Scatterometer and ECMWF-derived wind vorticity over the Mediterranean Basin

This article investigates the spatial and temporal structures of the monthly mean vorticity fields omega(-sc) and omega(-e) over the Mediterranean Basin, derived respectively from satellite scatterometers and ECMWF global atmospheric model (T799) wind fields from February 2006 to January 2010. Statistics show a mean difference between omega(-sc) and omega(-e) over the whole Mediterranean Sea (relative bias Delta(omega) over bar) of 0.108x10(-5) s(-1). Furthermore, both the cyclonic and the anticyclonic components of omega(-sc) are stronger than those of omega(-e). The analysis of the spatial features of omega(-sc) and omega(-e) shows that the greatest discrepancies occur along coasts and in the Adriatic Sea, due to the ability of omega(-sc) to describe vorticity features smaller than about 6.9x10(3) km(2), roughly corresponding to square areas of side 83 km or circular areas of radius 46 km, that are not present in omega(-e), given the effective spatial resolution of the model. The temporal features of omega(-sc) and omega(-e) have shown a substantially similar trend in anticyclonic and a deep difference in cyclonic circulations, again related to the limited ability of omega(-e) to describe small-scale vorticity patches as the main source of the differences. Local characterization of omega(-sc) and omega(-)e, along six transects across areas where the wind vorticity features are well known, has confirmed the results of substantial similarity of omega(-sc) and omega(-e) at spatial scales larger than 100 km or so and remarkable differences in those regions, such as the Adriatic and Crete seas, affected by vorticity variability at smaller scales. Copyright (C) 2012 Royal Meteorological Society