西藏冰雹的气候特征

利用1981 ～ 2008年的逐日冰雹资料和2007～2008年的天气图资料,通过线性倾向估计、功率谱和聚类分析等方法,分析了西藏冰雹的气候特征及天气背景,结果表明:西藏地区年均冰雹日数呈下降趋势,并呈现出2～3年的准周期变化.多雹区沿高原地形和山脉呈带状分布,北部较多,西部和东部相对较少.全区年均冰雹日数为20.8天,最大中心位于那曲；西藏地区冰雹具有明显的季、月、日变化,冰雹在3 ～ 10月均有发生,主要出现在6～9月,为典型的夏雹型,夜间和早晨很少降雹,主要发生在12 ～20时之间.西藏地区冰雹与海拔高度和雷暴有很好的正相关,冰雹的发生与低涡、切变线、西风槽和西太平洋副高等天气系统有着密切的联系.

Climatic Character of Hail in Tibet

With the method of correlation analysis,power spectrum and cluster analysis,the climatic character of hail in Tibet and the weather background were analyzed by using the daily data of hailing days in Tibet from 1981 to 2008 and the weather map data from 2007 to 2008.Results show that the average annual hail days have a downward trend and a significant sign of 2 to 3 years of quasi-periodic changes in Tibet.The distribution of hail-rich zone is zonal along high altitude and mountains and the hail events occur more frequently in the north than in the west and east.The average annual hail days are 20.8 days in Tibet,and the biggest center locates at Naqv.The seasonal change of hail days is obvious in Tibet,and hail often occurs from March to October.Most hails happen from June to September.Tibet is a typical summer-hail district.There is little hail happens in the morning or at night,instead,it happens mainly at 12 to 20 o’clock.There is a positive correlation among the hail,altitude and thunderstorm.The happening of hail is closely connected with the synoptic system,such as vortex,shear line,westerly trough and west pacific subtropical high.