Abstract:

Based on monthly average precipitation data of 83 stations in Hunan Province and NCEP/NCAR reanalysis data, the distribution characteristics of drought occurring in summer and autumn in Hunan Province were analyzed by using mathematical statistics method. The patterns of summer and autumn drought in Hunan were classified and their differences about atmospheric circulations and the earlier period sea surface temperature (SST) were analyzed. The results are as follows: (1) It experienced six periods including dry, wet, dry, wet, dry, wet in summer and autumn in Hunan during 1961-2016, and the spatial patterns were classified into three for drought in the whole province, north and south Hunan. (2) In the years of drought in the whole province, the intensity of Western Pacific subtropical high (WPSH) weakened and the ridge line of WPSH trended to northward, the South Asia high trended to northward and became stronger. The wave-train distribution of  “﹣, ﹢, ﹣” East Asia/Pacific (EAP) teleconnection pattern of geopotential height anomalies appeared from north to south in East Asia. The East Asian subtropical westerly jet (EAWJ) distributed northward and eastward meanwhile it had an anti-cyclonic circulation anomaly over the south of the Yangtze River at the low-level wind field. Most of Hunan was located in the divergence anomaly area, which directly resulted in less precipitation and forming drought. (3) In the years of drought in north Hunan, the WPSH weakened and its ridge line extended northward and eastward, both the South Asia high and the EAWJ occurred northward obviously meanwhile there was an easterly wind anomaly area in the lower reaches of the Yangtze River within the low-level wind field. Northern part of Hunan was located in the divergence anomaly area while the southern was in the convergence anomaly area, which led to drought in north and floods in south Hunan. (4) In the years of drought in south Hunan, the WPSH trended to become stronger and its ridge line was westward and southward, the South Asia high moved southward slightly. The wave-train distribution of  “﹢, ﹣, ﹢” EAP teleconnection pattern of geopotential height anomalies occurred from north to south in East Asia. The EAWJ was southward and an anticyclonic circulation on the low-level wind field occurred in South China. The South China was located in the divergence anomaly area and the Yangtze-Huai river region was in the convergence anomaly area, which led to floods in north and droughts in south Hunan.

Key words: Hunan, drought, circulation anomalies

摘要：

利用湖南83站降水资料和NCEP/NCAR再分析资料，采用数理统计方法，分析了湖南夏秋干旱的分布特征，对湖南夏秋干旱类型进行了划分，对比了3类干旱型在同期大气环流和前期海温上的差异。结果表明：（1）1961—2016年湖南夏秋干湿变化经历了“干、湿、干、湿、干、湿”6个时段，可分为全省、北部和南部干旱型；（2）全省干旱型年份西太平洋副热带高压（副高）偏弱、偏北，南亚高压偏强、偏北，东亚地区从北至南呈东亚/太平洋型遥相关（EAP）的负位相分布，东亚副热带西风急流偏东、偏北，低层风场在我国江南地区有一反气旋距平环流，湖南大部为辐散异常区，造成湖南大部降水偏少，形成干旱；（3）北部干旱型年份副高偏弱、偏北、偏东，南亚高压和东亚副热带西风急流明显偏北，低层风场在长江中下游地区有一较大的东风距平区，湖南北部为辐散异常区，南部为辐合异常区，形成湖南北旱南涝的空间格局；（4）南部干旱型年份副高偏强、偏西、偏南，南亚高压偏强、略偏南，东亚地区从北至南呈EAP的正位相分布，东亚副热带西风急流偏南，低层风场在我国华南地区有一反气旋距平环流，华南地区为辐散异常区，江淮地区为辐合异常区，形成湖南南旱北涝的空间格局。