南半球风暴路径的加强与南北扩张

Intensification and Expansion of Storm Tracks in the Southern Hemisphere

基于NCEP/NCAR再分析资料,分析了近60年来南半球300hPa风暴路径的变化趋势。研究发现,1956—2015年期间,南半球风暴路径出现了较为明显的增强趋势,尤其是在中高纬地区最为显著。通过构造的风暴路径边界指数,发现南半球风暴路径的北界和南界分别存在向赤道和向极的扩张趋势,其中以南界向极偏移趋势最为明显,整个南半球风暴活动带变得更加宽阔和靠近极地。作为风暴路径获取能量的主要来源,背景场西风急流以及下垫面海表面温度的变化对其强弱和位置变化有显著影响,南半球西风急流南强北弱和海表面温度南冷北暖的变化趋势,是南半球风暴路径增强和扩张的重要原因。

Trends of storm tracks in the Southern Hemisphere during the recent 60 years are analyzed by using the NCEP/NCAR Reanalysis data. It is found that storm tracks in the Southern Hemisphere intensified obviously during 1956—2015, especially for mid high latitude regions. Indicated by the defined storm track boundary index, storm tracks at 300 hPa in the Southern Hemisphere showed a slightly equatorward shift in its northern boundary and a significantly poleward shift in its southern boundary, meaning storm tracks in the Southern Hemisphere were getting broader and closer to the pole. As the primary energy sources of storm tracks, variations of its intensity and position were closely related to the westerly jet and sea surface temperature （SST）. Enhancement of the circumpolar westerlies and the SST meridional gradient are the main reasons for the intensification and expansion of storm tracks in the Southern Hemisphere.