Longitudinal variability of annual changes in activity of equatorial spread F and plasma bubbles

Abstract

Global distribution maps of equatorial spread F (ESF) activity for various annual periods were derived from the topside soundings by the Ionosphere Sounding Satellite b (ISS-b) in 1978-1980. The ESF activity during the northern winter period reveals maximum enhancement at the Atlantic longitudes of large westward geomagnetic declination, and during the northern summer at the Pacific longitudes of large eastward declination. On several orbits passing over the region of the ESF activity enhancement, abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km. It has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced ESF activity and asymmetric in the region of the suppressed ESF activity. These observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the Rayleigh-Taylor type plasma instability. 10,903 10,904 MARUYAMA AND MATUURA: ACTIVITY OF ESF AND BUBBLES

Measurement of the latitudinal distributions of total electron content during equatorial spread F events

“…If the transequatorial wind persists for several hours after sunset, a significant lowering of the F layer may occur, which initiates a rapid recombination of the F layer. This argument was used by Maruyama and Matuura [1984] to suggest that the transequatorial wind could be a stabilizing mechanism due to the lowering of the F region in the upwind hemisphere. We have not seen such an effect, but at the same time we acknowledge the lack of completeness in the Northern Hemisphere portion of our TEC distributions.…”

The effects of the pre-reversal ExB drift, the EIA asymmetry, and magnetic activity on the equatorial spread F during solar maximum

“…Maruyama and Matuura (1984) proposed that the asymmetry in the electron density distribution, which is caused by the meridional winds, could suppress the ESF activity. However, they did not show the seasonal variation in the asymmetry in the density distribution.…”

“…Now, it is known that there are some candidate mechanisms helping the ESF development. These are (1) the pre-reversal enhancement (PRE) in upward E×B drift and associated uplifting of the F-layer (Fejer et al, 1999;Whalen, 2002), (2) a small or null transequatorial component of the thermospheric winds and associated symmetry in the equatorial ionization anomaly (EIA) (Maruyama and Matuura, 1984;Maruyama, 1988;Mendillo et al, 2000Mendillo et al, , 2001, (3) a simultaneous decay of the E region conductivity at both ends of the field line (Tsunoda, 1985;Stephan et al, 2002), and (4) a sharp gradient at the bottomside of the F-layer (Kelley, 1989).…”

A comparison of the equatorial spread F derived by the International Reference Ionosphere and the S 4 index observed by FORMOSAT-3/COSMIC during the solar minimum period of 2007–2009

“…There have been many studies on the occurrence characteristics of ionospheric density irregularities using groundbased measurements (Rastogi, 1980;Abdu, 2001), satellitebased in situ measurements (Watanabe and Oya, 1986;Huang et al, 2002;Burke et al, 2004), and topside sounders (Maruyama and Matuura, 1984), and many important features of these have been reported including temporal variations (Sahai et al, 2000;Huang et al, 2002), seasonallongitudinal variability (Burke et al, 2004), several-day variation, and day-to-day variation (Basu et al, 1996) though several enigmatic features of them are yet to be revealed (Thampi et al, 2009). However, studies on continuous and global characteristic features of ionospheric plasma irregularities are very scanty due to the fact that the global coverage is difficult to obtain from ground-based observations.…”