Thunderstorm Top Structure Observed by Aircraft Overflights with an Infrared Radiometer

Robert F. Adler Goddard Laboratory for Atmospheric Sciences, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

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Michael J. Markus Goddard Laboratory for Atmospheric Sciences, NASA/Goddard Space Flight Center, Greenbelt, MD 20771
General Software Corporation, Landover, MD 20785

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Douglas D. Fenn Office of Hydrology, National Weather Service, Silver Spring, MD 20910

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Gerard Szejwach Goddard Laboratory for Atmospheric Sciences, NASA/Goddard Space Flight Center, Greenbelt, MD 20771
Laboratoire de Meteorologie Dynamique du CNRS, École Polytechnique Palaiseau, France

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William E. Shenk Goddard Laboratory for Atmospheric Sciences, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

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Abstract

Thunderstorm top structure is examined with high spatial resolution radiometric data (visible and infrared) from aircraft overflights together with other storm views, including geosynchronous satellite observations. Results show that overshooting cumuliform towers appear as distinct cold areas in the high resolution 11 μm infrared (IR) aircraft images, but that the geosynchronous satellite observations significantly overestimate the thunderstorm top IR brightness temperature (TB) due to field-of-view effects. Profiles of cloud top height and TB across overshooting features indicate an adiabatic cloud surface lapse rate. However, one-dimensional cloud model results indicate that when comparing thunderstorm top temperature and height at different times or different storms, a temperature-to-height conversion of ∼7 K km−1 is appropriate.

Examination of mature storm evolution indicates that during periods when the updraft is relatively intense the satellite IR “cold point” is aligned with the low-level radar reflectivity maximum, but during periods of updraft weakening and lowering cloud top heights, the satellite TB minimum occurs downwind with cirrus anvil debris. The growth period of a relatively weak cumulonimbus cluster is also examined with aircraft and satellite data.

Abstract

Thunderstorm top structure is examined with high spatial resolution radiometric data (visible and infrared) from aircraft overflights together with other storm views, including geosynchronous satellite observations. Results show that overshooting cumuliform towers appear as distinct cold areas in the high resolution 11 μm infrared (IR) aircraft images, but that the geosynchronous satellite observations significantly overestimate the thunderstorm top IR brightness temperature (TB) due to field-of-view effects. Profiles of cloud top height and TB across overshooting features indicate an adiabatic cloud surface lapse rate. However, one-dimensional cloud model results indicate that when comparing thunderstorm top temperature and height at different times or different storms, a temperature-to-height conversion of ∼7 K km−1 is appropriate.

Examination of mature storm evolution indicates that during periods when the updraft is relatively intense the satellite IR “cold point” is aligned with the low-level radar reflectivity maximum, but during periods of updraft weakening and lowering cloud top heights, the satellite TB minimum occurs downwind with cirrus anvil debris. The growth period of a relatively weak cumulonimbus cluster is also examined with aircraft and satellite data.

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