| Abstrakt: |
AbstractObserved 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) TEAover 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. |
