Magnetosheath dynamic pressure enhancements: occurrence and typical properties

Archer, Martin; Horbury, T. S.

doi:10.5194/angeo-31-319-2013

Cited by 109 publications

(251 citation statements)

References 43 publications

(108 reference statements)

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“…High-speed jets in the magnetosheath studied by Plaschke et al [2013] were observed behind the quasi-perpendicular bow shock or the foreshock region upstream and during radial IMF orientation with an average duration of around 30 s. These findings are consistent with the bow shock ripple based generation mechanism suggested by Hietala et al [2009]. The dynamic pressure transients in the magnetosheath containing increases in the density reported by Archer and Horbury [2013] exhibit similar properties.…”

Section: Introductionsupporting

confidence: 72%

Magnetosheath plasma structures and their relation to foreshock processes

2015

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We present simultaneous Time History of Events and Macroscale Interactions during Substormsobservations of plasma parameters upstream in the solar wind and downstream in the magnetosheath (MSH) from 2007 to 2008. We discuss the connection of foreshock (FSH) processes and magnetospheric disturbances to transmission mechanisms in the MSH. In 60% of the analyzed cases, the MSH was strongly influenced by the FSH. We analyze the results as a function of location, time scale, spatial orientation of the observed structures, and the prevailing interplanetary magnetic field (IMF) and solar wind plasma parameters. We find that plasma structures with density enhancement are mostly observed during radial IMF orientations and for small BN , the angle between the upstream magnetic field and the local bow shock normal; the observed structures are pressure balanced with strong anticorrelation between density and temperature; the scale size of the density fluctuations is about 0.4R E . We compare the observations with results from a 2.5-dimensional hybrid simulation to investigate the mechanisms by which the foreshock plasma structures are generated, propagate through the bow shock, and evolve.

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Section: Introductionsupporting

confidence: 72%

Magnetosheath plasma structures and their relation to foreshock processes

2015

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“…To complicate matters, the means of transporting mass, momentum and energy across the magnetopause involves a synthesis of magnetohydrodynamic (MHD), kinetic, and numerous wave-particle interaction processes. In spite of that, several candidates capable of facilitating transport across the magnetopause have been identified: magnetic reconnection (Dungey, 1961), impulsive penetration (Karlsson et al, 2012;Archer and Horbury, 2013;Plaschke et al, 2013), Kinetic Alfvén waves (Johnson and Cheng, 1997;Chaston et al, 2008) the Kelvin Helmholtz Instability (KHI) (Miura and Pritchett, 1982;Miura, 1992;Chen et al, 1997;Otto and Fairfield, 2000;Nykyri and Otto, 2001;Nykyri et al, 2006;Hasegawa et al, 2009) and flux transfer events (Russell and Elphic, 1978). It is noteworthy that each of these processes do not strictly operate independently, and during certain conditions, plasma transport may be a result of a combination of these processes operating simultaneously.…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

The dawn–dusk asymmetry of ion density in the dayside magnetosheath and its annual variability measured by THEMIS

et al. 2016

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Abstract. The local and global plasma properties in the magnetosheath play a fundamental role in regulating solar wind-magnetosphere coupling processes. However, the magnetosheath is a complex region to characterise as it has been shown theoretically, observationally and through simulations that plasma properties are inhomogeneous, non-isotropic and asymmetric about the Sun-Earth line. To complicate matters, dawn-dusk asymmetries are sensitive to various changes in the upstream conditions on an array of timescales. The present paper focuses exclusively on dawn-dusk asymmetries, in particularly that of ion density. We present a statistical study using THEMIS data of the dawn-dusk asymmetry of ion density in the dayside magnetosheath and its long-term variations between 2009 and 2015. Our data suggest that, in general, the dawn-side densities are higher, and the asymmetry grows from noon towards the terminator. This trend was only observed close to the magnetopause and not in the central magnetosheath. In addition, between 2009 and 2015, the largest asymmetry occurred around 2009 decreasing thereafter. We also concluded that no single parameter such as the Alfvén Mach number, plasma velocity, or the interplanetary magnetic field strength could exclusively account for the observed asymmetry. Interestingly, the dependence on Alfvén Mach number differed between data sets from different time periods. The asymmetry obtained in the THEMIS data set is consistent with previous studies, but the solar cycle dependence was opposite to an analysis based on IMP-8 data. We discuss the physical mechanisms for this asymmetry and its temporal variation. We also put the current results into context with the existing literature in order to relate THEMIS era measurements to those made during earlier solar cycles.

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“…In particular, the magnetosheath region downstream of the quasi-parallel shock is permeated by magnetosheath jets. Correspondingly, subsolar jet occurrence is found to be controlled -almost exclusively -by the cone angle of the interplanetary magnetic field (IMF), i.e., the angle between the IMF and the EarthSun line, while other solar wind parameters or their variability only play a minor role (Archer et al, 2012;Archer and Horbury, 2013;Plaschke et al, 2013). A substantial fraction of jets is believed to originate from bow shock ripples or undulations , which are common at the reforming, patchy, quasi-parallel bow shock (Schwartz and Burgess, 1991;Omidi et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Plasma flow patterns in and around magnetosheath jets

Plaschke¹,

Hietala²

2018

Ann. Geophys.

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Abstract. The magnetosheath is commonly permeated by localized high-speed jets downstream of the quasi-parallel bow shock. These jets are much faster than the ambient magnetosheath plasma, thus raising the question of how that latter plasma reacts to incoming jets. We have performed a statistical analysis based on 662 cases of one THEMIS spacecraft observing a jet and another (second) THEMIS spacecraft providing context observations of nearby plasma to uncover the flow patterns in and around jets. The following results are found: along the jet's path, slower plasma is accelerated and pushed aside ahead of the fastest core jet plasma. Behind the jet core, plasma flows into the path to fill the wake. This evasive plasma motion affects the ambient magnetosheath, close to the jet's path. Diverging and converging plasma flows ahead and behind the jet are complemented by plasma flows opposite to the jet's propagation direction, in the vicinity of the jet. This vortical plasma motion results in a deceleration of ambient plasma when a jet passes nearby.

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Magnetosheath dynamic pressure enhancements: occurrence and typical properties

Cited by 109 publications

References 43 publications

Magnetosheath plasma structures and their relation to foreshock processes

Magnetosheath plasma structures and their relation to foreshock processes

The dawn–dusk asymmetry of ion density in the dayside magnetosheath and its annual variability measured by THEMIS

Plasma flow patterns in and around magnetosheath jets

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