Classification of hydromagnetic emissions based on frequency‐time spectra

Fukunishi, H.; Toya, Takeshi; Koike, Kazuhara; Kuwashima, Masayuki; Kawamura, Makoto

doi:10.1029/ja086ia11p09029

Cited by 82 publications

(52 citation statements)

References 23 publications

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“…Clear Pc1 emission is observed in the 0.4-0.8 Hz band at all three stations. The characteristics of these dynamic spectra are classified as the combination of diffuse and periodic emissions according to a definition by Fukunishi et al [1981]. For the frequency range of 0.5-0.6 Hz, the coherence and all the polarization parameters show similar tendencies at the three stations.…”

Section: Event Analysismentioning

confidence: 99%

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes

et al. 2011

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Section: Event Analysismentioning

confidence: 99%

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes

et al. 2011

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“…FRASER-SMITH, 1982;ARNOLDY et al, 1986ARNOLDY et al, ,1988OLSON, 1986;GLASSMEIER, 1989). These include short-lived burst-like emissions with varied dispersion characteristics (MATVEEVA et al, 1976(MATVEEVA et al, , 1978MORRIS et al, 1982) and long-lived unstructured noise-like emissions with frequencies in the range 0.1-0.4 Hz (HEACOCK, 1974;FUKUNISHI et al, 1981;SATO and SAEMUNDSSON, 1990). One issue of continuing interest has been the association of such features with the cusp and boundary layer regions (MENK et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Multistation Observations of Pc1-2 ULF Pulsations in the Vicinity of the Polar Cusp.

Menk¹,

Fraser²,

Hansen³

et al. 1993

J. geomagn. geoelec

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Geomagnetic pulsations with frequencies in the range 0.1-2.5 Hz have been recorded with a six station Antarctic magnetometer array ranging in latitude from -62.3 to -80.6° invariant. The observed spectral characteristics were compared with the cusp and boundary layer locations for selected days in November and December, 1986, and July, 1990, in order to determine wave source regions. Specific pulsation features have been identified with different magnetospheric regions. The cusp is characterised by intense unstructured 0.15-0.45 Hz noise which diminishes rapidly away from this region. These signals are likely to result from a mixture of ion-cyclotron, Kelvin-Helmholtz and drift-wave instabilities. Narrowband unstructured Pc2 emissions typically around 0.2 Hz and short discrete Pc 1 packets or bursts with frequencies below 0.4 Hz, occur in the local morning at boundary layer latitudes, accompanied by generally enhanced power levels between about 0.1 and 0.5 Hz. These emissions are probably due to ioncyclotron waves generated near or below the He' gyrofrequency on boundary layer field lines. Propagation of such signals into the polar cap via the ionospheric waveguide is uncommon, perhaps due to the existence of severe ionospheric irregularity features near the dayside auroral oval. Structured and quasistructured emissions such as hydromagnetic chorus are recorded at the foot of plasmatrough field lines and are consistent with ion-cyclotron wave generation and propagation on closed field lines in the outer magnetosphere.

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“…Magnetospheric electromagnetic ion cyclotron (EMIC) waves in a frequency range from 0.2 to 5 Hz have been widely observed on the ground as Pc1 waves [e.g., Harang, 1936;Sucksdorff , 1936;Fukunishi et al, 1981]. It is generally accepted that these waves are excited by an instability driven by the temperature anisotropy of protons with the energy of a few tens keV in the equatorial region [e.g., Young et al, 1981;Gomberoff and Neira, 1983;Gendrin et al, 1984].…”

Section: Introductionmentioning

confidence: 99%

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

Nakamura

Omura

Motomizu³

et al. 2015

JGR Space Physics

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We report subpacket structures found in electromagnetic ion cyclotron (EMIC) rising tone emissions observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes. We investigate three typical cases in detail. The first case shows a continuous single rising tone with four obvious subpackets, and the second case is characterized by a patchy emission with multiple subpackets triggered in a broadband frequency. The third case looks like a smooth rising tone without any obvious subpacket in the fast Fourier transform spectrum, while its amplitude contains small peaks with increasing frequencies. The degree of polarization of each subpacket is generally higher than 0.8 with a left-handed polarization, and the wave direction of the subpackets is typically field aligned. We show that the time evolution of the observed frequency and amplitude can be reproduced consistently by nonlinear growth theory. We also compare the observed time span of each subpacket structure with the theoretical trapping time for second-order cyclotron resonance. They are consistent, indicating that an individual subpacket is generated through a nonlinear wave growth process which excites an element in accordance with the theoretically predicted optimum amplitude.

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Classification of hydromagnetic emissions based on frequency‐time spectra

Cited by 82 publications

References 23 publications

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes

Multistation Observations of Pc1-2 ULF Pulsations in the Vicinity of the Polar Cusp.

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

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