Localized density enhancements in the magnetosheath: Three‐dimensional morphology and possible importance for impulsive penetration

Karlsson, Tomas; Brenning, Nils; Nilsson, Hans; Trotignon, Jean-Gabriel; Vallières, Xavier; Facskó, G.

doi:10.1029/2011ja017059

Cited by 67 publications

(178 citation statements)

References 60 publications

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“…Nevertheless, large-scale jets with a cross-sectional diameter of over 2 R E (Earth radii) have been found to impact the subsolar magnetopause at relatively high rates (with respect to other transients) of once every 21 min, on average, and once every 6 min when the IMF cone angle is low (under 30 • ). These impact rates are even more remarkable when taking into account that jets of smaller scale occur more often and that typical jet scales are on the order of 1 R E (Karlsson et al, 2012;Archer et al, 2012;Hietala et al, 2012;Plaschke et al, 2013Plaschke et al, , 2016Gunell et al, 2014). When jets impact the magnetopause, the consequences can be substantial.…”

Section: Introductionmentioning

confidence: 97%

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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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Section: Introductionmentioning

confidence: 97%

“…Plasma jets defined as transient increases in dynamic pressure are a very common phenomenon in the subsolar magnetosheath (Němeček et al, 1998;Savin et al, 2008;Karlsson et al, 2012;Plaschke et al, 2016). In particular, the magnetosheath region downstream of the quasi-parallel shock is permeated by magnetosheath jets.…”

Section: Introductionmentioning

confidence: 99%

Plasma flow patterns in and around magnetosheath jets

Plaschke¹,

Hietala²

2018

Ann. Geophys.

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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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“…These jets had speeds a few times above that of the ambient magnetosheath plasma. Karlsson et al 33 performed an observational study of 56 plasmoids in the magnetosheath each with a maximum density at least 50 % above the density of the surrounding plasma. They found plasmoids in a size range between 0.1R E and 10R E .…”

Section: Introductionmentioning

confidence: 99%

Plasma penetration of the dayside magnetopause

et al. 2012

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Data from the Cluster spacecraft during their magnetopause crossing on 25 January 2002 are presented. The magnetopause was in a state of slow non-oscillatory motion during the observational period. Coherent structures of magnetosheath plasma, here typified as plasmoids, were seen on closed magnetic field lines on the inside of the magnetopause. Using simultaneous measurements on two spacecraft the inward motion of the plasmoids is followed from one spacecraft to the next, and it is found to be in agreement with the measured ion velocity. The plasma characteristics and the direction of motion of the plasmoids show that they have penetrated the magnetopause, and the observations are consistent with the concept of impulsive penetration, as it is known from theory, simulations, and laboratory experiments. The mean flux across the magnetopause observed was 0.2-0.5% of the solar wind flux at the time, and the peak values of the flux inside the plasmoids reached approximately 20% of the solar wind flux.

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Localized density enhancements in the magnetosheath: Three‐dimensional morphology and possible importance for impulsive penetration

Cited by 67 publications

References 60 publications

Plasma flow patterns in and around magnetosheath jets

Plasma flow patterns in and around magnetosheath jets

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

Plasma penetration of the dayside magnetopause

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