Periodically structured Pc 1 micropulsations during the recovery phase of intense magnetic storms

Heacock, R. R.; Akasofu, S.‐I.

doi:10.1029/ja078i025p05524

Cited by 31 publications

(23 citation statements)

References 30 publications

(8 reference statements)

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“…Of particular interest is the longer lag and better correlation for the occurrences during a higher range of AE (Figure 5c). This lag agrees well with that observed for pPc 1 versus Dst after intense magnetic storms [Heacock and Akasofu, 1973] and seems to be related to the higher occurrence frequency of substorms during the first several days of recovery of intense storms. The better correlation for this case could also be related to the closer proximity of the subcleft lines to Bar I for that range of AE (the cleft tends to move equatorward with increasing AE [ Yasuhara et al, 1973]).…”

Section: Discussionsupporting

confidence: 90%

“…According to Kennel and Petschek's [1966] theory, waves can be expected if there is a sufficient flux of energetic protons with suitable proton pitch angle anisotropy and if the total plasma density (cold, warm, plus hot) is high enough to bring the energetic protons to their stable trapping limit. We think that these conditions may be satisfied in the outer plasmasphere during the later part of the ring current recovery phase [Heacock and Akasofu, 1973]. Unfortunately, satellite measurements have not yet defined the plasma structure beyond the plasmapause in sufficient detail to permit a corresponding conclusion for the Bar I unstructured Pc 1-2 events.…”

Section: Discussionmentioning

confidence: 95%

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Midday Pc 1-2 pulsations observed at a subcleft location

Heacock¹

1974

J. Geophys. Res

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A class of unstructured Pc 1–2 pulsation activity, as identified on Bar I (70.2°N) records taken during 1968–1972, is found to be present in midday hours on about half of the days in summer months. The events have some tendency to occur in the later part of the ring current recovery phase, especially at times of moderate AE when the cleft lines are just poleward of Bar I. The source lines of the Pc 1–2 are found to lie essentially outside the plasmapause. In terms of the proton cyclotron resonance instability the most likely source regions of the Bar I Pc 1–2 are the detached plasma regions convecting sunward on the day side and the portion of the cleft plasma on the last closed field lines.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 95%

Midday Pc 1-2 pulsations observed at a subcleft location

Heacock¹

1974

J. Geophys. Res

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“…The micropu isat ion event discussed here is similar to the periodically structur ed Pc 1 micropulsations described by Heacock and Akasofu [1973] and Mullen and Heacock [1972). Those authors show that structured Pc 1 micropulsations occur during the late recovery …”

Section: Discussionsupporting

confidence: 66%

Stimulation of Pc 1 micropulsations by controlled VLF transmissions

Koons¹

1977

J. Geophys. Res.

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During controlled VLF transmission experiments from a site near Anchorage, Alaska (L = 4), Pc 1 micropulsations, which can be associated with the VLF transmission program, were observed by detectors at College, Alaska; Dunedin, New Zealand; and Macquarie Island. The micropulsation event started shortly after the transmitter began sending a simple repetitive pulse program at 6.6 kHz. The program consisted of a 5‐s‐long pulse transmitted every 30 s. Following the onset of the event a complex sequence of micropulsations appeared between 1.0 and 1.33 Hz. During the simple repetitive program the pulsations recurred every 90 s. The micropulsations began 15 min after satellite 1972‐76B, at low altitude in the conjugate region of the transmitter, observed proton fluxes which could be identified on a one‐for‐one basis with irregularly spaced pulses from the transmitter. Calculations suggest that the 6.6‐kHz whistler mode wave and a 1‐Hz hydromagnetic wave resonate with protons of the same parallel velocity near L = 4.0. The observations suggest that the micropulsations were stimulated by the VLF transmissions, the protons playing a role in the interaction.

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“… Manchester and Fraser [1970] studied the horizontal propagation of Pc1 signals in the ionospheric duct: Maximum signal attenuation in the duct occurred in midday‐afternoon hours when the E region electron density was maximum, and minimum attenuation occurred near 0500 LT. Heacock and Kivinen [1972] noted the attenuation of Pc1–Pc2 signals toward higher latitudes, and suggested that ionospheric disturbances (such as spread F) associated with storm and/or substorm activity would rather effectively scatter and attenuate Pc1 waves propagating poleward in the ionospheric duct. Heacock and Akasofu [1973] noted that the amplitudes of Pc1 events at sites very near the geomagnetic poles, Thule and Vostok, were almost always quite small, and attributed any amplitude variations to variations in propagation conditions in the F layer waveguide rather than variations in the distance to the source region.…”

Section: Discussionmentioning

confidence: 99%

Pc1–Pc2 waves and energetic particle precipitation during and after magnetic storms: Superposed epoch analysis and case studies

et al. 2008

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Magnetic pulsations in the Pc1–Pc2 frequency range (0.1–5 Hz) are often observed on the ground and in the Earth's magnetosphere during the aftermath of geomagnetic storms. Numerous studies have suggested that they may play a role in reducing the fluxes of energetic ions in the ring current; more recent studies suggest they may interact parasitically with radiation belt electrons as well. We report here on observations during 2005 from search coil magnetometers and riometers installed at three Antarctic stations, Halley (−61.84° magnetic latitude, MLAT), South Pole (−74.18° MLAT), and McMurdo (−79.96° MLAT), and from energetic ion detectors on the NOAA Polar‐orbiting Operational Environment Satellites (POES). A superposed epoch analysis based on 13 magnetic storms between April and September 2005 as well as case studies confirm several earlier studies that show that narrowband Pc1–Pc2 waves are rarely if ever observed on the ground during the main and early recovery phases of magnetic storms. However, intense broadband Pi1–Pi2 ULF noise, accompanied by strong riometer absorption signatures, does occur during these times. As storm recovery progresses, the occurrence of Pc1–Pc2 waves increases, at first in the daytime and especially afternoon sectors but at essentially all local times later in the recovery phase (typically by days 3 or 4). During the early storm recovery phase the propagation of Pc1–Pc2 waves through the ionospheric waveguide to higher latitudes was more severely attenuated. These observations are consistent with suggestions that Pc1–Pc2 waves occurring during the early recovery phase of magnetic storms are generated in association with plasmaspheric plumes in the noon‐to‐dusk sector, and these observations provide additional evidence that the propagation of waves to ground stations is inhibited during the early phases of such storms. Analysis of 30‐ to 250‐keV proton data from four POES satellites during the 24–27 August and 18–19 July 2005 storm intervals showed that the location of the inner edge of the ring current matched well with the plasmapause model of O'Brien and Moldwin (2003). However, the POES data showed no evidence of the consequences of electromagnetic ion cyclotron waves (localized proton precipitation) during main and early recovery phase. During later stages of the recovery phase, when such precipitation was observed, it was coincident with intense wave events at Halley, and it occurred at L shells near or up to 1 RE outside the modeled plasmapause but well equatorward of the isotropy boundary.

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Periodically structured Pc 1 micropulsations during the recovery phase of intense magnetic storms

Cited by 31 publications

References 30 publications

Midday Pc 1-2 pulsations observed at a subcleft location

Midday Pc 1-2 pulsations observed at a subcleft location

Stimulation of Pc 1 micropulsations by controlled VLF transmissions

Pc1–Pc2 waves and energetic particle precipitation during and after magnetic storms: Superposed epoch analysis and case studies

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