2013年夏季长江中下游地区降水异常与MJO的可能联系

Possible Linkage between MJO and Abnormal Precipitation in the Middle and Lower Reaches of Yangtze River in 2013 Summer

利用国家气象信息中心提供的753站降水资料,澳大利亚气象局提供的RMM-MJO指数资料和NECP/NCAR逐日再分析资料,分析了2013年夏季长江中下游地区降水持续异常与MJO位相异常的可能联系。结果表明:2013年夏季长江中下游地区持续干旱期间,MJO位相分布明显异常,MJO东传停滞,长时间维持在第1、8位相;西太平洋副热带高压偏北偏强。当MJO位于第1、8位相时,东亚高纬度地区的环流距平场呈现"西高东低"的分布特征,不利于西伯利亚地区的冷空气南下至长江中下游地区;当MJO位于第1位相时,副热带高压西北侧水汽主要输送至长江中下游地区,第8位相时,输送至长江中下游地区的水汽异常偏少。总之,当MJO位于第1、8位相时,冷空气活动较弱,冷暖空气无法在长江中下游地区交汇,同时该地区深厚的下沉运动从近地面一直延伸至对流层上层,不利于降水的发生,导致2013年夏季降水持续偏少。

Based on NECP/NCAR reanalysis data,rainfall data of 753 stations from National Meteorological Information Center and RMM-MJO index,the relationship between abnormal phase of MJO and persistent less precipitation in 2013 summer was analyzed.Results showed that the persistent drought in 2013 summer was severe and precipitation was significantly less than normal,and the phase of MJO showed an abnormal change,correspondingly.MJO was stagnant and maintained in phase 1 and8 for a long time.When MJO was in phase 1 and phase 8,the high-attitude circulation anomalies presented high values in the west and low values in the east,thus the cold air from Siberia areas was hard to flow to lower-middle reaches of Yangtze River.Moisture from western Pacific subtropical high was mainly transported to middle and lower reaches of the Yangtze River as MJO was in phase 1,while the vapor transportation was weak as MJO was in phase 8.The cold air activity was weak when MJO was in phase 1 and phase 8,the cold and warm air couldn＇t meet over the middle and lower reaches of Yangtze River,andthe descending motion was extended to the top of the troposphere,thus the persistent less precipitation occurred in2013 summer.