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

Author
Keywords
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 inline image, which suggests that the EMIC dispersion relation contains a frequency gap of around inline image.
Year of Publication
2016
Journal
Geophysical Research Letters
Volume
43
Number of Pages
28-34
Date Published
01/2016
URL
http://doi.wiley.com/10.1002/2015GL066893
DOI
10.1002/2015GL066893