Scatterometer and ECMWF-derived wind vorticity over the Mediterranean Basin

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Abstract

This article investigates the spatial and temporal structures of the monthly mean vorticity fields equation image and equation image 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 equation image and equation image over the whole Mediterranean Sea (relative bias equation image) of 0.108×10−5 s−1. Furthermore, both the cyclonic and the anticyclonic components of equation image are stronger than those of equation image. The analysis of the spatial features of equation image and equation image shows that the greatest discrepancies occur along coasts and in the Adriatic Sea, due to the ability of equation image to describe vorticity features smaller than about 6.9×103 km2, roughly corresponding to square areas of side 83 km or circular areas of radius 46 km, that are not present in equation image, given the effective spatial resolution of the model. The temporal features of equation image and equation image have shown a substantially similar trend in anticyclonic and a deep difference in cyclonic circulations, again related to the limited ability of equation image to describe small-scale vorticity patches as the main source of the differences. Local characterization of equation image and equation image, along six transects across areas where the wind vorticity features are well known, has confirmed the results of substantial similarity of equation image and equation image 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 © 2012 Royal Meteorological Society

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