Minimize Katabatic Winds

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Strait of Messina Strait of Messina

Latitude: 38° 26' N - Longitude: 15° 30' E

ERS-1 SAR image showing north-west of the Strait of Messina a bright mushroom like feature generated by a katabatic wind field which extends from the Calabrian coast near the Italian town Gioia into the Tyrrhenian Sea. Furthermore, between the island of Stromboli (upper left hand section of the image) and the Sicilian coast, mottled patterns can be delineated which are sea surface "imprints" of atmospheric convective cells. During the time of the data acquisition the air temperature was 16° and the water temperature 25°. Thus the water is heated from below and convective atmospheric cells are formed. This cellular structure is destroyed in the vicinity of the Sicilian coast by the katabatic wind blowing from the mountains onto the sea. In the lower section of the image an oceanic internal wave train can be seen propagating southwards in the Strait of Messina.
Strait of Messina Strait of Messina

Latitude: 39° 26' N - Longitude: 15° 34' E

Roughness pattern that stretches like a band along the western coast of Calabria (Southern Italy) and extending seawards for a distance of up to 28 km. Close to the shoreline, the pattern is strongly influenced by orographic features. Coastal valleys can be identified by the associated tongue-like bright patterns on the sea surface. The wind speed and direction measured at Lamezia Terme (located approximately 10 km south of the imaged area) were 2.1 m/s and 270°, respectively. The air temperature was 9.8°C and the water temperature 14.5°. The mottled structure in the left section of the image is the sea surface manifestation of convective cells.
Calabria Calabria

Latitude: 38° 30' N - Longitude: 16° 21' E

In the right-hand section of this image katabatic wind fields are visible at the eastern coast of Calabria. The roughness patterns closely mirror the coastal valleys.
Black Sea Black Sea

Latitude: 41° 11' N - Longitude: 31° 35' E

Katabatic wind fields at the Turkish coast of the Black Sea.
Andaman Sea Andaman Sea

Latitude: 05° 29' N - Longitude: 100° 05' E

ERS-1 SAR strip acquired over the Andaman Sea at the west coast of Malaysia and Thailand. The bright band starting slightly north of the Malaysian island of Pinang and extending southward along the coast line has its correspondence in a mountain range located approximately 20 km inland, which extends over this distance from north to south. The SAR data were acquired approximately at local midnight. Thus the bright band can only be caused by katabatic winds originating at this mountain range.
# Orbit Frame(s) Satellite Date Time Location
1 6014 765 ERS-1 08-Sep-1992 21:13
2 18839 0783 ERS-1 20-Feb-1995 21:13
3 9249 0765 ERS-1 22-Apr-1993 21:10
4 15882 0819 ERS-1 29-Jul-1994 20:08
5 25350 0081-0099-0117 ERS-1 20-May-1996 15:57

If you have any comments on these images please write an e-mail to alpers@ifm.uni-hamburg.de.

Introduction

Katabatic winds are cold winds blowing in the evening and night down a sloping terrain ("gravity flow") and, at a coast, over the adjacent sea surface. These winds are generated because during the evening and night, air near the surface cools faster over the land than over the sea. Over mountain slopes a horizontal density difference develops between the cooler air at the slope surface and the free air in the same altitude over the lower ground or sea. This results in a down-hill flow of the cold air. Sea surface manifestations of katabatic wind fields have often been identified on ERS-1 SAR images acquired during the summer over coastal regions adjacent to mountainous areas.

References

  • Alpers,W , Measurement of mesoscale oceanic and atmospheric phenomena by ERS-1 SAR, Radio Science Bull., 1995, 275,14-275,22.
  • Alpers, W., Pahl, U. & Gross, G., Katabatic wind fields in coastal areas studied by ERS-1 synthetic aperture radar imagery and numerical modeling, J. Geophys. Res., 1998, 103, 7875-7887.
  • Gross, G., Numerical simulation of the nocturnal flow systems in the Freiburg area for different topographies, Contrib. Atmos. Phys., 1989, 62, 57-72.
  • Gross, G., Anwendungsmöglichkeiten mesoskaliger Simulationsmodelle dargestellt am Beispiel Darmstadt, I, Wind- und Temperaturfelder, Meteorol. Rundsch., 1991, 43, 97-112.
  • Gudiksen, P.H., Leone, J.M., King, C.W., Ruffieux, D. & Neff, W.D., Measurements and modeling of the effects of ambient meteorology on nocturnal drainage flows, J. Appl. Meteorol., 1992, 31, 1023-1032.
  • McNider, R.T. & Pielke, R.A., Numerical simulation of slope and mountain flows, J. Appl. Meteorol., 1984, 23, 1441-1453.