Van Allen Probes and Arase Observations of Magnetospheric ULF Waves Associated with Pi2 Pulsations Observed on the Ground
Abstract
The concurrent operation of the Van Allen Probes and Arase spacecraft provides a new perspective of the longitudinal and latitudinal variations of magnetospheric ULF waves. We have studied nightside ULF waves detected by Van Allen Probes B and Arase in association with a series of ground Pi2 pulsations that were observed between 0100 and 0300 UT on 24 May 2017. Van Allen Probes B, which was located in the plasmasphere very near the magnetic equator, detected fast mode waves with waveforms closely matching those of the ground Pi2s. Arase, which was located outside the plasmasphere off the magnetic equator, detected fundamental toroidal waves following the Pi2 onsets. Each toroidal wave lasted longer than the corresponding ground Pi2, implying that the ionospheric dissipation of Alfvén waves was low. Unlike toroidal waves observed on the dayside in the Pc3-4 band, the nightside toroidal waves contained little power in higher harmonics. The toroidal waves are likely the result of mode conversion from the fast mode Pi2 waves propagating from a source region located in the near-Earth magnetotail, and the absence of higher harmonics has an implication to the spatial structure of the source disturbances. With the overall duration of the toroidal waves reaching 2 hours, we are able to use the frequency of the waves to estimate the plasma mass density at L = 6.1-8.3. The mass density (in amu cm-3) is higher than the electron density (in cm-3) by a factor of 6, which implies that 17-33 % of the ions were O+.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM12A..01T
- Keywords:
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- 2730 Magnetosphere: inner;
- MAGNETOSPHERIC PHYSICSDE: 2774 Radiation belts;
- MAGNETOSPHERIC PHYSICSDE: 7845 Particle acceleration;
- SPACE PLASMA PHYSICSDE: 7867 Wave/particle interactions;
- SPACE PLASMA PHYSICS