春季地表云辐射效应与7月高原低涡之间的联系

The Relationship between the Surface Cloud Radiative Effect in Spring and the Qinhai-Xizang Plateau Vortex in July

高原低涡是青藏高原夏季重要的降水系统,其移出高原还可在下游地区产生灾害性天气,探究前期因子对盛夏高原低涡的影响,可为高原低涡产生的灾害性天气预报提供参考依据.基于CERES辐射产品,ERA-Interim再分析资料及高原低涡数据集,采用相关分析、SVD分析、合成分析等方法,对2001-2017年春季地表净云辐射效应和7月高原低涡之间的联系进行了探讨.结果表明:当印度半岛春季云辐射加热作用偏强、中国东部及西太平洋地区云辐射冷却作用表现为北弱南强时,7月高原低涡(特别是暖性高原低涡)频数偏多、强度偏强,并且更容易移出高原.春季印度半岛云辐射加热通过增加地表温度,减小大气稳定度,从而增加印度半岛中低层气旋性环流,利于孟加拉湾的水汽向高原输送,为高原低涡提供水汽条件;同时加强高空辐散,进而造成南亚高压增强东伸,与低层系统配合,为低涡的生成及发展提供动力条件.中国东部及西太平洋地区云辐射冷却北弱南强地分布增加了向北和向南的温度梯度,增强了低层辐合、高层辐散的形势,从而有利于西太平洋副热带高压的增强西伸,从而使得洋面上的水汽更容易向内陆输送,为高原低涡的发生发展提供水汽条件.根据SVD分析结果定义了3个云辐射效应指数,它们对7月高原低涡的特征具有一定的指示意义.不同云辐射效应指数与环流场之间的相关关系验证了春季印度半岛(中国东部及西太平洋地区)地表净云辐射效应主要通过影响后期高原南侧的水汽输送和高层南亚高压(西太副高)的强度,进而影响有利于后期7月高原低涡生成和发展的条件.

The Tibetan Plateau Vortex(TPV)is an important kind of precipitation system over the Qinghai-Xizang(Tibetan)Plateau in summer,and TPVs can produce disastrous weather in the downstream area when they move off the Qinghai-Xizang(Tibetan)Plateau.Investigating the influence of early factors on the QXPVs in mid-summer can provide reference for the forecast of disastrous weather caused by QXPVs.Based on CERES radiation products,ERA-Interim reanalysis data,and QXPVs’datasets,the relationship between the surface net cloud radiative effect in Spring and the QXPV in July during 2001 to 2017 was discussed by using correlation analysis,SVD analysis,composite analysis methods.The results show that when the cloud radiative heating effect in the central India in spring is stronger,and the cloud radiative cooling effect in eastern China and the West Pacific region is weaker(stronger)in the north(south),the QXPVs in July(especially warm QXPVs)are more frequent,stronger,and easier to move out of the Qinghai-Xizang(Tibetan)Plateau.Cloud radiative heating effect in the central India in spring could increase the surface temperature and reduce the stability of the atmosphere,thereby increasing the mid-and low-level cyclonic circulation of the Indian Peninsula,which is conducive to the transportation of water vapor from the Bay of Bengal to the Qinghai-Xizang(Tibetan)Plateau and provides water vapor conditions for the QXPVs;At the same time,the high-level divergence is strengthened,which in turn causes the intensifying and eastward extension of South Asian High(SAH),and cooperates with the low-level system to provide dynamic conditions for the QXPVs.The Cloud radiative cooling effect weaker(stronger)in the north(south)of the eastern China and West Pacific region could increase the temperature gradient to the north and south,enhances the low(high)-level convergence(divergence),which is conducive to the intensifying and westward extension of the West Pacific Subtropical High(WPSH),thereby increasing the transportation of water vapor from the West Pacific to the inland,and provides water vapor conditions for the QXPVs.According to the results of SVD analysis,three Cloud Radiative Effect Indexes(CREI)are defined,which have certain indicative significance for the characteristics of the QXPVs in July.The relationship between the different CREIs and the circulation field verifies that the CRE of the Indian(eastern China and the Western Pacific region)in spring mainly affects the water vapor transportation on the southern side of the Qinghai-Xizang(Tibetan)Plateau and the intensifying of the high-level SAH(WPSH)in July,which affects the favorable conditions for the generation and development of QXPVs in July.