Subpacket structures in EMIC rising tone emissions observed by the THEMIS probes

Nakamura, Satoko; Omura, Yoshiharu; Motomizu, Shoji; Nosé, M.; Summers, Danny; Angelopoulos, V.

doi:10.1002/2014ja020764

Cited by 41 publications

(55 citation statements)

References 33 publications

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“…Nakamura et al [2015] showed using Time History of Events and Macroscale Interactions during Substorms (fleet of five satellites) satellite observations that the subpacket structures of EMIC-triggered emissions are in good agreement with the nonlinear transition time, supporting the model of Shoji and Omura [2013]. Thus, the time span of each subpacket structure of the EMIC-triggered emissions is also characterized by a nonlinear transition time, which is inversely proportional to the square root of the wave amplitude.…”

Section: Discussionmentioning

confidence: 56%

“…A portion of the scattered energetic ions falls into the upper atmospheric loss cone, and the ion precipitation can then be observed as a proton aurora [Frey et al, 2004;Yahnin et al, 2007]. They did not report many faster luminosity modulations of PPA that may be related to the subpacket structures of Pc1/EMIC waves observed with amplitude modulations [Usanova et al, 2010;Nakamura et al, 2015]. Isolated proton aurora can be displayed as an ionospheric projection of the location, duration, and evolution of the wave-particle interaction region in the magnetosphere .…”

Section: Introductionmentioning

confidence: 99%

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Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

Ozaki

Shiokawa

Kataoka

et al. 2016

Geophysical Research Letters

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To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave‐particle interactions at subauroral latitudes, high‐time‐resolution (1/8 s) images of proton‐induced N2+ emissions were recorded using a new electron multiplying charge‐coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising‐tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

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Section: Discussionmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

Ozaki

Shiokawa

Kataoka

et al. 2016

Geophysical Research Letters

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“…It should be noted that the change of instantaneous frequencies may include pseudo rising-or falling-tones due to frequency jumps from emission to another emission. of EMIC rising tones (and whistler-mode chorus as well), which are called "subpacket structure" (Nakamura et al, 2015;Shoji & Omura, 2013). We can read that several short rising tones around 07:06 UT have an order of~0.1 Hz/s of frequency sweep rate.…”

Section: Intense Emic Emissions During Magnetospheric Compressionmentioning

confidence: 99%

Rapid Precipitation of Relativistic Electron by EMIC Rising‐Tone Emissions Observed by the Van Allen Probes

et al. 2019

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On 23 February 2014, Van Allen Probes sensors observed quite strong electromagnetic ion cyclotron (EMIC) waves in the outer dayside magnetosphere. The maximum amplitude was more than 14 nT, comparable to 7% of the magnitude of the ambient magnetic field. The EMIC waves consisted of a series of coherent rising tone emissions. Rising tones are excited sporadically by energetic protons. At the same time, the probes detected drastic fluctuations in fluxes of MeV electrons. It was found that the electron fluxes decreased by more than 30% during the 1 min following the observation of each EMIC rising tone emissions. Furthermore, it is concluded that the flux reduction is a nonadiabatic (irreversible) process since holes in the particle flux levels appear as drift echoes with energy dispersion. We examine the process of electron pitch angle scattering by nonlinear wave trapping due to anomalous cyclotron resonance with EMIC rising tone emissions. The energy range of precipitated electrons agrees with the presumed energy for the threshold amplitude for nonlinear wave trapping. This is the first report of rapid precipitation (<1 min) of relativistic electrons by EMIC rising tone emissions and their drift echoes in time observed by spacecraft.

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“…Pickett et al [], Grison et al [], and Nakamura et al [, ] found rising tone emissions which have left‐handed circular polarization and frequency‐time dispersion of ∼30 s/Hz, using Cluster and Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations. Some of these rising tone emissions were in the helium band which is between the local oxygen and helium cyclotron frequencies and are in the Pc1 wave range of 0.2–5.0 Hz [ Jacobs et al , ].…”

Section: Introductionmentioning

confidence: 99%

Pulsating proton aurora caused by rising tone Pc1 waves

Nomura

Shiokawa

Omura³

et al. 2016

JGR Space Physics

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We found rising tone emissions with a dispersion of ∼1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over ∼30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude 61.7°N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all‐sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, ∼10% variations in intensity, and fine structures of 3° in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one‐to‐one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of ∼1 Hz in Pc1 rising tones. We suggest that EMIC‐triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.

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Subpacket structures in EMIC rising tone emissions observed by the THEMIS probes

Cited by 41 publications

References 33 publications

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

Rapid Precipitation of Relativistic Electron by EMIC Rising‐Tone Emissions Observed by the Van Allen Probes

Pulsating proton aurora caused by rising tone Pc1 waves

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