The planetary boundary layer (PBL) is the chemically most active and complex part of the atmosphere where freshly emitted reactive trace gases, tropospheric radicals, atmospheric 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.

  4. Test of a new near-wall SFS model in large-eddy simulations of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Zhou, Yong; Brasseur, James

    2000-11-01

    In previous work we have proposed a new ¡°resolvable subfilter-scale¡± (RSFS) model (Zhou, Brasseur, and Juneja, submitted to Phys. Fluids) specific to near-surface high Reynolds number turbulence where serious deficiencies exist in algebraic closures (Juneja and Brasseur, 1999, Phys. Fluids, 11, 3054) associated with necessary under-resolution of integral scales when the viscous layer cannot be resolved. It has been shown in anisotropic homogeneous turbulence that our RSFS model greatly improved model predictions of the anisotropic structure of subfilter-scale (SFS) acceleration and resolved velocity fields when integral scales are under-resolved. Here we test our RSFS model in LES of the inhomogeneous rough-wall atmospheric boundary layer, in which the horizontal integral scale of vertical velocity is necessarily under-resolved at the first few grid levels. It is known that mean velocity, variance and vertical velocity skewness are in error near the surface. We will compare the RSFS model with other model predictions and against field data. The partition of SFS acceleration between SFS stress divergence and SFS pressure force will be discussed.

  5. Acid-base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    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.

    2013-05-01

    Measurements of aerosol number distributions down to one molecule have provided information that we've used to develop a new approach for modeling atmospheric nucleation rates. Measurements were carried out with the Cluster Chemical Ionization Mass Spectrometer (Cluster CIMS), the scanning mobility spectrometer using a diethylene glycol condensation particle counter as detector (DEG SMPS), and an ambient pressure proton transfer mass spectrometer for ammonia and amines (AmPMS). The model explains nucleation as a result of cluster evolution due to a sequence of acid-base reactions. We conclude that the smallest stable cluster contains four sulfuric acid molecules. The model leads to a simple analytic expression for nucleation rates that is reasonably consistent (i.e., ± 10x) with atmospheric observations. The model predicts that nucleation rates are equal to a prefactor, P<1, times the sulfuric acid vapor collision rate, (i.e., J=Pṡ0.5ṡk11 *[H2SO4]2).

  6. Climatological perspectives of air transport from atmospheric boundary layer to tropopause layer over Asian monsoon regions during boreal summer inferred from Lagrangian approach

    NASA Astrophysics Data System (ADS)

    Chen, B.; Xu, X. D.; Yang, S.; Zhao, T. L.

    2012-02-01

    The Asian Summer Monsoon (ASM) region has been recognized as a key region that plays a vital role in troposphere-to-stratosphere transport (TST), which can significantly impact the budget of global atmospheric constituents and climate change. However, the details of transport from the boundary layer (BL) to tropopause layer (TL) over this region, particularly from a climatological perspective, remains an issue of uncertainty. In this study, we present the climatological properties of BL-to-TL transport over the ASM region during boreal summer season (June-July-August) from 2001 to 2009. A comprehensive tracking analysis is conducted based on a large ensemble of TST-trajectories departing from the atmospheric BL and arriving at TL. Driven by the winds fields from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) Global Forecast System, all TST-trajectories are selected from the high resolution datasets generated by the Lagrangian particle transport model FLEXPART using a domain-filling technique. Three key atmospheric boundary layer sources for BL-to-TL transport are identified with their contributions: (i) 38% from the region between tropical Western Pacific region and South China Seas (WP), (ii) 21% from Bay of Bengal and South Asian subcontinent (BOB), and (iii) 12% from the Tibetan Plateau, which includes the South Slope of the Himalayas (TIB). Controlled by the different patterns of atmospheric circulation, the air masses originating from these three source regions are transported along the different tracks into the TL. The spatial distributions of these three source regions remain similarly from year to year. The timescales of transport from BL to TL by the large-scale ascents range from 1 to 7 weeks, contributing up to 60-70% of the overall TST; whereas the transport governed by the deep convection overshooting becomes faster, with timescales of 1-2 days and contributions of 20-30%. These results provide

  7. The mean velocity profile in a sheared and thermally stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Katul, G. G.; Porporato, A. M.

    2011-12-01

    A universal stability correction function φ that accounts for distortions caused by thermal stratification to the logarithmic mean velocity profile (MVP) in the lower atmosphere was proposed by Monin and Obukhov in the 1950s using dimensional analysis. However, theories that predict the canonical shape of φ currently lag behind field experiments and numerical simulation. A recently proposed phenomenological theory that links the spectrum of turbulence to the MVP is expanded here by including the effects of thermal stratification on the turbulent kinetic energy dissipation rate and eddy-size anisotropy. The resulting theory explains all the canonical features of φ reported in field experiments, including the onset of power-laws and their concomitant exponents reported for mildly stable, mildly unstable, and the near-convective limit.

  8. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

    1984-01-01

    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 boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

  9. Simulation and modeling of the turbulent katabatic flow along a hyperbolic tangent slope for stably stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Brun, Ch.; Chollet, J. P.

    2009-04-01

    The behaviour of the Atmospheric Boundary layer (ABL) along alpine valleys is strongly dependent on the day-night thermodynamic cycle and might impact meteorology and air pollution prediction. At night, the ABL is stably stratified and the radiative cooling of the surface yields the development of a katabatic flow (Doran and Horst 1983, Monti et al. 2002). This flow consists of a downslope wall-jet which has the structure of both wall turbulence in the inner-layer zone and shear layer turbulence in the outer-layer zone and enhances a relative mixing eventhough stable stratification is considered (Baines 2005). A full 3D description of such flow by mean of Large Eddy Simulation of turbulence (LES) has not yet been achieved, except recently on relatively simple slopes (Skyllingstad 2003, Smith and Skyllingstad 2005) or including geostrophic wind forcing (Cuxart et al. 2006, Cuxart and Jimenez 2006). This is the purpose of the present study to accurately describe the ABL on a hyperbolic tangent slope with stable stratification. The numerical code used, Meso-NH, has been developed in CNRM/Meteo-France and Laboratoire d'Aérologie Toulouse, and consists of an anelastic non-hydrostatic model solving the pseudo-incompressible Navier-Stokes equations with a Boussinesq approximation. About 5 million grid points are necessary to afford a relatively precise description of the flow in the vicinity of the surface, with a special refinement in the vertical direction to capture the wall-jet developing along the slope. The setting of initial and boundary conditions is crucial for the simulation of stable ABL. Initial conditions consist of air at rest following a stable temperature profile with a constant Brunt-Väisälä frequency N=0.013. At the surface two sets of boundary conditions have been considered, first a rough surface condition, second an ideal case with slip conditions. A constant surface cooling q_w=-30 W/m2 is applied on the stably stratified fluid initially at rest

  10. High variability of atmospheric mercury in the summertime boundary layer through the central Arctic Ocean

    PubMed Central

    Yu, Juan; Xie, Zhouqing; Kang, Hui; Li, Zheng; Sun, Chen; Bian, Lingen; Zhang, Pengfei

    2014-01-01

    The biogeochemical cycles of mercury in the Arctic springtime have been intensively investigated due to mercury being rapidly removed from the atmosphere. 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

  11. Synoptic forcing of coastal-trapped disturbances in the marine atmospheric boundary layer

    SciTech Connect

    Rogerson, A.M.; Samelson, R.M.

    1994-12-31

    Throughout most of the summer, a strong temperature inversion exists off the west coast of the US due to the presence of a North Pacific subtropical high that dominates the area. The coastal mountains act as a barrier to the flow in the horizontal, making it possible for synoptic-scale forcing to give rise to coastal-trapped phenomena. In order to better understand the nature of these events, the authors have chosen to work within a simple framework for which they can obtain analytic solutions and answer fundamental questions concerning the generation, structure, and propagation of the disturbances. The authors use a homogeneous, reduced-gravity, shallow-water, f-plane model of the flow in which the coastal mountains are represented by a vertical wall with no alongshore variation. To maintain the tractability of an analytical solution, linearity is retained although no scale assumptions are made. The authors are interested in the response of the marine layer subject to forcing by upper-level pressure disturbances and dissipation in the form of wind stress at the sea surface.

  12. The impacts of summer monsoons on the ozone budget of the atmospheric boundary layer of the Asia-Pacific region.

    PubMed

    Hou, Xuewei; Zhu, Bin; Fei, Dongdong; Wang, Dongdong

    2015-01-01

    The seasonal and inter-annual variations of ozone (O3) in the atmospheric boundary layer 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.

  13. The Estimation of Surface Latent Heat Flux over the Ocean and its Relationship to Marine Atmospheric Boundary Layer (MABL) Structure

    NASA Technical Reports Server (NTRS)

    Palm, Stephen P.; Schwemmer, Geary K.; Vandemark, Doug; Evans, Keith; Miller, David O.; Demoz, Belay B.; Starr, David OC. (Technical Monitor)

    2001-01-01

    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 Atmospheric Boundary Layer (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.

  14. The impacts of summer monsoons on the ozone budget of the atmospheric boundary layer of the Asia-Pacific region.

    PubMed

    Hou, Xuewei; Zhu, Bin; Fei, Dongdong; Wang, Dongdong

    2015-01-01

    The seasonal and inter-annual variations of ozone (O3) in the atmospheric boundary layer 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

  15. Improving Wind Predictions in the Marine Atmospheric Boundary Layer Through Parameter Estimation in a Single Column Model

    DOE PAGES

    Lee, Jared A.; Hacker, Joshua P.; Monache, Luca Delle; Kosovic, Branko; Clifton, Andrew; Vandenberghe, Francois; Rodrigo, Javier Sanz

    2016-08-03

    A current barrier to greater deployment of offshore wind turbines is the poor quality of numerical weather prediction model wind and turbulence forecasts over open ocean. The bulk of development for atmospheric boundary layer (ABL) parameterization schemes has focused on land, partly due to a scarcity of observations over ocean. The 100-m FINO1 tower in the North Sea is one of the few sources worldwide of atmospheric profile observations from the sea surface to turbine hub height. These observations are crucial to developing a better understanding and modeling of physical processes in the marine ABL. In this paper we usemore » the WRF single column model (SCM), coupled with an ensemble Kalman filter from the Data Assimilation Research Testbed (DART), to create 100-member ensembles at the FINO1 location. The goal of this study is to determine the extent to which model parameter estimation can improve offshore wind forecasts. Combining two datasets that provide lateral forcing for the SCM and two methods for determining z0, the time-varying sea-surface roughness length, we conduct four WRF-SCM/DART experiments over the October-December 2006 period. The two methods for determining z0 are the default Fairall-adjusted Charnock formulation in WRF, and using parameter estimation techniques to estimate z0 in DART. Using DART to estimate z0 is found to reduce 1-h forecast errors of wind speed over the Charnock-Fairall z0 ensembles by 4%–22%. Finally, however, parameter estimation of z0 does not simultaneously reduce turbulent flux forecast errors, indicating limitations of this approach and the need for new marine ABL parameterizations.« less

  16. Boundary layer transition studies

    NASA Technical Reports Server (NTRS)

    Watmuff, Jonathan H.

    1995-01-01

    A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer 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 layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer 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 boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer 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 layer, 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 boundary layer. 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

  17. Application and Limitations of GPS Radio Occultation (GPS-RO) Data for Atmospheric Boundary Layer Height Detection over the Arctic.

    NASA Astrophysics Data System (ADS)

    Ganeshan, M.; Wu, D. L.

    2014-12-01

    Due to recent changes in the Arctic environment, it is important to monitor the atmospheric boundary layer (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 layer 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.

  18. 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.

    PubMed

    Payne, A W; Snyder, W H; Binkowski, F S; Watson, J E

    1982-12-01

    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 release points over surfaces of comparable roughness length. This information should prove useful in a variety of transport and diffusion studies over short to moderate downwind distances. It will be used in Part II as the baseline data set with which to compare diffusion downwind of standard-design nuclear power plants.

  19. Turbulent boundary layer heat

    NASA Astrophysics Data System (ADS)

    Finson, M. L.; Clarke, A. S.; Wu, P. K. S.

    1981-01-01

    A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me -9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant (roughness velocity,) it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels.

  20. A large-eddy simulation study of the impact of different land-atmosphere coupling schemes on the dynamics of the nocturnal boundary layer (Invited)

    NASA Astrophysics Data System (ADS)

    Stoll, J. R.; Shingleton, N. D.; Bosveld, F.

    2010-12-01

    Accurately reproducing the dynamic two-way interaction between the land surface and the atmosphere in the stable boundary layer (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 boundary 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 boundary layer. The impact of how this coupling is modeled on atmospheric boundary layer (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 atmosphere 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 boundary layer profiles and surface fluxes are compared to field data and results from simulations using three different levels of physical description as lower boundary 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 layer. Overall, simulations with all three types of boundary conditions compare fairly well with the general trends observed in the field data for surface fluxes and boundary layer 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 layer improves flux predictions during the night and early morning. Surface fluxes

  1. Recent Advances in Modeling of the Atmospheric Boundary Layer and Land Surface in the Coupled WRF-CMAQ Model

    EPA Science Inventory

    Advances in the land surface model (LSM) and planetary boundary layer (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...

  2. Variability of Atmospheric Boundary Layer height over the tropical oceans - A study using atmospheric refractivity profiles from multi campaign in-situ and satellite radio occultation data.

    NASA Astrophysics Data System (ADS)

    Santosh, M.

    2016-07-01

    Atmospheric Boundary Layer (ABL) over the tropical oceans controls and regulates the influx of water vapour into the free atmosphere 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. Atmospheric 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 atmospheric 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 atmospheric refractivity profiles from same data (using prevalent methods for RO) to quantify the over estimation. A new method of ABL detection from

  3. Wind-wave coupling in the atmospheric boundary layer over a reservoir: field measurements and verification of the model

    NASA Astrophysics Data System (ADS)

    Troitskaya, Yuliya; Papko, Vladislav; Baidakov, Georgy; Vdovin, Maxim; Kandaurov, Alexander; Sergeev, Daniil

    2013-04-01

    This paper presents the results of field experiments conducted at the Gorky Reservoir to test a quasi-linear model of the atmospheric boundary layer [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 atmospheric boundary layer: 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

  4. The Impact of Upstream Flow on the Atmospheric Boundary Layer in a Valley on a Mountainous Island

    NASA Astrophysics Data System (ADS)

    Adler, Bianca; Kalthoff, Norbert

    2016-03-01

    Comprehensive measurements on the mountainous island of Corsica were used to investigate how the mountain atmospheric boundary layer (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.

  5. Diagnosing the Sensitivity of Local Land-Atmosphere Coupling via the Soil Moisture-Boundary Layer Interaction

    NASA Technical Reports Server (NTRS)

    Santanello, Joseph A., Jr.; Peters-Lidard, Christa D.; Kumar, Sujay V.

    2011-01-01

    The inherent coupled nature of earth s energy and water cycles places significant importance on the proper representation and diagnosis of land atmosphere (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 boundary layers (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

  6. Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2015-11-01

    In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer 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 layer effects on wind-farm boundary layers. 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 boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer 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.

  7. Atmospheric Boundary Layer wind profile at a flat coastal site - wind speed lidar measurements and mesoscale modeling results during a summer period

    NASA Astrophysics Data System (ADS)

    Batchvarova, E.; Gryning, S.-E.; Hahmann, A.; Peña, A.; Mikkelsen, T.

    2010-09-01

    The wind profile above the surface layer up to 1 kilometer is presently a challenge for wind energy assessment studies and air pollution applications, as instruments for high resolution (in time and space) measurements were rarely available until recently and mesoscale meteorological models have difficulties to predict it, due to complex phenomena taking place in nature and not accounted for in the ABL parameterizations currently used. Worldwide an effort is going on to emphasize the important role of boundary layer research in various direct applications (as wind energy and air pollution) and in weather forecast models. Contributing to this effort are the Danish Research Agency Strategic Research Council (Sagsnr. 2104-08-0025) "Tall wind project" and the EU FP7-People-IEF VSABLA (PIEF-GA-2009-237471). The data analyzed here are presenting a summer period of wind lidar (WSL70) measurements at a site at the West coast of Jutland, Denmark, situated approximately 2 km inland. Therefore over water conditions are defining the structure of the boundary layer at westerly winds, while the land surface is felt only within the internal boundary layer estimated in previous studies as about 80 - 100 m deep at the site. Patterns of the wind field and wind profiles over the North Sea up to 1 km height are studied based on observations and mesoscale modelling results. Simultaneously, the height of the atmospheric boundary layer is estimated from aerosol lidars backscatter analysis and thus providing a rich data set for testing and development of new parametrizations for the wind profile within the entire atmospheric boundary layer over different surfaces.

  8. Planetary Boundary Layer Simulation Using TASS

    NASA Technical Reports Server (NTRS)

    Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael

    1996-01-01

    Boundary conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the atmospheric boundary layer. Several options are now available, including the use of a surface energy balance. In addition, we compare convective boundary layer 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 boundary simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.

  9. Climatology of diurnal trends and vertical distribution of ozone in the atmospheric boundary layer in urban North Carolina.

    PubMed

    Aneja, V P; Arya, S P; Li, Y; Murray, G C; Manuszak, T L

    2000-01-01

    Vertical measurements of ozone were made on a 610-m-tall tower located about 15 km southeast of Raleigh, NC, as part of an effort by the state of North Carolina to develop a state implementation plan (SIP) for ozone control in the Raleigh Metropolitan Statistical Area. During summer 1993, 1994, and 1995, ozone was monitored at ground level, 250 m, and 433 m. Boundary layer wind, temperature, and other meteorological variable profiles were determined from balloon soundings. During summer 1996 and 1997, ozone was monitored at ground level, 76 m, 128 m, and 433 m. This paper presents the analysis and discussion of the five-year data. The evolutions of the convective boundary layer during daytime and the stable nocturnal boundary layer (NBL) were found to have marked impacts on ozone concentrations. A strong diurnal pattern, with an afternoon maximum and an early morning minimum, was dominant at ground level, but it was much weaker at elevated levels and insignificant above the NBL at night. Ozone deposition velocities at night during the measurement periods were estimated to range from 0.09 to 0.64 cm/sec. We found evidence of regional transport of ozone and/or its precursors from northwest and north of the site, which may play a role in high ozone events in the Raleigh-Durham area. Ozone concentrations between the various elevated levels were well correlated, while correlations between the ground and upper levels were much weaker. However, a strong correlation was found between the nighttime and early morning ozone concentrations (CR) in the residual layer above the NBL and the maximum ground level concentration (Co max) the following afternoon. Based on this correlation, the latter may be predicted by an observational model Co max = 27.76e 0.016 CR.

  10. An evaluation and parameterization of stably stratified turbulence: Insights on the atmospheric boundary layer and implications for wind energy

    NASA Astrophysics Data System (ADS)

    Wilson, Jordan M.

    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 atmospheric boundary layer (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

  11. Modeling the urban boundary layer

    NASA Technical Reports Server (NTRS)

    Bergstrom, R. W., Jr.

    1976-01-01

    A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; 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 boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

  12. The Variability of Refractivity in the Atmospheric Boundary Layer of a Tropical Island Volcano Measured by Ground-Based Interferometric Radar

    NASA Astrophysics Data System (ADS)

    Wadge, G.; Costa, A.; Pascal, K.; Werner, C.; Webb, T.

    2016-11-01

    For 24 h we measured continuously the variability of atmospheric 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 atmospheric boundary layer 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 atmosphere 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 atmospheric variability. A diurnal cycle within the lower boundary layer producing a turbulence-dominated mixed layer during the day and stable layers at night is consistent with the observed refractivity.

  13. The Variability of Refractivity in the Atmospheric Boundary Layer of a Tropical Island Volcano Measured by Ground-Based Interferometric Radar

    NASA Astrophysics Data System (ADS)

    Wadge, G.; Costa, A.; Pascal, K.; Werner, C.; Webb, T.

    2016-06-01

    For 24 h we measured continuously the variability of atmospheric 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 atmospheric boundary layer 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 atmosphere 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 atmospheric variability. A diurnal cycle within the lower boundary layer producing a turbulence-dominated mixed layer during the day and stable layers at night is consistent with the observed refractivity.

  14. Impact of the Loess Plateau on the atmospheric boundary layer structure and air quality in the North China Plain: a case study.

    PubMed

    Hu, Xiao-Ming; Ma, ZhiQiang; Lin, Weili; Zhang, Hongliang; Hu, Jianlin; Wang, Ying; Xu, Xiaobin; Fuentes, Jose D; Xue, Ming

    2014-11-15

    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 atmospheric boundary layer structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the boundary layer 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 boundary layer, which acted as a lid and suppressed the mixed layer growth. As a result, pollutants accumulated in the shallow mixed layer 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 layer, 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 layer 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.

  15. Minnesota 1973 atmospheric boundary layer experiment: Micrometeorological and tracer data archive. Set 1 (revision 2) documentation report

    NASA Astrophysics Data System (ADS)

    Woodruff, R. K.; Droppo, J. G.; Glantz, C. S.

    1987-03-01

    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 Boundary Layer 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.

  16. Boundary Layer Control on Airfoils.

    ERIC Educational Resources Information Center

    Gerhab, George; Eastlake, Charles

    1991-01-01

    A phenomena, boundary layer 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)

  17. Modeling the summertime Arctic cloudy boundary layer

    SciTech Connect

    Curry, J.A.; Pinto, J.O.; McInnes, K.L.

    1996-04-01

    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 boundary layer. The presence of multiple cloud layers, 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 layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. 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 layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

  18. Removing Boundary Layer by Suction

    NASA Technical Reports Server (NTRS)

    Ackeret, J

    1927-01-01

    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 boundary-layer 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 boundary layer into the inside of a body through a slot or slots in its surface.

  19. Study of the effect of wind speed on evaporation from soil through integrated modeling of atmospheric boundary layer and shallow subsurface

    NASA Astrophysics Data System (ADS)

    Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan; Illangasekare, Tissa

    2013-04-01

    The study of the interaction between the land and atmosphere 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 atmospheric boundary layer to the shallow subsurface. The coupling between land and the atmosphere leads to highly dynamic interactions between the porous media properties, transport processes and boundary conditions, resulting in dynamic evaporative behavior. However, the coupling at the land-atmospheric 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 atmospheric conditions even though heat and mass flux are controlled by the coupled dynamics of the land and the atmospheric boundary layer. In earlier drying modeling concepts, imposing evaporation flux (kinetic of relative humidity) and temperature as surface boundary condition is often needed. With the goal of improving our understanding of the land/atmospheric 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 boundary

  20. Study of the Effect of Wind Speed on Evaporation from Soil Through Integrated Modeling of Atmospheric Boundary Layer and Shallow Subsurface

    NASA Astrophysics Data System (ADS)

    Smits, K. M.; Davarzani, H.; Illangasekare, T. H.

    2012-12-01

    The study of the interaction between the land and atmosphere 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 atmospheric boundary layer to the shallow subsurface. The coupling between land and the atmosphere leads to highly dynamic interactions between the porous media properties, transport processes and boundary conditions, resulting in dynamic evaporative behavior. However, the coupling at the land-atmospheric 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 atmospheric conditions even though heat and mass flux are controlled by the coupled dynamics of the land and the atmospheric boundary layer. In earlier drying modeling concepts, imposing evaporation flux (kinetic of relative humidity) and temperature as surface boundary condition is often needed. With the goal of improving our understanding of the land/atmospheric 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 boundary conditions at the porous medium-free flow medium interface include

  1. Southern Hemisphere Sea Ice and the Atmospheric Boundary Layer in a High-Resolution Simulation of the Community Earth System Model

    NASA Astrophysics Data System (ADS)

    Ordóñez, A.; Bitz, C. M.

    2015-12-01

    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 atmosphere/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/atmosphere 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 layer ocean models on a 0.1° grid (high resolution) or 1° grid (standard resolution) are coupled with atmosphere 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 atmosphere in the model. Correlations between sea ice concentration and boundary layer 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.

  2. Influences on the Height of the Stable Boundary Layer as seen in LES

    SciTech Connect

    Kosovic, B; Lundquist, J

    2004-06-15

    Climate models, numerical weather prediction (NWP) models, and atmospheric dispersion models often rely on parameterizations of planetary boundary layer height. In the case of a stable boundary layer, errors in boundary layer height estimation can result in gross errors in boundary-layer evolution and in prediction of turbulent mixing within the boundary layer.

  3. Boundary layer halogens in coastal Antarctica.

    PubMed

    Saiz-Lopez, Alfonso; Mahajan, Anoop S; Salmon, Rhian A; Bauguitte, Stephane J-B; Jones, Anna E; Roscoe, Howard K; Plane, John M C

    2007-07-20

    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 boundary layer 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 atmosphere. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic boundary layer.

  4. Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying Atmospheric Boundary Layer Due to an Extensive Wind Farm

    NASA Astrophysics Data System (ADS)

    Sharma, V.; Parlange, M. B.; Calaf, M.

    2016-08-01

    The effect of extensive terrestrial wind farms on the spatio-temporal structure of the diurnally-evolving atmospheric boundary layer 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 boundary 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 boundary layer (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.

  5. Climatic Variations In The Moisture and Instability Patterns Of The Atmospheric Boundary Layer On The East Mediterranean Coastal Plain Of Israel

    NASA Astrophysics Data System (ADS)

    Ben-Gai, T.; Bitan, A.; Manes, A.; Alpert, P.

    A long-term record (1964-1995) of radiosonde data observed atthe Bet-Dagan aerological station of the Israel Meteorological Service was analyzed to detect possible temporal trends in moisture content and instability of the atmospheric boundary layer. Bet-Dagan issituated in the central part of the south-east Mediterranean coastal plain. During this period surface characteristics in this region have changed drastically due to changes in land use, i.e., urbanization, development of irrigated agriculture and afforestation. The analysis of the radiosonde data reveals a clearly defined, statistically significant, increasing trend in the moisture content, mainly during summer. The stability of the surface layer, characterized by the bulk Richardson Number, shows adecreasing trend since the early 1960s. Relationships between these trends, land-use modifications and possible influence of large-scale influence are discussed.

  6. The implementation of a MiXed Layer model (MXL, v1.0) for the dynamics of the atmospheric boundary layer in the Modular Earth Submodel System (MESSy)

    NASA Astrophysics Data System (ADS)

    Janssen, R. H. H.; Pozzer, A.

    2014-10-01

    We present a new submodel for the Modular Earth Submodel System (MESSy): the MiXed Layer (MXL) model for the diurnal dynamics of the convective boundary layer, including explicit representations of entrainment and surface fluxes. Through the MESSy interface, MXL is coupled with modules that represent other processes relevant to chemistry in the atmospheric boundary layer (ABL). In combination, these provide 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.

  7. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.

    1995-01-01

    This final report was concerned with the ideas that: (1) magnetospheric boundary layers 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 boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, 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.

  8. Unsteady turbulent boundary layer analysis

    NASA Technical Reports Server (NTRS)

    Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.

    1973-01-01

    The governing equations for an unsteady turbulent boundary layer 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 boundary layers. 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 boundary layer.

  9. Quantifying the Boundary-Layer Dynamics of Carbon Dioxide from A Built Environment Using A Coupled Urban Land-Atmospheric Model

    NASA Astrophysics Data System (ADS)

    Song, J.; Wang, Z.

    2015-12-01

    Urban areas are significant carbon contributors in the global carbon cycle due to intense carbon emissions from traffic and other human activities and lack of vegetation for carbon absorption. A better understanding on urban carbon variations is important to quantify urban contributions to regional and global carbon budgets under the challenge of climate changes. In this study, we applied a coupled urban land-atmospheric model to simulate the diurnal and seasonal variations of carbon dioxide (CO2) fluxes in the urban boundary layer (UBL) for the Phoenix Metropolitan area, Arizona. The lower boundary conditions of this model are provided by the CO2 fluxes measured using an eddy covariance tower. By analyzing the tower measurements in the urban canopy layer, the highest concentrations of CO2 in a typical weekday coincide with the busiest traffic. Besides, there are more CO2 emissions in winter than in summer possibly due to additional natural gas consumptions for heating. Based on the coupled model, we simulated the diurnal and seasonal evolutions of the mean CO2 concentration as well as the vertical profiles of CO2 concentration in the UBL. It was found that the anthropogenic CO2 sources in a built terrain effectively altered the carbon dynamics in the overlying atmosphere in contrast to its rural surroundings. We also changed the urban landscape characteristics including vegetation fraction, surface roughness, and building density to study their impacts on the CO2 dynamics in the UBL. Overall, the coupled urban land-atmospheric model provides a useful stand-alone tool for quantifying the urban carbon cycle, and can be extended to more general applications such as urban air quality problems.

  10. Large-eddy simulation of the diurnal cycle of the atmospheric boundary layer and influence of the radiative forcing during the Wangara experiment.

    NASA Astrophysics Data System (ADS)

    Dall'Ozzo, Cédric; Carissimo, Bertrand; Milliez, Maya; Musson-Genon, Luc; Dupont, Eric

    2013-04-01

    The ability to simulate the whole diurnal cycle of the atmospheric boundary layer in order to study the complex turbulent structures remains a difficult topic. Consequently large-eddy simulations (LES) are performed with the open source CFD code Code_Saturne [Archambeau et al., 2004]. First the code is validated on an atmospheric convective case [Schmidt and Schumann, 1989] where different subgrid-scale (SGS) models are compared: two non-dynamical SGS models [Smagorinsky, 1963] [Nicoud and Ducros, 1999] and two dynamical SGS models [Germano et al., 1991 ; Lilly, 1992] [Wong and Lilly, 1994]. Then LES are performed to simulate the whole diurnal cycle of the Wangara experiment (Day 33-34). The results are compared to measurements , RANS "k-ɛ" model and other LES performed by [Basu et al., 2008] using a locally averaged scale-dependent dynamic (LASDD) SGS model. Thereafter the influence of the radiative forcing on the atmosphere is studied testing several SGS models. The results are especially discussed on nocturnal low level jet and potential temperature gradient in the stable boundary layer. References: [Archambeau et al., 2004] Archambeau F., Mehitoua N., Sakiz M. (2004). Code_Saturne: a finite volume code for the computation of turbulent incompressible flows. International Journal on Finite Volumes 1(1). [Basu et al., 2008] Basu S., Vinuesa J. F., and Swift A. (2008). Dynamic LES modeling of a diurnal cycle. Journal of Applied Meteorology and Climatology, 47 :1156-1174. [Germano et al., 1991] Germano M., Piomelli U., Moin P., and Cabot W. H. (1991). A dynamic subgrid-scale eddy-viscosity model. Physics of Fluids, A3 :1760-1765. [Lilly, 1992] Lilly D. K. (1992). A proposed modification of the Germano subgrid-scale closure method. Physics of Fluids, A 4 :633-635. [Schmidt and Schumann, 1989] Schmidt H. and Schumann U. (1989). Coherent structure of the convective boundary layer derived from lage-eddy simulation. Journal of Fluid Mechanics, 200 :511-562. [Smagorinsky

  11. Observation studies on the influence of atmospheric boundary layer characteristics associate with air quality in dry season over the Pearl River Delta, China

    NASA Astrophysics Data System (ADS)

    Fan, Shaojia; Wu, Meng; Li, Haowen; Liao, Zhiheng; Fan, Qi; Zhu, Wei

    2016-04-01

    The characteristics of atmospheric boundary layer (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 layer, recirculation factor (RF), atmospheric boundary layer height (ABLH) and ventilation index (VI). It was found that the vertical wind of PRD could be divided in typical three layers according two wind shears appeared in 800 m and 1300 m. The thickness of calm or lower wind speed layer 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 layer 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.

  12. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, I. H.

    1993-01-01

    The central ideas of this grant are that the magnetospheric boundary layers 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 boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, 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.

  13. BOREAS AFM-6 Boundary Layer Height Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric 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 boundary layer 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 boundary layer 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).

  14. Turbulent boundary layers over nonstationary plane boundaries

    NASA Technical Reports Server (NTRS)

    Roper, A. T.

    1976-01-01

    Methods of predicting integral parameters and skin-friction coefficients of turbulent boundary layers 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.

  15. Description and implementation of a MiXed Layer model (MXL, v1.0) for the dynamics of the atmospheric boundary layer in the Modular Earth Submodel System (MESSy)

    NASA Astrophysics Data System (ADS)

    Janssen, R. H. H.; Pozzer, A.

    2015-03-01

    We present a new submodel for the Modular Earth Submodel System (MESSy): the MiXed Layer (MXL) model for the diurnal dynamics of the convective boundary layer, including explicit representations of entrainment and surface fluxes. This submodel is embedded in a new MESSy base model (VERTICO), which represents a single atmospheric column. With the implementation of MXL in MESSy, MXL can be used in combination with other MESSy submodels that represent processes related to atmospheric 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 atmospheric boundary layer (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.

  16. Ground-Based Cloud and Atmospheric Boundary Layer Observations for the Project: High Definition Clouds and Precipitation for Advancing Climate Prediction, HD(CP)2

    NASA Astrophysics Data System (ADS)

    Hirsikko, A.; Ebell, K.; Ulrich, U.; Schween, J. H.; Bohn, B.; Görsdorf, U.; Leinweber, R.; Päschke, E.; Baars, H.; Seifert, P.; Klein Baltink, H.

    2014-12-01

    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 atmospheric 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 atmospheric boundary layer state (e.g. winds, mixing layer 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.

  17. A Wind-tunnel Study of Atmospheric Boundary-Layer Flow over Vegetated Surfaces to Suppress PM10 Emission on Owens (dry) Lake

    NASA Astrophysics Data System (ADS)

    Kim, Dae Seong; Cho, Greg H.; White, Bruce R.

    Dust storms on Owens (dry) Lake located 200 milesnortheast of Los Angeles, California, U.S.A., havecaused serious PM10 emission problems. Alaboratory-based experimental study was conducted toinvestigate the efficiency of ''vegetation cover'' onthe playa to suppress dust emission rates as part ofa mitigation plan.Erodible lakebed material and field vegetation (saltgrass) taken from Owens (dry) Lake were placed in awind tunnel to simulate near-surface wind flow in theatmospheric boundary layer. Vertical wind-speedprofiles and vertical PM10-concentration profileswere measured over six different levels of surfacevegetation cover. In order to understand the mechanismof aeolian particle transport and dust injection intothe atmosphere, the roughness parameter, z0, thefriction velocity, u*, and the surface dragcoefficient, CD, were carefully determined.

  18. Controlled meteorological (CMET) free balloon profiling of the Arctic atmospheric boundary layer around Spitsbergen compared to ERA-Interim and Arctic System Reanalyses

    NASA Astrophysics Data System (ADS)

    Roberts, Tjarda J.; Dütsch, Marina; Hole, Lars R.; Voss, Paul B.

    2016-09-01

    Observations from CMET (Controlled Meteorological) balloons are analysed to provide insights into tropospheric meteorological conditions (temperature, humidity, wind) around Svalbard, European High Arctic. Five Controlled Meteorological (CMET) balloons were launched from Ny-Ålesund in Svalbard (Spitsbergen) over 5-12 May 2011 and measured vertical atmospheric profiles 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 boundary layer (ABL) over a period of more than 10 h. Profiles from two CMET flights are compared to model output from ECMWF Era-Interim reanalysis (ERA-I) and to a high-resolution (15 km) Arctic System Reanalysis (ASR) product. To the east of Svalbard over sea ice, the CMET observed a stable ABL profile with a temperature inversion that was reproduced by ASR but not captured by ERA-I. In a coastal ice-free region to the west of Svalbard, the CMET observed a stable ABL with strong wind shear. The CMET profiles document increases in ABL temperature and humidity that are broadly reproduced by both ASR and ERA-I. The ASR finds a more stably stratified ABL than observed but captured the wind shear in contrast to ERA-I. Detailed analysis of the coastal CMET-automated soundings identifies small-scale temperature and humidity variations with a low-level flow and provides an estimate of local wind fields. We demonstrate that CMET balloons are a valuable approach for profiling the free atmosphere and boundary layer in remote regions such as the Arctic, where few other in situ observations are available for model validation.

  19. Impact of atmospheric boundary layer depth variability and wind reversal on the diurnal variability of aerosol concentration at a valley site.

    PubMed

    Pal, S; Lee, T R; Phelps, S; De Wekker, S F J

    2014-10-15

    The development of the atmospheric boundary layer (ABL) plays a key role in affecting the variability of atmospheric 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 boundary layer 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.

  20. Impact of atmospheric boundary layer depth variability and wind reversal on the diurnal variability of aerosol concentration at a valley site.

    PubMed

    Pal, S; Lee, T R; Phelps, S; De Wekker, S F J

    2014-10-15

    The development of the atmospheric boundary layer (ABL) plays a key role in affecting the variability of atmospheric 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 boundary layer 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

  1. Atmospheric conditions and transport patterns associated with high and low summer ozone levels in the lower troposphere and the boundary layer over the eastern Mediterranean

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    layer, there are extended regions of strong subsidence in the eastern Mediterranean but also in eastern and northern Europe and over these regions the atmosphere 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 atmospheric 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 boundary layer over the eastern Mediterranean (Cairo case), Tellus B, 67, 27853, http://dx.doi.org/10.3402/tellusb.v67.27853.

  2. Atmospheric boundary layer structures associated with the Ora del Garda wind in the Alps as revealed from airborne and surface measurements

    NASA Astrophysics Data System (ADS)

    Laiti, Lavinia; Zardi, Dino; de Franceschi, Massimiliano; Rampanelli, Gabriele

    2013-10-01

    The paper investigates a coupled lake-breeze and valley-wind system, known as Ora del Garda. The latter typically originates on clear-sky days over the northern shore of Lake Garda in the Alps. After channelling into the nearby Sarca Valley and Lakes Valley, this airflow finally breaks out, through an elevated saddle, into the adjacent Adige Valley, where it strongly interacts with the local valley wind. Two flights of an instrumented motorglider explored, under different synoptic conditions, the thermal structure of the atmospheric boundary layer (ABL) associated with this wind at selected vertical sections-namely over the lake shore, at mid-valley, and at the junction with the Adige Valley. Data from airborne measurements, as well as from weather stations disseminated along the valley floor, provided the basis for mapping 3D fields of potential temperature over high-resolution grids by means of a Residual Kriging (RK) technique. This representation allowed the identification of site-specific ABL features associated with the Ora del Garda. In particular, a typical daytime coastal-breeze structure is detected in the lake shore region, where the advection of colder air tends to stabilize the atmosphere throughout the ABL depth. Mid-valley vertical profiles from both flights display shallow convective mixed layers, surmounted by deeper weakly stable layers. On the other hand, RK-gridded temperature maps show cross-valley thermal asymmetries, amenable to the complex topography and to the inhomogeneous surface coverage, as well as to a curvature of the valley axis. Finally, in the area where the upper Lakes Valley joins the Adige Valley, specific features associated with the complex interaction between the Ora del Garda and the local up-valley wind are found.

  3. Vertical variations in the turbulent structure of the surface boundary layer over vineyards under unstable atmospheric conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Due to their highly-structured canopy, turbulent characteristics within and above vineyards, may not conform to those typically exhibited by other agricultural and natural ecosystems. Using data collected as a part of the Grape Remote sensing and Atmospheric Profiling and Evapotranspiration Experime...

  4. Modeling the feedback between aerosol and meteorological variables in the atmospheric boundary layer during a severe fog-haze event over the North China Plain

    NASA Astrophysics Data System (ADS)

    Gao, Yi; Zhang, Meigen; Liu, Zirui; Wang, Lili; Wang, Pucai; Xia, Xiangao; Tao, Minghui; Zhu, Lingyun

    2016-04-01

    The feedback between aerosol and meteorological variables in the atmospheric boundary layer 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 atmospheric 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, atmospheric 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 atmosphere 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 atmosphere is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10 %) and the atmosphere boundary layer height decreases by 40-200 m (5-30 %) during the daytime of this severe fog-haze event. Owing to this more stable atmosphere during 09:00-18:00, 10-15 January, compared to the surface PM2

  5. Modeling the feedback between aerosol and meteorological variables in the atmospheric boundary layer during a severe fog-haze event over the North China Plain

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Zhang, M.; Liu, Z.; Wang, L.; Wang, P.; Xia, X.; Tao, M.; Zhu, L.

    2015-04-01

    The feedback between aerosol and meteorological variables in the atmospheric boundary layer 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 atmospheric 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, atmospheric 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 atmosphere 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 atmosphere is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10%) and the atmosphere boundary layer height decreases by 40-200 m (5-30%) during the daytime of this severe fog-haze event. Owing to this more stable atmosphere during 09:00-18:00, 10-15~January, compared to the surface PM2

  6. Jupiter's deep magnetotail boundary layer

    NASA Astrophysics Data System (ADS)

    Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.

    2015-06-01

    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 boundary layer 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 boundary layer with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the boundary layer 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.

  7. Atmosphere-Ice-Ocean Interactions During Early Autumn Freeze-up: Boundary-Layer and Surface Observations from the ACSE Field Program

    NASA Astrophysics Data System (ADS)

    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

    2015-04-01

    Surface energy fluxes are key to the annual summer melt and autumn freeze-up of Arctic sea ice, but are strongly modulated by atmospheric, 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, boundary-layer 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, atmospheric advection, and the annual solar cycle have primary influence determining when energy fluxes are conducive for melt or freeze, mesoscale atmospheric 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 atmospheric processes, including thermal advection on various scales, that are important for the annual evolution of melt and freeze-up.

  8. Boundary layer receptivity and control

    NASA Technical Reports Server (NTRS)

    Hill, D. C.

    1993-01-01

    Receptivity processes initiate natural instabilities in a boundary layer. 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 boundary layer 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 boundary layer 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

  9. Large Amplitude Spatial and Temporal Gradients in Atmospheric Boundary Layer CO2 Mole Fractions Detected With a Tower-Based Network in the U.S. Upper Midwest

    SciTech Connect

    Miles, Natasha; Richardson, S. J.; Davis, Kenneth J.; Lauvaux, Thomas; Andrews, A.; West, Tristram O.; Bandaru, Varaprasad; Crosson, Eric R.

    2012-02-21

    This study presents observations of atmospheric 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 atmospheric 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 boundary layer 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}.

  10. The distribution of atmospheric black carbon in the marine boundary layer over the North Atlantic and the Russian Arctic Seas in July - October 2015

    NASA Astrophysics Data System (ADS)

    Shevchenko, Vladimir P.; Kopeikin, Vladimir M.; Evangeliou, Nikolaos; Novigatsky, Alexander N.; Pankratova, Natalia V.; Starodymova, Dina P.; Stohl, Andreas; Thompson, Rona

    2016-04-01

    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 atmosphere over the North Atlantic and the Russian Arctic Seas are scarce. We present measurement data on the distribution of atmospheric BC in the marine boundary layer 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.

  11. Modeling the feedback between aerosol and meteorological variables in the atmospheric boundary layer during a severe fog-haze event over the North China Plain

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Zhang, M.; Liu, Z.; Wang, L.; Wang, P.; Xia, X.; Tao, M.

    2015-01-01

    The feedback between aerosol and meteorological variables in the atmospheric boundary layer 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, atmospheric 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 atmosphere 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 atmosphere is much more stable and thus the surface wind speed decreases by up to 0.3 m s-1 (10%) and the atmosphere boundary layer height decreases by 40-200 m (5-30%) during the daytime of this severe fog-haze event. Owing to this more stable atmosphere, 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

  12. Measuring Vertical Profiles of Wind, Temperature and Humidity within the Atmospheric Boundary Layer using the Research UAVs 'M2AV Carolo'

    NASA Astrophysics Data System (ADS)

    Bange, J.; Martin, S.

    2009-09-01

    The measurement of vertical profiles is important to characterise the vertical structure of the atmospheric boundary layer (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 boundary layer, local scaling in the stable boundary layer). 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

  13. Consequences of the Large-Scale Subsidence Rate on the Stably Stratified Atmospheric Boundary Layer Over the Arctic Ocean, as seen in Large-Eddy Simulations

    SciTech Connect

    Mirocha, J D; Kosovic, B

    2006-01-19

    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 atmospheric boundary layer (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-layer 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.

  14. Atmospheric Planetary Boundary Layer response to sea surface temperature gradients in Tropical Instability Waves: Simulation with a high resolution climate model.

    NASA Astrophysics Data System (ADS)

    Small, R. J.; Xie, S.; Wang, Y.

    2002-12-01

    Tropical instability waves (TIWs) are 1000 km long waves which appear along the sea surface temperature (SST) front north of the cold equatorial tongue in the Eastern Pacific. The aim of this study is to investigate the atmospheric Planetary Boundary Layer (PBL) response to the TIWs using a high resolution regional climate model. The model responds to a prescribed SST distribution which is derived from daily Tropical Microwave Imager SST (from the Tropical Rainfall Measuring Mission), and the results are compared against observations from the QuikSCAT scatterometer and in situ data. The model predictions of the magnitude of perturbations of wind speed, column integrated water vapour and liquid water due to TIWs are similar to those observed. Further, the phase relationship between these quantities and the SST is well simulated. An investigation is made of the relative importance of vertical mixing, which is parameterized in the model by a 1.5 level turbulence closure, and pressure gradients induced by changes in air temperature and moisture. The model demonstrates how the mixing is initiated by surface instability over warm SST, and then extends throughout the boundary layer. Over cold SST a stable regime exists and mixing is suppressed. Turbulent fluxes of sensible and latent heat lead to changes in the hydrostatic pressure and in the height and structure of the PBL. The pressure change leads to the appearance of a secondary circulation cell. Clouds are formed in the ascending region of the cell. The model results are then used to suggest whether the secondary cell or the direct effect of vertical mixing is most important to the observed in-phase relationship between SST and wind speed.

  15. Real-Time Characterization of Aerosol Particle Composition above the Urban Canopy in Beijing: Insights into the Interactions between the Atmospheric Boundary Layer and Aerosol Chemistry.

    PubMed

    Sun, Yele; Du, Wei; Wang, Qingqing; Zhang, Qi; Chen, Chen; Chen, Yong; Chen, Zhenyi; Fu, Pingqing; Wang, Zifa; Gao, Zhiqiu; Worsnop, Douglas R

    2015-10-01

    Despite extensive efforts into the characterization of air pollution during the past decade, real-time characterization of aerosol particle composition above the urban canopy in the megacity Beijing has never been performed to date. Here we conducted the first simultaneous real-time measurements of aerosol composition at two different heights at the same location in urban Beijing from December 19, 2013 to January 2, 2014. The nonrefractory submicron aerosol (NR-PM1) species were measured in situ by a high-resolution aerosol mass spectrometer at near-ground level and an aerosol chemical speciation monitor at 260 m on a 325 m meteorological tower in Beijing. Secondary aerosol showed similar temporal variations between ground level and 260 m, whereas much weaker correlations were found for the primary aerosol. The diurnal evolution of the ratios and correlations of aerosol species between 260 m and the ground level further illustrated a complex interaction between vertical mixing processes and local source emissions on aerosol chemistry in the atmospheric boundary layer. As a result, the aerosol compositions at the two heights were substantially different. Organic aerosol (OA), mainly composed of primary OA (62%), at the ground level showed a higher contribution to NR-PM1 (65%) than at 260 m (54%), whereas a higher concentration and contribution (15%) of nitrate was observed at 260 m, probably due to the favorable gas-particle partitioning under lower temperature conditions. In addition, two different boundary layer structures were observed, each interacting differently with the evolution processes of aerosol chemistry.

  16. Real-Time Characterization of Aerosol Particle Composition above the Urban Canopy in Beijing: Insights into the Interactions between the Atmospheric Boundary Layer and Aerosol Chemistry.

    PubMed

    Sun, Yele; Du, Wei; Wang, Qingqing; Zhang, Qi; Chen, Chen; Chen, Yong; Chen, Zhenyi; Fu, Pingqing; Wang, Zifa; Gao, Zhiqiu; Worsnop, Douglas R

    2015-10-01

    Despite extensive efforts into the characterization of air pollution during the past decade, real-time characterization of aerosol particle composition above the urban canopy in the megacity Beijing has never been performed to date. Here we conducted the first simultaneous real-time measurements of aerosol composition at two different heights at the same location in urban Beijing from December 19, 2013 to January 2, 2014. The nonrefractory submicron aerosol (NR-PM1) species were measured in situ by a high-resolution aerosol mass spectrometer at near-ground level and an aerosol chemical speciation monitor at 260 m on a 325 m meteorological tower in Beijing. Secondary aerosol showed similar temporal variations between ground level and 260 m, whereas much weaker correlations were found for the primary aerosol. The diurnal evolution of the ratios and correlations of aerosol species between 260 m and the ground level further illustrated a complex interaction between vertical mixing processes and local source emissions on aerosol chemistry in the atmospheric boundary layer. As a result, the aerosol compositions at the two heights were substantially different. Organic aerosol (OA), mainly composed of primary OA (62%), at the ground level showed a higher contribution to NR-PM1 (65%) than at 260 m (54%), whereas a higher concentration and contribution (15%) of nitrate was observed at 260 m, probably due to the favorable gas-particle partitioning under lower temperature conditions. In addition, two different boundary layer structures were observed, each interacting differently with the evolution processes of aerosol chemistry. PMID:26348650

  17. Boundary layer control of rotating convection systems.

    PubMed

    King, Eric M; Stellmach, Stephan; Noir, Jerome; Hansen, Ulrich; Aurnou, Jonathan M

    2009-01-15

    Turbulent rotating convection controls many observed features of stars and planets, such as magnetic fields, atmospheric jets and emitted heat flux patterns. It has long been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force. Here, however, we present results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. We formulate a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers. This transition scaling theory unifies the disparate results of an extensive array of previous experiments, and is broadly applicable to natural convection systems.

  18. Boundary layer control of rotating convection systems.

    PubMed

    King, Eric M; Stellmach, Stephan; Noir, Jerome; Hansen, Ulrich; Aurnou, Jonathan M

    2009-01-15

    Turbulent rotating convection controls many observed features of stars and planets, such as magnetic fields, atmospheric jets and emitted heat flux patterns. It has long been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force. Here, however, we present results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. We formulate a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers. This transition scaling theory unifies the disparate results of an extensive array of previous experiments, and is broadly applicable to natural convection systems. PMID:19148097

  19. Two years observations on the diurnal evolution of coastal atmospheric boundary layer features over Thiruvananthapuram (8.5∘ N, 76.9∘ E), India

    NASA Astrophysics Data System (ADS)

    Anurose, T. J.; Subrahamanyam, D. Bala; Sunilkumar, S. V.

    2016-10-01

    The atmospheric boundary layer (ABL) over a given coastal station is influenced by the presence of mesoscale sea breeze circulation, together with the local and synoptic weather, which directly or indirectly modulate the vertical thickness of ABL (z ABL). Despite its importance in the characterization of lower tropospheric processes and atmospheric modeling studies, a reliable climatology on the temporal evolution of z ABL is not available over the tropics. Here, we investigate the challenges involved in determination of the ABL heights, and discuss an objective method to define the vertical structure of coastal ABL. The study presents a two year morphology on the diurnal evolution of the vertical thickness of sea breeze flow (z SBF) and z ABL in association with the altitudes of lifting condensation level (z LCL) over Thiruvananthapuram (8.5∘ N, 76.9∘ E), a representative coastal station on the western coastline of the Indian sub-continent. We make use of about 516 balloon-borne GPS sonde measurements in the present study, which were carried out as part of the tropical tropopause dynamics field experiment under the climate and weather of the sun-earth system (CAWSES)-India program. Results obtained from the present study reveal major differences in the temporal evolution of the ABL features in relation to the strength of sea breeze circulation and monsoonal wind flow during the winter and summer monsoon respectively. The diurnal evolution in z ABL is very prominent in the winter monsoon as against the summer monsoon, which is attributed to the impact of large-scale monsoonal flow over the surface layer meteorology. For a majority of the database, the z LCL altitudes are found to be higher than that of the z ABL, indicating a possible decoupling of the ABL with the low-level clouds.

  20. Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the atmospheric boundary layer

    SciTech Connect

    Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.

    1993-03-01

    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 atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric 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.

  1. Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the atmospheric boundary layer

    SciTech Connect

    Whiteman, C.D.; Alzheimer, J.M.; Anderson, G.A.; Shaw, W.J.

    1993-03-01

    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 atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric 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.

  2. Dynamic of the atmospheric boundary layer from the isotopic composition of surface water vapor at the Maïdo Observatory (La Réunion, Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Guilpart, Etienne; Vimeux, Francoise; Metzger, Jean-Marc; Evan, Stephanie; Brioude, Jerome; Cattani, Olivier

    2016-04-01

    Projections of tropical and subtropical precipitation strongly differ from one climate model to another, both in sign and in amplitude. This is the case for example in some parts of the West Indian Ocean. The causes of those uncertainties are numerous and a better understanding of humid processes in the tropical atmosphere is needed. We propose to address this burning question by using water stables isotopes. We have been measuring the isotopic composition of surface water vapor at the atmospheric Observatory of Maïdo located at La Reunion Island (21°S, 55°E, 2200m a.s.l) since November 2014. Our results exhibit a strong diurnal cycle all over the year (except during cyclonic activity), with almost constant isotopic values during the day (around -13.5±0.6‰ for oxygen 18 from November 2014 to November 2015) and variable and very depleted isotopic values during the night (down to -35‰ for oxygen 18 over the same period) associated with low humidity levels. We will show in this presentation that the diurnal isotopic variations are associated to a strong air masses mixing. During the day, the isotopic composition of the vapor is typical of marine boundary layer (BL) moisture transported from the close Ocean and lifted up to the Maïdo station. During the night, the depleted values and the low humidity could trace free troposphere moisture, which is consistent with previous studies suggesting that the Maïdo Observatory is above the BL during the night. We will explore the influence of the daily BL development on our observations, using a set of atmospheric vertical profiles done on site in May 2015 during the BIOMAIDO campaign. At last, we will discuss the most isotopic depleted values recorded in our observations during the night as a possible consequence of regional strong subsidences.

  3. Intercomparison of different subgrid-scale models for the Large Eddy Simulation of the diurnal evolution of the atmospheric boundary layer during the Wangara experiment

    NASA Astrophysics Data System (ADS)

    Dall'Ozzo, C.; Carissimo, B.; Musson-Genon, L.; Dupont, E.; Milliez, M.

    2012-04-01

    The study of a whole diurnal cycle of the atmospheric boundary layer evolving through unstable, neutral and stable states is essential to test a model applicable to the dispersion of pollutants. Consequently a LES of a diurnal cycle is performed and compared to observations from the Wangara experiment (Day 33-34). All simulations are done with Code_Saturne [1] an open source CFD code. The synthetic eddy method (SEM) [2] is implemented to initialize turbulence at the beginning of the simulation. Two different subgrid-scale (SGS) models are tested: the Smagorinsky model [3],[4] and the dynamical Wong and Lilly model [5]. The first one, the most classical, uses a Smagorinsky constant Cs to parameterize the dynamical turbulent viscosity while the second one relies on a variable C. Cs remains insensitive to the atmospheric stability level in contrary to the parameter C determined by the Wong and Lilly model. It is based on the error minimization of the difference between the tensors of the resolved turbulent stress (Lij) and the difference of the SGS stress tensors at two different filter scales (Mij). Furthermore, the thermal eddy diffusivity, as opposed to the Smagorinsky model, is calculated with a dynamical Prandtl number determination. The results are confronted to previous simulations from Basu et al. (2008) [6], using a locally averaged scale-dependent dynamic (LASDD) SGS model, and to previous RANS simulations. The accuracy in reproducing the experimental atmospheric conditions is discussed, especially regarding the night time low-level jet formation. In addition, the benefit of the utilization of a coupled radiative model is discussed.

  4. Influence of small-scale North Atlantic sea surface temperature patterns on the marine boundary layer and free troposphere: a study using the atmospheric ARPEGE model

    NASA Astrophysics Data System (ADS)

    Piazza, Marie; Terray, Laurent; Boé, Julien; Maisonnave, Eric; Sanchez-Gomez, Emilia

    2016-03-01

    A high-resolution global atmospheric model is used to investigate the influence of the representation of small-scale North Atlantic sea surface temperature (SST) patterns on the atmosphere 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 atmospheric boundary layer 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.

  5. Quantitative Interpretation of Air Radon Progeny Fluctuations in Terms of Stability Conditions in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Salzano, Roberto; Pasini, Antonello; Casasanta, Giampietro; Cacciani, Marco; Perrino, Cinzia

    2016-09-01

    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 layers 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.

  6. Turbulent dispersion in cloud-topped boundary layers

    NASA Astrophysics Data System (ADS)

    Verzijlbergh, R. A.; Jonker, H. J. J.; Heus, T.; Vilöguerau de Arellano, J.

    2009-02-01

    Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion - a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.

  7. Turbulent dispersion in cloud-topped boundary layers

    NASA Astrophysics Data System (ADS)

    Verzijlbergh, R. A.; Jonker, H. J. J.; Heus, T.; Vilöguerau de Arellano, J.

    2008-11-01

    Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.

  8. Outline of research on oscillating boundary layers

    NASA Technical Reports Server (NTRS)

    Cousteix, J.

    1979-01-01

    The state of the art in the field of unsteady boundary layers is outlined with emphasis on turbulent boundary layers. The unsteady flows considered are mainly periodic with the external velocity varying around a zero or nonzero mean time value. The principal results obtained on laminar boundary layers are also presented.

  9. Turbulent boundary layer of an airfoil

    NASA Technical Reports Server (NTRS)

    Fediaevsky, K

    1937-01-01

    A need has arisen for a new determination of the velocity profiles in the boundary layer. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the boundary layer, we shall consider the nature of the shear distribution for a boundary layer with a pressure gradient.

  10. Compressible turbulent boundary layer interaction experiments

    NASA Technical Reports Server (NTRS)

    Settles, G. S.; Bogdonoff, S. M.

    1981-01-01

    Four phases of research results are reported: (1) experiments on the compressible turbulent boundary layer flow in a streamwise corner; (2) the two dimensional (2D) interaction of incident shock waves with a compressible turbulent boundary layer; (3) three dimensional (3D) shock/boundary layer interactions; and (4) cooperative experiments at Princeton and numerical computations at NASA-Ames.

  11. A stochastic perturbation method to generate inflow turbulence in large-eddy simulation models: Application to neutrally stratified atmospheric boundary layers

    SciTech Connect

    Muñoz-Esparza, D.; Kosović, B.; Beeck, J. van; Mirocha, J.

    2015-03-15

    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 boundaries of the LES domain [Muñoz-Esparza et al., “Bridging the transition from mesoscale to microscale turbulence in numerical weather prediction models,” Boundary-Layer 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 atmospheric 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 boundary layers. 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, . In contrast, large-scale perturbations

  12. Modelling the transitional boundary layer

    NASA Technical Reports Server (NTRS)

    Narasimha, R.

    1990-01-01

    Recent developments in the modelling of the transition zone in the boundary layer 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 boundary layer 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.

  13. Coupled wake boundary layer model of windfarms

    NASA Astrophysics Data System (ADS)

    Stevens, Richard; Gayme, Dennice; Meneveau, Charles

    2014-11-01

    We present a coupled wake boundary layer (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 boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. 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.

  14. Operational Performance of Sensor Systems Used to Determine Atmospheric Boundary Layer Properties as Part of the NASA Aircraft Vortex Spacing System Project

    NASA Technical Reports Server (NTRS)

    Zak, J. Allen; Rodgers, William G., Jr.; Nolf, Scott; McKissick, Burnell T. (Technical Monitor)

    2001-01-01

    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 atmospheric boundary layer 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.

  15. Atmospheric Boundary Layer Wind Data During the Period January 1, 1998 Through January 31, 1999 at the Dallas-Fort Worth Airport. Volume 1; Quality Assessment

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    The quality of the Aircraft Vortex Spacing System (AVOSS) is critically dependent on representative wind profiles in the atmospheric boundary layer. 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.

  16. Boundary layer chemistry probed by in situ infrared spectroscopy during SiO2 deposition at atmospheric pressure from tetraethylorthosilicate and ozone.

    PubMed

    Flores, Lucio D; Crowell, John E

    2005-09-01

    The deposition of silicon dioxide films at 450 degrees C was studied in quasi real time by probing the thermally activated boundary layer region near the growing surface during atmospheric pressure chemical vapor deposition (APCVD). Potential tetraethylorthosilicate (TEOS)/O(3) reaction products have been investigated in an attempt to clarify the reaction mechanism leading to the observed silanol deposition intermediates and delineate the film formation process. The organic products formed during the TEOS/O(3) reaction are acetic acid, formic acid, formaldehyde, carbon monoxide, carbon dioxide, and water. Quantitative methods are developed using FT-IR (Fourier transform infrared) spectroscopy during ozonation of TEOS at elevated temperatures. The measurement of gaseous alcohols of silicon alkoxides by FT-IR is demonstrated by application of an in situ methodology that probes the high-temperature region within the CVD environment. Partial least squares (PLS) Beer's law absorption models are used in determining relative TEOS, ozone, and ethoxysilanol levels during the reaction. The reaction order in TEOS is measured at 1.65 +/- 0.02 over a 0.9 Torr pressure range. Similarly, the ratio of ethoxysilanol formed versus the amount of ozone consumed is ca. 1:3. A radical chain oxidative mechanism involving direct reaction of TEOS and ozone is proposed for formation of highly reactive silanol film growth intermediates.

  17. Nonequilibrium chemistry boundary layer integral matrix procedure

    NASA Technical Reports Server (NTRS)

    Tong, H.; Buckingham, A. C.; Morse, H. L.

    1973-01-01

    The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary 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 boundary layer.

  18. Seasonal, synoptic and diurnal variation of atmospheric water-isotopologues in the boundary layer of Southwestern Germany caused by plant transpiration, cold-front passages and dewfall.

    NASA Astrophysics Data System (ADS)

    Christner, Emanuel; Dyroff, Christoph; Kohler, Martin; Zahn, Andreas; Gonzales, Yenny; Schneider, Matthias

    2013-04-01

    Atmospheric 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 atmosphere (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 boundary layer (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 Atmospheric 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 atmospheric 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

  19. The marine atmospheric boundary layer during the HyMeX-ASICS-MED campaign: characterization of coherent structures and impact on turbulent flux estimates

    NASA Astrophysics Data System (ADS)

    Brilouet, Pierre-Etienne; Canut, Guylaine; Durand, Pierre

    2015-04-01

    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-atmosphere 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 atmospheric boundary layer (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.

  20. The structures of the atmospheric boundary layer in the Yellow Sea summer fog-a comparison study with the spring fog

    NASA Astrophysics Data System (ADS)

    Zhang, S.-P.; Ren, Z.-P.; Yang, Y.-Q.; Wang, X.-G.; Xu, X.-L.

    2010-07-01

    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 boundary layer 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 atmospheric boundary layer (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 layer). 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 layer 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

  1. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

  2. Boundary Layer Ventilation by Convection and Coastal Processes

    NASA Astrophysics Data System (ADS)

    Dacre, H.

    2008-12-01

    Several observational studies measuring aerosol in the atmosphere have found multiple aerosol layers located above the marine boundary layer. It is hypothesized that the existence of these layers is influenced by the diurnal variation in the structure of the upwind continental boundary layer. Furthermore, collision between a sea breeze and the prevailing wind can result in enhanced convection at the coast which can also lead to elevated layers of pollution. In this study we investigate the processes responsible for ventilation of the atmospheric boundary layer near the coast using the UK Met Office Unified Model. Pollution sources are represented by the constant emission of a passive tracer everywhere over land. The ventilation processes observed include shallow convection, a sea breeze circulation and coastal outflow. Vertical distributions of tracer at the coast are validated qualitatively with AMPEP (Aircraft Measurement of chemical Processing Export fluxes of Pollutants over the UK) CO aircraft measurements and are shown to agree well.

  3. Microgravity Effects on Plant Boundary Layers

    NASA Technical Reports Server (NTRS)

    Stutte, Gary; Monje, Oscar

    2005-01-01

    The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers 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 boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

  4. Boundary Layer Ventilation Processes During a High Pressure Event

    NASA Astrophysics Data System (ADS)

    Gray, S. L.; Dacre, H. F.; Belcher, S. E.

    2006-12-01

    It is often assumed that ventilation of the atmospheric boundary layer is weak during high pressure events. But is this always true? Here we investigate the processes responsible for ventilation of the atmospheric boundary layer during a high pressure event that occured on the 9 May 2005 using the UK Met Office Unifed Model. Pollution sources are represented by the constant emission of a passive tracer everywhere over land. The ventilation processes observed include a sea breeze circulation, turbulent mixing across the top of the boundary layer followed by large-scale ascent, and shallow convection. Vertical distributions of tracer are validated with AMPEP (Aircraft Measurement of chemical Processing Export fluxes of Pollutants over the UK) CO aircraft measurements and are shown to agree impressively well. Budget calculations of tracers are performed in order to determine the relative importance of these ventilation processes. The sea breeze circulation was found to ventilate 26% of the boundary layer tracer by sunset of which 2% was above 2km. A combination of the sea breeze circulation and turbulent mixing ventilated 46% of the boundary layer tracer, of which 10% was above 2km. Finally, the sea breeze circulation, turbulent mixing and shallow convection processes together ventilated 52% of the tracer into the free troposphere, of which 26% was above 2km. Hence this study shows that signicant ventilation of the boundary layer can occur during high pressure events; turbulent mixing and convection processes can double the amount of pollution ventilated from the boundary layer.

  5. A model for the estimation of the surface fluxes of momentum, heat and moisture of the cloud topped marine atmospheric boundary layer from satellite measurable parameters. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Allison, D. E.

    1984-01-01

    A model is developed for the estimation of the surface fluxes of momentum, heat, and moisture of the cloud topped marine atmospheric boundary layer 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 boundary layer, the model calculates the equivalent potential temperature and total water profiles of the boundary layer along with the boundary layer 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 boundary layer for the cases of cold air outbreak and California coastal stratus is presented.

  6. Turbulent boundary layers with secondary flow

    NASA Technical Reports Server (NTRS)

    Grushwitz, E.

    1984-01-01

    An experimental analysis of the boundary layer 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 boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

  7. Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface.

    PubMed

    Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

    2014-01-01

    In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer 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

  8. Impact of storm-induced cooling of sea surface temperature on large turbulent eddies and vertical turbulent transport in the atmospheric boundary layer of Hurricane Isaac

    NASA Astrophysics Data System (ADS)

    Zhu, Ping; Wang, Yuting; Chen, Shuyi S.; Curcic, Milan; Gao, Cen

    2016-01-01

    Roll vortices in the atmospheric boundary layer (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.

  9. Optical and physical characteristics of Bay of Bengal aerosols during W-ICARB: Spatial and vertical heterogeneities in the marine atmospheric boundary layer and in the vertical column

    NASA Astrophysics Data System (ADS)

    Moorthy, K. Krishna; Beegum, S. Naseema; Babu, S. Suresh; Smirnov, Alexander; John, Sherine Rachel; Kumar, K. Raghavendra; Narasimhulu, K.; Dutt, C. B. S.; Nair, Vijayakumar S.

    2010-12-01

    Analysis of the continuous and collocated measurements of columnar spectral aerosol optical depths (AODs) and mass size distributions in the marine atmospheric boundary layer (MABL) over the Bay of Bengal (BoB), carried out from 27 December 2008 to 29 January 2009 during the Winter Integrated Campaign for Aerosols, Gases and Radiation Budget (W-ICARB), revealed distinct regional features in the spatial variations of the aerosol properties in the MABL and column. In general, AODs were high over the northern and northwestern parts of the BoB, with pockets of very high values, within which the AODs were as high as ˜0.8 while the smallest values (˜0.1) were observed over the northeastern BoB, off the Myanmar and Bangladesh coasts. Interestingly, though, this region had the highest Angstrom wavelength exponent α (˜1.5), notwithstanding the generally high values that prevailed over the eastern as well as northern coastal regions of India. Back trajectory analyses revealed the significant role of the advected aerosols in the observed spatial pattern. Within the MABL, high accumulation mode mass concentrations (MA) prevailed over the entire BoB with the accumulation fraction ranging from 0.6 to 0.95, whereas very high fine-mode (r < 0.1 μm) aerosol mass fractions (˜0.8) were observed over the northeastern and western coastal BoB adjoining the Indian mainland (where α was high to very high). The vertical distributions, inferred from the columnar and MABL properties as well as from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations data, revealed better homogeneity in the northeastern and eastern BoB, whereas significant heterogeneity was seen over other regions.

  10. Implementation of non-local boundary layer schemes in the Regional Atmospheric Modeling System and its impact on simulated mesoscale circulations

    NASA Astrophysics Data System (ADS)

    Gómez, I.; Ronda, R. J.; Caselles, V.; Estrela, M. J.

    2016-11-01

    This paper proposes the implementation of different non-local Planetary Boundary Layer schemes within the Regional Atmospheric Modeling System (RAMS) model. The two selected PBL parameterizations are the Medium-Range Forecast (MRF) PBL and its updated version, known as the Yonsei University (YSU) PBL. YSU is a first-order scheme that uses non-local eddy diffusivity coefficients to compute turbulent fluxes. It is based on the MRF, and improves it with an explicit treatment of the entrainment. With the aim of evaluating the RAMS results for these PBL parameterizations, a series of numerical simulations have been performed and contrasted with the results obtained using the Mellor and Yamada (MY) scheme, also widely used, and the standard PBL scheme in the RAMS model. The numerical study carried out here is focused on mesoscale circulation events during the summer, as these meteorological situations dominate this season of the year in the Western Mediterranean coast. In addition, the sensitivity of these PBL parameterizations to the initial soil moisture content is also evaluated. The results show a warmer and moister PBL for the YSU scheme compared to both MRF and MY. The model presents as well a tendency to overestimate the observed temperature and to underestimate the observed humidity, considering all PBL schemes and a low initial soil moisture content. In addition, the bias between the model and the observations is significantly reduced moistening the initial soil moisture of the corresponding run. Thus, varying this parameter has a positive effect and improves the simulated results in relation to the observations. However, there is still a significant overestimation of the wind speed over flatter terrain, independently of the PBL scheme and the initial soil moisture used, even though a different degree of accuracy is reproduced by RAMS taking into account the different sensitivity tests.

  11. Seasonal variation of local atmospheric circulations and boundary layer structure in the Beijing-Tianjin-Hebei region and implications for air quality

    NASA Astrophysics Data System (ADS)

    Miao, Yucong; Hu, Xiao-Ming; Liu, Shuhua; Qian, Tingting; Xue, Ming; Zheng, Yijia; Wang, Shu

    2015-12-01

    The Beijing-Tianjin-Hebei (BTH) region experiences frequent heavy haze pollution in fall and winter. Pollution was often exacerbated by unfavorable atmospheric boundary layer (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.

  12. Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface

    PubMed Central

    Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

    2014-01-01

    In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer 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

  13. Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface.

    PubMed

    Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

    2014-01-01

    In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer 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.

  14. Structure of the low latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

    1980-01-01

    Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, 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 boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.

  15. Organised Coherent Motion in Atmospheric Boundary Layer Flow in the Proximity to Tall Plant Canopies as Detected in Acoustic Doppler Profiler and Tower-based Observations

    NASA Astrophysics Data System (ADS)

    Foken, T.; Thomas, C. K.

    2007-12-01

    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 atmospheric boundary layer scale and the horizontal flow in 4 % of all studied cases only, mainly under near-neutral stratification. Evaluation of the Mixing-Layer 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

  16. Boundary layers of the earth's outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Frank, L. A.

    1984-01-01

    The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers 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 boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer 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 boundaries 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.

  17. Control of Separated Boundary Layers

    NASA Astrophysics Data System (ADS)

    Huang, Shao-Ching; Kim, John

    2003-11-01

    The control of separated boundary layers are numerically investigated. Two types of flow geometry are considered. The first case is flow separation on a flat plate caused by an imposed adverse pressure gradient. The second case is flow separation downstream of a curved leading edge. These cases represent laminar separation with turbulent reattachment with and without curvature effects. Open-loop control, with distributed surface blowing and suction as control input, is first applied to establish base-line cases. We then use a system identification approach to construct approximate system models for design of closed-loop control. The models are based on the input-output relationship obtained from numerical simulations. The linear quadratic Gaussian (LQG) control synthesis is applied to the models to produce feedback control laws. The distributed sensors and actuators are confined to the walls. The efficacy of the controllers are quantified by pressure distribution, separation bubble size and Reynolds stresses. Visualization of the controlled and uncontrolled flow fields will also be presented.

  18. Modeling cathode boundary layer discharges

    NASA Astrophysics Data System (ADS)

    Munoz-Serrano, E.; Boeuf, J. P.; Pitchford, L. C.

    2009-10-01

    A Cathode Boundary Layer Discharge or CBL (Schoenbach, et al Plasma Sources Sci. Technol. 13, 177,2004) is an electrode/dielectric/electrode sandwich with a central hole pierced through the dielectric and one of the electrodes (the anode). Thus, the cathode surface area available to the discharge is limited by the annular dielectric, and the discharge operates in an abnormal glow mode with a positive V-I characteristic at higher current. Using a two-dimensional fluid model, we have studied the electrical properties of CBLs in argon at 100 and 400 torr pressure. The spatial profiles of charged particle and metastable densities, potential, and gas temperature, as well as calculated V-I characteristics will be shown for a range of conditions for a 800 micron hole diameter. One interesting result (anticipated in the work of Belostotskiy, et al, Plasma Sources Sci. Technol 17, 045018, 2008) is that there is a sharp increase in the slope of the V-I characteristic when gas heating is taken into account. This current limiting effect is not observed when the discharge is able to expand on the outer surface of the cathode as in the case of the MicroHollow Cathode Discharge (MHCD) configuration, for example.

  19. Toward evaluation of heat fluxes in the convective boundary layer

    SciTech Connect

    Sorbjan, Z.

    1995-05-01

    This article demonstrates that vertical profiles of the heat flux in the convective boundary layer 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 boundary layer, such as the mixed-layer height z{sub t}, the depth of the interfacial (entrainment) layer, 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 atmosphere. 12 refs., 12 figs., 1 tab.

  20. Cyclone separator having boundary layer turbulence control

    DOEpatents

    Krishna, Coimbatore R.; Milau, Julius S.

    1985-01-01

    A cyclone separator including boundary layer 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 boundary layer of the vortical fluid flow through the separator.

  1. Influence of small-scale North Atlantic surface temperature on the marine boundary layer and free atmosphere : a study using the ARPEGE model

    NASA Astrophysics Data System (ADS)

    Piazza, M.; Terray, L.; Boe, J.

    2012-12-01

    In recent years, high resolution satellite observations have renewed interest in air-sea coupling over sea surface temperature (SST) fronts, showing that sharp SST gradients can influence surface wind. Warm small-scale SST anomalies are associated with positive surface wind anomalies, and conversely. Two theoretical mechanisms have been proposed to be involved in the generation of surface wind anomalies : the effects of local surface pressure gradients and marine atmospheric boundary layer stability changes. Not only surface fields are affected but also precipitation. This suggests a strong impact of SST fronts on the free troposphere and eventually on the large-scale atmospheric circulation. In this presentation, those mechanisms are further explored over the North Atlantic thanks to the high resolution (0.25°x0.25°) global atmospheric model ARPEGE forced by observed high resolution SST (NOAA_OI dataset), from January 2003 to July 2011. In order to analyze the effects of small-scale SST in the North Atlantic, two simulations are compared : a control simulation (HRES) with a full high resolution SST, and a perturbed simulation (SMTH) with spatially smoothed SST in the Gulfstream region (Figure a). First, the capability of the model to represent the air-sea interaction has been evaluated against satellite observations (QuickScat for surface winds and AMSR-E for SST). The air-sea interaction coefficient is defined as the regression coefficient between SST anomalies and wind speed anomalies for spatially high-pass filtered fields. Results from the HRES simulation show a strong and realistic air-sea interaction coefficient, especially in winter. Then, the seasonal comparison between HRES and SMTH shows that small-scale SST structures drive anomalies of wind speed, vorticity and convergence at the surface. The surface heat budget is investigated. It shows an average increase of 30% of turbulent heat fluxes at the surface in HRES compared to SMTH. Precipitation

  2. Structure of relaminarizing turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Ramesh, O.; Patwardhan, Saurabh

    2014-11-01

    Relaminarization of a turbulent boundary layer 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 boundary layers. The experimental and numerical investigation of relaminarizing turbulent boundary layers undergoing same history reveals that the boundary layer 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 boundary layers is investigated. A mechanism for stabilization of near-wall low speed streaks is proposed.

  3. Boundary Layers of Air Adjacent to Cylinders

    PubMed Central

    Nobel, Park S.

    1974-01-01

    Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer 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 boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer 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 boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

  4. Instabilities in Time Dependent Boundary Layers

    NASA Astrophysics Data System (ADS)

    Otto, Stephen Robert

    Available from UMI in association with The British Library. The work in this thesis is concerned with instabilities known to occur in boundary layers. The boundary layers considered herein are of a temporal nature; that is they are time dependent. In Chapter 1 a general overview of the subject is given. In Chapter 2, we consider two Stokes layers found to occur on a sphere. Firstly, the case where the sphere oscillates along a radius, referred to as transverse oscillations, and secondly where the sphere oscillates about its axis, referred to as torsional oscillations. We also consider the oscillations to be of such an amplitude and frequency so that the resulting boundary layer is thin compared to the sphere's radius. Chapter 3, is concerned with the development of vortices in a temporally growing boundary layer occurring on an infinite flat plate, the fluid above which is started to move impulsively. Here we take account of the fact that the boundary layer is growing with time, in a similar manner as has been used for the Blasius layer to grow with a downstream coordinate. In Chapter 4, we consider a boundary layer found to occur outside a cylinder, which at a certain instant has a torsional velocity imparted to it, this layer grows with time. The development of vortices in considered in this layer, and certain parameter regimes are investigated namely those appropriate to the right hand branch of the neutral curve, and those appropriate to the development of inviscid Gortler modes.

  5. Halogen chemistry in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.

    2009-04-01

    Important atmospheric 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 atmospheric chemistry of these halogens (1), changes the oxidizing capacity of the marine boundary layer 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 boundary layer (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.

  6. LDV measurements of turbulent baroclinic boundary layers

    SciTech Connect

    Neuwald, P.; Reichenbach, H.; Kuhl, A.L.

    1993-07-01

    Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, 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 boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer 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 boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.

  7. Alpine lee cyclogenesis influence on air-sea heat exchanges and marine atmospheric boundary layer thermodynamics over the western Mediterranean during a Tramontane/Mistral event

    NASA Astrophysics Data System (ADS)

    Flamant, Cyrille

    2003-02-01

    Data from a recent field campaign are used to analyze the nonstationary aspects of air-sea heat exchanges and marine atmospheric boundary layer (MABL) thermodynamics over the Gulf of Lion (GoL) in connection with synoptic forcing. The data set includes measurements made from a wide range of platforms (sea-borne, airborne, and space-borne) as well as three-dimensional atmospheric modeling. The analysis focuses on the 24 March 1998 Tramontane/Mistral event. It is shown that the nonstationary nature of the wind regime over the GoL was controlled by the multistage evolution of an Alpine lee cyclone over the Tyrrhenian Sea (between Sardinia and continental Italy). In the early stage (low at 1014 hPa) the Tramontane flow prevailed over the GoL. As the low deepened (1010 hPa), the prevailing wind regime shifted to a well-established Mistral that peaked around 1200 UTC. In the afternoon the Mistral was progressively disrupted by a strengthening outflow coming from the Ligurian Sea in response to the deepening low over the Tyrrhenian Sea (1008 hPa) and the channelling induced by the presence of the Apennine range (Italy) and the Alps. In the evening the Mistral was again well established over the GoL as the depression continued to deepen (1002 hPa) but moved to the southeast, reducing the influence of outflow from the Ligurian Sea on the flow over the GoL. The air-sea heat exchanges and the structure of the MABL over the GoL were observed to differ significantly between the established Mistral period and the disrupted Mistral period. In the latter period, surface latent and sensible heat fluxes were reduced by a factor of 2, on average. During that latter period, air-sea moisture exchanges were mainly driven by dynamics, whereas during the former period, both winds and vertical moisture gradients controlled moisture exchanges. The MABL was shallower during the latter period (0.7 km instead of 1.2 km) because of reduced surface turbulent heat fluxes and increased wind shear

  8. Calculation methods for compressible turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

    1976-01-01

    Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer 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 boundary layers 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.

  9. Energy transport using natural convection boundary layers

    SciTech Connect

    Anderson, R

    1986-04-01

    Natural convection is one of the major modes of energy transport in passive solar buildings. There are two primary mechanisms for natural convection heat transport through an aperture between building zones: (1) bulk density differences created by temperature differences between zones; and (2) thermosyphon pumping created by natural convection boundary layers. The primary objective of the present study is to compare the characteristics of bulk density driven and boundary layer driven flow, and discuss some of the advantages associated with the use of natural convection boundary layers to transport energy in solar building applications.

  10. Boundary-layer linear stability theory

    NASA Technical Reports Server (NTRS)

    Mack, L. M.

    1984-01-01

    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 boundary layer 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 boundary layer, 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 boundary layer, 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 boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer 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

  11. Boundary-layer linear stability theory

    NASA Astrophysics Data System (ADS)

    Mack, L. M.

    1984-06-01

    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 boundary layer 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 boundary layer, 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 boundary layer, 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 boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer 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

  12. Boundary Layers in Laminar Vortex Flows.

    NASA Astrophysics Data System (ADS)

    Baker, Glenn Leslie

    A detailed experimental study of the flow in an intense, laminar, axisymmetric vortex has been conducted in the Purdue Tornado Vortex Simulator. The complicated nature of the flow in the boundary layer of laboratory vortices and presumably on that encountered in full-scale tornadoes has been examined. After completing a number of modifications to the existing facility to improve the quality of the flow in the simulator, hot-film anemometry was employed for making velocity-component and turbulence-intensity measurements of both the free-stream and boundary layer portions of the flow. The measurements represent the first experimental boundary layer investigation of a well-defined vortex flow to appear in the literature. These results were compared with recent theoretical work by Burggraf, Stewartson and Belcher (1971) and with an exact similarity solution for line-sink boundary layers developed by the author. A comparison is also made with the numerical simulation of Wilson (1981) in which the boundary conditions were matched to those of the present experimental investigation. Expressions for the vortex core radius, the maximum tangential velocity and the maximum pressure drop are given in terms of dimensionless modeling parameters. References. Burggraf, O. R., K. Stewartson and R. Belcher, Boundary layer. induced by a potential vortex. Phys. Fluids 14, 1821-1833 (1971). Wilson, T., M. S. thesis, Vortex Boundary Layer Dynamics, Univ. Calif. Davis (1981).

  13. Boundary-layer control for drag reduction

    NASA Technical Reports Server (NTRS)

    Harvey, William D.

    1988-01-01

    Although the number of possible applications of boundary-layer 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 boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (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, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.

  14. Boundary layer roll circulations during FIRE

    NASA Technical Reports Server (NTRS)

    Shirer, Hampton N.; Haack, Tracy

    1990-01-01

    The probable mechanism underlying the development of boundary layer roll circulations are studied using wind and temperature profiles measured by the National Center for Atmospheric 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 boundary layer 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 boundary 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 layer, 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

  15. Acoustic sounding in the planetary boundary layer

    NASA Technical Reports Server (NTRS)

    Kelly, E. H.

    1974-01-01

    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 boundary 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 layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.

  16. Boundary-layer stability and airfoil design

    NASA Technical Reports Server (NTRS)

    Viken, Jeffrey K.

    1986-01-01

    Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer 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 boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.

  17. Structure and Growth of the Marine Boundary Layer

    NASA Technical Reports Server (NTRS)

    Mccumber, M.

    1984-01-01

    LANDSAT visible imagery and a one-dimensional Lagrangian boundary layer model were used to hypothesize the nature and the development of the marine boundary layer 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 boundary layer model, initialized with data obtained from the MASEX, the marine boundary layer can be mapped over the entire Atlantic coastal domain and the evolution of the boundary layer can be studied as a function of different characteristics of important surface level forcings. The effects on boundary layer growth due to the magnitude and pattern of sea surface temperature, to the shape of the coastline, and to atmospheric conditions, such as the orientation of the prevailing wind are examined.

  18. Characterization of internal boundary layer capacitors

    SciTech Connect

    Park, H. D.; Payne, D. A.

    1980-05-01

    Internal boundary layer capacitors were characterized by scanning transmission electron microscopy and by microscale electrical measurements. Data are given for the chemical and physical characteristics of the individual grains and boundaries, and their associated electric and dielectric properties. Segregated internal boundary layers were identified with resistivities of 10/sup 12/-10/sup 13/ ..cap omega..-cm. Bulk apparent dielectric constants were 10,000-60,000. A model is proposed to explain the dielectric behavior in terms of an equivalent n-c-i-c-n representation of ceramic microstructure, which is substantiated by capacitance-voltage analysis.

  19. Nature, theory and modelling of geophysical convective planetary boundary layers

    NASA Astrophysics Data System (ADS)

    Zilitinkevich, Sergej

    2015-04-01

    Geophysical convective planetary boundary layers (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 boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. 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 boundaries (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 layer and entrainment layer (at the CPBL inner and outer boundaries) 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-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in

  20. Ground observations of magnetospheric boundary layer phenomena

    NASA Technical Reports Server (NTRS)

    Mchenry, Mark A.; Clauer, C. Robert; Friis-Christensen, Eigil; Newell, Patrick T.; Kelly, J. D.

    1990-01-01

    Several classes of traveling vortices in the dayside ionosphere convection have been detected and tracked using the Greenland magnetometer chain (Friis-Christensen et al., 1988, McHenry et al., 1989). One class observed during quiet times consists of a continuous series of vortices moving generally antisunward for several hours at a time. The vortices' strength is seen to be approximately steady and neighboring vortices rotate in opposite directions. Sondrestrom radar observations show that the vortices are located at the ionospheric convection reversal boundary. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, it is argued that this class of vortices is caused by the Kelvin-Helmholtz instability of the inner edge of the magnetospheric boundary layer.

  1. Effect of Derating and Shutting Down of Turbines on the Extracted Power of Large Wind Farms in Thermally-Stratified Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Adkins, K. A.

    2015-12-01

    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 boundary layer 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.

  2. Lear jet boundary layer/shear layer laser propagation experiments

    NASA Technical Reports Server (NTRS)

    Gilbert, K.

    1980-01-01

    Optical degradations of aircraft turbulent boundary layers with shear layers 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 boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-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 boundary layer. 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 boundary layer. 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 boundary layer.

  3. Investigation of the spatio-temporal variability of atmospheric boundary layer depths over mountainous terrain observed with a suite of ground-based and airborne instruments during the MATERHORN field experiment

    NASA Astrophysics Data System (ADS)

    Pal, S.; De Wekker, S.; Emmitt, G. D.

    2013-12-01

    We present first results of the spatio-temporal variability of atmospheric boundary layer depths obtained with a suite of ground-based and airborne instruments deployed during the first field phase of The Mountain Terrain Atmospheric 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 atmospheric boundary layer (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 boundary layer 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 boundary layer (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

  4. High enthalpy hypersonic boundary layer flow

    NASA Technical Reports Server (NTRS)

    Yanow, G.

    1972-01-01

    A theoretical and experimental study of an ionizing laminar boundary layer 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 boundary layer 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 boundary layer solution than in an equilibrium boundary layer 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 boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

  5. The Kinematics of Turbulent Boundary Layer Structure

    NASA Technical Reports Server (NTRS)

    Robinson, Stephen Kern

    1991-01-01

    The long history of research into the internal structure of turbulent boundary layers 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 boundary layer 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 boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer 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 boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.

  6. Boundary-Layer-Ingesting Inlet Flow Control

    NASA Technical Reports Server (NTRS)

    Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

    2008-01-01

    An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-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 boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-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 boundary layer, 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.

  7. Boundary Layer Cloudiness Parameterizations Using ARM Observations

    SciTech Connect

    Bruce Albrecht

    2004-09-15

    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 boundary layer 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 boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer 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 boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.

  8. Boundary Layer Flow Over a Moving Wavy Surface

    NASA Astrophysics Data System (ADS)

    Hendin, Gali; Toledo, Yaron

    2016-04-01

    Boundary Layer 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 boundary layer flow over surface gravity waves is of great importance as various atmosphere-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 boundary layer air flow over progressive, small-amplitude waves. It aims to extend the well-known Blasius solution for a boundary layer 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 boundary layer above the wavy surface. The assumption of a uniform flow in the outer layer, 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 boundary layer cannot be neglected. In the boundary layer, 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

  9. Pattern Formation in Cathode Boundary Layer Microdischarges

    NASA Astrophysics Data System (ADS)

    Schoenbach, K. H.; Moselhy, M. M.

    2003-10-01

    Direct current glow discharges in xenon between a planar, 100 μm thick cathode and a ring shaped anode, separated by 250 μm, were found to be stable up to atmospheric pressure. Photographs in the visible and VUV (172 nm) range of the spectrum show the transition from a homogeneous to a structured plasma. The plasma patterns, regularly arranged filaments that are most pronounced at lower pressures (100 Torr), show discrete changes when the current is decreased by fractions of mA. This selforganization of the plasma requires the presence of a second stable branch in addition to the abnormal cathode fall in the voltage-current density characteristic of the "cathode boundary layer" (CBL) discharges. A model of the cathode fall by von Engel and Steenbeck [1], which was modified to take thermal conduction as a loss process into account, in addition to radiation, indicates the presence of stable plasma filaments at current densities in the range from 10 to 100 A/cm^2, before transition into an arc. [1] A. von Engel and M. Steenbeck, "Elektrische Gasentladungen, ihre Physik und Technik," Vol. 2, p. 121. Work supported by NSF (CTS-0078618 and INT-0001438).

  10. Excimer Emission from Cathode Boundary Layer Discharges

    NASA Astrophysics Data System (ADS)

    Moselhy, M. M.; Ansari, J.; Schoenbach, K. H.

    2003-10-01

    The excimer emission from direct current glow discharges between a planar cathode and a ring shaped anode of 0.75 mm diameter, separated by only 250 μm, was studied in high-pressure xenon and argon. The thickness of the "cathode boundary layer" (CBL) plasma, approximately 150 μm, with a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. For currents on the order of 1 mA, the discharge in xenon changes from an abnormal glow into a mode showing selforganization of the plasma. At this transition, maximum excimer emission (at 172 nm) with internal efficiencies of 3 to 5% is observed. The maximum radiant emittance is 4 W/cm^2 for atmospheric pressure operation. In the case of argon, selforganization of the plasma was not seen, however the emission of the excimer radiation (128 nm) again shows a maximum, in this case at the transition from abnormal to normal glow, with efficiencies of 2%. The maximum radiant emittance is 1.6 W/cm^2 for argon at 600 Torr. The positive slope of the current-voltage characteristics at maximum excimer emission indicates the possibility to generate large area flat excimer sources. Work supported by NSF (CTS-0078618 and INT-0001438).

  11. Characteristics of the Martian atmosphere surface layer

    NASA Astrophysics Data System (ADS)

    Clow, G. D.; Haberle, R. M.

    Elements of various terrestrial boundary layer models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface ('constant flux') layer. The atmospheric surface layer 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 atmospheric boundary layer. It was found that under most Martian conditions, the interfacial and surface

  12. Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

    NASA Technical Reports Server (NTRS)

    Mack, L. M.

    1967-01-01

    The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer 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 boundary layer 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.

  13. Boundary layer emission in luminous LMXBs

    NASA Astrophysics Data System (ADS)

    Gilfanov, M.; Revnivtsev, M.

    We show that aperiodic and quasiperiodic variability of bright LMXBs -- atoll and Z- sources on sim sec -- msec time scales is caused primarily by variations of the luminosity of the boundary layer The kHz QPOs have the same origin as variability at lower frequencies i e independent of the nature of the clock the actual luminosity modulation takes place on the neutron star surface The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum In the investigated range of dot M sim 0 1-1 dot MEdd it depends weakly on the global mass accretion rate and in the limit dot M sim dot MEdd is close to Wien spectrum with kT sim 2 4 keV Its independence on the global value of dot M lends support to the theoretical suggestion by Inogamov Sunyaev 1999 that the boundary layer is radiation pressure supported Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z-track to changes of physically meaningful parameters Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z-track from conventional sim 50 on the horizontal branch to a rather small number on the normal branch This decrease can be caused for example by obscuration of the boundary layer by the geometrically thickened accretion disk at dot M sim dot MEdd Alternatively this can indicate significant change of

  14. Boundary-layer theory for blast waves

    NASA Technical Reports Server (NTRS)

    Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.

    1975-01-01

    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 boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.

  15. Calculation methods for compressible turbulent boundary layers, 1976

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

    1977-01-01

    Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.

  16. Study of the effect of soil disturbance on vapor transport through integrated modeling of the atmospheric boundary layer and shallow subsurface

    NASA Astrophysics Data System (ADS)

    Trautz, A.; Smits, K. M.; Cihan, A.; Wallen, B.

    2014-12-01

    Soil-water evaporation is one of the governing processes responsible for controlling water and energy exchanges between the land and atmosphere. Despite its wide relevance and application in many natural and manmade environments (e.g. soil tillage practices, wheel-track compaction, fire burn environments, textural layering 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 atmosphere 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

  17. Boundary Layer Transition on X-43A

    NASA Technical Reports Server (NTRS)

    Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert

    2008-01-01

    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 boundary layer 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 boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer 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 boundary layer 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.

  18. Flow visualization of turbulent boundary layer structure

    NASA Astrophysics Data System (ADS)

    Head, M. R.; Bandyopadhyay, P.

    1980-01-01

    The results from flow visualization experiments performed using an argon-ion laser to illuminate longitudinal and transverse sections of the smoke filled boundary layer in zero pressure gradient are discussed. Most of the experiments were confined to the range 600 Re sub theta 10,000. Results indicate that the boundary layer consists almost exclusively of vortex loops or hairpins, some of which may extend through the complete boundary layer thickness and all of which are inclined at a more or less constant characteristic angle of approximately 45 deg to the wall. Since the cross-stream dimensions of the hairpins appear to scale roughly with the wall variables U sub tau and nu, while their length is limited only by the boundary layer thickness, there are very large scale effects on the turbulence structure. At high Reynolds numbers (Re sub theta = 10,000) there is little evidence of large-scale coherent motions, other than a slow overturning of random agglomerations of the hairpins just mentioned.

  19. Planetary Boundary Layer from AERI and MPL

    SciTech Connect

    Sawyer, Virginia

    2014-02-13

    The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer 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 boundary-layer 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 boundary-layer processes.

  20. Boundary layer control device for duct silencers

    NASA Technical Reports Server (NTRS)

    Schmitz, Fredric H. (Inventor); Soderman, Paul T. (Inventor)

    1993-01-01

    A boundary layer 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.

  1. Astrophysical Boundary Layers: A New Picture

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail; Rafikov, Roman R.; Mclellan Stone, James

    2016-04-01

    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 boundary layer will be formed where the accretion disk touches its surfaces. The boundary layer 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 boundary layer 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 boundary layer due to the immense radial velocity shear present at the equator.Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.

  2. Nonlinear Transient Growth and Boundary Layer Transition

    NASA Technical Reports Server (NTRS)

    Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

    2016-01-01

    Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. 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 boundary layer 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 boundary layer without any streaks.

  3. Orbiter Boundary Layer Transition Prediction Tool Enhancements

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.

    2010-01-01

    Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer 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 boundary layer transition criteria utilized within the tool were updated based on new local boundary layer 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.

  4. Flow unsteadiness effects on boundary layers

    NASA Technical Reports Server (NTRS)

    Murthy, Sreedhara V.

    1989-01-01

    The development of boundary layers 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 boundary layer 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 Boundary Layer 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 boundary layer 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.

  5. Boundary layer emission in luminous LMXBs

    NASA Astrophysics Data System (ADS)

    Gilfanov, M.; Revnivtsev, M.

    2005-11-01

    We show that aperiodic and quasiperiodic variability of bright LMXBs - atoll and Z-sources - on ˜ sec-msec time scales is caused primarily by variations of the luminosity of the boundary layer. The emission of the accretion disk is less variable on these time scales and its power density spectrum follows P_disk(f)∝ f-1 law, contributing to observed flux variation at low frequencies and low energies only. The kHz QPOs have the same origin as variability at lower frequencies, i.e. independent of the nature of the "clock", the actual luminosity modulation takes place on the neutron star surface. The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum. In the investigated range of \\dot{M}˜ (0.1-1) \\dot{M}_Edd it depends weakly on the global mass accretion rate and in the limit \\dot{M}˜ \\dot{M}_Edd is close to Wien spectrum with kT˜ 2.4 keV. Its independence on the global value of \\dot{M} lends support to the theoretical suggestion by \\citet{inogamov99} that the boundary layer is radiation pressure supported. \\ Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z-track to changes of physically meaningful parameters. Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z-track from conventional ˜ 50% on the horizontal branch to a rather small number on the normal branch. This decrease can be caused, for example, by obscuration of the boundary layer by the geometrically thickened accretion disk at \\dot{M}˜\\dot{M}_Edd. Alternatively, this can indicate significant change of the structure of the accretion flow at \\dot{M}˜\\dot{M}_Edd and disappearance of the boundary layer as a distinct region of the significant energy release associated with the neutron star surface.

  6. Controls on boundary layer ventilation: Boundary layer processes and large-scale dynamics

    NASA Astrophysics Data System (ADS)

    Sinclair, V. A.; Gray, S. L.; Belcher, S. E.

    2010-06-01

    Midlatitude cyclones are important contributors to boundary layer ventilation. However, it is uncertain how efficient such systems are at transporting pollutants out of the boundary layer, and variations between cyclones are unexplained. In this study 15 idealized baroclinic life cycles, with a passive tracer included, are simulated to identify the relative importance of two transport processes: horizontal divergence and convergence within the boundary layer and large-scale advection by the warm conveyor belt. Results show that the amount of ventilation is insensitive to surface drag over a realistic range of values. This indicates that although boundary layer processes are necessary for ventilation they do not control the magnitude of ventilation. A diagnostic for the mass flux out of the boundary layer has been developed to identify the synoptic-scale variables controlling the strength of ascent in the warm conveyor belt. A very high level of correlation (R2 values exceeding 0.98) is found between the diagnostic and the actual mass flux computed from the simulations. This demonstrates that the large-scale dynamics control the amount of ventilation, and the efficiency of midlatitude cyclones to ventilate the boundary layer can be estimated using the new mass flux diagnostic. We conclude that meteorological analyses, such as ERA-40, are sufficient to quantify boundary layer ventilation by the large-scale dynamics.

  7. Simulation of chemical processes occurring in an atmospheric boundary layer. Influence of light and biogenic hydrocarbons on the formation of oxidants

    NASA Astrophysics Data System (ADS)

    Lopez, A.; Barthomeuf, M. O.; Huertas, M. L.

    A photochemical model has been developed to determine the impact of the emission of light and terpenic hydrocarbons (HCs) on the evolution of ozone, HNO 3 and PAN concentrations in the troposphere. The present model, of Lagrangian type, describes the evolution of trace gases in an air mass moving over a large and homogeneous source area. The respective cycles of O 3, NOx, methane and CO are considered. The vertical exchange is treated by introduction of a vertical diffusivity tensor Kz varying as a function of time and altitude. The results of this study indicate that both the intensity of vertical exchanges of airborne elements and the ground deposition play an important role on the evolution of vertical concentration profiles. The influence of diffusivity on the integrated concentrations in the boundary layer remains low. The introduction of light HCs (alkanes, alkenes) results in an increase in the O 3 concentration, correlated with the intensity of NOx and HC emissions. For a given level of NOx, both a decrease of the concentration in HNO 3 and an increase in the PAN concentration are observable when the production of light HCs increases. The sensitivity increases with the NOx source. The introduction of terpenic HCs causes a depletion of O 3 in the air masses characterized by low NOx emission rates, and an enrichment in those with higher emission rates. In both cases, the amplitude of the variation increases with the importance of the source of terpenic HCs, and is found higher for α-pinene than for isoprene. For a given NOx emission rate, the HNO 3 concentrations are seen to decrease when the source of natural HCs increase, whereas the concentration in PAN increases. As observed for light HCs, the sensitivity shows a dependence on the magnitude of the NOx source.

  8. Excimer emission from cathode boundary layer discharges

    NASA Astrophysics Data System (ADS)

    Moselhy, Mohamed; Schoenbach, Karl H.

    2004-02-01

    The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 μm, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the "cathode boundary layer" plasma, in the 100 μm range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm2 for atmospheric pressure operation in xenon. The maximum internal efficiency, however, decreases with pressure having highest values of 5% for 75 Torr operation. When the discharge current is reduced below a critical value, the discharge in xenon changes from an abnormal glow into a mode showing self-organization of the plasma. Also, the excimer spectrum changes from one with about equal contributions from the first and second continuum to one that is dominated by the second continuum emission. The xenon excimer emission intensity peaks at this discharge mode transition. In the case of argon, self-organization of the plasma was not seen, but the emission of the excimer radiation (128 nm) again shows a maximum at the transition from abnormal to normal glow. As was observed with xenon, the radiant emittance of argon increases with pressure, and the efficiency decreases. The maximum radiant emittance is 1.6 W/cm2 for argon at 600 Torr. The maximum internal efficiency is 2.5% at 200 Torr. The positive slope of the current-voltage characteristics at maximum excimer emission in both cases indicates the possibility of generating intense, large area, flat excimer lamps.

  9. INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

    EPA Science Inventory

    Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

  10. Benthic boundary layer - IOS modelling programme

    NASA Astrophysics Data System (ADS)

    Richards, K. J.

    1983-04-01

    Factors which control the height of the benthic boundary layer in the deep ocean and the residence time of fluid and a tracer within it, were modeled numerically. In one model, the effects of steady and unsteady currents and variations in fluid density are examined. In conditions similar to those observed in the abyssal regions of the E.N. Atlantic the model predicts an average bottom layer height close to the value observed. A second model examines the effects of spatial variations in currents. Due to convergences and divergences produced by these variations, the height of the bottom mixed layer is distorted. Where thinning is large, mixing results in warm patches flanked by benthic fronts. It is proposed that within the warm regions, the bottom mixed layer is exchanged within the ocean above. The residence time of a tracer released within the bottom mixed layer, average value 100 days, is predicted to vary between 20 and 800 days.

  11. Wind and boundary layers in Rayleigh-Bénard convection. II. Boundary layer character and scaling.

    PubMed

    van Reeuwijk, Maarten; Jonker, Harm J J; Hanjalić, Kemo

    2008-03-01

    The scaling of the kinematic boundary layer thickness lambda(u) and the friction factor C(f) at the top and bottom walls of Rayleigh-Bénard convection is studied by direct numerical simulation (DNS). By a detailed analysis of the friction factor, a new parameterisation for C(f) and lambda(u) is proposed. The simulations were made of an L/H=4 aspect-ratio domain with periodic lateral boundary conditions at Ra=(10(5), 10(6), 10(7), 10(8)) and Pr=1. The continuous spectrum, as well as significant forcing due to Reynolds stresses, clearly indicates a turbulent character of the boundary layer, while viscous effects cannot be neglected, judging from the scaling of classical integral boundary layer parameters with Reynolds number. Using a conceptual wind model, we find that the friction factor C(f) should scale proportionally to the thermal boundary layer thickness as C(f) proportional variant lambda(Theta)/H, while the kinetic boundary layer thickness lambda(u) scales inversely proportionally to the thermal boundary layer thickness and wind Reynolds number lambda(u)/H proportional variant (lambda(Theta)/H)(-1)Re(-1). The predicted trends for C(f) and lambda(u) are in agreement with DNS results.

  12. Bursting frequency prediction in turbulent boundary layers

    SciTech Connect

    LIOU,WILLIAM W.; FANG,YICHUNG

    2000-02-01

    The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.

  13. Logarithmic laws for compressible turbulent boundary layers

    SciTech Connect

    So, R.M.C.; Zhang, H.S.; Gatski, T.B.; Speziale, C.G.

    1994-11-01

    Dimensional similarity arguments proposed by Millikan are used with the Morkovin hypothesis to deduce logarithmic laws for compressible turbulent boundary layers as an alternative to the traditional van Driest analysis. It is shown that an overlap exists between the wall layer and the defect layer, and this leads to logarithmic behavior in the overlap region. The von Karman constant is found to depend parametrically on the Mach number based on the friction velocity, the dimensionless total heat flux, and the specific heat ratio. Even though it remains constant at approximately 0.41 for a freestream Mach number range of 0 to 4.544 with adiabatic wall boundary conditions, it rises sharply as the Mach number increases significantly beyond 4.544. The intercept of the logarithmic law of the wall is found to depend on the Mach number based on the friction velocity, the dimensionless total heat flux, the Prandtl number evaluated at the wall, and the specific heat ratio. On the other hand, the intercept of the logarithmic defect law is parametric in the pressure gradient parameter and all of the aforementioned dimensionless variables except the Prandtl number. A skin friction law is also deduced for compressible boundary layers. The skin friction coefficient is shown to depend on the momentum thickness Reynolds number, the wall temperature ratio, and all of the other parameters already mentioned. 26 refs.

  14. Toward parameterization of the stable boundary layer

    NASA Technical Reports Server (NTRS)

    Wetzel, P. J.

    1982-01-01

    Wangara data is used to examine the depth of the nocturnal boundary layer (NBL) and the height to which surface-linked turbulence extends. It is noted that a linearity of virtual temperature profiles has been found to extend up to a significant portion of the NBL, and then diverge where the wind shear rides over the surface-induced turbulence. A series of Richardson numbers are examined for varying degrees of turbulence and the significant cooling region is observed to have greater depth than the depth of the linear relationship layer. A three-layer parameterization of the thermodynamic structure of the NBL is developed so that a system of five equations must be solved when the wind velocity profile and the temperature at the surface are known. A correlation between the bulk Richardson number and the depth of the linear layer was found to be 0.89.

  15. Drizzle and Turbulence Variability in Stratocumulus-topped Boundary Layers

    NASA Astrophysics Data System (ADS)

    Kollias, P.; Luke, E. P.; Szyrmer, W.

    2015-12-01

    Marine stratocumulus clouds frequently produce light precipitation in the form of drizzle. The drizzle rate at the cloud base (RCB) dictates the impact of drizzle on the boundary layer turbulence and cloud organization. Here, synergistic observations from the US Department of Energy Atmospheric Radiation Measurement (ARM) program Eastern North Atlantic (ENA) site located on Graciosa Island in the Azores are used to investigate the relationship between RCB, and boundary layer turbulence and dynamics. The ARM ENA site is a heavily instrumented ground-based facility that offers new measurement capabilities in stratocumulus-topped boundary layers (STBL). The RCB is retrieved using a radar-lidar algorithm. The STBL turbulent structure is characterized using the Doppler lidar and radar observations. The profiling radar/lidar/radiometer observations are used to describe the cloud fraction and morphology. Finally, surface-based aerosol number concentration measurements are used to investigate the connection between the boundary layer turbulence, cloud morphology and aerosol loading. Preliminary correlative relationships between the aforementioned variables will be shown.

  16. DNS of stratified spatially-developing turbulent thermal boundary layers

    NASA Astrophysics Data System (ADS)

    Araya, Guillermo; Castillo, Luciano; Jansen, Kenneth

    2012-11-01

    Direct numerical simulations (DNS) of spatially-developing turbulent thermal boundary layers under stratification are performed. It is well known that the transport phenomena of the flow is significantly affected by buoyancy, particularly in urban environments where stable and unstable atmospheric boundary layers are encountered. In the present investigation, the Dynamic Multi-scale approach by Araya et al. (JFM, 670, 2011) for turbulent inflow generation is extended to thermally stratified boundary layers. Furthermore, the proposed Dynamic Multi-scale approach is based on the original rescaling-recycling method by Lund et al. (1998). The two major improvements are: (i) the utilization of two different scaling laws in the inner and outer parts of the boundary layer to better absorb external conditions such as inlet Reynolds numbers, streamwise pressure gradients, buoyancy effects, etc., (ii) the implementation of a Dynamic approach to compute scaling parameters from the flow solution without the need of empirical correlations as in Lund et al. (1998). Numerical results are shown for ZPG flows at high momentum thickness Reynolds numbers (~ 3,000) and a comparison with experimental data is also carried out.

  17. Boundary Layer Theory. Part 1; Laminar Flows

    NASA Technical Reports Server (NTRS)

    Schlichting, H.

    1949-01-01

    The purpose of this presentation is to give you a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.

  18. Shockwave-boundary layer interference heating analysis.

    NASA Technical Reports Server (NTRS)

    Hung, F. T.; Barnett, D. O.

    1973-01-01

    Interference heating correlations have been developed based on existing wind tunnel test data taken with simple configurations such as wedge/flat plate and compression corner models. For turbulent flow, peak interference heating was first correlated with shock strength (pressure ratio across shock wave) and then as a function of Reynolds number. The peak interference Stanton number was found to exhibit the same Reynolds number and Prandtl number characteristics as the Stanton number variation for undisturbed flow over a flat plate. Similar correlations were developed for laminar flow. Results indicated that for laminar flow at higher Reynolds number, the impinging shockwave may act as a boundary layer trip and cause boundary layer transition resulting in high interference heating. The correlations derived in this study can be used to scale wind tunnel model test data to a full-scale space vehicle at supersonic or hypersonic flight conditions.

  19. Analytic prediction for planar turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Chen, Xi; She, Zhen-Su

    2016-11-01

    Analytic predictions of mean velocity profile (MVP) and streamwise ( x) development of related integral quantities are presented for flows in channel and turbulent boundary layer (TBL), based on a symmetry analysis of eddy length and total stress. Specific predictions include the relations for momentum Reynolds number ( Re θ) with friction Re τ and streamwise Re x : Re θ ≈ 3.27 Re τ, and Re x / Re θ = 4.94 [(ln Re θ + 1.88)2 + 1]; the streamwise development of the friction velocity u τ: U e / u τ ≈ 2.22ln Re x + 2.86 - 3.83ln(ln Re x ), and of the boundary layer thickness δ e : x/δ e ≈ 7.27ln Re x -5.18-12.52ln(ln Re x ), which are fully validated by recent reliable data.

  20. Boundary layer transition detection by luminescence imaging

    NASA Technical Reports Server (NTRS)

    Mclachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.

    1993-01-01

    In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.

  1. The boundary layer on compressor cascade blades

    NASA Technical Reports Server (NTRS)

    Deutsch, S.

    1981-01-01

    Some redesign of the cascade facility was necessary in order to incoporate the requirements of the LDA system into the design. Of particular importance was the intended use of a combination of suction upstream of the blade pack with diverging pack walls, as opposed to blade pack suction alone, for spanwise dimensionality control. An ARL blade was used to redo some tests using this arrangement. Preliminary testing and boundary layer measurements began on the double circular arc blades.

  2. Calculation of a separated turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Baldwin, B.; Hung, C. M.

    1976-01-01

    The properties of a Navier-Stokes solution of a shock-separated turbulent flow over a flat wall are investigated. Refinements of an algebraic relaxation turbulence model previously shown to be of value for the simulation of separated flows are presented. A simplified analysis applicable near an adiabatic wall is developed and used to help verify the accuracy of the numerical solution. Features of the time-dependent response of a turbulent boundary layer to shock impingement are presented.

  3. Boundary Layer Control for Hypersonic Airbreathing Vehicles

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.

    2004-01-01

    Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.

  4. Shock-boundary-layer interaction in flight

    NASA Technical Reports Server (NTRS)

    Bertelrud, Arild

    1989-01-01

    A brief survey is given on the study of transonic shock/boundary layer effects in flight. Then the possibility of alleviating the adverse shock effects through passive shock control is discussed. A Swedish flight experiment on a swept wing attack aircraft is used to demonstrate how it is possible to reduce the extent of separated flow and increase the drag-rise Mach number significantly using a moderate amount of perforation of the surface.

  5. Pressure gradient influence in turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Reuther, Nico; Kaehler, Christian J.

    2015-11-01

    Understanding wall-bounded turbulence is still an ongoing process. Although remarkable progress has been made in the last decades, many challenges still remain. Mean flow statistics are well understood in case of zero pressure gradient flows. However, almost all turbulent boundary layers in technical applications, such as aircrafts, are subjected to a streamwise pressure gradient. When subjecting turbulent boundary layers to adverse pressure gradients, significant changes in the statistical behavior of the near-wall flow have been observed in experimental studies conducted however the details dynamics and characteristics of these flows has not been fully resolved. The sensitivity to Reynolds number and the dependency on several parameters, including the dependence on the pressure gradient parameter, is still under debate and very little information exists about statistically averaged quantities such as the mean velocity profile or Reynolds stresses. In order to improve the understanding of wall-bounded turbulence, this work experimentally investigates turbulent boundary layer subjected to favorable and adverse pressure gradients by means of Particle Image Velocimetry over a wide range of Reynolds numbers, 4200

  6. Representation of Clear and Cloudy Boundary Layers in Climate Models. Chapter 14

    NASA Technical Reports Server (NTRS)

    Randall, D. A.; Shao, Q.; Branson, M.

    1997-01-01

    The atmospheric general circulation models which are being used as components of climate models rely on their boundary layer parameterizations to produce realistic simulations of the surface turbulent fluxes of sensible heat. moisture. and momentum: of the boundary-layer depth over which these fluxes converge: of boundary layer cloudiness: and of the interactions of the boundary layer with the deep convective clouds that grow upwards from it. Two current atmospheric general circulation models are used as examples to show how these requirements are being addressed: these are version 3 of the Community Climate Model. which has been developed at the U.S. National Center for Atmospheric Research. and the Colorado State University atmospheric general circulation model. The formulations and results of both models are discussed. Finally, areas for future research are suggested.

  7. The role of nonlinear critical layers in boundary layer transition

    NASA Technical Reports Server (NTRS)

    Goldstein, M.E.

    1995-01-01

    Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.

  8. Dynamics of lee waves on the boundary layer inversion

    NASA Astrophysics Data System (ADS)

    Sachsperger, Johannes; Serafin, Stefano; Grubišić, Vanda

    2016-04-01

    Lee waves are horizontally propagating non-hydrostatic internal gravity waves that may be generated when stratified flow is lifted over a mountain. Depending on the upstream conditions, two types of lee waves can be distinguished. First, resonant lee waves, which are often explored in the context of Scorer's theory of wave trapping in a two-layer atmosphere, where a discontinuity in the Scorer parameter - with evanescent conditions in the upper layer - gives rise to trapped waves. Second, interfacial lee waves, which may form along a density discontinuity, e.g. a temperature inversion, similar to surface waves on a free water surface. While resonant lee waves have been studied extensively, interfacial lee waves were only rarely discussed in meteorological literature so far. For example, observational studies as well as systematic studies on the wavelength dependencies still seem to be lacking. In this work, we modify Scorer's wave trapping theory by applying a boundary condition that accounts for a density jump between the two fluid layers. In this case, wave resonance is possible along the density discontinuity even if the lower layer is neutrally stratified. The resulting linear theory can be applied for instance to atmospheric boundary layer flows over complex terrain, where part of the mountain wave energy can be trapped along the inversion that caps the boundary layer. We validate this model with observations taken in the area of Vienna and highlight the lee wavelength dependence on the flow parameters by systematically varying the upstream conditions. Since interfacial waves have transcendental frequency dispersion relationships that cannot be solved analytically, we also discuss the implications of the shallow- and deep-water approximations on the wavelength of the resonant mode.

  9. Leaky waves in boundary layer flow

    NASA Astrophysics Data System (ADS)

    Pralits, Jan

    2005-11-01

    Linear stability analysis of boundary layer flow is traditionally performed by solving the Orr-Sommerfeld equation (OSE), either in a temporal or a spatial framework. The mode structure of the OSE is in both cases composed of a finite number of discrete modes which decay at infinity in the wall- normal direction y, and a continuous spectrum of propagating modes behaving as (±ik y) when y->∞, with real k. A peculiarity of this structure is that the number of discrete modes changes with the Reynolds number, Re. They indeed seem to disappear behind the continuous spectrum at certain Re. This phenomenon is here investigated by studying the response of the Blasius boundary layer forced instantaneously in space and time. Since the solution of the forced and homogeneous Laplace-transformed problem both depend on the free-stream boundary conditions, it is shown here that a suitable change of variables can remove the branch cut in the Laplace plane. As a result, integration of the inverse Laplace transform along the two sides of the branch cut, which gives rise to the continuous spectrum, can be replaced by a sum of residues corresponding to an additional set of discrete eigenvalues. These new modes grow at infinity in the y direction, and are analogous to the leaky waves found in the theory of optical waveguides, i.e. optical fibers, which are attenuated in the direction of the waveguide but grow unbounded in the direction perpendicular to it.

  10. Turbulence spectra of the FIRE stratocumulus-topped boundary layers

    NASA Technical Reports Server (NTRS)

    Young, G. S.; Nucciarone, J. J.; Albrecht, Bruce A.

    1990-01-01

    There are at least four physical phenomena which contribute to the FIRE boundary layer turbulence spectra: boundary layer spanning eddies resulting from buoyant and mechanical production of turbulent kinetic energy (the microscale subrange); inertial subrange turbulence which cascades this energy to smaller scales; quasi-two dimensional mesoscale variations; and gravity waves. The relative contributions of these four phenomena to the spectra depend on the altitude of observation and variable involved (vertical velocity, temperature and moisture spectra are discussed). The physical origins of these variations in relative contribution are discussed. As expected from the theory (Kaimal et al., 1976), mixed layer scaling of the spectra (i.e., nondimensionalizing wavelength by Z(sub i) and spectral density by Z(sub i) and the dissipation rates) is successful for the microscale subrange and inertial subrange but not for the mesoscale subrange. The most striking feature of the normalized vertical velocity spectra is the lack of any significant mesoscale contribution. The spectral peak results from buoyant and mechanical production on scales similar to the boundary layer depth. The decrease in spectral density at larger scales results from the suppression of vertical velocity perturbations with large horizontal scales by the shallowness of the atmosphere. The spectral density also decreases towards smaller scales following the well known inertial subrange slope. There is a significant variation in the shape of the normalized spectra with height.

  11. Acoustic radar investigations of boundary layer phenomena

    NASA Technical Reports Server (NTRS)

    Marks, J. R.

    1974-01-01

    A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.

  12. Flow Quality and Boundary Layer Transition

    NASA Technical Reports Server (NTRS)

    Watmuff, Jonathan H; Tobak, M.; Davis, Sanford S. (Technical Monitor)

    1997-01-01

    The widely held view is that transition to turbulence in the Blasius boundary layer occurs via amplification and eventual nonlinear breakdown of initially small amplitude instabilities i.e. Tollmien-Schlichting (TS) waves. However this scenario is only observed for low amplitude free-stream turbulence levels, i.e. u/U < 0.1%. Bypass of linear TS instability mechanism occurs for higher EST levels, yet considerable differences exist between the few experiments carefully designed to assess the effect of EST on transition. The consensus is that EST leads to longitudinal streaks that form near the leading edge in the boundary layer . These streaks appeal to be regions of concentrated streamwise vorticity and they are often referred to as Klebanoff modes. The importance of mean flow free-stream nonuniformity (FSN) is not as widely appreciated as EST for characterizing wind tunnel flow quality. Here it is shown that, although the v like generated by a d=50micron wire located upstream of the contraction (Re(sub d)=6.6, x/d=45,000) is immeasurably small by the time it interacts with the leading edge in the test section, it is responsible for generation of a pair of weak streamwise vortices in the boundary layer downstream. The characteristics of these wake-induced vortices and their effect on TS waves are demonstrated. Small remnant FSN variations are also shown to exist downstream of a turbulence grid. The question arises Are the adverse effects introduced by the turbulence grid caused by FST or by small remnant FSN variations?

  13. Boundary-Layer-Ingesting Inlet Flow Control

    NASA Technical Reports Server (NTRS)

    Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

    2006-01-01

    This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

  14. Boundary-Layer-Ingesting Inlet Flow Control

    NASA Technical Reports Server (NTRS)

    Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

    2006-01-01

    This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

  15. Using a Modified Soil-Plant-Atmosphere Scheme (MSPAS) to study the sensitivity of land surface and boundary layer processes to soil and vegetation conditions

    NASA Astrophysics Data System (ADS)

    Liu, Shuhua; Yue, Xu; Liu, Huizhi; Hu, Fei

    2004-10-01

    A series of sensitivity tests are performed to test the stability and sensibility of the Modified Soil-Plant-Atmosphere Scheme (MSPAS), which was wholly introduced in a previous paper. The numerical simulation results from the experiments show good agreement with physical reality. Besides, some of the results are illuminating. Together with the first paper, it is concluded that MSPAS is a simple but effective model, and it is practically valuable in the research work of desertification control and reforestation in China.

  16. Statistical analysis of turbulence data from the NASA Marshall Space Flight Center atmospheric boundary layer tower array facility. [statistical correlations for aircraft design

    NASA Technical Reports Server (NTRS)

    Frost, W.; Lin, M. C.

    1983-01-01

    Statistical properties of atmospheric turbulence near the Earth's surface are presented. Emphasis is placed on the probability density distribution two point spatial correlation, length scale, and two point and single point spectrum. Comparison of the data with isotropic homogeneous models is made. In general, agreement with the models is poor. For the design of aircraft during operations in the lower levels associated with approach, takeoff, and terrain following, it appears necessary to improve existing models or develop new nonisotropic turbulence models.

  17. Boundary-layer Transition at Supersonic Speeds

    NASA Technical Reports Server (NTRS)

    Low, George M

    1956-01-01

    Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.

  18. Radiative transfer in a polluted urban planetary boundary layer

    NASA Technical Reports Server (NTRS)

    Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

    1977-01-01

    Radiative transfer in a polluted urban atmosphere is studied using a dynamic model. The diurnal nature of radiative transfer for summer conditions is simulated for an urban area 40 km in extent and the effects of various parameters arising in the problem are investigated. The results of numerical computations show that air pollution has the potential of playing a major role in the radiative regime of the urban area. Absorption of solar energy by aerosols in realistic models of urban atmosphere are of the same order of magnitude as that due to water vapor. The predicted effect of the air pollution aerosol in the city is to warm the earth-atmosphere system, and the net effect of gaseous pollutant is to warm the surface and cool the planetary boundary layer, particularly near the top.

  19. Measurements of a separating turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Simpson, R. L.; Chew, Y. T.; Shivaprasad, B. G.

    1980-04-01

    The directionally sensitive laser anemometer now provides the ability to accurately measure instantaneous flow direction and magnitude. The experimental results are concerned with a nominally two dimensional separating turbulent boundary layer for an airfoil type flow in which the flow was accelerated and then decelerated until separation. Upstream of separation single and cross wire hot wire anemometer measurements are also presented. Measurements obtained in the separated zone with a directionally sensitive laser anemometer system are presented. Results lead to significant conclusions about the nature of the separated flow when the thickness of the backflow region is small as compared with the shear laer thickness. The backflow is controlled by the large scale outer region flow. The small mean backflow does not come from far downstream, but appears to be supplied intermittently by large scale structures as they pass through the separated flow. Downstream of fully developed separation, the mean backflow appears to be divided into three layers.

  20. Direct radiative forcing and atmospheric absorption by boundary layer aerosols in the southeastern US: model estimates on the basis of new observations

    NASA Astrophysics Data System (ADS)

    Yu, Shaocai; Zender, Charles S.; Saxena, V. K.

    In an effort to reduce uncertainties in the quantification of aerosol direct radiative forcing (ADRF) in the southeastern United States (US), a field column experiment was conducted to measure aerosol radiative properties and effects at Mt. Mitchell, North Carolina, and at an adjacent valley site. The experimental period was from June 1995 to mid-December 1995. The aerosol optical properties (single scattering albedo and asymmetry factor) needed to compute ADRF were obtained on the basis of a procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, aerosol optical depth, and diffuse-to-direct solar irradiance ratio. The regional values of ADRF at the surface and top of atmosphere (TOA), and atmospheric aerosol absorption are derived using the obtained aerosol optical properties as inputs to the column radiation model (CRM) of the community climate model (CCM3). The cloud-free instantaneous TOA ADRFs for highly polluted (HP), marine (M) and continental (C) air masses range from 20.3 to -24.8, 1.3 to -10.4, and 1.9 to -13.4 W m -2, respectively. The mean cloud-free 24-h ADRFs at the TOA (at the surface) for HP, M, and C air masses are estimated to be -8±4 (-33±16), -7±4 (-13±8), and -0.14±0.05 (-8±3) W m -2, respectively. On the assumption that the fractional coverage of clouds is 0.61, the annual mean ADRFs at the TOA and the surface are -2±1, and -7±2 W m -2, respectively. This also implies that aerosols currently heat the atmosphere over the southeastern US by 5±3 W m -2 on annual timescales due to the aerosol absorption in the troposphere.

  1. Are atmospheric surface layer flows ergodic?

    NASA Astrophysics Data System (ADS)

    Higgins, Chad W.; Katul, Gabriel G.; Froidevaux, Martin; Simeonov, Valentin; Parlange, Marc B.

    2013-06-01

    The transposition of atmospheric turbulence statistics from the time domain, as conventionally sampled in field experiments, is explained by the so-called ergodic hypothesis. In micrometeorology, this hypothesis assumes that the time average of a measured flow variable represents an ensemble of independent realizations from similar meteorological states and boundary conditions. That is, the averaging duration must be sufficiently long to include a large number of independent realizations of the sampled flow variable so as to represent the ensemble. While the validity of the ergodic hypothesis for turbulence has been confirmed in laboratory experiments, and numerical simulations for idealized conditions, evidence for its validity in the atmospheric surface layer (ASL), especially for nonideal conditions, continues to defy experimental efforts. There is some urgency to make progress on this problem given the proliferation of tall tower scalar concentration networks aimed at constraining climate models yet are impacted by nonideal conditions at the land surface. Recent advancements in water vapor concentration lidar measurements that simultaneously sample spatial and temporal series in the ASL are used to investigate the validity of the ergodic hypothesis for the first time. It is shown that ergodicity is valid in a strict sense above uniform surfaces away from abrupt surface transitions. Surprisingly, ergodicity may be used to infer the ensemble concentration statistics of a composite grass-lake system using only water vapor concentration measurements collected above the sharp transition delineating the lake from the grass surface.

  2. Turbulent Plasmaspheric Boundary Layer: Observables and Consequences

    NASA Astrophysics Data System (ADS)

    Mishin, Evgeny

    2014-10-01

    In situ satellite observations reveal strong lower hybrid/fast magnetosonic turbulence and broadband hiss-like VLF waves in the substorm subauroral geospace at and earthward of the electron plasmasheet boundary. These coincide with subauroral ion drifts/polarization streams (SAID/SAPS) in the plasmasphere and topside ionosphere. SAID/SAPS appear in ~10 min after the substorm onset consistent with the fast propagation of substorm injection fronts. The SAID channel follows the dispersionless cutoff of the energetic electron flux at the plasmapause. This indicates that the cold plasma maintains charge neutrality within the channel, thereby short-circuiting the injected plasma jet (injection fronts over the plasmasphere. Plasma turbulence leads to the circuit resistivity and magnetic diffusion as well as significant electron heating and acceleration. As a result, a turbulent boundary layer forms between the inner edge of the electron plasmasheet and plasmasphere. The SAID/SAPS-related VLF emissions appear to constitute a distinctive subset of substorm/storm-related VLF activity in the region co-located with freshly injected energetic ions inside the plasmasphere. Significant pitch-angle diffusion coefficients suggest that substorm SAID/SAPS-related VLF waves could be responsible for the alteration of the outer radiation belt boundary during (sub)storms. Supported by the Air Force Office of Scientific Research.

  3. Boundary Layer Transition Flight Experiment Overview

    NASA Technical Reports Server (NTRS)

    Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.

    2011-01-01

    In support of the Boundary Layer Transition Flight Experiment (BLT FE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for STS-119, STS-128, STS-131 and STS-133 as well as Space Shuttle Endeavour for STS-134. Additional instrumentation was installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLT FE Project with emphasis on the STS-131 and STS-133 results. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that empirically correlated predictions for boundary layer transition onset time closely match the flight data, while predicted surface temperatures were significantly higher than observed flight temperatures. A thermocouple anomaly observed on a number of the missions is discussed as are a number of the mitigation actions that will be taken on the final flight, STS-134, including potential alterations of the flight trajectory and changes to the flight instrumentation.

  4. Soot profiles in boundary-layer flames

    SciTech Connect

    Beier, R.A.; Pagni, P.J.

    1981-12-01

    Carbon particulate volume fractions and approximate particle size distributions are measured in a free laminar combusting boundary layer for liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, toluene) and polymethylmethacrylate (PMMA). A multiwavelength laser transmission technique determines a most probable radius and the total particle concentration, which are two parameters in an assumed form for the size distribution. In the combusting boundary layer, a sooting region exists between the pyrolyzing fuel surface and the flame zone. The liquid fuel soot volume fractions, f/sub v/, range from f/sub v/ approx. 10/sup -7/ for n-heptane, a paraffin, to f/sub v approx. 10/sup -5/ for toluene, an aromatic. The PMMA volume fractions, f/sub v/ approx. 5 X 10/sup -7/, are approximately the same as the values previously reported for pool fires. The soot volume fractions increase with height; convection of carbon particles downstream widens the soot region with height. For all fuels tested, the most probable radius is between 20 nm and 50 nm, and it changes only slightly with height and distance from the fuel surface.

  5. Halogen chemistry in the trosopheric boundary layer

    NASA Astrophysics Data System (ADS)

    Plane, John M. C.; Mahajan, Anoop; Oetjen, Hilke

    Iodine and bromine chemistry can affect the lower troposphere in several important ways: (1), change the oxidizing capacity by destroying ozone and affecting the hydroxyl radical concentration; (2), react efficiently with dimethyl sulphide (in the marine boundary layer) and mercury (in the polar regions); and (3), form ultra-fine particles (iodine oxides are highly condensable), which may contribute to cloud condensation nuclei and hence affect climate. This paper will report measurements of IO, BrO, OIO and I2 , made by the technique of differential optical absorption spectroscopy (DOAS), in several contrasting environments: equatorial clean mid-ocean (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar boundary layer (Halley Bay, Antarctica and Hudson Bay, Canada). Both IO and BrO are observed in all these locations at concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. The concentrations of IO in coastal Antarctica, and coastlines rich in certain species of macro-algae, are large enough (> 10 pptv) to promote ultra-fine particle formation. Recently, the first satellite measurements of IO, using the SCIAMACHY instrument on ENVISAT, have been reported by two groups; their results will be compared with the ground-based measurements.

  6. X-33 Hypersonic Boundary Layer Transition

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II

    1999-01-01

    Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.

  7. Turbulent boundary layer over a chine.

    NASA Astrophysics Data System (ADS)

    Panchapakesan, N. R.; Joubert, P. N.

    1999-11-01

    The flow over an edge aligned with the streamwise direction is studied as a representative of the turbulent boundary layers developing over hard chines found on the hulls of ships and catamarans. We present results of a traditional experimental investigation of this geometry in a wind tunnel with pitot tubes and hot-wires. The chine model consisted of two surfaces made of varnished fibre boards with leading edges of airfoil sections and a 90 degree corner. The boundary layer was tripped with wires close to the leading edge. The model was housed in a test section of length 6.5 m in a closed circuit wind tunnel. The experiments were conducted at a unit Reynolds number of 680,000 /m corresponding to a nominal free stream velocity of 10 m/s. The mean velocity field and the associated integral parameters obtained with pitot tube measurements are presented for different streamwise locations from 0.2 to 4.7 m from the trip wire. The flow at the two farthest locations were also studied with single and 'x' hot-wires. The secondary mean flow and the turbulence field in the corner region are described with these measurements.

  8. Sound Radiation from a Turbulent Boundary Layer

    NASA Technical Reports Server (NTRS)

    Laufer, J.

    1961-01-01

    If the restriction of incompressibility in the turbulence problem is relaxed, the phenomenon of energy radiation in the form of sound from the turbulent zone arises. In order to calculate this radiated energy, it is shown that new statistical quantities, such as time-space correlation tensors, have to be known within the turbulent zone in addition to the conventional quantities. For the particular case of the turbulent boundary layer, indications are that the intensity of radiation becomes significant only in supersonic flows. Under these conditions, the recent work of Phillips is examined together with some experimental findings of the author. It is shown that the qualitative features of the radiation field (intensity, directionality) as predicted by the theory are consistent with the measurements; however, even for the highest Mach number flow, some of the assumptions of the asymptotic theory are not yet satisfied in the experiments. Finally, the question of turbulence damping due to radiation is discussed, with the result that in the Mach number range covered by the experiments, the energy lost from the boundary layer due to radiation is a small percentage of the work done by the wall shearing stresses.

  9. Performance and boundary-layer evaluation of a sonic inlet

    NASA Technical Reports Server (NTRS)

    Schmidt, J. F.; Ruggeri, R. S.

    1976-01-01

    Tests were conducted to determine the boundary layer characteristics and aerodynamic performance of a radial vane sonic inlet with a length/diameter ratio of 1 for several vane configurations. The sonic inlet was designed with a slight wavy wall type of diffuser geometry, which permits operation at high inlet Mach numbers (sufficiently high for good noise suppression) without boundary layer flow separation and with good total pressure recovery. A new method for evaluating the turbulent boundary layer was developed to separate the boundary layer from the inviscid core flow, which is characterized by a total pressure variation from hub to tip, and to determine the experimental boundary layer parameters.

  10. The Entrainment Interface Layer of Stratocumulus-topped Boundary Layers

    NASA Astrophysics Data System (ADS)

    Krueger, S.; Hill, S.

    2010-09-01

    The entrainment interface layer (EIL) is the layer between cloud top and the free atmosphere. It contains mixtures of air from the cloud layer and the free atmosphere. In addition to turbulent mixing, phase changes and radiative heating or ccoling also affect the thermodynamic properties of air in the EIL. Eventually, air from the EIL is entrained into the cloud layer. How do processes in the EIL affect the entrainment rate? What is the structure of the EIL? Is cloud-top an interface (a region of high gradients), or simply an iso-surface? We are using airborne measuurements taken in the EIL during POST (Physics of Stratocumulus Top), which took place during July and August 2008 near Monterey, California, USA, to address these questions. High-rate measurements of temperature and liquid water content made just 0.5 m apart allow us to perform a high-resolution analysis of a conserved variable (liquid water potential temperature). When combined with lower-rate measurements of water vapor, they also allow us to perform a mixture fraction analysis following vanZanten and Duynkerke (2002).

  11. Bypass transition in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Vandervegt, J. J.

    1992-01-01

    Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar

  12. Notes on an Internal Boundary-Layer Height Formula

    NASA Astrophysics Data System (ADS)

    Savelyev, Sergiya.; Taylor, Petera.

    The derivation of the Panofsky-Dutton internal boundary-layer(IBL) height formula has been revisited. We propose that the upwindroughness length (rather than downwind) should be used in theformula and that a turbulent vertical velocity (w) ratherthan the surface friction velocity (u*) should be considered asthe appropriate scaling for the rate of propagation ofdisturbances into the turbulent flow. A published set ofwind-tunnel and atmospheric data for neutral stratification hasbeen used to investigate the influence of the magnitude ofroughness change on the IBL height.

  13. Review of Orbiter Flight Boundary Layer Transition Data

    NASA Technical Reports Server (NTRS)

    Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.

    2006-01-01

    In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.

  14. A Parameterization of Intermittent Turbulence in the Stable Boundary Layer

    SciTech Connect

    Lundquist, J K; Nitao, E N; Loosmore, G A

    2003-08-01

    This model explores the interaction between a cooling vegetated surface and the lower atmosphere. Neglecting any possibility of intermittence generated from the top of the stable boundary layer, the frequency of intermittency can be defined as a function of the three input quantities--pressure gradient force, cloud cover fraction, and boundary layer height. It is not clear if the amplitude of the intermittency and the time to reach a quasi-steady state can also be described as a function of the inputs. In addition, time-dependent inputs have an effect on the overall intermittency. Fluctuations in the pressure gradient force have the most influence in decreasing the periods while varying cloud cover fraction decreases the amplitude of the intermittence. It is unclear whether the transition time is affected by the fluctuating inputs. To gauge the sufficiency of this model, the results must be compared to experimental studies and models that include the forcing at the top of the stable boundary layer.

  15. Cloud-Scale Numerical Modeling of the Arctic Boundary Layer

    NASA Technical Reports Server (NTRS)

    Krueger, Steven K.

    1998-01-01

    The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate models (GCMs) result in large differences between the Arctic, and global, climates simulated by different models. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary layer clouds must be accurately represented in climate models to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary layer clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary layer clouds in GCMs.

  16. Using UAV's to Measure the Urban Boundary Layer

    NASA Astrophysics Data System (ADS)

    Jacob, R. L.; Sankaran, R.; Beckman, P. H.

    2015-12-01

    The urban boundary layer is one of the most poorly studied regions of the atmospheric boundary layer. Since a majority of the world's population now lives in urban areas, it is becoming a more important region to measure and model. The combination of relatively low-cost unmanned aerial vehicles and low-cost sensors can together provide a new instrument for measuring urban and other boundary layers. We have mounted a new sensor and compute platform called Waggle on an off-the-shelf XR8 octo-copter from 3DRobotics. Waggle consists of multiple sensors for measuring pressure, temperature and humidity as well as trace gases such as carbon monoxide, nitrogen dioxide, sulfur dioxide and ozone. A single board computer running Linux included in Waggle on the UAV allows in-situ processing and data storage. Communication of the data is through WiFi or 3G and the Waggle software can save the data in case communication is lost during flight. The flight pattern is a deliberately simple vertical ascent and descent over a fixed location to provide vertical profiles and so flights can be confined to urban parks, industrial areas or the footprint of a single rooftop. We will present results from test flights in urban and rural areas in and around Chicago.

  17. On the Improvement of Satellite Temperature Retrievals by Means of Boundary Layer Models

    NASA Technical Reports Server (NTRS)

    Boers, R.

    1985-01-01

    The improvement of the accuracy of the satellite temperature retrievals close to the Earth's surface by boundary layer models was determined. The simplest type of boundary layer models that only consider time changes in the mean boundary layer quantities such as equivalent potential temperature and specific humidity, but neglect the details of the turbulent structure in the interior of the layer were used. They can be run with relatively few externally specified parameters: surface wind speed and divergence rate. Model verifications studies show that under certain conditions the mean atmospheric structure can be simulated very well.

  18. Comparison of Atmospheric Column Optical Depth Measurements for Urban Reno, NV with Three Different Sun Photometers and In Situ Measurements Combined with Boundary Layer Height Estimation

    NASA Astrophysics Data System (ADS)

    Loria Salazar, S. M.; Arnott, W. P.; Moosmuller, H.; Sumlin, B.; Karr, D.

    2011-12-01

    Reno, Nevada, USA is located in a mountain valley often characterized by very dry conditions, clear sky and red sunsets during the summer season, with rare incursions of monsoonal moisture. This city is subject to moderately strong nocturnal inversions nearly every day in summer. Urban aerosols, wind blown dust, as well as occasional biomass burning smoke from natural and non-natural fires all contribute to the optical depth. Because of its geographical position, drastic changes in weather conditions and variations in aerosol optical properties make Reno an excellent location for evaluating measurements of aerosol optical depth in order to determine particulate air pollution concentration as well as to provide input for models of atmospheric radiation transfer and evaluation of satellite-based aerosol optical sensing measurements. Aerosol optical depth can be calculated by in situ photoacoustic measurements of aerosol light absorption and reciprocal nephelometer scattering coefficients and estimation of aerosol mixing height. LED-based hand-held sun photometers are commonly used as inexpensive instruments for informal networks. However, the LED emission wavelength maximum and bandwidth are higher and narrower than the LED reception wavelength spectrum, necessitating empirical determination of an equivalent wavelength. The manually operated spectrometer and Cimel sun photometer measurements provide the most accurate and precise column aerosol optical depth. This paper makes a comparison between these four instruments for measurements obtained during the summer and fall seasons in order to study how the total and aerosol optical depth change during dry and moist conditions. Ångström exponents of extinction and absorption are also analyzed to provide insight on aerosol size distribution and composition, respectively.

  19. Assessment of Sea-Air Fluxes of Methane from the East Siberian Arctic Shelf Based on Multi-Year High-Precision Observations in the Atmospheric Boundary Layer and Seawater

    NASA Astrophysics Data System (ADS)

    Salyuk, A.; Semiletov, I. P.; Repina, I.; Chernykh, D.; Kosmach, D.; Shakhova, N. E.

    2015-12-01

    The latitude specific monthly mean (LSMM) methane (CH4) mixing ratio in the Arctic region atmospheric boundary layer (ABL) is established at 1.85 ppm (monitoring station at Barrow, Alaska, USA). This LSMM is about 10% higher than in Antarctica and about 5-7% higher than in the mid-latitudes, where the majority of anthropogenic activity occurs. So far, there is no reasonable explanation for the atmospheric CH4 maximum above the Arctic and no models have succeeded in satisfactorily reproducing the inter-polar gradient, due to the assumption that there are no Arctic region CH4 sources sufficient to serve year-round to maintain the existing maximum. The East Siberian Arctic Shelf (ESAS), from which extensive CH4 release was recently reported, has never been considered to be an atmospheric source of CH4, because no knowledge existed about this area until very recently. One focus of our multi-year ESAS investigations was to collect a comprehensive data set of continuous ABL CH4 mixing ratio measurements along with continuous measurements of dissolved CH4 in the surface water. When collecting the data set, we aimed to assess CH4 fluxes by using top-down and bottom-up approaches. Achieving representative spatial coverage of the study area with high-resolution, high-accuracy measurements was our priority. We collected data from 2006-2012 with a high-accuracy fast CH4 analyzer; two sonic anemometers measured the 3D wind vector and sonic temperature; a meteorological station measured wind speed and direction, moisture, and temperature; and an open path infrared gas analyzer measured H2O and CO2. Other instruments included a pressure transducer and a motion package that measured 6 components of ship's motion and also acceleration, magnetic field, and position. In 2011 and 2012 we performed such measurements in the outer ESAS seepage area. Data were synchronized in time and space to demonstrate correspondence of increased atmospheric CH4 levels (up to 3.2 ppm) to observed

  20. Fullerenes in the cretaceous-tertiary boundary layer

    SciTech Connect

    Heymann, D.; Chibante, L.P.F.; Smalley, R.E. ); Brooks, R.R. ); Wolbach, W.S. )

    1994-07-29

    High-pressure liquid chromatography with ultraviolet-visible spectral analysis of toluene extracts of samples from two Cretaceous-Tertiary (K-T) boundary sites in New Zealand has revealed the presence of C[sub 60] at concentrations of 0.1 to 0.2 parts per million of the associated soot. This technique verified also that fullerenes are produced in similar amounts in the soots of common flames under ambient atmospheric conditions. Therefore, the C[sub 60] in the K-T boundary layer may have originated in the extensive wildfires that were associated with the cataclysmic impact event that terminated the Mezozoic era about 65 million years ago.

  1. Atmospheric HCH concentrations over the Marine Boundary Layer from Shanghai, China to the Arctic Ocean: role of human activity and climate change.

    PubMed

    Wu, Xiaoguo; Lam, James C W; Xia, Chonghuan; Kang, Hui; Sun, Liguang; Xie, Zhouqing; Lam, Paul K S

    2010-11-15

    From July to September 2008, air samples were collected aboard the research expedition icebreaker XueLong (Snow Dragon) as part of the 2008 Chinese Arctic Research Expedition Program. Hexachlorocyclohexane (HCH) concentrations were analyzed in all of the samples. The average concentrations (± standard deviation) over the entire period were 33 ± 16, 5.4 ± 3.0, and 13 ± 7.5 pg m⁻³ for α-, β- and γ-HCH, respectively. Compared to previous studies in the same areas, total HCH (ΣHCH, the sum of α-, β-, and γ-HCH) levels declined by more than 10 × compared to those observed in the 1990s, but were approximately 4 × higher than those measured by the 2003 China Arctic Research Expedition, suggesting the increase of atmospheric ΣHCH recently. Because of the continuing use of lindane, ratios of α/γ-HCH showed an obvious decrease in North Pacific and Arctic region compared with those for 2003 Chinese Arctic Research Expedition. In Arctic, the level of α-HCH was found to be linked to sea ice distribution. Geographically, the average concentration of α-HCH in air samples from the Chukchi and Beaufort Seas, neither of which contain sea ice, was 23 ± 4.4 pg m⁻³, while samples from the area covered by seasonal ice (∼75°N to ∼83°N), the so-called "floating sea ice region", contained the highest average levels of α-HCH at 48 ± 12 pg m⁻³, likely due to emission from sea ice and strong air-sea exchange. The lowest concentrations of α-HCH were observed in the pack ice region in the high Arctic covered by multiyear sea ice (∼83°N to ∼86°N). This phenomenon implies that the re-emission of HCH trapped in ice sheets and Arctic Ocean may accelerate during the summer as ice coverage in the Arctic Ocean decreases in response to global climate change.

  2. Effects of shock on the stability of hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Chang, Chau-Lyan; Malik, Mujeeb R.; Hussaini, M. Yousuff

    1990-01-01

    A set of linearized shock boundary conditions is derived, which is then imposed at the shock to account for the interaction of the shock wave with the boundary/shock layer instability wave; these boundary conditions are used to study the effect of shock on hypersonic boundary layer stability under the assumption of quasi-parallel flow. The result show that the shock has little effect on the boundary layer instability (subsonic first and second mode disturbances) when the shock is located outside the boundary layer edge. When the shock is located near the boundary layer edge, it exerts a stabilizing influence on the first and second modes. The shock also induces unstable supersonic modes with oscillatory structure in the shock layer, but these modes grow slower than the subsonic modes.

  3. Geometric invariance of compressible turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Bi, Wei-Tao; Wu, Bin; She, Zhen-Su; Hussain, Fazle

    2015-11-01

    A symmetry based approach is applied to analyze the mean velocity and temperature fields of compressible, flat plate turbulent boundary layers (CTBL). A Reynolds stress length scale and a turbulent heat flux length scale are identified to possess the same defect scaling law in the CTBL bulk, which is solely owing to the constraint of the wall to the geometry of the wall-attached eddies, but invariant to compressibility and wall heat transfer. This invariance is called the geometric invariance of CTBL eddies and is likely the origin of the Mach number invariance of Morkovin's hypothesis, as well as the similarity of energy and momentum transports. A closure for the turbulent transport by using the invariant lengths is attainted to predict the mean velocity and temperature profiles in the CTBL bulk- superior to the van Driest transformation and the Reynolds analogy based relations for its sound physics and higher accuracy. Additionally, our approach offers a new understanding of turbulent Prandtl number.

  4. Some measurements in synthetic turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Savas, O.

    1980-01-01

    Synthetic turbulent boundary layers are examined which were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1,700,000. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft which displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e., the probability of observing turbulent flow at a particular point in space and time. The results are reported in x-t diagrams showing the evolution of various synthetic flows along the plate. The dimensionless celerity or phase velocity of the large eddies is found to be 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows which contained appreciable laminar regions. The large eddies shifted in formation to new positions, intermediate to their original ones, while preserving their hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, are used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study. The values recommended are: spanwise scale/thickness = 2.5, streamwise scale/thickness = 8.

  5. Acoustics of laminar boundary layers breakdown

    NASA Astrophysics Data System (ADS)

    Wang, Meng

    1994-12-01

    Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

  6. Soot and radiation in combusting boundary layers

    SciTech Connect

    Beier, R.A.

    1981-12-01

    In most fires thermal radiation is the dominant mode of heat transfer. Carbon particles within the fire are responsible for most of this emitted radiation and hence warrant quantification. As a first step toward understanding thermal radiation in full scale fires, an experimental and theoretical study is presented for a laminar combusting boundary layer. Carbon particulate volume fraction profiles and approximate particle size distributions are experimentally determined in both free and forced flow for several hydrocarbon fuels and PMMA (polymethylmethacrylate). A multiwavelength laser transmission technique determines a most probable radius and a total particle concentration which are two unknown parameters in an assumed Gauss size distribution. A sooting region is observed on the fuel rich side of the main reaction zone. For free flow, all the flames are in air, but the free stream ambient oxygen mass fraction is a variable in forced flow. To study the effects of radiation heat transfer, a model is developed for a laminar combusting boundary layer over a pyrolyzing fuel surface. An optically thin approximation simplifies the calculation of the radiant energy flux at the fuel surface. For the free flames in air, the liquid fuel soot volume fractions, f/sub v/, range from f/sub v/ approx. 10/sup -7/ for n-heptane, a paraffin, to f/sub v/ approx. 10/sup -7/ for toluene, an aromatic. The PMMA soot volume fractions, f/sub v/ approx. 5 x 10/sup -7/, are approximately the same as the values previously reported for pool fires. Soot volume fraction increases monotonically with ambient oxygen mass fraction in the forced flow flames. For all fuels tested, a most probable radius between 20 nm and 80 nm is obtained which varies only slightly with oxygen mass fraction, streamwise position, or distance normal to the fuel surface. The theoretical analysis yields nine dimensionless parameters, which control the mass flux rate at the pyrolyzing fuel surface.

  7. Acoustics of laminar boundary layers breakdown

    NASA Technical Reports Server (NTRS)

    Wang, Meng

    1994-01-01

    Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

  8. Two boundary layers in Titan's lower troposphere inferred from a climate model

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Lebonnois, Sébastien

    2012-02-01

    Saturn's moon Titan has a dense atmosphere, but its thermal structure is poorly known. Conflicting information has been gathered on the nature, extent and evolution of Titan's planetary boundary layer--the layer of the atmosphere that is influenced by the surface--from radio-occultation observations by the Voyager 1 spacecraft and the Cassini orbiter, measurements by the Huygens probe and by dune-spacing analyses. Specifically, initial analyses of the Huygens data suggested a boundary layer of 300m depth with no diurnal evolution, incompatible with alternative estimates of 2-3km (refs , , ). Here we use a three-dimensional general circulation model, albeit not explicitly simulating the methane cycle, to analyse the dynamics leading to the thermal profile of Titan's lowermost atmosphere. In our simulations, a convective boundary layer develops in the course of the day, rising to an altitude of 800m. In addition, a seasonal boundary of 2km depth is produced by the reversal of the Hadley cell at the equinox, with a dramatic impact on atmospheric circulation. We interpret fog that had been discovered at Titan's south pole earlier as boundary layer clouds. We conclude that Titan's troposphere is well structured, featuring two boundary layers that control wind patterns, dune spacing and cloud formation at low altitudes.

  9. Retrievals of boundary layer methane and isotope fractionation on Titan

    NASA Astrophysics Data System (ADS)

    Adamkovics, Mate; Lora, Juan M.; Mitchell, Jonathan L.

    2016-10-01

    The amount of methane in the boundary layer on Titan is an interesting diagnostic of whether or not it might be seeping out of the regolith. We know that kinetic fractionation of methane isotopes can be diagnostic of evaporation at the surface and condensation in the atmosphere. If a parcel is constrained to follow a moist adiabat while condensation occurs, we can predict the amount of fractionation that is expected (Ádámkovics & Mitchell, 2016). We will present our most recent efforts to measure boundary layer methane abundance and isotopic composition, which include our recently published Keck NIRSPAO observations from 17 July 2014 (Ádámkovics et al., 2016), as well as preliminary results from follow-up measurements made on 15 May 2016. Our measurements are tantalizingly close to being able to distinguish between different hydrological parameterizations of the polar regions in the Titan Atmospheric Model (Lora & Ádámkovics, 2016). We will discuss the systematic uncertainties that can be evaluated with the combination of these two datasets and the prospects for exceptionally high S/N observations via particularly deep integrations over multiple nights.

  10. Observations of Surface Energy Fluxes and Boundary-Layer Structure Over Heron Reef, Great Barrier Reef, Australia

    NASA Astrophysics Data System (ADS)

    MacKellar, Mellissa C.; McGowan, Hamish A.; Phinn, Stuart R.; Soderholm, Joshua S.

    2013-02-01

    Over warm, shallow coral reefs the surface radiation and energy fluxes differ from those of the open ocean and result in modification to the marine atmospheric boundary layer via the development of convective internal boundary layers. The complex interrelationships between the surface energy balance and boundary-layer characteristics influence local weather (wind, temperature, humidity) and hydrodynamics (water temperature and currents), as well as larger scale processes, including cloud field properties and precipitation. The nature of these inter-relationships has not been accurately described for coral reef environments. This study presents the first measurements of the surface energy balance, radiation budget and boundary layer thermodynamics made over a coral reef using an eddy-covariance system and radiosonde aerological profiling of the lower atmosphere. Results show that changes in surface properties and the associated energetics across the ocean-reef boundary resulted in modification to the marine atmospheric boundary layer during the Austral winter and summer. Internal convective boundary layers developed within the marine atmospheric boundary layer over the reef and were found to be deeper in the summer, yet more unstable during the winter when cold and drier flow from the mainland enhances heat and moisture fluxes to the atmosphere. A mixed layer was identified in the marine atmospheric boundary layer varying from 375 to 1,200 m above the surface, and was deeper during the summer, particularly under stable anticyclonic conditions. Significant cloud cover and at times rain resulted in the development of a stable stratified atmosphere over the reef. Our findings show that, for Heron Reef, a lagoonal platform reef, there was a horizontal discontinuity in surface energy fluxes across the ocean-reef boundary, which modified the marine atmospheric boundary layer.

  11. Improved Boundary Layer Depth Retrievals from MPLNET

    NASA Technical Reports Server (NTRS)

    Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette

    2013-01-01

    Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, MD since April 2001. However, because of issues with the operational PBL depth algorithm, the data is not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers, and in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System-version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by 410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they diered the most in the winter.

  12. Rapid cycling of reactive nitrogen in the marine boundary layer.

    PubMed

    Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L; Campos, Teresa; Weinheimer, Andrew; Hornbrook, Rebecca S; Apel, Eric C; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James N; Ortega, John; Knote, Christoph

    2016-04-28

    Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale. PMID:27064904

  13. Rapid cycling of reactive nitrogen in the marine boundary layer.

    PubMed

    Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L; Campos, Teresa; Weinheimer, Andrew; Hornbrook, Rebecca S; Apel, Eric C; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James N; Ortega, John; Knote, Christoph

    2016-04-28

    Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

  14. Rapid cycling of reactive nitrogen in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L.; Campos, Teresa; Weinheimer, Andrew; Hornbrook, Rebecca S.; Apel, Eric C.; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James N.; Ortega, John; Knote, Christoph

    2016-04-01

    Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A ‘renoxification’ process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth’s surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

  15. Planetary boundary layer response to surface temperature anomalies forcing

    NASA Astrophysics Data System (ADS)

    Perrot, Xavier; Lapeyre, Guillaume; Plougonven, Riwal

    2015-04-01

    Recent studies showed that strong sea surface temperature (SST) fronts, on the scale of the western boundary currents, strongly affect the planetary boundary layer (PBL) but also all the troposphere. This renewed the interest of air-sea interactions at oceanic meso-scales. Mainly two mechanisms are proposed in the literature, the first one (due to Wallace et al 1989) is based on the destabilization of the PBL above SST anomalies, the second one (Lindzen and Nigam 1987) is based on the pressure anomalies linked to the atmosphere temperature adjustment to the SST. These two mechanisms predict different responses of the PBL to the SST. We did numerical simulations with a meso-scale atmospheric model (WRF) with the same configuration as the one described in Lambert et al 2013. The model is forced by a SST anomaly which is first a zonally or meridionally constant field and secondly a field of meso-scale structures. Firstly we studied the influence of the initial wind strength on the PBL response for the two different types of SST anomalies. We showed that the dominant mechanism can change according to weak or strong wind and to the orientation of the SST anomaly. Secondly after considering a dry atmosphere we switched on the humidity in our configuration. We studied how it influences the PBL response and whether the mechanism driving the PBL response is still the same as in the dry case.

  16. Wind-tunnel simulation of thick turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Kornilov, V. I.; Boiko, A. V.

    2012-06-01

    An experimental study aimed at revealing the possibility of simulation, in a subsonic wind tunnel, of enhanced Reynolds numbers Re** via modeling a thick flat-plate boundary layer possessing the properties of a Clauser-equilibrium shear flow is reported. We show that turbulators prepared in the form of variable-height cylinders of height h and diameter d = 3 mm and installed in two rows along the normal to the streamlined wall offer rather an efficient means for modification of turbulent boundary layer in solving the problem. In the majority of cases, mean and fluctuating characteristics of the boundary layer exhibit values typical of naturally developing turbulent boundary layers at a distance of 530 cylinder diameters. The profiles of mean velocity with artificially enhanced boundary-layer thickness can be well approximated, in the law-of-the-wall variables, with the well-known distribution of velocities for canonical boundary layer.

  17. Simulating supercell thunderstorms in a convective boundary layer: Effects on storm and boundary layer properties

    NASA Astrophysics Data System (ADS)

    Nowotarski, Christopher J.

    Nearly all previous numerical simulations of supercell thunderstorms have neglected surface uxes of heat, moisture, and momentum as well as horizontal inhomogeneities in the near-storm environment from resulting dry boundary layer convection. This investigation uses coupled radiation and land-surface schemes within an idealized cloud model to identify the effects of organized boundary layer convection in the form of horizontal convective rolls (HCRs) on the strength, structure, and evolution of simulated supercell thunderstorms. The in uence of HCRs and the importance of their orientation relative to storm motion is tested by comparing simulations with a convective boundary layer (CBL) against those with a horizontally homogeneous base state having the same mean environment. The impact of anvil shading on the CBL is tested by comparing simulations with and without the effects of clouds in the radiative transfer scheme. The results of these simulations indicate that HCRs provide a potentially important source of environmental vertical vorticity in the sheared, near-storm boundary layer. These vorticity perturbations are amplified both beneath the main supercell updraft and along the trailing out ow boundary, leading to the formation of occasionally intense misovortices. HCRs perpendicular to storm motion are found to have a detrimental effect on the strength and persistence of the lowlevel mesocyclone, particularly during its initial development. Though the mean environment is less supportive of low-level rotation with a wind profile conducive to HCRs oriented parallel to storm motion, such HCRs are found to often enhance the low-level mesocyclone circulation. When anvil shading is included, stabilization results in generally weaker low-level mesocyclone circulation, regardless of HCR orientation. Moreover, HCRs diminish in the near-storm environment such that the effects of HCRs on the supercell are mitigated. HCRs are also shown to be a necessary condition for the

  18. Estimating convective boundary layer parameters for diffusion applications. Final report

    SciTech Connect

    Weil, J.

    1983-04-01

    Simple methods are presented for estimating those boundary layer parameters most important in controlling turbulence and diffusion within the convective boundary layer (CBL). These parameters include: surface heat flux, friction velocity, mean wind speed, and boundary layer height. Emphasis is on estimation methods requiring only routinely available data such as may exist at local airports. We focus on the CBL because the main diffusion application of interest is tall stacks, which generally produce their highest ground-level concentrations during convective conditions.

  19. Development of a laminar boundary layer behind a suction point

    NASA Technical Reports Server (NTRS)

    Wuest, Walter

    1952-01-01

    A theoretical investigation is made of the development of a laminar boundary layer behind a suction slot that is assumed to cut off part of the boundary layer without exerting any sink effect. The development, which is approximate, is based on the heat conduction equation. The heat conduction equation enters the analysis through a linearization of the Prandtl-Mises form of the boundary-layer equation.

  20. Self organized layering in the Earth's mantle, phase- and compositional boundary layers

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Dude, S.

    2012-04-01

    The thermal history of Earth an other planets, their chemical differentiation and reaction of the interior with the atmosphere was largely determined by convective processes. Convection does not always tend to homogenize the interior. Convection can rather establish structures and as such reservoirs which can stay intact for geological significant time. We employ. numerical models, ranging from simple 2D scenarios to fully 3D configurations with strongly temperature , pressure and compositionally dependent rheology , to explore the formation of such reservoirs. Layer formation plays a special role in the pattern formation process. . It will be shown that distinct convective layers can form as self-organized structures from non-layered states, without pre-existing density jumps., once effects of thermal - and compositional contributions to the density are taken into account. A stable compositional gradient, heated from below and/or cooled from above resembles one reasonable scenario for Earth-mantle after core formation. In this configuration a layered mantle structure emerges. the individual layers display different degrees of stability. Intermittent breakdown of individual layers leads to a strong episodicity in the thermal and chemical evolution. In a series of experiments we study the onset of plate tectonics in such a scenario by employing stress dependent rheologies We further investigate the effecfts of a pressure dependent thermal expansivity. Clearly, under these conditions even a small initial compositional density gradient strongly effects the dynamics We also investigate the scenario including a phase boundary and the combined effect of phase - and compositional boundaries on the dynamics .

  1. Characteristics of convective boundary layer over the Arabian sea region

    SciTech Connect

    Parasnis, S.S.

    1996-12-31

    The Convective Boundary Layer (CBL) over the oceanic regions plays an important role in regulating the transport of energy and moisture upward into the atmosphere from the surface. CBL structure over the Arabian sea region has been explored using the aerological soundings at two ships viz. SHIRSHOV (12.5{degrees}N, 68{degrees}E ) and OKEAN (14.5{degrees} N, 66{degrees} E) during MONSOON-77. Conserved variable analysis of the mean data sets obtained during the period of 29 June - 16 July, 1977 revealed salient features of the CBL over these regions. The vertical gradients of saturation point parameters viz. virtual potential temperature ({Theta}{sub v}), equivalent potential temperature ({Theta}{sub e}), saturated equivalent potential temperature ({Theta}{sub es}), saturation pressure deficit (P*) and the mixing ratio (q) were used to characterize the different sublayers such as subcloud layer, cloud layer and inversion/stable layer. The mean cloud base was around 950 hPa and the subcloud layer has nearly constant {Theta}{sub v}. The moist layer was associated with unstable {Theta}{sub es} with nearly constant value of P* ({approximately} -40 hPa). This cloud layer was capped by the stable (over OKEAN). The {Theta}{sub e} minimum over OKEAN was observed at 650 hPa (50 hPa above the CBL top) indicating that at some time the convection had reached deeper levels. The {Theta}{sub e} -q diagrams showed a characteristic mixing line up through the cloud and stable layer to the top of CBL. The low level stability analysis using the {Theta}{sub e} and {Theta}{sub es} profiles indicated conditions favorable for shallow convection over OKEAN and for deep convection over SHIRSHOV. The above characteristic features could be attributed to the prevailing weather conditions at OKEAN and SHIRSHOV. The results are discussed.

  2. Impact of nonlocal boundary-layer diffusion scheme on forecasts over Indian region

    NASA Astrophysics Data System (ADS)

    Sanjay, J.; Mukhopadhyay, P.; Singh, S. S.

    The results of incorporating a nonlocal boundary-layer diffusion scheme in a forecast model over Indian region are discussed. The simple formulation of atmospheric boundary layer height in the nonlocal diffusion scheme is examined in detail to understand how far the model simulated boundary layer height is realistic. Analyses of the temporal and spatial variability of the boundary height for three cases representing premonsoon, active monsoon and post monsoon conditions over Indian region show that it is comparable with the observational evidence. Further, for a case of active monsoon condition over Indian region, comparison of precipitation forecasts with the nonlocal scheme and the control local boundary-layer scheme clearly indicated that the model run with the nonlocal scheme is significantly more accurate in forecasting the intense precipitation locations.

  3. Boundary layer problem on a hyperbolic system arising from chemotaxis

    NASA Astrophysics Data System (ADS)

    Hou, Qianqian; Wang, Zhi-An; Zhao, Kun

    2016-11-01

    This paper is concerned with the boundary layer problem for a hyperbolic system transformed via a Cole-Hopf type transformation from a repulsive chemotaxis model with logarithmic sensitivity proposed in [23,34] modeling the biological movement of reinforced random walkers which deposit a non-diffusible (or slowly moving) signal that modifies the local environment for succeeding passages. By prescribing the Dirichlet boundary conditions to the transformed hyperbolic system in an interval (0 , 1), we show that the system has the boundary layer solutions as the chemical diffusion coefficient ε → 0, and further use the formal asymptotic analysis to show that the boundary layer thickness is ε 1 / 2. Our work justifies the boundary layer phenomenon that was numerically found in the recent work [25]. However we find that the original chemotaxis system does not possess boundary layer solutions when the results are reverted to the pre-transformed system.

  4. Secondary instabilities in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Ng, Lian; Erlebacher, Gordon

    1990-01-01

    Secondary instabilities are examined in compressible boundary layers at Mach numbers M(sub infinity) = 0, 0.8, 1.6, and 4.5. It is found that there is a broad-band of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M(sub infinity) is less than or equal to 1.6, fundamental resonance dominates at relatively high (2-d) primary disturbance amplitude, while subharmonic resonance is characterized by a low (2-d) primary amplitude. At M(sub infinity) = 4.5, the subharmonic instability which arises from the second mode disturbance is the strongest type of secondary instability. The influence of the inclination, theta, of the primary wave with respect to the mean flow direction on secondary instability is investigated at M(sub infinity) = 1.6 for small to moderate values of theta. It is found that the strongest fundamental instability occurs when the primary wave is inclined at 10 deg to the mean flow direction, although a 2-d primary mode yields the most amplified subharmonic. The subharmonic instability at a high value of theta (namely, theta = 45 deg) is also discussed. Finally, a subset of the secondary instability results are compared against direct numerical simulations.

  5. Effect of sound on boundary layer stability

    NASA Technical Reports Server (NTRS)

    Saric, William S.; Spencer, Shelly Anne

    1993-01-01

    Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic hear