On the Causes of Decreased Regional Extreme Wind Frequency over the Qinghai-Xizang Plateau during the Spring Season

Abstract

Extreme wind events （EWEs） not only are a kind of meteorological disaster， but also serve as an important natural resource.The Qinghai-Xizang Plateau （QXP）， well known as the "roof of the world"， is vulnerable to global and regional climate change.However， the characteristics and mechanism of variability of extreme wind events over this region and associated mechanisms remain elusive.Under the background of global change， Chinese Sichuan-Tibetan Railway construction， the exploration on changes in the EWEs could deepen our scientific understanding the regional climate.In order to explore the spatial-temporal distribution characteristics of regional extreme wind events （REWs） over the central and eastern QXP for the period of 1982 -2021， daily data of maximum wind speed are utilized to define REWs.Further， with the aid of thermal - thermodynamic diagnosis and the multiple statistical methods， such as trend analysis， EOF and composite analysis， we explore the potential causes leading to the decreased frequency of RWEs.The results show that： （1） The REWs over the QXP significantly decreased since 1980， varied consistently throughout the QXP and occurred mostly in the northeastern QXP.The REWs as defined in the 95th and 99th percentiles decline with the rate of 44d/10a and 11.6d/10a.（2） During periods of REWs， the circulation pattern is "high in the west and low in the east" in the middle and high latitudes and "low in the west and high in the east" in the low latitudes.The main characteristics are as follows： the abnormal positive geopotopic in Mongolia-Siberia， the abnormal cyclonic circulation in Mongolia， the abnormal westerly wind in the northeast of the plateau， and the abnormal negative surface temperature in Mongolia.（3） In the context of global change， the weakening of the Siberian high in spring and the strengthening of the East Asian trough in winter leads to decreasing pressure gradient between the north and south sides of the QXP， the weakening of the westerly jet stream leads to decreasing momentum downdraft， and the rise of non-uniform surface temperature in Asia leads to the decreasing temperature gradient between the north and south sides of the QXP.At the same time， the abnormal cyclonic circulation weakened in Mongolia.It may be resulted from the co-influence of these large-scale circulation and local thermal factors that reduce the frequency of regional extreme wind events in the central and eastern parts of the QXP.

Keywords

• qinghai-xizang plateau
• regional extreme wind
• east asian trough
• surface temperature