Akebono observations of EMIC waves in the slot region of the radiation belts

Sakaguchi, Kaori; Kasahara, Yoshiya; Motomizu, Shoji; Omura, Yoshiharu; Miyoshi, Yoshizumi; Nagatsuma, Tsutomu; Kumamoto, A.; Matsuoka, A.

doi:10.1002/2013gl058258

Cited by 42 publications

(51 citation statements)

References 24 publications

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“…The Pc1 rising tones appeared successively during the event with repetition periods of several tens of seconds. These rising tones are similar to EMIC‐triggered emissions found in situ [ Pickett et al , ; Grison et al , ; Sakaguchi et al , ; Nakamura et al , ] and in theoretical work [ Omura et al , ]. We also found that the simultaneously observed isolated proton aurora pulsates with periods of several tens of seconds, ∼10% variations in the intensity, and fine structures of 3° in MLON.…”

Section: Resultssupporting

confidence: 88%

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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Section: Resultssupporting

confidence: 88%

Pulsating proton aurora caused by rising tone Pc1 waves

Nomura

Shiokawa

Omura³

et al. 2016

JGR Space Physics

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“…When the wave frequencies reach f = 2.7 Hz (Case 1), 2.3 Hz (Case 2), 0.76 Hz (Case 3), and 0.6 Hz (Case 4), each pair of wave packets is terminated at the equator, respectively. The EMIC wave durations vary in a time scale of several tens of seconds to a few minutes, which agrees with observational results [e.g., Sakaguchi et al , ; Nakamura et al , ].…”

Section: Simulation Modelsupporting

confidence: 89%

“…Omura et al [] explained the growing amplitude and rising tone frequency mechanism of EMIC waves, proposing a nonlinear wave growth theory. EMIC rising tone emissions have been observed by Cluster satellites [ Pickett et al , ; Grison et al , ], Time History of Events and Macroscale Interactions during Substorms [ Nakamura et al , ], and Akebono satellites [ Sakaguchi et al , ]. Shoji and Omura [] have reproduced EMIC rising tone emissions by a hybrid code simulation, and these waves are consistent with the nonlinear wave growth theory.…”

Section: Introductionmentioning

confidence: 75%

Rapid precipitation of radiation belt electrons induced by EMIC rising tone emissions localized in longitude inside and outside the plasmapause

2017

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By performing test particle simulations of relativistic electrons scattered by electromagnetic ion cyclotron (EMIC) rising tone emissions, we find a nonlinear scattering process named SLPA (Scattering at Low Pitch Angle) totally different from the nonlinear wave trapping. The nonlinear wave trapping, occurring for high pitch angles away from the loss cone, scatters some of resonant electrons to lower pitch angles, and a fraction of the electrons is further transported into the loss cone by SLPA after being released from the wave trapping. SLPA as well as the nonlinear wave trapping can work in any cases with proton band or helium band and inside or outside the plasmapause. We clarify that the combined scattering process causes significant depletion of the outer radiation belt. In the time evolution of an electron distribution observed locally in longitude, we find echoes of the electron depletion by the localized EMIC emissions. Monitoring fluxes of electrons being lost into the atmosphere in the wave generation region, we also find that efficient relativistic electron precipitation in several seconds. The characteristics of the precipitating electron flux as a function of kinetic energy vary significantly depending on the wave frequency range and the plasma density.

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“…The wave intensity was about 10 −3 mV 2 /m 2 /Hz, which is relatively small compared to typical EMIC waves observed in the inner magnetosphere. The structure of the observed EMIC wave is similar to the EMIC‐triggered emissions observed in the inner magnetosphere that were reported by Pickett et al (), Grison et al (), and Sakaguchi et al (). However, the typical wave intensity they observed is different from the observed intensity of this EMIC wave.…”

Section: Observationssupporting

confidence: 86%

Spatial Distribution of Fine‐Structured and Unstructured EMIC Waves Observed by the Arase Satellite

Matsuda

Kasahara

Miyoshi

et al. 2018

Geophysical Research Letters

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We surveyed 378 electromagnetic ion cyclotron (EMIC) wave events using Arase during the first 12 months. We discriminated the observed EMIC waves into two types (fine‐structured EMIC waves and unstructured EMIC waves), according to whether or not they exhibited clear periodic amplitude modulations. We found a clear afternoon peak in the occurrence probability of unstructured EMIC waves in the region of L = 5–9. Fine‐structured EMIC waves were mainly distributed in the off‐equatorial region, and their occurrence probability was clearly high around the noon sector. Such noon sector EMIC wave peaks had not been found in the THEMIS, AMPTE, or Cluster measurements, due to their limited L shell coverages. The Van Allen probes, too, were not able to measure the major region of fine‐structured EMIC waves because of their limited latitudinal coverage. Our unique statistical results demonstrate the importance of discriminating the wave structures as well as of performing observations over a wide range of latitudes.

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Akebono observations of EMIC waves in the slot region of the radiation belts

Cited by 42 publications

References 24 publications

Pulsating proton aurora caused by rising tone Pc1 waves

Pulsating proton aurora caused by rising tone Pc1 waves

Rapid precipitation of radiation belt electrons induced by EMIC rising tone emissions localized in longitude inside and outside the plasmapause

Spatial Distribution of Fine‐Structured and Unstructured EMIC Waves Observed by the Arase Satellite

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