Fast earthward flows, electron cyclotron harmonic waves, and diffuse auroras: Conjunctive observations and a synthesized scenario

Liang, J.; Ni, Binbin; Spanswick, E.; Kubyshkina, M. V.; Donovan, E.; Uritsky, V. M.; Thorne, R. M.; Angelopoulos, V.

doi:10.1029/2011ja017094

Cited by 42 publications

(61 citation statements)

References 68 publications

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“…ECH waves, which do not play a significant role in the formation of the diffuse aurora at low L * [ Thorne et al , 2010], may thus ultimately play an important role at higher values of L *. Indeed, a recent case study involving conjugate ground and space measurements suggests that ECH waves can be the dominant driver of the diffuse aurora in the outer magnetosphere [ Liang et al , 2011; Ni et al , 2012].…”

Section: Discussionmentioning

confidence: 99%

Global model of lower band and upper band chorus from multiple satellite observations

Meredith¹,

Horne²,

Sicard³

et al. 2012

J. Geophys. Res.

260

407

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Gyroresonant wave particle interactions with whistler mode chorus play a fundamental role in the dynamics of the Earth's radiation belts and inner magnetosphere, affecting both the acceleration and loss of radiation belt electrons. Knowledge of the variability of chorus wave power as a function of both spatial location and geomagnetic activity, required for the computation of pitch angle and energy diffusion rates, is thus a critical input for global radiation belt models. Here we present a global model of lower band (0.1fce < f < 0.5fce) and upper band (0.5fce < f < fce) chorus, where fce is the local electron gyrofrequency, using data from five satellites, extending the coverage and improving the statistics of existing models. From the plasmapause out to L* = 10 the chorus emissions are found to be largely substorm dependent with the largest intensities being seen during active conditions. Equatorial lower band chorus is strongest during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 between 2300 and 1200 MLT. Equatorial upper band chorus is both weaker and less extensive with peak intensities of the order a few hundred pT2 during active conditions between 2300 and 1100 MLT from L* = 3 to L* = 7. Moving away from the equator midlatitude chorus is strongest in the lower band during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 but is restricted to the dayside between 0700 and 1400 MLT.

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Section: Discussionmentioning

confidence: 99%

Global model of lower band and upper band chorus from multiple satellite observations

Meredith¹,

Horne²,

Sicard³

et al. 2012

J. Geophys. Res.

260

407

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“…It is clear that use of T01s for chorusinduced electron scattering produces the largest precipitation electron flux, then use of T96 and T04s, and use of T01 gives the weakest precipitation flux due to the smallest degree of loss cone filling. Following the approach by Steele and McEwen (1990) and Liang et al (2011), we have further performed a Maxwellian-type fitting to the precipitation electron differential number flux to roughly estimate the total energy flux and characteristic energy of precipitating electrons. We have obtained a total precipitation electron energy flux of ∼0.08 erg cm −2 s −1 with a characteristic energy of ∼1.9 keV for use of T01, a total precipitation electron energy flux of ∼0.15 erg cm −2 s −1 with a characteristic energy of ∼1 keV for use of T96 and T04s, and a total precipitation electron energy flux of ∼0.6 erg cm −2 s −1 with a characteristic energy of ∼800 eV for use of T01s.…”

Section: Resonant Scattering By Dayside Chorus and Resultant Loss Conmentioning

confidence: 99%

Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields

Shi

Han

et al. 2012

Ann. Geophys.

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Abstract. Compared to the recently improved understanding of nightside diffuse aurora, the mechanism(s) responsible for dayside diffuse aurora remains poorly understood. While dayside chorus has been thought as a potential major contributor to dayside diffuse auroral precipitation, quantitative analyses of the role of chorus wave scattering have not been carefully performed. In this study we investigate a dayside diffuse auroral intensification event observed by the Chinese Arctic Yellow River Station (YRS) all-sky imagers (ASI) on 7 January 2005 and capture a substantial increase in diffuse auroral intensity at the 557.7 nm wavelength that occurred over almost the entire ASI field-of-view near 09:24 UT, i.e., ∼12:24 MLT. Computation of bounceaveraged resonant scattering rates by dayside chorus emissions using realistic magnetic field models demonstrates that dayside chorus scattering can produce intense precipitation losses of plasma sheet electrons on timescales of hours (even approaching the strong diffusion limit) over a broad range of both energy and pitch angle, specifically, from ∼1 keV to 50 keV with equatorial pitch angles from the loss cone to up to ∼85 • depending on electron energy. Subsequent estimate of loss cone filling index indicates that the loss cone can be substantially filled, due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8 for electrons from ∼500 eV to 50 keV that exactly covers the precipitating electrons for the excitation of green-line diffuse aurora. Estimate of electron precipitation flux at different energy levels, based on loss cone filling index profile and typical dayside electron distribution observed by THEMIS spacecraft under similar conditions, gives a total precipitation electron energy flux of the order of 0.1 erg cm −2 s −1 with ∼1 keV characteristic energy (especially when using T01s), which can be very likely to cause intense green-line diffuse aurora activity on the dayside. Therefore, dayside chorus scattering in the realistic magnetic field can greatly contribute to the YRS ASI observed intensification of dayside green-line aurora. Besides wave induced scattering and changes in the ambient magnetic field, variations in associated electron flux can also contribute to enhanced diffuse aurora emissions, the possibility of which we cannot exactly rule out due to lack of simultaneous observations of magnetospheric particles. Since the geomagnetic activity level was rather low during the period of interest, it is reasonable to infer that changes in the associated electron flux in the magnetosphere should be small, and consequently its contribution to the observed enhanced diffuse auroral activity should be small as well. Our results support the scenario that dayside chorus could play a major role in the production of dayside diffuse aurora, and also demonstrate that changes in magnetospheric magnetic field should be considered to reasonably interpret observations of dayside diffuse aurora.

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“…Recent studies suggest that diffuse auroras observed on the nightside are predominantly produced by the chorus waves in the inner (L < 8) magnetosphere and by the ECH waves in the outer (L > 8) magnetosphere [Liang et al, 2010[Liang et al, , 2011Ni et al, 2011cNi et al, , 2014Zhang et al, 2014]. Recent studies suggest that diffuse auroras observed on the nightside are predominantly produced by the chorus waves in the inner (L < 8) magnetosphere and by the ECH waves in the outer (L > 8) magnetosphere [Liang et al, 2010[Liang et al, , 2011Ni et al, 2011cNi et al, , 2014Zhang et al, 2014].…”

Section: Dayside Diffuse Aurora and Ech Wavesmentioning

confidence: 99%

“…Discrete auroras are characterized by intense luminosity in various auroral forms, such as arcs, bands, curls, and rays, and those observed near magnetic local noon (MLN) are caused by particles from the magnetosheath and are on the open field lines [Lockwood, 1997;Mende et al, 2016]. Diffuse auroras, appearing as relatively homogenous and weak emissions in green line (wavelength of 557.7 nm) auroral observations, are found on the equatorward edge of the auroral oval [Lui et al, 1973] and are caused by scattering the electrons from the central plasma sheet (CPS) [Meng et al, 1979] by whistler mode chorus [Ni et al, 2011a;Nishimura et al, 2010;Thorne et al, 2010] or electron cyclotron harmonic (ECH) [Horne and Thorne, 2000;Liang et al, 2011;Ni et al, 2011b;Zhang et al, 2014] waves. The diffuse auroras are strongest on the postmidnight sector [Newell et al, 2009] and also can be observed on the dayside [Newell and Meng, 1992;Sandholt et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Coordinated observations of two types of diffuse auroras near magnetic local noon by Magnetospheric Multiscale mission and ground all‐sky camera

Han

Nishimura

et al. 2017

Geophysical Research Letters

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Structured diffuse auroras are often observed near magnetic local noon (MLN), but their generation mechanisms are poorly understood. We have found that two types of structured diffuse auroras with obviously different dynamical properties often coexist near MLN. One type usually drifts from low to high latitude with higher speed and shows pulsation. The other type is always adjacent to the discrete aurora oval and drifts together with nearby discrete aurora with much lower speed. Using coordinated observations from MMS and ground all‐sky imagers, we found that the two types of diffuse auroras are well correlated with number density increase of O+ (from the ionosphere) and of He2+ (from magnetosheath) ions, respectively. These observations indicate that mangetosheath particles penetrated into the magnetosphere also can play an important role for producing the dayside diffuse aurora. In addition, for the first time, electron cyclotron harmonic waves are observed associated with dayside diffuse aurora.

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Fast earthward flows, electron cyclotron harmonic waves, and diffuse auroras: Conjunctive observations and a synthesized scenario

Cited by 42 publications

References 68 publications

Global model of lower band and upper band chorus from multiple satellite observations

Global model of lower band and upper band chorus from multiple satellite observations

Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields

Coordinated observations of two types of diffuse auroras near magnetic local noon by Magnetospheric Multiscale mission and ground all‐sky camera

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