Effects of Arctic sea ice in autumn on extreme cold events over the Tibetan Plateau in the following winter: possible mechanisms

Miao Bi,Song Yang,Dong Guo,Xiaoting Sun,Xinyong Shen,Qingquan Li

doi:10.1007/s00382-021-06007-0

Abstract

Extreme cold events (ECEs) on the Tibetan Plateau (TP) exert serious impacts on agriculture and animal husbandry and are important drivers of ecological and environmental changes. We investigate the temporal and spatial characteristics of the ECEs on the TP and the possible effects of Arctic sea ice. The daily observed minimum air temperature at 73 meteorological stations on the TP during 1980–2018 and the BCC_AGCM3_MR model are used. Our results show that the main mode of winter ECEs over the TP exhibits the same spatial variation and interannual variability across the whole region and is affected by two wave trains originating from the Arctic. The southern wave train is controlled by the sea ice in the Beaufort Sea. It initiates in the Norwegian Sea, and then passes through the North Atlantic Ocean, the Arabian Sea, and the Bay of Bengal along the subtropical westerly jet stream. It enters the TP from the south and brings warm, humid air from the oceans. By contrast, the northern wave train is controlled by the sea ice in the Laptev Sea. It originates from the Barents and Kara seas, passes through Lake Baikal, and enters the TP from the north, bringing dry and cold air. A decrease in the sea ice in the Beaufort Sea causes positive potential height anomalies in the Arctic. This change enhances the pressure gradient between the Artic and the mid-latitudes, leading to westerly winds in the northern TP, which block the intrusion of cold air into the south. By contrast, a decrease in the sea ice in the Laptev Sea causes negative potential height anomalies in the Artic. This change reduces the pressure gradient between the Artic and the mid-latitudes, leading to easterly winds to the north of the TP, which favors the southward intrusion of cold polar air. A continuous decrease in the amount of sea ice in the Beaufort Sea would reduce the frequency of ECEs over the TP and further aggravate TP warming in winter.

Highlights

Sea ice in the Arctic region has been melting at an unprecedented rate and record low coverage has been repeatedly observed
The Extreme cold events (ECEs) over the Tibetan Plateau (TP) show a uniform mode throughout the region, the variability in the northern TP is slightly greater than that in the south (Fig. 1a)
Considering that the HadEX3 data interpolated from 316 stations in China only include 35 stations in the eastern TP, we adopt the observation dataset from 73 stations in the following

Summary

Introduction

Sea ice in the Arctic region has been melting at an unprecedented rate and record low coverage has been repeatedly observed. Zhang et al (2019) analyzed the winter snow anomalies on the TP and showed that the wave activity from the Arctic could reach the TP through both northern and southern routes when the atmospheric circulation is in a coupled mode of the positive phase of the Arctic Oscillation (+ AO) and the negative phase of the Western Pacific (− WP) teleconnection This creates the dynamic and moisture conditions required for snowfall over the TP and connects the TP with the Arctic. The polar front jet is weakened when the North Atlantic subpolar SIC decreases, which reduces the amount of warm and humid oceanic air entering the northern Eurasian continent, further reducing snow cover in the Ural Mountains This strengthens both the highpressure ridge in the Ural Mountains and the East Asian trough, forming a quasi-stationary Rossby wave across the Eurasian continent. Effects of Arctic sea ice in autumn on extreme cold events over the Tibetan Plateau in the following

Data and methods

Temporal and spatial characteristics of ECEs over the Tibetan Plateau

Summary and discussion