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Abstract Excitation of toroidal mode standing Alfvén waves in the midnight sector of the inner magnetosphere in association with substorms is well documented, but studies are sparse on dayside sources for the waves. This paper reports observation of midnight toroidal waves by the Van Allen Probe B spacecraft during a geomagnetically quiet period on 12–13 May 2013. The spacecraft detected toroidal waves excited at odd harmonics below 30 mHz as it moved within the plasmasphere from2100 magnetic local time to0030 magnetic local time through midnight in the dipolerange 4.2–6.1. The frequencies and the relationship between the electric and magnetic field components of the waves are consistent with theoretical toroidal waves for a reflecting ionosphere. At the time of the nightside toroidal waves, compressional waves were observed by geostationary satellites located on the dayside, and the amplitudes of both types of waves varied with the cone angle of the interplanetary magnetic field. The nightside toroidal waves were likely driven by fast mode waves that resulted from transmission of upstream ultralow frequency waves into the magnetosphere. Ground magnetometers located near the footprint of the spacecraft did not detect toroidal waves.
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A Statistical Study of Lower Hybrid Waves in the Earth's Magnetosphere by Van Allen Probes
Abstract The lower hybrid (LH) waves are electrostatic emissions near the LH resonant frequency. They propagate perpendicularly with a small wavelength comparable to Larmor radius of thermal particles and can be capable of heating both ions and electrons. In this study, we statistically study the global distribution of LH waves in the inner magnetosphere by using Van Allen Probes observation from 2012 to 2018. We find that (a) LH waves are commonly observed in the inner magnetosphere. Most LH waves are confined near the magnetic equator with typical amplitudes of 0.02–0.2 mV/m and occurrence rates up to 10%. (b) LH waves extend to innerLregions with increasing wave amplitudes as AE* increases. (c) Weak LH waves occur at the nightside inside the plasmapause. Moderate and strong LH waves occur at the nightside and noon inside the plasmapause. As AE* increases, they extend to all magnetic local times inside the plasmapause and dawnside outside the plasmapause.
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- Award ID(s):
- 1702805
- PAR ID:
- 10444541
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 10
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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