Essential Role of the Midlatitude South Atlantic Variability in Altering the Southern Hemisphere Summer Storm Tracks

Abstract

Storm tracks are a pivotal component in extratropical weather and climate. The sea surface temperature (SST) front in the midlatitude South Indian Ocean has been found to anchor the climatological core of the Southern Hemisphere (SH) storm tracks. However, on interannual‐to‐decadal timescales, observational and modeling evidence is presented here that the strengthened SST front in the midlatitude western South Atlantic (SA) can intensify the SH summer storm tracks by supplying more baroclinic energy, which overwhelms contributions from other oceanic frontal zones. Idealized experiments suggest that such a predominant impact on synoptic storms lies in the strengthened SA SST front acting in concert with the favorable thermal background produced in the presence of the Andes (i.e., enhancements of downstream low‐level temperature gradients and synoptic temperature variability). Our findings imply that oceanic variability in the western SA frontal zone could be a remote regulator of the SH extratropical summer climate variability.

Atmospheric responses to the interannual variability of sea surface temperature front in the summertime Southern Ocean

“…The downstream development of synoptic eddies is a well-known character for the storm tracks, which features a series of coherent baroclinic wave packets propagating along the westerly jet (Lee and Held 1993;Zhang et al 2020b). The downwind development of new packets is attributed to energy transfer by the upwind packets via the ageostrophic geopotential fluxes.…”

Remote Influence of the Midlatitude South Atlantic Variability in Spring on Antarctic Summer Sea Ice

“…Particularly, synoptic‐eddy vorticity fluxes, closely linked to storm‐track activity, act to convert the response of atmospheric circulation from baroclinic to equivalent barotropic and amplify it downstream (Deser et al., 2007). Our previous studies have suggested that SST variation in the western SA frontal zone has predominant influence on the hemispheric storm‐track activity in austral summer (Zhang et al., 2018, 2020, hereinafter Z20). Hence, we hypothesize that the SA SST variation can lead to the planetary‐scale atmospheric response through synoptic‐eddy feedback on the time–mean flow, and in turn imprint on Antarctic summer sea ice.…”