Temporal and spatial distribution of the spring persistent rains over southeastern China.

The spring persistent rains (SPR) over southeastern China (SEC) is a unique synoptic and climatic phenomenon in East Asia. Sufficient evidences proved that it results from the mechanical and thermal effects of the giant Tibet Plateau (TP). But it isn’t clear about its temporal span and spatial distribution at present. The climatological mean analysis of NCEP/NCAR circulation and sensible data shows: at 1st pentad of March (13th pentad of solar year), there are remarkable increases of the variables of the sensible heating over the main and southeastern part of TP, the southwesterly velocity at southeast flank of TP and over SEC, and the rainfall over SEC, indicating the onset of SPR. In contrary, at 3rd pentad of May (27th pentad in solar year), these variables except the sensible heating over the main part of TP decrease rapidly. The ridge of the South China Sea (SCS) sub-high at mid-low troposphere slopes up-northward instead of southward before. The rain belt center over SEC shifts to SCS and the SCS monsoon breaks out, indicating the end of SPR. Hence, it is suitable to consider SPR temporal span as 13th-27th pentads of solar year. Data analysis and numerable sensitivity experiments shows, though the warm air and cold air converge at about 30°N in SPR period, the distribution and intensity of SPR rain belt are obviously influenced by the topography of the Nanling Mountains and the Wuyi Mountains. The mountains can block and lift cold and warm airs, strengthening frontogenesis and rainfall. As a result, they make the axes of SPR rain belt superpose the axes of themselves. From this point of view, the spatial distribution of SPR is over southeastern China, that is, to the south of the middle and lower reaches of the Yangtze River (30°N), and to the east of 110°E.