Pc 1 Waves and Associated Unstable Distributions of Magnetospheric Protons Observed During a Solar Wind Pressure Pulse

Details Pc 1 Waves and Associated Unstable Distributions of Magnetospheric Protons Observed During a Solar Wind Pressure Pulse Pc 1 Waves and Associated Unstable Distributions of Magnetospheric Protons Observed During a Solar Wind Pressure Pulse

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm23a0475e&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM23A-0475

Physics

2720 Energetic Particles, Trapped, 2731 Magnetosphere: Outer, 2752 Mhd Waves And Instabilities, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

We present observations of Pc 1 waves ( ˜0.6 Hz) that occurred shortly after a strong (>20 nPa) compression of Earth's magnetosphere at 1321 UT March 18, 2002. Intense Pc 1 waves were observed at several high latitude ground stations in Antarctica and Greenland from 1321 UT to beyond 1445 UT. Two wave bursts were recorded at the Polar satellite at 1338 and 1343-44 UT as it passed outbound in the southern hemisphere at 1154 local time and near L = 7.5, in good magnetic conjunction with the Antarctic sites. The pressure increase created a significant population of protons between a few hundred eV and several keV, whose fluxes were mostly perpendicular to B. These protons seem to have replaced the quiescent stream of protons (presumably convected from the plasma sheet) that existed before this increase. There was also a nearly two-order-of-magnitude increase in the population of thermal/suprathermal (0.32-410 eV) protons. Ion cyclotron waves are expected to limit the proton temperature anisotropy A = Tp_e_r_p/T|_|-1 roughly according to A*sqrt(β |_|) ˜ 1, where β |_| is the parallel plasma (proton) beta defined as β |_|= 8π nkT_|_|/B2. Peaks in the locally observed A*sqrt(β |_|) product as a function of time show excellent agreement with the times of the wave bursts. These observations confirm the importance of both the energization and/or increase in population of protons transverse to B in the several keV range, and the presence of greatly increased fluxes of lower energy protons (100s of eV to a few keV), predominantly aligned along B, in determining whether the particle population is unstable at a given time.

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