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Observations of Bora Events over the Adriatic Sea and Black Sea by Spaceborne Synthetic Aperture Radar

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  • 1 Institute of Oceanography, University of Hamburg, Hamburg, Germany
  • | 2 P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
  • | 3 GKSS Research Center, Geesthacht, Germany
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Abstract

Bora events over the Adriatic Sea and Black Sea are investigated by using synthetic aperture radar (SAR) images acquired by the advanced SAR (ASAR) on board the European satellite Envisat. It is shown that the sea surface roughness patterns associated with bora events, which are captured by SAR, yield information on the finescale structure of the bora wind field that cannot be obtained by other spaceborne instruments. In particular, SAR is capable of resolving 1) bora-induced wind jets and wakes that are organized in bands normal to the coastline, 2) atmospheric gravity waves, and 3) boundaries between the bora wind fields and ambient wind fields. Quantitative information on the sea surface wind field is extracted from the Envisat ASAR images by inferring the wind direction from wind-induced streaks visible on SAR images and by using the C-band wind scatterometer model CMOD_IFR2 to convert normalized cross sections into wind speeds. It is argued that spaceborne SAR images acquired over the east coasts of the Adriatic Sea and the Black Sea are ideal means to validate and improve mesoscale atmospheric models simulating bora events.

* Current affiliation: NATO Underwater Research Center, La Spezia, Italy

Corresponding author address: Werner Alpers, Institut für Meereskunde, Universität Hamburg, Bundesstrasse 53 D-20146, Hamburg, Germany. Email: alpers@ifm.uni-hamburg.de

Abstract

Bora events over the Adriatic Sea and Black Sea are investigated by using synthetic aperture radar (SAR) images acquired by the advanced SAR (ASAR) on board the European satellite Envisat. It is shown that the sea surface roughness patterns associated with bora events, which are captured by SAR, yield information on the finescale structure of the bora wind field that cannot be obtained by other spaceborne instruments. In particular, SAR is capable of resolving 1) bora-induced wind jets and wakes that are organized in bands normal to the coastline, 2) atmospheric gravity waves, and 3) boundaries between the bora wind fields and ambient wind fields. Quantitative information on the sea surface wind field is extracted from the Envisat ASAR images by inferring the wind direction from wind-induced streaks visible on SAR images and by using the C-band wind scatterometer model CMOD_IFR2 to convert normalized cross sections into wind speeds. It is argued that spaceborne SAR images acquired over the east coasts of the Adriatic Sea and the Black Sea are ideal means to validate and improve mesoscale atmospheric models simulating bora events.

* Current affiliation: NATO Underwater Research Center, La Spezia, Italy

Corresponding author address: Werner Alpers, Institut für Meereskunde, Universität Hamburg, Bundesstrasse 53 D-20146, Hamburg, Germany. Email: alpers@ifm.uni-hamburg.de

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