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Enhancement of ultralow frequency wave amplitudes at the plasmapause
Author(s) -
Clausen L. B. N.,
Glassmeier K.H.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja020072
Subject(s) - plasmasphere , amplitude , physics , computational physics , magnetosphere , geophysics , magnetohydrodynamics , discontinuity (linguistics) , plasma , geodesy , geology , optics , nuclear physics , mathematical analysis , mathematics
We present measurements of ultralow frequency (ULF) wave amplitudes measured by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes while crossing the plasmapause. During one crossing on 24 June 2007 which we study in detail, all three probes of which data that were obtained show an increase in the ULF compressional wave amplitude between 10 and 50 mHz by about 30%. These results are confirmed by a statistical study that examines the ULF compressional wave amplitude in the same frequency range averaged over 132 sharp plasmapause crossings between June 2007 and December 2007 made by THEMIS C, D, and E. Sharp plasmapause crossings are defined as those where the density increases by more than a factor of 50 over a spatial scale of 500 km. We find that assuming that the plasmapause can be approximated by a tangential MHD discontinuity, a ULF wave amplitude enhancement of 30% is in good agreement with theoretical transmission coefficient calculations if the plasma density increases from about 4 cm −3 on the magnetospheric trough side to about 540 cm −3 on the plasmaspheric side while simultaneously the magnetic field magnitude increases from 250 nT to 350 nT. These results might have important implications for the detection of global fast modes by satellites as their amplitude is hence expected to be higher inside the plasmasphere than outside.