EMIC Wave Distributions Observed by the Van Allen Probes

TL;DR

This study statistically analyzes EMIC wave characteristics observed by the Van Allen Probes over 33 months, revealing prevalence patterns, bandwidth ranges, and duration consistency across different wave-bands.

Contribution

It provides the first comprehensive statistical analysis of EMIC wave distributions, categorizing them by wave-band, bandwidth, and duration using extensive in-situ measurements.

Findings

He+-band waves are most prevalent among EMIC waves.

O+-band waves are rare compared to H+ and He+ bands.

Most EMIC waves have durations between 20 and 40 minutes.

Abstract

Characteristics of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen probes are statistically analyzed, particularly wave-band, bandwidth, and time duration. The Electric and Magnetic Field Instrument Suite and Integrated Science, an instrument on board the Van Allen Probes, provides the necessary magnetic field measurements to examine 33 months of EMIC wave occurrence (1 September 2013 to 31 May 2016). Upon visual identification, the waves are grouped into their respective wave-bands, H+, He+, or O+, defined by the frequencies they are observed at, manifested in the daily spectrograms as their location relative to gyrofrequency lines. Nearly 2,500 EMIC wave events are detected. Results suggest a prevalence of He+-band waves, and a rarity of O+-band waves (1,155 H+-band events, 1,176 He+-band events, and 125 O+-band events). The most prevalent bandwidth range for events in general is found to be 0.25 - 0.5 Hz. However, this appears to vary among the three wave-bands. Helium and oxygen wave-band events tend to have shorter bandwidths (0.25 - 0.5 Hz) than their hydrogen counterparts. Time duration is more consistent among wave-bands, and while H+-band events on average have a slightly shorter duration, the most common time duration for all wave-bands is between 20 and 40 minutes.