High-latitude day side electric field and particle measurements

Maynard, N. C.; Johnstone, A. D.

doi:10.1029/ja079i022p03111

Cited by 51 publications

(20 citation statements)

References 36 publications

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“…Figures 14 and 15 connect DMSP electron observations with the short-duration enhancements in 557.7-nm emissions. Filamentary electron structures were observed on the first sounding rocket into the cusp (Maynard and Johnstone, 1974). The observed electron bursts had significant fluxes above 500 eV.…”

Section: Implications Relative To the Source Electronsmentioning

confidence: 84%

Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images

Maynard¹,

Moen

Burke

et al. 2004

Ann. Geophys.

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Abstract. We demonstrate that high-resolution 557.7-nm all-sky images are useful tools for investigating the spatial and temporal evolution of merging on the dayside magnetopause. Analysis of ground and satellite measurements leads us to conclude that high-latitude merging events can occur at multiple sites simultaneously and vary asynchronously on time scales of 30 s to 3 min. Variations of 557.7 nm emissions were observed at a 10 s cadence at Ny-Ålesund on 19 December 2001, while significant changes in the IMF clock angle were reaching the magnetopause. The optical patterns are consistent with a scenario in which merging occurs around the rim of the high-latitude cusp at positions dictated by the IMF clock angle. Electrons energized at merging sites represent plausible sources for 557.7 nm emissions in the cusp. Polar observations at the magnetopause have directly linked enhanced fluxes of ≥0.5 keV electrons with merging. Spectra of electrons responsible for some of the emissions, measured during a DMSP F15 overflight, exhibit "inverted-V" features, indicating further acceleration above the ionosphere. SuperDARN spectral width boundaries, characteristic of open-closed field line transitions, are located at the equatorward edge of the 557.7 nm emissions. Optical data suggest that with IMF B Y >0, the Northern Hemisphere cusp divides into three source regions. When the IMF clock angle was ∼150 • structured 557.7-nm emissions came from east of the 13:00 MLT meridian. At larger clock angles the emissions appeared between 12:00 and 13:00 MLT. No significant 557.7-nm emissions were detected in the prenoon MLT sector. MHD simulations corroborate our scenario, showing that with the observed large dipole-tilt and IMF clock angles, Correspondence to: N. C. Maynard (nmaynard@mrcnh.com) merging sites develop near the front and eastern portions of the high-altitude cusp rim in the Northern Hemisphere and near the western part of the cusp rim in the Southern Hemisphere.

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Section: Implications Relative To the Source Electronsmentioning

confidence: 84%

Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images

Maynard¹,

Moen

Burke

et al. 2004

Ann. Geophys.

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“…An exception to this is the electron and electric field measurements made from a rocket flown into the polar cusp region near noon by Maynard and Johnstone (1974). The current density estimated by them from the measured electron flux is 1.3 x 10 -6 amp/O which is adequate for the current layer.…”

Section: Candidates (Or No Candidates) For Current Carriersmentioning

confidence: 96%

Net field-aligned currents observed by Triad

Sugiura¹,

Potemra²

1976

J. Geophys. Res.

109

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“…In these pulses of merging, open flux was added to the dayside ionosphere, which stimulated convective flow and the ionospheric convection pattern. Earlier, Maynard and Johnstone (1974) used sounding rocket observations to identify filaments of electrons of magnetosheath character occurring on faster temporal and/or narrower spatial scales. They postulated that direct access was through multiple filamentary structures located in the broader context of the cusp.…”

Section: Merging Primermentioning

confidence: 99%

Coupling the Solar-Wind/IMF to the Ionosphere Through the High Latitude CUSPS

Maynard¹

2005

Surv Geophys

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Magnetic merging is a primary means for coupling energy from the solar wind into the magnetosphere-ionosphere system. The location and nature of the process remain as open questions. By correlating measurements from diverse locations and using large-scale MHD models to put the measurements in context, it is possible to constrain our interpretations of the global and meso-scale dynamics of magnetic merging. Recent evidence demonstrates that merging often occurs at high latitudes in the vicinity of the cusps. The location is in part controlled by the clock angle in the interplanetary magnetic field (IMF) Y-Z plane. In fact, B Y bifurcates the cusp relative to source regions. The newly opened field lines may couple to the ionosphere at MLT locations of as much as 3 hr away from local noon. On the other side of noon the cusp may be connected to merging sites in the opposite hemisphere. In fact, the small convection cell is generally driven by opposite hemisphere merging. B X controls the timing of the interaction and merging sites in each hemisphere, which may respond to planar features in the IMF at different times. Correlation times are variable and are controlled by the dynamics of the tilt of the interplanetary electric field phase plane. The orientation of the phase plane may change significantly on time scales of tens of minutes. Merging is temporally variable and may be occurring at multiple sites simultaneously. Accelerated electrons from the merging process excite optical signatures at the foot of the newly opened field lines. All-sky photometer observations of 557.7 nm emissions in the cusp region provide a ''television picture'' of the merging process and may be used to infer the temporal and spatial variability of merging, tied to variations in the IMF.

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High-latitude day side electric field and particle measurements

Cited by 51 publications

References 36 publications

Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images

Temporal-spatial structure of magnetic merging at the magnetopause inferred from 557.7-nm all-sky images

Net field-aligned currents observed by Triad

Coupling the Solar-Wind/IMF to the Ionosphere Through the High Latitude CUSPS

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