青藏高原与黄土高原过渡区雷暴活动特征及东亚夏季风的影响

Variation of Thunderstorm Activities and Its Connection to East Asian Summer Monsoon in Transition Region Between Qinghai-Xizang Plateau and Loess Plateau

利用1951-2012年青藏高原与黄土高原过渡区(下称研究区)54个站点雷暴日数观测资料,分季节统计了研究区雷暴发生日数的年际和季节变化特征及其对东亚季风的响应。结果表明,研究区夏季雷暴日数最多,春季次之,秋季较少,冬季几乎无雷暴发生。青藏高原东部的甘南地区年平均雷暴日数最多,其次为祁连山东部的永登和乌鞘岭地区,靠近黄土高原地区的年平均雷暴日数相对较少,研究区雷暴日数总体呈下降趋势。夏季(6-8月)雷暴日数多年对应强夏季风年,雷暴日数少年对应弱夏季风年。东亚夏季风强年,研究区水汽通量明显偏大,西太平洋副热带高压西伸脊点位置偏东,新疆东侧和内蒙古西北侧500 hPa高度场偏低,蒙古热低压处于发展阶段,这些特点都有利于强对流天气的产生;东亚夏季风弱年,情况则相反。小波分析结果表明夏季雷暴日数与东亚夏季风都存在准30年的振荡周期。

Thunderstorm days data collected from 54 stations over the transition region between the Qinghai-Xizang Plateau and the Loess Plateau from 1951 to 2012 were used to study the variation of thunderstorm activities and its connection to the East Asian Summer Monsoon(EASM).The results show that thunderstorm is the most active in summer,followed by spring and autumn.While almost no thunderstorm occurs in winter.There are two centers with high number of thunderstorm days,one of which is located in the Gannan area close to the QinghaiXizang Plateau and the other is in the Yongdeng and Wushaoling area.The Loess Plateau has much less number of thunderstorm days.The number of thunderstorm days decreased during the study period and years with strong EASM corresponded to years with high number of summer thunderstorm days,while years with weak EASM corresponded to years of medium and low number of summer thunderstorm days.Years with strong EASM are characterized by relatively high water vapor flux to the study region,eastward position of the western ridge of Western Pacific subtropical high,low geopotential height on 500 hPa in the east of Xinjiang and the northwest of Inner Mongolia,and developed Mongolia thermal low.These characterized are conducive to the generation of severe convective weather.Wavelet analysis indicates a quasi-thirty year period for both the number of thunderstorm days in summertime and the EASM.