Substorm‐associated pulsations and magnetopause‐magnetosheath fluctuations

Heacock, R. R.; Chao, J. K.

doi:10.1029/ja086ia02p00711

Cited by 5 publications

(3 citation statements)

References 19 publications

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“…They must have been generated at the bow shock or in the magnetosheath. Heacock and Chao [1981] discussed -4-min oscillations in the magnetosheath magnetic field and suggested that they were associated with oscillations of similar period in high-latitude ground magnetograms. However, Kaufmann et al [1970] proposed that magnetosheath variations with similar or shorter periods were slow-mode magnetoacoustic waves with plasma and magnetic field pressures in antiphase, in which case the variations might have little effect on the magnetosphere.…”

Section: Magnetosheathmentioning

confidence: 98%

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

Sibeck¹

1990

J. Geophys. Res.

287

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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Section: Magnetosheathmentioning

confidence: 98%

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

Sibeck¹

1990

J. Geophys. Res.

287

308

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“…Observations consistent with these predictions have already been reported. Heacock and Chao [1981] reported simultaneous magnetosheath and ground magnetogram observations. Their Figure 5 shows the onset of --•4-min period oscillations in the polar magnetosheath magnetic field strength and in several highlatitude ground magnetograms at 2215 UT on October 4, 1974.…”

Section: We Do Not Consider Ftes or Magnetopause Boundary Waves Drivementioning

confidence: 99%

The magnetospheric response to 8‐minute period strong‐amplitude upstream pressure variations

et al. 1989

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This paper documents a series of brief, strong (Δp/p = 1), dynamic pressure oscillations that occurred in the region upstream of the Earth's bow shock during a period of radial interplanetary magnetic field (IMF). The analyzed set of oscillations, which may be either intrinsic solar wind or bow shock‐related phenomena, recur approximately every 8–10 min, and their magnetic field signatures occur nearly simultaneously over great distances transverse to the Earth‐Sun line. The pressure oscillations appear to drive tailward‐moving magnetopause surface wavelets. In turn, the surface wavelets can be identified as hydromagnetic waves with strong compressional components in the outer magnetosphere and as quasi‐periodic variations in electron precipitation and high‐latitude ground pulsations. We use observations by spacecraft in the outer dayside magnetosphere to predict geosynchronous and subsolar magnetic field strengths, the location of the subsolar magnetopause, the solar wind dynamic pressure, and variations in the energetic magnetospheric ion flux.

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“… Heacock [1967] suggested that Pi1B pulsations result from small‐scale, local ionospheric currents and these earlier studies were eventually followed by others that associated occurrences of these pulsations with substorm onset [ Heacock and Chao , 1981; Bösinger and Yahnin , 1987; Arnoldy et al , 1998]. Building on this work, Arnoldy et al [1998] discovered perhaps the most significant aspect of Pi1B pulsations, which is that these pulsations can also be seen at geosynchronous orbit at onset (i.e., by the GOES satellites), implying that their source does not originate within the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Pi1B pulsations as a possible driver of Alfvénic aurora at substorm onset

et al. 2011

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[1] Ground-based observations have shown Pi1B magnetic pulsations are associated with substorm onset. These pulsations can also be observed at geosynchronous orbit, suggesting that they propagate from (or beyond) geosynchronous orbit to the ionosphere at substorm onset. Independently, investigations have shown that the initial brightening of an arc at subtorm onset is Alfvénic in nature (i.e., that the aurora during the initial brightening is wave-driven). These results raise the question of whether Pi1B pulsations might drive Alfvénic aurora at substorm onset. In this paper, data from a single event are presented that show Pi1B pulsations observed simultaneously at geosynchronous orbit, by FAST just above the ionosphere and by various ground stations. The event is observed by FAST within a few minutes of the onset of Pi1B pulsations, with an electron signature of the onset arc that is quite characteristic of Alfvénic aurora, showing that at least a portion of the initial brightening is wave-driven and associating this with the presence of Pi1B pulsations. The implication of this work is that Pi1B pulsations propagate to the ionosphere from beyond geosynchronous orbit and provide the wave power to drive Alfvénic aurora at substorm onset, at least for this single, isolated event. The luminosity associated with the Alfvénic aurora, however, may only provide a small contribution to the total brightness.

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Substorm‐associated pulsations and magnetopause‐magnetosheath fluctuations

Cited by 5 publications

References 19 publications

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

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

The magnetospheric response to 8‐minute period strong‐amplitude upstream pressure variations

Pi1B pulsations as a possible driver of Alfvénic aurora at substorm onset

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