一次华北暴雨过程中边界层东风活动及作用

摘要

Using conventional observations,1°×1°NCEP analysis data,ground-based radiometer data,FY-2E meteorolgical satellite and radar data,the boundary layer east wind and its influence on a North China rain-storm on 4 Jun 2013 is analyzed. The boundary layer east wind is from Northeast China Plain,and it becomes moist when passing the Bohai Sea,resulting in cooling in boundary layer,and the sharpest drop is about 9°C at 925 hPa.The east wind influencing area is within about 300 km.The east wind and according temperature change are moni-tored accurately by the ground-based radiometer and profile radar,and the storm is triggered after the tem-perature decreases for about 5 hours. Main influencing weather systems of the rainstorm are the boundary layer east wind,wind shear at mid-low level,southwest low-level jet at 700 hPa and small-scale low trough at 500 hPa.The cold air caused by the boundary layer east wind meets the warm southwest air on the windward area of the Taihang and Yan Mountains,and the cold front is formed near Beijing area.The front lift and topographic lift effects are obvious and the according upward motion is about -0.8 Pa·s-1 ,which strengthens upward motion of the warm and moist air near 700 hPa at the north of Beijing.The east wind leads to cooling cush-ion and temperature inversion at boundary level,and cooling cushion effect triggers the thunderstorm again to some extent,which is generated above the boundary layer,and the most unstable convective available energy reaches 1517.5 J · kg-1 .The elevated thunderstorm is found first to the east of the Taihang Mountains because of topographic lift effect.The analysis of infrared TBB of FY-2E shows that middle convective systems develop obviously when they move near the cold front of east wind.The thunderstorm occurs again just over the east wind cooling cushion area according to radar reflectivity. The moist is sent to the storm area by east winds from boundary layer and southwest winds at mid-low level.The mid-low level warm moist air leads to the increase of stratification convective instability,and at 850 hPa is 8.2 K and 11.7 K more than that of 500 hPa at 0800 BT and 2000 BT,respectively.There is strong dynamic instability over the storm area because the distinct vertical wind shear is formed by bounda-ry layer east winds and strong southwest winds at middle level.%利用常规气象观测资料、NCEP 1°×1°逐6 h 分析资料、微波辐射计资料及 FY-2E 气象卫星及雷达探测资料，针对2013年6月4日发生在北京及周边地区的一次暴雨过程中边界层东风活动及作用进行了天气学诊断分析，结果表明：对流性暴雨过程伴随有源自东北平原的边界层东风活动，东风活动具有尺度小、降温明显和湿度大等特点。暴雨过程是边界层东风和中低空暖式切变线、偏南风急流和500 hPa 短波槽共同作用的结果；东风湿冷空气的锋面抬升和地形抬升作用共同加强了中低层暖湿气流的辐合上升运动，同时东风冷垫和地形抬升作用触发了雷暴的再次发生，相应雷暴具有高架对流特点。东风气流起到了边界层水汽输送作用，中低层偏南暖湿气流为暴雨的产生提供了充足的水汽和不稳定层结条件。