The Impact of Tibetan Plateau Snow Cover on the Summer Temperature in Central Asia

Abstract

The current work examines the impact of the snow cover extent (SCE) of the Tibetan Plateau (TP) on the interannual variation in the summer (June-July-August) surface air temperature (SAT) over Central Asia (CA) (SAT_CA) during the 1979–2019 period. The leading mode of the summer SAT_CA features a same-sign temperature anomalies in CA and explains 62% of the total variance in SAT_CA. The atmospheric circulation associated with a warming SAT_CA is characterized by a pronounced high-pressure system dominating CA. The high-pressure system is accompanied by warm advection as well as descending motion over CA, favoring the warming of the SAT_CA. Analysis shows that the interannual variation in the summer SAT_CA is significantly positively correlated with the April SCE over the central-eastern TP. In April, higher than normal SCE over the central-eastern TP has a pronounced cooling effect on the column of the atmosphere above the TP and can persist until the following early summer. Negative and positive height anomalies appear above and to the west of the TP. In the following months, the perturbation forcing generated by the TP SCE anomalies lies near the western center of the Asian subtropical westerly jet (SWJ), which promotes atmospheric waves in the zonal direction guided by the Asian SWJ. Associated with this atmospheric wave, in the following summer, a significant high-pressure system dominates CA, which is a favorable condition for a warm summer SAT_CA.

摘要

本文主要探究了1979-2019年青藏高原前期4月积雪(SCE)异常对中亚地区后期夏季(6-8月)气温的影响. 中亚夏季气温EOF第一主模态的方差解释率超过62%, 且呈现区域一致型分布. 当中亚地区夏季气温异常偏高时, 中亚地区上空是显著的异常高压控制, 异常高压系统的下沉运动使得地面增温, 此外, 高压系统南侧伴随有来自低纬度的异常暖平流, 也有利于中亚地区夏季气温增暖. 研究发现中亚地区夏季气温的年际变化与前期4月青藏高原中东部的积雪呈显著的正相关关系且青藏高原4月的积雪异常可以维持到初夏. 进一步分析发现, 当青藏高原中东部4月积雪异常偏多时, 可以对高原上空的局地大气产生冷却作用, 并在青藏高原的上空出现位势高度场负异常, 从而引起高空涡度异常扰动且位于亚洲副热带西风急流(SWJ)的核心区, 在之后的时间涡度扰动在西风急流里以罗斯贝波的形式发展并在西风的波导作用下传播. 在后期夏季, 该波列在中亚地区发展为显著的高压异常, 有利于中亚地区夏季气温异常偏高.