European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Werner Alpers Institute of Oceanography, University of Hamburg, Hamburg, Germany Andrei Ivanov P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia Knut-Frode Dagestad Nansen Environmental and Remote Sensing Center, Bergen, Norway Investigation of Bora and Foehn winds over the Black Sea using Envisat synthetic aperture radar images

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg The sea area off the east coast of the Black Sea is an area where often pronounced local winds are encountered due to its coastal topography. The most prominent one is the Novorossiskaya Bora, which is strong wind blowing from the coastal mountains onto the sea, which can attain speeds of up to 40 m/s. But often also Foehn winds are encountered.

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Novorossiyskaya boras Foehn winds Novorossiyskaya boras

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Envisat ASAR WSM image (VV polarization) acquired on 5 February 2010 at 0745 UTC during a bora event over the east coast of the Black Sea. Novorossiysk Tuapse

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Wind speed measured at the Novorossiysk (dark blue) and Tuapse (violet) weather stations from 00:00 local time (UTC +3 h) on 2 February to 21:00 local time on 8 February 2010 during a bora event. The time of the ASAR data on 5 February at 0745 UTC is marked by the vertical dark line. Wind speed measured at meteorological stations

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Near-surface wind field retrieved from the ASAR image by using the wind direction from the NCEP model showing wind jets with embedded atmospheric gravity waves. Atmospheric gravity waves

European Geophysical Union, Wien, 6 April 2011 a Streamlines associated with a nonlinear atmospheric gravity wave (lee wave). In the shadowed region the airflow associated with the wave is opposite to the ambient wind direction (adapted from Doyle, and Durran,2002). σ σ0σ0 b Variation of the normalized radar cross section σ caused by this nonlinear atmospheric gravity wave. σ 0 is the undisturbed (background) value. On the SAR SAR image the atmospheric gravity wave appears as a broad bright band bordered by two narrow dark bands. Wave propagation direction Wind direction a Atmospheric gravity waves behind a mountain (lee waves)

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Novorossiysk MODIS Terra color composite image of the east coast of the Black Sea around Novorossiysk acquired on 5 February 2010 at 0805 UTC showing in the cloud pattern a cyclonic eddy (marked by the inserted arrow) and atmospheric gravity waves near Novorossiysk). Tuapse Black Sea

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Left: Envisat ASAR WSM image (VV polarization) acquired on 02 November 2009 at 0731 UTC over the eastern section of the Black Sea showing in the northern section a wind jet. ace roughness pattern. The imaged area is 400 km x 470 km. Right: Wind field derived from ASAR image using wind direction from NCEP. Tuapse

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Novorossiyskaya boras Foehn winds Interaction of Foehn wind with an atmospheric eddy over the Black Sea (submitted to Monthly Weather Review as “Picture of the Month”)

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Section of a SAR image acquired by Envisat in the Wide Swath mode (VV polarization) at 0732 UTC (0932 LST) 13 September 2010 over the eastern section of the Black Sea. The imaged area is 400 km x 480 km. The inset shows the location of the SAR scene. The features denoted by numbers are explained in the text. © ESA Foehn wind

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg MODIS Terra color composite image acquired at 0830 UTC 13 September 2010 showing in the eastern section of the Black Sea a cyclonic eddy in the cloud pattern. The inserted latitude and longitude lines have a grid spacing of 5 0 x 5 0. © NASA GSFC. Eddy Black Sea

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Near-surface wind field calculated from the NCEP GFS model for 0900 UTC 13 September 2010.

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Near-surface wind field retrieved from the SAR image by using the wind retrieval algorithm of CLS.

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg MODIS Terra color composite image acquired at 0745 UTC 12 September 2010, approximately 24 hours before the SAR data acquisition, showing the eastern section of the Black Sea, the Caucasus area with the Kolkhida Lowland, and the western section of the Caspian Sea. The star denotes the location of the Kutaisi weather station. Note the blocking of the low-level clouds by the Likhi Ridge. © NASA GSFC. Likhi Ridge Black Sea Caspian Sea Kolkhida Lowland Cloud image

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Wind speed (top) and and relative humidity (bottom) measured at the weather station at Kutaisi, Georgia, from 0000 UTC 11 September to 2100 UTC 15 September The squares above the wind speed curve denote speeds of wind gusts. The vertical lines mark the time of the Envisat data acquisition at 0732 UTC 13 September (meteodata from «Расписание погоды» Wind speed and humidity measured at a meteorological station

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Zoom of the SAR image on the eastern section of the Black Sea. Visible are two local wind fronts and (faintly) the sea surface signature of an atmospheric gravity wave (AGW) packet. AGW Wind front

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Conclusions Synthetic Aperture Radar (SAR) images acquired from the Envisat satellite over the Black Sea have revealed unprecedented details of the near- surface wind fields that cannot be obtained by other other sensors.

European Geophysical Union, Wien, 6 April 2011 Institute of Oceanography University of Hamburg Thank you for your attention