Improving the vegetation dynamic simulation in a land surface model by using a statistical-dynamic canopy interception scheme     

梁妙玲  谢正辉 《大气科学进展》2008,25(4):610-618

Canopy interception of incident precipitation, as a critical component of a forest＇s water budget, can affect the amount of water available to the soil, and ultimately vegetation distribution and function. In this paper, a statistical-dynamic approach based on leaf area index and statistical canopy interception is used to parameterize the canopy interception process. The statistical-dynamic canopy interception scheme is implemented into the Community Land Model with dynamic global vegetation model （CLM-DGVM） to improve its dynamic vegetation simulation. The simulation for continental China by the land surface model with the new canopy interception scheme shows that the new one reasonably represents the precipitation intercepted by the canopy. Moreover, the new scheme enhances the water availability in the root zone for vegetation growth, especially in the densely vegetated and semi-arid areas, and improves the model＇s performance of potential vegetation simulation.  相似文献   

Variation of the Sectional Drag Coefficient of a Group of Buildings with Packing Density   总被引：2，自引：2，他引：0  

J. L. Santiago  O. Coceal  A. Martilli  S. E. Belcher 《Boundary-Layer Meteorology》2008,128(3):445-457

Reynolds-averaged Navier–Stokes (RANS) simulations of turbulent flow over groups of buildings with different packing densities are reported. The results for a selected packing density are compared with direct numerical simulations (DNS) previously validated against wind-tunnel data. The present study is focused on average properties of the flow, especially on the drag coefficients, and is a first attempt to provide information on these parameters (their values are not generally known) for a range of packing densities, for a given staggered arrangement of cubes using RANS methods. However, some of the limitations of RANS have come to light. Hence, it is recommended that such simulations are ‘calibrated’ against experimental or DNS data, as is done here.  相似文献   

鱼眼影像技术反演植被冠层结构参数的研究进展   总被引：1，自引：0，他引：1  

姚克敏  胡凝  吕川根  黄凤新 《南京气象学院学报》2008,31(1):139-144

快速、可靠、精确的评估植被冠层结构参数在大气一植被相互作用的研究中起着举足轻重的作用。从冠层结构参数的反演原理、冠层间隙度的提取、冠层结构的反演模型和丛生指数3个方面论述了冠层结构参数即叶面积指数（LAI,leaf area index）和叶倾角分布（LAD,leaf angle distribution）的反演方法,并从鱼眼像片的采集、分析和模型的假设等方面分析影响冠层结构参数反演精度的原因,指出未来鱼眼影像技术虽然是LAI和LAD间接测量的理想手段,但是受观测环境、相机光学特性和冠层本身的影响,反演结果需要通过验证来消除不确定因素。  相似文献   

The Influence of the City of Athens on the Evolution of the Sea-Breeze Front   总被引：1，自引：0，他引：1  

Aggeliki Dandou  Maria Tombrou  Nikolaos Soulakellis 《Boundary-Layer Meteorology》2009,131(1):35-51

In the present study, we examine the dynamics of a sea-breeze front and the urban heat island interacting with the heavily urbanized city of Athens. For this reason, simulations were performed with a modified version of the PSU/NCAR Mesoscale Model (MM5), whereby urban features are considered, and the model results were compared with surface routine meteorological data. An unrealistic run was also performed, where the city of Athens was replaced by dry cropland and pasture surface, as in the surrounding area. A delay in the sea-breeze front was found during daytime, together with frictional retardation concerning its penetration, as well as inland displacement of the heat island as the air moved over the city of Athens. During nighttime, the wind speed increased over the lower atmosphere in the city centre due to the enhanced urban heat island.  相似文献   

Exploring the Effects of Microscale Structural Heterogeneity of Forest Canopies Using Large-Eddy Simulations   总被引：4，自引：4，他引：0  

Gil Bohrer  Gabriel G. Katul  Robert L. Walko  Roni Avissar 《Boundary-Layer Meteorology》2009,132(3):351-382

The Regional Atmospheric Modeling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES), developed and evaluated here, is used to explore the effects of three-dimensional canopy heterogeneity, at the individual tree scale, on the statistical properties of turbulence most pertinent to mass and momentum transfer. In RAFLES, the canopy interacts with air by exerting a drag force, by restricting the open volume and apertures available for flow (i.e. finite porosity), and by acting as a heterogeneous source of heat and moisture. The first and second statistical moments of the velocity and flux profiles computed by RAFLES are compared with turbulent velocity and scalar flux measurements collected during spring and winter days. The observations were made at a meteorological tower situated within a southern hardwood canopy at the Duke Forest site, near Durham, North Carolina, U.S.A. Each of the days analyzed is characterized by distinct regimes of atmospheric stability and canopy foliage distribution conditions. RAFLES results agreed with the 30-min averaged flow statistics profiles measured at this single tower. Following this intercomparison, two case studies are numerically considered representing end-members of foliage and midday atmospheric stability conditions: one representing the winter season with strong winds above a sparse canopy and a slightly unstable boundary layer; the other representing the spring season with a dense canopy, calm conditions, and a strongly convective boundary layer. In each case, results from the control canopy, simulating the observed heterogeneous canopy structure at the Duke Forest hardwood stand, are compared with a test case that also includes heterogeneity commensurate in scale to tree-fall gaps. The effects of such tree-scale canopy heterogeneity on the flow are explored at three levels pertinent to biosphere-atmosphere exchange. The first level (zero-dimensional) considers the effects of such heterogeneity on the common representation of the canopy via length scales such as the zero-plane displacement, the aerodynamic roughness length, the surface-layer depth, and the eddy-penetration depth. The second level (one-dimensional) considers the normalized horizontally-averaged profiles of the first and second moments of the flow to assess how tree-scale heterogeneities disturb the entire planar-averaged profiles from their canonical (and well-studied planar-homogeneous) values inside the canopy and in the surface layer. The third level (three-dimensional) considers the effects of such tree-scale heterogeneities on the spatial variability of the ejection-sweep cycle and its propagation to momentum and mass fluxes. From these comparisons, it is shown that such microscale heterogeneity leads to increased spatial correlations between attributes of the ejection-sweep cycle and measures of canopy heterogeneity, resulting in correlated spatial heterogeneity in fluxes. This heterogeneity persisted up to four times the mean height of the canopy (h _c ) for some variables. Interestingly, this estimate is in agreement with the working definition of the thickness of the canopy roughness sublayer (2h _c –5h _c ).  相似文献   

荔枝越冬期间冠层气温与大气温度关系的初步分析   总被引：2，自引：0，他引：2  

谭宗琨  何鹏  尤明双  杨鑫  欧钊荣  黄兴春 《气象》2009,35(12):102-108

基于野外实测数据,按晴天、阴天、雨天、多云到晴等天气类型,分析2007/2008年、2008/2009年冬季荔枝果园大气温度、冠层气温与观测站大气温度的变化关系,结果表明:晴天荔枝冠层温度昼夜变化最为剧烈,多云到晴天气次之,阴天和雨天冠层大气温度变化相对平缓;果园和观测站大气温度昼夜变化同样与天气类型有关.按天气类型分别建立的观测站与荔枝冠层之间的夜间、白天和全天大气温度线性、曲线回归关系模型表明:阴天和雨天模型效果好于多云到晴、晴天天气,夜间模型好于全天和白天.这一结果对应用观测站大气温度开展荔枝寒害冻害监测有参考作用.  相似文献   

城市建筑物动力冠层方案的引入及应用研究     

周荣卫  蒋维楣  何晓凤 《气象学报》2010,68(1):137-146

文中将建筑物动力冠层方案引入到城市边界层精细模式中,该方案描叙了城市地Ⅸ建筑物对气流的拖曳作用以及建筑物形态对城市地区湍流活动动量输送的影响.采用建筑物拖曳法和建筑物动力冠层方案两种不同建筑物动力学处理方法对北京地区东南部进行模拟,通过城市地区水平风速的模拟结果与自动气象站实测资料对比发现模拟结果与实测相当吻合,建筑物动力冠层方案的引入能够更好地实施对城市地区的水平风速分布的数值模拟.分别采用建筑物拖曳法与建筑物动力冠层方案对一个实际小规模城市进行模拟试验,分析表明引入建筑物动力冠层方案可以模拟出小规模城市地区水平风速偏低的现象;还可以模拟出城市地区建筑物动力作用对湍流活动的影响;对湍流动能模拟结果表明比较符合实际分布情形.采用建筑物动力冠层方案对小规模城市地区建筑物高度变化对城市地区的流场及湍流活动的影响进行模拟分析,结果表明:城市地区建筑物高度增加,风速变小,但是高大建筑物底部风速略高于低矮建筑物底部;城市地区大气湍能增加,高大建筑物底部湍能较小,冠层高度内湍能随高度增加而增加;同时城市地Ⅸ的垂直扩散系数也随建筑物高度增加而增加;城市地区污染物排放高度处污染物浓度较低,下游乡村地区地面污染物浓度较低,但高空污染物浓度却较高.  相似文献   

植物冠层动量交换特征的实验研究   总被引：2，自引：1，他引：2       下载免费PDF全文

雷孝恩  田瑞明  韩志伟 《大气科学》1995,19(6):747-754

使用湍流梯度测试资料，对植物冠层动量交换特征进行了详细研究，结果表明:森林冠层内惯性副区能谱曲线仍可用幂指数描述，但斜率比-2/3更负；森林冠层内湍流尺度有变小的趋势；森林上层的耗散系数比下层大；由植被吸收引起动量及动量通量随冠层深度增加而明显减小；冠层下层的动量通量和耗散系数分别与上层的量有好的正相关；森林冠层内耗散系数和动量通量随大气稳定度有明显变化。  相似文献   

DETERMINATION OF AERODYNAMIC PARAMETERS OF CROP CANOPIES WITH A CENTER-OF-PRESSURE METHOD          下载免费PDF全文

Qin Wenhan 《Acta Meteorologica Sinica》1995,9(1):78-86

Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,thecenter-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.Aphysically-based model for directly calculating zero-displacement height (d) is derived.The comparison between thefriction velocity (u_*) estimated with CPM and that with eddy correlation technique shows that CPM not only works wellin the field,but also produces more steady and accurate estimates of aerodynamic parameters (which are hardly affectedby atmospheric thermal stability),than those with the widely-used log-profile fitting method in diabatic atmosphere.The results presented in this paper also demonstrate that the ratios of d,z_0 to crop height h usually vary with canopy ar-chitecture,atmospheric stratification and turbulent exchange intensity,and are not just constants as commonly assumedor used.d/h raises with an increase of relative height of the maximum foliage layer and wind extinction coefficientwithin the canopy.Only for crops with short stem and moderate foliage density,can the relations d= 0.64h,z_0=0.08hkeep stable.In addition,for long stem crops or sparse canopies,the fairly large shear stress at the soil surface and the va-riation of the exponent in the relationship between drag coefficient and wind speed undoubtedly influence the accuracyof CPM to a certain extent.  相似文献   

应用随机辐射传输模型反演云南松林分郁闭度   总被引：1，自引：0，他引：1  

李骁尧  黄华国 《遥感学报》2020,24(6):752-765

随机辐射传输模型可用于模拟水平分布不均一森林的辐射传输过程。本文以云南松林分为研究对象，提出一种应用随机辐射传输模型的郁闭度反演方法。该方法以随机辐射传输模型中参数与林分郁闭度的定量关系为基础，提出了针对云南松的冠型等效模型，构建了郁闭度和卫星反射率（GF-1和Landsat 8卫星影像）的查找表，并实施了反演。基于野外实测的30个样地进行了郁闭度数据验证，并和基于NDVI回归模型的反演方法进行对比。结果表明，反演结果能够较准确反映云南松林分郁闭状况（R²=0.8345，RMSE=0.0688），通过冠型修正能够降低反演误差，冠型等效模型是合理的。反演方法机理清晰且适用范围广，研究成果可为大面积森林郁闭度反演提供模型和方法支持。  相似文献