Storm time observations of electromagnetic ion cyclotron waves at geosynchronous orbit: GOES results

Abstract

[1] Electromagnetic ion cyclotron (EMIC) waves may contribute to ring current ion and radiation belt electron losses, and theoretical studies suggest these processes may be most effective during the main phase of geomagnetic storms. However, ground-based signatures of EMIC waves, Pc1-Pc2 geomagnetic pulsations, are observed more frequently during the recovery phase. We investigate the association of EMIC waves with various storm phases in case and statistical studies of 22 geomagnetic storms over 1996-2003, with an associated Dst < −30 nT. High-resolution data from the GOES 8, 9, and 10 geosynchronous satellite magnetometers provide information on EMIC wave activity in the 0-1 Hz band over ±3 days with respect to storm onset, defined as commencement of the negative excursion of Dst. Thirteen of 22 storms showed EMIC waves occurring during the main phase. In case studies of two storms, waves were seen with higher intensity in the main phase in one and the recovery phase in the other. Power spectral densities up to 500 nT 2 Hz −1 were similar in prestorm, storm, and early recovery phases. Superposed epoch analysis of the 22 storms shows 78% of wave events during the main phase occurred in the He + band. After storm onset the main phase contributed only 29% of events overall compared to 71% during recovery phase, up to 3 days. Some differences between storms were found to be dependent on the solar wind driver. Plasma plumes or an inflated plasmasphere may contribute to enhancing EMIC wave activity at geosynchronous orbit.

High-speed stream driven inferences of global wave distributions at geosynchronous orbit: relevance to radiation-belt dynamics

“…Statistically, the proxy and the wave observations agree quite consistently. Both the proxy and the space-based wave observations indicate an abundance of EMIC-wave activity in the storm main phase (Fraser et al 2010). In addition, Blum et al (2009b) found good agreement for some events when GOES and LANL satellites were relatively close to each other.…”

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP

“…The EMIC source region is typically confined within ≈10 degrees of the geomagnetic equatorial plane, and the Poynting flux at higher latitude is always directed away from the equator, dispelling the long-standing bouncing wave packet model (Loto'aniu et al 2005). EMIC waves are enhanced during magnetic storms (Fraser et al 2010), as anisotropic energetic ring current ions are injected into the inner magnetosphere (Jordanova et al 2001a). EMIC waves can cause rapid scattering and loss for ring current ions (Jordanova et al 2001b) and relativistic electrons above 0.5 MeV (Thorne and Kennel 1971;Lyons and Thorne 1973;Albert 2003;Summers and Thorne 2003;Meredith et al 2003b).…”

The controlling effect of ion temperature on EMIC wave excitation and scattering

“…Waves in the band below W He+ are found to be most intense (up to 1000 nT 2 /Hz) statistically during active conditions [Fraser et al, 2010].…”