Katabatic wind fields in coastal areas studied by ERS‐1 synthetic aperture radar imagery and numerical modeling

Abstract

Synthetic aperture radar (SAR) images acquired over Mediterranean coastal waters from the first European Remote Sensing Satellite (ERS‐1) showing sea surface manifestations of katabatic wind fields are presented. In particular, sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of Calabria (southern Italy) into the Gulf of Gioia is investigated. The ERS‐1 SAR images show that their areal extent and shape vary strongly, depending on the meteorological conditions. The roughness pattern sometimes has the form of a mushroom, an elongated tongue, a broad blob, or a narrow truncated band. For one event (September 8, 1992) we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ERS‐1 SAR image by using the C band wind scatterometer model CMOD4. The comparison shows that the atmospheric model reproduces quite well the mushroom‐like form of the wind field pattern, while the wind speed is obtained somewhat lower than the one inferred from the SAR image. This study demonstrates that SAR images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea.