Magnetospheric boundary shapes and internal structures

Formisano, V.

doi:10.1016/0273-1177(81)90110-1

Cited by 4 publications

(3 citation statements)

References 24 publications

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“…particle and optical measurements that show a gap in the oval in the same location as the average energy minimum [Snyder et al, 1975;Dandekar and Pike, 1978;Dandekar, 1979;Meng, 1981]. In addition, the spatial extent of the dayside entry layer [Paschmann et al, 1976] should map to a localized region such as we find for the average energy minimum, and the electrons in the dayside entry layer are found to be softer than in the low-latitude boundary layer [Formisano and Bavassano-Cattaneo, 1978;Formisano, 1981]. One should also note that in low-altitude electric field measurements, a region of rotational discontinuity in the field is found confined close to noon [Heelis, 1979, and references therein].…”

Section: Low-energy Electronsmentioning

confidence: 79%

A statistical model of auroral electron precipitation

Hardy¹,

Gussenhoven²,

Holeman³

1985

J. Geophys. Res.

484

395

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A statistical study has been completed using data from the Defense Meteorological Satellite Program F2 and F4 and the Satellite Test Program P78‐1 satellites to determine the average characteristics of auroral electron precipitation as a function of magnetic local time, magnetic latitude, and geomagnetic activity as measured by Kp. The characteristics were determined for each whole number value of Kp from 0 to 5 and for Kp ≥ 6‐. At each level of Kp, the high‐latitude region was gridded, and the average electron spectrum in the energy range from 50 eV to 20 keV was determined in each grid element. The results show that the high‐latitude precipitation region separates into two parts based on the electron average energy. There is a region of relatively hot electrons (EAVE ≥ 600 eV). In this region, the electron average energies are highest on the morningside of the oval. There are two average energy maxima at each Kp level: one postmidnight and the other prenoon. The hot electron region is generally not continuous in MLT but shows a gap between 1200 and 1800 MLT. The hotter electrons carry most of the energy flux into the oval. The energy flux on the nightside increases with Kp, while the level at noon increases with Kp when Kp is small but decreases at higher Kp. The average energy of the hot electrons increases from Kp = 0 to Kp = 3 but is approximately constant for higher Kp. In the second region, average energies are low (EAVE < 600 eV). This region extends from the poleward edge of the hot electron region to the pole. The precipitating electrons in this region carry the majority of the number flux at high latitudes. The largest number fluxes are found on the dayside. The highest fluxes are confined to a crescent‐shaped region centered slightly prenoon and extending in MLT over most of dayside and, in some cases, into the nightside. There is a prenoon maximum in the number flux that shows little variability in MLT or in intensity with Kp. The average energy shows a minimum typically between 1100 and 1200 MLT and located toward the poleward edge of the crescent‐shaped region of highest integral number flux. We identify the cusp as the region near the average energy minimum and the cleft as the crescent‐shaped region.

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Section: Low-energy Electronsmentioning

confidence: 79%

A statistical model of auroral electron precipitation

Hardy¹,

Gussenhoven²,

Holeman³

1985

J. Geophys. Res.

484

395

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“…To maintain pressure balance, magnetosheath magnetic field strengths must be enhanced within this plasma depletion layer (PDL). , Crooker et al [1979], and Formisano [1981] presented plasma observations that confirmed the existence of a reduced-density PDL just outside the magnetopause. Crooker et al discussed evidence for the associated enhanced magnetic field strengths.…”

Section: The Quiescent Magnetopausementioning

confidence: 83%

“…Pressure pulses generated at the quasi-parallel bow shock may also drive substantial magnetopause motion. Such boundary motion would be more significant during periods of radial IMF, when much of the dayside magnetopause lies behind the quasi-parallel bow shock [Formisano, 1981]. Under more-typical spiral IMF conditions, only the dawnside magnetopause lies behind the quasiparallel bow shock, and this is the region pressure pulses associated with the bow shock would strike.…”

Section: Magnetopause Boundary Motionmentioning

confidence: 99%

A model for the transient magnetospheric response to sudden solar wind dynamic pressure variations

Sibeck¹

1990

J. Geophys. Res.

286

308

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Brief, impulsive, large-amplitude (•ip/p -1) solar wind dynamic pressure pulses, recurring on time scales of 5 to 15 min, are common just upstream of the Earth's bow shock. When each pulse strikes the magnetopause, it launches a fast-mode compressional wave in the magnetosphere that can propagate antisunward faster than the magnetosheath flow. Consequently, the magnetopause bulges outward ahead of each contraction associated with a pressure pulse. These ridges generally propagate antisunward, although sunward motion is common on the early post-noon magnetopause. The greatest amplitude (-1 to 2 RE) magnetopause motion occurs on the prenoon magnetopause, at high-latitudes, and during periods of southward interplanetary magnetic field. The signatures of the pressure-pulse-driven magnetopause motion include a bipolar magnetic field signature normal to the nominal magnetopause, a rotation of the magnetic fidd away from both magnetosheath and magnetospheric orientations, a mixture of magnetosheath and magnetospheric plasmas, and high-speed magnetosheath plasma flows. The magnetopause boundary motion, in turn, drives transient compressions and shears in the dayside magnetospheric magnetic field. These compressions and shears map to the dayside auroral ionosphere, where the ground signatures produced by a single, brief, solar wind dynamic pressure pulse are an antisunward moving (sunward at early post-noon local times) double-convection vortex, associated with northsouth magnetic field perturbations, increased ELF/VLF wave activity, precipitating particles, and cosmic noise absorption. The ionospheric and magnetospheric signatures driven by solar wind pressure pulses greatly resemble those previously associated with flux transfer events. SOLAR WIND AND MAGNETOSHEATH DYNAMIC PRESSURE VARIATIONSIn this section, we consider the characteristics of previously reported solar wind and magnetosheath dynamic pressure variations, emphasizing the variations associated with solar wind shocks, holes, and tangential discontinuities. We discuss recent evidence that the bow shock itself may modulate the solar wind dynamic pressure applied to the magnetosphere. Solar WindAt least three solar wind features are associated with significant dynamic pressure variations: shocks, holes, and tangential discontinuities. The properties of corotating and traveling solar wind shocks are relatively well known. They bring increases (and occasionally decreases) in the solar wind density, velocity, and dynamic pressure to the Earth every several hours to days [Burlaga, 1969]. Although the dynamic pressure can increase by a factor of as much as 20 across solar wind shocks, factors of 3 are more common [Siscoe et al., 1968b]. Corotating shocks are aligned with the spiral IMF [Siscoe, 1972].By contrast, the dynamic pressure changes associated with tangential discontinuities [Burlaga, 1968[Burlaga, , 1969 and holes [Turner et al., 1977] are poorly known, partly because high time resolution plasma parameters were not previously available. Such small-scale fe...

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Electron Injection in the Polar Gusp

Johnstone

1985

The Polar Cusp

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Magnetospheric boundary shapes and internal structures

Cited by 4 publications

References 24 publications

A statistical model of auroral electron precipitation

A statistical model of auroral electron precipitation

A model for the transient magnetospheric response to sudden solar wind dynamic pressure variations

Electron Injection in the Polar Gusp

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