Satellite-based midlatitude cyclone statistics over the Southern Ocean: 1. Scatterometer-derived pressure fields and storm tracking

A wavelet-based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the European Centre for Medium-range Weather Forecasts (ECMWF). The resulting modified pressure fields are used to identify low-pressure centers over the Southern Ocean and to build statistics of midlatitude cyclones during 7 years of the SeaWinds-on-QuikSCAT operational period (July 1999 to June 2006). The impact of the scatterometer-derived pressure swaths is assessed with a statistical analysis of cyclone characteristics (central pressure, radius, depth) performed in parallel on the ECMWF and on the modified pressure fields. More low-pressure centers (5-10% depending on the season) are identified with the modified pressure fields, in particular incipient lows captured earlier than ECMWF and more short-lived mesoscale cyclones (with a life span less than 4 days). The cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average. A parallel spectral analysis reveals similar to 1% additional energy at scales less than 2000 km in the modified pressure fields.