Ocean and Atmosphere Storm Tracks: The Role of Eddy Vorticity Forcing

Signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period, 1992–2002. In the atmo-sphere, there are localized regions of eddy variability referred to as storm tracks. At the entrance of the storm track the eddies grow, providing a downgradient heat flux and accelerating the mean flow eastward. At the exit and downstream of the storm track, the eddies decay and instead provide a westward accel-eration. In the ocean, there are similar regions of enhanced eddy variability along the extension of mid-latitude boundary currents and the Antarctic Circumpolar Current. Within these regions of high eddy kinetic energy, there are more localized signals of high Eady growth rate and downgradient eddy heat fluxes. As in the atmosphere, there are localized regions in the Southern Ocean where ocean eddies provide statistically significant vorticity forcing, which acts to accelerate the mean flow eastward, provide torques to shift the jet, or decelerate the mean flow. These regions of significant eddy vorticity forcing are often associated with gaps in the topography, suggesting that the ocean jets are being locally steered by topog-raphy. The eddy forcing may also act to assist in the separation of boundary currents, although the diag-nostics of this study suggest that this contribution is relatively small when compared with the advection of planetary vorticity by the time-mean flow. 1