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Change in Sea Ice Cover is Responsible for Non-Uniform Variation in Winter Temperature over East Asia

LI Fei;WANG Hui-Jun;GAO Yong-Qi;Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences;Climate Change Research Center, Chinese Academy of Sciences;Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University for Information Science and Technology;Nansen Environmental and Remote Sensing Center and Bjerknes Centre for Climate Research;  
Observed winter(December–February) surface air temperature over East Asia(0°–60°N, 100– 140°E)(TEA) shows non-uniform variation during 1979– 2013, with cooling and weak warming north and south of 40°N. To understand this, the authors perform statistical analysis(linear regression and composite) on the observed data. The results suggest that reduced(increased) autumn sea ice cover in the Barents-Kara Sea(BK-ASIC) lowers(warms) TEA over northern East Asia, which is consistent with previous studies. In comparison, increased(decreased) winter sea ice cover in the Sea of Okhotsk(O-WSIC), warms(cools) the air over southern East Asia. The mechanism can be described as follows: When the BK-ASIC decreases, the East Asian winter monsoon tends to be stronger with an intensified Siberian high, leading to cooling over northern East Asia. An O-WSIC increase is associated with cold anomalies north of 50°N, altering the meridional temperature gradient between the midlatitudes and tropics, and leading to a northward shift of the East Asian jet steam in the upper troposphere. In the low atmosphere, anomalous northeasterly winds prevail north of 50°N and anomalous southerly winds control the southern coast of East Asia, contributing to the weak warming over southern East Asia. Version 3 of the Community Atmosphere Model also provides evidence for the impact of increased O-WSIC on the warm southern mode of TEA.
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