Meteosat-11 captures plume of Saharan dust coming from northern Africa
5 February 2021 09:00 UTC-7 February 11:00 UTC
On 5-6 February 2021, a massive amount of Saharan dust was advected across the Mediterranean Sea into central Europe, thanks to the favorable synoptic situation with a Low over Spain and a southerly jet stream over Morocco and the Mediterranean.
03 March 2021
08 February 2021
By Jochen Kerkmann (EUMETSAT), Mike Fromm (NRL), Miguel Angel Martinez (AEMET) and Ivan Smiljanic (CGI)
The dust plume can be clearly seen on the Terra MODIS True Colour RGB image from the morning of 6 February (Figure 1).
High dust concentrations turned skies and snow to orange across southern and central parts of Europe (Spain, Andorra, France, Switzerland, Germany), creating dramatic scenery. The dust plume left deposits along the east coast of Spain, in particular Valencia, and orange snow on the Pyrenees and western Alps. While acknowledging this happens a few times a year (see the well documented case Extensive DIBS in the Deformation Zone from April 2020), meteorologists also noted this event was particularly intense.
Figure 2 shows the animation of the Dust RGB from the beginning of the dust outbreak in the border area between Morocco and Algeria, to its arrival over Switzerland and southern Germany. The animation is centred on the dust plume, i.e. it follows the mid-to-high level flow. This allows monitoring of the development of the dust plume from the first signs to its ingestion in the baroclinic cloud (cirrus) over central Europe.
Figure 3 shows both, the dust plume over France, Italy and Switzerland at 12:00 UTC on 6 February (see Dust RGB, bright red colour, i.e. high level dust) and the DIBS (Dust‐Infused Baroclinic cyclone Storm clouds, also called 'dusty cirrus') cloud over France and southern Germany (see Convection RGB, strong yellow colour). The yellow colour indicates small ice particles, very characteristic for DIBS clouds. Another characteristic of DIBS clouds is their granular (pockmarked) structure, which is best seen in early morning HRV images.
RGB image comparison
Figure 3: Meteosat-11 Dust RGB (left) and Convection RGB (right), 6 February 2021, 12:00 UTC.
The Airmass RGB can be used to follow the further development of the DIBS cloud, day and night (Figures 4, 5 & 6). In fact, DIBS clouds are not only pockmarked and composed of small ice particles, but they also appear very bright in infrared images. Thus, in the Airmass RGB the dusty cirrus is shown in bright, white colours. Interestingly, the DIBS cloud, which takes much longer to dissipate than normal ice clouds, is extensively stretched along a deformation zone that runs from Denmark, across Poland and Ukraine, to southern Russia. When the DIBS cloud arrived over the Caspian Sea, it encountered a second deformation zone (Figure 5). Parts of the DIBS cloud went southward towards Iran; the main part went eastward crossing Kazakhstan and arriving over western Mongolia. There, it left the Meteosat-8 field of view and entered the Himawari-8 field of view. Figure 6 shows the final development of the DIBS cloud as seen in Himawari-8 Airmass RGB images (note the images are in satellite projection). It stretched a third time and ended it lifecycle over eastern China (the dusty cirrus particles finally sublimated).
Aerosol Index
In the early afternoon of 6 February, the Saharan dust generated a shield of absorbing aerosol index (AI) anomaly over western Europe. The cirrus shield of the DIBS, illustrated in VIIRS 11um brightness temperature < -50C in light grey (Figure 7, left)), arced over France, Switzerland, and southern Germany. The absorbing aerosol index appears on the image as a maroon layer, altering the shade of the cirrus, compared with this view without the AI layer (Figure 7, right). This shows that Saharan dust was widespread over western Europe, even including the opaque ice-cloud top, i.e. dust infused the storm cloud.
Aerosol Index comparison
Figure 7: Suomi NPP VIIRS I5 band (left, BTs below -50°C are shown in grey) and OMPS aerosol index (right). Credit: NASA.
Timelapse of the dust cloud
Dust advection over Alps was captured by the webcam in the mid-southern Austria — westward facing camera at Adlersruhe, 3454 m high (Figure 8). Shortly before local noon the dust cloud started to appear from the left side of the view (south). Visibility was reduced drastically after only few hours, from, an estimated, hundreds of kilometres to only few tens of kilometres. With the passage of the thickest dust cloud, visibility started to improve towards the end of the animation (together with the sunset).
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