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Observational Properties of Harmonic EMIC Waves: Statistical Study
Observational Properties of Harmonic EMIC Waves: Statistical Study
Shujie Gu
(Department of Physics William B. Hanson Center for Space Sciences University of Texas at Dallas Richardson TX USA)
Xu Liu
(Department of Physics William B. Hanson Center for Space Sciences University of Texas at Dallas Richardson TX USA)
Lunjin Chen
(Department of Physics William B. Hanson Center for Space Sciences University of Texas at Dallas Richardson TX USA)
M. E. Usanova
(Laboratory for Atmospheric and Space Physics University of Colorado Boulder Boulder CO USA)
Wenyao Gu
(Department of Physics William B. Hanson Center for Space Sciences University of Texas at Dallas Richardson TX USA)
Zhiyang Xia
(Department of Physics William B. Hanson Center for Space Sciences University of Texas at Dallas Richardson TX USA)
Journal: Geophysical Research Letters
•
• Wiley
• ISSN: 1944-8007
Abstract
Abstract Electromagnetic ion cyclotron (EMIC) waves are discrete electromagnetic emissions separated by multiple ion gyrofrequencies. Harmonic EMIC waves are defined as waves with a strong electric or magnetic field (or both) at the harmonics of the fundamental EMIC mode. In this paper, for the first time, we present a statistical study on harmonic EMIC waves by the Van Allen Probes. The EMIC waves are categorized into three types based on their harmonics: (a) Fundamental mode only (without higher harmonics), (b) electrostatic (ES) harmonics, and (c) electromagnetic (EM) harmonics. We find that most harmonic EMIC wave events are observed on the dayside, outside the plasmasphere and are associated with a low fpe/fce, a high proton βH, and a strong fundamental EMIC mode. ES harmonic EMIC waves tend to exhibit a larger Ew/cBw ratio compared to EM harmonic EMIC waves. The results advance our understanding of harmonic EMIC waves and their generation mechanisms.