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

Abstract

Abstract.Ion density enhancements at the topside lowlatitude 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 nearEarth 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.

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

“…The energy deposition of precipitating particles of various energies mainly through the ionization of atmospheric atoms occurs at different altitudes, particularly within the D, E, and F regions of the ionosphere and extends from high to midlatitudes and over the South-Atlantic Anomaly (SAA) at low latitudes [e.g., Voss and Smith, 1980;Vampola and Gorney, 1983;Rees et al, 1988;Abel et al, 1997]. An impact of precipitating particles in the lower ionosphere (the D and E layers) and the upper atmosphere in terms of enhanced ionization and other related aeronomical effects has been investigated in a large number of studies [e.g., Buonsanto, 1999, and references therein;Nishino et al, 2002;Peter et al, 2006;Clilverd et al, 2008Clilverd et al, , 2010Turunen et al, 2009;Lam et al, 2010;Dmitriev et al, 2011], while evidence for ionospheric signatures in the topside ionosphere (F region) in the midlatitudes and over the SAA at low latitudes have also been reported [e.g., Foster et al, 1994Foster et al, , 1998Abdu et al, 2005;Kunitsyn et al, 2008aKunitsyn et al, , 2008bDmitriev and Yeh, 2008;Pedatella et al, 2009;Ngwira et al, 2012].…”

“…[7] Focusing our work on the particle effect in the topside ionosphere (the F region), we list studies that provide important information regarding the F region signatures that appeared due to the direct ionization of thermospheric species by energetic electrons [Foster et al, 1998;Pedatella et al, 2009;Dmitriev and Yeh, 2008;Kunitsyn et al, 2008aKunitsyn et al, , 2008bNgwira et al, 2012]. Such studies demonstrate features such as the uplift of the F region and spots of enhanced ionization in the bottom-side F-layer at midlatitudes and in the topside region over the SAA.…”

Climatology of the inter-hemispheric field-aligned current system in the equatorial ionosphere as observed by CHAMP

“…In our opinion the solar cycle dependence of the latter process (e.g., Fig. 7 of Dmitriev and Yeh, 2008) is the one that causes the weakening of the Sq currents in the SAA region during solar minimum.…”

Low‐latitude ionospheric effects of energetic electrons during a recurrent magnetic storm

“…Studying storm‐time enhancements of ionization in the SAA area, Dmitriev and Yeh [] discuss local electrodynamic mechanisms related to disturbance electric fields, which are generated in the SAA region due to the presence of conductivity gradients produced by the enhanced particle precipitation [ Lin and Yeh , ; Foster and Coster , ]. Hence, ionization in the SAA region results from both direct particle impact to the topside ionosphere and electrodynamic effects produced by precipitating particles in the bottomside ionosphere.…”