SENSITIVITY TESTS OF INTERACTION BETWEEN LAND SURFACE PHYSICAL PROCESS AND ATMOSPHERIC BOUNDARY LAYER*

In this paper,an interactive model between land surface physical process and atmosphere boundary layer is established,and is used to simulate the features of soil environmental physics,surface heat fluxes,evaporation from soil and evapotranspiration from vegetation and structures of atmosphere boundary layer over grassland underlying.The sensitivity experiments are engaged in primary physics parameters.The results show that this model can obtain reasonable simulation for diurnal variations of heat balance,soil volumetric water content,resistance of vegetation evaporation,flux of surface moisture,and profiles of turbulent exchange coefficient,turbulent momentum,potential temperature,and specific humidity.The model developed can be used to study the interaction between land surface processes and atmospheric boundary layer in city regions,and can also be used in the simulation of regional climate incorporating a mesoscale model.     

Radiative Processes in the Stable Boundary Layer: Part I. Radiative Aspects

The structure of the radiatively dominated stable boundary layer is analysed using idealized calculations at high vertical and spectral resolution. The temperature profile of a nocturnal radiative boundary layer, developing after the evening transition, is found to be well described in terms of radiative cooling to the surface, although radiative exchanges within the atmosphere become increasingly important with time. The treatment of non-black surfaces is discussed in some detail and it is shown that the effect of reducing the surface emissivity is to decrease rather than to increase the radiative cooling rate in the surface layer. It is also argued that an accurate assessment of the impact of non-black surfaces requires careful attention to the spectral and directional characteristics of the surface emissivity. A polar nocturnal boundary layer, developing above snow-covered ground, is simulated and found to reach a slowly evolving state characterized by a strong radiative divergence near the surface that is comparable to observed values. Radiative boundary layers are characterized by large temperature gradients near the surface. An erratum to this article can be found at     

南京地区大气边界层晴空回波研究

以2005年6月23日南京多普勒雷达探测的晴空回波演变为例,分析了回波反射率与径向速度从夜间至上午的演变规律,利用实际的气象观测资料,对比了折射指数、地面温度、露点温度、水汽压和气压与回波强度的相关性,进一步探讨了边界层晴空回波与湍流混合特性之间的关系.研究表明:夜间大气的温、压、湿梯度使湍流出现,但湍流未充分混合使梯度维持,并导致折射指数的梯度增加,出现晴空回波;白天升温后湍流的增强使近地层大气充分混合,温、压、湿梯度减弱导致折射指数梯度减小,回波减弱消失.     

北太平洋海温与次年盛夏副热带高压的遥相关响应

选取1952-2005年北太平洋月平均海表温度（SST）资料，经过奇异值分解分析表明：6月份日界线附近西风漂流区的海温集中了北太平洋海温场的主要信息，西风漂流区与赤道冷水区的海温存在遥相关震荡，并且在6月份达到全年的最高值，11月份其振幅出现次高值。6月西风漂流区的海温（SST）可视为来年盛夏（7-8月）西太平洋副热带高压的强弱变化的信号：当6月份西风漂流区的海温（SST）偏低，则来年盛夏西太平洋副热带高压偏强；反之，则来年盛夏西太平洋副热带高压偏弱。     

Countergradient Fluxes of Conserved Variables in the Clear convective and Stratocumulus-topped Boundary Layer: The role of the Entrainment Flux

Large-eddy simulations of a clear convective boundary layer (CBL)and a stratocumulus-topped boundary layer are studied. Bottom-upand a top-down scalars were included in the simulations, and theprinciple of linear superposition of variables was applied toreconstruct the fields of any arbitrary conserved variable.This approach allows a systematic analysis of countergradient fluxesas a function of the flux ratio, which is defined as the ratio betweenthe entrainment flux and the surface flux of the conserved quantity.In general, the turbulent flux of an arbitrary conserved quantityis counter to the mean vertical gradient if the heights where thevertical flux and the mean vertical gradient change sign do notcoincide. The regime where the flux is countergradient is thereforebounded by the so-called zero-flux and zero-gradient heights. Becausethe vertical flux changes sign only if the entrainment flux has anopposite sign to the surface flux, countergradient fluxes arepredominantly found for negative flux ratios. In the CBL the fluxratio for the virtual potential temperature is, to a good approximation,constant, and equal to -0.2. Only if the moisture contribution to thevirtual potential temperature is negligibly small will the flux ratio forthe potential temperature be equal to this value. Otherwise, theflux ratio for the potential temperature can have any arbitrary(negative) value, and, as a consequence, the fluxes for thepotential temperature and the virtual potential temperature willbe countergradient at different heights. As a practical application ofthe results, vertical profiles of the countergradient correction termfor different entrainment-to-surface-flux ratios are discussed.     

论边界层中的大气扩散PDF模式

基于大气扩散Ｋ理论，用作为风速脉动均方差和拉氏时间尺度函数的湍流交换系数，得到了直接利用风速脉动几率密度而不用扩散参数的大气扩散ＰＤＦ模式。分别研究了对流边界层上升气流区与下降区垂直速度的统计特征，求得双正态ＰＤＦ模式。在给定ＣＢＬ自身参数如对流特征速度ｗ＊，顶高ｈｉ和源高度上的平均风速时，该模式计算出的无量纲浓度分布与室内外测试结果一致。     

青藏高原前期冬春季地面热源与我国夏季降水关系的初步分析

首先对青藏高原地表热通量再分析资料与自动气象站(AWS)实测资料进行对比, 结果表明: 相对于美国国家环境预报中心和国家大气中心20世纪90年代研制的NCEP/NCAR(Kalnay 等1996)和NCEP/DOE (Kanamitsu 等2002) 再分析资料, ECMWF(Uppala 等2004)资料在高原地区的地表热通量具有较好的代表性。进一步利用奇异值分解(SVD)方法分析了ECMWF资料反映的高原地面热源与我国夏季降水的关系, 发现前期青藏高原主体的冬季地面热源与长江中下游地区夏季降水量呈负相关, 与华北和东南沿海地区的夏季降水量呈正相关。而长江中下游地区夏季降水量还与春季高原南部的地面热源存在负相关、与高原北部的地面热源存在正相关。高原冬、春季地面热源场的变化是影响我国夏季降水的重要因子。     

An Observational Study of the Mesoscale Mistral Dynamics

We investigate the mesoscale dynamics of the mistral through the wind profiler observations of the MAP (autumn 1999) and ESCOMPTE (summer 2001) field campaigns. We show that the mistral wind field can dramatically change on a time scale less than 3 hours. Transitions from a deep to a shallow mistral are often observed at any season when the lower layers are stable. The variability, mainly attributed in summer to the mistral/land–sea breeze interactions on a 10-km scale, is highlighted by observations from the wind profiler network set up during ESCOMPTE. The interpretations of the dynamical mistral structure are performed through comparisons with existing basic theories. The linear theory of R. B. Smith [Advances in Geophysics, Vol. 31, 1989, Academic Press, 1–41] and the shallow water theory [Schär, C. and Smith, R. B.: 1993a, J. Atmos. Sci. 50, 1373–1400] give some complementary explanations for the deep-to-shallow transition especially for the MAP mistral event. The wave breaking process induces a low-level jet (LLJ) downstream of the Alps that degenerates into a mountain wake, which in turn provokes the cessation of the mistral downstream of the Alps. Both theories indicate that the flow splits around the Alps and results in a persistent LLJ at the exit of the Rhône valley. The LLJ is strengthened by the channelling effect of the Rhône valley that is more efficient for north-easterly than northerly upstream winds despite the north–south valley axis. Summer moderate and weak mistral episodes are influenced by land–sea breezes and convection over land that induce a very complex interaction that cannot be accurately described by the previous theories.     

太原城市下垫面扩张对边界层特征影响的个例研究

通过高分辨率卫星夜间灯光数据获取最新的城市地表分布,并利用高分辨率数值模式对2013年8月14~16日太原区域的一次高温过程进行研究,探讨城市下垫面扩张对大气边界层的影响。结果表明：基于DMSP/OLS夜间灯光数据对模式中地表参数修正后,能够更准确地反映太原主城区和高速公路沿线小规模建筑群的扩张,有效改善了模式的预报性能,显著提高对近地面气温、地表温度的预报能力。城市下垫面的扩张,使城区夜间升温明显,热岛强度增强。与1992年的城市化状况相比,晴空天气条件下,2012年太原城区夜间气温上升5℃,热岛强度升高2~3℃。城市下垫面扩张,改变了地表能量分配关系,使得地表感热传输明显加强,潜热通量明显减弱,城市冠层作用下的储热能力增强。边界层内部湍流交换、水汽输送等的进一步研究表明：城市地表水汽输送减弱,边界层水汽含量减少,2~4 km高度的水汽含量增加,湍流动能的影响高度增高,湍流混合加剧;14：00,城区边界层高度抬高了800 m,城市上空混合层加深,持续时间更长。