The instrumented NASA ER-2 aircraft overflew severe convection with infrared (IR) V features for the first time in the Midwest United States during May 1984. Measurements taken by the ER-2 were: visible and IR imagery, high-frequency passive microwave (92, 183 GHz) imagery, nadir lidar backscattered return, and flight altitude information. The 7 May and 13 May 1984 cases are analyzed in detail and the various data sources are combined and compared with GOES imagery. Topics addressed in the paper are 1) relation of thermal couplets and V features in aircraft IR measurements to previous findings from GOES data, 2) examination of the cloud radiative hypothesis for the V feature, and 3) stratospheric perturbations above severe thunderstorms and mesoscale convective systems.
The high resolution aircraft IR imagery shows that thermal couplets are considerably more pronounced than in GOES imagery. In one of the cases (7 May 1984) the minimum cloud-top IR temperature was located upshear of the overshooting cloud top in the lidar height field. This was suggested in previous papers to result from cloud top mixing with the stratospheric environment and subsidence. The IR temperatures in the downshear anvils were as much as 5°C warmer than the ambient air temperatures, implying that the upwelling IR radiance comes from about 0.5–1.0 km below the cloud top. Finally, the in situ ER-2 measurements of temperature and air velocity 3–4 km above the overshooting tops showed very intense temperature and vertical velocity perturbations. These perturbations are suggestive of 1) lee waves generated by the overshooting tops, or 2) a cold dome above the squall line possibly due to tropopause lifting by the storms.