共查询到20条相似文献，搜索用时 31 毫秒
1.
Ankur R. Desai Kenneth J. Davis Christoph J. Senff Syed Ismail Edward V. Browell David R. Stauffer Brian P. Reen 《Boundary-Layer Meteorology》2006,119(2):195-238
The atmospheric boundary-layer (ABL) depth was observed by airborne lidar and balloon soundings during the Southern Great Plains 1997 field study (SGP97). This paper is Part I of a two-part case study examining the relationship of surface heterogeneity to observed ABL structure. Part I focuses on observations. During two days (12–13 July 1997) following rain, midday convective ABL depth varied by as much as 1.5 km across 400 km, even with moderate winds. Variability in ABL depth was driven primarily by the spatial variation in surface buoyancy flux as measured from short towers and aircraft within the SGP97 domain. Strong correlation was found between time-integrated buoyancy flux and airborne remotely sensed surface soil moisture for the two case-study days, but only a weak correlation was found between surface energy fluxes and vegetation greenness as measured by satellite. A simple prognostic one-dimensional ABL model was applied to test to what extent the soil moisture spatial heterogeneity explained the variation in north–south ABL depth across the SGP97 domain. The model was able to better predict mean ABL depth and variations on horizontal scales of approximately 100 km using observed soil moisture instead of constant soil moisture. Subsidence, advection, convergence/divergence and spatial variability of temperature inversion strength also contributed to ABL depth variations. In Part II, assimilation of high-resolution soil moisture into a three-dimensional mesoscale model (MM5) is discussed and shown to improve predictions of ABL structure. These results have implications for ABL models and the influence of soil moisture on mesoscale meteorology 相似文献
2.
The need for a well-defined lower boundary condition for atmospheric numerical models is well documented. This paper describes the formulation of a land surface parameterization, which will be used in atmospheric boundary-layer and mesoscale numerical models. The land surface model has three soil layers for the prediction of soil moisture and soil temperature. Model soil properties depend on soil texture and moisture content. A homogeneous distribution of vegetation is also included, so that transpiration may be included, as well as the interception of precipitation by vegetation elements. The simulated vegetation also affects the mean surface albedo and roughness characteristics.First ISLSCP Field Experiment (FIFE) data are used to verify the model. Three cases during the growing season were chosen, each case having different amounts of vegetation cover. Stand alone simulations, where observations of atmospheric and radiation variables are input to the land surface model, were performed. These simulations show that the model is able to reproduce observed surface energy budgets and surface temperatures reasonably well. The RMS differences between modeled and obsered turbulent fluxes of heat and moisture are quite comparable to those reported by more detailed land surface models. 相似文献
3.
We investigate the cumulative added value of assimilating temperature, moisture, and wind observations in the three-dimensional non-hydrostatic Fifth-Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model MM5 and use these forecasts to analyze the relationship between surface forcing and planetary boundary-layer (PBL) depth. A data assimilation methodology focused on the surface and the PBL, previously tested in a one-dimensional version of MM5, is applied to 29 May, 6 June, and 7 June 2002 during the International $\hbox {H}_{2}\hbox {O}$ Project over the Southern Great Plains. Model-predicted PBL depth is evaluated against PBL depth diagnosed from data across 4,800 km of airborne lidar data (flight tracks 100–300 km long). The forecast with data assimilation verifies better against observations and is thus used to investigate the environmental conditions that govern PBL depth. The spatial structure in PBL depth is found to be most affected by spatial variations in surface buoyancy flux and capping inversion strength. The spatial scales of surface flux forcing reflected in the PBL depth are found through Fourier analysis and multiresolution decomposition. Correlations are ${<}0.50$ at scales of 64 km or less and increase at larger scales for 29 May and 6 June, but on 7 June low correlations are found at all scales, possibly due to greater within-PBL wind speeds, a stronger capping inversion on this day, and clouds. The results suggest a minimum scale, a function of wind speed, below which heterogeneity in surface buoyancy fluxes is not reflected directly in PBL depth. 相似文献
4.
Regional climate simulations in Asia from May 1997 to August 1998 were performed using the Seoul National University regional climate model （SNURCM） and Iowa State University regional climate model （ALT.MM5/LSM）, which were developed by coupling the NCAR/Land Surface Model （LSM） and the Mesoscale Model （MM5）. However, for physical processes of precipitation, the SNURCM used the Grell scheme for the convective parameterization scheme （CPS） and the simple ice scheme for the explicit moisture scheme （EMS）, while the ALT.MM5/LSM used the Betts-Miller scheme for CPS and the mixed phase scheme for EMS.
The simulated precipitation patterns and amounts over East Asia for the extreme climatic summer in 1997 （relative drought conditions） and 1998 （relative flood conditions） were especially focused upon. The ALT.MM5/LSM simulated more precipitation than was observed in 1997 due to more moisture and cloud water in the lower levels, despite weak upward motion. In the SNURCM, strong upward motion resulted in more precipitation than that was observed in 1998, with more moisture and cloud water in the middle levels. In the ALT.MM5/LSM, weak upward motion, unchanged moisture in the lower troposphere, and the decrease in latent heat flux at the surface increased convective precipitation only by 3% for the 1998 summer event. In the SNURCM, strong upward motion, the increase in moisture in the lower troposphere, and the increase in latent heat flux at the surface increased convective precipitation by 48% for the summer of 1998. The main differences between both simulations were moisture availability and horizontal momentum transport in the lower troposphere, which were also strongly influenced by large-scale forcing. 相似文献
The simulated precipitation patterns and amounts over East Asia for the extreme climatic summer in 1997 （relative drought conditions） and 1998 （relative flood conditions） were especially focused upon. The ALT.MM5/LSM simulated more precipitation than was observed in 1997 due to more moisture and cloud water in the lower levels, despite weak upward motion. In the SNURCM, strong upward motion resulted in more precipitation than that was observed in 1998, with more moisture and cloud water in the middle levels. In the ALT.MM5/LSM, weak upward motion, unchanged moisture in the lower troposphere, and the decrease in latent heat flux at the surface increased convective precipitation only by 3% for the 1998 summer event. In the SNURCM, strong upward motion, the increase in moisture in the lower troposphere, and the increase in latent heat flux at the surface increased convective precipitation by 48% for the summer of 1998. The main differences between both simulations were moisture availability and horizontal momentum transport in the lower troposphere, which were also strongly influenced by large-scale forcing. 相似文献
5.
J. Sanjay 《Boundary-Layer Meteorology》2008,129(1):159-177
Data collected during the Land Surface Processes Experiment (LASPEX) in a semi-arid region of the state of Gujarat in north-west
India for a clear sky day (16 May 1997) are used to assess the performance of the atmospheric boundary-layer (ABL) and land-
surface parameterizations in the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR)
Mesoscale Model (MM5). The ABL turbulence parameterizations examined are the Blackadar scheme coupled to a simple soil slab
model (SSM), and the Troen-Mahrt scheme coupled to SSM or to the more sophisticated Noah land-surface model (NSM). The comparison
of several two-way nested high resolution (9-km) MM5 short term 24-h simulations indicate that, although the model is able
to capture the trend in the observed data, the computed results deviate from observations. The NSM with a modest treatment
of vegetation outperforms the SSM in capturing the observed daily variations in surface heat fluxes and aspects of ABL structure
over the tropical land surface at local scales. Detailed analysis showed that, with the incorporation of observed local vegetation
and soil characteristics, the NSM reproduced a realistic surface energy balance and near-surface temperature. It is further
found that the coupling of the NSM with the Troen-Mahrt ABL scheme leads to excessive ABL mixing and a dry bias in the model
simulations. 相似文献
6.
Summary ¶This paper deals with the systematic evolution of the North American monsoon system by analyzing the evolution of tropospheric circulation, precipitation, moisture fluxes and the adjoining sea surface temperatures from observations and the Florida State University Nested Regional Spectral Model embedded within a coupled atmosphere–ocean coupled model. The atmospheric part is a global spectral model with triangular truncation T63 and a nested regional spectral model. The global atmospheric model is coupled with the Hamburgs Global Ocean Model. This model was integrated for six-months with 50km resolution in the North American monsoon domain. The NCEP/NCAR reanalysis were used as the observed state for comparison. The analyzed model results shows that the above model has the capability of capturing some of the features of the North American monsoon system. Besides the evolution of the monsoon system, the out-of-phase relationship between the Mexican monsoon with south-central United States precipitation and the largest moisture supply from the Gulf of Mexico are the principal findings of this study. It is also noted that during the mature phase of the monsoon, the Gulf of California and the Pacific Ocean dominates the Gulf of Mexico in order of moisture supply but immediately after the mature phase, the Gulf of Mexico dominates.Received January 18, 2002; accepted July 7, 2002
Published online: June 12, 2003 相似文献
7.
A regional scale (a few km to a few hundred km, minutes to days)planetary boundary layer (PBL) numerical model (RPBLM) has been successfully developed to simulateprecisely the boundary-layer three-dimensional characteristics. The RPBLM model with a high-resolutionnon-hydrostatic E - turbulence closure scheme has been applied to diagnose and prognosticate the PBL characteristicsover a complex underlying surface in the Hong Kong area of 60 km × 48 km. It is shown that the RPBLMmodel can be used to simulate the PBL characteristics including wind, temperature, water vapour andturbulence over such a complex underlying surface and that the simulated result is reasonably in agreementwith observations. 相似文献
8.
UNCERTAINTY IN THE SPECIFICATION OF SURFACE CHARACTERISTICS: A STUDY OF PREDICTION ERRORS IN THE BOUNDARY LAYER 总被引：1，自引：0，他引：1
The effects of uncertainty in the specification of surface characteristics on simulated atmospheric boundary layer (ABL) processes and structure were investigated using a one-dimensional soil-vegetation-boundary layer model. Observational data from the First International Satellite Land Surface Climatology Project Field Experiment were selected to quantify prediction errors in simulated boundary-layer parameters. Several numerical 12-hour simulations were performed to simulate the convective boundary-layer structure, starting at 0700 LT 6 June 1987.In the control simulation, measured surface parameters and atmospheric data were used to simulate observed boundary-layer processes. In the remaining simulations, five surface parameters – soil texture, initial soil moisture, minimum stomatal resistance, leaf area index, and vegetation cover – were varied systematically to study how uncertainty in the specification of these surface parameters affects simulated boundary-layer processes.The simulated uncertainty in the specification of these five surface parameters resulted in a wide range of errors in the prediction of turbulent fluxes, mean thermodynamic structure, and the depth of the ABL. Under certain conditions uncertainty in the specifications of soil texture and minimum stomatal resistance had the greatest influence on the boundary-layer structure. A lesser but still moderately strong effect on the simulated ABL resulted from (1) a small decrease (4%) in the observed initial soil moisture (although a large increase [40%] had only a marginal effect), and (2) a large reduction (66%) in the observed vegetation cover. High uncertainty in the specification of leaf area index had only a marginal impact on the simulated ABL. It was also found that the variations in these five surface parameters had a negligible effect on the simulated horizontal wind fields. On the other hand, these variations had a significant effect on the vertical distribution of turbulent heat fluxes, and on the predicted maximum boundary-layer depth, which varied from about 1400–2300 m across the 11 simulations. Thus, uncertainties in the specification of surface parameters can significantly affect the simulated boundary-layer structure in terms of meteorological and air quality model predictions. 相似文献
9.
On the contribution of atmospheric moisture to dew formation 总被引：4，自引：0，他引：4
The relative contributions of dewfall (a flux of water vapour from air to surface) and distillation (a flux of water vapour from soil to canopy) to dew formation on closed canopy and bare soil surfaces are assessed, and the dependence of dew amount upon wind speed, absolute temperature, atmospheric stability, relative humidity, soil characteristics and cloudiness, all of which are significant factors, is evaluated. Some of these evaluations provide refinements to similar ones given in Monteith (1961). High dewfall rates are usually 0.06 mm hr–1 over canopy or bare soil, though upon a canopy under soil-saturated and air-saturated conditions, rates of dew formation may reach 0.07–0.09 mm hr–1 with contributions from distillation. Various sets of observations are reanalyzed to illustrate the importance of the horizontal advection of moisture in the nocturnal boundary layer (NBL) to observed high rates of dew formation arising from the atmospheric contribution of water vapour (dewfall). These locally observed high dewfall rates must be the result of small-scale or mesoscale horizontal advection of moisture in the NBL, since the humidity changes within the typically shallow NBL required to balance the loss of water at the surface are not observed. Over extensive areas of uniform surface (horizontal scales 10 km), such continuously high dewfall rates could only be balanced by a local supply of atmospheric moisture since advection of moisture would necessarily be small. 相似文献
10.
The difficulties associated with the parameterization of turbulence in the stable nocturnal planetary boundary layer (PBL)
have been a great challenge for the nighttime predictions from mesoscale meteorological models such as MM5. As such, there
is a general consensus on the need for better stable boundary-layer parameterizations. To this end, two new turbulence parameterizations
based on the measurements of the Vertical Transport and Mixing (VTMX) field campaign were implemented and evaluated in MM5.
A unique aspect of this parameterization is the use of a stability-dependent turbulent Prandtl number that allows momentum
to be transported by the internal waves, while heat diffusion is impeded by the stratification. This improvement alleviates
the problem of over-prediction of heat diffusion under stable conditions, which is a characteristic of conventional atmospheric
boundary-layer schemes, such as the Medium Range Forecast (MRF) and Blackadar schemes employed in MM5. The predictions made
with the new PBL scheme for the complex terrain airshed of Salt Lake City were compared with those made with a default scheme
of MM5, and with observations made during the VTMX campaign. The new schemes showed an improvement in predictions, particularly
for the nocturnal near-surface temperature. Surface wind predictions also improved slightly, but not to the extent of temperature
predictions. The default MRF scheme showed a significantly higher surface temperature than observed, which could be attributed
to the enhanced vertical heat exchange brought about by its turbulence parameterization. The modified parameterizations reduced
the surface sensible heat flux, thus enhancing the strength of the near-surface inversion and lowering the temperature towards
the observed values. 相似文献
11.
12.
城市化对珠江三角洲强雷暴天气的可能影响 总被引：17，自引：5，他引：17
通过对2004年8月11日午后发生在珠江三角洲地区的一次强雷暴天气的高分辨数值模拟，研究了城市化发展可能对雷暴活动的影响问题，主要考察了与城市土地利用类型改变相关的“城市热岛”的形成和演变特征，城区粗糙度增大可能引起的低层辐合的增强过程，及其与雷暴发展强度变化的关系。结果表明:模拟的雷暴发展和演变过程与这一地区城市化的发展有密切的联系。引进了更加真实的关于珠江三角洲地区的土地利用类型资料之后，耦合了陆面模式Noah LSM的MM5模式可以更加成功地模拟出强雷暴天气的发展和演变过程。雷暴系统移经主要城市区后在珠江口西岸的增强过程与这一地区“城市热岛”的效应有关。中午时热岛开始形成于广州城区的上空，之后向南移动，范围扩大。另外，城区粗糙度增大引起的低层辐合增强可能在雷暴发展和演变过程中也起到了作用。模拟的与城市影响有关的低层辐合主要位于500 m以下的近地面层，开始时形成于城市的上风方向，并在下风方向增强， 由此引起的强烈上升运动有利于新的对流的启动和发展，促使雷暴强度增强。 相似文献
13.
藏北高原地表能量和边界层结构的数值模拟 总被引：2，自引：1，他引：1
利用耦合了NCAR LSM陆面过程的中尺度模式MM5V3.7和2002年8月CAMP/Tibet加强期的观测资料,对藏北高原地区地气交换过程进行了48 h模拟研究。模式较好地模拟了该地区的山谷风环流;并将模拟的地表通量在中尺度区域上与NCEP/NCAR全球大气再分析格点资料(NNRP)获得的结果进行了比较,同时也与单站的实测值进行了比较,结果显示:模拟的地表通量与NNRP得到的结果比较吻合,同时可以得到雨季时藏北、藏东地区潜热通量大于感热通量,而高原西部感热通量大于潜热通量,这与观测试验分析结果一致;与单站试验结果比较,模拟的感热通量与实测值一致,潜热通量的模拟值和实测值有一定差别。模拟的边界层位温廓线与实测值比较,模式模拟的对流混合层和夜间残留层都与实测结果吻合,但模拟的混合层高度较实测值高。由此来看,中尺度模式MM5V3.7能够较好地模拟藏北高原的地表能量和边界层结构特征,但还需要进一步完善陆面过程和物理过程参数化方案。 相似文献
14.
CCM3模式中LSM积雪方案的改进研究(Ⅰ):修改方案介绍及其单点试验 总被引：4，自引：3，他引：1
为了改进美国NCARCCM3全球模式中LSM陆面模型中的积雪方案的模拟效果,在Sun等[1]SAST积雪模型的基础上,作了部分修改后,加进CCM3模式LSM模型中.该方案根据格点区域平均积雪深度的不同,把地面雪盖划分为1到3层不等,能在积雪表层和中间层更好地描述温度的日变化和季节变化;较详细地考虑了雪的热传导、太阳辐射的穿透吸收、雪的融化、液态水的储存、渗透和再冻结等积雪内部的主要物理过程;根据Nimbus-7卫星实测雪深资料修改了积雪覆盖度和雪面反照率的计算方案.利用前苏联6个台站1978-1983年的实测积雪资料和大气强迫数据,进行了单点模拟试验,结果表明,新的积雪参数化方案能够较好地再现积雪深度和雪水当量的逐日和季节变化特征,部分提高了积雪参数化方案对积雪的模拟能力. 相似文献
15.
Yuling Wu Udaysankar S. Nair Roger A. PielkeSr. Richard T. McNider Sundar A. Christopher Valentine G. Anantharaj 《Boundary-Layer Meteorology》2009,133(3):367-389
Prior numerical modelling studies show that atmospheric dispersion is sensitive to surface heterogeneities, but past studies
do not consider the impact of a realistic distribution of surface heterogeneities on mesoscale atmospheric dispersion. While
these focussed on dispersion in the convective boundary layer, the present work also considers dispersion in the nocturnal
boundary layer and above. Using a Lagrangian particle dispersion model (LPDM) coupled to the Eulerian Regional Atmospheric
Modeling System (RAMS), the impact of topographic, vegetation, and soil moisture heterogeneities on daytime and nighttime
atmospheric dispersion is examined. In addition, the sensitivity to the use of Moderate Resolution Imaging Spectroradiometer
(MODIS)-derived spatial distributions of vegetation characteristics on atmospheric dispersion is also studied. The impact
of vegetation and terrain heterogeneities on atmospheric dispersion is strongly modulated by soil moisture, with the nature
of dispersion switching from non-Gaussian to near-Gaussian behaviour for wetter soils (fraction of saturation soil moisture
content exceeding 40%). For drier soil moisture conditions, vegetation heterogeneity produces differential heating and the
formation of mesoscale circulation patterns that are primarily responsible for non-Gaussian dispersion patterns. Nighttime
dispersion is very sensitive to topographic, vegetation, soil moisture, and soil type heterogeneity and is distinctly non-Gaussian
for heterogeneous land-surface conditions. Sensitivity studies show that soil type and vegetation heterogeneities have the
most dramatic impact on atmospheric dispersion. To provide more skilful dispersion calculations, we recommend the utilisation
of satellite-derived vegetation characteristics coupled with data assimilation techniques that constrain soil-vegetation-atmosphere
transfer (SVAT) models to generate realistic spatial distributions of surface energy fluxes. 相似文献
16.
Alexander C. Taylor Robert J. Beare David J. Thomson 《Boundary-Layer Meteorology》2014,153(3):389-407
We investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows ‘lofting’ of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent ‘trapping’ of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer. 相似文献
17.
利用国际协同强化观测期(CEOP)在中国半干旱区退化草地站——通榆站的观测资料,对一个较为完善的陆面过程模式NCAR_CLM4.5(Community Land Model 4.5)的模拟性能进行检验。模拟结果与观测资料的对比表明,CLM4.5能很好地模拟出观测站点的辐射通量、水热交换、土壤温湿的空间分布和时间变化特征。但地表吸收的辐射模拟值略低,土壤湿度偏低,地表吸收的辐射及土壤温度等日变化略大;大气强迫变量处于某些特定的形势下时,模拟存在较大误差,如8月底的模拟。此外,冬季辐射通量、水热交换以及土壤温湿的模拟均存在较大误差,说明CLM4.5模式在冬季地表物理过程的参数化方案上需要进一步改进。 相似文献
18.
We investigate the effect of the assimilation of surface and boundary-layer mass-field observations on the planetary boundary
layer (PBL) within a one-dimensional (1D) version of the non-hydrostatic Fifth-Generation Pennsylvania State University/National
Center for Atmospheric Research Mesoscale Model (MM5). We focus on the vertical extent and effects of mass-field nudging within
the PBL based on surface observations, and the added value of assimilating column mass observations within the PBL. Model
experiments for dynamic initialization and dynamic analysis are conducted and composited for 29 May, 6 June, and 7 June 2002
during the International H2O Project (IHOP) over the Southern Great Plains, U.S.A. Advantages are found when the data assimilation uses the innovation
(the difference between the modelled value and the observed value) calculated by comparing the surface mass-field observation
to the model value at the 2-m observation height rather than at the lowest model level. It is shown that this innovation can
be applied throughout the model-diagnosed PBL via nudging during free-convective conditions because of the well-mixed nature
of the PBL. However, in stable conditions, due to decreased vertical mixing the surface innovation may be best applied only
in a shallow layer adjacent to the surface. Surface air-temperature innovations were also applied to the top soil-layer temperature
to minimize disruption to the surface energy balance. In combination with the surface observations, the use of within-PBL
mass-field data assimilation improves the simulated PBL structure. 相似文献
19.
A regional mesoscale multi-level primitive equation model is used to predict the landfall and structure of a tropical cyclone. Three areas of model sensitivity are addressed in this paper; (1) the horizontal resolution, which includes the representation of orography; (2) the impact of an improved representation of the distribution of land surface soil moisture on the landfall problem; and (3) the sensitivity of the storm to lateral boundary conditions. A diagnostic part of this study describes a statistical regression approach to determining a ground wetness parameterization from moisture budget computations to derive estimates of surface fluxes, which are used to determine the parameterization. The model sensitivity analysis compares several versions of ground wetness parameterization. The experiment where perfect (i.e., based on analysis of observations) boundary conditions are used is defined as a bench-mark. At the highest horizontal resolution (=50km) using the ground wetness obtained from the regression, the best results were found for the structure and motion of the tropical cyclone. When the boundary conditions from a global model are used at a resolution T106 (roughly 100 km resolution for the transformed grid), the results degrade somewhat. The rain bands are predicted, but do not contain the same detail. Several other sensitivity experiments illustrate the degree of degradation of rain bands, precipitation distribution, hurricane structure, and phase speed errors as the lateral boundaries, resolution, and ground wetness parameterization are altered. 相似文献
20.
We compare the results of a local and a nonlocal scheme for vertical diffusion in the atmospheric boundary layer with observations at the 200 m tower at Cabauw. This is done for a 12 h period during daytime on 31 May 1978, which is characterised by strong insolation, clear skies, moderately strong winds and weak advection. The local diffusion scheme uses an eddy diffusivity determined independently at each point along the vertical based on local vertical gradients of wind and virtual potential temperature, similar to the usual approach in atmospheric models. The nonlocal scheme determines an eddy diffusivity profile based on a diagnosed boundary-layer height and a turbulent velocity scale. It also incorporates nonlocal (vertical) transport effects for heat and moisture. The boundary-layer diffusion schemes are forced with the locally observed fluxes for heat and moisture. The outputs of the scheme are compared with the observed mean structure along the Cabauw tower, and the radiosonde profile at a nearby location (De Bilt). Overall, the nonlocal scheme transports moisture away from the surface more rapidly than the local scheme, and deposits the moisture at higher levels. The local scheme tends to saturate the lowest model levels unrealistically in comparison with the observations. We also compare the outputs of the two diffusion schemes with the results of a transilient model simulation. Subsequently, we study the impact on the model behaviour by varying important parameters in both diffusion schemes and we investigate the sensitivity to uncertainty in the environmental conditions. Finally, we study the interaction of the diffusion schemes with a simple surface flux scheme. 相似文献