“05.6”华南暴雨中低纬度系统活动及相互作用

利用NCEP/NCAR再分析资料、FY-2C卫星逐时云顶亮温资料(分辨率为0.05°×0.05°)及射出长波辐射资料(分辨率为0.5°×0.5°)、实时地面加密观测和实况探空资料等,对"05.6"华南持续性暴雨过程期间南海季风活动、副热带高压演变、冷空气影响、高低空急流耦合等进行深入分析,探讨中低纬度不同尺度系统的活动特征及相互作用。结果表明:"05.6"华南暴雨是在中纬度地区位势高度场稳定的北高南低背景下,由东亚沿岸槽和青藏高原短波系统引导中纬度冷空气与低纬度地区季风系统相互作用下产生的;南海副热带季风的活跃与100°～120°E处越赤道气流通道的消失密切相关,其两次大规模向北推进是过程开始和结束的重要标志;副热带高压较多年平均明显偏南且强度达到最强,700 hPa中纬度冷空气的明显南侵对暴雨过程有重要贡献;高空急流入口区右后方与低空急流左侧由于强烈的高空辐散和非地转平衡强迫,构成一支横跨低空急流的经向次级环流,高低空急流耦合的正反馈机制是华南暴雨异常的重要原因之一。

The Evolution Characteristics of Mid-latitude and Low-latitude Synoptic Systems During the "05.6" Heavy Rain Event in South China

The evolution characteristics and interaction between mid latitude and low latitude synoptic systems during "05.6" heavy rainfall process in South China is studied in detail. The monsoon activity in South China Sea, basic characteristics of sub tropical high in west Pacific, the influence of the cold air in middle latitude, and the coupling mechanism between upper level and low level jet are analyzed based on NCEP/NCAR reanalysis data with the resolution of 1°×1° and a series of observation data. FY 2C satellite data, including the brightness blackbody temperature on cloud top (TBB) data with the resolution of 0.05°×0.05° and outgoing long wave radiation (OLR) observation with the resolution of 0.5°×0.5°, surface observation for 3 hour interval, and auto weather station observation for 1 hour interval are used for model initialization and verification. The results are as follows: Under the stable background of high pressure in the north and low in the south, the "05.6" heavy rainfall is produced by the interaction between monsoon system from low latitude and mid latitude cold air driven by east coast trough and plateau short wave. During the "05.6" heavy rainfall, the sub tropical monsoon in South China Sea blocks the cross equatorial flow path and leads to the abnormal equator west wind in area of 100°-120°E. It moves northward massively for 2 times, indicating the beginning and end of this rainfall process. The strength of sub tropical high maintains very strong and the position of high ridge changes in an abnormal pattern of west advancing east retreating west stretching and north advancing during the prophase stable north jump finally. The south invading of 700 hPa cold air in westerly belt in the beginning of the process has important impacts on this event, which may be the most important feature in this process. During the "05.6", there is a ULJ (upper level jet) on left front of South China and a LLJ (low level jet) on the right. Strong aloft divergence of ULJ and the ageostrophic force in the left of LLJ forms the secondary circulation across LLJ, so the positive feedback of coupling mechanism between ULJ and LLJ may be one of the prime causes for the "05.6" heavy rain event.