摘要
Arctic sea ice concentration (ASIC) in boreal autumn exhibits prominent interannual variability since 1979. The physical mechanism responsible for the year-to-year variation of ASIC is investigated through observational data analyses and idealized numerical modeling. It is found that the ASIC interannual variability is closely associated with the anomalous meridional circulations over the Northern Hemisphere, which is further linked with the tropical sea surface temperature (SST) forcing. A tropics-wide SST cooling anomaly leads to an enhanced meridional SST gradi- ent to the north of the equator in boreal summer, generating strengthened and northward shifting Hadley circulation over the Northern Hemisphere. Consequently, the meridional circulations are enhanced and pushed poleward, lead- ing to an enhanced descending motion at the North Pole, surrounded by an ascending motion anomaly; the surface outflow turns into easterly anomalies, opposing the mean-state winds. As a result, positive cloudiness and weakened surface wind speed emerge, which reduce ASIC through changes in the surface latent heat flux and the downward longwave radiation.
Arctic sea ice concentration (ASIC) in boreal autumn exhibits prominent interannual variability since 1979. The physical mechanism responsible for the year-to-year variation of ASIC is investigated through observational data analyses and idealized numerical modeling. It is found that the ASIC interannual variability is closely associated with the anomalous meridional circulations over the Northern Hemisphere, which is further linked with the tropical sea surface temperature (SST) forcing. A tropics-wide SST cooling anomaly leads to an enhanced meridional SST gradi- ent to the north of the equator in boreal summer, generating strengthened and northward shifting Hadley circulation over the Northern Hemisphere. Consequently, the meridional circulations are enhanced and pushed poleward, lead- ing to an enhanced descending motion at the North Pole, surrounded by an ascending motion anomaly; the surface outflow turns into easterly anomalies, opposing the mean-state winds. As a result, positive cloudiness and weakened surface wind speed emerge, which reduce ASIC through changes in the surface latent heat flux and the downward longwave radiation.
作者
Lei ZHANG
Tim LI
Lei ZHANG Tim LI(Climate Dynamics Research Center and Earth System Modeling Center, International Laboratory on Climate and Environment Change Nanjing University of Information Science & Technology, Nanjing 210044, China Department of Atmospheric Sciences, University of Hawaii, Honolulu,HI 96822, USA)
基金
Supported by National(Key)Basic Research and Development(973)Program of China(2015CB453200)
National Natural Science Foundation of China(41630423 and 41475084)
US Office of Naval Research(N00014-16-12260)
US Navy Resarch Laboratory(N00173-16-1-G906)
Jiangsu Province Natural Science Foundation Key Project(BK20150062)
Jiangsu Shuang-Chuang Team Fund(R2014SCT001)