Diffuse Auroral Electron Scattering by Electrostatic Electron Cyclotron Harmonic Waves in the Dayside Magnetosphere. Issue 5 (10th March 2021)

• Record Type: Journal Article
• Authors: Lou, Yuequn; Cao, Xing; Ni, Binbin; Tu, Weichao; Gu, Xudong; Fu, Song; Xiang, Zheng; Ma, Xin
• Is Part Of: Geophysical research letters. Volume 48:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-10
• Subjects: dayside diffuse aurora -- ECH waves -- wave‐particle interactions; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL092208
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Although electrostatic electron cyclotron harmonic (ECH) waves are frequently observed in the dayside magnetosphere, their effects on the formation of dayside diffuse aurora remain poorly understood. In this study, we quantitatively evaluate the efficiency of dayside ECH wave scattering in producing the electron diffuse aurora precipitation during a typical ECH wave event by calculating the quasi‐linear bounce‐averaged scattering rates. We find that dayside ECH waves can efficiently pitch angle scatter diffuse auroral electrons on timescales of a few hours to ∼1 day over a broad range of electron energy and equatorial pitch angle α eq, that is, from ∼300 eV to 10 keV with α eq from the loss cone to 45°. Especially for ∼300 eV–2 keV electrons, the scattering rates can even approach the strong diffusion limit, resulting in an almost fully filled loss cone. Our results confirm the significant role of ECH waves in driving the dayside diffuse aurora. Plain Language Summary: Electrostatic electron cyclotron harmonic (ECH) waves are electrostatic emissions observed between the harmonics of electron cyclotron frequency with wave normal near perpendicular to the ambient magnetic field. ECH waves are known to be excited by the loss cone instability of hot electron velocity distribution. In this study, we perform a detailed survey of a typical dayside ECH wave event observed by MMS1 spacecraft on 11 Dec 2015. Using a realistic magnetic field model and a latitudinal varying wave normal angle model based on well‐fitted electron velocity distribution, we calculate the quasi‐linear bounce‐averaged scattering rates of electrons. Our results demonstrate that ECH waves can efficiently pitch angle scatter hundreds of eV to tens of keV electrons, which are the source of diffuse aurora. ECH wave induced scattering of ~300 eV to 2 keV electrons at low pitch angles can even approach the strong diffusion limit, resulting in an almost fully filled loss cone. These electrons can be subsequently precipitated into the atmosphere and collide with neutral molecule, forming the dayside diffuse aurora. Our results demonstrate that ECH waves play an important role in the dayside diffuse auroral precipitation. Key Points: We quantitatively evaluate the scattering effect of dayside electron cyclotron harmonic (ECH) waves on diffuse auroral electrons ECH waves can efficiently pitch angle scatter electrons at energies from 300 eV to 10 keV on timescales from a few hours to ∼1 day Scattering of ∼300 eV–2 keV electrons can even approach the strong diffusion limit, resulting in an almost fully filled loss cone