Equivalent Blackbody Temperature of the Top of a Severe Storm

Abstract

An experiment was undertaken to measure the equivalent blackbody temperature of cloud tops of a severe storm. This was done to evaluate the common meteorological practice of determining cloud top altitude by equating the equivalent blackbody temperature to the corresponding temperature from a nearby radiosonde and to provide data for determining radiative heat transfer mechanisms in the cloud top. Near Graham, Tex., infrared spectra in the spectral range of 6.7 to 13.3 ?m were collected 29 April 1970 from the top of a severe storm 12.4 to 14.0 km in altitude. Absolute altitude of the cloud tops was determined by AS-11 Al plotter analysis of stereo pairs of photographs taken with an RC-8 camera. The equivalent blackbody temperature of the cloud top was determined by fitting the Planck radiation function to the data. The radiometrically derived temperature of the cloud top is ?4 to +7 K warmer than the environmental temperature as determined from radiosonde data for any given storm top altitude. Two temperature anomalies approximately 500 m in diameter were found near opposite sides of a 1 km wide and 13.8 km high cloud tower. Each of these anomalies is 6 to 9 K warmer than the surrounding cloud equivalent blackbody temperature of 209 K. It is proposed that the anomalies observed are dry air subsidence on the edge of an updraft that perturbs cloud particle spectra. The infrared extinction coefficient due to the cloud is decreased and thermal radiation from the interior of the warmer cloud is allowed to escape.