A statistical study of EMIC waves observed by Cluster: 1. Wave properties

Abstract

Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L‐shell (MLT‐L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.

Van Allen Probes, THEMIS, GOES, and Cluster observations of EMIC waves, ULF pulsations, and an electron flux dropout

“…These H + band waves do not appear in the wave normal analysis shown Figure because they were below the 10 −2 nT 2 /Hz amplitude threshold chosen for this figure. GOES 15 was located between 7.3 LT and 14.3 LT when the nearly perpendicular propagating, left‐hand to linearly polarized EMIC waves were observed, which is consistent with statistical studies showing that dawnside waves tend to be more linearly polarized and have large wave normal angles in the H + band (>45°) and even larger wave normal angles in the He + band (>60°) [e.g., Anderson et al , 1992; Min et al , ; Allen et al , ].…”

“…EMIC waves have traditionally been thought of as transverse, left‐hand polarized magnetic field fluctuations. However, right‐hand and linearly polarized EMIC waves have been observed [ Anderson et al , ; Min et al , ; Paulson et al , ; Allen et al , ]. Also, some published EMIC wave examples have weak parallel components, and statistical results indicate that propagation at large wave normal angles is possible [ Anderson et al , , 1992b; Min et al , ; Allen et al , ].…”

Full‐wave modeling of EMIC waves near the He+ gyrofrequency

“…Recent statistical studies [e.g., Min et al, 2012;Allen et al, 2015;Saikin et al, 2015] indicated that EMIC waves have a variety of wave normal angles. Recent statistical studies [e.g., Min et al, 2012;Allen et al, 2015;Saikin et al, 2015] indicated that EMIC waves have a variety of wave normal angles.…”

Direct evidence for EMIC wave scattering of relativistic electrons in space

“…Below we discuss factors that may be responsible for such a discrepancy. (1) A parallel propagation assumption was used to evaluate the EMIC wave scattering rates, whereas the observed EMIC wave normal angle can go up to ~60° [e.g., Min et al ., ; Allen et al ., ], which affects both the scattering rates and the resonance conditions. However, a recent parametric study of EMIC wave scattering pattern by Ni et al .…”