Southern Hemisphere Circulation and Relations with Sea Ice and Sea Surface Temperature

Abstract

Relationships on the seasonal timescale between Southern Hemisphere 500-hPa height, sea surface temperature, and Antarctic sea ice variability have been investigated using NCEP?NCAR reanalyses, NCEP sea surface temperatures, and Met Office sea surface temperature and sea ice data. The dominant region of interannual variability in the Southern Hemisphere circulation, over the southeast Pacific Ocean, is found to be related to ENSO variability in tropical Pacific sea temperatures, as shown in a number of earlier papers. It is also related to Antarctic sea ice variability, where an out-of-phase relationship is found between sea ice extent in the central Pacific and in the southwest Atlantic Ocean. Sea ice extent is enhanced in one region when the atmospheric flow anomaly is equatorward, presumably through a combination of anomalous heat flux and direct advection. At the same time, the atmospheric flow anomaly in the other region tends to be poleward, resulting in a poleward retreat in the sea ice edge. Such an interaction accounted for 63% of the total squared covariance between hemispheric 500-hPa height and sea ice edge anomalies. Averaged over the full data series used, no strong lag relationships were found, suggesting that circulation, sea ice, and sea surface temperatures respond to one another on intraseasonal timescales. However, a composite analysis with respect to the times of maxima or minima in Pacific sea ice extent did show apparently nonlinear lag behavior. The negative height anomalies over the southeast Pacific associated with maxima in Pacific sea ice tend to precede the ice maximum, or at least show no tendency to persist after the time of the ice maximum. However, positive height anomalies over the southeast Pacific associated with minima in Pacific sea ice tend to persist for some months after the ice minimum. The latter effect may be related to anomalous surface heat fluxes associated with the upstream reduction in sea ice.