Air Mass

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

Description:

The Air Mass 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 relies heavily on infrared channels in the water vapor and ozone absorption regions of the spectrum, it provides information primarily about the middle and upper levels of the troposphere, not so much the lower levels and near-surface conditions.

Current imagers with the spectral channels needed to produce the Air Mass RGB include Meteosat SEVIRI and Terra and Aqua MODIS.  The future GOES-R ABI and Advanced Himawai Imager (AHI) will also have the required WV and IR channels to produce an Air Mass RGB that is nearly identical to today’s Meteosat product, but at a higher spatial and temporal resolution.

Coverage: Day and nighttime

Channels:

  • Polar-orbiting satellites:
    • MODIS:
      Red: 6.715 µm WV 7.325 µm WV BT difference
      Green: 9.73 µm IR 11.03 µm IR BT diffierence
      Blue: 6.715 µm WV BT
  • Geostationary satellites:
    • MSG SEVIRI and future MTG FCI:
      Red: 6.2 µm WV 7.3 µm WV BT difference
      Green: 9.7 µm IR 10.8 µm IR BT diffierence
      Blue: 6.2 µm WV BT
    • Future GOES-R ABI and Advanced Himawari Imager (AHI):
      Red: 6.19 µm WV 7.34 µm WV BT difference
      Green: 9.61 µm IR 10.35 µm IR BT diffierence
      Blue: 6.19 µm WV BT

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 (due to limb darkening/cooling effect) and should be disregarded

Advantages:

  • 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

Limitations:

  • Air masses are only detectable in areas free of high cloud cover
  • 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, rather limb darkening/cooling due to the large satellite viewing angles

Live data links:

More information:

Example:

Airmass RGB over southern Europe and northern Africa from 7 - 8 July 2005

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.