Statistical Distributions of Dayside ECH Waves Observed by MMS

Abstract

Strong electrostatic electron cyclotron harmonic (ECH) waves on the dayside magnetosphere have been reported based on observations of the Magnetospheric Multiscale (MMS) spacecraft. In this study, we analyze high‐quality wave data from the four MMS satellites between 1 September 2015 and 30 August 2018 to investigate the statistical properties of dayside ECH emissions. The results show that dayside ECH waves are preferentially observed on the prenoon side in the outer magnetosphere (L = 8–12), with average wave amplitude Ew > 0.1 mV/m. In addition, besides the typical near‐equatorial (|MLAT| ≤ 15°) region, dayside ECH waves exhibit moderate occurrence rate and wave amplitude in higher latitudinal regions (i.e., 15 < |MLAT| ≤ 40°), possibly due to the off‐equatorial geomagnetic field minimum. Our reported double peaks of dayside ECH wave occurrence zone and considerable occurrence rates of prenoonside ECH waves suggest that dayside ECH waves can be a potentially important contributor to the formation of dayside diffuse aurora.

Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves in Saturn's Magnetosphere: A Survey of Over‐13‐Year Cassini RPWS Observations

“…To determine terrestrial dayside ECH waves in the fundamental band, Lou et al. (2018) implemented that the ratio between the maximum intensity in the frequency range of f ce − 2 f ce and the intensity at f ce should be over 5. To determine Saturnian ECH waves in this study, the ratio between the maximum and minimum wave intensity in the frequency range of n f ce − ( n + 1) f ce is set above 1.25 in order that Saturnian ECH waves can be identified reliably…”

“…To minimize the impacts of Saturn's E rings and of the background noise, the data with r < 4.4 R s are excluded. Since the spectral densities of |MLAT| > 40° are disturbed by Z-mode waves and Saturn kilometer radio (SKR), and ECH waves are hardly observed in the region of |MLAT| > 40°, only the observation data with the radial distance to the Saturn's center 4.4 R s < r < 10 R s and |MLAT| ≤ 40° are selected for analyses (2) To determine terrestrial dayside ECH waves in the fundamental band, Lou et al (2018) implemented that the ratio between the maximum intensity in the frequency range of f ce − 2 f ce and the intensity at f ce should be over 5. To determine Saturnian ECH waves in this study, the ratio between the maximum and minimum wave intensity in the frequency range of n f ce − (n + 1) f ce is set above 1.25 in order that Saturnian ECH waves can be identified reliably Over-13-year Cassini RPWS observations (Gurnett et al, 2004) provide an unprecedented opportunity to investigate in detail ECH wave events and their distribution features in Saturn's magnetosphere.…”

“…Terrestrial ECH waves were first reported by the OGO‐5 measurements (Kennel et al., 1970), with enhanced wave amplitudes (>1 mV/m) during geomagnetically disturbed periods and spatial confinement near the geomagnetic equator (e.g., Ni et al., 2011). Via cyclotron resonant interactions, terrestrial ECH emissions can pitch angle scatter plasma sheet electrons into the loss cone (e.g., Ni et al., 2016, 2008; Thorne et al., 2010), resulting in the formation of the diffuse aurora at Earth (e.g., Horne et al., 2003; Lou et al., 2018, 2021; Thorne et al., 2010; X. Zhang & Angelopoulos, 2014; X. Zhang et al., 2014; X.‐J. Zhang et al., 2015).…”

Global Simulation of Electron Cyclotron Harmonic Wave Instability in a Storm‐Time Magnetosphere

“…The dayside ECH waves are preferentially observed at the prenoon side in the equatorial region of the outer magnetosphere ( ) with electric field amplitude 0.1 mV/m. In addition, due to the off‐equatorial magnetic field minimum, dayside ECH waves can be also found at higher magnetic latitudes ( ) with a moderate occurrence rate of 30% and wave amplitude of 0.1 mV/m (Lou et al, ).…”

Global Occurrences of Electrostatic Electron Cyclotron Harmonic Waves Associated With Radiation Belt Electron Distributions

“…The statistical analysis of ECH waves using Time History of Events and Macroscale Interactions during Substorms data by Ni et al () shows that ECH waves occur throughout the outer magnetosphere ( L > 5), and expand to higher L ‐shells with enhanced occurrences when geomagnetic activity intensifies. Using the data from the Magnetospheric Multiscale spacecraft, Lou et al () have found double peaks of ECH wave occurrence zone on the dayside and high occurrence rates of prenoon ECH waves. They further propose that dayside ECH waves can potentially contribute to the formation of dayside diffuse aurora.…”