2009年2-3月我国南方连阴雨天气过程分析

Circulation Analyses on Persistence Rainy Days from February to March 2009

利用JRA-25再分析资料分析了2009年2—3月我国南方一次连阴雨过程的环流背景,以及该时期西太平洋副高和副热带西风急流的异常活动,并计算了降水区域内的水汽收支。结果表明:(1)这次过程中,欧亚大陆上空阻塞形势稳定,我国北方地区长期由槽后脊前的西北气流控制,而在中低纬地区,西太平洋副高稳定在菲律宾海上空,加强了南方地区对流层中低层的西南风。这种环流形势使得北方干冷空气和南方暖湿气流在长江流域长时间对峙,形成了稳定的准静止锋,是影响这次连阴雨过程的主要天气系统。(2)对流层高层的副热带西风急流异常偏北,急流轴入口处南侧的辐散环流与低层西南气流北侧的气旋性辐合环流相配合,在长江流域上空形成利于降水发展和维持的动力结构。(3)偏北的西太平洋副高伴随着反气旋性环流异常,其西边缘的偏南风造成了来自西太平洋及南海低纬地区至我国南方的偏南风水汽输送支异常,它主导的经向水汽输送是造成主降水区水汽通量辐合的重要原因,对降水发展和维持的影响更为显著。

Based on the JRA-25（1.25°×1.25°） reanalysis datasets,the circulation features and moist conditions of the persistence rainy days from February to March 2009 are investigated.The results show that： （a） at the middle-high latitudes,the blocking situations are stable over the Eurasia,and at the middle-low latitudes,the West Pacific subtropical high（WPSH） is intensified over the Philippine Sea.Under these stable circulations,the cold-dry air from the north contacts the warm-wet airflows from the south over the middle-lower reaches of Yangtze River for a long time,which forms a stationary front.（b） In the upper troposphere,the axis of the subtropical westerly jet stays around 35°N,enhancing the divergence above the stationary front.The divergence matches the cyclonic convergence north of the southwester lies on the low levels,which forms a favorable rain-producting dynamic structure.（c） The anticyclonic circulation anomaly,according to the intensified WPSH,results in a moisture transport anomaly from the West Pacific and the South China Sea to southern China.The meridional transport anomaly contributes the most of the moist convergence in the rainy area,having significant impacts on the development and persistence of the precipitation.