In situ ionospheric observations of severe weather-related gravity waves and associated small-scale plasma structure

On July 27, 1988, two sounding rockets were launched over a small thunderstorm cell which constituted the remnants of a large frontal event which had lasted for several hours over the eastern seaboard. One of the rockets was instrumented for detection of the electromagnetic impulse from lightning strikes and its subsequent interaction with the ionospheric plasma [Kelley et al., 1990]. The second had on board an absolute electron density probe, the results from which we report here. We present evidence that a gravity wave was spawned by the front and propagated nearly to the F peak in the ionosphere, where it steepened and created structure in the medium at scales much less than the vertical wavenumber of the major disturbance. The fluctuation spectrum along the rocket path was elevated for scales from 25 km down to less' than 10 m. At scales between 10 km and just under 100 m, characterization of the spectrum by a power law yields a spectral index less than that displayed by such well-studied processes as bottomside spread F and barium cloud striations. Similar results have been reported for gravity wave induced intermediate scale structures at midlatitudes [Wernik et al., 1986]. The mixing theory described by Fridman [1990] may be relevant to these observations.