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.