2009 Articles

Satellite-based midlatitude cyclone statistics over the Southern Ocean: 2. Tracks and surface fluxes

Yuan, Xiaojun; Patoux, Jérôme; Li, Cuihua

Midlatitude cyclone tracks over the Southern Ocean are constructed for the 1999–2006 period using two surface data sets: European Centre for Medium-range Weather Forecasts (ECMWF) sea-level pressure analyses on one hand, and on the other hand modified analyses in which high-wavenumber pressure variability derived from scatterometer swaths has been injected with a wavelet-based method. A comparison of track statistics reveals the differences between the two data sets. The fluxes of momentum and sensible and latent heat associated with these midlatitude cyclones are calculated and sorted by life span. Three aspects of these cyclone flux statistics are investigated. (1) The momentum flux into the ocean is stronger inside cyclones than over the rest of the Southern Ocean, while the ocean loses more sensible and latent heat outside of the cyclones. (2) The momentum flux into the ocean and the loss of sensible and latent heat by the ocean are larger when calculated from the scatterometer-modified analyses than when calculated from the original ECMWF analyses. (3) Mesoscale cyclones (short-lived cyclones) contribute a significant amount of the fluxes between the atmosphere and the Southern Ocean, although over slightly different geographic areas from longer-lived cyclones.