海温和MJO对2023年西南春旱的协同影响

The synergistic effect of sea temperature and MJO on spring drought in southwestern China in 2023

2023年春季,我国西南地区发生了严重的气象干旱,对当地社会经济造成严重影响。为深入认识这次干旱事件的成因、并为未来西南地区春旱的预测提供科学依据,本文利用站点观测数据、美国国家环境预测中心和国家大气研究中心(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)再分析数据、美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration,NOAA)的海表温度等,采用T-N波作用通量和合成分析等方法,从海温和热带大气季节内振荡(Madden-Julian Oscillation,MJO)的角度深入探讨此次春旱成因。结果表明:(1)2023年我国西南春旱是高温干旱复合事件,3月干旱发生在中部,4月干旱加剧并向西扩展,5月干旱持续。(2)3月北太平洋的马蹄形海温异常导致西风急流偏南偏西,抑制了西南地区的降水。(3)4月印度洋暖海温通过Kelvin波导致孟加拉湾附近的反气旋式环流异常,西北太平洋暖海温通过Rossby波导致南海至菲律宾的气旋式环流异常,造成西南地区南部出现偏北风,导致水汽辐散,加剧干旱。(4)5月MJO长时间维持在西太平洋,通过Gill响应引发南海至菲律宾对流层低层的气旋异常,减少偏南水汽的输送,从而使得西南干旱持续。

In the spring of 2023,a severe meteorological drought occurred in southwestern China,which had a serious impact on the local social economy.In order to deeply understand the causes of this drought event and further provide a basis for the prediction technology of spring drought in southwestern China,causes of the spring drought event were analyzed from the perspective of SST(sea surface tempera⁃ture)and MJO(Madden-Julian Oscillation)by using station-observed data,NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research)reanalysis data,NOAA(National Oceanic and Atmospheric Administration)SST and other data,choosing T-N wave activity flux,composite analysis and other methods.The results showed that:(1)The spring drought over south⁃western China in 2023 was a compound dought-heatwave event occurred in the middle in March,developed and expanded westward in April,and maintained in May.(2)In March,the horseshoe-shaped SST anomalies in the North Pacific caused the westerly jet stream to drift southward and westward,suppressing the precipitation in southwestern China.(3)In April,the anticyclonic circulation anomaly near the Bay of Bengal induced by warm SST in the Indian Ocean through Kelvin wave and the cyclonic circulation anomaly from the South China Sea to the Philippines triggered by warm SST in the Northwest Pacific through Rossby wave resulted in northerly winds in the south of southwestern China,which caused the divergence of water vapor and the development of drought in southwestern China.(4)MJO,which maintained in the western Pacific for a long time in May,stimulated the cyclonic anomaly from the South China Sea to the Philippines in lower troposphere due to Gill response,reduced the transport of southerly water vapor,and maintained drought in southwestern China.