Origins of the Earth’s Diffuse Auroral Precipitation

Ni, Binbin; Thorne, R. M.; Zhang, Xiaojia; Bortnik, J.; Pu, Z. Y.; Xie, Luhua; Hu, Zejun; Han, Desheng; Shi, Run; Zhou, Chen; Gu, Xudong

doi:10.1007/s11214-016-0234-7

Cited by 150 publications

(216 citation statements)

References 154 publications

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“…Davidson (1990) discussed the precipitating electrons as consisting of two different components: a steady diffuse component with an energy spectrum extending towards lower energies and a pulsating component caused by higher-energy flux electrons. The dominant source of electron precipitation causing diffuse aurora has been shown to be chorus waves Ni et al, 2016). Miyoshi et al (2015) showed with observations of energy spectra and simulations that while lower band chorus waves can lie behind the main modulation of the electron precipitation, causing pulsating aurora, upper band chorus waves can produce a simultaneous, constant precipitation at about 1 keV.…”

Section: Discussionmentioning

confidence: 94%

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

et al. 2017

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Abstract. High-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall.

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Section: Discussionmentioning

confidence: 94%

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

et al. 2017

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“…30, 31 andMourenas et al 2012a, Artemyev et al 2012a). In this sense, such very oblique whistler-mode lower-band chorus waves may partially take away the job from electron cyclotron harmonic (ECH) waves, which are often considered as the main wave mode responsible for keV electron scattering in the loss-cone and the subsequent formation of diffuse aurora (Horne and Thorne 2000;Horne et al 2003b;Ni et al 2011cNi et al , 2012Zhang et al 2015;Ni et al 2016), at least in the absence of significant upper-band chorus (i.e. whistler-mode waves with ω/Ω ce0 > 0.5) which may also be a good contender for electron scattering (Ni et al 2011d) and acceleration (Mozer et al 2014).…”

Section: Discussionmentioning

confidence: 99%

Oblique Whistler-Mode Waves in the Earth’s Inner Magnetosphere: Energy Distribution, Origins, and Role in Radiation Belt Dynamics

et al. 2016

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International audienceIn this paper we review recent spacecraft observations of oblique whistler-mode waves in the Earth’s inner magnetosphere as well as the various consequences of the presence of such waves for electron scattering and acceleration. In particular, we survey the statistics of occurrences and intensity of oblique chorus waves in the region of the outer radiation belt, comprised between the plasmapause and geostationary orbit, and discuss how their actual distribution may be explained by a combination of linear and non-linear generation, propagation, and damping processes. We further examine how such oblique wave populations can be included into both quasi-linear diffusion models and fully nonlinear models of wave-particle interaction. On this basis, we demonstrate that varying amounts of oblique waves can significantly change the rates of particle scattering, acceleration, and precipitation into the atmosphere during quiet times as well as in the course of a storm. Finally, we discuss possible generation mechanisms for such oblique waves in the radiation belts. We demonstrate that oblique whistler-mode chorus waves can be considered as an important ingredient of the radiation belt system and can play a key role in many aspects of wave-particle resonant interactions

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“…However, the conventional explanation of the diffuse precipitation attributes it to the pitch angle scattering of plasma sheet electrons into the loss cones (e.g., Ni et al, 2016), for which we usually do not expect any interhemispheric asymmetry. However, the conventional explanation of the diffuse precipitation attributes it to the pitch angle scattering of plasma sheet electrons into the loss cones (e.g., Ni et al, 2016), for which we usually do not expect any interhemispheric asymmetry.…”

Section: 1029/2019ja026707mentioning

confidence: 99%

Solar Illumination Dependence of the Auroral Electrojet Intensity: Interplay Between the Solar Zenith Angle and Dipole Tilt

Ohtani

Gjerloev

Johnsen³

et al. 2019

JGR Space Physics

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The present study investigates the dependence of the local auroral electrojet (AEJ) intensity on solar illumination by statistically examining northward geomagnetic disturbances in the auroral zone in terms of the solar zenith angle χ. It is found that on the dayside, both westward and eastward electrojets (WEJ and EEJ) are more intense for smaller χ, suggesting that the solar extreme ultraviolet‐induced conductance is the dominant factor for the AEJ intensity. On the nightside, in contrast, the χ dependence of the AEJ intensity, if sorted solely by the magnetic local time, apparently depends on the station longitude and hemisphere. However, if additionally sorted by the dipole tilt angle ψ, a consistent pattern emerges. That is, although χ and ψ are correlated, the solar zenith angle and dipole tilt angle have physically different effects on the AEJ intensity. The nightside AEJ, especially the WEJ, tends to be more intense for smaller |ψ|. Moreover, whereas the WEJ is statistically more intense when the ionosphere is dark, the EEJ is more intense when it is sunlit. The preference of the WEJ for the dark ionosphere prevails widely in magnetic local time from premidnight to dawn, and therefore, it cannot be attributed to the previously proposed processes of the preferred monoenergetic or broadband auroral precipitation in the dark ionosphere. Instead, it may be explained, at least morphologically, in terms of the conductance enhancement due to the diffuse auroral precipitation, which is also prevalent from premidnight to dawn and is more intense in the dark hemisphere.

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Origins of the Earth’s Diffuse Auroral Precipitation

Cited by 150 publications

References 154 publications

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

Oblique Whistler-Mode Waves in the Earth’s Inner Magnetosphere: Energy Distribution, Origins, and Role in Radiation Belt Dynamics

Solar Illumination Dependence of the Auroral Electrojet Intensity: Interplay Between the Solar Zenith Angle and Dipole Tilt

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