CNA pulsations associated with quasi‐periodic VLF emissions

Sato, Natsuo; Shibuya, Senkichi; Maezawa, K.; Higuchi, Yoshinori; Tonegawa, Yutaka

doi:10.1029/ja090ia11p10968

Cited by 8 publications

(3 citation statements)

References 14 publications

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“…The absence of a peak in the afternoon implies that the generation mechanism of these pulsations favors the morning sector. Similar results (albeit at a different magnetic latitude) were found for pulsations at Syowa Station [Sato et al, 1985].…”

Section: Time Dependencessupporting

confidence: 82%

Source regions of long‐period pulsation events in electron precipitation and magnetic fields at South Pole Station

Paquette¹,

Matthews²,

Rosenberg³

et al. 1994

J. Geophys. Res.

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Pulsation events with long (100‐1000 s) periods with a consistent frequency in both particle precipitation and surface geomagnetic field variations have been reported in the past from measurements made at various geomagnetic latitudes. An examination of broad beam riometer and magnetometer data from South Pole Station for the interval from 1982 to 1989 revealed nearly 200 such events. The onset times of these events were determined, and the results compared with predictions based on the work of Coroniti and Kennel (1970). This mechanism ascribes the occurrence of correlated magnetic and precipitation pulsations to ULF modulation of equatorial VLF wave‐particle interactions. For this reason, VLF data from South Pole Station were also examined. Taking into consideration the ULF wave and particle transit times from an interaction region near the magnetic equator to the ground leads to an expectation that the onset of pulsations in the magnetometer data will lag the onset of pulsations in the riometer data by several minutes. This disparity in onset times, together with modulation of VLF emissions in the 0.5‐1 kHz band, serves as an important indicator of whether or not an event can be explained by the above‐cited theory. While about a third of the events fit the prediction of Coroniti and Kennel, another third do not. In these events, the onset of magnetic and precipitation pulsations is nearly simultaneous, and possible alternative generation mechanisms are explored. In the remaining third of the events, magnetic pulsations begin substantially earlier than precipitation pulsations. Events of this type appear at first to be inexplicable in terms of any transit time argument. However, data from the imaging riometer at South Pole Station indicate that this third class of events is probably not physically distinct from the first two but is the result of the differing areas to which the riometer and magnetometer are sensitive and can be accounted for by considering the effects of transverse motion of a persistent precipitation region.

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Section: Time Dependencessupporting

confidence: 82%

Source regions of long‐period pulsation events in electron precipitation and magnetic fields at South Pole Station

Paquette¹,

Matthews²,

Rosenberg³

et al. 1994

J. Geophys. Res.

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“…These pulsating absorption events typically occur in the early morning sector and are accompanied by background absorption, indicating possible pitch angle diffusion due to ELF/VLF waves. Sato et al [ 1985] reported concurrent measurements of modulated ELF/VLF, riometer pulsations, and geomagnetic pulsations at Syowa Station and concluded that the pulsations in the precipitating electrons were caused by the modulation of ELFFV'LF by a compressional MHD wave in the equatorial plane. This modulation of ELFFV'LF by compressional MHD waves has also been seen in satellite data [Tixier and Cornilleau-Wehrlin, 1986].…”

Section: Paper Number 91ja00796mentioning

confidence: 99%

Observations of a detached, discrete arc in association with field line resonances

Samson¹,

Hughes²,

Creutzberg³

et al. 1991

J. Geophys. Res.

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Data from the Canadian Auroral Network for the OPEN Unified Study (CANOPUS) array in Canada are used to analyze the magnetic fields and auroral structures which were associated with a field line resonance which occurred near local midnight and in the early morning sector. The electric fields of this resonance, which have a frequency of about 1.95 mHz, were observed by the Johns Hopkins University, Applied Physics Laboratory HF radar at Goose Bay and had a maximum at about 70.7° invariant latitude. Effects of the field line resonance were seen in the 5577 Å, meridian scanning photometer data and the magnetometer data from the CANOPUS array. The field line resonance was accompanied by precipitating energetic electrons (energies greater than 3 keV) in a narrow auroral arc which was 3°–4° equatorward of the resonance structure seen in the radar data and approximately 1° equatorward of field lines threading the inner boundary of the proton plasma sheet. The electron precipitation in this arc was modulated at the frequency of the field line resonance. The effects of the resonance are also seen as pulsations in the magnetometer data, and the horizontal polarization of the pulsations showed a change in sense of rotation across the arc. The oscillations in the precipitating electrons might have been caused by modulation in the ELF/VLF growth rates due to the presence of the magnetohydrodynamic waves associated with the resonance, by mode conversion to kinetic Alfvén waves, or by the formation of electrostatic ion cyclotron waves due to field‐aligned currents associated with a second field line resonance collocated with the arc. The evidence presented here suggests that the modulation of ELF/VLF by magnetohydrodynamic waves on field lines near the plasmapause was the most likely cause of the auroral oscillations.

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“…The spatial distribution partially overlaps with that of the precipitating energetic electrons and chorus waves primarily seen in L =4–7 outside of the plasmapause on the dawnside [e.g., Lam et al ., ]. The ground Pc5 magnetic pulsations are sometimes accompanied by the CNA pulsations [e.g., Olson et al ., ; Poulter and Nielsen , ], VLF emissions (called “QP emissions”) [e.g., Kimura , ], or both [e.g., Sato et al ., ; Paquette et al ., ; Manninen et al ., ] with a high degree of correlation. Such an interrelationship between Pc5 magnetic pulsations and CNA pulsations and/or QP emissions provided further supporting evidence for the Coroniti and Kennell [] theory.…”

Section: Introductionmentioning

confidence: 98%

The role of compressional Pc5 pulsations in modulating precipitation of energetic electrons

et al. 2013

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[1] Pc5 (1.67-6.67 mHz) magnetic pulsations and the modulation of energetic electron precipitation are often observed simultaneously in the morning auroral-latitude data.Here we have investigated a conjunction event of Cluster spacecraft and Canadian auroral-latitude ground stations to identify the role of compressional Pc5 pulsations in modulating precipitation of energetic electrons observed by ground-based riometers. On 7 December 2002 as the spacecraft moved between L = 4.0 and 6.5 in the dawn sector (0600-0700 magnetic local time (MLT)), we found a monochromatic Pc5 magnetic pulsation at~4.0 mHz simultaneously in space and on the ground. Both Cluster and ground magnetometer data confirmed that the resonant oscillation at 4.0 mHz occurred around L =~6.0. Simultaneously, the four Cluster spacecraft identified the compressional Pc5, which was accompanied by similar temporal variations of the fluxes of medium energy (tens to hundreds of keV) electrons and of the intensity of whistler mode chorus waves. While the compressional Pc5 was present in the magnetosphere, the riometers near the spacecraft footprint observed the coincident modulation of electron precipitation at~4.0 mHz. Our coordinated observations indicate a convincing relationship between compressional Pc5 magnetic pulsations in the magnetosphere and the modulation of electron precipitation in the ionosphere, mediated by chorus waves modulated in the magnetosphere, as predicted by the theory of Coroniti and Kennell [1970]. Around the resonant shell, however, some additional contributions to the modulation of electron precipitation might also come from the effects of the resonant Pc5 oscillation.

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CNA pulsations associated with quasi‐periodic VLF emissions

Cited by 8 publications

References 14 publications

Source regions of long‐period pulsation events in electron precipitation and magnetic fields at South Pole Station

Source regions of long‐period pulsation events in electron precipitation and magnetic fields at South Pole Station

Observations of a detached, discrete arc in association with field line resonances

The role of compressional Pc5 pulsations in modulating precipitation of energetic electrons

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