江南春雨的时空分布

江南春雨是东亚独特的天气气候现象，已有充分证据表明，它是青藏高原高大地形的动力和热力强迫的结果，但目前其时空分布还不明确。NCEP/NCAR环流及感热资料气候平均分析表明：在3月第1候（全年第13候），高原主体和高原东南部的感热加热、高原东南侧西南风速、江南春雨区西南风速和江南春雨区雨量都提升到一个新的水平，标志着江南春雨的建立；在5月第3候（全年第27候）以后，高原东南部的感热加热、高原东南侧西南风速、江南春雨区西南风速和江南春雨区雨量都迅速减小，对流层中低层南海副高脊线由南倾转北倾，江南雨带中心南移至南海，南海季风爆发，标志着江南春雨期的结束。因此，将江南春雨的建立和终结时间定为第13候和第27候比较适当。资料分析和数值敏感性试验表明，江南春雨期对流层低层冷暖空气的交汇区在30°N附近，但江南春雨雨带的位置和强度明显受南岭、武夷山脉地形的影响：山脉地形能阻挡抬升冷暖空气，加强锋生，增强降水，使雨带中心位置与山脉主轴分布重合。因此，江南春雨的空间范围包括长江中下游（30°N）以南、110°E以东的中国东南部地区。

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.