Observed winter surface air temperature over East Asia (0°–60°N, 100–140°E) (T_EA) 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 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: 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 T_EA.

 Figure Regression patterns of (a) autumn and (b) winter Arctic sea ice cover (color scale; units:10² km²) anomalies against standardizedT1000 PC1 and PC2 during 1979–2013, respectively. Hatched regions indicate significant values based on the (a) 95% and (b) 90% confidence level from a two-tailed Student’st-test. Regression patterns of (c) autumn and (d) winter surface turbulent heat flux (colour scale; units: W m^？2) anomalies against standardized BK-ASIC|？ and O-WSIC|+, respectively. Hatched regions indicate significant values based on the 95% confidence level from a two-tailed Student’s t-test.

Citation: Li, F., H.-J. Wang, and Y.-Q. Gao, 2015: Change in sea ice cover is responsible for non-uniform variation in winter temperature over East Asia, Atmos. Oceanic Sci. Lett., 8, doi:10.3878/AOSL20150039.

Link: http://159.226.119.58/aosl/EN/abstract/abstract581.shtml