Spectrum of dust colours over Arabian Peninsula

by Ivan Smiljanic (DHMZ) and Hans Peter Roesli (Switzerland)

An interesting dust event happened on 1 April over the Arabian peninsula. The Dust RGB image (Figure 1) reveal different colours of the same dust, which is transported in different directions and to different layers of the troposphere.

Download animation, Meteosat-10 Dust RGB, 1 April 02:00 UTC–2 April 10:00 UTC
Download animation, Meteosat-10 Dust RGB, 1 April 00:00 UTC–8 April 06:00 UTC

The Meteosat-10 Dust RGB loop from 1–8 April shows the evolution of the dust storm. Among other interesting features note the vigorous and multicoloured initial dust uptake and the fast night time progression of the dust front on the night of 1–2 April, which speeds up to a 65km/h low-level jet.

Figure 2a shows the low pressure system apparent from the geopotential field at 500hPa. Background image is infrared 10.8µm image from the SEVIRI instrument. Dust can be seen as a brighter area on this image, due to the fact that dust itself reduces the radiation coming from the ground ('cooler' area).

Dust could also be seen in visible channels. One example is the Natural Colour RGB image in which dust can be recognised as a light-brown area (Figure 2b).

Early in the afternoon on 1 April the VIIRS Dust/Natural Colour RGB images (Figure 3a and 3b) show a sequence of dust fronts within the initial dust whirl and mostly dust-covered stratocumulus streets. The Dust RGB renders the dusty stratocumuli rather well, whereas they are hard to see in the Natural Colour RGB. There, only the dust-free part shows up (in white at the top left corner of Fig 3b). The shades of colour from pink to magenta reflect the varying density and/or height of the top of the dust.

The Dust RGBs from VIIRS in Fig 4a, 5a and 6a follow the further evolution of the lifted dust at 12 hours intervals until the evening of 2 April and local early morning of 3 April. As it moved down the Arabian peninsula and the Gulf of Persia, accompanied by a large dust sheet over Iran, the whirl pattern started to give way to more linear structures (Fig. 4a). In the early afternoon of 2 April (Figure 5a) the front of the dust area approached the coast of the Arabian Sea. The elongated front outlined the range of hills and rock formations running along the coast. Finally, in the early morning of 3 April (Fig 6a) the dust passed over the lower obstacles and started to be dispersed over the Arabian Sea. The dust then drifted for many days over the sea and also invaded some western states of India, as shown in AVHRR from Metop-B on 6 April 05:16 UTC (light-grey hue over the land as an extension of the dust over the Arabian Sea, Fig 7). Note that off the Indian coast SSW-NNE oriented sunglint overlays the dust signal. Also looking at the loop from 1–8 April the dust can be seen spreading into African countries (Eritrea, Ethiopia, a bit Somalia), see for example the situation on 4 April at 11.00 UTC.

The Dust RGBs are accompanied by True Colour RGBs or Day-Night-Band (DNB) images, according to the time of the day (Fig 4b, 5b and 6b). The TrueColour RGBs demonstrate the considerable density/thickness of the dust layer – terrain features remained completely hidden. Under the light of the first spring fullmoon also the DNB images show attractive scenes. However, the density thickness of the dust layer was not such to damp noticably the artificial lights sources and occasional gas flare.

Additional content

Download full resolution image, Suomi-NPP Dust RGB, 3 April 08:53 UTC
Download full resolution image, Suomi-NPP Natural Colour RGB, 3 April 08:53 UTC
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