Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A

Shoya Matsuda; Yoshiya Kasahara; Craig A Kletzing

doi:10.1002/2015GL066893

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Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A

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Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A

Shoya Matsuda, Yoshiya Kasahara and Craig A Kletzing

Geophysical research letters, Vol.43(1), pp.28-34

01/16/2016

DOI: 10.1002/2015GL066893

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Abstract

We report variations in the propagation of the H+ band ion cyclotron whistlers observed by Van Allen Probe A. Ion cyclotron whistlers are one of the EMIC (electromagnetic ion cyclotron) waves generated by mode conversion from lightning whistlers. Crossover frequency is an important frequency for the ion cyclotron whistlers, which is a function of the variations in the local heavy‐ion composition. We surveyed waveform data obtained by the Electric and Magnetic Field Instrument and Integrated Science instrument and found that 3461 H+ band ion cyclotron whistlers were observed from 572 km to 5992 km in altitude. The main finding is that the crossover frequencies of the observed events decreased with increasing altitude. These results support the hypothesis that the total heavy‐ion density decreases with increasing altitude. Furthermore, in 96% of all observed events, the crossover frequencies exceeded 0.5fH+, which suggests that the EMIC dispersion relation contains a frequency gap of around 0.5fH+. Key Points We found that 3441 H+ band ion cyclotron whistler waves were observed by Van Allen Probe A Crossover frequencies were high ( ∼0.8fH+) at low altitudes and decreased with increasing altitude We suggested that a frequency gap exists around 0.5fH+ in the EMIC dispersion relation

EMIC wave

heavy ion

ion cyclotron whistler

plasmasphere

Van Allen Probe

Details

Title: Subtitle: Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A
Creators: Shoya Matsuda - Kanazawa University
Yoshiya Kasahara - Kanazawa University
Craig A Kletzing - University of Iowa
Resource Type: Journal article
Publication Details: Geophysical research letters, Vol.43(1), pp.28-34
DOI: 10.1002/2015GL066893
ISSN: 0094-8276
eISSN: 1944-8007
Number of pages: 7
Grant note: Grant‐in‐Aid for Scientific Research from the Japan Society for the Promotion of Science (24360159; 24654157; 15H05815) Grant‐in‐Aid for JSPS Fellows
Language: English
Date published: 01/16/2016
Academic Unit: Physics and Astronomy
Record Identifier: 9984199750902771

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