副热带西风急流对云南雨季开始的影响
Influence of Subtropical Westerly Jet on the Onset of Rainy Season over Yunnan Province
中文摘要：
利用1961—2010年云南逐日降水观测资料和NCEP/NCAR再分析资料，研究了由春至夏季节转换期间副热带西风急流活动对云南雨季开始的影响，获得了一些新的发现。结果表明，云南雨季开始前后10天内东亚副热带西风急流有显著变化，但与传统认识不同，伴随云南雨季开始东亚副热带西风急流中心出现明显“南移”而不是“北跳”，即急流中心从35°N附近向南移动了近5个纬度。对逐日资料的分析还显示，东亚副热带西风急流在不断向北推进的过程中，急流中心普遍存在南北摆动的现象。当急流南移且急流入口区激发的次级环流上升支正好位于云南上空时，强而深厚的上升气流为雨季的开始提供了有利的动力扰动条件。
中文关键词：
云南雨季开始，副热带季风急流，次级环流
KeyWords：
rainy season onset of Yunnan, subtropical westerly jet, secondary circulation
Abstract：
By using daily observatory precipitation data and NCAP/NCAR reanalysis data 1961—2010, this paper explores the influence of subtropical westerly jet on the onset of rainy season over Yunnan province and some new results are obtained. The results show that there exits astonishing variation of the subtropical westerly jet stream over East Asia during 10 days around the onset day of Yunnan rainy season: the jet stream over East Asia sways southward from 35°N to near 30°N rather than jumps northward. With a sequence of jumping northward of the subtropical westerly jet, swaying southward generally exists during the transitional season. When the subtropical jet sways southward and its upward branch of the secondary circulation around the entry zone is right over Yunnan province, the updraft would provide favorable dynamic disturbing condition for the rainy season onset.