Links between the plasmapause and the radiation belt boundaries as observed by the instruments CIS, RAPID, and WHISPER onboard Cluster

Abstract

[1] In the present work, we study the relations between the position of the plasmapause and the position of the radiation belt boundaries. The Cluster mission offers the exceptional opportunity to analyze those different regions of the inner magnetosphere with identical sensors on multiple spacecraft. We compare the positions of the radiation belt edges deduced from CIS (Cluster Ion Spectrometry) observations (electrons with energy > 2 MeV) with the positions of the plasmapause derived from WHISPER (Waves of HIgh frequency and Sounder for Probing of the Electron density by Relaxation) data (electron plasma frequency). In addition, we compare those results with the edges positions determined from RAPID (Research with Adaptive Particle Imaging Detectors) observations (electrons with energy between 244.1 and 406.5 keV). The period of 1 April 2007 to 31 March 2009 has been chosen for the analysis because at that time Cluster's perigee was located at lower radial distances than during the earlier part of the mission. The perigee was then as close as 2 R E , deep inside the plasmasphere and the radiation belts. This time period corresponds to a long solar activity minimum. Differences are observed between the radiation belt boundary positions obtained from the two different instruments: The radiation belt positions are related to the energy bands. The results show that the plasmapause position is more variable than the radiation belt boundary positions, especially during small geomagnetic activity enhancements. A correspondence is observed between the plasmapause position determined by WHISPER and the outer edge of the outer radiation belt of energetic electrons (> 2 MeV) observed by CIS. This result is unexpected since previous studies based on other spacecraft observations indicated a correlation between the inner edge of the outer belt and the plasmapause. However, during higher geomagnetic activity time periods, the plasmapause is located closer to the inner boundary of the outer radiation belt. Also, the thickness of the slot region is found to follow the global evolution of the geomagnetic activity.

New model fit functions of the plasmapause location determined using THEMIS observations during the ascending phase of Solar Cycle 24

“…We notice that Darrouzet et al [2013] here, we find that the difference between the same WHISPER observations and the predictions of our model fit functions is similarly substantial. Comparison between the WHISPER observations on Cluster and those on THEMIS used in the present work may be worthwhile to do in a future work.…”

“…We notice that Darrouzet et al [] determined the plasmapause locations based on the observations by the WHISPER instrument onboard Cluster for a 2 year interval from April 2007. They compared the observed plasmapause locations with the predictions of the Dst ‐ and Kp ‐dependent model fit functions of O'Brien and Moldwin [] and those of the Kp ‐dependent model fit function of Carpenter and Anderson [].…”

The Energetic Particle Telescope: First Results

“…Using simultaneous observations of the Cluster instruments RAPID, CIS and WHISPER, Pierrard and Benck (2012) and Darrouzet et al (2013) showed also observed links between the position of the plasmapause and the locations of the electron radiation belts boundaries for different energies. Cluster spacecraft continue to provide observations that can be compared with EPT.…”

Remote sensing the plasmasphere, plasmapause, plumes and other features using ground-based magnetometers

“…The ring current arises from the azimuthal motion of trapped particles in the inner magnetosphere and roughly straddles the plasmapause (Darrouzet et al 2013). The main contributors to the current density are 1-100 keV ions.…”