Steepened structures in equatorial spread <i>F</i>: 1. New observations

Abstract

Sounding rocket data from the 1990 CRRES/EQUIS equatorial spread F campaign on Kwajalein Atoll are presented. Two Terrier Malamute sounding rockets were launched into active spread F conditions on July 30 and August 2, respectively, and achieved apogee slightly below 500 km, just above the F peak. Plasma frequency probes aboard both rockets showed that the unstable nighttime F region is characterized by propagating steepened structures. Power density spectra for the structures typically exhibit two regions that obey k −n scaling, where n is approximately equal to 2 at wavelengths greater than 80‐100 m and approximately equal to 5 at shorter wavelengths. These spectral indices are quite variable, and the long‐wavelength spectral index in particular seems to decrease with increasing amplitude of density fluctuations. The rocket payloads also measured vector electric fields in the plane perpendicular to B over wavelengths ranging from over 60 km to less than 6 m. Both vector components of the perpendicular electric field are proportional to δ n / n at wavelengths longer than 300 m but assume a Boltzmann relationship (with |δ E |² ∼ k ²|δ n / n |²) at smaller scales. The perturbed zonal electric field, δ E x , dominates the vertical field, δ E z , at long wavelengths, but the situation is reversed at smaller scales.