Abstract:By using the daily precipitation data of 68 stations in Hubei and NCEP/NCAR circulation reanalysis data, the characteristics of the heavy rain events and low frequency atmospheric features between the Meiyu and midsummer periods are studied. The results indicate that the quasi biweekly oscillation of precipitation exists obviously in summer over Hubei. Compared with the rains in the midsummer period, low frequency heavy rain events in the Meiyu period are seen more often with stronger intensities. There are significant differences of low frequency heavy rain events between the Meiyu and midsummer period. During Meiyu period, circulations show the distribution of north south wave trains above the East Asia Littoral in the mid level troposphere. The combined impact of strong Somali cross equatorial flow and south west air current around subtropical high contribute to the abudant water vapor. The saddle type field of circulations in East Asia and transformed flow field are beneficial to the formation of mesoscale cyclonic systems. In the midsummer period, however, circulations distribute in the pattern of Eurasian wave trains in middle troposphere. In lower troposphere, water vapor comes from subtropical peripheral with the weak Somali cross equatorial flow. The north air streams from the west of the cyclone to the west of Japan Sea and the south warm wet air streams from the periphery of subtropical high get intersected and maintained over 30°N. Before and after the heavy rain events, there are obvious differences of the low frequency positive vorticity propagation in low troposphere. The low frequency positive vorticity during the Meiyu period shows the characteristics of standing wave while in the midsummer, it propagates westward, southward and northward obviously.