Moisture boundary across the Arabian Peninsula.
More information and detailed analysis of the feature can be found in the In Depth section.
by Jochen Kerkmann, HansPeter Roesli (EUMETSAT) and Daniel Rosenfeld (HUJI)
As disussed in the case study Monitoring airmass/moisture boundaries with MSG (4–5 October 2005), the dust RGB composite image shown below, besides monitoring dust storms and tracking thin, high-level clouds, can also be used for the detection of low-level moisture boundaries.
The image shows a mostly cloud-free situation over the Arabian Peninsula where the southern part of the Peninsula appears with a strong blue colour whilst the northern part has a pale blue to cyan colour. The reason for this colour difference can mostly be attributed to an airmass/moisture boundary that crosses the Peninsula from south-west to north-east (see Interpretation, JPG, 520 KB).
Close inspection suggests that the moisture signal in mid Saudi Arabia is in part caused by optically thin clouds, which, in turn, raise the IR10.8–IR12.0 Brightness Temperature Differences (BTD) independently of the moisture (which does the same to the BTD). The existence of the moisture boundary is confimed by the Synop/Metar observations (see WV7.3 image with Synop/Metar observations, 09:00 UTC, PNG, 212 KB), the ECMWF analysis fields and the 12:00 UTC radiosoundings from Al Madinah (dry airmass) and Riyadh (humid airmass, see links under 'See also').
As shown by the surface wind field, the moisture boundary is related to a convergence line, with north-westerly winds to the north bringing dry air from northern latitudes and south-easterly winds to the south carrying moist air from the Indian Ocean far inland. Across the convergence line the surface dewpoints drop from around 10 °C on the moist side to about -5 °C on the dry side of the boundary.
Meteosat-8 RGB Composite Image
Dust storm over Northern Africa and the Eastern Mediterranean Sea (24 February 2006)
Monitoring airmass/moisture boundaries with MSG (4–5 October 2005)
Channel 02 (VIS0.8) image (12:00 UTC, GIF, 332 KB)
Channel 09 (IR10.8) image (12:00 UTC, GIF, 295 KB)
RGB composite NIR1.6, VIS0.8, VIS0.6 (12:00 UTC, JPG, 562 KB)
Channel 06 (WV7.3) image with Synop/Metar observations (09:00 UTC, PNG, 212 KB)
Dust RGB composite with ECMWF surface winds (12:00 UTC, JPG, 655 KB)
Dust RGB composite with ECMWF surface dewpoints (12:00 UTC, JPG, 697 KB)
Radiosounding from Al Madinah (12:00 UTC, JPG, 606 KB)
Radiosounding from Riyadh International Airport (12:00 UTC, JPG, 617 KB)