High level wave cloud spreading from Mt. Etna (11 April 2008)

by Jochen Kerkmann (EUMETSAT)

The images below show a high-level plume-like cloud extending downwind from Mt. Etna for about 200 km to the east. As this plume cloud is very cold and has a relatively high reflectance in channel IR3.9r, it appears with a strong yellow colour in the RGB composite (see also High level cloud spreading from Mt. Etna (9 March 2007)).

Principally, there are two possible explanations for this plume-like cloud: a) a cloud from a volcanic eruption or b) a mountain wave cloud. The first possibility is unlikely because there are no reports of an eruption of Mt. Etna on this day. Also, there are no signs of volcanic ash or sulfur dioxide (see Met-9 RGB composites under "See also") and the cloud temperature of -55°C speaks more for a wave cloud (a cloud from an eruption of Mt. Etna would normally be lower, at 4-5 km height, unless the eruption was very strong (which would have been reported on the news)). Finally, the synoptic situation on 11 April, with strong westerly winds over Sicily, was favourable for the formation of lee wave clouds over Mt. Etna.

Meteosat-9 RGB Composite Met-9, 11 April 2008, 11:00 UTC RGB Composite WV6.2-WV7.3, IR3.9-IR10.8, NIR1.6-VIS0.6 Large Area (JPG, 104 KB, source: NEMOC, US Navy) Animation (05:30-12:30 UTC, MPG, 3226 KB, source: NEMOC, US Navy) See also: Metop-A AVHRR RGB Composite NIR1.6-VIS0.8-IR11.0 (08:49 UTC, JPG, 41 KB) Met-9 RGB Composite HRV-HRV-IR10.8 (07:00 UTC, JPG, 185 KB) High level cloud spreading from Mt. Etna (9 March 2007)

Meteosat-9 HRV Channel Met-9, 11 April 2008, 11:00 UTC Channel 12 (HRV) Large Area (JPG, 106 KB, source: NEMOC, US Navy) Animation (06:00-15:45 UTC, MPG, 4539 KB, source: NEMOC, US Navy)

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