2009/2010年冬季云南严重干旱原因的进一步分析

A Further Study of Causes of the Severe Drought in Yunnan Province during the 2009/2010 Winter

为了揭示2009/2010年冬季云南出现严重干旱灾害的原因,本文利用NCEP/NCAR再分析资料以及云南省台站降水资料计算得到的云南冬季降水指数,讨论了在北半球冬季(12～2月)北大西洋涛动(North Atlantic Oscillation,简称NAO)和云南省降水(旱涝)之间的联系。分析结果表明,在1961/1962～2009/2010年间的49个冬季,冬季平均的云南降水指数和NAO指数的相关系数为0.373(超过95%信度),表明NAO和云南省冬季降水之间存在着一定的联系。云南省冬季降水指数和北半球300hPa位势高度异常场之间的回归结果表明,和云南冬季降水联系紧密的环流系统可分为南北两个主要部分:南支槽波列和贝加尔湖高压脊系统。研究表明,NAO可以通过在亚—非副热带急流中传播的准定常波列以及波的反射分别影响这两个系统。因此,NAO和云南冬季降水之间存在一定的联系。同时,我们的结果还表明NAO和云南冬季降水之间的关系还受ENSO事件的调制。在ENSO为暖位相的冬季,NAO和云南降水关系更为紧密,而在ENSO为冷位相的冬季,NAO和云南冬季降水的联系则不太显著。

To understand the mechanisms responsible for the severe drought in Yunnan Province during the boreal winter（DJF） of 2009/2010,by using NCEP/NCAR reanalysis data and winter precipitation index in Yunnan Province which is calculated from station precipitation data in Yunnan Province,this study investigates the relationship between the North Atlantic Oscillation（NAO） and the precipitation in Yunnan Province during boreal winters.In the 49 winters of 1961/1961-2009/2010 period,the correlation coefficient between the time series of winter mean precipitation indices in Yunnan Province and the NAO indices is 0.373（exceeds the 95% confidence level）,which indicates that the winter precipitation in Yunnan Province is linked to the variability of the NAO.Regression results between the winter precipitation indices in Yunnan Province and the northern hemispheric anomalous geopotential height at 300 hPa show that the circulation systems associated with the winter precipitation in Yunnan Province have a south and a north major components：the southern branch trough and the ridge of Lake Baikal.And the results show that the NAO can impact these two components through the quasi-stationary waves propagating along the Asia-Africa subtropical jet and the wave reflections,respectively.Therefore,the variations of the NAO and the winter precipitation in Yunnan Province are linked.The results also show that the linkage between the NAO and the winter precipitation in Yunnan Province is modulated by ENSO phenomenon.The relationship between the NAO and the winter precipitation in Yunnan Province is much close in the warm ENSO winters,while,they are barely linked in the cold ENSO winters.