Evolution of diamagnetic cavities in the solar wind

Thomas, V. A.; Brecht, S. H.

doi:10.1029/ja093ia10p11341

Cited by 80 publications

(98 citation statements)

References 20 publications

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“…The energetic plasma can then expel the magnetic field, creating a diamagnetic cavity and steepening Alfvén wave as the plasma expanded. This hybrid model has reproduced many features similar to those observed in HDCs (Thomas and Brecht 1988).…”

Section: Properties Of Density Holessupporting

confidence: 59%

“…The basic mechanism for producing these nonlinear structures is due to the interaction of the current sheets in the IMF with the bow shock (Burgess and Schwartz 1988;Burgess 1989). Hybrid simulations have reproduced many magnetic and particle features of HFAs (Thomas and Brecht 1988;Thomas et al 1991). The original simulation model of HFA excluded the SW and the high temperature is produced by the energetic reflected particles from the bow shock and it did not include instabilities.…”

Section: Nonlinear Structures and Waves Upstream Of Bow Shockmentioning

confidence: 99%

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Shocks in collisionless plasmas

Parks

Lee

et al. 2017

Rev. Mod. Plasma Phys.

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The Earth's bow shock is the best-known collisionless shock in space. Although much is known about the bow shock, the mechanisms of heating and thermalization processes still remain poorly understood. Collisionless shocks are different from ordinary fluid shocks, because a fraction of the incident solar wind is reflected from the bow shock and the transmitted particles are not immediately thermalized. The reflected particles interact with the incident solar wind producing waves and instabilities that can heat and accelerate particles to high energies. Some of the waves can grow to large amplitudes such as Short Large Amplitude Magnetic Structures. Other upstream nonlinear structures include hot flow anomalies and density holes. The upstream nonlinear structures subsequently convect Earthward with the SW and could impact the structure and dynamics of the bow shock. These observations have clearly indicated that the upstream dynamics are an integral part of the bow shock system. Although much has been learned about the behavior of Earth's bow shock dynamics from the existing data, many fundamental questions remain not answered. This article will review observations of ion dynamics of Earth's bow shock system, what we have learned from recent and past observations. We provide new perspectives from multi-spacecraft Cluster observations about the spatial and temporal variations including the fundamental shock heating, acceleration, and entropy generation processes.

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Section: Properties Of Density Holessupporting

confidence: 59%

Section: Nonlinear Structures and Waves Upstream Of Bow Shockmentioning

confidence: 99%

Shocks in collisionless plasmas

Parks

Lee

et al. 2017

Rev. Mod. Plasma Phys.

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“…Pressure variations generated within the foreshock, and those intrinsic to the solar wind, launch fast mode waves when they strike the bow shock (Thomas and Brecht, 1988). Because the sum of the fast mode and magnetosheath velocities is approximately equivalent to that of the solar wind itself, pressure fronts in the magnetosheath keep pace with those in the solar wind.…”

Section: Pre-noon Foreshock and Magnetospheric Observationsmentioning

confidence: 90%

Radial dependence of foreshock cavities: a case study

et al. 2004

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Abstract. We present a case study of Geotail, Interball-1, IMP-8, and Wind observations of density and magnetic field strength cavities excavated by the enhanced pressures associated with bursts of energetic ions in the foreshock. Consistent with theoretical predictions, the pressure of the energetic ions diminishes rapidly with upstream distance due to a decrease in the flux of energetic ions and a transition from near-isotropic to streaming pitch angle distributions. Consequently, the cavities can only be observed immediately upstream from the bow shock. A comparison of conditions upstream from the pre-and post-noon bow shock demonstrates that foreshock cavities introduce perturbations into the oncoming solar wind flow with dimensions smaller than those of the magnetosphere. Dayside geosynchronous magnetic field strength variations observed by GOES-8 do not track the density variations seen by any of the spacecraft upstream from the bow shock in a one-to-one manner, indicating that none of these spacecraft observed the precise sequence of density variations that actually struck the subsolar magnetopause.

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“…[24] The origin of density and field depressions was initially attributed to the enhanced pressure of energetic backstreaming ions, which are able to push away the magnetic field creating a depressed plasma density and magnetic field structure, flanked by enhanced density and field regions [Thomas and Brecht, 1988]. Our simulations suggest that the origin of density cavitons deep in the foreshock is related to the nonlinear evolution of the two types of waves present in the region, i.e., the parallel propagating sinusoidal waves and the highly oblique, linearly polarized, fast magnetosonic (FLO) waves.…”

Section: Cavitonsmentioning

confidence: 99%

Global hybrid simulations: Foreshock waves and cavitons under radial interplanetary magnetic field geometry

2009

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[1] We use global hybrid (kinetic ions and fluid electrons) simulations to study the solar wind interaction with the magnetosphere for a radial (q vB = 0) interplanetary magnetic field (IMF) geometry. Global hybrid simulations provide a collective picture of processes taking place in the foreshock, bow shock, and magnetosheath. Because ions are treated as particles, these codes also give information on ion-scale microphysics. Under radial IMF geometry, the foreshock forms in front of the dayside magnetosphere, and the plasma convecting downstream is very perturbed. The foreshock is permeated by weakly compressive ultralow frequency (ULF) waves that propagate at angles up to 30°to the ambient field. These weakly compressive waves are generated by field-aligned ions. Wave-Particle interaction results in ion scattering, while wave amplitude grows and fluctuations become compressive as they approach the shock. While weakly compressive waves are dominant far from the shock, a second population of ULF fluctuations arises close to it. These fast magnetosonic waves propagate at large angles to the magnetic field and are linearly polarized. We find that, in addition to the ULF waves, large depressions in density and magnetic field magnitude form near the shock. These density cavitons or depressions are bounded by enhanced magnetic fields, and inside them, hot diffuse ions are present. Foreshock density cavitons in our simulations are embedded in regions with ULF activity, which is in contrast to the isolated character of ''foreshock cavities'' reported previously. We show that density cavitons form due to the nonlinear interaction of the two types of waves present in the foreshock. Wave interaction also modifies the characteristics of weakly compressive waves. A comparison of our results with Cluster observations reveals that the characteristics of weakly compressive waves in our simulation resemble the properties of right-handed 30-s waves found in the terrestrial foreshock. Likewise, we show the existence of density cavitons, or depressions, in regions of Earth's foreshock permeated by ULF waves. The properties of these observed Cluster cavitons are similar to the ones we find in the simulations.Citation: Blanco-Cano, X., N. Omidi, and C. T. Russell (2009), Global hybrid simulations: Foreshock waves and cavitons under radial interplanetary magnetic field geometry,

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Evolution of diamagnetic cavities in the solar wind

Cited by 80 publications

References 20 publications

Shocks in collisionless plasmas

Shocks in collisionless plasmas

Radial dependence of foreshock cavities: a case study

Global hybrid simulations: Foreshock waves and cavitons under radial interplanetary magnetic field geometry

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