F-Region electron density irregularities during the development of equatorial plasma bubbles

Abstract

The height variation of the ionospheric electron density was measured with rocket-borne electron density probes in two campaigns conducted from Alcantara (2.31°S; 35.2°W), Brazil. A Black Brant X sounding rocket was launched on 14 October 1994 at 1955hrs (LT) to investigate the phenomenon of high-altitude equatorial spread-F events. A Brazilian-made SONDA III rocket was launched on 18 December, 1995 at 2117 hrs (LT). Ground equipment was operated during these campaigns to ensure that the rockets were launched under conditions favourable for the generation of plasma bubbles in the F-region. The rockets, in both occasions, passed through several developing plasma bubbles. The k-spectra of plasma irregularities were obtained by spectral analysis of the electron density fluctuation data. The electron density irregularites associated with plasma bubbles had sharp lines in their k-spectra, extending over a wide range of altitudes. Existing theories on the generation of small scale irregularities by cascading predict a flat k-spectrum. Present results may be indicative of the presence of preferred wave modes in developing plasma bubbles.