Volcanic Ash

Table describing some of the most widely used RGB products, with a sample image for the volcanic ash RGB

Description: Using infrared channel data, this RGB detects ash, sulphur dioxide, and ice crystals from volcanic eruptions and can be used to track plumes for long distances downstream. The product helps forecasters track volcanic effluents and the information is used to provide warnings to aviation authorities and emergency managers. Note that the ash RGB is nearly identical to the dust RGB but has slightly different tuning.

Coverage: Both day and nighttime

Channels: MSG 8.7-µm IR; 10.8-µm IR; 12.0-µm IR

Color interpretation:

  • Sulphur dioxide cloud is green
  • Depending on the height, temperature and particle size, ash goes from being red (when it is very cold) to magenta (when it is warm) to yellow (when it is composed of very small ash particles)
  • Thin cirrus is black
  • High clouds and thunderstorms are brown
  • Near-surface features are in shades of blue and green

Advantages: Shows the three major volcanic effluents (ash, sulfur dioxide, and ice crystals) in distinct colors, enabling users to observe effluents drifting from the site of an eruption


  • Some everyday features can be mistaken for volcanic effluents
  • Black cirrus can be a part of non-volcanic cloud systems
  • Green clouds can resemble sulfur dioxide
  • Cannot detect ash or sulfur dioxide embedded in ice (mixed volcanic cloud)

Data links:

For more information, see EUMETSAT training materials, http://www.eumetsat.int/groups/ops/documents/file/zip_ash_20060823.zip

MSG RGB Ash Product from 24-25 Nov 2005 showing an eruption near Madagascar
Click to play animation.

Loop: This animation shows the volcanic eruption of Mount Karthala, with sulfur dioxide in green, volcanic ash in red/magenta, and thin cirrus in black. The volcanic ash and cirrus appear first, followed by the sulfur dioxide. Notice how the volcanic effluents suppress the deep convection in brown over northern Madagascar. We see the effects of wind shear during the entire loop. Low-level clouds are moving toward the west while high-level effluents are moving toward the east. This lets us infer that sulfur dioxide is at low levels because it moves very slowly, unlike the ash and cirrus that are advected by faster winds aloft.


MSG RGB Ash Product from 24-25 Nov 2005 showing an eruption near Madagascar

In this nighttime scene taken from the animation, what effluents are apparent in the vicinity of Mouth Karthala? (Choose all that apply.)

All of the choices are correct.

Sulfur dioxide is bright green, volcanic ash is bright magenta, and cirrus cloud is black.