Cluster observations of band-limited Pc 1 waves associated with streaming H+ and O+ ions in the high-altitude plasma mantle

M. J. Engebretson, C. R G Kahlstorf, D. L. Murr, J. L. Posch, A. Keiling, B. Lavraud, H. Rme, M. R. Lessard, E. H. Kim, J. R. Johnson, J. Dombeck, B. Grison, P. Robert, K. H. Glassmeier, P. M E Décréau

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Bursts of band-limited Pc 1 waves (0.2 to ∼1.0 Hz) with normalized frequency f/fH+ ∼ 0.5 have been observed by the Cluster spacecraft during many passes through the high-latitude plasma mantle. These transverse, left-hand polarized waves are associated with regions of H + and O+ ions streaming away from Earth along magnetic field lines at the same velocity (∼140 km/s). Waves were observed only when H+ fluxes increased by factors of 10-1000 and energies of both ion species increased by factors of up to 10. We present two satellite-ground conjunctions to demonstrate the high latitude localization of these waves and their ability to reach the polar ionosphere and two extended examples of waves and associated ion distribution functions near the southern dusk flank magnetopause. We also present the results of a search for all such events during Cluster's 2002 and 2003 passages through the magnetotail, with orbital precession covering dawn to dusk on Earth's night side (June through December). A total of 46 events (band-limited Pc 1-2 waves accompanied by a sustained population of streaming H+ and O+ ions, separated by at least 12 min) were observed on 29 days. The waves were generally associated with intervals of southward IMF Bz and/or large IMF By (times of active cusp reconnection), and often but not always occurred during the main phase or early recovery phase of magnetic storms. Analysis of selected events shows that the waves are associated with large H+ temperature anisotropy, and that the waves propagate opposite to the direction of the streaming ions. A wave instability analysis using the WHAMP code confirms that the generation of these waves, via the ion cyclotron instability, is basically consistent with known physics. Their extended region of wave growth is likely, however, to reach tailward significantly beyond the Cluster orbit.

Original languageEnglish (US)
Article numberA10219
JournalJournal of Geophysical Research: Space Physics
Issue number10
StatePublished - 2012


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