2019年江西严重夏秋连旱特征及成因分析

Analysis of the Characteristics and Causes of Severe Summer and Autumn Droughts in Jiangxi in 2019

2019年江西出现罕见夏秋连旱过程,为有气象记录以来范围最广、强度最强的气象干旱,持续时间长达5个多月之久。期间出现了4轮大范围持续晴热高温天气过程,全省平均高温日数达45.4 d,多项气象指标创历史之最。利用MICAPS观测资料、江西省93个气象台站降水、气温资料以及NCEP/NCAR再分析资料、NOAA海表温度和向外长波辐射资料,对此次夏秋连旱天气过程的特征及成因进行了分析,结果表明:1)中高纬环流平直,强盛西风气流阻挡了南北气流交换,冷空气难以南下,而副热带高压面积偏大、强度偏强、位置偏西,切断西南气流路径,暖湿空气难以北上,使得冷暖空气不能在长江及其以南地区交汇,是江西长时间持续干旱的主要原因;大气环流在本该发生调整的时期没有及时调整,是江西夏旱连秋旱的另一主要原因。2)东海和南海的水汽偏南向西北方向输送,孟加拉湾的水汽偏西向北方向输送,三条水汽通道在四川及以北地区汇合,到达江西的水汽通量输送较常年同期异常偏弱,不利于江西降水的产生。3)赤道中东太平洋海面异常降温,引起赤道太平洋Walker环流发展,Hadley环流加强,使得包括江西在内的长江中下游以南地区下沉运动增强;而副热带西太平洋低值系统活跃,使得副热带高压长时间稳定维持在偏北的位置,加剧了江西干旱的发生。

In 2019,Jiangxi experienced a rare continuous drought in summer and autumn,the influence of which was the widest and strongest since meteorological records,and lasted more than 5 months.During the period,4 rounds of continuous sunny and hot high temperature weather in a wide range occurred.The average number of high temperature days reached 45.4 days,and many meteorological indicators hit record heights.Based on MICAPS observation data,precipitation and temperature data from 93 meteorological stations in Jiangxi province,NCEP/NCAR reanalysis data,NOAA sea surface temperature and outward long-wave radiation data,the characteristics and causes of the dry weather process were analyzed.The results showed that:1)The mid-to-high latitude circulation was straight,and the strong westerly airflow blocked the exchange of north-south airflow,making it difficult for cold air to move southward,while the subtropical high presented large area,strong intensity,and westward position,cutting off the path of southwest airflow,making it difficult for warm and humid air to move northward,and the cold and warm air hard to converge in the Yangtze River and the southern regions.Above-mentioned were the main reasons for the prolonged drought in Jiangxi.The atmospheric circulation did not adjust during the period when the adjustment should have occurred,which was another main reason for the drought.2)The water vapor in East China Sea and South China Sea was transported from south to northwest,and the water vapor in the Bay of Bengal was transported from west to north.The three water vapor channels converged in Sichuan and the northern regions,and the water vapor flux transported to Jiangxi was abnormally weaker than normal,which was bad for the production of precipitation in Jiangxi.3)The abnormal cooling of the sea surface in the central and eastern equatorial Pacific caused the development of the equatorial Pacific Walker circulation,and the strengthening of the Hadley circulation increased the subsidence in the south area of the middle and lower reaches of the Yangtze River,including Jiangxi;while the subtropical western Pacific low-value system was active,making the subtropical high pressure lasted longer time and remained stable in a northerly position,exacerbating the occurrence of drought in Jiangxi.