青藏高原东坡地形短波辐射效应的模拟研究

Simulation of Topography Effects on the Shortwave Radiation over the Eastern Slope of the Tibet Plateau

本文选择2012年8月16-17日降水个例,利用WRFV3.5天气模式模拟研究青藏高原东坡的地形坡度、坡向及覆盖短波辐射效应（Effect of Slope,Aspect and Shading,ESAS）。结果显示,ESAS产生的短波辐射强迫（强迫）空间分布与坡度大小一致,表现为坡度大时强迫大,坡度小时强迫小;朝西坡向为负强迫,坡向朝东为正强迫,正负强迫分别超过20和32W m-2。地形覆盖使得坡度和坡向在青藏高原东坡（高原东坡）上产生的地面短波辐射通量变化（辐射通量变化）整体向东南移入盆地,位移后的辐射通量增减仍然和高原东坡的坡度、坡向分布一致。地表热通量、地表温度在白天的变化和辐射通量变化分布一致,均在四川盆地内有一条高值带,且形状类似高原东坡和盆地的衔接线;EASA对地面各热通量的影响可以延续到夜间,使得夜间地表热通量变化和高值区位置与白天相似,但变化幅度减小。水汽混合比和风场的变化均具有与潜热变化相似的空间形态,在夜间尤其明显。潜热的增加（减小）可能引起风速增减加（减小）,并最终导致降水的改变。

In this study,a precipitation case happing from Aug. 16 to17,2012 was simulated by using Weather Research and Forecasting model 3. 5（ WRFV3. 5） to investigate the shortwave radiation effect of topographic slope angel,aspect and shading（ESAS） over eastern slope of the Tibetan Plateau（TP）. Firstly,the shortwave radiation forcing derived by ESAS was estimated,and the results show that the bigger the slope angle is,the higher the forcing is,and the westward slopes will produce negative forcing while the eastward slopes can induce positive forcing. The forcing can exceed- 32 and 20 W m- 2respectively. It is different that the variation of net shortwave radiation flux at surface shows a southeasterly shift caused by shading effect from the eastern slope of TP（ESTP） toward the Sichuan Basin（SCB）. But its spatial distribution even through shifting to the SCB is still similar to slope angle and aspect of the ESTP. Furthermore,the distributions of variations of land surface heat flux and ground temperature in daytime agree well with the changes of net shortwave radiation flux： they all have an own high values belt like the adjacence of the TP and SCB in the SCB. In the night,the changes of surface heat flux represent the familiar features of distribute and the location of high-value areas with declining extent comparing with those in daytime. It can be concluded that the impact of net shortwave radiation flux changes on various heat flux at surface due to the ESAS will continue to night. Both of the changes of vapor water mixing ratio and wind field have the distribution pattern with a high values belt similar to changes of latent heat flux,especially in nighttime. The increase（decrease） of latent heat flux can improve（reduce） the wind speed and finally results in the changes of precipitations.