中国西北地区冰雹的气候特征

利用1971-2000年西北185个站3～9月逐月和年冰雹次数,分析了西北冰雹的空间分布特征和时间演变规律.西北年冰雹次数有3个高值中心,一个在青海的曲麻莱,为19.6次,另一个在新疆西部的昭苏,为17.6次,第3个在青海的刚察,为12.7次.185个站冰雹的月变化呈单峰型,主要出现在6～8月.西北185个站冰雹的历年变化呈现出下降的趋势.从春季到秋季,冰雹强中心先起于新疆的昭苏这一中心有很强的持续性.青海南部的冰雹强中心5月在斑马,6月西伸到曲玛莱,7月再西移到托托河,8月东退到清水河,9月又南退到杂多,10月又东退到久治,然后基本消失.

Climatic Characteristics of Summer Precipitation in Northwest China

Based on the data of summer precipitation observed by 119 meteorological stations in northwest China during the period of 1961-2000,in this paper the spatial distribution and temporal change of summer precipitation in northwest China are analyzed,and the relationships between the occurrence of rainy years,arid years and summer precipitation in northwest China and the American upper air current of NCEP/NCAR 500 hPa,ground-air long-wave radiation field and north sea temperature of the equatorial Pacific Ocean.The results show that the spatial difference of summer precipitation in northwest China is great,and the minimum summer precipitation(6.7 mm) occurs at Turpan Meteorological Station in Xinjiang Uygur Autonomous Region,and the maximum one(446.9 mm) at Foping Meteorological Station in Shaanxi Province.In rainy years,the polar vortex at 500 hPa over the Northern Hemisphere is obviously shallow,the subtropical high over the west Pacific Ocean is strong,northwest China is a convergence area of the summer vector wind anomaly field of 700 hPa,the summer humidity anomaly center of 700 hPa is over northwest China,the main part of the summer ground-air long-wave radiation field is also over northwest China,and the negative anomaly of north sea temperature of the equatorial Pacific Ocean is mainly over the east equatorial Pacific Ocean.In arid years,the polar vortex at 500 hPa over the Northern Hemisphere is very deep,northwest China is a divergence area of the summer vector wind anomaly field of 700 hPa,summer humidity positive anomaly center of 700 hPa is over the west Bay of Bengal,the main part of positive anomaly of the summer ground-air long-wave radiation field is over northwest China,and the positive anomaly of north sea temperature of the equatorial Pacific Ocean is mainly over the east equatorial Pacific Ocean.