Two-way coupling between sea surface temperature (SST) variations in the midlatitude southern oceans and changes of synoptic-scale (2–8 day) eddy activities in the lower and upper troposphere throughout the year is investigated based on lagged maximum covariance analysis using reanalysis datasets from 1951 to 2000. Results show a strong seasonal dependence of the coupling, as characterized by the most prominent one in austral midsummer (January). On one hand, SST variations in austral late spring (primarily October) are likely to influence storm tracks in the following January. That is, significant warm SST anomalies in the western midlatitude areas of South Atlantic and south Indian Ocean could result in the systematic strengthening of the low-level and upper-level eddy activities, which is presumably attributed to the coherent intensification of the SST front and the lower-tropospheric baroclinicity. Particularly, interannual variability (a spectral peak at 4 yr) of SST in the western midlatitude South Atlantic in October could play a predominant role in driving the corresponding variability of the Southern Hemisphere storm tracks three months later. The timing of the discernible response of storm tracks is also discussed based on the preliminary results of sensitivity experiments. On the other hand, the strengthened eddy activities in January continue to induce the dipolelike patterns of SST anomalies in the midlatitude southern oceans. Those SST response patterns are, to the first order, determined by changes of the net surface heat flux. The anomalous Ekman advections in part driven by the storm-track changes also contribute to SST anomalies in the southern subtropical South Atlantic and the western midlatitude South Pacific.
Antarctic sea ice plays an important role in polar ecosystems and global climate, while its variability is affected by many factors. Teleconnections between the tropical and high latitudes have profound impacts on Antarctic climate changes through the stationary Rossby wave mechanism. Recent studies have connected long-term Antarctic sea ice changes to multidecadal variabilities of the tropical ocean, including the Atlantic Multidecadal Oscillation and the Interdecadal Pacific Oscillation. On interannual timescales, whether an impact exists from teleconnection of the tropical Atlantic is not clear. Here we find an impact of sea surface temperature (SST) variability of the tropical Atlantic meridional dipole mode on Antarctic sea ice that is most prominent in austral autumn. The meridional dipole SST anomalies in the tropical Atlantic force deep convection anomalies locally and over the tropical Pacific, generating stationary Rossby wave trains propagating eastward and poleward, which induce atmospheric circulation anomalies affecting sea ice. Specifically, convective anomalies over the equatorial Atlantic and Pacific are opposite-signed, accompanied by anomalous wave sources over the subtropical Southern Hemisphere. The planetary-scale atmospheric response has significant impacts on sea ice concentration anomalies in the Ross Sea, near the Antarctic Peninsula, and east of the Weddell Sea.
Antarctic sea ice, a sensitive indicator of climate change, has profound influence on global weather and climate (Hobbs et al., 2016). Since the satellite era, Antarctic sea ice experienced a modest increase of extent (Zhang et al., 2019), in contrast to the accelerating melt of Arctic sea ice (Stroeve et al., 2007). Sea ice simulated by climate models, however, shows a decreasing trend over both the Arctic and Antarctica (Eisenman et al., 2011; Turner et al., 2013). Therefore, much attention has recently been focused on understanding Antarctic climate and sea ice variability. Many studies have revealed the responses of Antarctic sea ice to the extrapolar ocean and atmosphere variability, through thermal and mechanical processes (Lefebvre & Goosse, 2005). On seasonal to interannual timescales, El Niño/Southern Oscillation (ENSO) and Southern Annular Mode (SAM) play key roles in influencing Antarctic sea ice variability, primarily through the processes of the ENSO/SAM-induced atmospheric advection and wind-driven sea ice drift (Doddridge & Marshall, 2017; Kohyama & Hartmann, 2016; Simpkins et al., 2012). Concerning the increasing trend in Antarctic sea ice, several mechanisms have been
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