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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. 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)

  3. The atmospheric boundary layer

    SciTech Connect

    Garratt, J.R.

    1992-01-01

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

  4. The Lowest Atmosphere: Atmospheric Boundary Layer Including Atmospheric Surface Layer.

    DTIC Science & Technology

    1996-04-01

    of motion of the atmosphere— "second order closure"—to such applications as the SCIPUFF -PC code for tracer dispersion (see Sykes, 1994). Now, for...Turbulence, Methuen, London, 2nd Ed., 1955. Sykes, R.I., "The SCIPUFF -PC Code," ARAP Draft Report, 1994. Tennekes, H., "The Atmospheric Boundary Layer

  5. The Martian Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Petrosyan, A.; Galperin, B.; Larsen, S. E.; Lewis, S. R.; Määttänen, A.; Read, P. L.; Renno, N.; Rogberg, L. P. H. T.; Savijärvi, H.; Siili, T.; Spiga, A.; Toigo, A.; Vázquez, L.

    2011-09-01

    The planetary boundary layer (PBL) represents the part of the atmosphere that is strongly influenced by the presence of the underlying surface and mediates the key interactions between the atmosphere and the surface. On Mars, this represents the lowest 10 km of the atmosphere during the daytime. This portion of the atmosphere is extremely important, both scientifically and operationally, because it is the region within which surface lander spacecraft must operate and also determines exchanges of heat, momentum, dust, water, and other tracers between surface and subsurface reservoirs and the free atmosphere. To date, this region of the atmosphere has been studied directly, by instrumented lander spacecraft, and from orbital remote sensing, though not to the extent that is necessary to fully constrain its character and behavior. Current data strongly suggest that as for the Earth's PBL, classical Monin-Obukhov similarity theory applies reasonably well to the Martian PBL under most conditions, though with some intriguing differences relating to the lower atmospheric density at the Martian surface and the likely greater role of direct radiative heating of the atmosphere within the PBL itself. Most of the modeling techniques used for the PBL on Earth are also being applied to the Martian PBL, including novel uses of very high resolution large eddy simulation methods. We conclude with those aspects of the PBL that require new measurements in order to constrain models and discuss the extent to which anticipated missions to Mars in the near future will fulfill these requirements.

  6. Soft turbulence in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Jánosi, Imre M.; Vattay, Gábor

    1993-08-01

    In this work we compare the spectral properties of the daily medium temperature fluctuations with the experimental results of the Chicago Group, in which the local temperature fluctuations were measured in a helium cell. The results suggest that the dynamics of the daily temperature fluctuations is determined by the soft turbulent state of the atmospheric boundary layer, which state is significantly different from low dimensional chaos.

  7. Stable Layers in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Mahalov, A.; Berman, N. S.; Fernando, H. J. S.; Yu, F.; Pardyjak, E.

    1998-11-01

    Field experimental studies on the establishment and growth of the nocturnal stable layer near the ground were made in January, 1998 using a tethered balloon at a site in Phoenix, Arizona. Days and nights with clear skies and light surface winds were of particular interest because small particle and carbon monoxide concentrations can be high during such times. Closest to the ground a shallow stable layer 20 meters deep with a buoyancy frequency (N) of 0.05 1/s rapidly developed before sundown. The height of this layer and N remained constant throughout the night. Above the 20-meter level, there was a transition layer which was also stable with N = 0.025 1/s. This transition layer grew throughout the night and reached 120 meters by dawn. Above the transition layer was a neutrally stable (residual) layer left over from the previous day. An unsteady layer 10 to 100 m thick with N = 0.025 1/s was also found at the top of the troposphere with the neutrally stable troposphere below and the stable stratosphere above. The growth and/or decay of turbulence in such stable layers will be discussed in light of recent theoretical developments.

  8. Helicity in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kurgansky, Michael; Koprov, Boris; Koprov, Victor; Chkhetiani, Otto

    2017-04-01

    An overview is presented of recent direct field measurements at the Tsimlyansk Scientific Station of A.M. Obukhov Institute of Atmospheric Physics in Moscow of turbulent helicity (and potential vorticity) using four acoustic anemometers positioned, within the atmospheric surface-adjacent boundary layer, in the vertices of a rectangular tetrahedron, with an approximate 5 m distance between the anemometers and a 5.5 m elevation of the tetrahedron base above the ground surface (Koprov, Koprov, Kurgansky and Chkhetiani. Izvestiya, Atmospheric and Oceanic Physics, 2015, Vol.51, 565-575). The same ideology was applied in a later field experiment in Tsimlyansk with the tetrahedron's size of 0.7 m and variable elevation over the ground from 3.5 to 25 m. It is illustrated with examples of the statistical distribution of instantaneous (both positive and negative) turbulent helicity values. A theory is proposed that explains the measured mean turbulent helicity sign, including the sign of contribution to helicity from the horizontal and vertical velocity & vorticity components, respectively, and the sign of helicity buoyant production term. By considering a superposition of the classic Ekman spiral solution and a jet-like wind profile that mimics a shallow breeze circulation over a non-uniformly heated Earth surface, a possible explanation is provided, why the measured mean turbulent helicity sign is negative. The pronounced breeze circulation over the Tsimlyansk polygon which is located nearby the Tsimlyansk Reservoir was, indeed, observed during the measurements period. Whereas, essentially positive helicity is injected into the boundary layer from the free atmosphere in the Northern Hemisphere.

  9. Convection Cells in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Fodor, Katherine; Mellado, Juan-Pedro

    2017-04-01

    In dry, shear-free convective boundary layers (CBLs), the turbulent flow of air is known to organise itself on large scales into coherent, cellular patterns, or superstructures, consisting of fast, narrow updraughts and slow, wide downdraughts which together form circulations. Superstructures act as transport mechanisms from the surface to the top of the boundary layer and vice-versa, as opposed to small-scale turbulence, which only modifies conditions locally. This suggests that a thorough investigation into superstructure properties may help us better understand transport across the atmospheric boundary layer as a whole. Whilst their existence has been noted, detailed studies into superstructures in the CBL have been scarce. By applying methods which are known to successfully isolate similar large-scale patterns in turbulent Rayleigh-Bénard convection, we can assess the efficacy of those detection techniques in the CBL. In addition, through non-dimensional analysis, we can systematically compare superstructures in various convective regimes. We use direct numerical simulation of four different cases for intercomparison: Rayleigh-Bénard convection (steady), Rayleigh-Bénard convection with an adiabatic top lid (quasi-steady), a stably-stratified CBL (quasi-steady) and a neutrally-stratified CBL (unsteady). The first two are non-penetrative and the latter two penetrative. We find that although superstructures clearly emerge from the time-mean flow in the non-penetrative cases, they become obscured by temporal averaging in the CBL. This is because a rigid lid acts to direct the flow into counter-rotating circulation cells whose axis of rotation remains stationary, whereas a boundary layer that grows in time and is able to entrain fluid from above causes the circulations to not only grow in vertical extent, but also to move horizontally and merge with neighbouring circulations. Spatial filtering is a useful comparative technique as it can be performed on boundary

  10. Nonstationary atmospheric boundary layer turbulence simulation

    NASA Technical Reports Server (NTRS)

    Fichtl, G. H.; Perlmutter, M.

    1974-01-01

    Report on a new and general technique for simulating atmospheric turbulence-like random processes which are statistically homogeneous along the horizontal and nonhomogeneous along the vertical. This technique is general in the sense that it can be used for a broad class of similar problems. Like the other presently available schemes, the techniques presented are based on the Dryden hypothesis and Taylor's frozen eddy hypothesis; however, they go a step further by utilizing certain self-similarity properties of the Dryden spectral density function which permits the development of height invariant filters. These filters are in turn used to generate vertically homogeneous (statistically) random processes from which turbulence at any specified level in the boundary layer can be simulated, thus facilitating the simulation of a nonstationary turbulence process along the flight path of an aircraft during take-off or landing.

  11. Turbulence in the Stable Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Fernando, Harindra; Kit, Eliezer; Conry, Patrick; Hocut, Christopher; Liberzon, Dan

    2016-11-01

    During the field campaigns of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program, fine-scale measurements of turbulence in the atmospheric boundary layer (ABL) were made using a novel sonic and hot-film anemometer dyad (a combo probe). A swath of scales, from large down to Kolmogorov scales, was covered. The hot-film was located on a gimbal within the sonic probe volume, and was automated to rotate in the horizontal plane to align with the mean flow measured by sonic. This procedure not only helped satisfy the requirement of hot-film alignment with the mean flow, but also allowed in-situ calibration of hot-films. This paper analyzes a period of nocturnal flow that was similar to an idealized stratified parallel shear flow. Some new phenomena were identified, which included the occurrence of strong bursts in the velocity records indicative of turbulence generation at finer scales that are not captured by conventional sonic anemometers. The spectra showed bottleneck effect, but its manifestation did not fit into the framework of previous bottleneck-effect theories and was unequivocally related to bursts of turbulence. The measurements were also used to evaluate the energetics of stratified shear flows typical of the environment. ONR # N00014-11-1-0709; NSF # AGS-1528451; ISF 408/15.

  12. FIFE atmospheric boundary layer budget methods

    NASA Technical Reports Server (NTRS)

    Betts, A. K.

    1992-01-01

    The budget methods and the mixed layer model employed to analyze the aircraft data from the First ISLSCP Field Experiment (FIFE) are described. Vector budgets for the mixed layer are discussed on conserved variable diagrams. Theoretical solutions are presented for the critical surface Bowen ratio that produces no boundary layer moistening or equivalent potential temperature rise as a function of the Bowen ratio at the inversion.

  13. Atmospheric Boundary-Layer Turbulence Intermittency Revisited

    NASA Astrophysics Data System (ADS)

    Mezemate, Y.; Fitton, G. F.; Tchiguirinskaia, I.; Schertzer, D. J. M.

    2015-12-01

    Turbulence has been and still is the focus of countless experimental, numerical, and theoretical studies. A common physics based approach to complex problems involving extremely large (possibly infinite) degrees of freedom is to consider the possible symmetries of the governing equations. In turbulence, the scaling symmetry of the Navier-Stokes equation justifies a multiple scaling (multifractal) analysis of the phenomena. Kolmogorov's famous 1941 hypotheses led to the 2/3rds law (essentially hypothesizing fractal velocity statistics) for the velocity increments and later in 1962 corrected his hypothesis to include an intermittency correction (essentially allowing the velocity to have multiple scaling exponents). Both hypotheses have been tested in numerous wind tunnel experiments but empirical validation of the hypotheses in the atmospheric boundary-layer have been difficult due to complex symmetry breaking effects. Using 50Hz Sonic Anemometer velocity data measured on the site of École des Ponts ParisTech we test Kolmogorov's hypotheses. We find that contrary to numerous wind tunnel testing results, we do not observe a slight increase of the spectral exponent, but a significant decrease this exponent, therefore that intermittency favorise small eddies. We show that it is necessary to reconsider the classical and frequently used assumptions regarding the normalization of the energy flux through scales.

  14. Spectral scales in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Weber, A. H.; Irwin, J. S.; Mathis, J. J., Jr.; Kahler, J. P.; Petersen, W. B.

    1982-01-01

    Wind data taken from 10 levels between 18 and 305 m were examined to determine the properties of atmospheric turbulence within and above the atmospheric surface layer into the PBL. The samples were averaged over 40 min intervals, with all periods of rain, fog, and other disturbances being eliminated from the 16 days of monitoring. Turbulence spectra were calculated using a fast Fourier transformation. The tower was located in rolling terrain covered with pine forests, waist-high scrub, and cultivated fields. Results are presented for the wavelength and Eulerian length scales, considering the neutral, stable, and unstable PBL. Correlation coefficients were found between velocity fluctuations and wavelengths for the stability classes. Good agreements were found for measured and computed spectra in all but unstable conditions.

  15. Spectral scales in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Weber, A. H.; Irwin, J. S.; Mathis, J. J., Jr.; Kahler, J. P.; Petersen, W. B.

    1982-01-01

    Wind data taken from 10 levels between 18 and 305 m were examined to determine the properties of atmospheric turbulence within and above the atmospheric surface layer into the PBL. The samples were averaged over 40 min intervals, with all periods of rain, fog, and other disturbances being eliminated from the 16 days of monitoring. Turbulence spectra were calculated using a fast Fourier transformation. The tower was located in rolling terrain covered with pine forests, waist-high scrub, and cultivated fields. Results are presented for the wavelength and Eulerian length scales, considering the neutral, stable, and unstable PBL. Correlation coefficients were found between velocity fluctuations and wavelengths for the stability classes. Good agreements were found for measured and computed spectra in all but unstable conditions.

  16. An interpretation of radiosonde errors in the atmospheric boundary layer

    Treesearch

    Bernadette H. Connell; David R. Miller

    1995-01-01

    The authors review sources of error in radiosonde measurements in the atmospheric boundary layer and analyze errors of two radiosonde models manufactured by Atmospheric Instrumentation Research, Inc. The authors focus on temperature and humidity lag errors and wind errors. Errors in measurement of azimuth and elevation angles and pressure over short time intervals and...

  17. 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.

  18. Electrodynamic properties and height of atmospheric convective boundary layer

    NASA Astrophysics Data System (ADS)

    Anisimov, S. V.; Galichenko, S. V.; Mareev, E. A.

    2017-09-01

    We consider the relations between the mixed layer height and atmospheric electric parameters affected by convective mixing. Vertical turbulent transport of radon, its progeny and electrically charged particles is described under Lagrangian stochastic framework, which is the next step to develop a consistent model for the formation of electrical conditions in the atmospheric boundary layer. Using the data from detailed and complex measurements of vertical profiles of the temperature and turbulence statistics as input, we calculated non-stationary vertical profiles of radon and its daughter products concentrations, atmospheric electric conductivity and intensity of electric field in the convective boundary layer from the morning transition through early afternoon quasi-stationary conditions. These profiles demonstrate substantial variability due to the changing turbulent regime in the evolving boundary layer. We obtained quantitative estimates of the atmospheric electric field variability range essentially related to the sunrise and convection development. It is shown that the local change in the electrical conductivity is the only factor that can change the intensity of electric field at the earth's surface more than twice during the transition from night to day. The established relations between electric and turbulent parameters of the boundary layer indicate that the effect of sunrise is more pronounced in the case when development of convection is accompanied by an increase in aerosol concentration and, hence, a decrease in local conductivity.

  19. Atmospheric boundary layer processes during a total solar eclipse

    SciTech Connect

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

    1980-01-01

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

  20. Atmospheric boundary layer evening transitions over West Texas

    USDA-ARS?s Scientific Manuscript database

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

  1. Atmospheric boundary layer studies in FIFE - Challenges and advances

    NASA Technical Reports Server (NTRS)

    Kelly, Robert D.

    1992-01-01

    A review is presented of a number of other articles concerning the atmospheric boundary layer (ABL) that focus on challenges and progress in experimental design and analysis represented by those studies. The articles address problems posed by the experimental site itself (inhomogeneity of terrain, size, and vegetation) and examine relationships between the ABL and remote sensing measurements.

  2. 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.

  3. 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.

  4. Large-scale intermittency in the atmospheric boundary layer.

    PubMed

    Kholmyansky, M; Moriconi, L; Tsinober, A

    2007-08-01

    We find actual evidence, relying upon vorticity time series taken in a high-Reynolds-number atmospheric experiment, that to a very good approximation the surface boundary layer flow may be described, in a statistical sense and under certain regimes, as an advected ensemble of homogeneous turbulent systems, characterized by a log-normal distribution of fluctuating intensities. Our analysis suggests that the usual direct numerical simulations of homogeneous and isotropic turbulence, performed at moderate Reynolds numbers, may play an important role in the study of turbulent boundary layer flows, if supplemented with appropriate statistical information concerned with the structure of large-scale fluctuations.

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

    NASA Technical Reports Server (NTRS)

    Dobrovolskis, A. R.

    1983-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  7. Turbulence and mixing in the stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Yagüe, C.; Morales, G.; Terradellas, E.; Cuxart, J.

    2003-04-01

    Transport and mixing in the Stable Atmospheric Boundary Layer is not well understood yet. However this is an important feature in atmospheric pollution as well as in other environmental studies. A Stable Atmospheric Boundary Layer Experiment in Spain (SABLES98) took place from the 10th to the 28th of September 1998. Two masts (100 m and 10 m) were instrumented with five sonic anemometers, 14 thermocouples, 8 cup anemometers, vanes,radiometers, etc. In addition, a sodar, a tethered balloon and a triangular array of cup anemometers were operating during the campaign. The experiment showed three different regimes, being specially interesting the one between 14th and 21st of September where stable and very stable conditions were present. In this work we present the behaviour of turbulent and stability parameters at several heights. The different evolutions of the Nocturnal Boundary Layer and the main parameters that controle its behaviour are discussed.The influence of internal gravity waves and their interaction with turbulence is also studied using wavelets.

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

    NASA Astrophysics Data System (ADS)

    Pietroni, I.; Argentini, S.

    2009-09-01

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

  9. Surface fluxes in atmospheric boundary layer flows over complex terrain

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Markfort, Corey; Porté-Agel, Fernando

    2016-11-01

    Interactions between the atmosphere and the land/water surface can be described by fluxes of momentum, heat and other scalars. While predicting the atmospheric boundary-layer (ABL) flows and modeling regional/global weather and climate, these surface fluxes need to be specified as boundary conditions. It is a common practice to use formulations based on the Monin-Obukhov similarity theory even for flows over a wide range of complex terrain, which maybe deviate significantly from the conditions of steady, fully-developed ABL flow, due to the knowledge gap for turbulent transport of fluxes across the interface. This work aims to provide insights for spatial distribution of the surface fluxes in ABL flows involving typical complex terrain cases, including surface roughness transition, steep topography and canopy patches. Results from wind-tunnel experiments will be presented to characterize the surface momentum and heat fluxes for different flow regimes and their correlation to the turbulent flow properties in thermally-stratified boundary layers. Application of the similarity theory to such cases is evaluated by comparing to the measurements. Ultimately, new knowledge of surface fluxes will help to improve parameterization of the surface-atmosphere interaction in numerical models.

  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 boundary layer modification in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Bennett, Theodore J., Jr.; Hunkins, Kenneth

    1986-01-01

    A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. The model is a two-dimensional, multilevel, linear model with turbulence, lateral and vertical advection, and radiation. Good agreement between observed and modeled temperature cross sections is obtained. In contrast to the hypothesis of Andreas et al., the air flow is found to be stable to secondary circulations. Adiabatic lifting and, at long fetches, cloud top longwave cooling, not an air-to-surface heat flux, dominate the cooling of the boundary layer. The accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress. It is speculated that the Andreas et al. estimates of the drag coefficient over the compact sea ice are too high.

  12. 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.

  13. 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.

  14. 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

  15. Interaction between the atmospheric and oceanic boundary layers

    NASA Technical Reports Server (NTRS)

    Yeh, G.-T.

    1974-01-01

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

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

    PubMed

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

    2007-03-15

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

  17. A helicopter observation platform for atmospheric boundary layer studies

    NASA Astrophysics Data System (ADS)

    Holder, Heidi Eichinger

    HOP data collected using the current set of sensors is discussed, including the novel use of the Empirical Mode Decomposition (EMD) to detrend and filter the data. The EMD separates the data into a finite number of Intrinsic Mode Functions (IMFs), each of which is unique and orthogonal. The basis is determined by the data itself, so that it need not be known a priori, and it is adaptive. The EMD is shown to be an ideal tool for the filtering and detrending of the HOP data gathered during the Cloud and Land Surface Interaction Campaign (CLASIC). The ability of the HOP to accurately measure atmospheric profiles of atmospheric variables is demonstrated. During experiments conducted in the marine boundary layer (MBL) and the convective boundary layer (CBL), HOP profiles of potential temperature are evaluated using an elastic backscatter lidar. The HOP and the lidar agree on the height of the boundary layer in both cases, and the HOP effectively locates other atmospheric structures. Atmospheric sensible and latent heat fluxes, turbulence kinetic energy (TKE) and horizontal momentum fluxes are also measured, and the resulting information is used to provide context to tower-based data collected concurrently. A brief comparison made over homogeneous ocean conditions yields good results. A more exhaustive evaluation is made using short HOP flights performed above an orchard during the Canopy Horizontal Turbulence Study (CHATS). Randomly selected one-minute sections of tower data are used to calculate fluxes to which the HOP fluxes can be more directly compared, with good results. Profiles of atmospheric fluxes are used to provide context to tower-based measurements. In conclusion, the research conducted here demonstrates unambiguously that the HOP is a unique platform that fills an important gap in observation facilities for the atmospheric boundary layer. It is now available to the scientific community for performing research, which is likely to help bridging existing

  18. Three velocity component, nonhomogeneous atmospheric boundary layer turbulence modeling

    NASA Technical Reports Server (NTRS)

    Perlmutter, M.; Frost, W.; Fichtl, G. H.

    1976-01-01

    The vertical nonhomogeneous character of turbulence in the atmospheric boundary layer results in a non-stationary turbulence process relative to an aircraft during takeoff and landing despite the fact that the turbulence statistics can be horizontally homogeneous. The simulation of the three components of the turbulent winds which include the nonstationary aspect of atmospheric turbulence is the subject of this paper. A procedure is developed and demonstrated to generate the three components of a turbulence ramdom process field, u sub i(x,z) where x and z denote horizontal and vertical coordinates and u sub i, i = 1,2,3 are the three orthogonal components of the turbulent random field. This field satisfies any desired one point auto spectra as well as two point statistics (interlevel correlations). By use of Taylors frozen eddy hypothesis we can transform the turbulent random field into the time domain and obtain the random turbulence along an aircraft trajectory.

  19. Parameterization of meandering phenomenon in a stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Carvalho, Jonas da Costa; Degrazia, Gervásio Annes; de Vilhena, Marco Túlio; Magalhães, Sergio Garcia; Goulart, Antonio G.; Anfossi, Domenico; Acevedo, Otávio Costa; Moraes, Osvaldo L. L.

    2006-08-01

    Accounting for the current knowledge of the stable atmospheric boundary layer (ABL) turbulence structure and characteristics, a new formulation for the meandering parameters to be used in a Lagrangian stochastic particle turbulent diffusion model has been derived. That is, expressions for the parameters controlling the meandering oscillation frequency in low wind speed stable conditions are proposed. The classical expression for the meandering autocorrelation function, the turbulent statistical diffusion theory and ABL similarity theory are employed to estimate these parameters. In addition, this new parameterization was introduced into a particular Lagrangian stochastic particle model, which is called Iterative Langevin solution for low wind, validated with the data of Idaho National Laboratory experiments, and compared with others diffusion models. The results of this new approach are shown to agree with the measurements of Idaho experiments and also with those of the other atmospheric diffusion models. The major advance shown in this study is the formulation of the meandering parameters expressed in terms of the characteristic scales (velocity and length scales) describing the physical structure of a turbulent stable boundary layer. These similarity formulas can be used to simulate meandering enhanced diffusion of passive scalars in a low wind speed stable ABL.

  20. Lidar analysis techniques for use in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Eichinger, William E.; Cooper, Daniel I.; Hof, Doug; Holtkamp, David; Quick, Robert, Jr.; Tiee, Joe; Karl, Robert

    1992-01-01

    There is a growing body of observational and theoretical evidence which suggests that local climate characteristics are associated with variations in the earth's surface. The link between surface variability and local-scale processes must be made if we are to improve our understanding of the feedback mechanisms involved in surface-atmosphere dynamics. However, to understand these interactions, the surface-atmosphere interface must be studied as a large-scale spatial system. Lidars are ideal tools to study the spatial properties of the atmosphere. The described techniques were developed for use with the Los Alamos Water Raman-Lidar, but are applicable to many other types of lidar. The methodology of the analysis of lidar data is summarized in order to determine meteorological parameters in the atmospheric boundary layer. The techniques are not exhaustive but are intended to show the depth and breadth of the information which can be obtained from lidars. Two methods for the computation of water-vapor fluxes were developed. The first uses the fact that the water vapor concentration in the vertical direction follows a logarithmic profile when corrected for atmospheric stability. The second method involves using inertial dissipation techniques in which lidar-derived spatial and temporal power spectra are used to determine the flux.

  1. Lidar analysis techniques for use in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Eichinger, William E.; Cooper, Daniel I.; Hof, Doug; Holtkamp, David; Quick, Robert, Jr.; Tiee, Joe; Karl, Robert

    1992-01-01

    There is a growing body of observational and theoretical evidence which suggests that local climate characteristics are associated with variations in the earth's surface. The link between surface variability and local-scale processes must be made if we are to improve our understanding of the feedback mechanisms involved in surface-atmosphere dynamics. However, to understand these interactions, the surface-atmosphere interface must be studied as a large-scale spatial system. Lidars are ideal tools to study the spatial properties of the atmosphere. The described techniques were developed for use with the Los Alamos Water Raman-Lidar, but are applicable to many other types of lidar. The methodology of the analysis of lidar data is summarized in order to determine meteorological parameters in the atmospheric boundary layer. The techniques are not exhaustive but are intended to show the depth and breadth of the information which can be obtained from lidars. Two methods for the computation of water-vapor fluxes were developed. The first uses the fact that the water vapor concentration in the vertical direction follows a logarithmic profile when corrected for atmospheric stability. The second method involves using inertial dissipation techniques in which lidar-derived spatial and temporal power spectra are used to determine the flux.

  2. Vegetation-atmosphere interactions and boundary layer cumulus clouds

    NASA Astrophysics Data System (ADS)

    Freedman, Jeffrey Michael

    2000-07-01

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

  3. 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.

  4. 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

  5. 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.

  6. 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).

  7. Velocity Spectra In The Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Smedman, A.

    In some respects the turbulence structure in the marine atmospheric boundary layer (MABL) reacts in the same way as the boundary layer over land, that is to say Monin-Obukhov similarity theory can be applied. There are, however, frequently situations when the similarity between the two breaks down. Analysis of measurements, taken at the flat, small island Oestergarnsholm in the middle of the Baltic Sea, clearly shows the influence of the sea state on MABL. The measurements comprise turbulence and mean variables taken at several heights on a 30 m tower, as well as wave parameters from a Wave Rider Buoy deployed 3 km outside the island. Model results of the wave field around the island together with foot-print analysis indicate that the wave field is almost un disturbed for low to moderate wind speeds but has to be corrected for limited water depth for the highest wind speeds. Our earlier analysis shows a strict similarity with over-land conditions for both mean and turbulence variables (mean wind gradient, fluxes, spectra etc.) for growing waves (young waves) travelling slower than the wind. But as soon as some waves become mature and get a speed faster than the wind speed, similarity breaks down. Thus the turbulence structure in the MABL needs to be described in terms of additional parameters such as wave age and maybe boundary layer height. Spectra of the velocity components in the MABL have been analyzed taking sea state into account. During neutral stability and young sea spectra follow the new similarity theory proposed by Hunt and Carlotti (2000) and Högström, Hunt and Smedman (2001). But with increasing wavelength of the surface waves spectra gradually change both shape and energy level, beginning at the low frequency end and continuing towards higher frequencies. For cp/U ~ 1 (where cp is the peak phase speed) the `breaking point' can be seen in the inertial subrange, which actually gives two frequency intervals with a ­2/3 slope but with different

  8. Direct Numerical Simulations of Very Stable Atmospheric Boundary Layers

    DTIC Science & Technology

    2012-01-10

    Ekman boundary layers. Very high resolution, three-dimensional, time-dependent simulations are carried out on computational grids of the order of...turbulent Ekman layers", Annual Meeting of the Division of Fluid Dynamics of the American Physical Society, Long Beach. O Flores and JJ Riley. August...September, 2011. "DNS of a strati ed Ekman layer with a capping inversion", 13th European Turbulence Conference, Warsaw, Poland. Number of

  9. Interaction of Atmospheric Turbulence with Blade Boundary Layer Dynamics on a 5MW Wind Turbine using Blade-Boundary-Layer-Resolved CFD with hybrid URANS-LES.

    SciTech Connect

    Vijayakumar, Ganesh; Brasseur, James; Lavely, Adam; Jayaraman, Balaji; Craven, Brent

    2016-01-04

    We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.

  10. 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.

  11. 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.

  12. 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.

  13. Shallow marine cloud topped boundary layer in atmospheric models

    NASA Astrophysics Data System (ADS)

    Janjic, Zavisa

    2017-04-01

    A common problem in many atmospheric models is excessive expansion over cold water of shallow marine planetary boundary layer (PBL) topped by a thin cloud layer. This phenomenon is often accompanied by spurious light precipitation. The "Cloud Top Entrainment Instability" (CTEI) was proposed as an explanation of the mechanism controlling this process in reality thereby preventing spurious enlargement of the cloudy area and widely spread light precipitation observed in the models. A key element of this hypothesis is evaporative cooling at the PBL top. However, the CTEI hypothesis remains controversial. For example, a recent direct simulation experiment indicated that the evaporative cooling couldn't explain the break-up of the cloudiness as hypothesized by the CTEI. Here, it is shown that the cloud break-up can be achieved in numerical models by a further modification of the nonsingular implementation of the Mellor-Yamada Level 2.5 turbulence closure model (MYJ) developed at the National Centers for Environmental Prediction (NCEP) Washington. Namely, the impact of moist convective instability is included into the turbulent energy production/dissipation equation if (a) the stratification is stable, (b) the lifting condensation level (LCL) for a particle starting at a model level is below the next upper model level, and (c) there is enough turbulent kinetic energy so that, due to random vertical turbulent motions, a particle starting from a model level can reach its LCL. The criterion (c) should be sufficiently restrictive because otherwise the cloud cover can be completely removed. A real data example will be shown demonstrating the ability of the method to break the spurious cloud cover during the day, but also to allow its recovery over night.

  14. Impact Wind Farms on the Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Volker, P.; Capps, S. B.; Huang, H. J.; Sun, F.; Badger, J.; Hahmann, A.

    2012-12-01

    We introduce a new, validated wind farm parametrization (Explicit Wake Parametrization, EWP) which is based on the assumption that the downstream propagation of a single turbine wake can be described by a turbulent diffusion process. Thus, the downstream velocity deficit distribution can be described explicitly. Additionally, it allows us to take into account turbine interactions, making it possible to determine the unresolved turbine hub height velocities. Both the EWP wind farm parametrization and the wind farm scheme available in the Weather Research & Forecasting Model (WRF) have been validated against in situ measurements from Horns Rev I (A large offshore wind farm consisting of 80 2MW turbines situated near the west coast of Denmark). The main quantities of interest are the thrust applied to the flow, a consequence of the energy extracted by the wind turbines which determines mainly the wind farm wake extension (around 50 km for Horns Rev I) and the vertical velocity deficit distribution. Results show that the thrust in the WRF-WF scheme is overestimated inside the wind farm. We noticed that the velocity deficit propagates from the first turbine-containing-grid-cell up to the boundary layer top, which is in contrast to the theoretical expected expansion (confirmed by turbulence resolving models and wind tunnel results). The vertical expansion of the velocity deficit is a consequence of the additional turbulence source term in the WRF-WF scheme. The EWP scheme estimates the total amount of thrust correctly and is also able to follow the reduced thrust downstream since it considers the turbine interaction. From the good agreement with the far wake measurement, we can conclude that the formulation of the sub grid scale vertical extension of the velocity deficit must be correct. We will present results from WRF simulations in which we analyze the atmospheric response within the wake of wind farms resulting from the energy extraction of wind turbines. We place

  15. Estimating vertical fluxes of ozone within the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Belan, Boris D.; Antokhin, Pavel N.; Antokhina, Olga Yu.; Arshinov, Mikhail Yu.; Belan, Sergey B.; Davydov, Denis K.; Krasnov, Oleg A.; Penenko, Alexey V.; Savkin, Denis E.; Sklyadneva, Tatayna K.; Tolmahev, Gennadii N.

    2017-04-01

    Investigation of the vertical distribution of ozone within the atmospheric boundary layer (ABL) was carried out by use of AN-2 light aircraft as a research platform. Vertical fluxes of ozone and their direction from the ground to the free-tropospheric level were calculated based on the in situ measurement data. Research flights have been performed over the greenhouse gas monitoring station located in a background area (56.1-56.4 N, 84.2-84.8 E) in the vicinity of abandoned village of Berezorechka (West Siberia). The schedule of diurnal flights was as follows: the first one just after the sunrise; the second one at noon; the third one 2-3 hours after noon, when a well-developed turbulence is observed; and the last one just before the sunset. A total of 10 diurnal cycles of measurements were undertaken. Analysis of the obtained data showed that the rate of ozone influx from upper layers of the atmosphere is 3-10 times less than the ozone production rate in the ABL. Average rate of ozone influx from the free troposphere was about 1 μg m-3 h-1, but ozone production rate in the ABL was about 5 μg m-3 h-1, so the major part of ozone is formed by photochemical reactions that occur within the ABL and only 20 % of its content is determined by the influx from the free troposphere. The vertical profiles of the ozone fluxes have shown that their maximum values are observed at heights from 200 to 600 m AGL. The height of the maximum depends on the season: in winter it is lower than 200-300 m, and in summer the maximum is observed at 500-600 m. The value of the ozone flux maximum also depends on the season and varies from 1 μg m-2 s-1in winter to 4.2 μg m-2 s-1 in spring. This work was supported by the Russian Foundation for Basic Research (grant No 17-05-00374).

  16. Spatiotemporal structure of wind farm-atmospheric boundary layer interactions

    NASA Astrophysics Data System (ADS)

    Cervarich, Matthew; Baidya Roy, Somnath; Zhou, Liming

    2013-04-01

    Wind power is currently one of the fastest growing energy sources in the world. Most of the growth is in the utility sector consisting of large wind farms with numerous industrial-scale wind turbines. Wind turbines act as a sink of mean kinetic energy and a source of turbulent kinetic energy in the atmospheric boundary layer (ABL). In doing so, they modify the ABL profiles and land-atmosphere exchanges of energy, momentum, mass and moisture. This project explores theses interactions using remote sensing data and numerical model simulations. The domain is central Texas where 4 of the world's largest wind farms are located. A companion study of seasonally-averaged Land Surface Temperature data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on TERRA and AQUA satellites shows a warming signal at night and a mixed cooling/warming signal during the daytime within the wind farms. In the present study, wind farm-ABL interactions are simulated with the Weather Research and Forecasting (WRF) model. The simulations show that the model is capable of replicating the observed signal in land surface temperature. Moreover, similar warming/cooling effect, up to 1C, was observed in seasonal mean 2m air temperature as well. Further analysis show that enhanced turbulent mixing in the rotor wakes is responsible for the impacts on 2m and surface air temperatures. The mixing is due to 2 reasons: (i) turbulent momentum transport to compensate the momentum deficit in the wakes of the turbines and (ii) turbulence generated due to motion of turbine rotors. Turbulent mixing also alters vertical profiles of moisture. Changes in land-atmosphere temperature and moisture gradient and increase in turbulent mixing leads to more than 10% change in seasonal mean surface sensible and latent heat flux. Given the current installed capacity and the projected installation across the world, wind farms are likely becoming a major driver of anthropogenic land use change on Earth. Hence

  17. 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...

  18. 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...

  19. Study of EM Signals Propagation Through Marine Atmospheric Boundary Layer

    DTIC Science & Technology

    2002-09-30

    transmision properties. REFERENCES Barrick, D.E., and Weber, B.L., ’On the nonlinear theory for gravity waves on the ocean’s surface. Part II...and Friehe C., 2000. Boundary-Layer Meteorology, 97, 293-307. Ishimaru, A. 1978, Wave propagation and scattering in random media . Academic Press...Irvine. Rytov, S. M., Y. A. Kravtsov, and V. I. Tatarskii: 1987, Principles of statistical radiophysics 4: Wave propagation through random media

  20. 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

  1. 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.

  2. Determination of the Atmospheric Boundary Layer Height from Radiosonde and Lidar Backscatter

    NASA Astrophysics Data System (ADS)

    Hennemuth, Barbara; Lammert, Andrea

    2006-07-01

    The height of the atmospheric boundary layer is derived with the help of two different measuring systems and methods. From radiosoundings the boundary layer height is determined by the parcel method and by temperature and humidity gradients. From lidar backscatter measurements a combination of the averaging variance method and the high-resolution gradient method is used to determine boundary layer heights. In this paper lidar-derived boundary layer heights on a 10 min basis are presented. Datasets from four experiments two over land and two over the sea are used to compare boundary layer heights from both methods. Only the daytime boundary layer is investigated because the height of the nighttime stable boundary layer is below the range of the lidar. In many situations the boundary layer heights from both systems coincide within ±200 m. This corresponds to the standard deviation of lidar-derived 10-min values within a 1-h interval and is due to the time and space variability of the boundary layer height. Deviations appear for certain situations and depend on which radiosonde method is applied. The parcel method fails over land surfaces in the afternoon when the boundary layer stabilizes and over the ocean when the boundary layer is slightly stable. An automatic radiosonde gradient method sometimes fails when multiple layers are present, e.g. a residual layer above the growing convective boundary layer. The lidar method has the advantage of continuous tracing and thus avoids confusion with elevated layers. On the other hand, it mostly fails in situations with boundary layer clouds

  3. The climatic features of the atmospheric boundary layer above the south of western Siberia

    NASA Astrophysics Data System (ADS)

    Komarov, V. S.; Lomakina, N. Ya.

    2006-11-01

    Troposphere and, in particular, the atmospheric boundary layer play a considerable role in propagation and transformation of optical radiation. Therefore, data on vertical statistical structure of meteorological fields in the boundary layer are necessary for solution of various applied problems of atmospheric optics. In the work, climatic features of the atmospheric boundary layer above the south of Western Siberia are considered. The research was conducted for winter and summer using the date of four-years (2002.2005 years) observations of 4 aerologic stations (Ekaterinburg, Omsk, Novosibirsk and Krasnoyarsk). The vertical structures of average values and mean square deviations of temperature, humidity and wind for 10 high-altitude levels (up to 1600 M), as well as the corresponding correlation matrixes and results of their expansion on empirical orthogonal functions were used for detailed studying of climatic features of atmospheric boundary layer. The obtained results are presented.`

  4. 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...

  5. 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...

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

    SciTech Connect

    SethuRaman, S

    1981-01-01

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

  7. 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.

  8. 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.

  9. Mechanics of chemical species transport in the marine atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Hanson, Howard P.

    1989-01-01

    Marine atmospheric boundary layer (MABL) drafts are modeled as steady-state plumes using the approach proposed by Telford (1966), and the model response to varying forcing and boundary conditions is examined. Since most of the chemical species are passive tracers within the MABL, variations in the implied fluxes are determined as a combination of the boundary conditions for the chemical species and the thermodynamic forcing implied by the stability and thermal boundary conditions.

  10. 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.

  11. 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 ...

  12. Atmospheric boundary layer investigations in the Laptev Sea area

    NASA Astrophysics Data System (ADS)

    Schwarz, Pascal; Heinemann, Günther; Drüe, Clemens; Makshtas, Alexander

    2016-04-01

    In the winter season 2014/2015 a field campaign at the Tiksi observatory (71°38'N, 128°52'E) was carried out by the University of Trier with support of the Arctic and Antarctic Research Institute (AARI) and the GEOMAR Kiel in framework of the interdisciplinary Transdrift project. One goal of the campaign is to help to improve the understanding of processes within the Arctic stable boundary layer (SBL). Within the SBL, there are several important phenomena and processes like low-level jets, surface and lifted inversions, the development of the mixing height or the determination of the energy balance, which can be best investigated with a mix of high-resolution ground-based remote sensing systems and flux tower measurements. We mainly used a SODAR/RASS, a scintillometer, a ceilometer as well as the local flux tower to investigate the SBL for the Arctic winter. Baroclinity is found to be the main driven mechanism for low-level jets with jet core heights above 200 m due to the strong temperature gradient between the Laptev Sea and the Siberian continent. Strong temperature changes at short time scale (few hours) were often closely related to a change of wind direction and therefore advection. LLJs with heights below 200 m are likely influenced by local topography. In addition, regional climate model simulations using the COSMO-CLM (COnsortium for Small-scale MOdelling - Climate Limited area Mode) driven by ERA-Interim reanalysis data have been performed. The COSMO-CLM simulations show a good agreement with ERA-Interim reanalysis data and in-situ measurements (tower, soundings).

  13. 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.

  14. Climatic equilibrium of the atmospheric convective boundary layer over a tropical ocean

    NASA Technical Reports Server (NTRS)

    Ridgway, W.; Betts, Alan K.

    1989-01-01

    A radiative-convective boundary layer model was developed by coupling a thermodynamic model of a partially mixed convective boundary layer (CBL) with a radiation model, and energy balance constraints were used to study coupled boundary layer (CBL) equilibrium over three timescales (about 1 day, about 10 days, and more than 100 days). It is shown that the variation in cloud top decreases with greater coupling to the atmosphere and the ocean. The slope of the latent heat flux with increasing SST decreases with more tropospheric coupling, and reverses sign with a coupled ocean.

  15. 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.

  16. 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.

  17. High resolution properties of the equatorial Pacific marine atmospheric boundary layer from lidar and radiosonde observations

    SciTech Connect

    Cooper, D.I.; Eichinger, W.E.; Hynes, M.V.; Keller, C.F.; Lebeda, C.F.; Poling, D.A.

    1994-10-01

    Water vapor and relative aerosol concentration were measured with two shipboard lidars from the ocean surface to tropospheric and lower stratospheric altitudes in support of the Central Equatorial Pacific Experiment (CEPEX) program. The goal of CEPEX is to evaluate the ``thermostat`` hypothesis regarding feedback mechanisms between the tropical ocean and the atmosphere. This paper describes some of the features observed with the first two kilometers of the equatorial troposphere, known as the marine Atmospheric Boundary Layer (ABL), as well as the coupling between the ocean and the atmosphere. This paper will present the initial analysis of the structure of the atmospheric boundary layer. Finally, we will look at the implications of this structure for ocean-atmosphere coupling by comparing the height of the mixing layer with sea surface temperatures and other factors.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Improvements in simulation of atmospheric boundary layer parameters through data assimilation in ARPS mesoscale atmospheric model

    NASA Astrophysics Data System (ADS)

    Subrahamanyam, D. Bala; Ramachandran, Radhika; Kunhikrishnan, P. K.

    2006-12-01

    In a broad sense, 'Data Assimilation' refers to a technique, whereby the realistic observational datasets are injected to a model simulation for bringing accurate forecasts. There are several schemes available for insertion of observational datasets in the model. In this piece of research, we present one of the simplest, yet powerful data assimilation techniques - known as nudging through optimal interpolation in the ARPS (Advanced Regional Prediction System) model. Through this technique, we firstly identify the assimilation window in space and time over which the observational datasets need to be inserted and the model products require to be adjusted. Appropriate model variables are then adjusted for the realistic observational datasets with a proper weightage being given to the observations. Incorporation of such a subroutine in the model that takes care of the assimilation in the model provides a powerful tool for improving the forecast parameters. Such a technique can be very useful in cases, where observational datasets are available at regular intervals. In this article, we demonstrate the effectiveness of this technique for simulation of profiles of Atmospheric Boundary Layer parameters for a tiny island of Kaashidhoo in the Republic of Maldives, where regular GPS Loran Atmospheric Soundings were carried out during the Intensive Field Phase of Indian Ocean Experiment (INDOEX, IFP-99).

  1. Physical modeling of the atmospheric boundary layer in the UNH Flow Physics Facility

    NASA Astrophysics Data System (ADS)

    Taylor-Power, Gregory; Gilooly, Stephanie; Wosnik, Martin; Klewicki, Joe; Turner, John

    2016-11-01

    The Flow Physics Facility (FPF) at UNH has test section dimensions W =6.0m, H =2.7m, 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) using upstream roughness arrays. The American Society for Civil Engineers defines standards for simulating ABLs for different terrain types, from open sea to dense city areas (ASCE 49-12). The standards require the boundary layer to match a power law shape, roughness height, and power spectral density criteria. Each boundary layer type has a corresponding power law exponent and roughness height. The exponent and roughness height both increase with increasing roughness. A suburban boundary layer was chosen for simulation and a roughness element fetch was created. Several fetch lengths were experimented with and the resulting boundary layers were measured and compared to standards in ASCE 49-12: Wind Tunnel Testing for Buildings and Other Structures. Pitot tube and hot wire anemometers were used to measure average and fluctuating flow characteristics. Velocity profiles, turbulence intensity and velocity spectra were found to compare favorably.

  2. A numerical model of the atmospheric boundary layer over a marginal ice zone

    NASA Astrophysics Data System (ADS)

    Kantha, Lakshmi H.; Mellor, George L.

    1989-04-01

    A two-dimensional, multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off-ice, on-ice, and along-ice edge wind conditions. The model incorporates a second-moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects. For off-ice winds, as the atmospheric boundary layer passes from cold smooth ice onto warm open water, the onset of intense convection raises the inversion. Over the transition zone of rough rafted ice with open leads, the shear stress on the ice cover increases significantly before dropping down to the downstream values over water. Such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone. These results are in agreement with the one-layer model simulations of off-ice winds by Overland et al. (1983). For on-ice wind conditions, as the warm flow in the boundary layer encounters the cold ice conditions, the resulting stable stratification could rapidly suppress the turbulence in the boundary layer, leading to the development of a shallow inversion and an associated jet. When the wind is predominantly along the ice edge, the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence. More observations are needed to verify these model predictions. Nevertheless, these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions.

  3. 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.

  4. Measurement Science of the Intermittent Atmospheric Boundary Layer

    DTIC Science & Technology

    2014-01-01

    meridionally by 40 m), eight ultrasonic anemometers, two low-response thermometers, two low-response hygrometers, three quartz-crystal barometers , and...has been operating with eight sonics and three quartz-crystal barometers almost without interruption since June 2013 1 • The quartz-crystal... barometers have been arranged in the form of a triangle of 40 m spacing, and the barometer array has effectively detected atmospheric infrasound (including

  5. Coherent Vortical Structures in the Atmospheric Boundary Layer Near Ground.

    NASA Astrophysics Data System (ADS)

    Cropley, Ford

    Available from UMI in association with The British Library. Vorticity has been fundamental to the description of turbulence. Despite this there have been few measurements of vorticity in the atmosphere. An array of twelve digital vane anemometers was used as a probe to measure atmospheric vorticity. Data was taken in neutrally stable conditions, in a range of wind speeds. The velocity vector was measured at four points at 5 or 10 Hz. The coded velocity signals were transmitted by cable for storage in a microcomputer. The assumption of linear velocity fields allowed the subsequent calculation of the local vorticity vector and the divergence. Particular care was taken with the interaction of the various length scales associated with the instrument. Characteristic spacing of the anemometers was 2m. Probability distributions and spectra of the vorticity components are calculated. A literature review examines developments in conditional sampling in controlled flows, and reviews the sparse measurements of ordered motions in the atmosphere. A conditional sampling scheme used the smoothed cross-wind vorticity component as a detector. Further partitioning of the traces using the vertical vorticity component revealed a recurring vortical structure. This appeared to be part of a system of horseshoe vortices. The work ends with a summary of findings, and recommendations for further study.

  6. Modeling Turbulence Generation in the Atmospheric Surface and Boundary Layers

    DTIC Science & Technology

    2015-10-01

    components, solar direct and diffuse radiation, foliage-cover effects, and a detailed discussion of gravity -wave influences. The discussion and conclusions...Development 158 9.3 Small-Scale Nocturnal Turbulence Generation 159 9.4 Gravity -Wave Turbulence in the Stable Surface Layer 163 9.5 Gravity -Wave...Equation Set 164 9.6 Vertical Wind Perturbation Equation 170 9.7 Vertical Wind Structure 178 9.8 Gravity -Wave Breakdown 181 10. Conclusions 186 References

  7. Preliminary comparison of model and prototype wakes. [building wake effects on atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Logan, E., Jr.; Camp, D. W.

    1978-01-01

    Velocity and turbulence profiles previously measured in the wake of a long building 3.2 m high, located in the field, transverse to the wind and in an atmospheric boundary layer several hundred meters thick are compared with wake profiles at corresponding longitudinal stations for a scale model of the building located in a large meteorological wind tunnel having a boundary layer thickness of 0.61 m to assess the accuracy of full scale wake profile predictions based on model tests. Results are presented which show that disparities in nondimensional profiles result from differences in relative depth of logarithmic layers and in surface conditions.

  8. Modeling pollutant transport in the atmosphere boundary layer

    SciTech Connect

    O`Steen, B.L.

    1990-12-31

    The two basic methods for modeling the atmospheric transport of pollutants (diagnostic and prognostic) are examined along with the current models utilized at SRS for emergency response (WINDS). The ability of a limited-area (mesoscale) model, nested within a synoptic scale model, to represent a wide range of flow behavior, makes it the method of choice for predicting pollutant transport. Such a mesoscale model can provide an invaluable research tool and, with a periodic processing strategy for wind field calculation and/or sufficient computer capability, can be utilized in an emergency response capacity. Various models are compared.

  9. Modeling pollutant transport in the atmosphere boundary layer

    SciTech Connect

    O'Steen, B.L.

    1990-01-01

    The two basic methods for modeling the atmospheric transport of pollutants (diagnostic and prognostic) are examined along with the current models utilized at SRS for emergency response (WINDS). The ability of a limited-area (mesoscale) model, nested within a synoptic scale model, to represent a wide range of flow behavior, makes it the method of choice for predicting pollutant transport. Such a mesoscale model can provide an invaluable research tool and, with a periodic processing strategy for wind field calculation and/or sufficient computer capability, can be utilized in an emergency response capacity. Various models are compared.

  10. 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

  11. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  13. 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

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  15. 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).

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

    USDA-ARS?s Scientific Manuscript database

    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...

  17. Inverted floor wind-tunnel simulation of stably stratified atmospheric boundary layer flow

    NASA Astrophysics Data System (ADS)

    Grainger, Clive; Meroney, Robert N.

    Most of the critical transport processes in the atmosphere are dominated by density stratification; hence, physical modeling facilities which neglect the important contributions of buoyancy are limited to the examination of high winds or those brief moments after sunrise or before sunset when the atmosphere is nominally neutrally stratified. Large new facilities constructed specifically to simulate the atmosphere offer new opportunities to study the physics of mixing processes dominated by stratification. A novel arrangement to simulate stably stratified atmospheric boundary layer flows in large wind tunnels using distributed electrical heaters and an inverted ground plane to simulate nighttime inversions is described, together with initial measurements.

  18. 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.

  19. Formulation of a Prototype Coupled Atmospheric and Oceanic Boundary Layer Model.

    DTIC Science & Technology

    1982-12-01

    layers. The approach will be to compare observed evolutions in the oceanic and atmospheric boundary layers with predictions from bulk modelo wherein...evaporatiJon. The slight predicted increase in salinity from 33.5 to 33.5038 pp -:, shown inFig- ure 16, is due to evaporation. An unstable ccnditi-on...P.&.,..1977: "Santa A gsociated Offshore Foe: Forecast.ng wth a Sequentiai’o itN . Thesis, Na Pcstgraduate School, Monterey, CA., 112 pp . Brower

  20. Identification of atmospheric boundary layer thickness using doppler radar datas and WRF - ARW model in Merauke

    NASA Astrophysics Data System (ADS)

    Putri, R. J. A.; Setyawan, T.

    2017-01-01

    In the synoptic scale, one of the important meteorological parameter is the atmospheric boundary layer. Aside from being a supporter of the parameters in weather and climate models, knowing the thickness of the layer of the atmosphere can help identify aerosols and the strength of the vertical mixing of pollutants in it. The vertical wind profile data from C-band Doppler radar Mopah-Merauke which is operated by BMKG through Mopah-Merauke Meteorological Station can be used to identify the peak of Atmospheric Boundaryu Layer (ABL). ABL peak marked by increasing wind shear over the layer blending. Samples in January 2015 as a representative in the wet and in July 2015 as the representation of a dry month, shows that ABL heights using WRF models show that in July (sunny weather) ABL height values higher than in January (cloudy)

  1. Measurements and Modelling of the Wind Speed Profile in the Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Peña, Alfredo; Gryning, Sven-Erik; Hasager, Charlotte B.

    2008-12-01

    We present measurements from 2006 of the marine wind speed profile at a site located 18 km from the west coast of Denmark in the North Sea. Measurements from mast-mounted cup anemometers up to a height of 45 m are extended to 161 m using LiDAR observations. Atmospheric turbulent flux measurements performed in 2004 with a sonic anemometer are compared to a bulk Richardson number formulation of the atmospheric stability. This is used to classify the LiDAR/cup wind speed profiles into atmospheric stability classes. The observations are compared to a simplified model for the wind speed profile that accounts for the effect of the boundary-layer height. For unstable and neutral atmospheric conditions the boundary-layer height could be neglected, whereas for stable conditions it is comparable to the measuring heights and therefore essential to include. It is interesting to note that, although it is derived from a different physical approach, the simplified wind speed profile conforms to the traditional expressions of the surface layer when the effect of the boundary-layer height is neglected.

  2. Empirical Observations of Scaling and Symmetry in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Fitton, G. F.; Mezemate, Y.; Tchiguirinskaia, I.; Schertzer, D. J. M.

    2015-12-01

    Using multiple measurement techniques from five locations, including Ecole des Ponts, we study the scaling and symmetries of measured atmospheric quantities in space and time in the atmospheric boundary-layer. Combining LIDAR, SODAR, RADAR, and sonic anemometer data, provides a means to analyse time-scales from 0.02 seconds to 15 years! and heights from 10m to 8km! Understanding and modelling the properties of the atmosphere over these immense ranges of space and time scales with a unique model is only possible through the scales. Moreover, the complex relationships between space and time-scales in the boundary- layer means symmetries differ greatly from classical turbulence theory. Small-temporal scale analysis (<15 minutes) of the velocity fluctuations shows (now) classical models for turbulence are respected over all measurement locations; classical in the sense that a Kolmogorov turbulence model with a significant intermittency correction is respected. Above these time-scales the stability of the atmosphere plays a key role. As such the time-scaling of the velocity is much more complex and classical space-time symmetries aren't respected. Using empirically estimated spectral energies and simple scaling and symmetry arguments we propose a model for the atmospheric boundary-layer that predicts only two possible profiles for the vertical transfer of energy. We discuss the space-time scaling properties of this model and the consequences thereof for the velocity fluctuations.

  3. Dynamics of the atmospheric boundary layer response to ocean mesoscale sea surface temperatures

    NASA Astrophysics Data System (ADS)

    Schneider, Niklas; Taguchi, Bunmei; Nonaka, Masami; Kuwano-Yoshida, Akira; Nakamura, Hisashi

    2017-04-01

    A recent theory for the mid-latitude atmospheric response to ocean mesoscale sea surface temperature (SST) variations is tested in the Southern Ocean using an extended integration of an atmospheric general circulation model. The theory is based on a linearization of the steady state, atmospheric boundary-layer dynamics, and yields the atmospheric response as classical Ekman dynamics extended to include advection, and sea surface temperature induced changes of atmospheric mixing and hydrostatic pressure. The theory predicts the response at each horizontal wave number to be governed by spectral transfer function between sea surface temperature and boundary layer variables, that are dependent on large-scale winds and the formulation of boundary layer mixing. The general circulation model, AFES, is shown to reproduce observed regressions between surface wind stress and sea surface temperatures. These 'coupling coefficients' are explained by SST induced changes of the surface stability, that directly impact surface stress, and changes of the surface winds. Estimates of the spectral transfer function between the latter and surface temperature are consistent with the theory, and suggest that it faithfully captures the underlying physics.

  4. 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, S.; Newsom, R. K.

    2015-10-01

    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.

  5. 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.

  6. Decadal change in the troposphere and atmospheric boundary layer over the South Pole

    SciTech Connect

    Neff, W.D.

    1994-12-31

    During the austral winter of 1993, the Environmental Technology Laboratory carried out a detailed field study of the atmospheric boundary layer at Amundsen-Scott South Pole Station to determine the effect of transitory synoptic disturbances on the surface-energy budget. This study used newly developed 915-megahertz radar wind-profiling technology for the first time in the Antarctic in combination with conventional boundary layer instrumentation that included a short tower, sonic anemometer, microbarograph array, and doppler sodar. Recent discussions, however, of interdecadal variability in the circumpolar circulation around Antarctica and of decadal changes in summer cloudiness at the South Pole, motivated our study of the long-term variability in boundary layer characteristics, cloudiness, and tropospheric flow behavior to provide a climatological context for our single year`s observations. 7 refs., 3 figs.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Large-eddy simulation studies of sea spray in the hurricane atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kelly, Mark

    The growth and maintenance of hurricanes is highly dependent upon the exchange of heat and momentum between the ocean and atmosphere. Because sea spray can significantly affect this ocean-air exchange, accurate hurricane models need to account for spray effects. We incorporate sea spray into large-eddy simulations (LES) to explore its role in the atmospheric boundary layer (ABL) of hurricanes, allowing us to assess the validity of and offer improvements to the simple spray parameterizations currently used in hurricane models. We investigate thermodynamic feedback between spray and surface heat fluxes, and examine the effects of spray upon the dynamics of the hurricane boundary layer. Results of preliminary LES, which use a bulk representation of the dominant range of spray sizes and a simplified diagnostic phase change scheme, indicate an appreciable amount of spray-air heat transfer---consistent with theory---and demonstrate a form of spray-induced thermodynamic feedback. The LES model of the hurricane atmospheric boundary layer (HABL) is adapted to account for variations in spray generation due to wave-breaking, momentum transfer between air and spray in both the vertical (liquid loading and stratification) and horizontal (drag), and dissipative heating in an emulsion-like two-phase environment. These modifications are accompanied by extension of the phase change and spray generation schemes to account for different droplet sizes, and implementation of a moving three-dimensional boundary. Collective inclusion of all these pieces of modeled physics in the LES provides results which offer a better view of the limitations of current spray-flux models, and motivates a simpler and improved alternative model. The refined results of the 'full' LES-HABL model are consistent with early simulations, and underscore the significance of boundary-layer scale thermodynamic balance, spray-induced fluxes, and wind-dependent thermodynamic feedback.

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

    NASA Technical Reports Server (NTRS)

    Grossman, Robert L.

    1990-01-01

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

  14. 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.

  15. 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

  16. Evolution of the atmospheric boundary-layer structure of an arid Andes Valley

    NASA Astrophysics Data System (ADS)

    Khodayar, S.; Kalthoff, N.; Fiebig-Wittmaack, M.; Kohler, M.

    2008-04-01

    The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near the coast and in the valley. Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze winds of 3-4 m s-1 prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night. The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day, no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about 150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection of moist air results in the accumulation of moisture during the noon and afternoon period, while

  17. 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.

  18. A multiscale eddy simulation methodology for the atmospheric Ekman boundary layer

    NASA Astrophysics Data System (ADS)

    Alam, Jahrul; Rokibul Islam, Mo

    2015-01-01

    In a large eddy simulation (LES), resolving the wide spectrum of large turbulent eddies from O(m) to O(km) in the atmospheric boundary layer (ABL) requires O(109) computational degrees of freedom; however, these eddies are intermittent in space and time. In this research, we take advantage of the spatial intermittency in a neutrally stratified atmospheric Ekman boundary layer, and study the development of a novel LES methodology. Using the second generation wavelet transform, the proposed model filters the large eddies into distinct groups of significant and insignificant eddies. We show that the significant eddies are sufficient to resolve the physics of the flow. The effects of insignificant eddies are modelled with the proposed multiscale parameterization scheme. The results of the proposed model have been found to be in good agreement with that of an equivalent reference model, experimental data, and asymptotic boundary layer theory. We have found that the number of significant eddies in a neutrally stratified ABL is much lower than the number of resolved eddies in a reference model. The overall algorithm is asymptotically optimal - the CPU time is approximately proportional to the number of resolved eddies. The proposed methodology suggests a potentially novel research direction that may be employed to address a number of computational challenges that must be faced in the field of atmospheric modeling.

  19. Strange drift of passive tracers from horizontal blowing out sources in the atmospheric boundary layer

    SciTech Connect

    Koeltzsch, K.

    1995-12-31

    In the past many scientists running a wind tunnel observed the following strange phenomenon. Plumes blowing out from horizontal sources (with the same momentum as the adjacent flow) and located inside the planar boundary layer, drift stronger towards the ground than described physically by the conventional dispersion equation. This effect occurs clearly in regard to greater surface roughness. If the dispersion by Gauss is used in connection with a term of reflection, the descending of a plume only occurs after the reflection of tracers on the surface, contrary to the observations. On the other hand a dispersion model is used to describe this phenomenon, which depends on height diffusivity coefficients and a power law for the mean velocity profile (Berljand, 1982; Smith, 1957). The aim of the investigation is to provide a contribution to the causes for this phenomenon. The influence of the roughness length is explored more closely for the above named model. The paper studies the properties of basic flow inside the atmospheric boundary layer generated by a wind tunnel with an open test section. The neutral atmosphere over a suburb terrain is modeled. The following presents measurements by hot-wire with a four-wire-probe of the higher, statistical moments related to all three velocities and measurements of concentration by a Flame-Ionization-Detector in an atmospheric boundary layer of the model. In this connection it is of special interest to investigate the skewness of vertical velocity. This quantity is important for the Lagrangian dispersion model.

  20. Numerical Simulation of Atmospheric Boundary Layer Flow Over Battlefield-scale Complex Terrain: Surface Fluxes From Resolved and Subgrid Scales

    DTIC Science & Technology

    2015-07-06

    SECURITY CLASSIFICATION OF: The large-eddy simulation (LES) tool has been used to study the transient characteristics of turbulent mixing in atmospheric ...Approved for Public Release; Distribution Unlimited Final Report: Numerical Simulation of Atmospheric Boundary Layer Flow Over Battlefield-scale Complex...ABSTRACT Number of Papers published in peer-reviewed journals: Final Report: Numerical Simulation of Atmospheric Boundary Layer Flow Over Battlefield

  1. 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.

  2. Spatial Variability of Atmospheric Boundary Layer Structure over the Eastern Equatorial Pacific.

    NASA Astrophysics Data System (ADS)

    Yin, Bingfan; Albrecht, Bruce A.

    2000-05-01

    Variations in the atmospheric boundary layer structure over the eastern equatorial Pacific are analyzed using 916 soundings collected during the First Global Atmospheric Research Program Global Experiment. Unstable boundary layer structures are observed much more frequently in soundings north of the ocean front located near 2.5°N in the eastern equatorial Pacific than in soundings south of the front. An objective criterion is applied to identify the presence of the transition layer, a weak stable layer near cloud base, in the soundings. The transition is observed in about 45% of the soundings in both the unstable and the inversion categories. A comparison of soundings over the cold tongue with those over the ITCZ indicates that differences in static stability between these regions are limited to the layer from the surface to about 850 mb, which is the mean height of the inversions capping the cloud layer over the cold tongue. The cold tongue soundings on average are found to be drier from the surface to 300 mb than the ITCZ soundings with the largest average difference (5 g kg1) between these two groups of soundings observed just above the inversion layer. Compensating subsidence from the ITCZ may account for some of the drying observed just above the cold tongue inversions, although horizontal advection may also be a factor. North-south cross sections (10°S-15°N) of potential temperature, mixing ratio, equivalent potential temperature, and meridional wind across the cold tongue-ITCZ complex (CTIC) were constructed for two longitudinal bands: 95°-105°W and 105°-115°W. There is little latitudinal variation of the average height of the trade inversion and the height of the transition layer across the CTIC. Although the average lifting condensation level (LCL) at 980 mb is located near the average top of the transition layers observed over the cold tongue, the average 980-mb LCL is close to the average height of the base of the transition layers observed over

  3. Application of large eddy simulations for the parameterization of stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Jin, Emilia; Na, Ji Sung; Lee, Joon Sang; Kim, Young-Joon

    2013-04-01

    Authors investigated the parameter space of the stable atmospheric boundary layer by varying geostrophic winds, surface cooling rates and special/temporal resolutions using the large eddy simulations. The NCAR LES model based on a mixed pseudo-spectral finite difference method with third-order Runge-Kutta time stepping utilizing a staggered vertical grid and Smagorinsky subgrid-scale eddy viscosity model and PArallelized Les Model (PALM) based on a central finite differences method with a Cartesian staggered grid and turbulent kinetic energy (TKE) model were used and compared. The basic structure of the potential temperature, winds, stochastic turbulent profile and TKE budget were analyzed and the vortical structure with horizontal layering in the stable atmospheric boundary layer was investigated. Based on these results, authors validated the state-of-the-art k-profile planetary boundary layer parameterization schemes of the global numerical weather prediction models. Han and Pan (2011), Lock et al. (2000) and YSU (Hong 2010) schemes are evaluated.

  4. Study of the diurnal variability of atmospheric chemistry with respect to boundary layer dynamics during DOMINO

    NASA Astrophysics Data System (ADS)

    van Stratum, B. J. H.; Vilà-Guerau de Arellano, J.; Ouwersloot, H. G.; van den Dries, K.; van Laar, T. W.; Martinez, M.; Lelieveld, J.; Diesch, J.-M.; Drewnick, F.; Fischer, H.; Hosaynali Beygi, Z.; Harder, H.; Regelin, E.; Sinha, V.; Adame, J. A.; Sörgel, M.; Sander, R.; Bozem, H.; Song, W.; Williams, J.; Yassaa, N.

    2012-03-01

    We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model (MXLCH) coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: MOZART-4 and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O3-NOx-VOC-HOx diurnal cycle during conditions characterised by a low NOx regime and small O3 tendencies (less than 1 ppb per hour). By focussing on the budget equations of chemical species in the mixed-layer model, we show that for species like O3, NO and NO2, the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the daily cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Lee, Tsengdar John

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

  7. Marine atmospheric boundary layer over some Southern Ocean fronts during the IPY BGH 2008 cruise

    NASA Astrophysics Data System (ADS)

    Messager, C.; Speich, S.; Key, E.

    2012-11-01

    A set of meteorological instruments was added to an oceanographic cruise crossing the Southern Ocean from Cape Town to 57°33' S during the summer of 2008. The Cape Cauldron, the Subtropical, Subantarctic, Polar and southern Antarctic Circumpolar current fronts were successively crossed. The recorded data permitted to derive the exchange of momentum, heat and water vapour at the ocean-atmosphere interface. A set of 38 radiosonde releases complemented the dataset. The marine atmospheric boundary layer characteristics and air-sea interaction when the ship crossed the fronts and eddies are discussed. The specific role of the atmospheric synoptic systems advection on the air-sea interaction over these regions is highlighted. Additionally, the Subantarctic front mesoscale variability induced an anticyclonic eddy considered as part of the Subantarctic front. The specific influence of this Agulhas ring on the aloft atmosphere is also presented.

  8. Quadrant Analysis of the Heat and Momentum Fluxes at the Transition Layer between the Marine Atmospheric Boundary Layer and the developed Internal Boundary Layer close to the coastline

    NASA Astrophysics Data System (ADS)

    Panagiotis Raptis, Ioannis; Helmis, Constantinos

    2013-04-01

    The purpose of this work is to study the main characteristics and the micro-structure of the Transition Layer between the Marine Atmospheric Boundary Layer (MABL) and the developed Internal Boundary Layer (IBL), which is created downwind close to the coastline. The dynamics and the structure of this Transition Layer, which could be defined as the region where the growing IBL perturbations enter the MABL and mix the air, are of major interest affecting a variety of MABL' parameters. For this study data collected from CBLAST field campaign, conducted during summer 2003 at Nantucket Island USA, were used. More specifically data from sonic anemometer measurements at 20 Hz sampling frequency, at 10m height and 80m distance from the coastline were studied. According to our measurements during the night the recorded characteristics of the surface layer at 10m height had the behavior of the MABL, while during the day in most cases the developed IBL was recorded. Thus a diurnal cycle was noticed with the mechanically generated IBL during the night, being lower than the height of our instruments (10m) while a thermally generated IBL during the day was easily observed with characteristic perturbations. In many cases an intermediate state was observed, indicating the existence of the Transition Layer. In order to identify the layers and their characteristics, a conditional analysis was developed using multiple criteria, based mainly on values of the heat and momentum fluxes estimated by the eddy covariance method. We used the quadrant analysis method to study the coherent structures and compare the results under different atmospheric conditions. This method decomposes shear stress into four quadrants, separating the events that contribute to the downward and upward momentum fluxes. Events in quadrants 2 (ejections) and 4 (sweeps) compose the coherent turbulent structures while events in quadrants 1 and 3 compose the incoherent structures. The parameters γ and exuberance

  9. 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.

  10. 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.

  11. Large-eddy simulation of particle-laden atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Ilie, Marcel; Smith, Stefan Llewellyn

    2008-11-01

    Pollen dispersion in the atmospheric boundary layer (ABL) is numerically investigated using a hybrid large-eddy simulation (LES) Lagrangian approach. Interest in prediction of pollen dispersion stems from two reasons, the allergens in the pollen grains and increasing genetic manipulation of plants leading to the problem of cross pollination. An efficient Eulerian-Lagrangian particle dispersion algorithm for the prediction of pollen dispersion in the atmospheric boundary layer is outlined. The volume fraction of the dispersed phase is assumed to be small enough such that particle-particle collisions are negligible and properties of the carrier flow are not modified. Only the effect of turbulence on particle motion has to be taken into account (one-way coupling). Hence the continuous phase can be treated separate from the particulate phase. The continuous phase is determined by LES in the Eulerian frame of reference whereas the dispersed phase is simulated in a Lagrangian frame of reference. Numerical investigations are conducted for the convective, neutral and stable boundary layer as well different topographies. The results of the present study indicate that particles with small diameter size follow the flow streamlines, behaving as tracers, while particles with large diameter size tend to follow trajectories which are independent of the flow streamlines. Particles of ellipsoidal shape travel faster than the ones of spherical shape.

  12. The influence of a very large wind farm on turbulent transport in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Abkar, M.; Porté-Agel, F.

    2012-04-01

    Predicting wind and turbulent transport of heat, water vapor and pollutants through wind farms is of great importance for wind engineering, wind energy and environmental applications. It requires detailed knowledge of atmospheric boundary-layer (ABL) over a wide range of spatial and temporal scales. The complexity of such flows makes it difficult to obtain all the needed information through field experiments alone, and often necessitates high-resolution eddy-resolving numerical tools such as large-eddy simulation (LES). In this study, Large-eddy simulation is used to simulate atmospheric boundary-layer flow through a very large wind farm. To do this, tuning-free Lagrangian scale-dependent dynamic models (Stoll and Porte-Agel 2006) are used to model the subgrid-scale fluxes and the turbine-induced forces are parameterized using the actuator disk model (Wu and Porte-Agel 2011). The effect of large arrays of wind turbines on local/regional fluxes of momentum and scalar quantities under different stability conditions is assessed. Also, it will be shown how wind farms can change the vertical distribution of momentum and scalar fluxes inside the ABL. Particular attention is placed on the growth of the boundary layer height due to the presence of the wind turbines.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  14. 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.

  15. [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.

  16. [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.

  17. 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.

  18. The atmospheric boundary layer response to the dynamic new Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Wu, D. L.; Ganeshan, M.

    2016-12-01

    The increasing ice-free area in the Arctic Ocean has transformed its climate system to one with more dynamic boundary layer clouds and seasonal sea ice. During the fall freeze season, the surface sensible heat flux (SSHF) is a crucial mechanism for the loss of excessive ocean heat to the atmosphere, and it has been speculated to play an important role in the recent cloud cover increase and boundary layer (BL) instability observed in the Beaufort and Chukchi seas. Based on multi-year Japanese cruise ship observations from the ice-strengthened R/V Mirai, we are able to characterize the late summer and early fall ocean-BL interactions in this region. Although the BL is found to be well-mixed more than 90% of the time, the SSHF can explain only 10% of the mixed layer height variability. It is the cloud-generated convective turbulence that apparently dominates BL mixing in this ice-free region, which is similar to previous in-situ observations (SHEBA, ASCOS) over sea ice. The SSHF, however, may contribute to BL instability during conditions of uplift (low-pressure), and the presence of the highly stable stratus cloud regime. The efficiency of sensible heat exchange is low during cold air advection (associated with the stratocumulus cloud regime) despite an enhanced ocean-atmosphere temperature difference (ΔT). In general, surface-generated mixing is favored during episodes of high surface wind speeds as opposed to pronounced ΔT. Our analysis suggests a weak local response of the boundary layer stability to the loss of sea ice cover during late summer, which is masked by the strong influence of the large-scale circulation (and clouds). Apart from the fall season, we also studied the Arctic Ocean BL properties during the cold months (Nov-Apr) using multi-year satellite measurements (COSMIC RO). As the boundary layer is typically stable at this time, one might expect major differences in the nature of surface-atmosphere coupling compared to that observed during late

  19. Stable Atmospheric Boundary-Layer Experiment in Spain (SABLES 98): A Report

    NASA Astrophysics Data System (ADS)

    Cuxart, J.; Yague, C.; Morales, G.; Terradellas, E.; Orbe, J.; Calvo, J.; Fernandez, A.; Soler, M.R.; Infante, C.; Buenestado, P.; Espinalt, A.; Joergensen, H.E.; Rees, J.M.; Vila, J.; Redondo, J.M.; Cantalapiedra, I.R.; Conangla, L.

    This paper describes the Stable AtmosphericBoundary Layer Experiment in Spain (SABLES 98),which took place over the northern Spanish plateaucomprising relatively flat grassland,in September 1998. The main objectives of the campaign were to study the properties of themid-latitude stable boundary layer (SBL).Instrumentation deployed on two meteorologicalmasts (of heights 10 m and 100 m)included five sonic anemometers, 15 thermocouples,five cup anemometers and three propeller anemometers,humidity sensors and radiometers.A Sensitron mini-sodar and a tetheredballoon were also operated continuously. Atriangular array of cup anemometers wasinstalled to allow the detection ofwave events. Two nocturnal periods analysedon 14-15 and 20-21 September are used toillustrate the wide-ranging characteristics of the SBL.

  20. 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

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

    PubMed

    Davy, Richard; Esau, Igor

    2016-05-25

    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.

  2. Statistical-mechanical approach to study the hydrodynamic stability of the stably stratified atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Nevo, G.; Vercauteren, N.; Kaiser, A.; Dubrulle, B.; Faranda, D.

    2017-08-01

    We study the hydrodynamic equilibrium properties of the stably stratified atmospheric boundary layer from measurements obtained in the Snow-Horizontal Array Turbulence Study campaign at the Plaine Morte Glacier in the Swiss Alps. Our approach is based on a combination of dynamical systems techniques and statistical analysis. The main idea is to measure the deviations from the behavior expected by a turbulent observable when it is close to a transition between different metastable states. We first assess the performance of our method on the Lorenz attractor, then on a turbulent flow. The results show that the method recognizes subtle differences among different stable boundary layer turbulence regimes and may be used to help characterize their transitions.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Waggy, Scott B.

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

  5. Coherent Structures in the Turbulent Atmospheric Boundary Layer: modulation by static stability and role in transport

    NASA Astrophysics Data System (ADS)

    Bou-Zeid, E.; Li, D.; Shah, S.

    2012-12-01

    Understanding the turbulent transport of momentum, scalars, and particles in the atmospheric boundary layer is important in many disciplines such as meteorology, hydrology, and desert morphodynamics. At present, similarity theories that rely on a significant degree of empiricism remain the main approach to understand and model these fluxes. One of the hurdles to developing more fundamental and robust theories is our lack of understanding of the topology and dynamics of turbulent coherent structures, which perform these fluxes, and how they are modulated by atmospheric stability. Using field data sets and numerical simulations of atmospheric surface layer flows under a range of stabilities, we revisit these links between coherent structures, atmospheric stability, and turbulent transport. The results confirm that the topology of the coherent structures is very sensitive to stability. The findings point to a gradual transformation of the structures from hairpin vortices under neutral stability, to thermals under unstable conditions, and to more horizontal structures under stable conditions. Under unstable conditions, this change then induces a decorrelation of the momentum and scalar fluxes in the surface layer: the eddies transporting heat and momentum become distinct leading to an increase in the transport efficiency of heat and a decrease in the transport efficiency of momentum. Under stable conditions, the reduction in the transport of momentum to the surface leads to reductions in the friction velocity and the turbulent kinetic energy (TKE) production. The effect of reduced production can be more important than the effect of direct TKE destruction in the stable ABL.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  7. 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.

  8. Controlled meteorological (CMET) balloon profiling of the Arctic atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Roberts, Tjarda; Hole, Lars; Voss, Paul

    2017-04-01

    We demonstrate profiling of the atmospheric boundary layer over Arctic ice-free and sea-ice covered regions by free-floating controllable CMET balloons. The CMET observations (temperature, humidity, wind-speed, pressure) provide in-situ meteorological datasets in very remote regions for comparison to atmospheric models. Controlled Meteorological (CMET) balloons are small airborne platforms that use reversible lift-gas compression to regulate altitude. These balloons have approximately the same payload mass as standard weather balloons but can float for many days, change altitude on command, and transmit meteorological and system data in near-real time via satellite. Five Controlled Meteorological (CMET) balloons were launched from Ny-Ålesund in Svalbard (Spitsbergen) over 5-12 May 2011 and measured vertical atmospheric profiles (temperature, humidity, wind) over coastal and remote areas to both the east and west. One notable CMET flight achieved a suite of 18 continuous soundings that probed the Arctic atmospheric 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 show that CMET balloons are a valuable approach for

  9. 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.

  10. Approximate Analytical Solution to Diurnal Atmospheric Boundary-Layer Growth Under Well-Watered Conditions

    NASA Astrophysics Data System (ADS)

    Rigby, J. R.; Yin, Jun; Albertson, John D.; Porporato, Amilcare

    2015-07-01

    Simplified numerical models of the atmospheric boundary layer (ABL) are useful both for understanding the underlying dynamics and potentially providing parsimonious modelling approaches for inclusion in larger models. Herein the governing equations of a simplified slab model of the uniformly mixed, purely convective, diurnal ABL are shown to allow immediate solutions for the potential temperature and specific humidity as functions of the ABL height and net radiation when expressed in integral form. By employing a linearized saturation vapour relation, the height of the mixed layer is shown to obey a non-linear ordinary differential equation with quadratic dependence on ABL height. A perturbation solution provides general analytical approximations, of which the leading term is shown to represent the contribution under equilibrium evaporation. These solutions allow the diurnal evolution of the height, potential temperature, and specific humidity (i.e., also vapour pressure deficit) of the mixed layer to be expressed analytically for arbitrary radiative forcing functions.

  11. 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.

  12. Giant aeolian dune size determined by the average depth of the atmospheric boundary layer.

    PubMed

    Andreotti, Bruno; Fourrière, Antoine; Ould-Kaddour, Fouzia; Murray, Brad; Claudin, Philippe

    2009-02-26

    Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.

  13. Giant aeolian dune size determined by the average depth of the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Claudin, P.; Fourrière, A.; Andreotti, B.; Murray, A. B.

    2009-12-01

    Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.

  14. A boundary layer approach to the analysis of atmospheric motion over a surface obstruction

    NASA Technical Reports Server (NTRS)

    Frost, W.; Maus, J. R.; Simpson, W. R.

    1973-01-01

    A boundary layer approach for the solution of the flow field induced over a two-dimensional surface obstruction, such as a building or other man-made structure, is proposed. Adopting a specific geometry in the form of a semi-elliptical cylinder, the characteristics of atmospheric shear flow over a rough terrain are coupled with the well-known boundary layer equations. Two approaches are presented to incorporate the pressure field and boundary conditions which exist within the large viscous region over the obstruction. The first considers a region in the immediate vicinity of the body in which the pressure distribution and outer boundary condition on the velocity are computed from potential theory for flow over the elliptical cylinder. The second approach considers a much larger region of influence, extending from the surface to the undisturbed flow at large heights above the obstruction. Methods which appear to provide an improved theoretical model of the flow over the ellipse, such as a technique for simulating the effect of the seperation regions upstream and downstream of the body, are also presented.

  15. Large eddy simulation for atmospheric boundary layer flow over flat and complex terrains

    NASA Astrophysics Data System (ADS)

    Han, Yi; Stoellinger, Michael; Naughton, Jonathan

    2016-09-01

    In this work, we present Large Eddy Simulation (LES) results of atmospheric boundary layer (ABL) flow over complex terrain with neutral stratification using the OpenFOAM-based simulator for on/offshore wind farm applications (SOWFA). The complete work flow to investigate the LES for the ABL over real complex terrain is described including meteorological-tower data analysis, mesh generation and case set-up. New boundary conditions for the lateral and top boundaries are developed and validated to allow inflow and outflow as required in complex terrain simulations. The turbulent inflow data for the terrain simulation is generated using a precursor simulation of a flat and neutral ABL. Conditionally averaged met-tower data is used to specify the conditions for the flat precursor simulation and is also used for comparison with the simulation results of the terrain LES. A qualitative analysis of the simulation results reveals boundary layer separation and recirculation downstream of a prominent ridge that runs across the simulation domain. Comparisons of mean wind speed, standard deviation and direction between the computed results and the conditionally averaged tower data show a reasonable agreement.

  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

    2017-01-01

    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. 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

  18. Mean horizontal wind profiles measured in the atmospheric boundary layer about a simulated block building

    NASA Technical Reports Server (NTRS)

    Frost, W.; Connell, J. R.; Hutto, M. L.; Fichtl, G.

    1977-01-01

    Instrumented wind towers are used to measure the three components of wind about a simulated block building. The mean horizontal wind profiles over the building are compared with wind profiles measured in the absence of the building and the wind speed deficit in the wake of the building is correlated. The turbulence intensity is of the order of 20% in the undisturbed flow whereas the free stream turbulence intensity of wind-tunnel studies is generally not more than 5%. The velocity profiles measured in the undisturbed flow zones support the representation of a neutrally stable atmospheric boundary layer with a logarithmic wind profile.

  19. A parametrization of the convective atmospheric boundary layer and its application into a global climate model

    NASA Astrophysics Data System (ADS)

    Holtslag, A. A. M.; Boville, B. A.; Moeng, C.-H.

    Vertical diffusion of heat and passive scalars (like moisture) in the convective atmospheric boundary layer are focused upon. Flux equations are analyzed with data obtained from large eddy simulations. The findings can be used in a modified flux gradient approach, which takes into account the nonlocal convective vertical exchange using the so called counter gradient transport and a nonlocal diffusivity coefficient. Previous findings are simplified and applied to a community climate model. The impact of the nonlocal approach is illustrated in comparison with the usual local diffusion approach.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Radiation and atmospheric circulation controls on carbonyl sulfide concentrations in the marine boundary layer

    NASA Astrophysics Data System (ADS)

    Berkelhammer, M.; Steen-Larsen, H. C.; Cosgrove, A.; Peters, A. J.; Johnson, R.; Hayden, M.; Montzka, S. A.

    2016-11-01

    A potential closure of the global carbonyl sulfide (COS or OCS) budget has recently been attained through a combination of remote sensing, modeling, and extended surface measurements. However, significant uncertainties in the spatial and temporal dynamics of the marine flux still persist. In order to isolate the terrestrial photosynthetic component of the global atmospheric OCS budget, tighter constraints on the marine flux are needed. We present 6 months of nearly continuous in situ OCS concentrations from the North Atlantic during the fall and winter of 2014-2015 using a combination of research vessel and fixed tower measurements. The data are characterized by synoptic-scale ˜100 pmol mol-1 variations in marine boundary layer air during transitions from subtropical to midlatitude source regions. The synoptic OCS variability is shown here to be a linear function of the radiation history along an air parcel's trajectory with no apparent sensitivity to the chlorophyll concentration of the surface waters that the air mass interacted with. This latter observation contradicts expectations and suggests a simple radiation limitation for the combined direct and indirect marine OCS emissions. Because the concentration of OCS in the marine boundary layer is so strongly influenced by an air parcel's history, marine and atmospheric concentrations would rarely be near equilibrium and thus even if marine production rates are held constant at a given location, the ocean-atmosphere flux would be sensitive to changes in atmospheric circulation alone. We hypothesize that changes in atmospheric circulation including latitudinal shifts in the storm tracks could affect the marine flux through this effect.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    A coupled model is used to study the equilibrium state of the ocean-atmosphere boundary layer in the tropics. The atmospheric model is a one-dimensional thermodynamic model for a partially mixed, partly cloudy convective boundary layer (CBL), including the effects of cloud-top subsidence, surface momentum and heat (latent and sensible) fluxes, and realistic radiative transfer for both shortwaves and longwaves (Betts and Ridgway, 1988; 1989). The oceanic model is a thermodynamic model for a well-mixed layer, with a closure constraint based on a one-dimensional turbulent kinetic energy (TKE) equation following Kraus and Turner (1967). Results of several sets of experiments are reported in this paper. In the first two sets of experiments, with sea surface temperature (SST) specified, we solve the equilibrium state of the coupled system as a function of SST for a given surface wind (case 1) and as a function of surface wind for a given SST (case 2). In both cases the depth of the CBL and the ocean mixed layer (OML) increases and the upwelling below the OML decreases, corresponding to either increasing SST or increasing surface wind. The deepening of the equilibrium CBL is primarily linked to the increase of CBL moisture with increasing SST and surface wind. The increase of OML depth and decrease of upwelling are due to a decrease of net downward heat flux with increasing SST and the generation of TKE by increasing wind. In another two sets of experiments, we solve for the coupled ocean-atmosphere model iteratively as a function of surface wind for a fixed upwelling (case 3) and a fixed OML depth (case 4). SST falls with increasing wind in both cases, but the fall is steeper in case 4, because the OML depth is fixed, whereas in case 3 the depth is allowed to deepen and the cooling is spread over a larger mass of water. The decrease of evaporation with increasing wind in case 4 leads to a very dry and shallow CBL. Results of further experiments with surface wind and SST

  7. Scaling Characteristics of Mesoscale Wind Fields in the Lower Atmospheric Boundary Layer: Implications for Wind Energy

    NASA Astrophysics Data System (ADS)

    Kiliyanpilakkil, Velayudhan Praju

    Atmospheric motions take place in spatial scales of sub-millimeters to few thousands of kilometers with temporal changes in the atmospheric variables occur in fractions of seconds to several years. Consequently, the variations in atmospheric kinetic energy associated with these atmospheric motions span over a broad spectrum of space and time. The mesoscale region acts as an energy transferring regime between the energy generating synoptic scale and the energy dissipating microscale. Therefore, the scaling characterizations of mesoscale wind fields are significant in the accurate estimation of the atmospheric energy budget. Moreover, the precise knowledge of the scaling characteristics of atmospheric mesoscale wind fields is important for the validation of the numerical models those focus on wind forecasting, dispersion, diffusion, horizontal transport, and optical turbulence. For these reasons, extensive studies have been conducted in the past to characterize the mesoscale wind fields. Nevertheless, the majority of these studies focused on near-surface and upper atmosphere mesoscale regimes. The present study attempt to identify the existence and to quantify the scaling of mesoscale wind fields in the lower atmospheric boundary layer (ABL; in the wind turbine layer) using wind observations from various research-grade instruments (e.g., sodars, anemometers). The scaling characteristics of the mesoscale wind speeds over diverse homogeneous flat terrains, conducted using structure function based analysis, revealed an altitudinal dependence of the scaling exponents. This altitudinal dependence of the wind speed scaling may be attributed to the buoyancy forcing. Subsequently, we use the framework of extended self-similarity (ESS) to characterize the observed scaling behavior. In the ESS framework, the relative scaling exponents of the mesoscale atmospheric boundary layer wind speed exhibit quasi-universal behavior; even far beyond the inertial range of turbulence (Delta

  8. Determination of the Vertical Extinction Coefficient Profile in the Atmospheric Boundary Layer and the Free Troposphere

    NASA Astrophysics Data System (ADS)

    Adam, M.; Pahlow, M.; Kovalev, V.; Ondov, J.; Balin, I.; Simeonov, V.; van den Bergh, H.; Parlange, M.

    2003-04-01

    Elastic lidars were deployed in Baltimore (USA) and Jungfraujoch (Switzerland) with the goal of determining aerosol vertical extinction coefficient profiles in the atmospheric boundary layer (ABL) and free troposphere, respectively. This talk focuses on a comparision of methods to obtain the vertical extinction coefficient, specifically, 1) One Angle Method (OAM), 2) Optical Depth Method (ODM) and 3) Klett Method. The reference extinction coefficient values for the near point in the first method were obtained using Mie theory with particle size distribution and estimates of the refractive index from supporting ground measurements. For the ODM we use the optical depth measurements using a sun photometer. The reference far field value for the Klett method was obtained using standard atmospheric profiles.

  9. 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.

  10. 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.

  11. 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.

  12. Scale effects in wind tunnel modeling of an urban atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kozmar, Hrvoje

    2010-03-01

    Precise urban atmospheric boundary layer (ABL) wind tunnel simulations are essential for a wide variety of atmospheric studies in built-up environments including wind loading of structures and air pollutant dispersion. One of key issues in addressing these problems is a proper choice of simulation length scale. In this study, an urban ABL was reproduced in a boundary layer wind tunnel at different scales to study possible scale effects. Two full-depth simulations and one part-depth simulation were carried out using castellated barrier wall, vortex generators, and a fetch of roughness elements. Redesigned “Counihan” vortex generators were employed in the part-depth ABL simulation. A hot-wire anemometry system was used to measure mean velocity and velocity fluctuations. Experimental results are presented as mean velocity, turbulence intensity, Reynolds stress, integral length scale of turbulence, and power spectral density of velocity fluctuations. Results suggest that variations in length-scale factor do not influence the generated ABL models when using similarity criteria applied in this study. Part-depth ABL simulation compares well with two full-depth ABL simulations indicating the truncated vortex generators developed for this study can be successfully employed in urban ABL part-depth simulations.

  13. 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.

  14. 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.

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

    NASA Technical Reports Server (NTRS)

    Tillman, James E.

    1994-01-01

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

  16. Numerical Modeling of the Propagation Environment in the Atmospheric Boundary Layer over the Persian Gulf.

    NASA Astrophysics Data System (ADS)

    Atkinson, B. W.; Li, J.-G.; Plant, R. S.

    2001-03-01

    Strong vertical gradients at the top of the atmospheric boundary layer affect the propagation of electromagnetic waves and can produce radar ducts. A three-dimensional, time-dependent, nonhydrostatic numerical model was used to simulate the propagation environment in the atmosphere over the Persian Gulf when aircraft observations of ducting had been made. A division of the observations into high- and low-wind cases was used as a framework for the simulations. Three sets of simulations were conducted with initial conditions of varying degrees of idealization and were compared with the observations taken in the Ship Antisubmarine Warfare Readiness/Effectiveness Measuring (SHAREM-115) program. The best results occurred with the initialization based on a sounding taken over the coast modified by the inclusion of data on low-level atmospheric conditions over the Gulf waters. The development of moist, cool, stable marine internal boundary layers (MIBL) in air flowing from land over the waters of the Gulf was simulated. The MIBLs were capped by temperature inversions and associated lapses of humidity and refractivity. The low-wind MIBL was shallower and the gradients at its top were sharper than in the high-wind case, in agreement with the observations. Because it is also forced by land-sea contrasts, a sea-breeze circulation frequently occurs in association with the MIBL. The size, location, and internal structure of the sea-breeze circulation were realistically simulated. The gradients of temperature and humidity that bound the MIBL cause perturbations in the refractivity distribution that, in turn, lead to trapping layers and ducts. The existence, location, and surface character of the ducts were well captured. Horizontal variations in duct characteristics due to the sea-breeze circulation were also evident. The simulations successfully distinguished between high- and low-wind occasions, a notable feature of the SHAREM-115 observations. The modeled magnitudes of duct

  17. 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.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  20. Deviations from Equilibrium in Daytime Atmospheric Boundary Layer Turbulence arising from Nonstationary Mesoscale Forcing

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    LES of the "canonical" daytime atmospheric boundary layer (ABL) over flat topography is developed as an equilibrium ABL with steady surface heat flux, Q0 and steady unidirectional "geostrophic" wind vector Vg above a capping inversion. A strong inversion layer in daytime ABL acts as a "lid" that sharply separates 3D "microscale" ABL turbulence at the O(10) m scale from the quasi-2D "mesoscale" turbulent weather eddies (O(100) km scale). While "canonical" ABL is equilibrium, quasi-stationary and characterized statistically by the ratio of boundary layer depth (zi) to Obukhov length scale (- L) , the real mesoscale influences (Ug and Q0) that force a true daytime ABL are nonstationary at both diurnal and sub-diurnal time scales. We study the consequences of this non-stationarity on ABL dynamics by forcing ABL LES with realistic WRF simulations over flat Kansas terrain. Considering horizontal homogeneity, we relate the mesoscale and geostrophic winds, Ug and Vg, and systematically study the ABL turbulence response to non-steady variations in Q0 and Ug. We observe significant deviations from equilibrium, that manifest in many ways, such as the formation of "roll" eddies purely from changes in mesoscale wind direction that are normally associated with increased surface heat flux. Support from DOE. Compute resources from Penn State ICS.

  1. The relative importance of ejections and sweeps to momentum transfer in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Katul, Gabriel; Poggi, Davide; Cava, Daniela; Finnigan, John

    2006-09-01

    Using an incomplete third-order cumulant expansion method (ICEM) and standard second-order closure principles, we show that the imbalance in the stress contribution of sweeps and ejections to momentum transfer (Δ S o ) can be predicted from measured profiles of the Reynolds stress and the longitudinal velocity standard deviation for different boundary-layer regions. The ICEM approximation is independently verified using flume data, atmospheric surface layer measurements above grass and ice-sheet surfaces, and within the canopy sublayer of maturing Loblolly pine and alpine hardwood forests. The model skill for discriminating whether sweeps or ejections dominate momentum transfer (e.g. the sign of Δ S o ) agrees well with wind-tunnel measurements in the outer and surface layers, and flume measurements within the canopy sublayer for both sparse and dense vegetation. The broader impact of this work is that the “genesis” of the imbalance in Δ S o is primarily governed by how boundary conditions impact first and second moments.

  2. Atmospheric boundary layer response to sea surface temperatures during the SEMAPHORE experiment

    NASA Astrophysics Data System (ADS)

    Giordani, Hervé; Planton, Serge; Benech, Bruno; Kwon, Byung-Hyuk

    1998-10-01

    The sensitivity of the marine atmospheric boundary layer (MABL) subjected to sea surface temperatures (SST) during the Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment in 1993 has been studied. Atmospheric analyses produced by the Action de Recherche, Petite Echelle, Grande Echelle (ARPEGE) operational model at the French meteorological weather service assimilated data sets collected between October 7 and November 17, 1993, merged with the Global Telecommunication System (GTS) data. Analyses were validated against independent data from aircraft instruments collected along a section crossing the Azores oceanic front, not assimilated into the model. The responses of the mean MABL in the aircraft cross section to changes in SST gradients of about 1°C/100 km were the presence of an atmospheric front with horizontal gradients of 1°C/100 km and an increase of the wind intensity from the cold to the warm side during an anticyclonic synoptic situation. The study of the spatiotemporal characteristics of the MABL shows that during 3 days of an anticyclonic synoptic situation the SST is remarkably stationary because it is principally controlled by the Azores ocean current, which has a timescale of about 10 days. However, the temperature and the wind in the MABL are influenced by the prevailing atmospheric conditions. The ocean does not appear to react to the surface atmospheric forcing on the timescale of 3 days, whereas the atmospheric structures are modified by local and synoptic-scale advection. The MABL response appears to be much quicker than that of the SSTs. The correlation between the wind and the thermal structure in the MABL is dominated by the ageostrophic and not by the geostrophic component. In particular, the enhancement of the wind on either side of the SST front is mainly due to the ageostrophic component. Although the surface heat fluxes are not the only cause of ageostrophy, the

  3. Sensitivity of Radar Wave Propagation Power to the Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Lentini, N.; Hackett, E. E.

    2014-12-01

    Radar is a remote sensor used for scientific, meteorological, and military applications. Radar waves are affected by the medium through which they propagate, impacting the accuracy of radar measurements. Thus, environmental effects should be understood and quantified. The marine atmospheric boundary layer (MABL) is highly dynamic and turbulent, and affects radar wave propagation. The ocean surface roughness impacts scattering behavior. These effects cause variability in constructive and destructive interference patterns due to reflection from the ocean surface, known as multipath. The atmospheric effects cause radar waves to attenuate and refract; this study focuses on the refractive effects. A high-fidelity, physics-based, parabolic wave equation simulation is used to model the radar propagation and accounts for effects of the rough ocean surface (wind seas and swell) as well as variable refractivity with height and range. We use a robust, variance based, sensitivity analysis method called the Extended Fourier Amplitude Sensitivity Test to quantify which environmental parameters have the most significant effect on the modeled radar wave propagation. In this sensitivity study, the environment is parameterized by 16 variables, 8 ocean surface and 8 atmospheric. Sensitivity analysis is performed for 3 radar frequencies (3, 9, and 15 GHz) and 2 polarizations (horizontal and vertical). Results indicate that radar wave propagation is more sensitive to atmospheric parameters than ocean surface parameters. The mixed layer has the most far-reaching effect over the entire model domain (a range of 60 km and altitudes up to 1 km), characterized by its height and refractivity gradient. The remaining important factors have a predominantly local effect in the region where they occur in the MABL atmospheric structure. At low altitudes, radar wave propagation power is most sensitive to the gradient and curvature of the vertical refractivity profile. This research provides insight

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  5. 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.

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Wildmann, Norman; Bange, Jens

    2014-05-01

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

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1992-08-01

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

  12. Continuous atmospheric boundary layer observations in the coastal urban area of Barcelona, Spain

    NASA Astrophysics Data System (ADS)

    Pandolfi, M.; Martucci, G.; Querol, X.; Alastuey, A.; Wilsenack, F.; Frey, S.; O'Dowd, C. D.; Dall'Osto, M.

    2013-01-01

    Continuous measurements of Surface Mixed Layer (SML), Decoupled Residual/Convective Layer (DRCL) and aerosol backscatter coefficient were performed within the Barcelona (NE Spain) boundary layer from September to October 2010 (30 days) in the framework of the SAPUSS (Solving Aerosol Problems Using Synergistic Strategies) field campaign. Two near-infrared ceilometers (Jenoptik CHM15K) vertically and horizontally-probing (only vertical profiles are discussed) were deployed during SAPUSS and compared with potential temperature profiles measured by daily radiosounding (midnight and midday) to interpret the boundary layer structure in the urban area of Barcelona. Ceilometer-based DRCL (1761±363 m a.g.l.) averaged over the campaign duration were twice as high as the mean SML (904±273 m a.g.l.) with a marked SML diurnal cycle. The overall agreement between the ceilometer-retrieved and radiosounding-based SML heights (R2=0.8) revealed overestimation of the SML by the ceilometer (Δh=145±145 m). After separating the data in accordance with different atmospheric scenarios, the lowest SML (736±183 m) and DRCL (1573±428 m) were recorded during warm North African (NAF) advected air mass. By contrast, higher SML and DRCL were observed during stagnant regional (REG) (911±234 m and 1769±314 m, respectively) and cold Atlantic (ATL) (965±222 m and 1878±290 m, respectively) air masses. The SML during the NAF scenario frequently showed a flat upper boundary throughout the day because of strong winds from the Mediterranean Sea that limit the midday SML convective growth observed during ATL and REG scenarios. The mean backscatter coefficients were calculated at two selected heights as representative of middle and top SML portions, i.e. β500=0.59±0.45 M m-1 sr-1 and β800=0.87±0.68 M m-1 sr-1 at 500 m and 800 m a.g.l., respectively. The highest backscatter coefficients were observed during NAF (β500=0.77±0.57 M m-1 sr-1) when compared with ATL (β500= 0.51±0.44 M m-1 sr-1

  13. Unsteady Flow in Different Atmospheric Boundary Layer Regimes and Its Impact on Wind-Turbine Performance

    NASA Astrophysics Data System (ADS)

    Gohari, Iman; Korobenko, Artem; Yan, Jinhui; Bazilevs, Yuri; Sarkar, Sutanu

    2016-11-01

    Wind is a renewable energy resource that offers several advantages including low pollutant emission and inexpensive construction. Wind turbines operate in conditions dictated by the Atmospheric Boundary Layer (ABL) and that motivates the study of coupling ABL simulations with wind turbine dynamics. The ABL simulations can be used for realistic modeling of the environment which, with the use of fluid-structure interaction, can give realistic predictions of extracted power, rotor loading, and blade structural response. The ABL simulations provide inflow boundary conditions to the wind-turbine simulator which uses arbitrary Lagrangian-Eulerian variational multiscale formulation. In the present work, ABL simulations are performed to examine two different scenarios: (i) A neutral ABL with zero heat-flux and inversion layer at 350m, in which the wind turbine experiences maximum mean shear; (2) A shallow ABL with the surface cooling-rate of -1 K/hr, in which the wind turbine experiences maximum mean velocity at the low-level-jet nose height. We will discuss differences in the unsteady flow between the two different ABL conditions and their impact on the performance of the wind turbine cluster in the coupled ABL-wind turbine simulations.

  14. Analytical Reduced Models for the Non-stationary Diabatic Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Momen, Mostafa; Bou-Zeid, Elie

    2017-09-01

    Geophysical boundary-layer flows feature complex dynamics that often evolve with time; however, most current knowledge centres on the steady-state problem. In these atmospheric and oceanic boundary layers, the pressure gradient, buoyancy, Coriolis, and frictional forces interact to determine the statistical moments of the flow. The resulting equations for the non-stationary mean variables, even when succinctly closed, remain challenging to handle mathematically. Here, we derive a simpler physical model that reduces these governing unsteady Reynolds-averaged Navier-Stokes partial differential equations into a single first-order ordinary differential equation with non-constant coefficients. The reduced model is straightforward to solve under arbitrary forcing, even when the statistical moments are non-stationary and the viscosity varies in time and space. The model is successfully validated against large-eddy simulation for, (1) time-variable pressure gradients, and (2) linearly time-variable buoyancy. The new model is shown to have a superior performance compared to the classic Blackadar solutions (and later improvements on these solutions), and it covers a much wider range of conditions.

  15. Influence of Evaporating Droplets in the Turbulent Marine Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Peng, Tianze; Richter, David

    2017-08-01

    Sea-spray droplets ejected into the marine atmospheric boundary layer take part in a series of complex transport processes. By capturing the air-droplet coupling and feedback, we focus on how droplets modify the total heat transfer across a turbulent boundary layer. We implement a high-resolution Eulerian-Lagrangian algorithm with varied droplet size and mass loading in a turbulent open-channel flow, revealing that the influence from evaporating droplets varies for different dynamic and thermodynamic characteristics of droplets. Droplets that both respond rapidly to the ambient environment and have long suspension times are able to modify the latent and sensible heat fluxes individually, however the competing signs of this modification lead to an overall weak effect on the total heat flux. On the other hand, droplets with a slower thermodynamic response to the environment are less subjected to this compensating effect. This indicates a potential to enhance the total heat flux, but the enhancement is highly dependent on the concentration and suspension time.

  16. 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.

  17. 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.

  18. Analytical Reduced Models for the Non-stationary Diabatic Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Momen, Mostafa; Bou-Zeid, Elie

    2017-04-01

    Geophysical boundary-layer flows feature complex dynamics that often evolve with time; however, most current knowledge centres on the steady-state problem. In these atmospheric and oceanic boundary layers, the pressure gradient, buoyancy, Coriolis, and frictional forces interact to determine the statistical moments of the flow. The resulting equations for the non-stationary mean variables, even when succinctly closed, remain challenging to handle mathematically. Here, we derive a simpler physical model that reduces these governing unsteady Reynolds-averaged Navier-Stokes partial differential equations into a single first-order ordinary differential equation with non-constant coefficients. The reduced model is straightforward to solve under arbitrary forcing, even when the statistical moments are non-stationary and the viscosity varies in time and space. The model is successfully validated against large-eddy simulation for, (1) time-variable pressure gradients, and (2) linearly time-variable buoyancy. The new model is shown to have a superior performance compared to the classic Blackadar solutions (and later improvements on these solutions), and it covers a much wider range of conditions.

  19. Observations and Modelling of the Atmospheric Boundary Layer Over Sea-Ice in a Svalbard Fjord

    NASA Astrophysics Data System (ADS)

    Mäkiranta, Eeva; Vihma, Timo; Sjöblom, Anna; Tastula, Esa-Matti

    2011-07-01

    Sonic anemometer and profile mast measurements made in Wahlenbergfjorden, Svalbard Arctic archipelago, in May 2006 and April 2007 were employed to study the atmospheric boundary layer over sea-ice. The turbulent surface fluxes of momentum and sensible heat were calculated using eddy correlation and gradient methods. The results showed that the literature-based universal functions underestimated turbulent mixing in strongly stable conditions. The validity of the Monin-Obukhov similarity theory was questionable for cross-fjord flow directions and in the presence of mesoscale variability or topographic effects. The aerodynamic roughness length showed a dependence on the wind direction. The mean roughness length for along-fjord wind directions was (2.4 ± 2.6) × 10-4 m, whereas that for cross-fjord directions was (5.4 ± 2.8) × 10-3 m. The thermal stratification and turbulent fluxes were affected by the synoptic situation with large differences between the 2 years. Channelling effects and drainage flows occurred especially during a weak large-scale flow. The study periods were simulated applying the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution in the finest domain. The results for the 2-m air temperature and friction velocity were good, but the model failed to reproduce the spatial variability in wind direction between measurement sites 3 km apart. The model suggested that wind shear above the stable boundary layer provided a non-local source for the turbulence observed.

  20. Atmospheric boundary layer and ozone-aerosol interactions under Saharan intrusions observed during AMISOC summer campaign

    NASA Astrophysics Data System (ADS)

    Adame, J. A.; Córdoba-Jabonero, C.; Sorribas, M.; Toledo, D.; Gil-Ojeda, M.

    2015-03-01

    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 in addition 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 were lower during dusty 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. Dust also disturbed the typical daily ABL evolution. Stable conditions were observed in 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 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 the surface ozone.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  4. Application of transilient turbulent theory to study interactions between the atmospheric boundary layer and forest canopies

    NASA Astrophysics Data System (ADS)

    Inclán, M. G.; Forkel, R.; Dlugi, R.; Stull, R. B.

    1996-06-01

    The new Forest-Land-Atmosphere ModEl called FLAME is presented. The first-order, nonlocal turbulence closure called transilient turbulence theory (Stull, 1993) is applied to study the interactions between a forested land-surface and the atmospheric boundary layer (ABL). The transilient scheme is used for unequal vertical grid spacing and includes the effects of drag, wake turbulence, and interference to vertical mixing by plant elements. Radiation transfer within the vegetation and the equations for the energy balance at the leaf surface have been taken from Norman (1979). Among others, the model predicts profiles of air temperature, humidity and wind velocity within the ABL, sensible and latent heat fluxes from the soil and the vegetation, the stomata and aerodynamic resistances, as well as profiles of temperature and water content in the soil. Preliminary studies carried out for a cloud free day and idealized initial conditions are presented. The canopy height is 30 m within a vertical domain of 3 km. The model is able to capture some of the effects usually observed within and above forested areas, including the relative wind speed maximum in the trunk space and the counter gradient-fluxes in the lower part of the plant stand. Of special interest is the determination of the location and magnitude of the turbulent mixing between model layers, which permits one to identify the effects of large eddies transporting momentum and scalar quantities into the canopy. A comparison between model simulations and field measurements will be presented in a future paper.

  5. Laboratory modelling of the transfer processes between the ocean and atmosphere in the boundary layers

    NASA Astrophysics Data System (ADS)

    Sergeev, Daniil; Kandaurov, Alexander; Troitskaya, Yuliya; Vdovin, Maxim

    The processes of momentum and heat transfer between ocean and atmosphere in the boundary layer were investigated within laboratory modeling for a wide range of wind speed and surface wave including hurricane conditions. Experiments were carried out on the Wind-Wave Flume of the Large Thermostratified Tank of IAP RAS. A special net located under the surface at different depths allows to vary parameters of surface waves independently on wind parameters. Theory of self-similarity of air flow parameters in the flume was used to calculate values aerodynamic and heat transfer coefficients from the measured velocity and temperature profiles by Pito and hotfilm gauges respectively. Simultaneous measurements of surface elevation with system wire allow to obtain spectra and integral parameters of waves. It was demonstrated that in contrast to the drag coefficient, heat transfer coefficient is virtually independent of wind speed and wave parameters to the moment of the beginning of spray generation and then increases rapidly.

  6. POD Analysis of a Wind Turbine Wake in a Turbulent Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Bastine, D.; Witha, B.; Wächter, M.; Peinke, J.

    2014-06-01

    The wake of a single wind turbine is modeled using an actuator disk model and large eddy simulations. As inflow condition a numerically generated turbulent atmospheric boundary layer is used. The proper orthogonal decomposition (POD) is applied to a plane perpendicular to the main flow in the far wake of the turbine. Reconstructions of the field are investigated depending on the numbers of POD modes used. Even though a great number of modes is needed to recover a great part of the turbulent kinetic energy, our results indicate that relevant aspects of a wake flow can be recovered using only a few modes. Particularly, the dynamics of the average velocity over a potential disk in the wake can partially be captured using only three modes.

  7. 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.

  8. Spectral link for the mean velocity profile in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Zhang, Dongrong; Gioia, Gustavo; Chakraborty, Pinaki

    2016-11-01

    Turbulent flow in the atmospheric boundary layer is sheared and stratified. For this flow, we consider the mean velocity profile (MVP), the vertical profile of the time-averaged horizontal wind velocity. We employ the theoretical framework of the spectral link, originally proposed for MVP in sheared flows (Gioia et al., 2010) and later extended to stratified flows (Katul et al., 2011). Accounting for the whole structure of the turbulent energy spectrum-the energetic range, the inertial range, and the dissipative range-we examine the scaling of the MVP in the "wall coordinates" and in the Monin-Obukhov similarity coordinates, for both stable and unstable stratification. Our results are in excellent accord with field measurements and numerical simulations. Okinawa Institute of Science and Technology.

  9. Single-column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer

    NASA Technical Reports Server (NTRS)

    Cuxart, J.; Holtslag, A. A. M.; Steeneveld, G-J; Beare, R. J.; Bazile, E.; Beljaars, A.; Cheng, A.; Conangla, L.; Ek, M.; Freedman, F.; hide

    2004-01-01

    The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, which has a large impact on the medium-range weather forecasts and on climate integrations. A non-strongly stratified arctic case is simulated by nineteen single-column turbulence schemes. The statistics from the Large-eddy simulation (LES) intercomparison made for the same case by eight different models are used as a guiding reference. The single-column parameterizations include research schemes and operational schemes from major forecast and climate research centres. First order schemes, a large number of turbulence kinetic energy closures, and other proposals have submitted results. There is a large spread in the results; in general, the operational schemes mix more efficiently than the research ones, and the TKE and other higher order closures give results closer to the LES statistics. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.

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

    SciTech Connect

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

    1998-12-31

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

  12. A stable and accurate scheme for nonlinear diffusion equations: Application to atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Nazari, Farshid; Mohammadian, Abdolmajid; Zadra, Ayrton; Charron, Martin

    2013-03-01

    Stability concerns are always a factor in the numerical solution of nonlinear diffusion equations, which are a class of equations widely applicable in different fields of science and engineering. In this study, a modified extended backward differentiation formulae (ME BDF) scheme is adapted for the solution of nonlinear diffusion equations, with a special focus on the atmospheric boundary layer diffusion process. The scheme is first implemented and examined for a widely used nonlinear ordinary differential equation, and then extended to a system of two nonlinear diffusion equations. A new temporal filter which leads to significant improvement of numerical results is proposed, and the impact of the filter on the stability and accuracy of the results is investigated. Noteworthy improvements are obtained as compared to other commonly used numerical schemes. Linear stability analysis of the proposed scheme is performed for both systems, and analytical stability limits are presented.

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

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

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

    PubMed Central

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

    2012-01-01

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

  15. Single-column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer

    NASA Technical Reports Server (NTRS)

    Cuxart, J.; Holtslag, A. A. M.; Steeneveld, G-J; Beare, R. J.; Bazile, E.; Beljaars, A.; Cheng, A.; Conangla, L.; Ek, M.; Freedman, F.; Hamdi, R.

    2004-01-01

    The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, which has a large impact on the medium-range weather forecasts and on climate integrations. A non-strongly stratified arctic case is simulated by nineteen single-column turbulence schemes. The statistics from the Large-eddy simulation (LES) intercomparison made for the same case by eight different models are used as a guiding reference. The single-column parameterizations include research schemes and operational schemes from major forecast and climate research centres. First order schemes, a large number of turbulence kinetic energy closures, and other proposals have submitted results. There is a large spread in the results; in general, the operational schemes mix more efficiently than the research ones, and the TKE and other higher order closures give results closer to the LES statistics. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.

  16. 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.

  17. Generation of atmospheric boundary layer in the IIUM low speed wind tunnel

    NASA Astrophysics Data System (ADS)

    Za'aba, Khalid Aldin Bin; Asrar, Waqar; Dheeb, Mohamad Al

    2017-03-01

    The purpose of this paper is to describe an attempt made to simulate the atmospheric boundary layer (ABL) in the Low Speed Wind Tunnel (LSWT) at IIUM. This was performed through modifications of the inlet and surface conditions of the test section. Devices such as spires, fences and surface roughness were used. The ASCE 7-10 standard was used as a reference to validate the results between the wind tunnel data and the full-scale ABL flow characteristics. The velocity profile and turbulence intensity were measured using a one-dimensional hotwire (CTA) probe. The data obtained show good agreement with ASCE 7-10 velocity profiles for exposures B and C while using a scale of 1:488 to match the wind tunnel data. The turbulence intensity profiles do not show a good agreement.

  18. Linking NO2 surface concentration and integrated content in the urban developed atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Dieudonné, E.; Ravetta, F.; Pelon, J.; Goutail, F.; Pommereau, J.-P.

    2013-03-01

    A statistical linear relationship between NO2 surface concentration and its integrated content in the atmospheric boundary layer (ABL) is established in urban conditions, using ABL depth as an ancillary parameter. This relationship relies on a unique data set including 20 months of observations from a ground-based UV-visible light spectrometer and from an aerosol lidar, both located in Paris inner city center. Measurements show that in all seasons, large vertical gradients of NO2 concentration exist in Paris developed ABL, explaining why the average concentration retrieved is only about 25% of NO2 surface concentration. This result shows that the commonly used hypothesis of constant mixing ratio in the ABL is not valid over urban areas, where large NOx emissions occur. Moreover, the relationship obtained is robust, and the studied area lacks of any particular orographic features, so that our results should be more widely applicable to pollution survey from space-borne observations.

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

    NASA Astrophysics Data System (ADS)

    Momen, M.; Bou-Zeid, E.

    2013-12-01

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

  20. Continuous atmospheric boundary layer observations in the coastal urban area of Barcelona during SAPUSS

    NASA Astrophysics Data System (ADS)

    Pandolfi, M.; Martucci, G.; Querol, X.; Alastuey, A.; Wilsenack, F.; Frey, S.; O'Dowd, C. D.; Dall'Osto, M.

    2013-05-01

    Continuous measurements of surface mixed layer (SML), decoupled residual/convective layer (DRCL) and aerosol backscatter coefficient were performed within the Barcelona (Spain) boundary layer from September to October 2010 (30 days) in the framework of the SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) field campaign. Two near-infrared ceilometers (Jenoptik CHM15K), vertically and horizontally probing (only vertical profiles are herein discussed), were deployed. Ceilometer-based DRCLs (1761 ± 363 m a.g.l.) averaged over the campaign duration were twice as high as the mean SML (904 ± 273 m a.g.l.). Both DRCL and SML showed a marked SML diurnal cycle. Ceilometer data were compared with potential temperature profiles measured by daily radiosounding (twice a day, midnight and midday) to interpret the boundary layer structure in the coastal urban area of Barcelona. The overall agreement (R2 = 0.80) between the ceilometer-retrieved and radiosounding-based SML heights (h) revealed overestimation of the SML by the ceilometer (Δh=145 ± 145 m). After separating the data in accordance with different atmospheric scenarios, the lowest SML (736 ± 183 m) and DRCL (1573 ± 428 m) were recorded during warm North African (NAF) advected air mass. By contrast, higher SML and DRCL were observed during stagnant Regional (REG) (911 ± 234 m and 1769 ± 314 m, respectively) and cold Atlantic (ATL) (965 ± 222 m and 1878 ± 290 m, respectively) air masses. In addition to being the lowest, the SML during the NAF scenario frequently showed a flat upper boundary throughout the day possibly because of the strong winds from the Mediterranean Sea limiting the midday SML convective growth. The mean backscatter coefficients were calculated at two selected heights representative of middle and top SML portions, i.e. β500 = 0.59 ± 0.45 Mm-1 sr-1 and β800 = 0.87 ± 0.68 Mm-1 sr-1 at 500 m and 800 m a.g.l., respectively. The highest backscatter coefficients were observed

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

  4. Vertical distribution of CO2 in the atmospheric boundary layer: Characteristics and impact of meteorological variables

    NASA Astrophysics Data System (ADS)

    Li, Yanli; Deng, Junjun; Mu, Chao; Xing, Zhenyu; Du, Ke

    2014-07-01

    Knowledge of vertical CO2 distribution is important for development of CO2 transport models and calibration/validation of satellite-borne measurements. In this study, vertical profiles of CO2 concentration within 0-1000 m were measured using a tethered balloon at a suburban site in Xiamen, which is undergoing fast urbanization. The characteristics of CO2 vertical distribution were investigated under both stable and convective boundary-layer conditions. The correlation of ground level CO2 concentrations and those at high altitudes decreased with altitude and show significant correlation in the first 300 m with R = 0.78 at 100 m, R = 0.52 at 200 m, R = 0.40 at 300 m (P < 0.01). The correlation keeps almost constant for 300-800 m, and there is no obvious correlation at 800 m, indicating that the impact of ground level CO2 was restricted within the 300 m above the ground. When comparing the vertical profiles obtained at different times during a 24 h period, it was found that CO2 concentration exhibited more obvious diurnal pattern at surface level than at high altitude because of the variation of sources and sinks of CO2 at ground level. Most profiles demonstrated declining trends of CO2 concentration with increasing altitude. The vertical profiles of CO2 were fitted to obtain an empirical equation for estimating CO2 vertical concentration in the lower atmosphere (0-1000 m): y = -75.04 + 1.17 × 109e-x/28.01, R2 = 0.59 (P < 0.05). However, for some cases opposite patterns were observed that the CO2 concentration profiles showed a turning point at a certain altitude or little variation with altitude under certain meteorological conditions. The atmospheric boundary layer depth and atmospheric stability are two major factors controlling the vertical structure of CO2 profile. The results would improve our understanding of the spatial and temporal variation of CO2 in urban environment, which would facilitate using 3-D transport model to study the impacts of CO2 on urban

  5. 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.

  6. 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.

  7. Acoustic pulse propagation through a fluctuating stably stratified atmospheric boundary layer.

    PubMed

    Chunchuzov, Igor; Kulichkov, Sergey; Otrezov, Alexander; Perepelkin, Vitaly

    2005-04-01

    Mesoscale wind speed and temperature fluctuations with periods from 1 min to a few hours significantly affect temporal variability and turbulent regime of the stable atmospheric boundary layer (ABL). Their statistical characteristics are still poorly understood, although the knowledge of such statistics is required when modeling sound propagation through the stable ABL. Several field experiments have been conducted to study the influence of mesoscale wind speed fluctuations on acoustic pulse propagation through the stable ABL. Some results of these experiments are described in this paper. A special acoustic source was used to generate acoustic pulses by the detonation of an air-propane mixture with a repetition period 30 s. The mean wind speed and temperature profiles were continuously measured by Doppler sodar and temperature profiler, whereas mesoscale wind fluctuations were measured by anemometers placed on a 56-m mast. From the measurements of the pulse travel time fluctuations at different distances from the source, the statistical characteristics of the mesoscale wind fluctuations, such as frequency spectra, coherences, horizontal phase speeds and scales, have been obtained. Some of the obtained results are interpreted with the use of a recently developed model for the internal wave spectrum in a stably stratified atmosphere.

  8. Correlation between Atmospheric Boundary Layer Height and Polybrominated Diphenyl Ether Concentrations in Air.

    PubMed

    Dien, Nguyen Thanh; Hirai, Yasuhiro; Sakai, Shin-Ichi

    2017-01-03

    In this study, we aim to determine the correlation between the height of the atmospheric boundary layer (ABL) and the concentrations of polybrominated diphenyl ether (PBDE) congeners, in an effort to improve comprehension of the atmospheric behavior of PBDEs. We used the PBDE data in air (n = 298), which were measured by the Japan Ministry of Environment (JMOE) at 50 sites across Japan during the period 2009-2012. The height of the ABL, which directly affects the PBDE concentrations in the near-surface air, was estimated by employing data retrieved from the Japanese global reanalysis (JRA-55) database, using the parcel and Richardson number method. The ABL has shown a strong inverse relationship with BDE-47 and BDE-99 (p < 0.01). In contrast, there was less correlation between BDE-209 and the ABL (p = 0.258). These differing behaviors could be explained by differences in particle size distribution of PBDEs, where BDE-47 and BDE-99 are associated with gas phases and fine particles and BDE-209 is associated with coarse particles. To our knowledge, this paper represents the first large-scale analysis of correlations between the ABL and the concentrations of PBDEs in the air.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  10. Review of wave-turbulence interactions in the stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Sun, Jielun; Nappo, Carmen J.; Mahrt, Larry; Belušić, Danijel; Grisogono, Branko; Stauffer, David R.; Pulido, Manuel; Staquet, Chantal; Jiang, Qingfang; Pouquet, Annick; Yagüe, Carlos; Galperin, Boris; Smith, Ronald B.; Finnigan, John J.; Mayor, Shane D.; Svensson, Gunilla; Grachev, Andrey A.; Neff, William D.

    2015-09-01

    Flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. Understanding turbulence intermittency and wave-turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave-turbulence interaction is a potential mechanism for turbulence intermittency. A workshop on wave-turbulence interactions in the SABL addressed the current understanding and challenges of wave-turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave-turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent turbulence and wave-turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.

  11. The simultaneous effects of complex topography and vegetation structure on turbulence within the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Katul, G. G.; Poggi, D.

    2009-12-01

    The modulation of turbulent energetics and their canonical length scales inside tall and dense canopies on complex terrain remains largely an unexplored topic though interest in these properties is now proliferating. These interests are motivated by footprint analysis when interpreting eddy-covariance derived evapo-transpiration (ET) measurements from towers, or when coupling land-surface fluxes to the various dynamical regions within the atmospheric boundary layer (ABL). Both applications require clear quantification of how topography modifies higher order statistics such as the velocity variances (and spectra). To investigate how these velocity variances (and spectra) are modified by the simultaneous action of topography and canopy, two flume experiments were carried out on a train of gentle cosine hills differing only in surface cover. The first experiment was conducted above a bare surface while the second experiment was conducted within and above a densely arrayed rod canopy. The velocity variances (and spectra) from these two experiments were compared in the middle, inner, and near-surface layers of the ABL with particular attention paid to phase-relationships between the velocity variances (and covariances) and the topography. Phase-predictions from rapid distortion theory, equilibrium theories, and canopy flow theories within these various layers are discussed. The addition of a canopy on hills alters the energy spectrum of turbulence inside the canopy by short-circuiting the energy cascade and by injecting energy by wake production. Moreover, inside the canopy and on the lee side of the hill, a re-circulation region occurs that is absent in the bare surface experiment. Hence, by comparison to the bare surface case, we show that these canopy processes modify significantly the phase-relationships between topography and higher-order flow statistics via novel mechanisms not previously explored, and the effects of these processes propagates to dynamical regions

  12. Modeling the Evolution of the Atmospheric Boundary Layer Coupled to the Land Surface for Three Contrasting Nights in CASES-99.

    NASA Astrophysics Data System (ADS)

    Steeneveld, G. J.; van de Wiel, B. J. H.; Holtslag, A. A. M.

    2006-03-01

    The modeling and prediction of the stable boundary layer over land is a persistent, problematic feature in weather, climate, and air quality topics. Here, the performance of a state-of-the-art single-column boundary layer model is evaluated with observations from the 1999 Cooperative Atmosphere Surface Exchange Study (CASES-99) field experiment. Very high model resolution in the atmosphere and the soil is utilized to represent three different stable boundary layer archetypes, namely, a fully turbulent night, an intermittently turbulent night, and a radiative night with hardly any turbulence (all at clear skies). Each archetype represents a different class of atmospheric stability. In the current model, the atmosphere is fully coupled to a vegetation layer and the underlying soil. In addition, stability functions (local scaling) are utilized based on in situ observations.Overall it is found that the vertical structure, the surface fluxes (apart from the intermittent character) and the surface temperature in the stable boundary layer can be satisfactorily modeled for a broad stability range (at a local scale) with the current understanding of the physics of the stable boundary layer. This can also be achieved by the use of a rather detailed coupling between the atmosphere and the underlying soil and vegetation, together with high resolution in both the atmosphere and the soil. This is especially true for the very stable nights, when longwave radiative cooling is dominant. Both model outcome and observations show that in the latter case the soil heat flux is a dominant term of the surface energy budget.


  13. STRUCTURE OF TURBULENCE IN THE URBAN ATMOSPHERIC BOUNDARY LAYER DETECTED IN THE DOPPLER LIDAR OBSERVATION

    NASA Astrophysics Data System (ADS)

    Oda, Ryoko; Iwai, Hironori; Ishii, Shoken; Sekizawa, Shinya; Mizutani, Kohei; Murayama, Yasuhiro

    Doppler lidar observation was conducted to investigate the statistical and structural characteristics of the atmospheric boundary layer (ABL) over urban area, Koganei, Tokyo, on 21 February 2010. Vertical distribution of the vertical velocity was measured at the height between 150 m to about 2,000 m from the ground with a constant interval of 76 m. The potential temperature (PT) profiles were also measured by radiosonde. Vertical velocity spectra in the ABL show two dominant time scales; one is about 15 minute, and the other is less than 5 minutes. The higher frequency motion extends up to the top of ABL determined by PT profiles, which would be attributed to the individual thermal plumes. The lower frequency motion penetrates into the capping inversion. This would be the contribution of the organized thermal cells which propagates into the capping inversion as gravity wave during daytime. Surface layer depth was estimated about 300 m. It is due to the enhanced mechanical production of turbulence in urban roughness.

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Atmospheric boundary layer dynamics in the Grenoble valley during strongly stable episodes

    NASA Astrophysics Data System (ADS)

    Staquet, C.; Largeron, Y.; Chollet, J.

    2013-12-01

    This paper addresses the dynamics of the atmospheric boundary layer in the Grenoble valley under strongly stable and polluted conditions. Numerical modeling is used for this purpose, along with available ground temperature measurements. Though the Grenoble valley is the most populated area in the Alps and is subjected to serious pollution episodes in winter, no such study had been conducted previously. We first analyzed ground temperature data within the valley at altitudes ranging between 220 m (valley bottom) and 1730 m during 5 months of winter 2006-2007. These data were provided by Meteo-France et by Air Rhône-Alpes, the air quality agency of Région Rhône-Alpes. Our purpose was to detect strongly stable episodes, these being defined by the episode-averaged vertical gradient of the absolute temperature being larger than the winter average during at least three days. Five episodes were selected from this criterion. We also analyzed air quality data recorded by Air Rhône-Alpes during the same winter to detect strongly polluted events for PM10 and found that the five episodes were also strongly polluted ones. To perform a more detailed analysis of these five episodes, we used the numerical code Meso-NH developed by Météo-France and the Laboratory of Aérology in Toulouse and simulated the dynamics of the atmospheric boundary layer during each episode. Four nested domains were used, the horizontal resolution of the innermost (and smallest) domain, containing the Grenoble valley, being 333 m; from comparison with the ground temperature data, we found that the vertical resolution above ground level had to be as low as 4 meters. As expected, the boundary layer dynamics in the numerical simulation for each episode was found to be decoupled from the (anticyclonic, weak) synoptic flow, consistent with the value of the Froude number associated with the inversion layer. These dynamics are controlled by thermal (mostly katabatic) winds flowing from the higher altitude

  2. Lidar observations of atmospheric internal waves in the boundary layer of the atmosphere on the coast of Lake Baikal

    NASA Astrophysics Data System (ADS)

    Banakh, Viktor A.; Smalikho, Igor N.

    2016-10-01

    Atmospheric internal waves (AIWs) in the boundary layer of atmosphere have been studied experimentally with the use of Halo Photonics pulsed coherent Doppler wind lidar Stream Line. The measurements were carried out over 14-28 August 2015 on the western coast of Lake Baikal (51°50'47.17'' N, 104°53'31.21'' E), Russia. The lidar was placed at a distance of 340 m from Lake Baikal at a height of 180 m above the lake level.

    A total of six AIW occurrences have been revealed. This always happened in the presence of one or two (in five out of six cases) narrow jet streams at heights of approximately 200 and 700 m above ground level at the lidar location. The period of oscillations of the wave addend of the wind velocity components in four AIW events was 9 min, and in the other two it was approximately 18 and 6.5 min. The amplitude of oscillations of the horizontal wind velocity component was about 1 m s-1, while the amplitude of oscillations of the vertical velocity was 3 times smaller. In most cases, internal waves were observed for 45 min (5 wave oscillations with a period of 9 min). Only once the AIW lifetime was about 4 h.

  3. 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

  4. 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.

  5. Atmospheric boundary-layer structure from simultaneous SODAR, RASS, and ceilometer measurements

    NASA Astrophysics Data System (ADS)

    Emeis, Stefan; Münkel, Christoph; Vogt, Siegfried; Müller, Wolfgang J.; Schäfer, Klaus

    A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ceilometer is presented. One important structure is the mixing-layer height (MLH). The comparison is focused on 3 days with an evolution of a convective boundary layer over a larger city in Germany. The three instruments give information that partly agree and partly complement each other. By this, a picture of the diurnal evolution of the vertical structure of this urban boundary layer is presented. The ceilometer gives information on the aerosol content of the air and the RASS provides a direct measurement of the vertical temperature distribution in the boundary layer. The RASS and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. Especially the temperature information from the RASS agrees well with lifted inversions derived from the analysis of the SODAR data. The ceilometer, being the smallest instrument, has a potential to be used in future MLH studies.

  6. Three-Dimensional Mapping of Atmospheric Boundary Layer Structure and Winds with a High Performance Lidar

    DTIC Science & Technology

    1991-04-01

    layer (usually less than half the boundary layer height) for each of the shots in a PPI scan using 12 Si 12--F1 S ( 1 ) 2- 1 1 = 11 where Sil is the natural...between 1 and 1024), and ( 11 to 12) is the range segment located well within the boundary layer. Within this range interval, the aerosol contribution...the CBL, mean CBL wind, surface wind, and the wind at a height of 1 . 1 Zi. The orientation of the aerosol structures is also shown. Figure 11 . The

  7. Lidar Investigations of Atmospheric Boundary Layer Clouds over Coastal Environment and its Diurnal Evolution

    NASA Astrophysics Data System (ADS)

    Mishra, Manoj; Rajeev, Kunjukrishnapillai; Nair, Anish Kumar M.

    Over the high pressure region, diurnal evolution of atmospheric boundary layer (ABL) leads to the development of fair weather clouds, which in turn play an important role in modulating the thermodynamic structure of ABL, radiation balance at surface, and further development of ABL. As they usually cap the ABL, aerosol-cloud interaction in these clouds are expected to be quite large. Notwithstanding their importance, characteristics of the ABL clouds, their diurnal evolution and the resulting feedback are least explored. Major objectives of this study are to: (i) quantify the diurnal evolution of fair-weather ABL clouds and their characteristics (in terms of their altitude of occurrence, physical thickness and optical depth) based on multi-year (2008-2011) Micropulse Lidar observations at the coastal station, Thumba (8.5(°) N, 77(°) E), and (ii) explore the potential impact of these clouds in modulating the downwelling shortwave radiative flux at surface and further development of ABL. Altitude of occurrence of ABL clouds is found to undergo significant diurnal variation during the development of convective ABL (CABL). Typically, the ABL cloud base increases from <500 m at ˜09 LT to >1500 m at ˜12 LT. Base altitude of the ABL clouds is rather steady during the afternoon, associated with the stabilization of CABL development. Clouds in the nocturnal ABL (NABL) generally occur at the altitude of the preceding afternoon CABL height. Simultaneous occurrence of clouds in the thermal internal boundary layer (TIBL) and developed CABL/residual layer (RL) are also observed, through they are less frequent. The TIBL clouds are distinctly separated from those formed at the top of CABL/RL. Base heights of clouds are distinctly lower in TIBL and evolving CABL compared to those in developed CABL and RL, though their mean physical thickness are comparable (typically ˜250m). Optically thin clouds dominate the TIBL, compared to the other three regimes. Reduction in the

  8. Structure of marine atmospheric boundary layer under contrasting conditions of tropospheric dynamics, convection and cloudiness

    NASA Astrophysics Data System (ADS)

    Santosh, M.; Rajeev, Kunjukrishnapillai

    Atmospheric boundary layer (ABL) processes play a pivotal role in the exchange of energy and minor constituents between the surface and free-troposphere. Temporal variations of the marine ABL (MABL) are mainly controlled by large-scale circulation and surface conditions. Diurnal variation of mixing height over the oceanic regions is significantly smaller than that over the continental regions. This study investigates the MABL characteristics under contrasting conditions of large-scale circulation, sea surface temperature (SST), convection and cloudiness based on the altitude profiles of atmospheric thermo-dynamic variables observed using balloon-borne GPS Radiosondes launched during three ship based campaigns in the tropical Indian Ocean, the Arabian Sea and the Bay of Bengal. These observations were carried out during July-November period and the ship tracks transacted through the ITCZ, regions of deep convection and the descending limb of Hadley cell. The prevailing cloud conditions corresponding to the time of radiosonde observations were obtained using collocated data from geostationary satellite Kalpana-1-VHRR, which were used to classify the data into highly cloudy and clear sky categories. The mixing height at the descending limb of the Hadley cell typically extends up to an altitude of ˜1200 m, which is capped by a region of thin cloud that is sandwiched between the top of MABL and the strong trade wind inversion at ˜2 km altitude. The moist static energy in the surface layer at the deep convective regions is significantly larger than that at the descending limb of Hadley cell. Notwithstanding this, the mixing height in the deep convective cases is rather shallow, though significantly humid. Remarkably, the MABL over these deep convective regions are generally capped by a relatively cloud-free altitude band marked by a distinct inversion in virtual potential temperature, which is followed by a deep convective cloud layer in the altitude band of ˜2-13 km

  9. Description of coherent structures in the atmospheric boundary layer by model reduction of the surface pressure

    NASA Astrophysics Data System (ADS)

    Lyons, Gregory William

    The flow of coherent turbulent structures into a wind turbine is associated with vibrational blade excitation. Successful forecasting of such turbulent events for control system input would increase the lifetime of turbine components. The coherence of these features suggests description by model reduction. To this end, an array of pressure transducers was deployed on the ground at Reese Technology Center in Lubbock, Texas, and the pressure fluctuations were recorded over nearly two diurnal cycles. A program for computation of the dynamic mode decomposition was developed with special consideration for the case of a non-stationary, nonlinear system. A simulated surface-pressure perturbation was first decomposed, to inform the interpretation of experimental data. Several sets of surface-pressure data were decomposed for various meteorological conditions. The resulting dynamic modes and eigenvalues describe the spatial and temporal coherence of local features in the atmospheric boundary layer. In each case, modes were identified that can be associated with wave-like pressure fluctuations that propagate either at convective or acoustic speeds.

  10. 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.

  11. Experimental investigation on the wake interference among wind turbines sited in atmospheric boundary layer winds

    NASA Astrophysics Data System (ADS)

    Tian, W.; Ozbay, A.; Wang, X. D.; Hu, H.

    2017-08-01

    We examined experimentally the effects of incoming surface wind on the turbine wake and the wake interference among upstream and downstream wind turbines sited in atmospheric boundary layer (ABL) winds. The experiment was conducted in a large-scale ABL wind tunnel with scaled wind turbine models mounted in different incoming surface winds simulating the ABL winds over typical offshore/onshore wind farms. Power outputs and dynamic loadings acting on the turbine models and the wake flow characteristics behind the turbine models were quantified. The results revealed that the incoming surface winds significantly affect the turbine wake characteristics and wake interference between the upstream and downstream turbines. The velocity deficits in the turbine wakes recover faster in the incoming surface winds with relatively high turbulence levels. Variations of the power outputs and dynamic wind loadings acting on the downstream turbines sited in the wakes of upstream turbines are correlated well with the turbine wakes characteristics. At the same downstream locations, the downstream turbines have higher power outputs and experience greater static and fatigue loadings in the inflow with relatively high turbulence level, suggesting a smaller effect of wake interference for the turbines sited in onshore wind farms.

  12. 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.

  13. The formation of snow streamers in the turbulent atmosphere boundary layer

    NASA Astrophysics Data System (ADS)

    Huang, Ning; Wang, Zheng-Shi

    2016-12-01

    The drifting snow in the turbulent atmosphere boundary layer is an important type of aeolian multi-phase flow. Current theoretical and numerical studies of drifting snow mostly consider the flow field as steady wind velocity. Whereas, little is known about the effects of turbulent wind structures on saltating snow particles. In this paper, a 3-D drifting snow model based on Large Eddy Simulation is established, in which the trajectory of every snow grain is calculated and the coupling effect between wind field and snow particles is considered. The results indicate that the saltating snow particles are re-organized by the suction effect of high-speed rotating vortexes, which results in the local convergence of particle concentration, known as snow streamers. The turbulent wind leads to the spatial non-uniform of snow particles lifted by aerodynamic entrainment, but this does not affect the formation of snow streamers. Whereas the stochastic grain-bed interactions make a great contribution to the final shapes of snow streamers. Generally, snow streamers display a characteristic length about 0.5 m and a characteristic width of approximately 0.16 m, and their characteristic sizes are not sensitive to the wind speed. Compared to the typical sand streamer, snow streamer is slightly narrower and the occurrence of other complex streamer patterns is later than that of sand streamers due to the better follow performance of snow grains with air flow.

  14. 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. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. 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.

  16. Investigation of the atmospheric boundary layer characteristics on gust factor for the calculation of wind load

    NASA Astrophysics Data System (ADS)

    Ghanadi, Farzin; Emes, Matthew; Yu, Jeremy; Arjomandi, Maziar; Kelso, Richard

    2017-06-01

    Dynamic amplification and gust effects from turbulence can increase wind loads significantly over and above the static wind loads that have been used for heliostat design. This paper presents the results of analyzing the relationship between gust factor and turbulence intensity within the atmospheric boundary layer (ABL) based on the high fidelity measurements of wind velocity at the SLTEST facility in the Utah desert. Results showed that there are distinct characteristics of a low roughness ABL that deviate from semi-empirical relationships derived for open country and urban terrains with larger surface roughness heights. The analysis also indicated that gust factor is increased by 2.4% when lowering the gust period from 3s to 1s in the low roughness field experiment ABL, compared to a 3.6% increase in a suburban terrain at a 10m height. Although 3s gust periods are recommended in AS/NZS 1170.2 [1], comparison of gust factor data with a 1s gust period is recommended particularly in high roughness ABLs such as in urban areas, to ensure that buildings are adequately designed to withstand higher frequency gusts. This research proved the strength of the correlation between gust factor and turbulence intensity is dependent on the surface roughness height of the terrain. It is recommended that the coefficient in the previous semi-empirical equation must be adjusted to be fitted to the low roughness desert terrain in the field experiment ABL.

  17. Is geometry more universal than physics in atmospheric boundary layer flow?

    NASA Astrophysics Data System (ADS)

    BelušIć, D.; Mahrt, L.

    2012-05-01

    We show that the geometry of motions in atmospheric boundary-layer time series exhibits considerable independence from scale in spite of changing physics. The scale-independence of structure shapes is shown by using a simple technique to extract basic shapes from the time series for timescales between 3 s and 2 h. A set of predefined basic shapes is chosen subjectively as those that occur most frequently in the time series: sine, step, ramp-cliff and cliff-ramp. The frequency of occurrence of shapes changes with the timescale, with a pronounced minimum at scales between 2 and 10 min depending on the stability and the shape function. This is in accordance with the minimum of kinetic energy between turbulence and mesoscales. However, the ratios of occurrences between different shapes are approximately scale-independent. What shapes are preferred depends only on the variable examined. The physics of different shapes and scales is examined from characteristics of individual shapes. Steep edges of shapes seem to be predominantly related to downward transport of heat and momentum, which weakens with increasing scale. Sine shapes on the other hand seem to be related to turbulent eddies and shear instability at small scales, and to internal gravity waves at larger scales with stable stratification. Therefore, the physics of individual shapes is shown to change with scale, while the geometry seems to remain approximately scale-independent.

  18. Experimental investigation on the wake interference among wind turbines sited in atmospheric boundary layer winds

    NASA Astrophysics Data System (ADS)

    Tian, W.; Ozbay, A.; Wang, X. D.; Hu, H.

    2017-06-01

    We examined experimentally the effects of incoming surface wind on the turbine wake and the wake interference among upstream and downstream wind turbines sited in atmospheric boundary layer (ABL) winds. The experiment was conducted in a large-scale ABL wind tunnel with scaled wind turbine models mounted in different incoming surface winds simulating the ABL winds over typical offshore/onshore wind farms. Power outputs and dynamic loadings acting on the turbine models and the wake flow characteristics behind the turbine models were quantified. The results revealed that the incoming surface winds significantly affect the turbine wake characteristics and wake interference between the upstream and downstream turbines. The velocity deficits in the turbine wakes recover faster in the incoming surface winds with relatively high turbulence levels. Variations of the power outputs and dynamic wind loadings acting on the downstream turbines sited in the wakes of upstream turbines are correlated well with the turbine wakes characteristics. At the same downstream locations, the downstream turbines have higher power outputs and experience greater static and fatigue loadings in the inflow with relatively high turbulence level, suggesting a smaller effect of wake interference for the turbines sited in onshore wind farms.

  19. 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.

  20. Micro-pulse upconversion Doppler lidar for wind and visibility detection in the atmospheric boundary layer.

    PubMed

    Xia, Haiyun; Shangguan, Mingjia; Wang, Chong; Shentu, Guoliang; Qiu, Jiawei; Zhang, Qiang; Dou, Xiankang; Pan, Jianwei

    2016-11-15

    For the first time, to the best of our knowledge, a compact, eye-safe, and versatile direct detection Doppler lidar is developed using an upconversion single-photon detection method at 1.5 μm. An all-fiber and polarization maintaining architecture is realized to guarantee the high optical coupling efficiency and the robust stability. Using integrated-optic components, the conservation of etendue of the optical receiver is achieved by manufacturing a fiber-coupled periodically poled lithium niobate waveguide and an all-fiber Fabry-Perot interferometer (FPI). The double-edge technique is implemented by using a convert single-channel FPI and a single upconversion detector, incorporating a time-division multiplexing method. The backscatter photons at 1548.1 nm are converted into 863 nm via mixing with a pump laser at 1950 nm. The relative error of the system is less than 0.1% over nine weeks. In experiments, atmospheric wind and visibility over 48 h are detected in the boundary layer. The lidar shows good agreement with the ultrasonic wind sensor, with a standard deviation of 1.04 m/s in speed and 12.3° in direction.

  1. Backscattering and reflection of acoustic waves in the stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Kallistratova, M. A.

    2008-05-01

    Among different applications of sodars in studies of the atmospheric boundary layer (ABL), the remote sensing of the temperature structure parameter CT2 and the closely associated structure parameter of refraction index Cn2 occupies an important place. These parameters are calculated from sodar return signal with the help of the theory of Bragg volumetric scattering of sound by small-scale turbulent irregularities of temperature. According to the Kolmogorov-Oboukhov conception, the irregularities are assumed to be locally homogeneous and isotropic. The theory was confirmed by experiments and universally recognized as a classical one. However, detailed comparisons are still being made between CT2 values derived from sodar data and from aircraft and meteorological-tower measurements. The results of such comparisons performed by different researchers under different conditions contradict to each other. In this paper, the results of comparisons between remote and in situ measurements of CT2 in the ABL are briefly reviewed. Some examples of a systematic overestimation of CT2 calculated from sodar data obtained under stable stratification of the ABL are given. Technical and physical causes of these discrepancies are discussed. The following factors are considered as possible physical factors: contribution of a partial (Fresnel) reflection of sound from layers with a sharp temperature jump, anisotropy of small-scale turbulence, intermittency, and contribution of quasi-wave air-density inhomogeneities. It is shown that these factors can explain some short-lived increase of the sodar return signal, but not a systematic overestimation of CT2. The role of sound-beam refraction (which regularly occurs in the stable ABL due to strong air-temperature and wind-speed gradients) is discussed. Due to a refraction turn of sodar beam, the angle of scattering changes, and scattering by turbulent wind-speed irregularities could permanently contribute to return signal of a monostatic

  2. [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.

  3. A boundary-layer analysis of atmospheric motion over a semi-elliptical surface obstruction

    NASA Technical Reports Server (NTRS)

    Frost, W.; Maus, J. R.; Fichtl, G. H.

    1974-01-01

    Flow over surface obstructions can produce adverse flying conditions for helicopters, V/STOL vehicles, etc. The disturbed boundary-layer concept is applied in approximating the localized flow field induced around a surface obstruction (modeled by a two-dimensional cylinder with elliptical cross section) by an impinging wind. The analysis concludes that: (1) localized wind-speed maxima occur at the top of a surface obstruction, which are expected in physically real flows; (2) increased elliptical aspect ratio decreases with speed within the boundary layer at the top of the ellipse; (3) increased surface roughness decreases velocity in the boundary layer; (4) Reynolds number has a negligible effect on the overall flow for the Re range considered; (5) decreased elliptical aspect ratio and increased surface roughness cause larger separation regions.

  4. The atmospheric boundary layer at Dome C on the Antarctic plateau

    NASA Astrophysics Data System (ADS)

    Barral, H.; Genthon, C.; Six, D.; Gallée, H.; Brun, C.

    2012-04-01

    Dome C on the Antarctic plateau (75°06' S, 123°20' E, 3233 m a.s.l.) was selected as one of the 119 CF-sites for the CMIP5/IPCC intercomparison project. For these sites, the participating climate modeling groups have been asked to produce a special set of high frequency diagnostics. Dome C has been selected because of the extreme weather and climate of the Antarctic plateau, but also because of the year-long continuous observations, performed with support from the permanent French-Italian Concordia station. The lower atmospheric boundary layer at Dome C is monitored since January 2008 (Genthon et al., J. Geophys. Res., 2010). Anemometers, thermometers and hygrometers were deployed at 6 levels above the surface up to ~42 m. Harsh local conditions (extreme cold temperatures, frost deposition) have affected the operation of the instruments. Several failed during winter 2008 but improvements have allowed almost continuous records with only limited interruptions since 2009. Cases of thermal convective mixing (adiabatic temperature profile, in summer) as well as cases of very strong inversions (more than 2°C per meter locally, in winter) were recorded. In 2010, the temperature at the lowest level dropped below -80°C, whereas in 2009 the minimal temperature is 10 degrees higher. Winter 2009, milder but twice as much windswept than the next winter, is remarkable for the occurrences of extreme "warm events" : for two days, the temperature approached the -30°C in the depths of winter. Independently, the Antarctic Meteorological Research Center automatic weather station at Dome C indicates that these two winters are the warmest and coldest on record over the past decade. Therefore, it may be supposed that the 2009-2010 time series together contain enough variability to be used for the evaluation of climate models. The data have been compared with the ECMWF meteorological analyzes, and with AMIP simulations of CMIP5 models. The coarse vertical resolution of general

  5. Large-Eddy Simulation of Thermally Stratified Atmospheric Boundary-Layer Flow Using a Minimum Dissipation Model

    NASA Astrophysics Data System (ADS)

    Abkar, Mahdi; Moin, Parviz

    2017-08-01

    A generalized form of a recently developed minimum dissipation model for subfilter turbulent fluxes is proposed and implemented in the simulation of thermally stratified atmospheric boundary-layer flows. Compared with the original model, the generalized model includes the contribution of buoyant forces, in addition to shear, to the production or suppression of turbulence, with a number of desirable practical and theoretical properties. Specifically, the model has a low computational complexity, appropriately switches off in laminar and transitional flows, does not require any ad hoc shear and stability corrections, and is consistent with theoretical subfilter turbulent fluxes. The simulation results show remarkable agreement with well-established empirical correlations, theoretical predictions, and field observations in the atmosphere. In addition, the results show very little sensitivity to the grid resolution, demonstrating the robustness of the model in the simulation of the atmospheric boundary layer, even with relatively coarse resolutions.

  6. 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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Zhou, Bowen

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

  9. Wind Shear Effects on the Structure and Dynamics of the Daytime Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Haghshenas, Armin; Mellado, Juan Pedro

    2017-04-01

    The daytime atmospheric boundary layer (ABL), in which the positive buoyancy flux at the surface creates convective instability and generates turbulence, has been a subject of extensive research during the last century. However, fewer studies have considered wind shear in detail and most of them are single-case studies. So most of the available theories and parameterizations have not been sufficiently tested over a wide range of atmospheric conditions. Moreover, since previous numerical studies were mostly carried out by large eddy simulation, a complete understanding of the physics of the problem is still missing due to the lack of information about the small-scale dynamics. Specifically, despite the consensus in the community that wind shear enhances the entrainment process, the amount of enhancement is still matter of contention. In order to investigate the effects of wind shear on the structure and dynamics of the ABL in detail, direct numerical simulations are used in this study. Shear is prescribed by a height-constant velocity in the troposphere and the simulation runs until a fully turbulent, quasi-equilibrium regime is observed. Despite the simplification of neglecting the Coriolis force, our configuration reproduces the main features observed in the previous studies, which had taken the Coriolis force into account. As a novelty compared to previous single-case studies, we introduce a dimensionless parameter that allows us to study systematically any combination of surface buoyancy flux, buoyancy stratification, and wind shear; We refer to this dimensionless number as shear number. Seven simulations with shear numbers ranging from 0 (no wind) to 20 (moderate wind) are conducted; this range of shear numbers corresponds to wind strength from 0 to 15 m/s in the free troposphere for typical midday atmospheric conditions. In general, we find that shear effects are negligibly small when the shear number is below 10, and for larger values the effects remain

  10. SAR-Related Stress Variability in the Marine Atmospheric Boundary Layer (MABL)

    DTIC Science & Technology

    1992-01-01

    boundary-layer-spanning eddies. Dave Ledvina is testing an alternative approach using principal component analysis to distinguish the modes of surface stress...research associate (Dave Ledvina ) has developed software that uses principal component analysis to relate surface stress variability to variability in other

  11. An observational investigation of transitory turbulence in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Jensen, Derek D.

    Within the atmospheric boundary layer (ABL), atmospheric fluid flow is in a constant state of transition in both time and space. Under calm conditions through the mid-daytime hours and over quasi-uniform terrain, the temporal and spatial evolution of the atmosphere is gradual. The structure and governing equations are well understood, allowing for numerical models to accurately forecast the evolution of the ABL. Under nocturnal conditions, the atmospheric processes are more complicated, yet numerical models still perform reasonably well. When changes in the state of the atmosphere occur abruptly, whether in time or space, the fidelity of most numerical weather models diminishes appreciably. This occurs because many of the simplifying assumptions intrinsic in most numerical models are no longer valid. The objective of this dissertation is to use observational data collected within such transitions to gain more insight into the mechanisms responsible for the evolution of the rapidly evolving ABL. First, near-surface turbulence data are used to study countergradient heat fluxes that occur through the evening transition. The countergradient heat flux may be produced by the sign change of the sensible heat flux preceding the sign change of the local temperature gradient and vice versa. The phenomenon is studied by considering the budget equations of both temperature and sensible heat flux. The behaviour of the countergradient heat flux is governed by the surface and subsurface characteristics. The duration of the countergradient flux may be prognosed by considering a ratio of terms in the heat flux budget equation evaluated during the mid- to late afternoon. Next, data collected over an arid shallow slope (2-4°) are used to study the structure and onset of katabatic flow through the evening transition. The katabatic onset, jet velocity and jet height all show a large degree of interdiurnal variability. The slope-aligned budgets of momentum and potential temperature are

  12. Atmospheric planetary boundary layer feedback in climate system and triggering of climate change at high latitudes

    NASA Astrophysics Data System (ADS)

    Esau, I.; Zilitinkevich, S.

    2009-04-01

    Recent publications have revealed that modern, state-of-the-art climate-change models (CCMs) are not sensitive enough to reproduce some fine features of the observed changes in the surface air temperature (SAT) especially at high latitudes. We propose that this problem results from inaccurate representation of the very shallow long-lived stable (LS) and conventionally neutral (CN) atmospheric planetary boundary layers (PBLs) typical of high latitudes, especially of Polar regions. LS and CN PBLs, not yet included in the context of climate modelling, are almost an order of magnitude shallower than mid-latitudinal nocturnal stable (NS) and truly neutral (TN) PBLs, which are the only concern of the traditional theory of stable PBLs. In is only natural that factually observed shallow PBLs respond to thermal impacts (e.g. to the changes in the surface heat balance) much stronger than much deeper PBLs reproduced by the current PBL schemes. In this paper we investigate analytically the PBL feedback in climate system for all known kinds of PBL: stable (distinguishing between NS and LS), neutral (distinguishing between TN and CN) and also convective). Besides very high sensitivity of LS PBLs, quite consistent with the observed variability in SAT, our analyses reveal that in some specific conditions global warming could cause "strange cases" of local cooling. We also obtained analytically that the daily minimum temperatures are more sensitive to the global warming than the daily maximum temperatures, which, at least partially, explains such observed phenomena as asymmetry in the diurnal temperature trends and almost global reduction of the diurnal temperature range.

  13. Upper limit of applicability of the local similarity theory in the stable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Grachev, A. A.; Andreas, E. L.; Fairall, C. W.; Guest, P. S.; Persson, P. O. G.

    2012-04-01

    The applicability of the classical Monin-Obukhov similarity theory (1954) has been limited by constant flux assumption, which is valid in a narrow range z/L < 0.1 in the stable boundary layer (SBL). Nieuwstadt (1984) extended the range of applicability of the original theory using the local scaling (height-dependent) in place of the surface scaling, but the limits of applicability of the local similarity theory in the SBL have been blurred. Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to clarify this issue. Based on spectral analysis of wind velocity and temperature fluctuations, it is shown that when both gradient Richardson number, Ri, and flux Richardson number, Rf, exceed a "critical value" about 0.2-0.25, inertial subrange associated with a Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in the supercritical regime but this is non-Kolmogorov turbulence and it decays rapidly with further increasing stability. The similarity theory is based on the turbulent fluxes in the high frequency part of the spectra associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band collapse along with the Kolmogorov energy cascade. Therefore, applicability of the local Monin-Obukhov similarity theory in the SBL is limited by inequalities Ri < Ri_cr and Rf < Rf_cr (however, Rf_cr = 0.2-0.25 is a primary threshold). Application of this prerequisite shows that both the flux-profile and flux-variances relationships follow to the classical Monin-Obukhov local z-less predictions after the irrelevant cases have been filtered out.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  15. Dissipation of Turbulent Kinetic Energy in the Atmospheric Boundary Layer: Observations and Theory

    NASA Astrophysics Data System (ADS)

    Blumen, W.

    2002-05-01

    Two aspects of atmospheric dissipation will be examined, namely, the measurement of dissipation in frontal zones that are embedded in the boundary layer, and a theoretical examination of the dissipation length, used for parameterization purposes in some numerical models. The observations were acquired during two field programs carried out in southeast Kansas:MICROFRONTS-1995 and CASES-1999. Data were collected by both hot-wire and sonic anemometers. The hot-wire voltages were converted to wind speeds and the dissipation computed under the assumption of local isotropy. Taylor's hypothesis, including correction terms, was applied to convert spatial to time derivatives, since these data were collected on towers and presented as time series. This approach represents the direct dissipation method. The inertial method computes the dissipation from inertial subrange measurements, making use of the Kolmogorov five-thirds law and Taylor's hypothesis. The turbulent kinetic energy dissipation rate ɛ increased by over an order of magnitude in the frontal zone that passed the MICROFRONTS tower array, from values of the order of ɛ =0.01m2s-3 in the prefrontal region. After passage of the front the dissipation rate relaxed back to prefrontal values. The dissipation rate within the frontal zone that passed through the CASES site could not be determined because of flow distortion by the tower. Both prefrontal and post frontal dissipation rates were similar in magnitude to those measured during MICROFRONTS.In each case, no significant differences in the magnitudes of ɛ determined by the direct dissipation and inertial dissipation calculations, were evident. Numerical models require a parameterization of the dissipation rate ɛ that is appropriate for the unresolved scales of motion. One approach is to employ the dissipation length l as a surrogate for ɛ , where l=e3/2/ɛ and e is the turbulent kinetic energy. The aim is to represent l as a function of the vertical wind shear and

  16. Evolution of the cross-equatorial atmospheric boundary layer in the east Pacific: Observations and models

    NASA Astrophysics Data System (ADS)

    de Szoeke, Simon P.

    The NCAR C-130 research aircraft flew eight missions observing the atmospheric boundary layer (ABL) along 95°W, 1°S--12°N. The positive air-sea temperature difference over the equatorial cold tongue results in a shallow stable layer with reduced surface winds. Stratocumulus clouds at the ABL top tend to clear over the cold water, especially at times of enhanced humidity above the ABL. In the 0°--4°N ABL heat budget, cold advection and radiative cooling were balanced by surface and entrainment heating, where each of the four terms was about 30 W m-2. The humidity budget was a near balance between dry advection and surface evaporation (each about 150 W m-2). The entrainment rate estimated from the downstream-deepening of the inversion was 12 +/- 3 mm s -1. Principal component analysis of the sea-level pressure along 95°W, 1°S--12°N from daily TAO buoy observations and the eight flights shows that the principal mode of variability in the perturbation pressure explains 77% of the pressure variability. The pressure anomalies are the same at 1.6 km as at the surface. The timeseries of the first mode of the TAO observations shows that most of the variance is in the 2--7 day window. Low pressure at 12°N is associated with southerly and westerly surface wind anomalies, and enhanced convection in the ITCZ. A "quasi-Lagrangian" large-eddy simulation (LES) is used to model the ABL along 95°W from 8°S to 4°N. Large-scale tendencies are prescribed as a function of latitude. Surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north, in accordance with Wallace, Mitchell, and Deser (1989). Additional simulations show the robustness of the model ABL to changes in pressure gradients, zonal advection, free-tropospheric humidity, and initial conditions. Once formed at the southern edge of the cold tongue, modeled stratus clouds demonstrate a remarkable ability to maintain themselves over the

  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, 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.

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ridout, James A.; Reynolds, Carolyn A.

    1998-07-01

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

  1. The effect of thermal stratification and evaporation on geostrophic drag coefficient in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Yeh, G.-T.

    1973-01-01

    It is shown that the fields of velocity, eddy viscosity, potential temperature, and specific humidity in a planetary boundary layer are decoupled by the introduction of a free parameter, Q, which combines the effects of thermal and humidity stratification. Solutions of the whole system are shown to be obtainable by the method of trial and error on Q. Results show good agreement when both the thermal and humidity stratification are accounted for.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Methods for extraction of boundary layer parameters from measurements of a short pulse CO2 Doppler lidar are presented. Assuming that the turbulence is horizontally homogeneous, the mean wind, its standard deviations, and the momentum fluxes are estimated. Regarding the analysis method, it is shown that for a horizontally homogeneous turbulence the mean wind, its variance and the vertical momentum fluxes can be determined from single Doppler lidar data.

  3. The effect of thermal stratification and evaporation on geostrophic drag coefficient in the atmospheric boundary layer

    NASA Technical Reports Server (NTRS)

    Yeh, G.-T.

    1973-01-01

    It is shown that the fields of velocity, eddy viscosity, potential temperature, and specific humidity in a planetary boundary layer are decoupled by the introduction of a free parameter, Q, which combines the effects of thermal and humidity stratification. Solutions of the whole system are shown to be obtainable by the method of trial and error on Q. Results show good agreement when both the thermal and humidity stratification are accounted for.

  4. 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

  5. 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.

  6. Dual polarization micropulse lidar observations of the diurnal evolution of atmospheric boundary layer over a tropical coastal station

    NASA Astrophysics Data System (ADS)

    Rajeev, K.; Mishra, Manoj K.; Sunilkumar, S. V.; Sijikumar, S.

    2016-05-01

    High-resolution dual polarized micropulse lidar (MPL) observations have been used to investigate the diurnal evolution of atmospheric boundary layer (ABL) during winter (2008-2011) over Thiruvananthapuram (8.5°N, 77°E), a tropical coastal station located at southwest Peninsular India, adjoining the Arabian Sea. The lidar observations are compared with the boundary layer characteristics derived from concurrent balloon-borne radiosonde observations. This study shows that the mixed layer height over this coastal station generally increases from <300 m in the morning to 1500 m by the afternoon. Growth rate of the mixed layer height is rapid ( 350 m/hr) during 09-11 IST and slows down with time to <150 m/hr during 11-14 IST and <90 m/hr during 14-16 IST. Thermal internal boundary layer during the afternoon, caused by sea breeze circulation, extends up to 500 m altitude and is characterized by highly spherical aerosols, while a distinctly non-spherical aerosol layer appear above this altitude, in the return flow arising from the landmass.

  7. Monin-Obukhov similarity and convective organization in the unstable atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Salesky, Scott Thomas

    this scatter is debated in the literature and, although many researchers attribute the scatter to random errors (i.e. due to an insufficient averaging period for the time average to converge to the true ensemble mean), others suggest that the scatter is physically meaningful and is due to physical processes that are neglected by MOST. In order to determine the extent to which random errors and physical processes each contribute to the observed scatter in experimental measurements, it is necessary to have a reliable method for estimating random errors. Using the new error estimation method, together with error propagation analysis, the influence of random errors on the observed scatter in MOST functions calculated from experimental data is explored. Errors in the turbulent fluxes and gradients are propagated to z/L, φ m, and the dimensionless mean temperature gradient φ h. Errors in the MOST stability parameter z/L are found to be large for unstable conditions, reaching values of 40% or more. Statistical hypothesis tests are used to demonstrate that random errors in z/L and φm or φ h do not explain the observed scatter. In addition, deviations of φm from empirical curves are found to have strong diurnal variation and to increase with height, which suggests that physical processes related to the daytime growth of the convective boundary layer are responsible for the observed deviations from MOST. Finally, the large scale structure of convective organization in the unstable atmospheric boundary layer is investigated using large eddy simulation. Both observational and numerical studies have revealed that convective updrafts are organized into longitudinal rolls for slightly convective conditions and into open cells for highly convective conditions. However, the physical processes responsible for the transition from roll- to cellular- type convection, the nature of the transition (i.e. whether it occurs rapidly or gradually), and the criteria for the transition are not

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  9. Dynamics of Atmospheric Boundary Layers: Large-Eddy Simulations and Reduced Analytical Models

    NASA Astrophysics Data System (ADS)

    Momen, Mostafa

    Real-world atmospheric and oceanic boundary layers (ABL) involve many inherent complexities, the understanding and modeling of which manifestly exceeds our current capabilities. Previous studies largely focused on the "textbook ABL", which is (quasi) steady and barotropic. However, it is evident that the "real-world ABL", even over flat terrain, rarely meets such simplifying assumptions. The present thesis aims to illustrate and model four complicating features of ABLs that have been overlooked thus far despite their ubiquity: 1) unsteady pressure gradients in neutral ABLs (Chapters 2 and 3), 2) interacting effects of unsteady pressure gradients and static stability in diabatic ABLs (Chapter 4), 3) time-variable buoyancy fluxes (Chapter 5) , and 4) impacts of baroclinicity in neutral and diabatic ABLs (Chapter 6). State-of-the-art large-eddy simulations will be used as a tool to explain the underlying physics and to validate analytical models we develop for these features. Chapter 2 focuses on the turbulence equilibrium: when the forcing time scale is comparable to the turbulence time scale, the turbulence is shown to be out of equilibrium, and the velocity profiles depart from the log-law; However, for longer, and surprisingly for shorter forcing times, quasi-equilibrium is maintained. In Chapter 3, a reduced analytical model, based on the Navier-Stokes equations, will be introduced and shown to be analogous to a damped oscillator where inertial, Coriolis, and friction forces mirror the mass, spring, and damper, respectively. When a steady buoyancy (stable or unstable) is superposed on the unsteady pressure gradient, the same model structure can be maintained, but the damping term, corresponding to friction forces and vertical coupling, needs to account for stability. However, for the reverse case with variable buoyancy flux and stability, the model needs to be extended to allow time-variable damper coefficient. These extensions of the analytical model are

  10. The structure of the atmospheric boundary layer in the central equatorial Pacific during January and February of FGGE

    NASA Technical Reports Server (NTRS)

    Firestone, James K.; Albrecht, Bruce A.

    1986-01-01

    The structure of the atmospheric boundary layer for a region between Hawaii and the equator is studied using dropwindsonde data (about 900 soundings) collected in January and February 1979 as part of the First GARP Global Experiment. These data were used to establish the longitudinal and latitudinal variations in the thermodynamic and wind structure of the boundary layer and describe differences in the structure for convectively active and inactive conditions. Low-level inversions (at a pressure of approximately 850 mb) were found to be an important feature of the structure of the boundary layer for undisturbed conditions. Although the frequency of low-level inversions decreased equatorward from Hawaii, the average height of the inversions observed in these regions did not vary significantly in the north-south direction. For convectively undisturbed conditions, low-level inversions are on the average of sufficient strength to suppress deep convection. However, it is shown they could easily be modified by upward vertical motion to give a boundary layer structure similar to that observed in areas where deep convection was observed.

  11. The structure of the atmospheric boundary layer in the central equatorial Pacific during January and February of FGGE

    NASA Technical Reports Server (NTRS)

    Firestone, James K.; Albrecht, Bruce A.

    1986-01-01

    The structure of the atmospheric boundary layer for a region between Hawaii and the equator is studied using dropwindsonde data (about 900 soundings) collected in January and February 1979 as part of the First GARP Global Experiment. These data were used to establish the longitudinal and latitudinal variations in the thermodynamic and wind structure of the boundary layer and describe differences in the structure for convectively active and inactive conditions. Low-level inversions (at a pressure of approximately 850 mb) were found to be an important feature of the structure of the boundary layer for undisturbed conditions. Although the frequency of low-level inversions decreased equatorward from Hawaii, the average height of the inversions observed in these regions did not vary significantly in the north-south direction. For convectively undisturbed conditions, low-level inversions are on the average of sufficient strength to suppress deep convection. However, it is shown they could easily be modified by upward vertical motion to give a boundary layer structure similar to that observed in areas where deep convection was observed.

  12. Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer.

    PubMed

    Wilcox, Eric M; Thomas, Rick M; Praveen, Puppala S; Pistone, Kristina; Bender, Frida A-M; Ramanathan, Veerabhadran

    2016-10-18

    The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events.

  13. Black carbon solar absorption suppresses turbulence in the atmospheric boundary layer

    PubMed Central

    Wilcox, Eric M.; Thomas, Rick M.; Praveen, Puppala S.; Pistone, Kristina; Bender, Frida A.-M.; Ramanathan, Veerabhadran

    2016-01-01

    The introduction of cloud condensation nuclei and radiative heating by sunlight-absorbing aerosols can modify the thickness and coverage of low clouds, yielding significant radiative forcing of climate. The magnitude and sign of changes in cloud coverage and depth in response to changing aerosols are impacted by turbulent dynamics of the cloudy atmosphere, but integrated measurements of aerosol solar absorption and turbulent fluxes have not been reported thus far. Here we report such integrated measurements made from unmanned aerial vehicles (UAVs) during the CARDEX (Cloud Aerosol Radiative Forcing and Dynamics Experiment) investigation conducted over the northern Indian Ocean. The UAV and surface data reveal a reduction in turbulent kinetic energy in the surface mixed layer at the base of the atmosphere concurrent with an increase in absorbing black carbon aerosols. Polluted conditions coincide with a warmer and shallower surface mixed layer because of aerosol radiative heating and reduced turbulence. The polluted surface mixed layer was also observed to be more humid with higher relative humidity. Greater humidity enhances cloud development, as evidenced by polluted clouds that penetrate higher above the top of the surface mixed layer. Reduced entrainment of dry air into the surface layer from above the inversion capping the surface mixed layer, due to weaker turbulence, may contribute to higher relative humidity in the surface layer during polluted conditions. Measurements of turbulence are important for studies of aerosol effects on clouds. Moreover, reduced turbulence can exacerbate both the human health impacts of high concentrations of fine particles and conditions favorable for low-visibility fog events. PMID:27702889

  14. 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.

  15. 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.

  16. Marine-atmospheric boundary layer characteristics over the South China Sea during the passage of strong Typhoon Hagupit

    NASA Astrophysics Data System (ADS)

    Cheng, Xueling; Wu, Lin; Song, Lili; Wang, Binglan; Zeng, Qingcun

    2014-06-01

    The structures and characteristics of the marine-atmospheric boundary layer over the South China Sea during the passage of strong Typhoon Hagupit are analyzed in detail in this paper. The typhoon was generated in the western Pacific Ocean, and it passed across the South China Sea, finally landfalling in the west of Guangdong Province. The shortest distance between the typhoon center and the observation station on Zhizi Island (10 m in height) is 8.5 km. The observation data capture the whole of processes that occurred in the regions of the typhoon eye, two squall regions of the eye wall, and weak wind regions, before and after the typhoon's passage. The results show that: (a) during the strong wind (average velocity m s-1) period, in the atmospheric boundary layer below 110 m, is almost independent of height, and vertical velocity is greater than 0, increasing with and reaching 2-4 m s-1 in the squall regions; (b) the turbulent fluctuations (frequency > 1/60 Hz) and gusty disturbances (frequency between 1/600 and 1/60 Hz) are both strong and anisotropic, but the anisotropy of the turbulent fluctuations is less strong; (c) can be used as the basic parameter to parameterize all the characteristics of fluctuations; and (d) the vertical flux of horizontal momentum contributed by the average flow is one order of magnitude larger than those contributed by fluctuation fluxes ( and ), implying that strong wind may have seriously disturbed the sea surface through drag force and downward transport of eddy momentum and generated large breaking waves, leading to formation of a strongly coupled marine-atmospheric boundary layer. This results in in the atmosphere, and some portion of the momentum in the sea may be fed back again to the atmosphere due to.

  17. 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

  18. Investigating the early springtime stable atmospheric boundary layer in Adventdalen (Spitsbergen) - a case study

    NASA Astrophysics Data System (ADS)

    Mayer, Stephanie; Jonassen, Marius O.; Reuder, Joachim; Sandvik, Anne

    2010-05-01

    During the night of 31.03-01.04.2009, very cold temperatures (≤ 30 °C) were observed at the old Auroral station in Adventdalen (Spitsbergen). A group of german and norwegian scientists operated the Small Unmanned Meteorological Observer SUMO as a ‘recoverable radiosonde' in high temporal resolution. SUMO aircraft measurements will be shown in comparison to high resolution runs using the numerical weather prediction model WRF. With support of surface measurements from a 10 m mast and boundary layer profiles measured by SUMO it can be tested, if the model is able to forecast such extreme temperature.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. High-Frequency Response of the Atmospheric Electric Potential Gradient Under Strong and Dry Boundary-Layer Convection

    NASA Astrophysics Data System (ADS)

    Conceição, Ricardo; Silva, Hugo Gonçalves; Bennett, Alec; Salgado, Rui; Bortoli, Daniele; Costa, Maria João; Collares Pereira, Manuel

    2017-09-01

    The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection.

  4. Assessing State-of-the-Art Capabilities for Probing the Atmospheric Boundary Layer: The XPIA Field Campaign

    SciTech Connect

    Lundquist, Julie K.; Wilczak, James M.; Ashton, Ryan; Bianco, Laura; Brewer, W. Alan; Choukulkar, Aditya; Clifton, Andrew; Debnath, Mithu; Delgado, Ruben; Friedrich, Katja; Gunter, Scott; Hamidi, Armita; Iungo, Giacomo Valerio; Kaushik, Aleya; Kosovic, Branko; Langan, Patrick; Lass, Adam; Lavin, Evan; Lee, Joseph C. Y.; McCaffrey, Katherine L.; Newsom, Rob K.; Noone, David C.; et al.

    2016-06-17

    To assess current capabilities for measuring flow within the atmospheric boundary layer, including within wind farms, the U.S. Dept. of Energy sponsored the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign at the Boulder Atmospheric Observatory (BAO) in spring 2015. Herein, we summarize the XPIA field experiment, highlight novel measurement approaches, and quantify uncertainties associated with these measurement methods. Line-of-sight velocities measured by scanning lidars and radars exhibit close agreement with tower measurements, despite differences in measurement volumes. Virtual towers of wind measurements, from multiple lidars or radars, also agree well with tower and profiling lidar measurements. Estimates of winds over volumes from scanning lidars and radars are in close agreement, enabling assessment of spatial variability. Strengths of the radar systems used here include high scan rates, large domain coverage, and availability during most precipitation events, but they struggle at times to provide data during periods with limited atmospheric scatterers. In contrast, for the deployment geometry tested here, the lidars have slower scan rates and less range, but provide more data during non-precipitating atmospheric conditions. Microwave radiometers provide temperature profiles with approximately the same uncertainty as Radio-Acoustic Sounding Systems (RASS). Using a motion platform, we assess motion-compensation algorithms for lidars to be mounted on offshore platforms. Finally, we highlight cases for validation of mesoscale or large-eddy simulations, providing information on accessing the archived dataset. We conclude that modern remote sensing systems provide a generational improvement in observational capabilities, enabling resolution of fine-scale processes critical to understanding inhomogeneous boundary-layer flows.

  5. Assessing state-of-the-art capabilities for probing the atmospheric boundary layer: The XPIA field campaign

    DOE PAGES

    Lundquist, Julie K.; Wilczak, James M.; Ashton, Ryan; ...

    2017-03-07

    To assess current capabilities for measuring flow within the atmospheric boundary layer, including within wind farms, the U.S. Dept. of Energy sponsored the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign at the Boulder Atmospheric Observatory (BAO) in spring 2015. Herein, we summarize the XPIA field experiment, highlight novel measurement approaches, and quantify uncertainties associated with these measurement methods. Line-of-sight velocities measured by scanning lidars and radars exhibit close agreement with tower measurements, despite differences in measurement volumes. Virtual towers of wind measurements, from multiple lidars or radars, also agree well with tower and profiling lidar measurements. Estimates of windsmore » over volumes from scanning lidars and radars are in close agreement, enabling assessment of spatial variability. Strengths of the radar systems used here include high scan rates, large domain coverage, and availability during most precipitation events, but they struggle at times to provide data during periods with limited atmospheric scatterers. In contrast, for the deployment geometry tested here, the lidars have slower scan rates and less range, but provide more data during non-precipitating atmospheric conditions. Microwave radiometers provide temperature profiles with approximately the same uncertainty as Radio-Acoustic Sounding Systems (RASS). Using a motion platform, we assess motion-compensation algorithms for lidars to be mounted on offshore platforms. As a result, we highlight cases for validation of mesoscale or large-eddy simulations, providing information on accessing the archived dataset. We conclude that modern remote sensing systems provide a generational improvement in observational capabilities, enabling resolution of fine-scale processes critical to understanding inhomogeneous boundary-layer flows.« less

  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, 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  8. Impact of atmospheric boundary layer turbulent temperature fluctuations on remote detection of vapors by passive infrared spectroscopy.

    PubMed

    Ifarraguerri, Agustin; Ben-David, Avishai

    2008-10-27

    A computational model to simulate the effects of boundary layer isotropic atmospheric turbulence on the radiative transfer process is presented. We perform a large number of simulations with stochastic ambient conditions to estimate the statistics necessary to predict the detection limit of a given trace gas. We find that the radiance and transmittance variability are primarily determined by the optical depth of the emitting atmosphere, and that the relative variability of the transmittance is an order of magnitude smaller than that of the radiance. We estimate that the atmospheric detection limit of a DMMP vapor cloud at 30 meters altitude for a ground-based observer ranges from 3.5 to 12 ppb-m, depending on the horizontal range to the cloud. Addition of uncorrelated detector noise has a disproportionate effect on the detection limit over the spectrally correlated turbulence noise. These calculations appear to be the first predictions of vapor detection limits that explicitly incorporate the effects of turbulence.

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

    PubMed

    Smits, Kathleen; Eagen, Victoria; Trautz, Andrew

    2015-06-08

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

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

    PubMed Central

    Smits, Kathleen; Eagen, Victoria; Trautz, Andrew

    2015-01-01

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

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

    PubMed Central

    2016-01-01

    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

  12. 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'.

  13. Large-eddy simulation of stable atmospheric boundary layers to develop better turbulence closures for climate and weather models

    NASA Astrophysics Data System (ADS)

    Bou-Zeid, Elie; Huang, Jing; Golaz, Jean-Christophe

    2011-11-01

    A disconnect remains between our improved physical understanding of boundary layers stabilized by buoyancy and how we parameterize them in coarse atmospheric models. Most operational climate models require excessive turbulence mixing in such conditions to prevent decoupling of the atmospheric component from the land component, but the performance of such a model is unlikely to be satisfactory under weakly and moderately stable conditions. Using Large-eddy simulation, we revisit some of the basic challenges in parameterizing stable atmospheric boundary layers: eddy-viscosity closure is found to be more reliable due to an improved alignment of vertical Reynolds stresses and mean strains under stable conditions, but the dependence of the magnitude of the eddy viscosity on stability is not well represented by several models tested here. Thus, we propose a new closure that reproduces the different stability regimes better. Subsequently, tests of this model in the GFDL's single-column model (SCM) are found to yield good agreement with LES results in idealized steady-stability cases, as well as in cases with gradual and sharp changes of stability with time.

  14. The deep atmospheric boundary layer and its significance to the stratosphere and troposphere exchange over the Tibetan Plateau.

    PubMed

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

    2013-01-01

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

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

    PubMed Central

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

    2013-01-01

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

  16. 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

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Senocak, Inane

    2003-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Brutsaert, Wilfried; Sugita, Michiaki

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Brutsaert, Wilfried; Sugita, Michiaki

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Pallmann, A. J.

    1983-01-01

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

  5. CFD modelling of small particle dispersion: The influence of the turbulence kinetic energy in the atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Gorlé, C.; van Beeck, J.; Rambaud, P.; Van Tendeloo, G.

    When considering the modelling of small particle dispersion in the lower part of the Atmospheric Boundary Layer (ABL) using Reynolds Averaged Navier Stokes simulations, the particle paths depend on the velocity profile and on the turbulence kinetic energy, from which the fluctuating velocity components are derived to predict turbulent dispersion. It is therefore important to correctly reproduce the ABL, both for the velocity profile and the turbulence kinetic energy profile. For RANS simulations with the standard k- ɛ model, Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.) proposed a set of boundary conditions which result in horizontally homogeneous profiles. The drawback of this method is that it assumes a constant profile of turbulence kinetic energy, which is not always consistent with field or wind tunnel measurements. Therefore, a method was developed which allows the modelling of a horizontally homogeneous turbulence kinetic energy profile that is varying with height. By comparing simulations performed with the proposed method to simulations performed with the boundary conditions described by Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.), the influence of the turbulence kinetic energy on the dispersion of small particles over flat terrain is quantified.

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

    NASA Astrophysics Data System (ADS)

    Postylyakov, Oleg; Borovski, Alexander; Ivanov, Victor

    2015-11-01

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

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

    PubMed

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

    2006-03-01

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

  9. A Model of Atmospheric Vapor Isotopes at Their Source: the Marine Boundary Layer

    NASA Astrophysics Data System (ADS)

    Posmentier, E. S.; Fan, N.; Sonder, L. J.; Feng, X.

    2015-12-01

    The stable isotopes of water vapor and precipitation are widely used for studying modern and past climates, but the framework for interpreting isotope variations remains incomplete. The most significant gap is a full description of vapor isotopes and transport in the marine boundary layer (MBL) connecting the sea surface and the free troposphere. Increasingly available vapor isotope measurements in the MBL highlight the need to fill this gap. We introduce the first moderate complexity, vertically resolved MBL model that incorporates several important processes, including 1) entrainment of subsided mid tropospheric air with original mixing ratio rE, 2) height-dependent vapor diffusivity that is purely molecular at the surface and increases linearly with turbulence to a maximum Kmax in the mid MBL, and 3) vertical velocity wa.. Furthermore, the model does not require specification of either humidity or isotope ratios above the laminar layer, or kinetic fractionation within it. It computes all of these values as well as evaporation rate, isotopic profiles and fluxes, while the isotope flux ratios are the only output from earlier evaporation models. Analytical solutions are found for the profiles of δD, δ18O, and d-excess in the MBL. Simulations coincide remarkably well with the region of the δD vs. δ18O plane populated by global marine observations. Numerical experiments create a family of straight lines in the δD vs. δ18O plane corresponding to different combinations of conditions. These "vapor lines" are mixing lines between isotopically enriched vapor above the laminar layer and depleted vapor in subsiding air. Their slope and/or extent are most strongly influenced by rE and Kmax, to a lesser extent by sea surface temperature (SST) and the fraction of subsided air in the MBL (α), and only slightly by other parameters. We show that these effects of rE, Kmax and SST on the δD vs. δ18O relationship result from their combined influence on (1) the thickness of

  10. Atmospheric boundary layer adjustment to the synoptic cycle at the Brazil-Malvinas Confluence, South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Acevedo, OtáVio C.; Pezzi, Luciano P.; Souza, Ronald B.; Anabor, Vagner; Degrazia, GerváSio A.

    2010-11-01

    This study analyzes and discusses atmospheric boundary layer vertical profiles of potential temperature, specific humidity, and wind speed at each of the sides of the Brazil-Malvinas Confluence in the southwestern Atlantic Ocean. Such confluence is characterized by the meeting of water masses with very different characteristics: the southern waters of the Malvinas current can be several degrees colder and appreciably less salty than the northern Brazil current waters. At the same time, a synoptic cycle can be identified at the region, marked by the successive passages of frontal systems and extratropical cyclones. The different phases of the synoptic cycle lead to different thermal advections at the confluence, causing respective different patterns of atmospheric boundary layer adjustment to the surface heterogeneity induced by the confluence. In the present study, this adjustment along the synoptic cycle is analyzed using data from five experiments performed across the confluence from 2003 to 2008. In each of the campaigns a number of soundings were launched from a ship at both sides of the confluence. A climatological analysis with respect to the closest frontal passage is presented, and it suggests that the observations collected at each of the years analyzed are referent to a different day of the synoptic cycle. The average profiles at each side of the confluence are in agreement with previous modeling studies of warm and cold thermal advection patterns over an oceanic front. Furthermore, our study shows that peculiar transitional characteristics are also observed between the conditions of well-established warm and cold advection. At many phases of the synoptic cycle a strongly stratified boundary layer occurs at one or both sides of the confluence. Some of the observed characteristics, such as a large moisture accumulation near the surface, suggest that existing sensible and latent heat fluxes parameterizations fail under very strong stratifications, and the

  11. Improving Wind Predictions in the Marine Atmospheric Boundary Layer through Parameter Estimation in a Single-Column Model

    SciTech Connect

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

    2016-12-14

    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 study, we use 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.

  12. 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.

  13. Ventilated Oscillatory Boundary Layers

    DTIC Science & Technology

    1993-02-01

    AD-A266 226IllII !i III ll11111 II •" Ventilated Oscillatory Boundary Layers 0 Daniel -. Conley Douglas L. I nman C 0 UM U U U U till 1% w 1% W" Z t...A SIGNIFICANT NUMBER OF PAGES WHICH DO NOT REPRODUCE LEGIBLY. VENlTILATiD SCIILLAORY BOUNDARY LAYERS Daniel C. C7onley DoL’laN L. . ... La olDla...Wave Crest ........ 5. Boundary Layer Development Under the Wave Trough W 6 . Laboratory Observations .................. ................ 7

  14. 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.

  15. 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.

  16. Two years of atmospheric boundary layer observations on a 45-m tower at Dome C on the Antarctic plateau

    NASA Astrophysics Data System (ADS)

    Genthon, Christophe; Six, Delphine; GalléE, Hubert; Grigioni, Paolo; Pellegrini, Andrea

    2013-04-01

    The lower atmospheric boundary layer at Dome C on the Antarctic plateau has been continuously monitored along a 45-m tower since 2009. Two years of observations (2009 and 2010) are presented. A strong diurnal cycle is observed near the surface in summer but almost disappears at the top of the tower, indicating that the summer nocturnal inversion is very shallow. Very steep inversions reaching almost 1 °C m-1 on average along the tower are observed in winter. They are stronger and more frequent during the colder 2010 winter, reaching a maximum in a layer ~10-15 m above the surface. Winter temperature is characterized by strong synoptic variability. An extreme warm event occurred in July 2009. The temperature reached -30 °C, typical of midsummer weather. Meteorological analyses which agree with the observations near the surface confirm that heat is propagated downward from higher elevations. A high total water column indicates moist air masses aloft originating from the lower latitudes. The coldest temperatures and strongest inversions are associated with characteristic synoptic patterns and a particularly dry atmosphere. Measurement of moisture in the clean and cold Antarctic plateau atmosphere is a challenging task. Supersaturations are very likely but are not revealed by the observations. This is possibly an instrumental artifact that would affect other moisture measurements made in similar conditions. In spite of this, such observations offer a stringent test of the robustness of the polar boundary layer in meteorological and climate models, addressing a major concern raised in the IPCC 2007 report.

  17. Using Surface-based Downwelling Spectral Infrared Radiance Observations to Understand Atmospheric Boundary Layer Structure and Evolution: The Evening Transition

    NASA Astrophysics Data System (ADS)

    Turner, D. D.; Blumberg, W. G.; Khosravian, K.

    2016-12-01

    The downwelling spectral infrared radiance at the surface depends on the vertical structure of temperature and trace gases such as water vapor and carbon dioxide, as well as the presence and optical properties of any cloud and aerosol layers. A 1-dimensional variational retrieval algorithm has been developed that retrieves profiles of temperature and humidity in the lowest 3 km of the troposphere, cloud properties, and limited information on carbon dioxide and methane from 20-s measurements of infrared radiance from a ground-based interferometer. These retrievals will be used to look at the evolution of the atmosphere during the afternoon-to-evening transition, when solar heating of the surface diminishes rapidly and a stable boundary layer develops.

  18. Characterization of the atmospheric boundary layer from radiosonde observations along eastern end of monsoon trough of India

    NASA Astrophysics Data System (ADS)

    Chandra, Sagarika; Dwivedi, Arun K.; Kumar, Manoj

    2014-08-01

    In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature ( 𝜃 v ) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number ( R i B ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.

  19. Characterization of the atmospheric boundary layer from radiosonde observations along eastern end of monsoon trough of India

    NASA Astrophysics Data System (ADS)

    Chandra, Sagarika; Dwivedi, Arun K.; Kumar, Manoj

    2014-08-01

    In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature (𝜃 v ) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number (R i B ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.

  20. A Comprehensive Modelling Approach for the Neutral Atmospheric Boundary Layer: Consistent Inflow Conditions, Wall Function and Turbulence Model

    NASA Astrophysics Data System (ADS)

    Parente, Alessandro; Gorlé, Catherine; van Beeck, Jeroen; Benocci, Carlo

    2011-09-01

    We report on a novel approach for the Reynolds-averaged Navier-Stokes (RANS) modelling of the neutral atmospheric boundary layer (ABL), using the standard k-{\\varepsilon} turbulence model. A new inlet condition for turbulent kinetic energy is analytically derived from the solution of the k-{\\varepsilon} model transport equations, resulting in a consistent set of fully developed inlet conditions for the neutral ABL. A modification of the standard k-{\\varepsilon} model is also employed to ensure consistency between the inlet conditions and the turbulence model. In particular, the turbulence model constant C μ is generalized as a location-dependent parameter, and a source term is introduced in the transport equation for the turbulent dissipation rate. The application of the proposed methodology to cases involving obstacles in the flow is made possible through the implementation of an algorithm, which automatically switches the turbulence model formulation when going from the region where the ABL is undisturbed to the region directly affected by the building. Finally, the model is completed with a slightly modified version of the Richards and Hoxey rough-wall boundary condition. The methodology is implemented and tested in the commercial code Ansys Fluent 12.1. Results are presented for a neutral boundary layer over flat terrain and for the flow around a single building immersed in an ABL.

  1. Large-eddy simulation of atmospheric boundary layer flow and passive scalar dispersion over idealized urban surfaces

    NASA Astrophysics Data System (ADS)

    Cheng, Wai Chi; Porté-Agel, Fernando

    2015-04-01

    Accurate prediction of atmospheric boundary layer (ABL) flow and its interaction with urban surfaces is critical for understanding the transport of momentum and scalars within and above cities. This, in turn, is essential for predicting the local climate and pollutant dispersion patterns in urban areas. Large-eddy simulation (LES) explicitly resolves the large-scale turbulent eddy motions and, therefore, can potentially provide improved understanding and prediction of flows and scalar transport inside and above urban canopies. In this study, LES is used to simulate the dispersion of passive scalar over idealized urban surfaces represented by uniform arrays of cubes. A modulated gradient subgird-scale (SGS) model is used to parametrize the SGS fluxes of momentum and scalar, and an immersed boundary method is used to model the presence of cubes. A similar LES framework for flow was validated in our previous studies in simulations of turbulent boundary-layer flow past a 2D block and a uniform array of cubes. Here, the LES framework is further validated with wind tunnel experimental data of passive scalar dispersion within and above a staggered array of cubes with a localized scalar source at ground level. Good agreement between the simulation results and experimental data are found in the vertical and horizontal profiles of scalar concentration in different streamwise locations. After the validation, the LES framework is used to simulate the scalar transport at rural-to-urban flow transition region and the results obtained are presented.

  2. 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.

  3. Hg(II) Sources, Sinks, and Reactions with Halogens in the Remote Atmospheric Marine Boundary Layer

    NASA Astrophysics Data System (ADS)

    Holmes, C. D.; Jacob, D. J.; Mason, R. P.; Jaffe, D.

    2007-12-01

    We investigate the chemistry and sinks of reactive gaseous mercury (RGM) in the remote marine boundary layer, using a box model to interpret observations from the Atlantic and Pacific Oceans and from a coastal site in Okinawa. The diurnal cycles of RGM at all sites have morning increases that we show are quantitatively consistent with RGM production primarily from the oxidation of Hg0 by atomic halogens. Atomic bromine may generate the midday peak in RGM and could be the major daytime oxidant of Hg0, while atomic Cl could play a secondary role in the morning. Because RGM concentrations fall rapidly in the afternoon but persist above detection limit at night, we posit a photosensitive sink for RGM, possibly involving reduced sulfur species in marine aerosol. Alternately or in addition, a nocturnal oxidant, such as NO3, could supply detectable amounts of RGM at night. We find much larger amplitude diurnal cycles over tropical and sub-tropical oceans compared with the extra-tropics. The tropical enhancement of RGM concentration occurs in areas with little chlorophyll A, but where previous studies found significant biogenic halocarbon emissions.

  4. Hydrogen Peroxide and Methylhydroperoxide Budgets in the Marine Boundary Layer During the Pacific Atmospheric Sulfur Experiment

    NASA Astrophysics Data System (ADS)

    O'Sullivan, D. W.; Heikes, B. G.; Higbie, A.; Merrill, J. T.; Bandy, A. R.; Mauldin, L.; Cantrell, C.; Anderson, R. S.; Campos, T.; Lenschow, D.; Bloomquist, B.; Faloona, I. C.; Conley, S. A.; Wang, Y.; Pollack, I. B.; Heizer, C. G.; Weinheimer, A. J.

    2008-12-01

    Airborne gas phase measurements of hydrogen peroxide, methylhydroperoxide, ozone, carbon monoxide, dimethylsulfide, sulfur dioxide, hydroxyl, and perhydroxyl, together with meteorological parameters are used to assess the photochemical budget of hydrogen peroxide and methylhydroperoxide in the marine boundary layer (MBL). The observations come from 14 research flights using the NCAR C-130 flown mostly southeast of Kiritimati in relatively cloud- and precipitation-free MBL air. This region was expected to have extremely low nitrogen oxide mixing ratios and minimal horizontal gradients in composition. Eddy-correlation methods are used to estimate entrainment rates at the top of the MBL. Surface deposition rates are calculated from wind and molecular properties. Gas phase photolysis rates are calculated and reaction rate constants are estimated from the literature. The measurements and budgets are discussed in terms of their ability to constrain net ozone production, nitrogen oxide levels, reactive hydrocarbons, and halogen radical chemistry. On occasion the aircraft flew within its advected exhaust plume and a decrease in methylhydroperoxide, but not in hydrogen peroxide, was noted.

  5. 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.

  6. Modeling of particulate matter transport in atmospheric boundary layer following dust emission from source areas

    NASA Astrophysics Data System (ADS)

    Katra, Itzhak; Elperin, Tov; Fominykh, Andrew; Krasovitov, Boris; Yizhaq, Hezi

    2016-03-01

    A two-dimensional model for particulate matter (PM) dispersion due to dust emission from soils is presented. Field experiments were performed at a dust source site (Negev loess soil) with a portable boundary layer wind tunnel to determine the emitted PM fluxes for different wind speeds and varying soil conditions. The numerical model is formulated using parameterizations based on the aeolian experiments. The wind velocity profiles used in the simulations were fitted from data obtained in field measurements. Size distribution of the emitted dust particles in the numerical simulations was taken into account using a Monte Carlo method. The PM concentration distributions at a distance of several kilometers from the dust source under specific shear velocities and PM fluxes from the soil were determined numerically by solving advection-diffusion equation. The obtained PM10 concentrations under typical wind and soil conditions are supported by PM data recorded over time in a standard environmental monitoring station. The model enhances our capacity of quantification of dust processes to support climate models as well as health risk assessment.

  7. 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

  8. 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.

  9. Investigating the diurnal and spatial variability of flows in the atmospheric boundary layer: A large eddy simulation study

    NASA Astrophysics Data System (ADS)

    Kumar, Vijayant

    Large-eddy simulation (LES) studies of the atmospheric boundary layer (ABL) have historically modeled the daytime (convective), nighttime (stable) and dawn/dusk windy (neutral) regimes separately under the assumption of a quasi-steady ABL. The real-world ABL however, continuously transitions between the different stability regimes and development of an LES capable of simulating the entire diurnal evolution of the ABL is needed. We have developed an LES tool (The JHU-LES code) with the new-generation Lagrangian dynamic models capable of dynamic adjustment of the subgrid-scale stresses thereby, making it apt for LES over entire diurnal cycles of the ABL. Preliminary LES studies demonstrate that the JHU-LES code reproduces well-known features of the quasi-steady convective and stable boundary layers, such as the well-known spectral scalings for production and inertial subranges. LES of the entire 24-hour diurnal evolution of the atmospheric boundary layer is then performed and compared successfully to field observations (HATS dataset). Important features of the diurnal ABL such as entrainment-based growth of the CBL, development of the stable boundary layer and evolution of the nocturnal low-level jet are well reproduced. The advantages of using a local Obukhov length-scale to normalize the results are highlighted. To investigate the role of surface boundary conditions and geostrophic wind forcing, LES investigations of multi-day evolution of the ABL flow are then performed with several combinations of surface boundary conditions (imposed temperature and heat flux) and geostrophic forcing (constant, time-varying, time and height varying). The variable geostrophic forcing significantly improves the agreement of LES results with surface flux observations but shows poor agreement with daytime surface fluxes and, daytime and nighttime mean profiles. The LES setup using an imposed surface temperature almost always yields better results than cases where the heat flux is

  10. 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

  11. Turbulence Generation in the Atmospheric Boundary Layer and Limitations of the Monin-Obukhov Similarity Theory

    NASA Astrophysics Data System (ADS)

    Sun, Jielun; Lenschow, Donald; LeMone, Margaret; Mahrt, Larry

    2015-04-01

    Turbulent fluxes from the Cooperative Atmosphere-Surface Exchange Study in 1999 (CASES-99) field experiment are further analyzed for both day- and nighttime as a follow-on to the investigation of the nighttime turbulence in Sun et al. (2012). The behavior of momentum and heat fluxes is investigated as functions of wind speed and the bulk temperature difference between observation heights and the surface. Vertical variations of momentum and heat flux at a given height z are correlated and are explained in terms of the energy and heat balance in a layer above the ground surface in which the surface heating/cooling and momentum sink need to be included. In addition, the surface also plays an important role in constraining the size of the dominant turbulent eddies, which is directly related to turbulence strength and the length scale of turbulence generation. The turbulence generation is not related to local vertical gradients especially under neutral condition as assumed in Monin-Obukhov similarity theory. Based on the observed relationships between momentum and heat fluxes, a new bulk formula for turbulence parameterization is developed to mainly examine the above-mentioned surface effects on vertical variation of turbulent momentum and heat fluxes. The new understanding of the observed relationships between these turbulent variables and mean variables explains the observed nighttime turbulence regime change observed in Sun et al. (2012) as well as the daytime momentum and heat flux variations with height up to the maximum observation height of 55 m.

  12. 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.

  13. 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.

  14. Atmospheric boundary layer characteristics based on the observations at the Climate Change Tower in Ny Alesund( Svalbard).

    NASA Astrophysics Data System (ADS)

    Schiavon, Mario; Mazzola, Mauro; Lupi, Angelo; Drofa, Oxana; Tampieri, Francesco; Pelliccioni, Armando; Choi, Taejin; Vitale, Vito; Viola, Angelo P.

    2017-04-01

    At high latitudes, the Atmospheric Boundary Layer ( ABL) is often characterized by extremely stable vertical stratification since the surface radiative cooling determines inversions in temperature profiles especially during the polar night over land, ice and snow surfaces. Improvements are required in the theoretical understanding of the turbulent behavior of the high-latitude ABL. The parameterizations of surface-atmosphere exchanges employed in numerical weather prediction and climate models have also to be tested in the Arctic area. Moreover, the boundary layer structure and dynamics influence the vertical distribution of aerosol. The main issue is related to the height of PBL: the question is whether some decoupling occurs between the surface layer and the atmosphere aloft when the PBL is shallow or the mechanical mixing due to the synoptic circulation provides an overall vertical homogeneity of the concentration of the aerosol irrespective of the stability conditions. In this aim, the work investigates the features of the high-latitude ABL with particular attention to its vertical structure, the relationships among the main turbulent statistics (in a similarity approach) and their variation with the ABL state. The used data refer to measurements collected since 2012 to 2016 by slow and fast response sensors deployed at the 34 m high Amundsen-Nobile Climate Change Tower (CCT) installed at Ny-Ålesund, Svalbard. Data from four conventional Young anemometers and Väisäla thermo-hygrometers at 2, 4.8, 10.3 and 33.4 m a.g.l., alternated by three lined up sonic anemometers at 3.7, 7.5 and 21 m a.g.l., are used in the analysis. The presented results highlight that the performance of the commonly adopted ABL similarity schemes (e.g. flux-gradient relationships and parameterizations for the stable ABL height) depends upon the ABL state, determined mainly by the wind speed and the shape of the profiles of second order moments (the two being related) . For neutral or

  15. Sudden high concentration of TSP affected by atmospheric boundary layer in Seoul metropolitan area during duststorm period.

    PubMed

    Choi, H; Zhang, Y H; Kim, K H

    2008-07-01

    Hourly concentrations of TSP, PM(10), PM(2.5) near the surface at Seoul city were examined from March 20 to March 25, 2001 (duststorm event) in order to investigate the effect of a duststorm generated in China on the local aerosol concentration in Korea, The ratios of fine to coarse particles such as TSP to PM(10), TSP to PM(2.5) and PM(10)-PM(2.5) to PM(2.5) showed that a great amount of dust transported from the origin of the duststorm was remarkable with a maximum ratio of 9.77 between TSP and PM(2.5). Back trajectories every 6 h showed the movement of dust particles in the lower atmosphere near 500 m to 1500 m (atmospheric boundary layer), which implied transport from Baotou in inner Mongolia of northern China to the direction of Seoul city in Korea and then the back trajectories passed near the southern border of Mongolia and Baotou through Zengzhou in the midlevels (3000 m) and low levels (500 m) of China, finally reaching Seoul city. So, the TSP concentration at Seoul city was partially influenced by the duststorm, under the prevailing westerly wind and the transported aerosols could influence high concentrations of pollutants of TSP, PM(10) and PM(2.5) in Seoul. The sudden high concentrations of TSP and PM(10) were found for a few hours, especially at 1500 to 1800 LST, March 22. At 1200 LST, before the passage of a cold front through the Korean peninsula, the convective boundary layer (CBL) near Seoul was not shallow, but at 1500 LST, under the frontal passage, the CBL was remarkably thinner (less than 300 m), due to the compression of the boundary layer by the intrusion of cold air. This resulted in the increase of the TSP concentration, even though the mixed layer above maintained almost the same depth. At 1800 LST shortly after the frontal passage, that is, near sunset, the nocturnal cooling of the ground caused air parcels to cool, thereby enhancing the shallower nocturnal surface inversion layer and producing the maximum concentration of TSP of 1388

  16. 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

  17. 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.

  18. 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.

  19. Analysis of planetary boundary layer fluxes and land-atmosphere coupling in the regional climate model CLM

    NASA Astrophysics Data System (ADS)

    Jaeger, E. B.; Stöckli, R.; Seneviratne, S. I.

    2009-09-01

    Land-atmosphere interactions and associated boundary layer processes are crucial elements of the climate system and play a major role in several feedback processes, in particular for extreme events. In this article, we provide a detailed validation of land surface processes and land-atmosphere interactions in the climate version of the Lokal Modell (CLM), a regional climate model that has been recently developed and is now used by a wide research community. For the evaluation of the model, we use observations from the FLUXNET network and meteorological data. Moreover, we also compare the performance of the CLM with that of its driving data set, the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis, and simulations of the Inter-Continental Transferability Study (ICTS). The results show that most of the land-atmosphere coupling characteristics are consistent in CLM and the observations. Nonetheless, the analysis also allows identification of specific weaknesses of the CLM such as an underestimation of the incoming surface shortwave radiation due to cloud cover overestimation, leading to an underestimation of the sensible heat flux. The comparisons with the ECMWF operational analysis and the ICTS models suggest, however, that all models have biases of comparable magnitude. This study demonstrates the utility of flux observations for diagnosing biases in land-atmosphere exchanges and interactions in current climate models and highlights perspectives for our improved understanding of the relevant processes.

  20. 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

  1. Representation of the Saharan atmospheric boundary layer in the Weather and Research Forecast (WRF) model: A sensitivity analysis.

    NASA Astrophysics Data System (ADS)

    Todd, Martin; Cavazos, Carolina; Wang, Yi

    2013-04-01

    The Saharan atmospheric boundary layer (SABL) during summer is one of the deepest on Earth, and is crucial in controlling the vertical redistribution and long-range transport of dust in the Sahara. The SABL is typically made up of an actively growing convective layer driven by high sensible heating at the surface, with a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ˜5-6km. These two layers are usually separated by a weak (≤1K) temperature inversion. Model representation of the SPBL structure and evolution is important for accurate weather/climate and aerosol prediction. In this work, we evaluate model performance of the Weather Research and Forecasting (WRF) to represent key multi-scale processes in the SABL during summer 2011, including depiction of the diurnal cycle. For this purpose, a sensitivity analysis is performed to examine the performance of seven PBL schemes (YSU, MYJ, QNSE, MYNN, ACM, Boulac and MRF) and two land-surface model (Noah and RUC) schemes. In addition, the sensitivity to the choice of lateral boundary conditions (ERA-Interim and NCEP) and land use classification maps (USGS and MODIS-based) is tested. Model outputs were confronted upper-air and surface observations from the Fennec super-site at Bordj Moktar and automatic weather station (AWS) in Southern Algeria Vertical profiles of wind speed, potential temperature and water vapour mixing ratio were examined to diagnose differences in PBL heights and model efficacy to reproduce the diurnal cycle of the SABL. We find that the structure of the model SABL is most sensitive the choice of land surface model and lateral boundary conditions and relatively insensitive to the PBL scheme. Overall the model represents well the diurnal cycle in the structure of the SABL. Consistent model biases include (i) a moist (1-2 gkg-1) and slightly cool (~1K) bias in the daytime convective boundary layer (ii

  2. The Martian Surface Boundary Layer

    NASA Technical Reports Server (NTRS)

    Wilson, G. R.; Joshi, M.

    1999-01-01

    The acquisition of meteorological data from the surface of Mars by the two Viking Landers and Mars Pathfinder make it possible to estimate atmospheric boundary layer parameters and surface properties at three different locations on the planet. Because the Martian atmosphere is so thin the majority of the solar radiance is converted to heat at the surface. The difference between surface and atmospheric temperature can also constraint surface albedo, thermal inertia, and infrared emissivity. The Mars Pathfinder Atmospheric Structure Instrument/Meteorological package (ASI/MET) was the most capable weather monitoring system ever sent to the surface of another planet to date. One of the prime objectives of the ASI/MET package is to characterize the surface boundary layer parameters, particularly the heat and momentum fluxes, scaling temperature and friction velocity, and estimate surface roughness. Other important boundary layer parameters, such as Richardson Number, Monin-Obukhov length, analysis of turbulence characteristics of wind and temperature, and atmospheric stability class can also be determined from these measurements.

  3. 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

    2016-12-01

    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.

  4. 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.

  5. Analysis and approximation of linear and nonlinear partial differential equations: Boundary layers, atmospheric equations, change of phase

    NASA Astrophysics Data System (ADS)

    Hong, Youngjoon

    My thesis is in the area of mathematical analysis of computational fluid dynamics and geophysical fluid dynamics. My thesis contains three main objectives. Theoretical and numerical analysis of the singularly perturbed problems are considered in Chapter 2 and 3. One major focus and contribution in this subject is to study the boundary layers of the convection-diffusion equations in the presence of characteristic points. Theoretical results on the boundary layers is used to improve on their computations. The numerical analysis of the singularly perturbed convection-diffusion equations raises substantial difficulties when we consider a standard finite element space. To remedy this difficulty, the profile of the boundary layer is introduced. New avenues are explored to study the two dimensional inviscid primitive equations of the atmosphere with humidity and saturation, in presence of topography and subject to physically plausible boundary conditions for the system of equations. Spatial discretization is done by first order finite volume methods. A version of the projection method is introduced to enforce the compatibility condition on the horizontal velocity field, which comes from the boundary conditions. The resulting scheme allows for a significant reduction of the errors near the topography when compared to more standard finite volume schemes. In the numerical simulations, we first present the associated convergence results that are satisfied by the solutions simulated by our scheme when compared to particular analytic solutions. We then report on numerical experiments using realistic parameters. Finally, the effects of a random small-scale forcing on the velocity equation is numerically investigated. It is well known that the solutions of the 3D Navier--Stokes equations remain bounded for all time if the initial data and the forcing are sufficiently small relative to the viscosity, and for a finite time given any bounded initial data. We consider two temporal

  6. 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.

  7. Two-micrometer heterodyne differential absorption lidar measurements of the atmospheric CO2 mixing ratio in the boundary layer

    NASA Astrophysics Data System (ADS)

    Gibert, Fabien; Flamant, Pierre H.; Bruneau, Didier; Loth, Claude

    2006-06-01

    A 2 μm heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique (Paris) to monitor the CO2 mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO2 is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.

  8. Two-micrometer heterodyne differential absorption lidar measurements of the atmospheric CO2 mixing ratio in the boundary layer.

    PubMed

    Gibert, Fabien; Flamant, Pierre H; Bruneau, Didier; Loth, Claude

    2006-06-20

    A 2 microm heterodyne differential absorption lidar (HDIAL) has been operated at the Instïtut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique (Paris) to monitor the CO(2) mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO(2) is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.

  9. Investigation of Turbulence Parametrization Schemes with Reference to the Atmospheric Boundary Layer Over the Aegean Sea During Etesian Winds

    NASA Astrophysics Data System (ADS)

    Dandou, A.; Tombrou, M.; Kalogiros, J.; Bossioli, E.; Biskos, G.; Mihalopoulos, N.; Coe, H.

    2017-08-01

    The spatial structure of the marine atmospheric boundary layer (MABL) over the Aegean Sea is investigated using the Weather Research and Forecasting (WRF) mesoscale model. Two `first-order' non-local and five `1.5-order' local planetary boundary-layer (PBL) parametrization schemes are used. The predictions from the WRF model are evaluated against airborne observations obtained by the UK Facility for Airborne Atmospheric Measurements BAe-14 research aircraft during the Aegean-GAME field campaign. Statistical analysis shows good agreement between measurements and simulations especially at low altitude. Despite the differences between the predicted and measured wind speeds, they reach an agreement index of 0.76. The simulated wind-speed fields close to the surface differ substantially among the schemes (maximum values range from 13 to 18 m s^{-1} at 150-m height), but the differences become marginal at higher levels. In contrast, all schemes show similar spatial variation patterns in potential temperature fields. A warmer (1-2 K) and drier (2-3 g kg^{-1}) layer than is observed, is predicted by almost all schemes under stable conditions (eastern Aegean Sea), whereas a cooler (up to 2 K) and moister (1-2 g kg^{-1}) layer is simulated under near-neutral to nearly unstable conditions (western Aegean Sea). Almost all schemes reproduce the vertical structure of the PBL and the shallow MABL (up to 300 m) well, including the low-level jet in the eastern Aegean Sea, with non-local schemes being closer to observations. The simulated PBL depths diverge (up to 500 m) due to the different criteria applied by the schemes for their calculation. Under stable conditions, the observed MABL depth corresponds to the height above the sea surface where the simulated eddy viscosity reaches a minimum; under neutral to slightly unstable conditions this is close to the top of the simulated entrainment layer. The observed sensible heat fluxes vary from -40 to 25 W m^{-2}, while the simulated

  10. Variation of short-lived beta radionuclide (radon progeny) concentrations and the mixing processes in the atmospheric boundary layer.

    PubMed

    Veleva, B; Valkov, N; Batchvarova, E; Kolarova, M

    2010-07-01

    Radon is emitted to the atmosphere with quasi constant emission rates depending on the radium concentration in the earth's crust and soil physical properties. In this way, the 222Rn and 220Rn concentration in air reflects significantly the thickness of the atmospheric boundary layer (ABL). The aerosol-associated, beta-emitting progeny nuclides of 222Rn were measured daily in the framework of the atmospheric radioactivity monitoring program of NIMH at Sofia. The 214Pb concentration was estimated from the measured short-lived beta activity of 24-h filter samples, changed daily at 6:00 GMT. The impact of some meteorological factors such as wind direction, wind velocity, humidity, and temperature on short-lived beta radionuclides is estimated, and the results show no simple statistical relationship. A seasonal pattern was observed with winter minima and late summer-early autumn maxima. High variability in daily morning concentrations and mean monthly values was observed. There were well pronounced differences between years. The height of the convective ABL was estimated from daily radio-soundings at 12:00 GMT for the period 2001-2006 and from seven soundings per day during the experimental campaign in Sofia in October 2003. In general, concentrations of short-lived 222Rn progeny nuclides decreased with increased convective ABL height. 2009 Elsevier Ltd. All rights reserved.

  11. Atmospheric concentrations of the Cl atom, ClO radical, and HO radical in the coastal marine boundary layer.

    PubMed

    Chang, Chang-Tang; Liu, Tsun-Hsien; Jeng, Fu-Tien

    2004-01-01

    Atmospheric concentrations of chlorine atom (Cl*), chlorine monoxide radical (ClO*), and hydroxyl radical (HO*) in the coastal marine boundary layer are estimated in this study. A steady-state approach to their concentrations in equilibrium with other atmospheric chemical species is used. Measurements of atmospheric trace species, HCl, Cl2, HCHO, H2O2, CH3OOH, CH4, CO, SO2, NO, NO2, and O3, were performed at four sites in Taiwan during the spring of 1999. The results indicate that the concentrations of the Cl* atom and the ClO* and HO* radicals decrease significantly with cloud cover. The calculated average daytime concentrations of Cl*, ClO*, and HO* are 3 x 10(5), 1 x 10(7), and 6 x 10(5) molecules/cm3, respectively. Due to the high reactivity of Cl* with hydrocarbons and its concentration level competitive to that of HO*, Cl* should be a significant sink for hydrocarbons in these cases.

  12. Observed response of the marine atmospheric boundary layer to the Southern Ocean fronts during the IPY BGH 2008 cruise

    NASA Astrophysics Data System (ADS)

    Messager, C.; Speich, S.; Key, E.

    2012-03-01

    A set of meteorological instruments was added to an oceanographic cruise crossing the Southern Ocean from Cape Town to 57°33' S on board the R/V Marion Dufresne during the summer 2008. The Cape Cauldron, the subtropical, subantarctic, polar and southern Antarctic circumpolar current fronts were successively crossed. The recorded data permitted to derive the exchange of momentum, heat and water vapour at the ocean-atmosphere interface. A set of 38 radiosonde releases complemented the dataset. The marine atmospheric boundary layer characteristics and air-sea interaction when ship crossed the fronts and eddies are discussed. The specific role of the atmospheric synoptic systems advection on the air-sea interaction is highlighted over these regions. The dynamic associated with these systems drive the vertical mixing of the MABL by wind shear effect and/or the vertical thermal mixing. The MABL is stabilized (destabilized) and mixing is inhibited (enhanced) over the warm front sides if meridional wind component is northerly (southerly).

  13. Evolution of the atmospheric boundary layer in southern West Africa - an overview from the DACCIWA field campaign

    NASA Astrophysics Data System (ADS)

    Kalthoff, Norbert; Lohou, Fabienne; Brooks, Barbara; Jegede, Gbenga; Adler, Bianca; Ajao, Adewale; Ayoola, Muritala; Babić, Karmen; Bessardon, Geoffrey; Delon, Claire; Dione, Cheikh; Handwerker, Jan; Jambert, Corinne; Kohler, Martin; Lothon, Marie; Pedruzo-Bagazgoitia, Xabier; Smith, Victoria; Sunmonu, Lukman; Wieser, Andreas

    2017-04-01

    In southern West Africa, extended low-level stratus clouds form very frequently during night-time and persist long into the following day influencing the diurnal cycle of the atmospheric boundary layer (ABL). During the course of the day, a transition from nocturnal low-level stratus to stratocumulus, cumulus, and sometimes congestus and possibly cumulonimbus clouds is observed. In June and July 2016, a ground-based field campaign took place in southern West Africa within the framework of the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) project with the aim to identify the meteorological controls on the stratus and the evolution of the ABL. During the measurement period, extensive remote sensing and in-situ measurements were performed at three supersites in Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). We give an overview of the atmospheric conditions during the whole measurement period focusing on the vertical and temporal distribution of the stratus and relevant related atmospheric features.

  14. 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.

  15. 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.

  16. Chasing quicksilver: modeling the atmospheric lifetime of Hg(0)(g) in the marine boundary layer at various latitudes.

    PubMed

    Hedgecock, Ian M; Pirrone, Nicola

    2004-01-01

    The lifetime of elemental mercury in the marine boundary layer(MBL) has been studied using AMCOTS (Atmospheric Mercury Chemistry Over The Sea), a box model of MBL photochemistry including aerosols and detailed mercury chemistry. Recently measured Hg(0)(g) oxidation reactions have been included, and the studies were performed as a function of latitude, time of year, boundary layer liquid water content (LWC) and cloud optical depth. The results show that Hg has the shortest lifetime when air temperatures are low and sunlight and deliquescent aerosol particles are plentiful. Thus the modeled lifetime for clear-sky conditions is actually shorter at mid-latitudes and high latitudes than near the equator, and for a given latitude and time of year, cooler temperatures enhance the rate of Hg oxidation. Under typical summer conditions (for a given latitude) of temperature and cloudiness, the lifetime (tau) of Hg(0)(g) in the MBL is calculated to be around 10 days at all latitudes between the equator and 60 degrees N. This is much shorter than the generally accepted atmospheric residence time for Hg(0)(g) of a year or more. Given the relatively stable background concentrations of Hg(0)(g) which have been measured, continual replenishment of Hg(0)(g) must take place, suggesting a "multihop" mechanism for the distribution of Hg, rather than solely aeolian transport with little or no chemical transformation between source and receptor. Inclusion of an empirical Hg(0)(g) emission factor related to insolation was used to stabilize the Hg(0)(g) concentration in the model, and the emission rates necessarily agree well with estimated emission fluxes for the open ocean.

  17. 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.

  18. 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.

  19. Forcing of global ocean models using an atmospheric boundary layer model: assessing consequences for the simulation of the AMOC

    NASA Astrophysics Data System (ADS)

    Abel, Rafael; Boening, Claus

    2015-04-01

    Current practice in the atmospheric forcing of ocean model simulations can lead to unphysical behaviours. The problem lies in the bulk formulation of the turbulent air-sea fluxes in conjunction with a prescribed, and unresponsive, atmospheric state as given, e.g., by reanalysis products. This forcing formulation corresponds to assuming an atmosphere with infinite heat capacity, and effectively damps SST anomalies even on basin scales. It thus curtails an important negative feedback between meridional ocean heat transport and SST in the North Atlantic, rendering simulations of the AMOC in such models excessively sensitive to details in the freshwater fluxes. As a consequence, such simulations are known for spurious drift behaviors which can only partially controlled by introducing some (and sometimes strong) unphysical restoring of sea surface salinity. There have been several suggestions during the last 20 years for at least partially alleviating the problem by including some simplified model of the atmospheric boundary layer (AML) which allows a feedback of SST anomalies on the near-surface air temperature and humidity needed to calculate the surface fluxes. We here present simulations with a simple, only thermally active AML formulation (based on the 'CheapAML' proposed by Deremble et al., 2013) implemented in a global model configuration based on NEMO (ORCA05). In a suite of experiments building on the CORE-bulk forcing methodology, we examine some general features of the AML-solutions (in which only the winds are prescribed) in comparison to solutions with a prescribed atmosperic state. The focus is on the North Atlantic, where we find that the adaptation of the atmospheric temperature the simulated ocean state can lead to strong local modifications in the surface heat fluxes in frontal regions (e.g., the 'Northwest Corner'). We particularly assess the potential of the AML-forcing concept for obtaining AMOC-simulations with reduced spurious drift, without

  20. 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.

  1. Development of a Microcomputer Coupled Atmospheric and Oceanic Boundary Layer Prediction Model.

    DTIC Science & Technology

    1983-12-01

    temperature permits the model to be applied in situations where evaporation and precipitation contribute significantly to the surface bouyacy flux...34, submitted, CA, 39 pp., Journal of Applied Meteorology, 1983, 28 pp. 2. Fleagle, R. G. and Businger, J. A., An Introduction to Atmospheric Physics...Application to a Cold Air Outbreak Episode", Journal of Atmospheric Science, 1981, 38, 2230-2242. 12. Tabata, S., A Study of the Main PhyIsical Factors

  2. Atmospheric boundary layer testing: hot-wire anemometry measurements of turbulent boundary layer flow past a two-dimensional obstacle. 1982-1983 equipment loan report. Supplement 2

    SciTech Connect

    White, B.R.; Strataridakis, C.J.

    1984-11-01

    Measurements of a zero-pressure-gradient turbulent boundary layer flow past a two-dimensional obstacle were made in the present study. Measurements were made for both smooth and rough surfaces using single and X hot-wire probes. The Reynolds number based on obstacle height and freestream velocity was about 15,302. Profiles of mean velocity, turbulent intensity and probability density functions in two dimensions were determined. Also, Reynolds stress profiles, energy spectra and second moments of energy spectra were obtained. From the results evidence emerged that upstream, over, and downstream of the obstacle there zones of recirculating flow. The flow-field was dominated by the obstacle presence, such that no distinction between smooth-and rough-surface measurements could be made.

  3. Seasonal variations in stable isotope ratios of atmospheric nitrate in a tropical boundary layer environment (Cape Verde Observatory).

    NASA Astrophysics Data System (ADS)

    Savarino, Joël.; Morin, Samuel; Erbland, Joseph; Grannec, Francis; Patey, Matthew; Achterberg, Eric

    2010-05-01

    seasonal cycle of the nitrate isotope systematic at the Cap Verde (lat. 16° 85'N, lon. 24° 87' W) characteristic of a tropical oceanic boundary layer. Both ?17O and δ15N display a marked seasonal cycle in opposing phase. ?17O values are maximum in winter (≠ƒ 30 permil) and minimal in summer (≠ƒ 26 permil) while δ15N display the opposite trend with maximum in summer (-2.9 permil) and minimum in winter (-8.8 permil). No correlation is found with the nitrate atmospheric loading for any of the isotope ratio. ?17O seasonal variations correlate with the monthly averaged daytime depletion of ozone whose seasonal variation have been attributed mainly to halogen oxides. This observation suggests that part of the maximum nitrate oxygen anomaly (?17O) could result from halogen chemistry in the marine boundary layer via probably the strong NOx oxidant BrO. For δ15N, a broad correlation is found with the atmospheric concentration of NO and solar radiation intensity, confirming that δ15N of nitrate retranscribes principally a source and/or a photochemical equilibrium effect between NO and NO2.

  4. The Characterization of Atmospheric Boundary Layer Depth and Turbulence in a Mixed Rural and Urban Convective Environment

    NASA Astrophysics Data System (ADS)

    Hicks, Micheal M.

    A comprehensive analysis of surface-atmosphere flux exchanges over a mixed rural and urban convective environment is conducted at Howard University Beltsville, MD Research Campus. This heterogeneous site consists of rural, suburban and industrial surface covers to its south, east and west, within a 2 km radius of a flux sensor. The eddy covariance method is utilized to estimate surface-atmosphere flux exchanges of momentum, heat and moisture. The attributes of these surface flux exchanges are contrasted to those of classical homogeneous sites and assessed for accuracy, to evaluate the following: (I) their similarity to conventional convective boundary layer (CBL) processes and (II) their representativeness of the surrounding environment's turbulent properties. Both evaluations are performed as a function of upwind surface conditions. In particular, the flux estimates' obedience to spectrum power laws and similarity theory relationships is used for performing the first evaluation, and their ability to close the surface energy balance and accurately model CBL heights is used for the latter. An algorithm that estimates atmospheric boundary layer heights from observed lidar extinction backscatter was developed, tested and applied in this study. The derived lidar based CBL heights compared well with those derived from balloon borne soundings, with an overall Pearson correlation coefficient and standard deviation of 0.85 and 223 m, respectively. This algorithm assisted in the evaluation of the response of CBL processes to surface heterogeneity, by deriving high temporal CBL heights and using them as independent references of the surrounding area averaged sensible heat fluxes. This study found that the heterogeneous site under evaluation was rougher than classical homogeneous sites, with slower dissipation rates of turbulent kinetic energy. Flux measurements downwind of the industrial complexes exhibited enhanced efficiency in surface-atmosphere momentum, heat, and

  5. 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 ...

  6. 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 ...

  7. Modeling Sea-Surface Variability Caused by Kilometer-Scale Marine Atmospheric Boundary Layer Circulations

    DTIC Science & Technology

    1994-05-01

    implemented by Mr. Dave V. Ledvina based on work done by Dr. Chris W. Fairall, was crucial to Julie’s development of the boundary conditions. Dr. Young also...The parameter values z. and L are determined from a subroutine supplied by Dr. George S. Young. This subroutine was implemented by Mr. Dave V. Ledvina

  8. 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.

  9. Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

    NASA Astrophysics Data System (ADS)

    Mehta, Sanjay Kumar; Venkat Ratnam, Madineni; Sunilkumar, Sukumarapillai V.; Narayana Rao, Daggumati; Krishna Murthy, Boddapaty V.

    2017-01-01

    The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010-March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33-55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (˜ 14:00 IST) and remains elevated until evening (˜ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the

  10. Boundary Layer Dust Occurrence IV Atmospheric Dust Over Selected Geographical Areas

    DTIC Science & Technology

    1977-06-01

    limiting factor in the propagation of electromagnetic energy through the atmosphere. The primary purpose of this series of reports is to provide a...West Germany 4 Friedrichshafen, West Germany 4 Galati , Rumania 4 Gao, Mali 1,8 Geneva/Cointrin, Switzerland 4 Girardot, Colombia 4 Gorlitz, East

  11. Case Studies of the Structure of the Atmospheric Boundary Layer Entrainment Zone.

    DTIC Science & Technology

    1985-01-01

    geographical placement of the sensors. One of the unique features of BLX83 was the concurrent measurement of the atmosphere by a wide variety of in...Stephens (1980) used a conditional sampling criteria for thermals that any segement of thermal or non-thermal conditions had to persist for at least 25 m

  12. 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.

  13. Atmospheric stability of surface boundary layer in coastal region of the Wol-Ryong site

    NASA Astrophysics Data System (ADS)

    Lim, Hee-Chang

    2012-08-01

    In order to provide statistically reliable information of a wind energy site, accurate analysis on the atmospheric stability and climate characteristics in a certain area is a prerequisite. Two 2-D ultrasonic anemometers and one cup anemometer, located perpendicular to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in coastal region of the Wol-Ryong, Jeju, South Korea. The study is aiming to understand the atmospheric stability about a coastal region, and the effect of roughness length. We calculate the Monin-Obukhov length for division of atmospheric stability about unstable regime, neutral regime and stable regime. The distribution of diurnal Monin-Obukhov length is highly sporadic in the coastal region due to the effect of radiant heat from the surface or other environmental effects. In order to calculate the roughness length in coastal region, three different methods are applied in terms of the surface roughness, flow fluctuation and gust wind, which are called logarithmic profile, standard deviation and gust factor methods. In the study, the atmospheric stability was insignificant when applying these three methods. In the results, three different roughness length scales sufficiently showed the effect of obstacle and surface conditions around the measurement position. On the basis of an overall analysis of the short-term data measured in the Wol-Ryong area, Jeju Island, it is concluded that for the development of future wind energy resources, the Wol-Ryong site could be a good candidate for a future wind energy site.

  14. Observations of the Atmospheric Boundary Layer Across the Land-Sea Transition Zone Using an Elastic Scanning Lidar

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Bergant, Klemen; Filipčič, Andrej; Forte, Biagio; Stanič, Samo; Veberič, Darko; Zavrtanik, Marko

    2010-05-01

    In the case of uneven terrain, atmospheric effects in the land-sea transition zone are numerous and diverse due to frequent changes in the wind direction and different effects of the heat flux on the sea and land surface. Such a case is the coastal region of the northernmost part of the Adriatic sea. Behind the coastal line the terrain rapidly rises to a Karst plateau (about 300 m a.s.l.), falls into the Vipava valley (60 m a.s.l.) and rises again to a mountainous region with maximum altitudes at about 1500 m a.s.l. To obtain complete meteorological status of the atmosphere in this region, a series of remote sensing experiments of the atmospheric boundary layer (ABL) across the land-sea transition zone were performed on 1 July 2009 using an elastic scattering lidar. The lidar system, which has vertical scanning and long-range detection functionality, was located at Otlica observatory in Slovenia, within 30 km of the coastal line and at an elevation of 945 m a.s.l. The atmosphere was scanned for elevation angles between 0° and 20° and the lidar data was processed into Cartesian 2-dimensional range-height-indicator plots with a spatial resolution of 50 m in both coordinates. Each pixel of the plot represents the weighted logarithm range-squared-corrected signal at that position and contains all the atmospheric information. Assuming horizontal atmospheric homogeneity, the optical depth, the extinction coefficients and the height of the ABL were calculated. The increase of the lidar detection range and the steepening of the optical depth profiles with time were observed, showing that on average the extinction coefficients in the ABL were decreasing during the experiment. The height of the ABL changed from 1.8 km to 0.55 km in about 3 hours. Rapid drop of the ABL height indicates highly variable atmospheric conditions in the land-sea transition zone and the adjacent mountainous region.

  15. Investigation of atmospheric boundary layer temperature, turbulence, and wind parameters on the basis of passive microwave remote sensing

    NASA Astrophysics Data System (ADS)

    Kadygrov, Evgeny N.; Shur, Genrih N.; Viazankin, Anton S.

    2003-06-01

    The MTP-5, a microwave temperature profiler, has been widely used since 1991 for investigation of the atmospheric boundary layer (ABL). The MTP-5 is an angular scanning single-channel instrument with a central frequency of about 60 GHz, designed to provide continuous, unattended observations. It can measure the thermal emission of the atmosphere with high sensitivity (0.03 K at 1 s integration time) from different zenith angles. On the basis of this measurement, it is possible to retrieve temperature profiles at the altitude range up to 600 m, to calculate wind speed and wind direction at the lowest 250 m, and to get information about some parameters of atmospheric turbulence. This report presents some applications of the MTP-5 instrument data collected in 1998-2001 within a number of international field projects: the dynamics of ABL temperature inversion in a mountain valley (Mesoscale Alpine Program (MAP)), as well as along an island coast (north part of Sakhalin Island, Russia-Japan Project); continuous measurements of the ABL temperature profile provided from a special scientific train that crossed the territory of Russia (the Transcontinental Observations of the Chemistry of the Atmosphere Project (TROICA)); and simultaneous measurements of the ABL temperature profile provided over the central and northern part of Moscow in a continuous mode (the Global Urban Research Meteorology and Environment Project (GURME)). In 1999, two MTP-5 instruments were installed on a platform that was rotating in the azimuth direction at the 310 m Obninsk Meteorological Research Tower (Meteo Tower) to validate the method and microwave equipment for measurement of wind speed and wind direction and investigation of atmospheric turbulence. Spectral analyses of the integrated signal provided an opportunity to estimate the inertial subrange low-frequency limit and its height dependence for thermal turbulence at the lowest 200 m layer. Wavelet analysis of the signal made it possible to

  16. The profile of upwelling 11-micron radiance through the atmospheric boundary layer overlying the ocean

    NASA Technical Reports Server (NTRS)

    Hagen, Denise E.

    1988-01-01

    Measurements of the gradient of 11-micron radiance from the ocean surface were made with spaceborne AVHRR and with radiometers carried on research vessels in California and east Florida waters. The results obtained for the radiance gradient at a variety of atmospheric conditions are in good agreement with radiative transfer calculations, suggesting that there was no significant error in the water vapor absorption parameters used in the calculations. The results confirm earlier predictions that, for a typical viewing factor (i.e., zenith angle 60 deg) and for mid-latitude standard water vapor conditions, the 11-micron radiant flux measured by a spaceborne sensor will be dominated by the atmospheric contribution to the total outgoing radiation in this 'window' region.

  17. Effect of artificial length scales in large eddy simulation of a neutral atmospheric boundary layer flow: A simple solution to log-layer mismatch

    NASA Astrophysics Data System (ADS)

    Chatterjee, Tanmoy; Peet, Yulia T.

    2017-07-01

    A large eddy simulation (LES) methodology coupled with near-wall modeling has been implemented in the current study for high Re neutral atmospheric boundary layer flows using an exponentially accurate spectral element method in an open-source research code Nek 5000. The effect of artificial length scales due to subgrid scale (SGS) and near wall modeling (NWM) on the scaling laws and structure of the inner and outer layer eddies is studied using varying SGS and NWM parameters in the spectral element framework. The study provides an understanding of the various length scales and dynamics of the eddies affected by the LES model and also the fundamental physics behind the inner and outer layer eddies which are responsible for the correct behavior of the mean statistics in accordance with the definition of equilibrium layers by Townsend. An economical and accurate LES model based on capturing the near wall coherent eddies has been designed, which is successful in eliminating the artificial length scale effects like the log-layer mismatch or the secondary peak generation in the streamwise variance.

  18. A Description of the Framework of the Atmospheric Boundary Layer Environment (ABLE) Model

    DTIC Science & Technology

    2012-09-01

    dynamics ( CFD ) models are mostly developed for specific industrial usages, and therefore, lack important atmospheric processes such as turbulent transport...Gowardhan, A.; Kaplan , H.; Alexander, Y.; Moussafir, J.; Wang, Y.; Williamson, C.; Hannan, J.; Hendrick , E. Comparisons of JU2003...Remote Sensing Journal 2010, 3, 17–27. Wilcox, D. C. Turbulence Modeling for CFD ; Birmingham Press, 515 pp, 2006. Wyngaard, J. C. Turbulence in

  19. Field deployment of thin film passive air samplers for persistent organic pollutants: a study in the urban atmospheric boundary layer.

    PubMed

    Farrar, N J; Harner, T; Shoeib, M; Sweetman, A; Jones, K C

    2005-01-01

    This paper reports on the first field deployment of rapidly equilibrating thin-film passive air samplers under ambient conditions. The POlymer-coated Glass (POG) samplers have a coating of ethylene vinyl acetate (EVA) less than 1 microm thick applied to a glass surface. This can be dissolved off after exposure and prepared for the quantification of persistent organic pollutants (POPs) that have partitioned into the film during field exposure. In this study, POGs were deployed at various heights on the CN Tower in Toronto, Canada, to investigate the vertical distribution of selected compounds (PCBs, PAHs, organochlorine pesticides) in the atmospheric boundary layer of an urban area. The feasibility of the method to detect POPs from a few cubic meters of air was demonstrated, indicating the potential for rapid, low-volume sampling of air for ambient levels of POPs. PAH levels declined sharply with height, confirming ground-level emissions in urban areas as sources of these compounds; PCBs did the same, although less strongly. Different sampling events detected different vertical distributions of OC pesticides which could be related to local or distantsources, and variations in POPs on the samplers in these different events/heights demonstrate the dynamic nature of sources and atmospheric mixing of POPs.

  20. 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.

  1. Nested mesoscale-to-LES modeling of the atmospheric boundary layer in the presence of under-resolved convective structures

    DOE PAGES

    Mazzaro, Laura J.; Munoz-Esparza, Domingo; Lundquist, Julie K.; ...

    2017-07-06

    Multiscale atmospheric simulations can be computationally prohibitive, as they require large domains and fine spatiotemporal resolutions. Grid-nesting can alleviate this by bridging mesoscales and microscales, but one turbulence scheme must run at resolutions within a range of scales known as the terra incognita (TI). TI grid-cell sizes can violate both mesoscale and microscale subgrid-scale parametrization assumptions, resulting in unrealistic flow structures. Herein we assess the impact of unrealistic lateral boundary conditions from parent mesoscale simulations at TI resolutions on nested large eddy simulations (LES), to determine whether parent domains bias the nested LES. We present a series of idealized nestedmore » mesoscale-to-LES runs of a dry convective boundary layer (CBL) with different parent resolutions in the TI. We compare the nested LES with a stand-alone LES with periodic boundary conditions. The nested LES domains develop ~20% smaller convective structures, while potential temperature profiles are nearly identical for both the mesoscales and LES simulations. The horizontal wind speed and surface wind shear in the nested simulations closely resemble the reference LES. Heat fluxes are overestimated by up to ~0.01 K m s–1 in the top half of the PBL for all nested simulations. Overestimates of turbulent kinetic energy (TKE) and Reynolds stress in the nested domains are proportional to the parent domain's grid-cell size, and are almost eliminated for the simulation with the finest parent grid-cell size. Furthermore, based on these results, we recommend that LES of the CBL be forced by mesoscale simulations with the finest practical resolution.« less

  2. The effect of entrainment through atmospheric boundary layer growth on observed and modeled surface ozone in the Colorado Front Range

    NASA Astrophysics Data System (ADS)

    Kaser, L.; Patton, E. G.; Pfister, G. G.; Weinheimer, A. J.; Montzka, D. D.; Flocke, F.; Thompson, A. M.; Stauffer, R. M.; Halliday, H. S.

    2017-06-01

    Ozone concentrations at the Earth's surface are controlled by meteorological and chemical processes and are a function of advection, entrainment, deposition, and net chemical production/loss. The relative contributions of these processes vary in time and space. Understanding the relative importance of these processes controlling surface ozone concentrations is an essential component for designing effective regulatory strategies. Here we focus on the diurnal cycle of entrainment through atmospheric boundary layer (ABL) growth in the Colorado Front Range. Aircraft soundings and surface observations collected in July/August 2014 during the DISCOVER-AQ/FRAPPÉ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality/Front Range Air Pollution and Photochemistry Éxperiment) campaigns and equivalent data simulated by a regional chemical transport model are analyzed. Entrainment through ABL growth is most important in the early morning, fumigating the surface at a rate of 5 ppbv/h. The fumigation effect weakens near noon and changes sign to become a small dilution effect in the afternoon on the order of -1 ppbv/h. The chemical transport model WRF-Chem (Weather Research and Forecasting Model with chemistry) underestimates ozone at all altitudes during this study on the order of 10-15 ppbv. The entrainment through ABL growth is overestimated by the model in the order of 0.6-0.8 ppbv/h. This results from differences in boundary layer growth in the morning and ozone concentration jump across the ABL top in the afternoon. This implicates stronger modeled fumigation in the morning and weaker modeled dilution after 11:00 LT.

  3. Integrating surface, entrainment and mesoscale in the Atmospheric Boundary Layer dynamics: a 10-year study in Cabauw (The Netherlands)

    NASA Astrophysics Data System (ADS)

    Ander Arrillaga, Jon; Bosveld, Fred; Jiménez, Pedro A.; Baltink, Henk K.; Yagüe, Carlos; Hensen, Arjan; van Dinther, Danielle; Frumau, Arnoud; Dudhia, Jimy; Zhao, Wanjun; Vilà-Guerau de Arellano, Jordi

    2017-04-01

    The diurnal evolution of the Atmospheric Boundary Layer (ABL) in Cabauw (Netherlands) is investigated by considering the role of local and non-local forcings. By local, we understand, the surface fluxes that drive the growing of the ABL in addition to the non-local entrained fluxes. We study potential disruptions occurring in spring and particularly in summer driven by the formation of sea-breeze flows in the form of density currents, due to the proximity of both The North Sea and the Ijsselmeer closed sea. Moreover, this interactive system of surface, boundary layer and mesoscale may play a role in the transport of carbon dioxide and its diurnal variability. Our method is based on the analysis of a comprehensive 10-yr observational database (2001-2010), which gives the opportunity to understand the ABL dynamics from a robust perspective. To support the analysis, modelling results obtained from the WRF mesoscale model are available during the entire 10-year period. The model is run every 48 h to maintain it close to the synoptic conditions calculated by the ERA-Interim state. A fine horizontal resolution of 2 km is used, and the vertical levels are set to match the observational ones (2, 10, 20, 40, 80, 140 and 200 m). In order to identify the sea-breeze arrival, we apply a sea-breeze criteria selection algorithm. It is developed and adapted after a sea-breeze observational study in the Cantabrian Coast (Spain) to filter the sea-breeze events occurring in Cabauw, and consequently analyse their impact in the ABL and the surface fluxes. Preliminary results show that this criteria is able to distinguish between the two main wind directions related to the sea breeze in Cabauw. Our finding shows that the sea-breeze days are characterized by a sharp increment of the wind speed and a noticeable increase of the specific humidity at around 16-17 UTC.

  4. The marine atmospheric boundary layer under strong wind conditions: Organized turbulence structure and flux estimates by airborne measurements

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    During winter, cold air outbreaks take place in the northwestern Mediterranean sea. They are characterized by local strong winds (Mistral and Tramontane) which transport cold and dry continental air across a warmer sea. In such conditions, high values of surface sensible and latent heat flux are observed, which favor deep oceanic convection. The HyMeX/ASICS-MED field campaign was devoted to the study of these processes. Airborne measurements, gathered in the Gulf of Lion during the winter of 2013, allowed for the exploration of the mean and turbulent structure of the marine atmospheric boundary layer (MABL). A spectral analysis based on an analytical model was conducted on 181 straight and level runs. Profiles of characteristic length scales and sharpness parameter of the vertical wind spectrum revealed larger eddies along the mean wind direction associated with an organization of the turbulence field into longitudinal rolls. These were highlighted by boundary layer cloud bands on high-resolution satellite images. A one-dimensional description of the vertical exchanges is then a tricky issue. Since the knowledge of the flux profile throughout the entire MABL is essential for the estimation of air-sea exchanges, a correction of eddy covariance turbulent fluxes was developed taking into account the systematic and random errors due to sampling and data processing. This allowed the improvement of surface fluxes estimates, computed from the extrapolation of the stacked levels. A comparison between those surface fluxes and bulk fluxes computed at a moored buoy revealed considerable differences, mainly regarding the latent heat flux under strong wind conditions.

  5. Seasonal variations of aerosol residence time in the lower atmospheric boundary layer.

    PubMed

    Ahmed, A A; Mohamed, A; Ali, A E; Barakat, A; Abd El-Hady, M; El-Hussein, A

    2004-01-01

    During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the atmospheric air activity concentrations of short- and long-lived (222Rn) decay products 214Pb and 210Pb. The samples were taken by using a single-filter technique and gamma-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of 214Pb and 210Pb in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of 214Pb and 210Pb within the whole year was found to be 1.4+/-0.27 Bq m(-3) and 1.2+/-0.15 mBq m(-3), respectively. Different 210Pb:214Pb activity ratios during the year varied between 1.78 x 10(-4) and 1.6 x 10(-3) with a mean value of 8.9 x 10(-4) +/- 7.6 x 10(-5). From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time (MRT) of aerosol particles in the atmosphere of about 10.5+/-0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the atmospheric air.

  6. Unmanned aircraft system measurements of the atmospheric boundary layer over Terra Nova Bay, Antarctica

    NASA Astrophysics Data System (ADS)

    Knuth, S. L.; Cassano, J. J.; Maslanik, J. A.; Herrmann, P. D.; Kernebone, P. A.; Crocker, R. I.; Logan, N. J.

    2012-11-01

    In September 2009, a series of long-range unmanned aircraft system (UAS) flights collected basic atmospheric data over the Terra Nova Bay polynya in Antarctica. Air temperature, wind, pressure, relative humidity, radiation, skin temperature, GPS, and operational aircraft data were collected and quality controlled for scientific use. The data has been submitted to the United States Antarctic Program Data Coordination Center (USAP-DCC) for free access (doi:10.1594/USAP/0739464).

  7. Unmanned aircraft system measurements of the atmospheric boundary layer over Terra Nova Bay, Antarctica

    NASA Astrophysics Data System (ADS)

    Knuth, S. L.; Cassano, J. J.; Maslanik, J. A.; Herrmann, P. D.; Kernebone, P. A.; Crocker, R. I.; Logan, N. J.

    2013-02-01

    In September 2009, a series of long-range unmanned aircraft system (UAS) flights collected basic atmospheric data over the Terra Nova Bay polynya in Antarctica. Air temperature, wind, pressure, relative humidity, radiation, skin temperature, GPS, and operational aircraft data were collected and quality controlled for scientific use. The data have been submitted to the United States Antarctic Program Data Coordination Center (USAP-DCC) for free access (doi:10.1594/USAP/0739464).

  8. Effect of Atmospheric Conditions on Coverage of Fogger Applications in a Desert Surface Boundary Layer

    DTIC Science & Technology

    2012-01-01

    305 -21.1 20.8 18.6 [a] SRm, U, Udir, H, θv, θg, and RH are 2 min averages of modified stability ratio (eq. 2), wind speed, wind direction, surface...R. T. H. 1968. Lidar observations of atmospheric motion in forest valleys. Bull. American Meteorol. Soc . 49(9): 918- 922. Farooq, M., W. C...theoretical distribution of airborne pollution from factory chimneys. Qtly. J. Royal Meteorol. Soc . 73(317-318): 426-436. USACHPPM. 2005. Diagnosis and

  9. MPAS Atmospheric Boundary Layer Simulation under Selected Stability Conditions: Evaluation Using the SWIFT Datasen

    SciTech Connect

    Kotamarthi, V. Rao; Feng, Yan

    2016-10-12

    Modeling the transition from mesoscale to microscale is necessary in order to model different processes that affect a wind farm and to develop forecasting tools that operate at the farm scale. The mesoscale-to-microscale coupling (MMC) project is an A2e (Atmosphere-toelectrons) coordinated activity for developing modeling capabilities at the wind farm scale. By moving the focus of the research from a single wind turbine to the collection of turbines that comprise a wind farm, A2e extends the range of spatial and timescales that need representation in a model from tens of meters to hundreds of kilometers and timescales from a few seconds to days (Bokharaie et al. 2016). In the atmosphere, these scales are represented by mesoscale-tomicroscale models. The modeling available at these scales has differed in its representation of various physical processes. The MMC group is responsible for evaluating existing models at these scales and recommending a set of options for coupling the mesoscale and microscale with the best-performing models. The group was organized in 2015 and will explore options for coupling strategies with real-world test problems in fiscal year (FY) 2017. The model of choice for this exercise is WRF (Weather Research Forecasting) for mesoscale and WRF-LES (Large Eddy Simulation) for microscale simulations. The MPAS (Model Prediction Across Scales) variable mesh model that can be continuously refined; it has dynamic core and physics options adopted from WRF, which offer an alternative platform for modeling the mesoscale.

  10. Daytime sources of nitrous acid (HONO) in the atmospheric boundary layer.

    PubMed

    Kleffmann, Jörg

    2007-06-04

    Nitrous acid (HONO) is an important precursor of the hydroxyl radical (OH), the self-cleaning agent of the atmosphere and a key species in the formation of harmful photooxidants during summer smog. Recent field measurements using very sensitive HONO instruments have shown that daytime HONO concentrations are much higher than has been assumed previously and that the contribution of HONO to the radical formation was underestimated in the past. A strong photochemical HONO source has been proposed, which contributes to the primary OH radical production up to 56 %. These exciting results initiated new laboratory studies, in which new sources of HONO have been identified. It is demonstrated that HONO is photochemically formed 1) on surfaces treated with nitric acid, 2) by reduction of NO(2) on photosensitized organic surfaces like humic acids and c) in the gas phase photolysis of ortho-substituted nitroaromatics. Although significant uncertainties still exist on the exact mechanisms, these additional sources might explain daytime observations in the atmosphere and demonstrate that HONO should be generally measured in field campaigns, besides other radical sources.

  11. Random-walk model simulation of air pollutant dispersion in atmospheric boundary layer in China.

    PubMed

    Wang, Peng; Mu, Hailin

    2011-01-01

    In this study, the land-sea breeze circulation model coupled with a random-walk model is developed by the analysis of the formation and the mechanism of the land-sea breeze. Based on the data of the land-sea circulation in Dalian, China, the model simulated the diurnal variation of pressure, flow, temperature, and turbulent kinetic energy field and also provides a basis for solving the air pollutant concentration in the land-sea breeze circulation so as to estimate the economic cost attributable to the atmospheric pollution. The air pollutant concentration in the background of land-sea circulation is also simulated by a Gaussian dispersion model, and the results revealed that the land-sea circulation model coupled with the random-walk model gives a reasonable description of air pollutant dispersion in coastal areas.

  12. Mean velocity profile in a sheared and thermally stratified atmospheric boundary layer.

    PubMed

    Katul, Gabriel G; Konings, Alexandra G; Porporato, Amilcare

    2011-12-23

    A stability correction function φ(m)(ζ) that accounts for distortions to the logarithmic mean velocity profile (MVP) in the lower atmosphere caused by thermal stratification was proposed by Monin and Obukhov in the 1950s using dimensional analysis. Its universal character was established from many field experiments. However, theories that describe the canonical shape of φ(m)(ζ) are still lacking. A previous link between the spectrum of turbulence and the MVP is expanded here to include the effects of thermal stratification on the turbulent kinetic energy dissipation rate and eddy-size anisotropy. The resulting theory provides a novel explanation for the power-law exponents and coefficients already reported for φ(m)(ζ) from numerous field experiments.

  13. Observational and modeling studies of urban atmospheric boundary-layer height and its evolution mechanisms

    NASA Astrophysics Data System (ADS)

    He, Q. S.; Mao, J. T.; Chen, J. Y.; Hu, Y. Y.

    With a new retrieval method, the mixed layer height (MLH) over the urban area of Beijing is studied using data observed by an eye-safe, compact micro pulse lidar (MPL). The retrieval results show that the retrieved MLH agrees well with that from radiosonde data. The MLH and its growth rate are estimated from the MPL measurements. Entrainment zone thickness (EZT) is extracted from MPL datasets. Entrainment ratio calculated from MLH and EZT is about 0.24. Regional surface sensible heat fluxes are retrieved with a common thermodynamic model. The contribution of mechanical production on MLH evolution is also studied. These results determined from lidar remote sense are useful for modeling air pollution diffusion and transportation.

  14. 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

  15. Physical Processes in the Atmospheric Boundary Layer with Implications for Air Quality

    NASA Astrophysics Data System (ADS)

    Baker, Barry D., II

    Ozone (O3) is a secondary pollutant dependent on complex photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) and is sensitive to meteorological conditions that govern solar radiation, temperature, and wind speed/direction (Stockwell, 2011). The U.S. Environmental Protection Agency (USEPA) has classified O 3 as one of the six criteria pollutants that is considered harmful to both plants and human health (Hollingsworth, 2007). The current study investigates the influence of the diurnal cycle of the BL on the surface air pollutants. Specifically, it examines how the nighttime and transition period turbulence impacts the concentration of ozone at the surface and in the atmospheric column during the following day. In order to complete the study, a series of models including the Weather Research and Forecasting (WRF) model and the Comprehensive Air Quality model with Extensions (CAMx) are used to simulate atmospheric conditions in the Maryland and Texas areas. BL processes such as the minimum diffusivity or BL parameterization within CAMx are investigated. The Blackadar scheme was found to artificially suppress the nocturnal BL height and appears to be the cause of a 15 ppbv high model bias. An experiment is then conducted where a minimum BL height of 160 m and an improvement of 7% in the median model bias are found in the Maryland area. With Maryland being in a NOx-limited regime, the same process of setting a minimum height is tested in the Texas area using the YSU scheme but minimal differences produced minuscule changes in the vertical diffusivity. The use of the Ri number improved the model bias by another 5 ppbv or 13% over using the Blackadar BL scheme. A new algorithm to predict the nocturnal BL depth is implemented into the WRF YSU scheme, which scales the Ribc with the Obukhov length adding a dependency on near surface properties of the flow. The algorithm is tested using meteorological surface measurements and tower

  16. 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

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

    PubMed

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

    2014-08-15

    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/m(3) to 4.58 ng/m(3)), and displayed a normal distribution with an average of 1.23 ± 0.61 ng/m(3). The highest frequency range was 1.0-1.5 ng/m(3), 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.

  18. Atmospheric polycyclic aromatic hydrocarbons in remote European and Atlantic sites located above the boundary mixing layer.

    PubMed

    Van Drooge, Barend Leendert; Fernández, Pilar; Grimalt, Joan O; Stuchlík, Evzen; Torres García, Carlos J; Cuevas, Emilio

    2010-07-01

    Ambient air concentrations of polycyclic aromatic hydrocarbons (PAH) were determined at five elevated mountain sites on the European continent and the Atlantic Ocean. All sites can be considered remote background areas since they are situated above the timberline and they lack local emission sources of these compounds. Average gas phase concentrations of SigmaPAH were 165, 1,475, 1,553, 1,822 and 4,443 pg m(-3) for Tenerife, Pyrenees, Central Norway, Tyrolean Alps and High Tatras, respectively. Particulate phase concentrations were 55, 70, 383, 196 and 708 pg m(-3), respectively. The PAH profiles of samples from the different sites are very similar, being typical of PAH mixtures after long-range atmospheric transport. Part of the fluctuations in PAH concentrations are explained by the influence of temperature on the particulate/gas phase partitioning. The differences in PAH levels between sites, with the lowest concentrations found in Tenerife and the highest in the High Tatras, suggest the geographical influence of regional emissions on the sites, especially in the cold periods and for the sites in the eastern sector of the European continent. This is supported by air mass back-trajectories analysis for the samples on the different sites. The influence of the continent is not detectable in the case of the elevated site of Tenerife where the free troposphere has been sampled. The results in this study are consistent with the PAH levels found in soils and/or high mountain lake sediments from these areas.

  19. Periodic bedforms generated by sublimation on terrestrial and martian ice sheets under the influence of the turbulent atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Bordiec, Maï; Carpy, Sabrina; Perret, Laurent; Bourgeois, Olivier; Massé, Marion

    2017-04-01

    The redistribution of surface ice induced the wind flow may lead to the development and migration of periodic bedforms, or "ice ripples", at the surface of ice sheets. In certain cold and dry environments, this redistribution need not involve solid particle transport but may be dominated by sublimation and condensation, inducing mass transfers between the ice surface and the overlying steady boundary layer turbulent flow. These mass transfers diffuse the water vapour sublimated from the ice into the atmosphere and become responsible for the amplification and propagation of ripples in a direction perpendicular to their crests. Such ice ripples, 24 cm in wavelength, have been described in the so-called Blue Ice Areas of Antarctica. In order to understand the mechanisms that generate and develop these periodic bedforms on terrestrial glaciers and to evaluate the plausibility that similar bedforms may develop on Mars, we performed a linear stability analysis applied to a turbulent boundary layer flow perturbed by a wavy ice surface. The model is developed as follow. We first solve the flow dynamics using numerical methods analogous to those used in sand wave models assuming that the airflow is similar in both problems. We then add the transport/diffusion equation of water vapour following the same scheme. We use the Reynolds-averaged description of the equation with a Prandtl-like closure. We insert a damping term in the exponential formula of the Van Driest mixing length, depending on the pressure gradient felt by the flow and related to the thickness of the viscous sublayer at the ice-atmosphere interface. This formulation is an efficient way to properly represent the transitional regime under which the ripples grow. Once the mass flux of water vapour is solved, the phase shift between the ripples crests and the maximum of the flux can be deduced for different environments. The temporal evolution of the ice surface can be expressed from these quantities to infer the

  20. 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.

  1. The study of the effects of sea-spray drops on the marine atmospheric boundary layer by direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Druzhinin, Oleg A.; Troitskaya, Yuliya I.; Zilitinkevich, Sergej S.

    2017-04-01

    Detailed knowledge of the interaction of wind with surface water waves is necessary for correct parameterization of turbulent exchange at the air-sea interface in prognostic models. At sufficiently strong winds, sea-spray-generated droplets interfere with the wind-waves interaction. The results of field experiments and laboratory measurements (Andreas et al., JGR 2010) show that mass fraction of air-borne spume water droplets increases with the wind speed and their impact on the carrier air-flow may become significant. Phenomenological models of droplet-laden marine atmospheric boundary layer (Kudryavtsev & Makin, Bound.-Layer Met. 2011) predict that droplets significantly increase the wind velocity and suppress the turbulent air stress. The results of direct numerical simulation (DNS) of a turbulent particle-laden Couette flow over a flat surface show that inertial particles may significantly reduce the carrier flow vertical momentum flux (Richter & Sullivan, GRL 2013). The results also show that in the range of droplet sizes typically found near the air-sea interface, particle inertial effects are significant and dominate any particle-induced stratification effects. However, so far there has been no attempt to perform DNS of a droplet-laden air-flow over waved water surface. The objective of the present paper is to elucidate possible effects of sea spray on the momentum transfer in marine boundary layer under strong wind-forcing conditions by performing direct numerical simulation (DNS) of turbulent, droplet-laden air-flow over a waved water surface. Three-dimensional, turbulent Couette air-flow is considered in DNS as a model of a constant-flux layer in the atmospheric surface layer. Two-dimensional stationary waves at the water surface are prescribed and assumed to be unaffected by the air-flow and/or droplets. Droplets are considered as non-deformable spheres and tracked in a Lagrangian framework, and their impact on the carrier flow is modeled with the use of

  2. A diagram of wind speed versus air-sea temperature difference to understand the dynamics of the marine atmospheric boundary layer off northwest Europe

    NASA Astrophysics Data System (ADS)

    Kettle, Anthony

    2015-04-01

    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 land-sea coastline discontinuities. In these offshore environments, the boundary layer processes are often best understood directly from time series measurements from measurement platforms or buoys, in spite of potential difficulties from platform flow distortion as well as the spatial sparseness of the data sets. This contribution presents updated results of measurements from offshore platforms in the North Sea and Norwegian Sea in terms of a summary diagnostic - wind speed versus air-sea temperature difference (U-ΔT) - with important implications for understanding atmospheric boundary layer processes. The U-ΔT diagram was introduced in earlier surveys of data from coastal and offshore 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 North Sea illustrates how the wind characteristics vary spatially over large distances. The results are important for the offshore wind industry because of the way that wind turbines accrue fatigue damage in different conditions of atmospheric stability and wind speed.

  3. 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. Copyright © 2014 Elsevier B.V. All rights reserved.

  4. Tedlar bag sampling technique for vertical profiling of carbon dioxide through the atmospheric boundary layer with high precision and accuracy.

    PubMed

    Schulz, Kristen; Jensen, Michael L; Balsley, Ben B; Davis, Kenneth; Birks, John W

    2004-07-01

    Carbon dioxide is the most important greenhouse gas other than water vapor, and its modulation by the biosphere is of fundamental importance to our understanding of global climate change. We have developed a new technique for vertical profiling of CO2 and meteorological parameters through the atmospheric boundary layer and well into the free troposphere. Vertical profiling of CO2 mixing ratios allows estimates of landscape-scale fluxes characteristic of approximately100 km2 of an ecosystem. The method makes use of a powered parachute as a platform and a new Tedlar bag air sampling technique. Air samples are returned to the ground where measurements of CO2 mixing ratios are made with high precision (< or =0.1%) and accuracy (< or =0.1%) using a conventional nondispersive infrared analyzer. Laboratory studies are described that characterize the accuracy and precision of the bag sampling technique and that measure the diffusion coefficient of CO2 through the Tedlar bag wall. The technique has been applied in field studies in the proximity of two AmeriFlux sites, and results are compared with tower measurements of CO2.

  5. Wind-Tunnel Experiments for Gas Dispersion in an Atmospheric Boundary Layer with Large-Scale Turbulent Motion

    NASA Astrophysics Data System (ADS)

    Michioka, Takenobu; Sato, Ayumu; Sada, Koichi

    2011-10-01

    Large-scale turbulent motions enhancing horizontal gas spread in an atmospheric boundary layer are simulated in a wind-tunnel experiment. The large-scale turbulent motions can be generated using an active grid installed at the front of the test section in the wind tunnel, when appropriate parameters for the angular deflection and the rotation speed are chosen. The power spectra of vertical velocity fluctuations are unchanged with and without the active grid because they are strongly affected by the surface. The power spectra of both streamwise and lateral velocity fluctuations with the active grid increase in the low frequency region, and are closer to the empirical relations inferred from field observations. The large-scale turbulent motions do not affect the Reynolds shear stress, but change the balance of the processes involved. The relative contributions of ejections to sweeps are suppressed by large-scale turbulent motions, indicating that the motions behave as sweep events. The lateral gas spread is enhanced by the lateral large-scale turbulent motions generated by the active grid. The large-scale motions, however, do not affect the vertical velocity fluctuations near the surface, resulting in their having a minimal effect on the vertical gas spread. The peak concentration normalized using the root-mean-squared value of concentration fluctuation is remarkably constant over most regions of the plume irrespective of the operation of the active grid.

  6. 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.

  7. 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; ...

    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

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

    SciTech Connect

    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 use 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.

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

    SciTech Connect

    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 use 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.

  10. Superfluid Boundary Layer

    NASA Astrophysics Data System (ADS)

    Stagg, G. W.; Parker, N. G.; Barenghi, C. F.

    2017-03-01

    We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

  11. Interaction Between the Atmospheric Boundary Layer and Wind Energy: From Continental-Scale to Turbine-Scale

    NASA Astrophysics Data System (ADS)

    St. Martin, Clara Mae

    Wind turbines and groups of wind turbines, or "wind plants", interact with the complex and heterogeneous boundary layer of the atmosphere. We define the boundary layer as the portion of the atmosphere directly influenced by the surface, and this layer exhibits variability on a range of temporal and spatial scales. While early developments in wind energy could ignore some of this variability, recent work demonstrates that improved understanding of atmosphere-turbine interactions leads to the discovery of new ways to approach turbine technology development as well as processes such as performance validation and turbine operations. This interaction with the atmosphere occurs at several spatial and temporal scales from continental-scale to turbine-scale. Understanding atmospheric variability over continental-scales and across plants can facilitate reliance on wind energy as a baseload energy source on the electrical grid. On turbine scales, understanding the atmosphere's contribution to the variability in power production can improve the accuracy of power production estimates as we continue to implement more wind energy onto the grid. Wind speed and directional variability within a plant will affect wind turbine wakes within the plants and among neighboring plants, and a deeper knowledge of these variations can help mitigate effects of wakes and possibly even allow the manipulation of these wakes for increased production. Herein, I present the extent of my PhD work, in which I studied outstanding questions at these scales at the intersections of wind energy and atmospheric science. My work consists of four distinct projects. At the coarsest scales, I analyze the separation between wind plant sites needed for statistical independence in order to reduce variability for grid-integration of wind. At lower wind speeds, periods of unstable and more turbulent conditions produce more power than periods of stable and less turbulent conditions, while at wind speeds closer to

  12. Concentrations of PM 10, PM 2.5, and PM 1 influenced by atmospheric circulation and atmospheric boundary layer in the Korean mountainous coast during a duststorm

    NASA Astrophysics Data System (ADS)

    Choi, Hyo; Choi, Doo Sun

    2008-09-01

    Particle size concentrations of 100 ng m - 3 to 203" in the main text were changed to "100 ng m- 3". Please check if appropriate.--> μg m - 3 were measured at two sampling points over the eastern coastal region of Korea by two GRIMM aerosol samplers from March 7-17, 2004. One sampling point was located on the western upwind side of the mountains, and the other sampling point was located in the city of Kangnung in the coastal basin downwind and adjacent to the East Sea. Concentrations of PM 10, PM 2.5, and PM 1 were measured near the ground in Kangnung on March 8, 2004, until 1200 LST before the passage of a duststorm. Values of about 40, 35, and 30 μg m - 3 , respectively, were detected indicating little variation among sample concentrations. Before the duststorm, maximum concentrations for PM 10 occurred around 0800 and 1700 LST due to increased fuel combustion from road vehicles. From the afternoon of March 10-16 when the largest amount of dust from China had passed over Kangnung under the influence of a westerly wind, PM 10 concentration reached 340 μg m - 3 , and PM 2.5 and PM 1 concentrations reached 105 μg m - 3 and 60 μg m - 3 , respectively, indicating double the PM 10 concentration as compared to PM 2.5. Most of the dust transported from China consisted of particle sizes larger than PM 2.5 and PM 1. Dust transported from the western, upwind side of the mountains combined with the particulates emitted from road vehicles and industrial and residential boilers in the city after sunrise under the influence of westerly winds resulted in a high particulate concentration at 0900 LST. However, a low concentration of particulates in the city was detected near 1200 LST due to changes in the structure of the atmospheric boundary layer, while a high concentration over the mountains occurred due to a stable layer. High-particulate concentrations in the city occurred again after 1700 LST owing to increased fuel combustion from road vehicles and residential boilers

  13. Understanding the Structure of Atmospheric Boundary Layer in Response to the Synoptic Forcing over the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lang, Francisco; Siems, Steven; Huang, Yi; Manton, Michael; Belusic, Danijel

    2017-04-01

    Boundary layer clouds over the oceans are one of the most important contributors to the global radiation budget due to their large shortwave radiative effects. In-situ observations of the atmospheric boundary layer (ABL) over the Southern Ocean (SO) suggest that a complex, multi-level structure is commonly present beneath the free troposphere (e.g. Russell et al., 1998), which presents a challenge to the coarse-resolution climate models and reanalysis data sets. Recent studies (e.g. Bodas-Salcedo et al., 2012; Williams et al., 2013) suggest that the poor representation of ABL and their clouds may be a major contributor to the large shortwave radiative bias in the cold sector of extra-tropical cyclones over the SO. Most studies have used satellite observations to characterize the influence of synoptic meteorology in the ABL (e.g. Huang et al. 2014, Naud et al. 2014). In this research, 16-year high resolution upper air soundings from Macquarie Island (54.62°S, 158.85°E) are used to explore the structure of the ABL over the SO in relation to the synoptic meteorology. Cyclones (Bauer and Del Genio, 2006) and fronts (Berry et al. 2011) identified with the ECMWF ERA-Interim data set are employed for a compositing analysis of ABL height and inversion strength, with a specific focus on the post-cold-frontal environment. Furthermore, thermodynamic profiles from the ERA-Interim reanalysis are compared against Macquarie Island soundings. Cyclone composites of observations indicate that the ABL is higher near/within the fronts and lower in the non-frontal conditions, with the highest heights present in the cold sector, being on average 550 meters higher than the warm sector. Evaluation of ERA-Interim profiles shows that the main temperature inversion heights under the influence of cold front passages are underestimated by the reanalysis data set. As direct consequence, significant differences are found in the moisture profiles within the ABL, under both pre- and post

  14. Detection of atmospheric boundary layer height in the plum rain season over Hangzhou area with three-dimensional scanning polarized lidar

    NASA Astrophysics Data System (ADS)

    Tang, Peijun; Liu, Dong; Xu, Peituo; Zhou, Yudi; Bai, Jian; Liu, Chong; Wang, Kaiwei; Yang, Yongying; Shen, Yibing; Luo, Jing; Cheng, Zhongtao; Zhang, Yupeng; Liu, Yanyang

    2016-10-01

    The atmospheric boundary layer can be directly influenced by the ground and it is closely related to human activities, so the detection and investigation of the atmospheric boundary layer is very important. Due to the abundant rainfall in the plum rain season in southern China, the atmospheric boundary layer height (ABLH) is very different from any other time of the year. Lidar is an active remote-sensing instrument, and the advantage of high spatial and temporal resolution makes it very suitable for the detection of the atmosphere. In this paper, a three-dimensional (3D) polarized lidar is introduced and the structure will be given in detail. Compared to traditional one-direction ground-based lidar, the pointing of the 3D scanning lidar is very flexible and can be adjusted to any direction within the up hemisphere (360 degrees by 90 degrees) in a very short time. The ABLH in the plum rain season (from June to July 2016) over Hangzhou area (30°16' N, 120°07' E) was observed and different derivation methods, such as the wavelet covariance method, the gradient method, and the profile fitting method were carried out and compared in detail. The results show that the wavelet covariance method exhibits better stability than the gradient method and better accuracy than the profile fitting method. This work brings a more flexible and accuracy way for the ABLH detection and will be of great importance to the atmospheric study during the plum rain season.

  15. 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

  16. Boundary layer transition studies

    NASA Astrophysics Data System (ADS)

    Watmuff, Jonathan H.

    1995-02-01

    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. Comments on Symmetric and Asymmetric Structures of Hurricane Boundary Layer in Coupled Atmosphere-Wave-Ocean Models and Observations

    DTIC Science & Technology

    2014-07-01

    main conclusions was that ‘‘the azimuthally averaged inflow layer tends to misrepresent the overall inflow structure in tropical cyclones , espe- cially...essential for the development and maintenance of a tropical cyclone (Ooyama 1969; Emanuel 1986, 1995; Smith et al. 2009; Smith and Montgomery 2010...Bryan and Rotunno 2009; Bryan 2012). However, the boundary layer is the least-observed part of a storm —in particular, its turbulence structure. With the

  18. 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

  19. 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...

  20. 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...

  1. 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

  2. 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.

  3. Performance of WRF in simulating terrain induced flows and atmospheric boundary layer characteristics over the tropical station Gadanki

    NASA Astrophysics Data System (ADS)

    Hari Prasad, K. B. R. R.; Srinivas, C. V.; Rao, T. Narayana; Naidu, C. V.; Baskaran, R.

    2017-03-01

    In this study the evolution of the topographic flows and boundary layer features over a tropical hilly station Gadanki in southern India were simulated using Advanced Research WRF (ARW) mesoscale model for fair weather days during southwest monsoon (20-22 July 2011) and winter (18-20 Jan. 2011). Turbulence measurements from an Ultra High Frequency (UHF) Wind Profiler, Ultra Sonic Anemometer, GPS Sonde and meteorological tower were used for comparison. Simulations revealed development of small-scale slope winds in the lower boundary layer (below 800 m) at Gadanki which are more prevalent during nighttime. Stronger slope winds during winter and weaker flows in the monsoon season are simulated indicating the sensitivity of slope winds to the background synoptic flows and radiative heating/cooling. Higher upward surface fluxes (sensible, latent heat) and development of very deep convective boundary layer ( 2500 m) is simulated during summer monsoon relative to the winter season in good agreement with observations. Four PBL parameterizations (YSU, MYJ, MYNN and ACM) were evaluated to simulate the above characteristics. Large differences were noticed in the simulated boundary layer features using different PBL schemes in both the seasons. It is found that the TKE-closures (MYJ, MYNN) produced extremities in daytime PBL depth, surface fluxes, temperature, humidity and winds. The differences in the simulations are attributed to the eddy diffusivities, buoyancy and entrainment fluxes which were simulated differently in the respective schemes. The K-based YSU followed by MYNN best produced the slope winds as well as daytime boundary layer characteristics realistically in both the summer and winter synoptic conditions at Gadanki hilly site though with slight overestimation of nocturnal PBL height.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The transitory nature of the atmospheric boundary layer few hours before and after the time of sunset has been studied comprehensively over a tropical station, Gadanki (13.45° N, 79.18° E), using a suite of in-situ and remote sensing devices. This study addresses the following fundamental and important issues related to the afternoon-to-evening transition (AET). Which state variable first identifies it? Which variable best identifies it? Does the start time of AET varies with season and height? If so, which physical mechanism is responsible for the observed height variation in the start time of transition? The transition is seen first in temperature (T) and wind variance (σ2ws) variations at the surface, ∼ 100 min prior to the time of sunset, then in vertical temperature gradient and finally in water vapour mixing ratio variation. Aloft, the AET is observed nearly at the same time in signal to noise ratio (SNR) and spectral width (σ) measurements of wind profiler and sodar. TheT at the surface and SNR aloft identify the signature of transition unambiguously. Also, their distributions for start time of AET with reference to the time of sunset are narrow and consistent in total and seasonal plots. The start time of transition shows some seasonal variation with delayed transitions occurring mostly in the rainy and humid season of northeast monsoon. Interestingly, in contrast to the general perception, the signature of the transition is first seen in the profiler data then in sodar data and finally in the surface data, suggesting that the transition follows top-to-bottom evolution. It indicates that other forcings, like entrainment, play a major role in altering the structure of ABL during the AET, when the sensible heat flux decreases progressively. These forcing terms are quantified using a unique high-resolution dataset to understand their variation in light of the intriguing height dependency of the start time of AET.

  5. Direct and large-eddy simulations of the stable atmospheric boundary layer: the effect of unsteadiness and surface variability

    NASA Astrophysics Data System (ADS)

    Shah, S.; Bou-Zeid, E.

    2013-12-01

    Understanding and parameterizing turbulent fluxes in statically-stable atmospheric boundary layers (SABLs), where buoyant forces destroy turbulent kinetic energy, remains a challenging yet very important problem in geophysical fluid dynamics. The complexities of these flows are further exacerbated by the increased sensitivity to unsteadiness and surface variability. To address the role of these exacerbating factors, direct numerical simulations and large eddy simulations are performed. Under the highest stabilities, global intermittency (the almost compete decay of turbulence and then its regeneration) is observed. The intermittent bursts are important to study under these conditions since they become the main agent of vertical transport in the SABL. Under more moderate stabilities, continuous turbulence is maintained, but it is significantly damped compared to neutral flows. This reduction of the TKE under stable conditions is very well known; however, in this study, we show that it is mainly triggered by reduced mechanical production associated with reduced transport of Reynolds stresses from aloft toward the surface, rather than by direct destruction of TKE by buoyancy. Variability of surface temperature is shown to result in excepted flow patterns: TKE is potentially higher under the more stable patches due to advection, and the subsidence and lofting of air over the different patches can counteract the effect of spatial TKE variability on the vertical fluxes. Re_f = 600. (a) Surface Richardson number (R_{i0;t}) versus non-dimensional time (tf) for different stabilities. (b) Non-dimensional volume integrated turbulent kinetic energy per unit area (E). (c) Friction velocity (u_*) and its variation with time and stability. (d) Variation of the angle (Beta) between the geostrophic wind direction and the surface shear stress direction with time and stability. Colormap of the TKE from a heterogeneous surface temperature LES, showing the effect of advection.

  6. 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 t