天气尺度扰动流场对区域暴雨的指示能力

观测的大气流场可以物理分解为气候流场、行星尺度纬圈平均扰动流场和天气尺度扰动流场.低层大气的天气尺度扰动流场中的切变线、南方气旋、北方气旋、冷锋槽线、西南涡暖切变线、热带气旋、倒槽切变线、东风波切变线等对区域暴雨具有指示意义.扰动流场中的环流系统更适合天气分析的原理.中国的暴雨带多为扰动辐合线两侧气流对峙的结果.观测流场中,暴雨带出现在低空急流的左侧,是因为气候流场掩盖或削弱了天气尺度扰动流场的作用.对切变线暴雨,天气尺度扰动流场有99%的诊断能力,而原始流场只有66%的指示能力.

Capability of regional-scale transient wind anomalies to indicate regional heavy rains

The observational atmospheric airflow can be physically interpreted as the combination of climatic airflow,planetary-scale zonal-mean wind anomalies and regional-scale wind anomalies.The regional-scale wind anomalies in lower atmosphere,such as shear lines,southern cyclones,northern cyclones,cold frontal troughs,warm shear lines with vortex in southwestern China,tropical cyclones,shear lines in inverted troughs and easterly waves,can indicate regional heavy rains.These circulation systems in wind anomalies agree with principles of synoptic analysis better than actual wind observations.The heavy rainfall bands in China are mainly the result of confrontation between airflows from both sides of convergence line in anomalous wind fields.Rainfall bands in actual observations are located to the left of low level jets because the climatic airflow and zonal-mean wind anomalies masked or weakened the role of regional-scale wind anomalies.For heavy rainfall caused by shear lines,almost 99% cases can be diagnosed with regional-scale wind anomalies.By comparison,only 66% cases can be indicated by actual observational airflows.