A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere 2. Wave properties

Details A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere 2. Wave properties A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere 2. Wave properties

Mar 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992jgr....97.3089a&link_type=abstract

Journal of Geophysical Research, Volume 97, Issue A3, p. 3089-3101

Physics

Plasma Physics

95

Magnetospheric Physics: Plasma Waves And Instabilities, Space Plasma Physics: Wave/Particle Interactions, Space Plasma Physics: Waves And Instabilities

Scientific paper

A statistical study of narrowband transverse 0.1- to 4.0-magnetic pulsations, essentially Pc 1-2 (0.1-5.0 Hz), occurring from L=3.5 to L=9, ||MLAT||<16°, and all local times, has been made using data from the AMPTE CCE satellite. This work is reported in a pair of papers of which this is the second. In the first paper (Anderson et al., this issue) the occurrence distributions of Pc 1-2 were reported, and here we present statistical distributions of normalized frequency, X = F/FH+(F and F and FH+ are the wave frequency and proton gyrofrequency, respectively); ellipticity, ɛ and spectral power. Events occurring from 1000 to 1800 MLT are left-hand to linearly polarized and exhibited properties corresponding to previous reports.
The normalized frequency was found to depend systematically on MLT and L, decreasing from 0.5-0.45 at 1000 MLT to 0.30 at 1800 MLT and increasing from 0.28 at L=3-5 to 0.39 at L=8-9(for 12-15 MLT). The average X dependence on MLT and L can be accounted for by several mechanisms including variations in cold or hot plasma density, He+ concentration, and hot proton parameters T⊥ and T⊥/T∥. A decrease (increase) in T⊥/T∥ with MLT (L) is shown to be necessary, and increases (decreases) in either T⊥ or plasma densities with MLT (L) are also required to reproduce the observed X variation. The role of He+ in causing the X variations is unclear. Events occurring at dawn, 0300-0900 MLT, and L>7 have not previously been discussed and are found to exhibit remarkable polarization behavior. The A.M. events have the highest X observed in the data base, with X averaging 0.4 to 0.5, but most remarkably, they are linearly polarized at all magnetic latitudes sampled. Given the high normalized frequency, the equatorial linear polarization of the A.M. events cannot be explained in terms of a crossover from left- to right-hand polarization occurring during propagation from low to high magnetic field strengths. Oblique propagation or the effects of multiple reflection through the wave growth region might lead to linear polarizations. The results suggest that a new examination of EMIC wave generation specifically addressing the properties of this A.M. population may be needed.

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