Tropical and extratropical SST effects on the midlatitude storm track

Effects of zonal variations in sea surface temperature (SST) on synoptic eddy activity are examined using an atmospheric general circulation model under the perpetual January and the aqua-planet conditions. In the presence of zonal variations in tropical SST, upper tropospheric zonal wind displays large zonal asymmetry and the storm track is located downstream of the maximum westerly speed. When only extratropical SST varies in the east-west direction, a storm track develops along the sharp meridional SST gradient despite a nearly zonally uniform westerly jet in the upper troposphere. The latter result suggests that zonal variations in upper tropospheric westerlies contribute to but are not necessary for zonally confined storm tracks.