Analysis on the Circulation Features of a Continuous Rainstorm in Eastern Part of Northwest China

Based on the NCEP reanalysis data,the large-scale circulation features and physical quantity field of a continuous rainstorm occurred in Shaanxi from August 15 to September 9,1981 were analyzed.As indicated by the results,the middle and high latitude circulation of Eurasia was stable "L" type,the northerly westerly and stronger subtropical high was the direct cause of this continuous rainstorm;the active and long live low-latitude tropical cyclone activity was conducive to the stable maintenance of mid-latitude circulation.Warm air outside the tropical cyclone,strong Indian monsoon and the warm air outside the West Pacific subtropical high rainfall combined to provide continuous water vapour and energy;high-latitude westerly jet and subtropical easterly jet stably existed,heavy rain occurred in overly area of the South Asia high divergence and the divergence at the right of upper level jet stream entrance area,the jet stream which bringed constantly cold air invaded downward,superimposing on the low-level warm air of the storm zone,which increased the instability of atmospheric stratification of the storm zone and was conducive to the occurrence of deep convection.