12,000

We have over 12,000 students, from over 100 countries, within one of the safest campuses in the UK

93%

93% of Lancaster students go into work or further study within six months of graduating

Home > Research > Publications & Outputs > Free energy to drive equatorial magnetosonic wa...
View graph of relations

« Back

Free energy to drive equatorial magnetosonic wave instability at geosynchronous orbit

Research output: Contribution to journalJournal article

Published

Article numberA08220
Journal publication date23/08/2011
JournalJournal of Geophysical Research
Volume116
Number of pages13
Pages-
Original languageEnglish

Abstract

The magnetosonic (or ion Bernstein) instability is driven by a positive slope in the ion distribution function perpendicular to the magnetic field at energies above about 1 keV. Fifteen years of multisatellite geosynchronous observations are used to determine the statistical occurrence of ion distributions with positive slopes as a function of energy, local time, geomagnetic activity, and phase of the solar cycle. There is no discernable dependence on phase of the solar cycle, but there are clear dependences on the other parameters. Positive slopes are seen primarily in the energy range between similar to 3 and similar to 24 keV. The peak occurrence of positive slopes is between midmorning and dusk and moves progressively toward earlier local times for higher energies. The occurrence is significantly greater and extends over a broader local time range for low levels of geomagnetic activity than for high activity, for all energies. At high activity levels, the occurrence tends to be more closely confined near noon. Peak occurrence rates are similar to 30% at energies just below 10 keV. A superposed epoch analysis of 77 coronal mass ejection (CME)-driven storms and 93 high-speed solar wind (HSS)-driven storms shows a relative suppression of the occurrence frequency of positive slopes during the recovery phase. The suppression is particularly long-lived for HSS-driven streams.

Bibliographic note

©2011. American Geophysical Union. All Rights Reserved.