Mixed volcanic ash and sulphur dioxide gas plume

Mixed volcanic ash and sulphur dioxide gas plumes appear yellow in the Ash RGB images.

The images below show ash cloud (red) and mixed ash and SO2 plumes (yellow) meandering over the Southern Atlantic. These clouds were ejected by the Puyehuè-Cordón Caulle Volcanic Complex in Chile.

Meteosat, SEVIRI Ash RGB for 06 June 2011, 12:00 UTC (Source: EUMETSAT, Image Library)

Meteosat, SEVIRI Ash RGB for 07 June 2011, 12:00 UTC (Source: EUMETSAT, Image Library)

Explanation of the colours of mixed volcanic sulphur dioxide gas and ash plumes (see the recipe):

• For ash clouds the red component is high, (because a thin ash cloud is more transparent in the 12.0 micrometer channel than in the 10.8 micrometer channel.)
• For SO2 gas plume the green component is high, (because SO2 gas has absorption band around 8.7 micrometer, while does not absorb the radiation at 10.8 micrometer channel).

Ash contributes with reddish and SO2 with greenish hues to the RGB, resulting in the yellow colouring.