Atmosphere (Jan 2022)
Can Arctic Sea Ice Influence the Extremely Cold Days and Nights in Winter over the Tibetan Plateau?
Abstract
The Arctic, Antarctic, and Tibetan Plateau (TP) are the northernmost, the southernmost, and the highest places of the Earth, respectively, known as Earth’s “three poles”. The Arctic and TP are the “North Pole” and “Third Pole”, and they exert a significant influence on the regional and global climate. This study analyzed the changing characteristics of Arctic sea ice and explored relationships between extreme cold days on the TP and sea ice concentration in the Arctic. From 1979 to 2019, the sea ice concentration of August–October decreased significantly. The low concentration of sea ice leads to a warmer Arctic and causes cold air over the Arctic to be unstable and more likely to move into the southern. Over the TP, the frequent cold air activities lead to more extreme cold events. This article aims to investigate the response characteristics of atmospheric circulation via the NCAR–CAM5.1 model (National Center for Atmospheric Research Community Atmosphere Model, Version 5.1). In order to verify the mechanism of Arctic sea ice concentration impacts on the extreme low temperature of the TP, we designed three experimental plans with different sea ice concentrations and sea surface temperatures (SST). In the two sensitivity experiments, the decrease in sea ice concentration and the increase in SST from August to October in the key areas are amplified simultaneously. The simulation results show that the increases in atmosphere thickness of 950–500 hPa in the Arctic from November to the following February reduce the meridional thickness-gradients between the Arctic and the middle latitudes. The westerly flow in middle–high latitudes weakened. As a result, the polar vortex over the Arctic is more likely to move south. There are negative geopotential height anomalies at 500 hPa over the Arctic and TP and positive anomalies over Eurasia. The anticyclonic system at 500 hPa slightly strengthens in the high latitudes of Eurasia (northerly winds in the TP). Strongly negative anomalies of temperature in the northern parts of the TP generate the cold source. To the north of the TP, the strengthened meridional propagation in middle–high latitudes causes more cold extremes.
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