2015年夏季，全国平均降水量297．6 mm，较常年同期偏少8．5％，空间分布呈“北少南多”的显著特征，长江中下游及江淮地区降水显著偏多，梅雨雨季持续时间长，雨量偏多。进一步研究表明，2015年5月以来热带印度洋海温一致偏暖模态正位相发展，激发出西升东降的局地异常纬向环流，有利于西太平洋副热带高压强度偏强，位置偏西。加强西伸的西太平洋副热带高压造成我国东南部地区西南低空急流频发，强度偏强。低空急流将来自南海的水汽向江淮等地输送，并激发不稳定能量释放，有利于对流活动的发展和降水的产生，导致梅雨雨季持续时间长，雨量偏多。%In summer 2015,the mean precipitation over China was 297.6 mm,which is less than normal by 8.5%.The spatial distribution of precipitation anomalies showed the north-less and south-more pattern, and precipitation over the middle and lower reaches of Yangtze River and the Yangtze-Huaihe River Valley was significantly more than normal.The Meiyu rainy season lasted longer with more rainfall than normal. Further study indicated that positive Indian Ocean basin-wide mode (IOBW)has been enhanced since May 2015,triggering a local zonal circulation with upward flow in the west and downward motion in the east. This circulation is favorable for the establishment of a strong and westward Northwest Pacific subtropical high,resulting in high frequency of strong southwest low-level jet in the southeast of China.The low-level jet transported water vapor from the South China Sea to the Yangze-Huai River Valley and released unsta-ble energy,and such combined condition is useful for the development of convection and the occurrence of precipitation,extending the Meiyu season and increasing the amount of rainfall.
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