【作者】 尹晗；

【导师】 李耀辉；

【作者基本信息】 兰州大学 ， 大气物理学与大气环境， 2013， 硕士

【摘要】 在气候变化背景下,全球干旱频率和强度出现增加趋势。我国是世界上受旱灾危害最为严重的国家之一,近年来干旱更是频繁重发,受旱区域不断增大,并由北方干旱半干旱区易旱区向南方湿润区发展。历史上雨水充沛、气候湿润的西南地区,最近几年屡屡发生严重的干旱灾害,尤其是2009年秋季到2010年春季西南地区出现了60年一遇的特人干旱事件,造成了难以估量的损失,同时也引起了国内外的广泛关注。本文首先对西南十旱的最新研究进展进行了综述,然后分析了1960-2012年西南地区干旱强度和范围的时空分布特征以及干旱趋势变化；用Morlct小波分析方法分析了西南干旱的周期特征。在干旱时空特征分析的基础上,通过选取西南地区典型多雨年和少雨年,对比分析了降水异常偏多/偏少所对应的人气环流异常特征,揭示了造成2009-2012年西南连续干旱,特别是2009-2010年特大干旱事件的直接环流异常特征。研究表明,西南南地区降水空间上呈“东南-西北”型分布,从东南到西北递减；时间上西南绝大部分区域降水有减少趋势,2000年以后尤其是2009年后减少最明显,季风期和非季风期降水在近十年都有明显减少。利用SPI指数表征干旱变化,发现西南地区的大部分区域干旱有增加的趋势,且主要集中在西南中部,2009～2012年的干旱中心位于云南东部：进入21世纪后,西南干旱范围和干旱强度都达到了1960年以来的最大值,尤其是2009年到2010年的秋冬春跨季节持续强干旱是有记录以来最严重的。西南干旱具有周期性,主要存在25年、15年、8年和3年的周期特征。复杂的大气环流异常引起了我国西南地区的降水异常,形成干旱。分析造成西南干旱的直接环流系统发现,当西太平洋副热带高压面积异常偏大、强度偏强、位置异常偏西时,西南地区处于明显下沉气流控制,区域内偏北气流显著加强,水汽输送减少,对流层中低层水汽含量异常偏低,使得降水异常偏少,干旱发生。2009-2012年持续干旱、特别是2009～2010特大干旱发生期间,这种异常特征十分明显。更多还原

【Abstract】 The frequency and intensity of global drought had a increasing tendency under the climatic changing. China had always been one of the worst-hit countries, drought occurred more frequently in recent years, and drought area had a tendency to increase constantly, at the same time, the drought started to develop from arid and semi-arid regions to humid regions. Southwest of China, which had sumptuous rainfalls and humid climate in the history, repeatedly occurred severe drought disasters in recently years. Especially a once-in-60yeas extremely severe drought from autumn of2009to spring of2010took place in southwest and caused unquantifiable losses, and it had attracted great attention of more and more meteorologists at home and abroad. In this paper, firstly, the latest advances of drought study in southwest China were summarized. Then the drought intensity’s and range’s spatial-temporal distribution characteristics in southwest from1960to2012were analyzed based on the SPI drought index by means of objective statistics; period signature of southwestern drought was discussed and analyzed by means of the wavelet transform. Based on the analyses of spatial-temporal characteristics of drought, by picking rainy year and drought year, atmospheric circulation exceptional characteristics of different precipitation years were comparatively analyzed and the direct atmospheric circulation anomaly characteristics which caused continuous drought from2009to2012,especially the extreme drought event from2009to2010were revealed.According to our research, southwestern precipitation showed a type of "southwest-northeast" in space, which decreased from southwest to northeast; and the precipitation of most part of southwest tended to decrease in time and decreased most obviously after2000especially after2009; the precipitation decreased apparently both in summer monsoon season and in winter monsoon season in recent10years,Based on the SPI drought index,the drought of most part of southwest had a increasing tendency and was relatively concentrated in the middle of southwest, and the drought center position was in the east part of Yunnan from2009to2012, after entering the21st century, southwestern drought range and intensity both reached maximum since1960, especially the autumn-winter-spring continuous drought from2009to2010was the most severe since record began. Southwestern drought had a certain periodicity and mainly existed25-year,15-year and8-year periods. Complicated atmospheric circulation anomaly caused the precipitation anomaly of southwest, then the drought appeared. Based on the analysis on the main atmospheric circulation systems which directly influenced southwestern drought we could find that while west pacific subtropical high’s area was bigger and intensity was higher, with lying to the north or west of the normal position, southwest was under the control of abnormal down draft, the northern air significantly strengthened, and moisture transport decreased, and moisture content in middle-lower troposphere was abnormally less, which made precipitation become abnormally less and drought occur. The abnormal characteristics were very obvious during the continuous drought from2009to2012, especially the extreme drought event from2009to2010.更多还原