Dust over the Sea of Oman
21 November 04:00 UTC–22 November 2016 19:00 UTC
A large area of dust was seen by both Meteosat and Sentinel-3A as it travelled across parts of the Middle East in November 2016.
22 October 2020
21 November 2016
By HansPeter Roesli (Switzerland) and Jochen Kerkmann (EUMETSAT)
On 21-22 November a deep trough extending southwards to the Arabian/Persian Gulf and associated to a mid-level low east of the Caspian Sea (Figure 1), induced northerly low-level winds from the Iran-Pakistan border region (Sistan-Balochistan). These winds lifted dust from the coastal areas and drove it out across the Sea of Oman.
The dust veil was very faint and remained at low levels. For these reasons the contrast in the Dust RGB was very weak and the dust difficult to detect.
However, the dust can be seen in an animated sequence of the Meteosat-8 Dust RGBs , 21 Nov 04:00 UTC–22 November 19:00 UTC where, watching more closely, the expanding veil can be identified, in particular some dust streamers blown off the Pakistani coast around local noon on 22 November.
Notwithstanding the weak dust signal, Meteosat-8 provides a much improved horizontal resolution from its new IODC position (41.5°E) — especially clear when you compare this case to a similar event on 21 February 2012: Dust Veil over the Sea of Oman .
In this particular case, with the dust moving over (dark) water and the more favourable viewing angle of the re-positioned Meteosat-8, Natural Colour RGBs were superior to the Dust RGB, albeit only during the day.
The Meteosat-8 Natural Colour two day image sequence , 21 November 02:00 UTC–22 November 16:00 UTC shows the diverging dust flow.
The Meteosat-10 High Resolution Visible imagery sequence (Animated gif) shows the 'dust front' moving towards Muscat, where it arrived 4 pm (12:00 UTC) with a slight drop in temperature, decrease in moisture and wind shift to an easterly direction.
On 22 November the west-moving dust front between Qatar and Iran was marked by a line of convective clouds, with the highest tops being blown away to the east by the mid-level winds.
Also on 22 November at 05:40 UTC Sentinel-3A flew over the area south of the Pakistani coast. The Sea and Land Temperature Radiometer (SLSTR) picked details of the dust streamers at 500m spatial resolution (Figure 2).
The spreading dust matches the analysis of the low-level winds of the Global Forecast Model (GFS) on 22nd November at 06:00 UTC (Figure 3).
The model sounding (Figure 4) taken over the area shown by the orange dot on Figure 3, and the radiosonde from Muscat International Airport (Figure 5) six hours earlier show a significant temperature inversion below 900 hPa and 700 hPa respectively. This confirms the fact that in the Dust RGBs the temperature contrast did not get stronger over time due to it being restrained to this maritime boundary and not being able to rise to higher (cooler) levels.
According to the Muscat METAR observations during the two days the horizontal visibility generally was around 6 km, with a minimum of 3 km, and the winds were moderate easterly.
By 23 November the dust had travelled over the Indian Ocean, as can be seen on the Meteosat-10 Dust and Natural Colour RGBs from 04:00 UTC (Figure 6).
Two glimpses by the Ocean and Land Colour Imager (OLCI) on Sentinel-3A give details of the dust outbreak. These are True Colour RGBs that use three virtual channels composed of the radiances of the 10 bands Oa01 to Oa10 (400 nm to 681.25 nm).
Figure 7 shows widespread but faint dust over the Sea of Oman. More consistent dust streams off the Iranian coast and covered the Street of Hormus. Figure 8 shows the the scene the day after and further east, where numerous dust streamers fed a veil that had advanced far south into the Arabian Sea.
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