THEMIS observations of electron cyclotron harmonic emissions, ULF waves, and pulsating auroras

Liang, J.; Uritsky, V. M.; Donovan, E.; Ni, Binbin; Spanswick, E.; Trondsen, T.; Bonnell, J. W.; Roux, A.; Auster, U.; Larson, D. E.

doi:10.1029/2009ja015148

Cited by 49 publications

(66 citation statements)

References 64 publications

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“…As more and more high-quality ground-based and in situ observations became available, particularly the multi-probe missions Cluster (Escoubet et al 1997), THEMIS (Angelopoulos 2008) and ground-based high-temporal resolution auroral stations (Mende et al 2007) in the past two decades, it is now widely accepted that bursty bulk flows (BBFs) play an important role in triggering substorm expansions and developing substorm current systems (Angelopoulos et al 1999Birn and Hesse 2014;Yao et al 2012). On the other side, near-earth instabilities have been confirmed to be a common feature at the beginning of substorm expansion phase (Kalmoni et al 2015;Liang et al 2010;Lui et al 2008a;Nishimura et al 2016;Rae et al 2009). It is thus very likely that both the reconnection outflows and near-earth instabilities are essential in triggering substorms.…”

Section: Introductionmentioning

confidence: 94%

Auroral streamer and its role in driving wave-like pre-onset aurora

Yao

Rae³

et al. 2017

Geosci. Lett.

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The time scales of reconnection outflow, substorm expansion, and development of instabilities in the terrestrial magnetosphere are comparable, i.e., from several to tens of minutes, and their existence is related. In this paper, we investigate the physical relations among those phenomena with measurements during a substorm event on January 29, 2008. We present conjugate measurements from ground-based high-temporal resolution all-sky imagers and in situ THEMIS measurements. An auroral streamer (north-south aligned thin auroral layer) was formed and propagated equatorward, which usually implies an earthward propagating plasma flow in the magnetotail. At the most equatorward part of the auroral streamer, a wave-like auroral band was formed aligning in the east-west direction. The wave-like auroral structure is usually explained as a consequence of instability development. Using AM03 model, we trace the auroral structure to magnetotail and estimate a wavelength of ~0.5 R E . The scale is comparable to the drift mode wavelength determined by the in situ measurements from THEMIS-A, whose footpoint is on the wave-like auroral arc. We also present similar wave-like aurora observations from Cassini ultraviolet imaging spectrograph at Saturn and from Hubble space telescope at Jupiter, suggesting that the wave-like aurora structure is likely a result of fundamental plasma dynamics in the solar system planetary magnetospheres.

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Section: Introductionmentioning

confidence: 94%

Auroral streamer and its role in driving wave-like pre-onset aurora

Yao

Rae³

et al. 2017

Geosci. Lett.

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“…In particular, lower‐band chorus waves, which frequently show intensity modulation on a timescale comparable with that of PA and can resonate with tens of keV electrons in the near‐Earth plasma sheet, have been suggested to be specifically responsible for pitch angle scattering [ Gough et al , 1981; Ward et al , 1982; Johnstone , 1983]. In addition to this process, resonance with electron cyclotron harmonic (ECH) waves [ Liang et al , 2010], acceleration by a field‐aligned potential drop [ Sato et al , 2004], and an active ionospheric role (formation of a polarization electric field and finite relaxation time) [ Stenbaek ‐ Nielsen , 1980; Hosokawa et al , 2010] have also been proposed. Despite many years of observation, the driver of PA has not been uniquely determined because of the low probability of conjugate measurements between space and ground instruments, as well as the appreciable uncertainty inherent in field‐line mapping used to connect a region in space to a unique point in the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

et al. 2011

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[1] A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of ∼5000 km diameter for corresponding azimuthally elongated patches with ∼100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.Citation: Nishimura, Y., et al. (2011), Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions,

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“…Such mapping is particularly difficult because adjacent auroral patches typically pulsate independently of each other (16). Additionally, the simultaneous existence of multiple magnetospheric plasma waves (13,17) makes it difficult to identify the specific wave mode responsible for electron scattering leading to PA.…”

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confidence: 99%

Identifying the Driver of Pulsating Aurora

Nishimura

Bortnik

et al. 2010

Science

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Pulsating aurora, a spectacular emission that appears as blinking of the upper atmosphere in the polar regions, is known to be excited by modulated, downward-streaming electrons. Despite its distinctive feature, identifying the driver of the electron precipitation has been a long-standing problem. Using coordinated satellite and ground-based all-sky imager observations from the THEMIS mission, we provide direct evidence that a naturally occurring electromagnetic wave, lower-band chorus, can drive pulsating aurora. Because the waves at a given equatorial location in space correlate with a single pulsating auroral patch in the upper atmosphere, our findings can also be used to constrain magnetic field models with much higher accuracy than has previously been possible.

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THEMIS observations of electron cyclotron harmonic emissions, ULF waves, and pulsating auroras

Cited by 49 publications

References 64 publications

Auroral streamer and its role in driving wave-like pre-onset aurora

Auroral streamer and its role in driving wave-like pre-onset aurora

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

Identifying the Driver of Pulsating Aurora

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