Convection

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

Description:

This RGB can identify important microphysical characteristics and trends in convection, including small ice particles that point to intense updrafts and are potential indicators of imminent severe weather.

The MODIS and MSG SEVIRI imagers have the necessary channels to make this product.  With the future GOES-R ABI, 1-minute or 30-second imaging during severe weather will give forecasters unprecedented views of convective development across the contiguous U.S. Future Chinese FY-4 and Japanese Himawari geostationary satellites will also be able to provide this product.

Coverage: Daytime only, requires solar reflectance information

Channels:

  • Polar-orbiting satellites:
    • MODIS:
      Red: 6.7 minus 7.3 µm WV BT difference
      Green: 3.9 minus 11.0 µm IR BT difference
      Blue: 1.64 minus 0.645 µm reflectance difference
  • Geostationary satellites:
    • MSG SEVIRI and future MTG FCI:
      Red:6.2 minus 7.3 µm WV BT difference
      Green: 3.9 minus 10.8 µm IR BT difference
      Blue: 1.6 minus 0.64 µm reflectance difference
    • Future GOES-R ABI:
      Red: 6.19 minus 7.34 µm WV BT difference
      Green: 3.9 minus 10.35 µm IR BT difference
      Blue: 1.61 minus 0.64 µm reflectance difference
    • Future Himawari AHI:
      Red: 6.25 minus 7.35 µm WV BT difference
      Green: 3.85 minus 10.45 µm IR BT difference
      Blue: 1.61 minus 0.645 µm reflectance difference
    • Future FY-4 AGRI:
      Red: 6.25 minus 7.1 µm WV BT difference
      Green: 3.75 minus 10.7 µm IR BT difference
      Blue: 1.61 minus 0.64 µm reflectance difference

Color scheme:

  • The background is dark blue and magenta
  • High-level, thick, ice clouds, including convective cumulonimbus clouds, appear red
  • Yellow is usually indicative of small ice particles within convective cloud tops, but may also be associated with elevated updrafts such as in high altitude orographic wave clouds

Advantages:

  • Compared to many satellite images, this RGB highlights the youngest and most intense cells, showing overshooting thunderstorm tops, which can help distinguish new convection from dissipating convective activity.

Limitations:

  • Daytime only, requires solar reflectance information
  • Not effective for observing or discriminating types of weather other than convection
  • Yellow is indicative of small ice particles, which can be associated with either strong convection or in some cases thick high level ice clouds such as found with orographic wave clouds

Live data links:

Additional information:

References:

Heymsfield, A. J., L. M. Miloshevich, C. Schmitt, A. Bansemer, C. Twohy, M. R. Poellot, A. Fridlind, and H. Gerber, 2005: Homogeneous ice nucleation in subtropical and tropical convection and its influence on cirrus anvil microphysics. J. Atmos. Sci., 62, 4164.

Rosenfeld, D., W. L. Woodley, T. W. Krauss, and V. Makitov, 2006: Aircraft microphysical documentation from cloud base to anvils of hailstorm feeder clouds in Argentina. J. Appl. Meteorol., 45, 12611281.

Rosenfeld, D., W. L. Woodley, A. Lerner, G. Kelman, and D. T. Lindsey, 2008: Satellite detection of severe convective storms by their retrieved vertical profiles of cloud particle effective radius and thermodynamic phase. J. Geophys. Res., 113, 22 p.

Example 1:

Animation of MSG Convection RGB showing Hurricane Isabel, June 2006

Loop: In this RGB animation of Hurricane Isabel, the reds and oranges show cloud tops composed of fairly large ice particles. The yellow suggests very small ice particles at high altitudes, which is indicative of intense updrafts.


MSG Severe Weather RGB, South of France & Italy  20 May 2003 1330 UTC

Example 2: This RGB over southern France and Italy shows strong convection in yellow, an indicator of potential severe weather. Here again, the yellow areas indicate cells with very small ice particles at cloud top, suggesting overshooting tops, intense updrafts and potential severe weather. The more reddish regions indicate larger ice particles associated with older or more benign, less threatening convection.


Exercise:

MSG Convection RGB 27 Oct 2004 1300

In this convection RGB over South Africa, three of the five circled areas could be associated with severe weather? The other two are not. Choose the circled areas that indicate a potential for severe thunderstorm conditions. (Choose all that apply.)

The correct answers are A, B, and C.

The yellow in these areas usually indicates small particles within convective cloud tops that are associated with strong updrafts. Strong updrafts often indicate the potential for severe thunderstorm conditions. The red areas are usually seen with non-severe convection and other cloud types.