TEC evidence for near-equatorial energy deposition by 30-keV electrons in the topside ionosphere

TL;DR

This study shows that 30-keV electrons can cause significant ionization in the near-equatorial ionosphere during geomagnetic storms, contributing to positive ionospheric storms and observed electron content increases.

Contribution

It provides evidence that storm-time energetic electrons drift into low-latitude regions, causing ionization and affecting the ionosphere, which was previously not well understood.

Findings

Extreme electron fluxes correlate with increased ionospheric electron content.

Quasi-trapped electrons can produce enough ionization to match observed TEC increases.

Electron fluxes are associated with elevation of the low-latitude F-layer during storms.

Abstract

Observations of energetic electrons (10 - 300 keV) by NOAA/POES and DMSP satellites at heights <1000 km during the period from 1999 to 2010 allowed finding abnormal intense fluxes of ~10^6 - 10^7 cm-2 s-1 sr-1 for quasi-trapped electrons appearing within the forbidden zone of low latitudes over the African, Indo-China, and Pacific regions. Extreme fluxes appeared often in the early morning and persisted for several hours during the maximum and recovery phase of geomagnetic storms. We analyzed nine storm-time events when extreme electron fluxes first appeared in the Eastern Hemisphere, then drifted further eastward toward the South-Atlantic Anomaly. Using the electron spectra, we estimated the possible ionization effect produced by quasi-trapped electrons in the topside ionosphere. The estimated ionization was found to be large enough to satisfy observed storm-time increases in the ionospheric total electron content determined for the same spatial and temporal ranges from global ionospheric maps. Additionally, extreme fluxes of quasi-trapped electrons were accompanied by the significant elevation of the low-latitude F-layer obtained from COSMIC/FORMOSAT-3 radio occultation measurements. We suggest that the storm-time ExB drift of energetic electrons from the inner radiation belt is an important driver of positive ionospheric storms within low-latitude and equatorial regions.