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Robert M Banta - One of the best experts on this subject based on the ideXlab platform.
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turbulence regimes and turbulence intermittency in the Stable Boundary Layer during cases 99
Journal of the Atmospheric Sciences, 2012Co-Authors: Jielun Sun, L Mahrt, Robert M Banta, Yelena L PichuginaAbstract:AbstractAn investigation of nocturnal intermittent turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three turbulence regimes at each observation height: 1) regime 1, a weak turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate turbulence regime when top-down turbulence sporadically bursts into the otherwise weak turbulence regime. For regime 1, the strength of small turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the turbulence strength increases systematically with wind speed as a result of turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the Boundary Layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluc...
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horizontal velocity and variance measurements in the Stable Boundary Layer using doppler lidar sensitivity to averaging procedures
Journal of Atmospheric and Oceanic Technology, 2008Co-Authors: Yelena L Pichugina, Robert M Banta, N D Kelley, Bonnie Jonkman, Sara C Tucker, Rob K Newsom, Alan W BrewerAbstract:Abstract Quantitative data on turbulence variables aloft—above the region of the atmosphere conveniently measured from towers—have been an important but difficult measurement need for advancing understanding and modeling of the Stable Boundary Layer (SBL). Vertical profiles of streamwise velocity variances obtained from NOAA’s high-resolution Doppler lidar (HRDL), which have been shown to be approximately equal to turbulence kinetic energy (TKE) for Stable conditions, are a measure of the turbulence in the SBL. In the present study, the mean horizontal wind component U and variance σ2u were computed from HRDL measurements of the line-of-sight (LOS) velocity using a method described by Banta et al., which uses an elevation (vertical slice) scanning technique. The method was tested on datasets obtained during the Lamar Low-Level Jet Project (LLLJP) carried out in early September 2003, near the town of Lamar in southeastern Colorado. This paper compares U with mean wind speed obtained from sodar and sonic an...
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Stable Boundary Layer regimes from the perspective of the low level jet
Acta Geophysica, 2008Co-Authors: Robert M BantaAbstract:This paper reviews results from two field studies of the nocturnal Stable atmospheric Boundary Layer (SBL) over the Great Plains of the United States. Data from a scanning remote-sensing system, a High-Resolution Doppler Lidar (HRDL), provided measurements of mean and turbulent wind components at high spatial and temporal resolution through the lowest 500–1000 m of the atmosphere. This data set has allowed the characteristics of the low-level jet (LLJ) maximum (speed, height, direction) to be documented through entire nights. LLJs form after sunset and produce strong shear in the Layer below the LLJ maximum or nose, which is a source of turbulence and mixing in the SBL. Simultaneous HRDL measurements of turbulence quantities related to turbulence kinetic energy (TKE) has allowed the turbulence in the subjet Layer to be related to LLJ properties. Turbulence structure was found to be a function of the bulk stability of the subjet Layer. For the strong-LLJ (> 15 m s−1), weakly Stable cases the strength of the turbulence is proportional to the strength of the LLJ. For these cases with nearly continuous turbulence in the subjet Layer, low-level jet scaling, in which lengths are scaled by the LLJ height and velocity variables are scaled by the LLJ speed, was found to be appropriate. For the weak-wind (< 5 m s−1 in the lowest 200 m), very Stable Boundary Layer (vSBL), the Boundary Layer was found to be very shallow (sometimes < 10 m deep), and turbulent fluxes between the earth’s surface and the atmosphere were found to be essentially shut down. For more intermediate wind speeds and stabilities, the SBL shows varying degrees of intermittency due to various mechanisms, including shearinstability and other gravity waves, density currents, and other mesoscale disturbances.
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Stable Boundary Layer regimes from the perspective of the low level jet
Acta Geophysica, 2008Co-Authors: Robert M BantaAbstract:This paper reviews results from two field studies of the nocturnal Stable atmospheric Boundary Layer (SBL) over the Great Plains of the United States. Data from a scanning remote-sensing system, a High-Resolution Doppler Lidar (HRDL), provided measurements of mean and turbulent wind components at high spatial and temporal resolution through the lowest 500–1000 m of the atmosphere. This data set has allowed the characteristics of the low-level jet (LLJ) maximum (speed, height, direction) to be documented through entire nights. LLJs form after sunset and produce strong shear in the Layer below the LLJ maximum or nose, which is a source of turbulence and mixing in the SBL. Simultaneous HRDL measurements of turbulence quantities related to turbulence kinetic energy (TKE) has allowed the turbulence in the subjet Layer to be related to LLJ properties. Turbulence structure was found to be a function of the bulk stability of the subjet Layer. For the strong-LLJ (> 15 m s−1), weakly Stable cases the strength of the turbulence is proportional to the strength of the LLJ. For these cases with nearly continuous turbulence in the subjet Layer, low-level jet scaling, in which lengths are scaled by the LLJ height and velocity variables are scaled by the LLJ speed, was found to be appropriate. For the weak-wind (< 5 m s−1 in the lowest 200 m), very Stable Boundary Layer (vSBL), the Boundary Layer was found to be very shallow (sometimes < 10 m deep), and turbulent fluxes between the earth’s surface and the atmosphere were found to be essentially shut down. For more intermediate wind speeds and stabilities, the SBL shows varying degrees of intermittency due to various mechanisms, including shearinstability and other gravity waves, density currents, and other mesoscale disturbances.
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turbulent velocity variance profiles in the Stable Boundary Layer generated by a nocturnal low level jet
Journal of the Atmospheric Sciences, 2006Co-Authors: Robert M Banta, Yelena L Pichugina, Alan W BrewerAbstract:Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind Stable Boundary Layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for Stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was f...
Albert A. M. Holtslag - One of the best experts on this subject based on the ideXlab platform.
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On the turbulence structure of deep katabatic flows on a gentle mesoscale slope
Quarterly Journal of the Royal Meteorological Society, 2020Co-Authors: Ivana Stiperski, Albert A. M. Holtslag, Manuela Lehner, Sebastian W. Hoch, C. David WhitemanAbstract:A comprehensive analysis of the turbulence structure of relatively deep midlatitude katabatic flows (with jet maxima between 20 and 50 m) developing over a gentle (1°) mesoscale slope with a long fetch upstream of the Meteor Crater in Arizona is presented. The turbulence structure of flow below the katabatic jet maximum shows many similarities with the turbulence structure of shallower katabatic flows, with decreasing turbulence fluxes with height and almost constant turbulent Prandtl number. Still stark differences occur above the jet maximum where turbulence is suppressed by strong stability, is anisotropic and there is a large sub-mesoscale contribution to the flux. Detecting the Stable Boundary-Layer top depends on the method used (flux- vs. anisotropy-profiles) but both methods are highly correlated. The top of the Stable Boundary Layer, however, mostly deviates from the jet maximum height or the top of the near-surface inversion. The flat-terrain formulations for the Boundary-Layer height correlate well with the detected top of the Stable Boundary Layer if the near-surface and not the background stratification is used in their formulations; however, they mostly largely overestimate this Boundary-Layer height. The difference from flat-terrain Boundary Layers is also shown through the dependence of size of the dominant eddy with height. In katabatic flows the eddy size is semi-constant with height throughout the Stable Boundary-Layer depth, whereas in flat terrain, eddy size varies significantly with height. Flux-gradient and flux-variance relationships show that turbulence data from different Stable Boundary-Layer scaling regimes collapse on top of each other showing that the dominant dependence is not on the scaling regime but on the local stability.
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Stable atmospheric Boundary Layers and diurnal cycles challenges for weather and climate models
Bulletin of the American Meteorological Society, 2013Co-Authors: Albert A. M. Holtslag, Joan Cuxart, Sukanta Basu, Gunilla Svensson, Peter W Baas, B Beare, Anton Beljaars, F C Bosveld, Jenny Lindvall, Gert-jan SteeneveldAbstract:The representation of the atmospheric Boundary Layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the Stable Boundary Layer and the diurnal cycle over land in clear-sky conditions. For thi...
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evaluation and improvement of the wrf mesoscale model for the Stable Boundary Layer and the representation of the low level jet
20th Symposium on Boundary Layers and Turbulence 18th Conference on Air-Sea Interaction American Meteorological Society (9-13 July 2012 Boston MA), 2012Co-Authors: M A Kleczek, Gert-jan Steeneveld, Albert A. M. HoltslagAbstract:Correct forecasting of the diurnal cycle of the atmospheric Boundary Layer (ABL) is of key importance for many applications like for wind energy, weather forecasting and climate, agriculture and air quality. Previous research has shown models are very sensitive to the selected Boundary-Layer parameterization. In this contribution we extend the GABLS3 single-column model intercomparison (Bosveld et al., 2012; http://www.knmi.nl/samenw/gabls/), by evaluating the WRF three dimensional model (version 3.2.1) for the same case and the 7 analogue cases of Baas et al (2010). Results show satisfactory model behaviour for net radiation with comparison to Cabauw observations (Netherlands), although a negative bias in long wave downward radiation of about 20 W/m2 as in the single-column model studies is seen. Typically, two meter temperatures are slightly underestimated during daytime, and substantially underestimated at night. Concerning the vertical profiles, the YSU ABL scheme in WRF overestimates the ABL depth and low level jet (LLJ) altitude substantially. Also, the modelled LLJ speed is too low with respect to Cabauw tower observations and the nearby radio-sounding measurements of de Bilt . To improve the performance of the YSU scheme for the LLJ, the YSU scheme has been modified by implementing the Stable Boundary Layer height definition in Vogelezang and Holtslag (1996). The latter uses a modified definition of the bulk Richardson number based on a Layer between the ABL height and a level several tens of meters above the ground, rather than the ground surface itself. In that way, near surface shear production does not directly affect the ABL height, which make physically sense under relatively high wind geostrophic speed conditions (as in GABLS3) . The revised scheme results in a more accurate forecast of the Stable Boundary Layer. In particular, the LLJ, the Boundary-Layer height and the near surface stability improves compared to observations. In more detail, we find significant increase in the LLJ speed by ~1.5ms-1 and decrease in LLJ altitude by ~100m which is in closer agreement to the observations than with the original YSU formulation.
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estimation of orographically induced wave drag in the Stable Boundary Layer during the cases 99 experimental campaign
Acta Geophysica, 2009Co-Authors: Gert-jan Steeneveld, Carmen J Nappo, Albert A. M. HoltslagAbstract:This paper addresses the quantification of gravity wave drag due to small hills in the Stable Boundary Layer. A single column atmospheric model is used to forecast wind and temperature profiles in the Boundary Layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flux.
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An inconvenient “truth” about using sensible heat flux as a surface Boundary condition in models under stably stratified regimes
Acta Geophysica, 2008Co-Authors: Sukanta Basu, Bas J H Van De Wiel, Albert A. M. Holtslag, Arnold F. Moene, Gert-jan SteeneveldAbstract:In single column and large-eddy simulation studies of the atmospheric Boundary Layer, surface sensible heat flux is often used as a Boundary condition. In this paper, we delineate the fundamental shortcomings of such a Boundary condition in the context of Stable Boundary Layer modelling and simulation. Using an analytical approach, we are able to show that for reliable model results of the Stable Boundary Layer accurate surface temperature prescription or prediction is needed. As such, the use of surface heat flux as a Boundary condition should be avoided in Stable conditions.
Yelena L Pichugina - One of the best experts on this subject based on the ideXlab platform.
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turbulence regimes and turbulence intermittency in the Stable Boundary Layer during cases 99
Journal of the Atmospheric Sciences, 2012Co-Authors: Jielun Sun, L Mahrt, Robert M Banta, Yelena L PichuginaAbstract:AbstractAn investigation of nocturnal intermittent turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three turbulence regimes at each observation height: 1) regime 1, a weak turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate turbulence regime when top-down turbulence sporadically bursts into the otherwise weak turbulence regime. For regime 1, the strength of small turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the turbulence strength increases systematically with wind speed as a result of turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the Boundary Layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluc...
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horizontal velocity and variance measurements in the Stable Boundary Layer using doppler lidar sensitivity to averaging procedures
Journal of Atmospheric and Oceanic Technology, 2008Co-Authors: Yelena L Pichugina, Robert M Banta, N D Kelley, Bonnie Jonkman, Sara C Tucker, Rob K Newsom, Alan W BrewerAbstract:Abstract Quantitative data on turbulence variables aloft—above the region of the atmosphere conveniently measured from towers—have been an important but difficult measurement need for advancing understanding and modeling of the Stable Boundary Layer (SBL). Vertical profiles of streamwise velocity variances obtained from NOAA’s high-resolution Doppler lidar (HRDL), which have been shown to be approximately equal to turbulence kinetic energy (TKE) for Stable conditions, are a measure of the turbulence in the SBL. In the present study, the mean horizontal wind component U and variance σ2u were computed from HRDL measurements of the line-of-sight (LOS) velocity using a method described by Banta et al., which uses an elevation (vertical slice) scanning technique. The method was tested on datasets obtained during the Lamar Low-Level Jet Project (LLLJP) carried out in early September 2003, near the town of Lamar in southeastern Colorado. This paper compares U with mean wind speed obtained from sodar and sonic an...
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turbulent velocity variance profiles in the Stable Boundary Layer generated by a nocturnal low level jet
Journal of the Atmospheric Sciences, 2006Co-Authors: Robert M Banta, Yelena L Pichugina, Alan W BrewerAbstract:Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind Stable Boundary Layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for Stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was f...
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turbulent velocity variance profiles in the Stable Boundary Layer generated by a nocturnal low level jet
Journal of the Atmospheric Sciences, 2006Co-Authors: Robert M Banta, Yelena L Pichugina, Alan W BrewerAbstract:Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind Stable Boundary Layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for Stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was f...
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relationship between low level jet properties and turbulence kinetic energy in the nocturnal Stable Boundary Layer
Journal of the Atmospheric Sciences, 2003Co-Authors: Robert M Banta, Yelena L Pichugina, Rob K NewsomAbstract:Abstract In the nighttime Stable Boundary Layer (SBL), shear and turbulence are generated in the Layer between the maximum of the low-level jet (LLJ) and the earth's surface. Here, it is investigated whether gross properties of the LLJ—its height and speed—could be used to diagnose turbulence intensities in this subjet Layer. Data on the height and speed of the LLJ maximum were available at high vertical and temporal resolution using the high-resolution Doppler lidar (HRDL). These data were used to estimate a subjet Layer shear, which was computed as the ratio of the speed to the height of the jet maximum, and a jet Richardson number RiJ, averaged at 15-min intervals for 10 nights when HRDL LLJ data were available for this study. The shear and RiJ values were compared with turbulence kinetic energy (TKE) values measured near the top of the 60-m tower at the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) main site. TKE values were small for RiJ greater than 0.4, but as RiJ decreased to less ...
Gert-jan Steeneveld - One of the best experts on this subject based on the ideXlab platform.
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Stable atmospheric Boundary Layers and diurnal cycles challenges for weather and climate models
Bulletin of the American Meteorological Society, 2013Co-Authors: Albert A. M. Holtslag, Joan Cuxart, Sukanta Basu, Gunilla Svensson, Peter W Baas, B Beare, Anton Beljaars, F C Bosveld, Jenny Lindvall, Gert-jan SteeneveldAbstract:The representation of the atmospheric Boundary Layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the Stable Boundary Layer and the diurnal cycle over land in clear-sky conditions. For thi...
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evaluation and improvement of the wrf mesoscale model for the Stable Boundary Layer and the representation of the low level jet
20th Symposium on Boundary Layers and Turbulence 18th Conference on Air-Sea Interaction American Meteorological Society (9-13 July 2012 Boston MA), 2012Co-Authors: M A Kleczek, Gert-jan Steeneveld, Albert A. M. HoltslagAbstract:Correct forecasting of the diurnal cycle of the atmospheric Boundary Layer (ABL) is of key importance for many applications like for wind energy, weather forecasting and climate, agriculture and air quality. Previous research has shown models are very sensitive to the selected Boundary-Layer parameterization. In this contribution we extend the GABLS3 single-column model intercomparison (Bosveld et al., 2012; http://www.knmi.nl/samenw/gabls/), by evaluating the WRF three dimensional model (version 3.2.1) for the same case and the 7 analogue cases of Baas et al (2010). Results show satisfactory model behaviour for net radiation with comparison to Cabauw observations (Netherlands), although a negative bias in long wave downward radiation of about 20 W/m2 as in the single-column model studies is seen. Typically, two meter temperatures are slightly underestimated during daytime, and substantially underestimated at night. Concerning the vertical profiles, the YSU ABL scheme in WRF overestimates the ABL depth and low level jet (LLJ) altitude substantially. Also, the modelled LLJ speed is too low with respect to Cabauw tower observations and the nearby radio-sounding measurements of de Bilt . To improve the performance of the YSU scheme for the LLJ, the YSU scheme has been modified by implementing the Stable Boundary Layer height definition in Vogelezang and Holtslag (1996). The latter uses a modified definition of the bulk Richardson number based on a Layer between the ABL height and a level several tens of meters above the ground, rather than the ground surface itself. In that way, near surface shear production does not directly affect the ABL height, which make physically sense under relatively high wind geostrophic speed conditions (as in GABLS3) . The revised scheme results in a more accurate forecast of the Stable Boundary Layer. In particular, the LLJ, the Boundary-Layer height and the near surface stability improves compared to observations. In more detail, we find significant increase in the LLJ speed by ~1.5ms-1 and decrease in LLJ altitude by ~100m which is in closer agreement to the observations than with the original YSU formulation.
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estimation of orographically induced wave drag in the Stable Boundary Layer during the cases 99 experimental campaign
Acta Geophysica, 2009Co-Authors: Gert-jan Steeneveld, Carmen J Nappo, Albert A. M. HoltslagAbstract:This paper addresses the quantification of gravity wave drag due to small hills in the Stable Boundary Layer. A single column atmospheric model is used to forecast wind and temperature profiles in the Boundary Layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flux.
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An inconvenient “truth” about using sensible heat flux as a surface Boundary condition in models under stably stratified regimes
Acta Geophysica, 2008Co-Authors: Sukanta Basu, Bas J H Van De Wiel, Albert A. M. Holtslag, Arnold F. Moene, Gert-jan SteeneveldAbstract:In single column and large-eddy simulation studies of the atmospheric Boundary Layer, surface sensible heat flux is often used as a Boundary condition. In this paper, we delineate the fundamental shortcomings of such a Boundary condition in the context of Stable Boundary Layer modelling and simulation. Using an analytical approach, we are able to show that for reliable model results of the Stable Boundary Layer accurate surface temperature prescription or prediction is needed. As such, the use of surface heat flux as a Boundary condition should be avoided in Stable conditions.
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Diagnostic Equations for the Stable Boundary Layer Height: Evaluation and Dimensional Analysis
Journal of Applied Meteorology and Climatology, 2007Co-Authors: Gert-jan Steeneveld, Bas J H Van De Wiel, Albert A. M. HoltslagAbstract:Abstract The performance of diagnostic equations for the Stable Boundary Layer height h is evaluated with four observational datasets that represent a broad range of latitudes, land use, and surface roughness. In addition, large-eddy simulation results are used. Special care is given to data-quality selection. The diagnostic equations evaluated are so-called multilimit equations as derived by Zilitinkevich and coworkers in a number of papers. It appears that these equations show a serious negative bias, especially for h < 100 m, and it was found that the parameters involved could not be determined uniquely with calibration. As an alternative, dimensional analysis is used here to derive a formulation for h that is more robust. The formulation depends on the surface friction velocity u*, surface buoyancy flux Bs, Coriolis parameter, and the free-flow stability N. The relevance of the Coriolis parameter for the Boundary Layer height estimation in practice is also discussed. If the Coriolis parameter is ignor...
Joan Cuxart - One of the best experts on this subject based on the ideXlab platform.
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Stable atmospheric Boundary Layers and diurnal cycles challenges for weather and climate models
Bulletin of the American Meteorological Society, 2013Co-Authors: Albert A. M. Holtslag, Joan Cuxart, Sukanta Basu, Gunilla Svensson, Peter W Baas, B Beare, Anton Beljaars, F C Bosveld, Jenny Lindvall, Gert-jan SteeneveldAbstract:The representation of the atmospheric Boundary Layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the Stable Boundary Layer and the diurnal cycle over land in clear-sky conditions. For thi...
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an intercomparison of large eddy simulations of the Stable Boundary Layer
Boundary-Layer Meteorology, 2006Co-Authors: Robert J Beare, Joan Cuxart, Albert A. M. Holtslag, M. A. Jiménez, M K Macvean, Igor Esau, Jeanchristophe Golaz, Marat Khairoutdinov, Branko Kosovic, D C LewellenAbstract:Results are presented from the first intercomparison of large-eddy simulation (LES) models for the Stable Boundary Layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately Stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.
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large eddy simulations of the Stable Boundary Layer using the standard kolmogorov theory range of applicability
Boundary-Layer Meteorology, 2005Co-Authors: M. A. Jiménez, Joan CuxartAbstract:Large-eddy simulations (LES) of the Stable Atmospheric Boundary Layer (SBL) are difficult because the turbulence is not isotropic for strong stratification and the Kolmogorov theory might be no longer valid. This fact compells us to work on modifications to the subgrid turbulence schemes, although there is not any widely accepted theory on anisotropic turbulence. In this work, a LES model is used to see what range of Stable stratification can still be simulated with a subgrid turbulence scheme using the Kolmogorov theory for the dissipation. Twenty simulations of increasing stability have been performed using a horizontal resolution of 5 m. The model is able to simulate weakly and moderately Stable conditions and experiences runaway cooling for strong stability. The goodness of the successful simulations is inspected through comparison to observations from the experimental campaigns SABLES-98 and CASES-99. Other supplementary tests have been performed on the resolution and the surface Boundary condition.
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Intermittent Turbulence Associated with a Density Current Passage in the Stable Boundary Layer
Boundary-Layer Meteorology, 2002Co-Authors: Jielun Sun, Sean P. Burns, Donald H. Lenschow, Robert Banta, Rob Newsom, Richard Coulter, Stephen Frasier, Turker Ince, Carmen Nappo, Joan CuxartAbstract:Using the unprecedented observational capabilities deployed duringthe Cooperative Atmosphere-Surface Exchange Study-99 (CASES-99),we found three distinct turbulence events on the night of 18October 1999, each of which was associated with differentphenomena: a density current, solitary waves, and downwardpropagating waves from a low-level jet. In this study, we focus onthe first event, the density current and its associatedintermittent turbulence. As the cold density current propagatedthrough the CASES-99 site, eddy motions in the upper part of thedensity current led to periodic overturning of the stratifiedflow, local thermal instability and a downward diffusion ofturbulent mixing. Propagation of the density current induced asecondary circulation. The descending motion following the head ofthe density current resulted in strong stratification, a sharpreduction in the turbulence, and a sudden increase in the windspeed. As the wind surge propagated toward the surface, shearinstability generated upward diffusion of turbulent mixing. Wedemonstrate in detail that the height and sequence of the localthermal and shear instabilities associated with the dynamics ofthe density current are responsible for the apparent intermittentturbulence.
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study of coherent structures and estimation of the pressure transport terms for the nocturnal Stable Boundary Layer
Boundary-Layer Meteorology, 2002Co-Authors: Joan Cuxart, Gracia Morales, Enric Terradellas, Carlos YagueAbstract:During the CASES-99 field experiment, three quartz-based microbarographs were installed on the 58-m main tower at the Central Site. These devices measuredabsolute pressure with temperature compensated output at a resolution better than 0.2 Pa and a sampling frequency of 2 s-1 during the whole campaign. This sampling rate is not adequate to compute turbulent pressure fluxes with the classic averaging method, but the wavelet transform allows flux estimations at a wide range of scales. The resolution of the devices is suitable to study pressure perturbations such as internal gravity waves. The night period of the Intensive Operational Period number 6 (IOP6), where wave-like structures were present, is chosen to illustrate the method. A complete wavelet analysis of pressure recordsand data from sonic anemometers located at the same heights in the tower is performed. Wavelet methods make it possible to identify the relevant scales in the flowand to study the vertical structure of pressure perturbations, including coherent structures and small-scale motions.A study of a simplified turbulence kinetic energy budget equation is made and the contribution of the pressure terms is discussed.