Effects of surface drag on low-level frontogenesis within baroclinic waves

作     者：ZHANG Yi TAN ZheMin 

作者机构：Key Laboratory of Mesoscale Severe Weather of Ministry of Educationand Department of Atmospheric SciencesNanjing Univer-sityNanjing 210093China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2007年第50卷第2期

页      面：306-319页

核心收录：

学科分类：07[理学] 070601[理学-气象学] 0706[理学-大气科学] 

基　　金：Supported by the State Key Basic Research Program (Grant. No. 2004CB-18301) the National Natural Science Foundation of China (Grant Nos. 40325014, 40333031) TRAPOYT, FANEDD 11999, SRFDP (20030284019) the Key Science and Technology Project of the Ministry of Education of China 

主　　题：surface drag baroclinic wave frontogenesis diabatic heating frontal rainband 

摘      要：Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope espe- cially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection domi- nates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are re- duced.