摘要
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 of40°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 of50°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.
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 of40°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 of50°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.
基金
supported by the Public Science and Technology Research Funds Projects of Ocean(No.201205007)
the National Natural Science Foundation of China(Grant Nos.41421004 and 41130103)
the Special Fund for Public Welfare Industry(Meteorology)(Grant No.GYHY2013-06026)
the Nord Forsk-funded project GREENICE(No.61841):Impacts of Sea-Ice and Snow-Cover Changes on Climate,Green Growth,and Society