Storm-time ionization enhancements at the topside low-latitude ionosphere

A Dmitriev,H.-C Yeh

doi:10.5194/angeo-26-867-2008

Abstract

Abstract. Ion density enhancements at the topside low-latitude ionosphere during a Bastille storm on 15–16 July 2000 and Halloween storms on 29–31 October 2003 were studied using data from ROCSAT-1/IPEI experiment. Prominent ion density enhancements demonstrate similar temporal dynamics both in the sunlit and in the nightside hemispheres. The ion density increases dramatically (up to two orders of magnitude) during the main phase of the geomagnetic storms and reaches peak values at the storm maximum. The density enhancements are mostly localized in the region of a South Atlantic Anomaly (SAA), which is characterized by very intense fluxes of energetic particles. The dynamics of near-Earth radiation was studied using SAMPEX/LEICA data on >0.6 MeV electrons and >0.8 MeV protons at around 600 km altitude. During the magnetic storms the energetic particle fluxes in the SAA region and in its vicinity increase more than three orders of magnitude. The location of increased fluxes overlaps well with the regions of ion density enhancements. Two mechanisms were considered to be responsible for the generation of storm-time ion density enhancements: prompt penetration of the interplanetary electric field and abundant ionization of the ionosphere by enhanced precipitation of energetic particles from the radiation belt.

Highlights

Geomagnetic storms are accompanied with strong perturbations in the entire ionosphere, which have been observed using various techniques (e.g. Basu et al, 2001)
Very strong ion density enhancements up to two orders of magnitude have been observed by the ROCSAT-1/ionospheric Plasma and Electrodynamics Instrument (IPEI) in the topside ionosphere at low latitudes during the Bastille and Halloween magnetic storms
Electric field, which causes an expansion of the equatorial ionization anomaly (EIA) crest regions toward the higher latitudes during the main phase of geomagnetic storms

Summary

Introduction

Geomagnetic storms are accompanied with strong perturbations in the entire ionosphere, which have been observed using various techniques (e.g. Basu et al, 2001). Significant ionospheric effects require a very strong southward interplanetary magnetic field (IMF) and/or an extremely fast solar wind plasma flow Another source of the abundant ionization and heating at low- and mid-latitudes is the particle precipitation, which. Based on analyses of the Bastille magnetic storm on 16– 17 July, Lin and Yeh (2005) proposed that energetic particle precipitation plays an important role in the SEDs observed in the South Atlantic Anomaly (SAA) region on the nightside. They demonstrate that the precipitation of energetic electrons from the radiation belt in the SAA region significantly increases Hall conductivity in the E-region.

Storm-time ionospheric disturbances

Energetic particle precipitation

Discussion

Conclusion