USING SAR AND LAM WIND FIELDS TO INVESTIGATE THE EFFECTS OF LAND/ATMOSPHERE INTERACTION

摘要

Satellite-borne Synthetic Aperture Radar (SAR) images provide data sets at exceptionally high spatial resolutions, appropriate for investigating several kinds of atmospheric phenomena occurring in theMarine Atmospheric Boundary Layer (MABL). Also the present atmospheric Limited AreaModels (LAM), thanks to their high spatial resolution (1 km or so), permit to represent the small scale forcing linked, for instance, to topographic features and, more in general, to the MABL internal dynamics. This paper tries to contribute to solve the question on how LAM and SAR can be used together, particularly to study the effects of the land/atmosphere interaction. This has been carried out over an area around the Crete island in the eastern Mediterranean Sea, a region subject to complex wind patterns, due to the interaction of the almost steady northerly etesian wind with the orography of the many islands in the region. The Weather Research & Forecasting (WRF) atmospheric model has been used to hindcast the wind field at a horizontal resolution of 1 km over the area imaged by an Envisat ASAR image, from which the wind field has been extracted using a methodology based on the two-dimensional continuous wavelet transform. The winds derived from these two different tools have been compared statistically but also examining the similarities and differences of the gravity wave trains and of the areas subject to wind shielding at the islands lee side, present in both the wind fields. The figure emerging from the analysis is that both the approaches to the wind field determination are not fully satisfactory. Further careful investigations are needed to understand the reasons of the incorrect description of the meteorological features imprinted on the sea surface backscatter signature, which was taken as a reference.