Atmospheric Response to Zonal Variations in Midlatitude SST: Transient and Stationary Eddies and Their Feedback*

Abstract

Midwinter storm track response to zonal variations in midlatitude sea surface temperatures (SSTs) has been investigated using an atmospheric general circulation model under aquaplanet and perpetual-January conditions. Zonal wavenumber-1 SST variations with a meridionally confined structure are placed at various latitudes. Having these SST variations centered at 30N leads to a zonally localized storm track, while the storm track becomes nearly zonally uniform when the same SST forcing is moved farther north at 40 and 50N. Large (small) baroclinic energy conversion north of the warm (cold) SST anomaly near the axis of the storm track (near 40N) is responsible for the large (small) storm growth. The equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction.