小振幅背风波的非线性特征及水汽敏感性试验  

Numerical Simulations of Lee Wave's Nonlinear Characteristics and Vapor Sensitivity

作　　者：徐良韬[1,2] 林文实[1] 张义军[2] 

机构地区：[1]中山大学大气科学系,广州510275 [2]中国气象科学研究院雷电物理与防护工程实验室,北京100081

出　　处：《应用气象学报》2011年第5期597-603,共7页Journal of Applied Meteorological Science

基　　金：国家重点基础研究发展规划项目(2010CB428504);国家自然科学基金项目(41030960;41005006)

摘　　要：从Scorer的背风波发生理论条件出发,首先考虑3层均匀干空气,利用WRF模式模拟出干空气条件下的小振幅拦截背风波动,波动主要发生在2～5 km的高度范围,波长为8 km左右,这与之前的观测和模拟结果相一致。分析表明:形成平稳背风波动过程中,存在能量波包向下游传播的性质,各位置振动的强度会发生周期性的增强和衰减。引入水汽进行的敏感性试验表明:随着水汽增多,背风波动的波长会增加,且波动传播中所能达到的最大垂直速度有变小趋势。Based on the Scorer＇s theory of the lee wave, the trapped lee wave of small amplitude is successfully simulated using the Weather Research and Forecasting（WRF） model, considering the dry atmosphere with three even layers. Results show that in the linear theory, the trapped lee wave of the flow over terrain can be simulated well. The wave appears primarily from 2 km to 5 km in the vertical direction and the wavelength is on the order of 8 km. These results are in accordance with previous observation and numerical simulations. The analysis shows that the energy wave packet drifts downstream in the forming process of stationa- ry lee wave and the oscillation intensity of each location periodically amplifies and weakens. At the same time, before the stable trapped lee wave forms, small disturbances have been generated, which would have significant impacts on vertical velocity of the wave. The process of introducing vapor is deemed to be creditable according to the original relative humidity vertical profile by WRF model output data. Small disturbances mentioned make vapor oscillate and easily initiate cumulus convection. Further, with vapor content increasing, cumulus convection appears earlier in the simulation. When vapor is introduced in the model, the lee wave would interact with cumulus convection, which has not been discussed in detail. Sensitivity experiments are conducted by changing the relative humidity of air, and the simulated re- suits about the vapor＇s effect to the lee wave show that as the vapor increases, the wavelength becomes longer. In the simulation, the wavelength increases from 8 km to 9 km when relative humidity increases from 0 to 60%. In essence, it is buoyancy oscillation in the vertical direction of lee wave. The increase of the turbulent friction is attributed to the air density changes because of the variation of humidity, and then the damp of the oscillation increases. As a result, the oscillation frequency in the moist air is smaller than that in the dry air, accordingly the

关 键 词：背风波动 WRF模式 非线性 水汽 数值模拟 

分 类 号：P433[天文地球—大气科学及气象学]