湘西州夏季干旱及其成因分析

利用湘西州8个气象台站1960—2013年逐日气温和降水资料计算的夏季干旱指数CI和NCEP/NCAR再分析资料、NOAA海温等分析了该区域夏季干旱的年际变化及可能成因。结果表明,1960—2013年期间,湘西州夏季干旱严重的年份有1961、1972、1981、1994、2009、2013年。湘西州夏季干旱的发生既跟中高纬环流异常有关,又与低纬度到热带的环流相关。其中西太平洋经菲律宾到孟加拉湾附近降水异常对应的热力强迫可引起西太平洋副高南北位置的变化而导致湘西州干旱的发生。即当西太平洋经菲律宾到孟加拉湾附近降水偏多时,西太平洋副高易偏北,该地区多受高压控制,容易发生干旱。

Analysis of summer drought events in Xiangxi of Hunan Province

The interannual variation of summer droughts in Xiangxi of Hunan Province is investigated,and the underlying causes for the drought events are explored,based on the drought index(CI) of Xiangxi,as well as the NCEP/NCAR reanalysis data and NOAA SST data.The CI is calculated by daily temperature and precipitation data from 1960 to 2013 recorded by 8 meteorological stations in Xiangxi.The results show that severe drought events occurred in summer of year 1961,1972,1981,1994,2009,and 2013,and the droughts are closely related to the mid-and high-latitude circulation anomaly patterns,and circulations at low latitudes and the tropics as well.The thermal external forcing near the Philippines from West Pacific to the Bay of Bengal,associated with the rainfall anomalies,is able to lead to the anomalous movement of the western Pacific Subtropical high,which probably results in the drought events.When the rainfall is positive with stronger than normal convection near the Philippines,the subtropical high moves northward anomaly and controls the Xiangxi area with less rainfall,then the drought will easily occur in Xiangxi.