2020 Volume 29 Issue 1 Pages 1-17
Interannual variations of sea-surface temperature (SST) in the subtropics and mid-latitudes of the Southern Hemisphere are characterized by a dipole pattern of SST anomalies over the northeastern and southwestern parts of each ocean basin, known as the Subtropical Dipole. This study first demonstrates that over the positive SST anomalies associated with the Subtropical Dipole, the ocean mixed-layer thicknesses become anomalously thin (thick) and enhance warming (cooling) of the mixed-layer by the shortwave radiation, resulting in the development of the positive (negative) SST anomalies. The variations of the mixed-layer thicknesses are attributed to the latent heat flux anomalies associated with the overlying subtropical high variations. However, decadal SST variations over the South Atlantic and southern Indian Oceans tend to migrate eastward and interact with the overlying sea-level pressure (SLP) variations. The ocean temperature anomalies are found in the subsurface ocean where the ocean density anomalies propagate eastward as quasi-stationary oceanic Rossby waves under the influence of the eastward Antarctic Circumpolar Current. A series of ocean-atmosphere coupled model experiments shows skillful predictions of the decadal SST variabilities observed over the South Atlantic and southern Indian Oceans.
