Dust associated with thermal low over Oman

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Dust circulation associated with the seasonal thermal low-pressure system over the north-eastern Arabian Peninsula could be seen by Meteosat on 12-13 July.

Dust associated with thermal low over Oman
Date & Time
11 July 2015 18:00 UTC—13 July 12:00 UTC
Satellites
Meteosat-10, Suomi-NPP
Instruments
SEVIRI, VIIRS
Channels/Products
Dust RGB, Infrared

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

 

In Depth

By Zamzam AL.Rawahi and Sami AL.Mamari (Oman DGMAN)

 
Figure 2: Meteosat-10 Dust RGB 11 July 18:00 UTC (Source: EUMeTrain)

Usually the summer thermal low pressure over the north-eastern Arabian Peninsula is hardly visible on satellite imagery, and it has no significant effects. However, dust may help to identify such a low.

In the Meteosat-10 Dust RGB imagery from 12 and 13 July a pink dust whirl was very visible, see image from 13 July, 12:00 UTC (Figure 1, above right). It was related to a thermal low (central pressure 994 hPa) over the same area.

The dust circulation during 12 July 03:30 UTC–05:30 UTC can be seen in the short animated sequence of Meteosat-10 IR10.8 images (MP4, 4 MB).

The dust was lifted from the central parts of Saudi Arabia on 11 July 2015 (red circle in Figure 2) and then moved in a south-easterly direction.

Finally, it was redirected northward to form the distinct whirl shown in Figure 1.

The Mean Sea Level Pressure (MSLP) map from the COSMO model on 12 July 12:00 UTC (Fig 3, left panel) shows the extent of the thermal low-pressure system that built up due to further heating. The Meteosat-10 Airmass RGB, 13 July at 12:00 UTC (Figure 3, right panel) reveals the position of the heat low as a dark black spot, due to the presence of dry hot air.

Figure 3
 
Figure 3: MSLP map, 12 July 12:00 UTC (left), Meteosat-10 Airmass RGB, 13 July at 12:00 UTC (right)

The geopotential height of the 700 hPa surface from COSMO on 12 July 00:00 UTC (Figure 4), shows a cut-off low that dropped off a trough over the North Arabian Gulf on 11 July, the trough extended up to 500 hPa.

 
Figure 4: Geopotential height of the 700 hPa, 12 July 00:00 UTC

The vertical alienation on 12 July of the heat low and the cut-off low, in combination with high pressure over the eastern Mediterranean, afforded a strong pressure gradient along the Arabian Peninsula.

In turn the gradient produced moderate north to north-westerly surface winds ~15kt), sufficiently strong to pick up dust.

The dust, initially transported southwards, was finally pulled into the circulation of the thermal low. The location of the thermal low also helped to transport massive amounts moisture from the Arabian Sea to mid and northern Oman.

Details of the dust whirl may also be gleaned from Suomi-NPP VIIRS imagery. The Dust RGB shows the tail of the dust whirl (Figure 5, left). The IR10.8 image shows the dust as brighter (cooler) band over the ground (Figure 5, right).

Image comparison
Suomi-NPP VIIRS Dust RGB, 12 July 09:18 UTC Suomi-NPP VIIRS IR10.8, 12 July 09:18 UTC
Figure 5: Comparison of Suomi-NPP VIIRS images.

Previous Oman dust case studies

 
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