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1.
The turning of wind with height and the related cross-isobaric (ageostrophic) flow in the thermally stable stratified boundary
layer is analysed from a variety of model results acquired in the first Global Energy and Water Cycle Experiment (GEWEX) Atmospheric
Boundary Layer Study (GABLS1). From the governing equations in this particular simple case it becomes clear that the cross-isobaric
flow is solely determined by the surface turbulent stress in the direction of the geostrophic wind for the quasi-steady state
conditions under consideration. Most models indeed seem to approach this relationship but for very different absolute values.
Because turbulence closures used in operational models typically tend to give too deep a boundary layer, the integrated total
cross-isobaric mass flux is up to three times that given by research numerical models and large-eddy simulation. In addition,
the angle between the surface and the geostrophic wind is typically too low, which has important implications for the representation
of the larger-scale flow. It appears that some models provide inconsistent results for the surface angle and the momentum
flux profile, and when the results from these models are removed from the analysis, the remaining ten models do show a unique
relationship between the boundary-layer depth and the surface angle, consistent with the theory given. The present results
also imply that it is beneficial to locate the first model level rather close to the surface for a proper representation of
the turning of wind with height in the stable boundary layer. 相似文献
2.
Evaluation of the Weather Research and Forecasting Mesoscale Model for GABLS3: Impact of Boundary-Layer Schemes,Boundary Conditions and Spin-Up 总被引：3，自引：3，他引：0
Michal A. Kleczek Gert-Jan Steeneveld Albert A. M. Holtslag 《Boundary-Layer Meteorology》2014,152(2):213-243
We evaluated the performance of the three-dimensional Weather Research and Forecasting (WRF) mesoscale model, specifically the performance of the planetary boundary-layer (PBL) parametrizations. For this purpose, Cabauw tower observations were used, with the study extending beyond the third GEWEX Atmospheric Boundary-Layer Study (GABLS3) one-dimensional model intercomparison. The WRF model (version 3.4.1) contains 12 different PBL parametrizations, most of which have been only partially evaluated. The GABLS3 case offers a clear opportunity to evaluate model performance, focusing on time series of near-surface weather variables, radiation and surface flux budgets, vertical structure and the nighttime inertial oscillation. The model results revealed substantial differences between the PBL schemes. Generally, non-local schemes tend to produce higher temperatures and higher wind speeds than local schemes, in particular, for nighttime. The WRF model underestimates the 2-m temperature during daytime (about \(2\) K) and substantially underestimates it at night (about \(4\) K), in contrast to the previous studies where modelled 2-m temperature was overestimated. Considering the 10-m wind speed, during the night turbulent kinetic energy based schemes tend to produce lower wind speeds than other schemes. In all simulations the sensible and latent heat fluxes were well reproduced. For the net radiation and the soil heat flux we found good agreement with daytime observations but underestimations at night. Concerning the vertical profiles, the selected non-local PBL schemes underestimate the PBL depth and the low-level jet altitude at night by about 50 m, although with the correct wind speed. The latter contradicts most previous studies and can be attributed to the revised stability function in the Yonsei University PBL scheme. The local, turbulent kinetic energy based PBL schemes estimated the low-level jet altitude and strength more accurately. Compared to the observations, all model simulations show a similar structure for the potential temperature, with a consistent cold bias ( \(\approx \) 2 K) in the upper PBL. In addition to the sensitivity to the PBL schemes, we studied the sensitivity to technical features such as horizontal resolution and domain size. We found a substantial difference in the model performance for a range of 12, 18 and 24 h spin-up times, longer spin-up time decreased the modelled wind speed bias, but it strengthened the negative temperature bias. The sensitivity of the model to the vertical resolution of the input and boundary conditions on the model performance is confirmed, and its influence appeared most significant for the non-local PBL parametrizations. 相似文献
3.
A one-dimensional atmospheric boundary-layer model is developed using the finite element method and a 1.5-order e-l turbulence closure scheme. A vertical adaptive strategy is implemented, based upon an heuristic error estimator that depends
upon properties of the layer, such as the stratification. The model is used to simulate a moderately stratified stable boundary
layer as described in the GABLS (GEWEX Atmospheric Boundary-Layer Study, where GEWEX is the Global Water and Energy Cycle
Experiment) First Intercomparison Project, and then a more complicated diurnal cycle, as used in the GABLS Second Intercomparison
Project. In the stable boundary-layer experiment, it is shown that including the adaptive strategy can improve the performance
of the model such that the error in the model is significantly less (greater than an order of magnitude with an effective
resolution of 8 m) than that of the model without adaptivity. The model’s turbulence closure scheme and the adaptivity strategy
also successfully simulate the different stability regimes present in the diurnal cycle simulation, and represented all of
the expected features. 相似文献
4.
Spurious inertial oscillations are induced in boundary-layer models if a geostrophic wind is prescribed which changes in time. A simple technique is proposed to eliminate these oscillations. The scheme is successfully applied to idealized cases of boundary-layer flow and to a real situation where a pronounced turning of the geostrophic wind has been observed. 相似文献
5.
G. Svensson A. A. M. Holtslag V. Kumar T. Mauritsen G. J. Steeneveld W. M. Angevine E. Bazile A. Beljaars E. I. F. de Bruijn A. Cheng L. Conangla J. Cuxart M. Ek M. J. Falk F. Freedman H. Kitagawa V. E. Larson A. Lock J. Mailhot V. Masson S. Park J. Pleim S. S?derberg W. Weng M. Zampieri 《Boundary-Layer Meteorology》2011,140(2):177-206
We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today??s numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled near-surface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified. 相似文献
6.
7.
A two-dimensional time-dependent Earth-atmosphere model is developed which can be applied to the study of a class of atmospheric boundary-layer flows which owe their origin to horizontal inhomogeneities with respect to surface roughness and temperature. Our main application of the model is to explore the governing physical mechanisms of nocturnal urban atmospheric boundarylayer flow.A case study is presented in which a stable temperature stratification is assumed to exist in the rural upwind area. It is shown through integration of the numerical model that as this air passes over a city, the heat is redistributed due to increased surface friction (and hence increased turbulent mixing). This redistribution of heat results in the formation of an urban heat island.Additional numerical integrations of the model are conducted to examine the dependence of induced perturbations on: (1) the upwind temperature inversion; (2) the geostrophic wind speed; and (3) urbanization. The results show a linear relationship between heat-island intensity and the rural temperature inversion with the heat island increasing in intensity as the upwind inversion becomes stronger; that the heat-island intensity close to the surface is inversely proportional to the geostrophic wind; and that the effects of anthropogenic heat cause an increase in the perturbation temperature with the perturbation extending to higher altitudes. From this study, we conclude that with an upwind temperature inversion, a city of any size should generate a heat island as a result of increased surface roughness. The heat-island intensity should increase with city size because of two factors: larger cities are usually aerodynamically rougher; and larger cities have a larger anthropogenic heat output.Research supported in part by NSF Grant GA-16822. 相似文献
8.
Inland and Offshore Propagation Speeds of a Sea Breeze from Simulations and Measurements 总被引：1，自引：1，他引：0
Klara Finkele 《Boundary-Layer Meteorology》1998,87(2):307-329
The inland and offshore propagation speeds of a sea breeze circulation cell are simulated using a three-dimensional hydrostatic model within a terrain-following coordinate system. The model includes a third-order semi-Lagrangian advection scheme, which compares well in a one-dimensional stand-alone test with the more complex Bott and Smolarkiewicz advection schemes. Two turbulence schemes are available: a local scheme by Louis (1979) and a modified non-local scheme based on Zhang and Anthes (1982). Both compare well with higher-order closure schemes using the Wangara data set for Day 33–34 (Clark et al., 1971).Two-dimensional cross-sections derived from airborne sea breeze measurements (Finkele et al. 1995) constitute the basis for comparison with two-dimensional numerical model results. The offshore sea breeze propagation speed is defined as the speed at which the seaward extent of the sea breeze grows offshore. On a study day, the offshore sea breeze propagation speed, from both measurements and model, is -3.4 m s-1. The measured inland propagation speed of the sea breeze decreased somewhat during the day. The model results show a fairly uniform inland propagation speed of 1.6 m s-1 which corresponds to the average measured value. The offshore sea breeze propagation speed is about twice the inland propagation speed for this particular case study, from both the model and measurements.The influence of the offshore geostrophic wind on the sea breeze evolution, offshore extent and inland penetration are investigated. For moderate offshore geostrophic winds (-5.0 m s-1), the offshore and inland propagation speeds are non-uniform. The offshore extent in moderate geostrophic wind conditions is similar to the offshore extent in light wind conditions (-2.5 m s-1). The inland extent is greater in light offshore geostrophic winds than in moderate ones. This suggests that the offshore extent of the sea breeze is less sensitive to the offshore geostrophic wind than its inland extent. However, these results hold only if it is possible to define an inland propagation speed. For stronger offshore geostrophic winds (-7.5 m s-1), the sea breeze is completely offshore and the inland propagation speed is ill-defined. 相似文献
9.
Jinmei Shen 《Boundary-Layer Meteorology》1998,87(3):481-498
The influence of vegetation and environmental conditions on the lake breeze and associated boundary-layer turbulence structure has been studied using a two-dimensional nonhydrostatic, compressible mesoscale model coupled with the SiB2 land-surface scheme. The results show that the impacts of vegetation on the lake effects are dependent on the environmental conditions, such as soil wetness and background wind, as well as vegetation characteristics. Both soil wetness and background wind play important roles in modifying lake effects on boundary-layer turbulence and the lake breeze, while the effects of vegetation type are secondary compared to the other factors. Without background wind, and under the same soil wetness, the maximum horizontal windspeed of the lake breeze is insensitive to the type of vegetation. Soil wetness can greatly affect both the maximum horizontal windspeed and the maximum vertical velocities of the lake breeze. With background wind, the lake-breeze circulations, upward motion regions, and boundary-layer turbulence structure all change markedly. A weaker background wind can strengthen the lake breeze, while stronger background wind suppresses the lake breeze circulations. The distribution of sensible and latent heat fluxes is also very sensitive to the soil wetness and background wind. However, for the same soil wetness (0.25 and 0.4 were chosen), there is only a small difference in the distribution of sensible and latent heat fluxes between the bare soil and vegetated soil or between the types of vegetated soils. 相似文献
10.
Numerical results indicate that advection of momentum in the boundary layer may significantly alter both the structure of the planetary boundary layer and its influence on the overlying free atmosphere. However, due to the nonlinearity of the inertial terms, it is always difficult to obtain the analytical solution of the boundary-layer model that retains the flow acceleration. In order to overcome this difficulty, the geostrophic momentum (hereafter GM) approximation has been introduced into boundary-layer models. By replacing the advected momentum with the geostrophic wind, the effect of the flow acceleration is partially considered and the original nonlinear partial differential equation set is converted to ordinary differential equations, the solutions of which can be obtained easily with standard techniques. However, the model employing GM fails to capture the features of the boundary layer when the spatio-temporal variation of the boundary-layer flow cannot be properly approximated by the geostrophic wind. In the present work, a modified boundary-layer model with the inertial acceleration in a different approximate form is proposed, in which the advecting wind instead of the advected momentum is approximated by the geostrophic wind (hereafter GAM).Comparing the horizontal velocity and boundary-layer pumping obtained from the classical Ekman theory, and the model incorporating (i) GM and (ii) GAM, it is found that the model with GAM describes most facets of the steady well-mixed layer beneath a north-westerly flow with embedded mesoscale perturbations that is considered in the present work. Inspection of the solution of the model with GAM shows that, within the limit of the validation of the model (i.e., the Rossby number RO is not very large and the drag coefficient CD is not too small), the horizontal convergence (divergence) is strengthened by the effect of the inertial acceleration in the region of maximum positive (negative) geostrophic vorticity. Consequently, the boundary-layer pumping there is intensified. It is found that the intensification is firstly strengthened and then weakened as RO or CD increases. 相似文献
11.
In this paper, Wu and Blumen’s boundary layer geostrophic momentum approximation model (Wu and Blumen, 1982) is applied to baroclinic and non-neutral PBL, the motion equations for the PBL under the geostrophic momentum approximation are solved, in which the eddy transfer coefficient is a function of the distributions of the wind and temperature. The results are compared with those in barotropic and neutral conditions with the geostrophic momentum approximation. It is found that in the baroclinic condition, the wind distribution has both the characteristics of a steady, homogeneous and baroclinic PBL and those caused by the geostrophic momentum approximation. Those in non-neutral conditions show that they retain the intrinsic characteristics for the wind in non-neutral PBL, at the same time, the effects of the large-scale advection and local variation are also included. We can predict the wind in the non-neutral and baroclinic PBL by use of the geostrophic mo-mentum approximation when the temporal and spatial distributions of the geostrophic wind, as well as the po-tential temperatures and their variation rates at the upper and lower boundary of the PBL are given by large-scale model. Finally, the model is extended to the case over sea surface. 相似文献
12.
Measurements and Modelling of the Wind Speed Profile in the Marine Atmospheric Boundary Layer 总被引：1，自引：1，他引：0
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. 相似文献
13.
Four procedures of specifying model initial temperature were described and tested in the present study. It was found that the use of observed temperatures along with a proper vertical interpolation scheme was not only acceptable, but produced less error than the use of temperatures derived from geopotential height through the hydrostatic equation did. Use of the difference form of the hydrostatic equation would produce unacceptable errors in the initial temperatures, unrealistic horizontal and vertical distribution of temperature, and these errors would influence the calculation of the pressure gradient force, resulting in substantial, artificial disturbances within the model domain.In addition, an approach to check the initial data was described. Taking advantage of the fact that the geostrophic wind in sigma coordinates should be nondivergent, geopotential height and temperature were used to calculate the pressure gradient force terms and an initial divergence of the geostrophic wind. This approach can he used for comparing different initialization schemes for identical input data. 相似文献
14.
For the interpretation of many boundary-layer field experiments the geostrophic wind is needed as an external parameter. However, quite often and especially in remote areas this wind is not known at all or difficult to determine because there are not enough measurements of the surface pressure.Here it is shown how measurements carried out with the HELIPOD system, a helicopter-borne meteorological turbulence measuring system, may be used to evaluate the geostrophic wind. This is done by the analysis of the pressure field at different heights. An additional analysis of the temperature field in the same heights allows for the discussion of the quality of the derived geostrophic wind. An intercomparison with the vertical wind profile enables us to discuss the influence of the curvature of the isobars. From this, finally, also the gradient wind can be estimated. 相似文献
15.
边界层特征参数对边界层顶垂直速度的影响 总被引：1，自引：1，他引：1
本文从正斜压及有层结时的边界层相似理论及阻力定律出发，由边界层顶垂直速度与地面湍应力的关系求出了层结、粗糙度、它们的水平梯度及地转风的水平梯度、斜压性对w的影响的解析式，可用于模式计算。计算结果表明层结影响可使w差1-２个量级，不稳定时粗糙度影响也使w差几倍。除地转涡度决定w外，地转风、层结稳定度和粗糙度及其水平梯度也起了重要作用，还讨论了斜压性的影响。 相似文献
16.
An ice breeze mechanism for boundary-layer jets 总被引：1，自引：0，他引：1
The existence of a low-level (z=~1000 m) jet adjacent to a sea-ice boundary is investigated with a two-dimensional numerical model. A thermally-direct ice breeze circulation is induced by specifying an ice-sea surface temperature gradient, with the mean geostrophic wind parallel to the ice edge. Pressure changes associated with over-water mixed-layer development create an increase in geostrophic velocity that accounts for most of the increase in wind speed. A change in initial geostrophic wind direction has significant effects on location and intensity of the low-level jet; geostrophic winds parallel to the ice edge result in stronger jets than occur with cross-ice geostrophic winds. An inertial oscillation simulated by the model in 1-D makes a negligible contribution to the low-level jet. 相似文献
17.
WRF模式对福建沿海风电场风速预测的效果分析 总被引：2，自引：1，他引：1
在WRF模式中选取不同的边界层、近地面层以及陆面过程参数化方案,设计了4种不同物理过程参数化方案,组合模拟福建沿海某测风塔站2010年1月1—11日和7月1—11日的逐时风速,将数值模拟结果和同期测风塔观测数据进行对比,以寻求最佳参数化方案。经分析比较,采用MYJ边界层方案,Monin-Obukhov近地面层方案以及Noah陆面过程方案的方案2模拟效果最好。使用该方案对2010年1月和7月的风速进行模拟,按不同风速级别分别对数值模拟结果进行对比分析,结果表明:方案2对6~15m/s风速模拟的平均相对误差在20%左右,能够满足风电预测的精度需求;而对0~6m/s风速模拟的误差相对较大,这可能是由于模式地形分辨率不够精细以及风塔所处海陆交界处的特殊位置,使低风速容易受地面扰动以及海陆气流影响所致。 相似文献
18.
A dataset collected during a measurement campaign in the middle of the Po Valley, Italy, is used to investigate the boundary-layer structure in stable conditions. Empirical formulations for temperature and wind profiles derived from Monin–Obukhov similarity theory are used as regression curves to fit radiosounding profiles in the lower half of the boundary-layer. The best fitting parameters of the regression are then compared to the surface turbulent fluxes as measured by a co-located sonic anemometer. This comparison shows significant discrepancies and supports earlier results showing that surface fluxes, in the limit of high stability, are not adequate scalings for mean profiles. The most evident differences are found for cases for which the bulk Richardson number turns out to be quite large. One of the practical consequences is that boundary-layer height diagnostic formulations that mainly rely on surface fluxes are in disagreement with those obtained by inspecting the thermodynamic profiles recorded during the radiosounding ascent. Moreover the incorrect scaling of similarity profiles in stable conditions leads to the erroneous diagnosis of 2-m air temperatures used in numerical weather prediction validation. 相似文献
19.
P. J. Mason 《Boundary-Layer Meteorology》1983,27(1):43-68
Observations of the planetary boundary layer under conditions with strong or moderate winds often show the large-scale boundary-layer motions to be highly elongated in a direction close to that of the geostrophic wind. The properties of such large-scale motions are examined by means of a two-dimensional numerical model. The small-scale turbulence is parameterized using a buoyancy-dependent mixing-length hypothesis. The objective is to understand how the properties and dynamics of such rolls depend upon the relative importance of shear and buoyancy forces. 相似文献
20.
A model for the time and space variation of the internal boundary-layer height over a land area with an irregular coastline is presented. It is based on the analytical model of the boundary-layer height proposed by Gryning and Batchvarova (1990) and Batchvarova and Gryning (1991), The model accounts for the temperature jump and the mean vertical air motion at the top of the internal boundary-layer. Four cases from experiments in Nanticoke and Vancouver are used for model validation. The agreement between the calculated and measured internal boundary layer height at the observational sites is fairly good. The input information for the model consist of wind speed and direction, friction velocity and kinematic heat flux in time and space for the area, and the potential temperature gradient and the mean vertical air motion above the internal boundary layer. For the experiments used in the validation the effect of subsidence is relatively important in the afternoon under low wind speed high pressure conditions, lowering the height of the internal boundary layer by up to 10%, and it is negligible in the morning hours. The effect of the mixing height over the sea is found to be negligible. 相似文献