夏季青藏高原及周边上对流层水汽质量及其向平流层传输年际异常. I：水汽质量异常主导型

本文利用逐年7~8月平均的ERA-Interim再分析资料并结合SWOOSH(Stratospheric water and ozone satellite homogenized)水汽数据,分析了青藏高原及周边地区330~360 K层次水汽质量分布的年际异常特征及其成因。结果表明,水汽质量分布异常表现为整体异常型、东西偶极异常型和南北偶极异常型三个主导分布型。整体异常型在水汽质量整体偏多时,青藏高原地区对流和垂直向上的水汽质量非绝热传输偏强,上对流层为异常偏强的水汽质量非绝热辐合;此时对应南亚高压偏强,青藏高原地区上对流层的水汽质量绝热辐散和高原以西地区的水汽质量绝热辐合都异常偏强,水汽质量整体偏少时则相反。东西偶极异常型水汽质量呈西多/东少分布时,青藏高原西部(中东部)对流和垂直向上的水汽质量非绝热传输异常偏强(弱),上对流层的水汽质量非绝热辐合和水汽质量绝热辐散也异常偏强(偏弱);同时对应南亚高压偏西,青藏高原以西到伊朗高原的上对流层有异常的自东向西的水汽质量绝热输送和水汽质量绝热辐合。水汽质量呈西少/东多分布时则有相反的结果。南北偶极异常型水汽质量呈北多/南少分布时,对应南亚高压偏北,青藏高原北部的上对流层有异常自南向北的水汽质量绝热输送所造成的水汽质量辐合,同时该地区低层异常偏强的自下向上的水汽质量非绝热输送也加强水汽质量辐合,而青藏高原南侧上对流层则为异常偏弱的水汽质量绝热辐散和水汽质量非绝热辐合,水汽质量呈北少/南多分布时相反。

Interannual Anomalies of Upper Tropospheric Water Vapor Mass and Its Transport into the Stratosphere over the Tibetan Plateau Area in Summer. Part I: Leading Patterns of Water-Vapor-Mass Anomalies

In this study, we used monthly averaged ERA-Interim reanalysis datasets and SWOOSH (Stratospheric water and ozone satellite homogenized) water vapor data to analyze the interannual geographic pattern of water-vapor-mass anomalies in the 340-360 K layers and its maintenance over the Tibetan Plateau (TP) region in July-August. Results show that interannual variations in the geographic patterns of water-vapor-mass anomalies have three dominant modes, namely, uniform, abnormal east-west dipole, and south-north dipole modes. In association with the positive phase of the uniform mode, that is, more water vapor mass over the entire TP area, stronger convective and upward diabatic water-vapor-mass transport over the TP region leads to an enhanced convergence of the water vapor mass. The strengthened South Asian high (SAH) results in an enhanced divergence and convergence of the adiabatic water-vapor-mass transport over the TP and to its west. The opposite occurs when there is less water vapor mass over the entire TP area. For the positive phase of the east-west diploe mode when the water vapor mass is more/less in the west/east of the TP area, the convective and diabatic water-vapor-mass transport, and the convergence and divergence of diabatic and adiabatic water vapor mass in the upper troposphere all enhanced over the western TP but weakened over the central and eastern TP. Meanwhile, the center of the SAH shifts westward, giving rise to an abnormal westward adiabatic water-vapor-mass transport and contribute to the abnormal convergence of water vapor mass from the TP to the Iranian Plateau in the upper troposphere. When the water vapor mass is less/more in the west/east of the TP area, the results are opposite. For the positive phase of the south-north dipole mode when the water vapor mass is more/less in the northern/southern TP, the center of the SAH shifts northward, giving rise to an abnormal northward adiabatic water-vapor-mass transport in the northern TP in the upper troposphere and a stronger upward diabatic water-vapor-mass transport in the lower layers, which both lead to abnormal convergence of the water vapor mass. In contrast, the divergence of adiabatic water-vapor-mass transport and the convergence of diabatic water-vapor-mass transport are weakened in the southern TP, and vice versa when less/more water vapor mass occurs in the northern/southern TP.