GEV指数表征的贵州夏旱分布特征及干旱事件的异常环流特征

On interannual distribution variations of summer drought in Guizhou and analysis of abnormal circulation on drought event

利用贵州省81个台站的夏季降水资料、NCEP/NCAR再分析资料以及英国哈德雷中心(MOHC)提供的海温资料,基于广义极值分布理论(Generalized Extreme Value Distribution,GEVD),构建了一种新的干旱指数I_(Gev),研究了该指数所表征的贵州夏季干旱的时空分布特征,并对贵州夏季干旱时的环流背景进行了分析.结果表明:贵州省的夏季降水更接近于服从Weibull分布,且省内南部与东北部的夏季降水具有较大的年际变率;贵州夏季GEV干旱指数I_(Gev)具有显著的年际变化,就干旱事件的表征而言,季尺度的GEV干旱指数能够更好地反映贵州干旱事件的分布与发生发展特征;贵州夏季干旱的形成与对流层低层在中南半岛及南海地区上空出现的异常的气旋式环流以及西北太平洋日本南部洋面上空的异常反气旋式环流有关,且异常垂直环流中贵州地区受到显著的下沉运动控制,使得来自于南方的暖湿气流和来源于北方的冷空气较常年均有所偏弱,贵州省成为水汽通量的辐散区,不利于当地降水的形成,从而导致干旱的发生;最后,贵州夏季GEV干旱指数与同期印度洋北部及西北太平洋的海温的存在密切的关系,印度洋及西北太平洋海温的异常偏低可作为预测贵州夏季干旱的一个重要的前期信号.

By the use of summer precipitation data of 81 stations, NCEP/NCAR monthly data reanalysis and SST data provided by Hadley Centre, we have introduced a new approach to constructing drought index based on the Generalized Extreme Value （GEV） distribution.Meanwhile the circulation background of summer drought in Guizhou has been analyzed.The results show that the precipitation in Guizhou parallels Weibull distribution pattern, and distribution scale parameters show that the summer precipitation south and northeast Guizhou has great interannual variability.Summer drought index of Guizhou witnesses obvious interannual variations, and can monitor the distribution of drought to a certain extent. The summer drought index of Generalized Extreme Value （GEV） in Guizhou can help us to analyze the summer drought anomalous cyclonic circulation formation.The lower troposphere in the Indo China Peninsula and the South China Sea and the Pacific Northwest, over the Southern Ocean anomalies over the anticyclonic circulation can reduce water vapor transport in the area of the bay of Ben- gal and India ocean, and result in water vapor flux divergence in Guizhou, which is not conducive to the formation of the local precipitation.At the same time, the abnormal vertical circulation in Guizhou is significant in sinking motion control, whether it is from the South warm moist air flow or northern cold air is often an average somewhat weak, leading to drought.Finally, the drought index in the same period in the northern Indian Ocean and Northwest Pacific SST presents close relationship.The anomaly SST in the northwest Pacific and Indian Ocean can be used as an early signal to predict summer drought of Guizhou region.