近50年河南初夏旱涝异常特征分析

对1958～2006年河南38站的6月降水量进行分析,发现EOF第一模态呈全省一致的分布型,因此用38站平均降水量代表全省初夏降水.选取旱、涝年,对异常合成场进行分析,在涝年,北太平洋和日本以南洋面为负的潜热通量异常;500 hPa贝加尔湖以北有正的高度异常,我国东部和近海为正的高度异常,北太平洋为正的高度异常;850 hPa河南省西部是异常的东北风,东部是异常的西南风.通过定义高度指数,得到与河南省初夏降水关系密切的500 hPa高度场分布型,即贝加尔湖高压脊偏强,东亚大槽偏弱和西太副高偏北同时存在.对海洋要素场的相关分析表明,前期太平洋黑潮区的SST较高,海洋持续向大气输送潜热通量偏多,后期其东北侧太平洋从大气吸收热量,导致上空的位势高度偏高,有利于河南省降水.

ANALYSES OF THE CHARACTERISTICS OF EARLY-SUMMER DROUGHT AND FLOODIN IN HENAN IN THE PAST 50 YEARS

An analysis of June precipitation in 38 stations of Henan province from 1958 to 2006 has shown that the 1st mode of EOF is consistently distributed across the whole province. Therefore the averaged precipitation in the 38 stations is used to represent the amount for the whole province. The drought years and flood years are selected to calculate the anomaly composite field. During the flood years, there are negative latent heat anomalies over the northern Pacific Ocean and in the south of Japan, and positive height anomalies in the north of Baikal, the east and offshore areas of China and over the northern Pacific Ocean on 500 hPa and 850 hPa; there is anomalous northeasterly in the west of Henan and anomalous southwesterly in the east of it. By defining an index for the geopotential height, a 500 hPa height field mode, which has close relationship with the precipitation in early summer, is determined. That is to say, a strong high ridge in Baikal coexists with a weak East Asian trough and a northward-than-normal subtropical high in the western Pacific Ocean. Correlation analysis of the oceanic elements indicates that higher precedent SST over the Kuroshio Extension is accompanied by persistent transfer of more latent heat from the ocean to the atmosphere and the ocean in the northeast of this area absorbs heat from the atmosphere at a later stage, which leads to the rise of the 500 hPa geopotential height field and is beneficial to the precipitation in Henan province.