Electrodynamics of the equatorial ionosphere and occurrence of equatorial spread F during the Western Pacific (WestPac) ionospheric campaign

Abstract

During post sunset hours the equatorial ionosphere often becomes unstable and severe ionospheric irregularities are formed. These irregularities are called equatorial spread F (ESF). ESF causes radio communication disturbances in the trans-ionospheric radio system in a wide frequency range up to several GHz. Kelley et al. (1981) observed that the ESF commenced just after the F-region ionosphere drifted upward, which is due to the enhanced eastward electric field in the evening hours or evening enhancement. It is well known that a Rayleigh-Taylor instability is responsible for initiating ESF (Kelley, 1989) in conjunction with the evening enhancement of the eastward electric field. Recently, Kudeki and Bhattacharyya (1999) observed a complex vortex-like feature of plasma flow due to the evening enhancement at the equatorial IS radar station.
In order to investigate plasma dynamics and ionospheric structure in the equatorial region, cooperative observation campaign has been held several times since 1997 in the Western Pacific region. Many universities and institutes participated in the campaign. We will present early results of the campaign conducted in 1998 (WestPac98).