Extreme Snow Decrement on the Tibetan Plateau in Early Spring of 2022

Abstract

In early spring (March–April) of 2022, the snow depth on the Tibetan Plateau (TP) witnessed a historic decrement, breaking its records in the past few decades. The snow decrement was marked by an early beginning, a rapid pace of decline and extensive spatial coverage, which may play an important role in triggering the extreme events in the upcoming summer. This study investigated the underlying causes of this extreme snow decrement from the perspectives of local air–land interaction and crucial atmospheric circulations modulation. The extreme snow decrement can be attributed to a combination of factors, including an initial surplus in snow depth, anomalously high solar radiation influx, reduced precipitation and warm surface air temperature. Amongst these, the latter two factors were the key contributors leading to weakened snowfall (lowest) and increased snowmelt. Analysis of large-scale atmospheric circulation reveals the influence of a barotropically abnormal anticyclone (strongest) over the TP. The peripheral flow of this anticyclone suppressed the moisture supply, and the associated sinking motion (second strongest) enhanced the adiabatic heating (second highest). Further investigation suggests that this peculiar anticyclone might be linked to a robust positive North Atlantic Oscillation (NAO) signal. In conjunction with other favourable forcing and atmospheric conditions, the NAO triggered a wave train that propagated to the TP and contributed to the formation of the exceptional anticyclone.