Logbook Nr. 3
| Polarstern Satellite Logbook Nr. 3 | |
|---|---|
| Region | Central Atlantic |
| Conceptual Model | Northeast Trade Winds Dust Outbreak |
| Date/Time | 30 April to 1 May 2012 |
| Longitude/Latitude |
12,4°N / 22,2°W (1 May, 12:00 UTC) |
| Expedition |
PS79 (ANT-XXVIII/5) 10 April - 15 May 2012 Punta Arenas - Bremerhaven |
Figure L3-1: 30 April 2012, 12:00 UTC. Dust Outbreak. Source: DWD.
The Polarstern is sailing from south to north during a dust outbreak. Figure L3-1 shows three dust outbreaks across Africa; one in Egypt, another in the Bodélé Depression in Chad, and a large one stretching along southern Sahara from Senegal and Guinea. Dust shows in magenta in these images. The contrast is not as good over sea, but the dust still clearly reaches the Polarstern's position.
Fig. L3-2 shows a sequence of Dust RGB images. The dust is moving westward and the Polarstern's course runs through this area. Normally the sky would be nearly clear and here you can see the effects of dense dust.
Figure L3-2: Dust RGBs from 30 April 2012, 21:00 UTC to 1 May 2012 in 3-hour steps, a picture of the dust from 1 May 2012 at 12 UTC, and wind barbs from 30 April 2012, 12:00 UTC.
Copyright for the dust image: Juliane Hempelt (DWD).
In the Colour Interpretation Guide you will find the explanation why sand and atmospheric dust are depicted in magenta in the Dust RGB. The guide has more information about the difference in absorption between the two channels, IR10.8 μm and IR12.0 μm.
http://www.eumetrain.org/resources/MSG_dust_magenta_sandstorm.html
Figure L3-3: Dust deposit on the ship on 30 April 2012 (right), and a view of the hazy sky and ocean surface with the SYNOP code at 12 UTC (left). Source: Juliane Hempelt (DWD).
The dust particles are so big and heavy that they fall down and settle on the deck of the ship. The visibility was reduced to 4 km and the sun looks very weak through the dust.
Figure L3-4: Saharan Air Layer (SAL).
Source: Topics in Tropical Meteorology (COMET - MetEd).
Fig. L3-4 shows one of the strongest dust outbreaks in recent years. The training module from COMET has interesting information about this conceptional model.