2012-2013年中国西南地区秋、冬、春季持续干旱的成因

利用多种资料从大尺度大气环流、水汽输送、热带海表温度、北极涛动、平流层极涡等方面分析了2012-2013年中国西南地区秋、冬、春季持续干旱的成因。结果表明, 西南水汽输送偏弱、高纬度地区南下冷空气路径偏东、冷暖空气难以在西南地区上空交汇, 是此次持续干旱的直接原因。这段时间西南地区大都受平直西风气流控制, 孟加拉湾和中南半岛地区位势高度较常年偏高, 不利于这些地区气旋性环流的发展;热带海表温度异常变化,特别是冬春季印度洋海表温度的持续偏高, 使得菲律宾地区上空低层反气旋异常环流增强。这些都导致了西南向水汽输送偏弱。此外, 北极涛动异常变化对西南地区的干旱也有重要影响, 北极涛动持续处于负位相, 不仅使南支槽减弱变浅, 西南水汽输送减少, 还导致贝加尔湖高压脊偏弱, 使北方南下冷空气主体偏东。冬季平流层极涡强度的变化在各个高度的位势高度场和位势涡度场上都有体现, 其变化对冷空气的强度及路径有明显影响。

Causes of Continuous Drought in Southwest China from Autumn of 2012 to Spring of 2013

In this paper, the causes of the continuous drought occurred in Southwest China from October of 2012 to April of 2013 are analyzed with a variety of data by diagnosing the influence of large scale atmospheric circulation, water vapor transportation, tropical sea surface temperature, Arctic Oscillation and stratospheric polar vortex. The results show that the difficult intersection of cold and warm air over the Southwest China caused by the decrease of the southwestern water vapor transportation and the eastward pathway of the cold air from high latitudes was the direct cause of the continuous drought in the Southwest China. The Southwest China was dominated by the straight westerly flow and the geopotential heights of the Bay of Bengal and Indo-China Peninsula were higher than normal during this time. It was not conducive to the development of cyclonic circulation over these regions. Changes of the tropical sea surface temperature especially for the Indian Ocean which was persistently high have enhanced the abnormal low-level anticyclone circulation over the Philippine area during winter and spring. All above these have led to weaken the southwestern water vapor transportation. In addition, the abnormal changes of Arctic Oscillation also played an important role in the continuous drought. The sustained negative phase of Arctic Oscillation not only made the Southern Trough become weaker so that the southwestern water vapor transportation reduces, but also weakened the Lake Baikal ridge so that the pathway of the boreal cold air shifts eastwardly. Changes of the strength of stratospheric polar vortex had a significant effect on the intensity and pathway of the cold air which can be reflected by geopotential height and potential vorticity at different levels in winter.