南大西洋副热带偶极子的年际变化

The Interannual Variability of the South Atlantic Subtropical Dipole

南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。

South Atlantic Subtropical Dipole(SASD)is dominant mode of the air-sea coupling in the South Atlantic Ocean,and its sea surface temperature(SST)anomalies represents a northeast-southwest oriented dipole pattern.The SASD index is computed from SST anomalies between southwestern and northeastern pole.The positive and negative SASD events are defined as the years when SASD index exceeds±℃.This leads to 6 positive events and 9 negative events in 57 years from 1960 to 2016 using HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)dataset.The SASD index clear shows interannual variability with a period of 5~8 years.Then using ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)dataset for the period 1992-2016 and temperature tendency equation we diagnose mixed-layer temperature in southwestem and northeastern pole separately.Diagnosis reveals that interannual variability of SASD is due to the anomaly contribution from the surface thermal forcing terms,which is dominated by the shortwave radiation terms.