How Many Facets are Needed to Represent the Surface Energy Balance of an Urban Area?

We investigate the question of how many facets are needed to represent the energy balance of an urban area by developing simplified 3-, 2- and 1-facet versions of a 4-facet energy balance model of two-dimensional streets and buildings. The 3-facet model simplifies the 4-facet model by averaging over the canyon orientation, which results in similar net shortwave and longwave balances for both wall facets, but maintains the asymmetry in the heat fluxes within the street canyon. For the 2-facet model, on the assumption that the wall and road temperatures are equal, the road and wall facets can be combined mathematically into a single street-canyon facet with effective values of the heat transfer coefficient, albedo, emissivity and thermodynamic properties, without further approximation. The 1-facet model requires the additional assumption that the roof temperature is also equal to the road and wall temperatures. Idealised simulations show that the geometry and material properties of the walls and road lead to a large heat capacity of the combined street canyon, whereas the roof behaves like a flat surface with low heat capacity. This means that the magnitude of the diurnal temperature variation of the street-canyon facets are broadly similar and much smaller than the diurnal temperature variation of the roof facets. Consequently, the approximation that the street-canyon facets have similar temperatures is sound, and the road and walls can be combined into a single facet. The roof behaves very differently and a separate roof facet is required. Consequently, the 2-facet model performs similarly to the 4-facet model, while the 1-facet model does not. The models are compared with previously published observations collected in Mexico City. Although the 3- and 2-facet models perform better than the 1-facet model, the present models are unable to represent the phase of the sensible heat flux. This result is consistent with previous model comparisons, and we argue that this feature of the data cannot be produced by a single column model. We conclude that a 2-facet model is necessary, and for numerical weather prediction sufficient, to model an urban surface, and that this conclusion is robust and therefore applicable to more general geometries.     

岚县2007年春季一次强降水天气过程初步分析

2007年5月21日08时到22日08时岚县出现的强降水过程,24h雨量36．0mm,是1991年以后岚县5月下旬出现的雨量最大值,由于2007年3月-4月岚县已出现了4次小-中雨过程,这次过程的出现使得地表积水严重,对春播作物的生长带来不利影响。本文从天气形势、云图分析、物理量以及本站要素等方面进行了初步探讨,重点分析吕梁市春季出现强降雨的成因,以求得在县局预报此类天气的思路。     

Impact of Horizontal Resolution and Cumulus Parameterization Scheme on the Simulation of Heavy Rainfall Events over the Korean Peninsula

In this paper, we present the results from high-resolution numerical simulations of three heavy rainfall events over the Korean Peninsula. The numerical results show that the prediction accuracy for heavy rainfall events improved as horizontal resolution increased. The fine-grid precipitation fields were much closer to the real precipitation fields in the case of large synoptic forcing over the Korean Peninsula. In the case of large convective available potential energy and weak synoptic forcing, it seems that even when using a high resolution, the models still showed poor performance in reproducing the observed high precipitation amounts. However, activation of the cumulus parameterization scheme in the intermediate resolution of 9 km, even at a grid spacing of 3 km, had a positive impact on the simulation of the heavy rainfall event.     

Interdecadal Variability in Surface Solar Radiation over Northwest China and Its Possible Cause

The present study investigates the interdecadal variability of seasonal mean surface solar radiation over Northwest China using station observations from 1961-2003. Spring and summer surface solar radiation over Northwest China was lower in the late 1970s through 1990s than in the 1960s through the mid-1970s, and fall and winter surface solar radiation displayed similar patterns. These results indicate that the decrease in spring and summer surface solar radiation may be associated with increased low-cloud cover over Northwest China. Rainfall anomalies were closely related to the low-cloud cover over Northwest China and with the Northern Hemisphere circumglobal teleconnection in spring, summer, and winter.     

一种提高气候模式对PNA年际变化模拟能力的方法

The climate modeling community has been challenged to develop a method for improving the simulation of the Pacific-North America (PNA) teleconnection pattern in climate models. The accuracy of PNA teleconnection simulation is significantly improved by considering mesoscale convection contributions to sea surface fluxes. The variation in the PNA over the past 22 years was simulated by the Grid Atmospheric Model of IAP LASG version 1.0 (GAMIL1.0) model, which was guided by observational sea surface temperature (SST) from January 1979 to December 2000. Results show that heating in the tropical central-eastern Pacific is simulated more realistically, and sea surface latent heat flux and precipitation anomalies are more similar to the reanalysis data when mesoscale enhancement is considered during the parameterization scheme of sea surface turbulent fluxes in GAMIL1.0. Realistic heating in the tropical central-eastern Pacific in turn significantly improves the simulation of interannual variation and spatial patterns of PNA.     

Numerical Simulations of the Physical Process for Hailstone Growth

1. IntroductionTheoretical and experimental studies on the phys-ical processes of hail growth (Schumann, 1938; Lud-lan, 1958; List, 1963) showed that its growth rate andstructural characteristics depend on the heat and masstransfers; its dynamic characteristics determine hail-stone's movement and stay in clouds and damage doneto ground bodies, actually controlling the growth in-side clouds. As we know, the heat transfers affectsdirectly hailstone's wet growth, melting and evapo-ration. In the…     

雨滴谱谱形参数对梅雨降水模拟能力的影响

实际观测表明雨滴谱的谱形参数(μ_r)具有显著的时空分布特征,而微物理参数化方案中往往将其设定为常数。基于WRF 3.5.1模式中的Milbrandt 2-mon(MY)双参数方案,针对四次典型的江淮梅雨降水过程,利用江淮梅雨的实际雨滴谱观测资料结果,分析MY方案中诊断雨滴谱谱形参数的处理方法对梅雨降水模拟效果的影响。结果表明:利用雨滴谱斜率诊断μ_r的处理方式对梅雨降水的系统性偏差有一定的改善能力,对降水落区分布的局地性特征能够发挥一定的修正作用。较强降水对μ_r的完善表现出更显著的改善倾向。耦合经验公式后,μ_r总体增加,对流层中低层的μ_r随降水强度增加而降低。与μ_r直接相关的雨滴质量加权末速度的增加和雨水含水量的减小是改进试验中降水变化的直接原因。环境场的水汽与动力条件的改变是降水变化的重要间接原因,云物质的响应变化以及降水位置强度的宏观特征演变与此密切相关。强弱降水的改善程度的差异主要源于各自物理量场的响应特征的不同。强降水的暖云云物质特征变化趋势虽与弱降水时一致,但变化幅度等差异显著。弱降水时,物理量场对μ_r的响应特征表现出较为一致的变化趋势和一定的线性特征;而强降水条件下,云物理过程以及同环境条件之间的反馈作用更加复杂,冰云和环境场的响应特征往往没有显著规律可循。     

单层不同类型云系统的特性及高云重叠的影响

通过时空匹配主动遥感产品（2B-CLDCLASS-LIDAR）的云类型参数与被动遥感产品（Clouds and the Earth's Radiant Energy System-Single Scanner Footprint: CERES-SSF）的云宏微观物理特性和大气层顶处辐射通量参数（2007/01~2010/12），本文在全球尺度上统计分析了不同类型单层云以及高云重叠的双层云的云特性和大气层顶云辐射强迫。尽管主动和被动卫星遥感产品相互独立，但被动遥感反演的云光学厚度和云相态等参数能够合理反映不同类型云之间的差异。不同类型单层云表现出的云特性差异能进一步影响大气层顶的辐射能量收支。本文通过对比不同类型单层云的Clouds and the Earth's Radiant Energy System（CERES）视场样本数量随短波和长波云辐射强迫的分布，发现它们的高值区形状、位置和面积存在差异，反映了其各自独特的辐射特性。层积云的CERES视场样本数量密集区类似椭球结构，而其它云类型则趋于指数曲线结构。当进一步考虑高云重叠的影响时，统计结果表明:重叠的高云比高云单层状态有更蔽光和更厚的云体；高云重叠的底层云类型则比其单层状态有更透光和更薄的云体；高云重叠的双层云（除了高云重叠积云）对地气系统的净冷却效应要弱于其低层云类型单层状态。本文研究结果旨在加深理解云辐射反馈机制，并为改进模式中云重叠参数化方案提供一定观测依据。     

联合星载毫米波雷达和中分辨率光谱成像仪的云底高度反演

云底高度是云重要的宏观物理参数。本文基于MODIS和CPR探测得到的可见光、红外和毫米波数据,提出了用主成分分析(Principal Component Analysis,PCA)和BP神经网络反演云底高度的新方法,并以相对湿度阈值法处理探空资料所获取的云底高度为基准,对PCA-BP法和CloudSat产品获取的云底高度进行了对比分析。结果表明:对绝大部分类型的云,PCA-BP法的反演偏差小于CloudSat产品。PCA-BP法和CloudSat产品反演的云底高度在夏季偏低,在其他季节偏高,且PCA-BP法与探空仪的均方根误差在所有季节均小于CloudSat产品,两者反演的云底高度具有一致的季节特征,即夏高冬低。PCA-BP法和CloudSat产品所获取的云底高度随纬度升高有减小趋势,在不同地区,两者具有不同的反演效果,反演误差随纬度升高而逐渐减小,对比结果说明了PCA-BP法反演云底高度具有一定的可行性。     

Representing Model Uncertainty by Multi-Stochastic Physics Approaches in the GRAPES Ensemble

To represent model uncertainties more comprehensively, a stochastically perturbed parameterization(SPP) scheme consisting of temporally and spatially varying perturbations of 18 parameters in the microphysics, convection, boundary layer, and surface layer parameterization schemes, as well as the stochastically perturbed parameterization tendencies(SPPT) scheme, and the stochastic kinetic energy backscatter(SKEB) scheme, is applied in the Global and Regional Assimilation and Prediction Enhanced S...