Use of transient features to identify eastward currents in the Southern Ocean

Sea surface temperatures and sea surface slopes, measured by the ERS‐I satellite, are used to investigate the propagation of mesoscale features in the Southern Ocean. The Antarctic Circumpolar Current (ACC) is clearly identifiable as a region of eastward propagation surrounded by mostly westward propagation. This confirms predictions based on results from the Fine Resolution Antarctic Model, which suggest that the ACC is a region of flow which is supercritical with respect to the propagation of baroclinic Rossby waves. This supercriticality allows the ACC to penetrate deep enough to interact with bottom topography and so may be an important part of the mechanism by which the current achieves a balance of angular momentum. The propagation directions derived from the two independent data sources agree in remarkable detail, and many dynamical features can be identified, including the South Atlantic Current and the Tasman Front. The wavelengths calculated using the two data sets are quite sensitive to details of the processing. While this means they can be said to be “not inconsistent,” the relationship between temperature gradients and slopes demands further investigation. The results on direction of propagation, however, are robust.