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After a period of several weeks without significant dust storms in the field of view of Meteosat-8, on 23-24 November 2004 a major dust storm was observed in the Middle East. It started, as is often the case, in Western Iraq (at around 05:30 UTC) moving quickly in a south-east direction. At around 12:00 UTC the whole southern part of Iraq was covered with thick dust. As in the case of 13 May 2004, the dust storm was created by a strong post-frontal north-westerly winds. This situation, which typically persists for 24-36 hours and occurs 2-3 times a month, is called Shamal (from the arabic for "north").
During the night of 23-24 November the dust storm (and the cold air) moved into Saudi Arabia. At 07:00 UTC it had already reached the southern part of the Arabian Peninsula and was moving into Oman and Yemen. The high-resolution visible (HRV) image shows the dust cloud as bright, featureless area when compared with the well-structured desert surface. Looking at the HRV animation, the dust storm is best visible in the early morning due to the strong forward scattering of the solar radiation by the dust particles, which are of roughly the same size as the wavelength of the incident solar radiation. On top of the dust cloud, there are some high-level clouds which cast shadows on the dust cloud below.
During daytime, the dust storm can also be monitored in the IR10.8 images, where it appears as a relative cold area when compared to the hot desert surface. This effect is best seen around local noon, when the temperature contrast between the desert surface and the dust cloud is greatest. This "thermal method" of detecting dust storms, like the "optical method", does however not work during night-time. During night-time, dust storms can be detected in Meteosat-8 images using IR10.8-IR8.7 and IR12.0- IR10.8 brightness temperature difference images, or even better, by combining these difference images into an RGB composite, as shown in the top left image shown below (which is called the "dust RGB"). Further details on the dust RGB are given in the MSG Interpretation Guide, under "Introduction to MSG Channels".
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