Dust storm over Northern Africa and the Eastern Mediterranean Sea

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Dust storm over Northern Africa and the Eastern Mediterranean Sea.

Date & Time
24 February 2006 00:00 UTC
Satellites
Meteosat-8, Terra/Aqua

More information and detailed analysis of the feature can be found in the In Depth section.

 

In Depth

by Maria Putsay, Kornel Kollath (Hungarian Meteorological Service), Jochen Kerkmann (EUMETSAT) and Jarno Schipper (ZAMG)

Jump to images

Dust clouds usually develop above the desert. Strong winds blow the sand into the air and it can remain airborne for a long time, thus dust clouds can travel long distances. Sand storms originating in the Sahara can travel across the Mediterranean Sea and reach the European continent.

Dust clouds can be seen on a short-wave satellite image since the dust particles scatter the solar radiation. Unfortunately, the desert sand below the dust cloud also reflects strongly, only the blurring of the usual surface structure gives a hint of its presence. The dust cloud only becomes clearly visible on a short-wave satellite image when the wind blows it over the darker sea surface.

An example for such a dust storm can be seen near the Greek island of Crete on the high-resolution visible (HRV) image (lower images). Well structures gravity waves produced by the mountains of Crete can also be observed.

Many features can be seen better in RGB images. A frequently used RGB is the one that combines the three solar channels (NIR1.6,VIS0.8,VIS0.6, see image, JPG, 265 KB). In this image the dust cloud is easily distinguished from ice clouds. However, some types of water clouds (like stratiform water clouds) may show quite similar structure and colour. This can make recognition of dust clouds difficult.

Using the new channels on MSG satellites, a new approach has been developed to recognise dust clouds. This RGB composite image, the Dust RGB, does not use short-wave channels, it combines infrared channels and their differences (IR12.0–IR10.8, IR10.8–IR8.7, IR10.8). The infrared spectral features of the dust are a little different from those of water/ice clouds. Using the channel differences, the dust cloud becomes recognisable. The advantage of this method is that it works even during night-time. The dust clouds are easily separable from water or ice clouds and clearly visible, even over the desert.

The Dust RGB can be seen in the images below. Two animations are also presented. In the Dust RGB, the dust clouds appear in magenta/pink colour, the thick high-level clouds in red to brown, the thin high clouds (semitransparent ice clouds) in black, the mid-level clouds in brown-yellow, and the semitransparent mid-level clouds in greenish colours, while the low clouds are closer to yellow.

It should be noted that dust storms in Greece are not unusual, where such strong dust clouds are observed two or three times a year, causing extreme low visibility. Based on synoptic observations (see RGB images with Synop observations from 06:15 UTC (PNG, 281) and 09:00 UTC (PNG, 1 MB)) in the Southern Aegean Sea there was significantly reduced visibility with reports of 800 metres visibility on Crete and only 200 metres on Naxos.

 

Meteosat-8 Dust & Airmass RGB Composites — 22/02/06

Met-8, 22 February 2006, 12:00 UTC
Dust RGB Composite
IR12.0–IR10.8, IR10.8–IR8.7, IR10.8
Full Resolution (967 KB)
Met-8, 22 February 2006, 12:00 UTC
Airmass RGB Composite
WV6.2–WV7.3, IR9.7–IR10.8, WV6.2
Full Resolution (737 KB)

See also:

Monitoring airmass/moisture boundaries with MSG (4 October 2005)
Sahara dust outbreak across the Western Mediterranean (28 July 2005)
Dense stream of dust between Greece and Libya (17 April 2005)
Dust storm over the Mediterranean Sea (21 February 2004)
Met-8 Airmass RGB composite (23 Feb. 2006, 00:00 UTC, JPG, 723 KB)
Met-8 Dust RGB composite (23 Feb. 2006, 00:00 UTC, JPG, 723 KB)
Met-8 Dust RGB composite (24 Feb. 2006, 09:00 UTC, JPG, 963 KB)
Aqua MODIS image (23 Feb. 2006, JPG, 60 KB, source: NASA Earth Observatory)

Meteosat-8 Dust & Airmass RGB Composites — 23/02/06

Met-8, 23 February 2006, 12:00 UTC
Dust RGB Composite
IR12.0–IR10.8, IR10.8–IR8.7, IR10.8
Full Resolution (945 KB)
Interpretation (967 KB)
Animation (AVI, 1 MB)
(23 Feb. 10:45 UTC– 24 Feb. 07:45 UTC)
Met-8, 23 February 2006, 12:00 UTC
Airmass RGB Composite
WV6.2–WV7.3, IR9.7–IR10.8, WV6.2
Full Resolution (703 KB)


Meteosat-8 Dust & Airmass RGB Composites — 24/02/06

Met-8, 24 February 2006, 12:00 UTC
Dust RGB Composite
IR12.0–IR10.8, IR10.8–IR8.7, IR10.8
Full Resolution (619 KB)
Animation (hourly, 00:00–14:00 UTC, AVI, 2 MB)
Met-8, 24 February 2006, 12:00 UTC
Airmass RGB Composite
WV6.2–WV7.3, IR9.7–IR10.8, WV6.2
Full Resolution (493 KB)
 


Meteosat-8 HRV Images

Met-8, 24 February 2006, 05:30 UTC
RGB Composite HRV, HRV, IR10.8
Full Resolution (1 MB)
Animation (05:30–14:00 UTC, MPG, 4 MB)
Met-8, 24 February 2006, 12:00 UTC
RGB Composite HRV, HRV, IR10.8
Full Resolution (1 MB)
Close-up Look (198 KB)
 
 
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