Sensitivity of the atmospheric storm-track to an oceanic SST front

Over the last years, the emphasis of air-sea interaction studies has shifted from the effect of sea surface temperature (SST) anomalies occurring over large portions of an ocean basin to the effect of SST fronts such as the Gulf Stream or the Kuroshio Extension.

To understand the response of the atmospheric storm-track to such SST fronts, we use a modified version of a well-known, three-level quasi-geostrophic (QG) model on the sphere that has been modified to include simple parameterization of moist processes and surface exchanges. Its response is analyzed in terms of the upper-level atmospheric jet for sea surface temperature (SST) fronts of different profiles and located at different latitudes.

When the SST front is sufficiently strong, the mean atmospheric jet and storm-tracks tend to shift at the same time as the latitude of the SST front is shifted. This suggests that the jet's spatial location and pattern is mainly affected by the latitude of the SST front. When the SST front and the upper-level jet are vertically phase-locked, the change in strength of the SST front gives the strongest change in strength of the upper-level winds. Changes in the jet's pattern are studied in term of surface sensible heat flux and moist effects (through latent heat release). It is found that latent heat release due to moist processes is modified when the SST front is changed, and this is responsible of the meridional displacement of the jet. Moreover both latent heat release and surface sensible heat flux contribute to the jet strengthening. These results reveal how SST fronts of significant amplitude affect the upper troposphere.