Upper-Level Structure of Oklahoma Tornadic Storms on 2 May 1979. I: Radar and Satellite Observations

Abstract

This paper discusses the observational characteristics of the upper level structure of severe tornadic storms in Oklahoma on 2 May 1979 during SESAME. The data analyzed consist of limited-scan GOES-East and West visible, infrared (11 ?m), and stereo satellite data, dual-Doppler radar observations, and special storm scale soundings. The time-histories of stereo cloud top height, minimum equivalent blackbody temperature (TBB) and radar reflectivity are followed for three severe storms over a several hour period; two of the storms are tornadic. Cloud top IR growth rates and vertical velocities of the storms are computed and found to have maxima which fall into Adler and Fenn's severe storm classification. For one of the storms there is an interesting coupling between cloud top parameters and low-level radar echoes; the other tornadic storm showed no unique relationship. Hail damage began shortly after tropopause penetration by thee storms. Two major IR cold areas associated with the leading downwind storm (i.e., Lahoma storm), are both about 10°C lower than the minimum (tropopause) temperature in an upwind sounding. One is displaced upwind about 15 km from the visible cloud top and the inferred updraft position from radar; the other is located about 15 km to the south of the visible cloud top. A ?V? pattern of lower TBB with embedded higher temperature (warm areas) developed after tropopause penetration by the Lahoma storm. Composites of stereo height contours on IR images indicated that TBB is not uniquely related to height. The warm areas are deduced to be of two types: one called the ?close-in? warm am is located about 10?20 km downwind of the cloud top of the Lahoma storm, and the other called the ?distant? warm area is about 50?75 km downwind. The close-in warm area has a motion similar to that of the storms and appears to be dynamically linked to the leading storm. A model is proposed to explain this warm area based on mixing processes and subsidence near cloud top. The distant warm area advects with a direction similar to the 9?14 km upper level winds but with a speed 10?20 m s?1 lower. This appears to be anvil cirrus material. However, the TBB in this area are several degrees warmer the stratospheric environmental temperatures at the anvil top. Stratospheric above-anvil cirrus (Fujita) explains neither the ?V? shape nor the internal warm areas. Doppler radar derived winds are presented to add insight into the development of the upper level structure of the storms.