Air Mass

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

Description: This RGB is designed and tuned for monitoring the evolution of cyclones, in particular, rapid cyclogenesis, jet streaks, and potential vorticity (PV) anomalies. Since the product is made from infrared channels, it provides information primarily about the middle and upper levels of the troposphere, not the lower levels and near-surface conditions.

Coverage: Day and nighttime

Channels: MSG 6.2-µm WV; 7.3-µm WV; 9.7-µm IR; 10.8-µm IR

Color scheme:

  • Ozone-poor tropical air masses are green
  • Ozone-rich polar air masses are blue
  • Dry air masses in the upper troposphere (such as those related to sub-tropical high pressure systems, PV anomalies, jet streaks, and deformation zones) are red to orange
  • High-level clouds are white
  • Mid-level clouds are brown
  • Magenta often appears at the edge of the full disk and should be disregarded


  • Can see important boundaries between air masses, such as tropical and polar, at a glance; these are often invisible on single channel images
  • Helps detect the position of jet streams and areas of dry, descending stratospheric air with high PV; these appear in red
  • Can detect features commonly seen in water vapor images, such as deformation zones, wave features, and PV anomalies
  • The infrared channels make it possible to monitor cloud development at low, middle, and high altitudes


  • Air masses are only detectable in areas free of high cloud tops
  • Tends to depict conditions in the middle and upper troposphere, but not at the surface
  • At the edge of the Earth’s disk, air masses can have a magenta color but this does not represent true air mass characteristics

More information:

Live data links:

Airmass RGB over southern Europe and northern Africa from 7 - 8 July 2005
Click to play animation.

Loop: The polar front, marked by the clouds of several moving frontal systems, divides the scene into polar air to the north and subtropical air to the south. The bright red area to the north of the polar front may indicate stratospheric intrusion into the troposphere. Brown, cloud-free air masses to the southeast of the polar front mark dry air masses at middle and upper levels.

Exercise: This image shows a series of midlatitude waves moving across Europe.

MET9 Airmass RGB  10 Mar 2008  0700 UTB, with several countries labeled

Where is the strongest intrusion of dry stratospheric air down into the troposphere? (Choose the best answer.)

The correct answer is D.

The area of intense red (very dry air) over Ireland marks the intrusion of stratospheric air.