Journal article
Quasiperiodic Whistler Mode Emissions Observed by the Van Allen Probes Spacecratt
Journal of geophysical research. Space physics, Vol.123(11), pp.8969-8982
11/01/2018
DOI: 10.1029/2018JA026058
Abstract
Quasiperiodic (QP) emissions are whistler mode electromagnetic waves observed in the inner magnetosphere that exhibit a QP time modulation of the wave intensity. We analyze 768 QP events observed during the first 5 years of the operation of the Van Allen Probes spacecraft (September 2012 to October 2017). Multicomponent wave measurements performed in the equatorial region, where the emissions are likely generated, are used to reveal new experimental information about their properties. We show that the events are observed nearly exclusively inside the plasmasphere. Wave frequencies are mostly between about 0.5 and 4 kHz. The events observed at larger radial distances and on the duskside tend to have slightly lower frequencies than the emissions observed elsewhere. The maximum event frequencies are limited by half of the equatorial electron gyrofrequency, suggesting the importance of wave ducting. Modulation periods are typically between about 0.5 and 5 min, and they increase with the in situ measured plasma number density. This increase is consistent with the main mechanisms suggested to explain the origin of the QP modulation. Two-point measurements performed by the Van Allen Probes are used to estimate a typical spatial extent of the emissions to about 1 R-E in radial distance and 1.5 hr in magnetic local time. Detailed wave analysis shows that the emissions are right-hand circularly polarized, and they usually come from several different directions simultaneously. They, however, predominantly propagate at rather low wave normal angles and away from the geomagnetic equator.
Details
- Title: Subtitle
- Quasiperiodic Whistler Mode Emissions Observed by the Van Allen Probes Spacecratt
- Creators
- F. Nemec - Charles UniversityG. B. Hospodarsky - University of IowaB. Bezdekova - Charles UniversityG. Demekhov - Polar (Finland)D. L. Pasmanik - Institute of Applied PhysicsO. Santolik - Charles UniversityW. S. Kurth - University of IowaD. Hartley - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.123(11), pp.8969-8982
- DOI
- 10.1029/2018JA026058
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Amer Geophysical Union
- Number of pages
- 14
- Grant note
- 921647; NAS5-01072 / JHU/APL under NASA 18-00844S / GACR; Grant Agency of the Czech Republic 15-12-20005 / Russian Science Foundation; Russian Science Foundation (RSF) 300216 / GAUK Praemium Academiae award from the CAS LTAUSA17070 / MSMT; Ministry of Education, Youth & Sports - Czech Republic
- Language
- English
- Date published
- 11/01/2018
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455362502771
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