Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF

Hoilijoki, Sanni; Ganse, Urs; Sibeck, D. G.; Cassak, P. A.; Turc, Lucile; Battarbee, Markus; Fear, R. C.; Blanco‐Cano, X.; Dimmock, A. P.; Kilpua, Emilia; Järvinen, R.; Juusola, Liisa; Pfau‐Kempf, Yann; Palmroth, Minna

doi:10.1029/2019ja026821

Cited by 40 publications

(64 citation statements)

References 63 publications

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“…They also extend further out in the quasi-perpendicular magnetosheath than downstream of the quasi-parallel shock, due to the IMF orientation. Similar features due to pile-up are also observed in the statistical maps compiled by Dimmock et al (2017) nents are enhanced at the bow shock crossing, while the normal component remains unchanged (Treumann, 2009;Hoilijoki et al, 2019).…”

Section: Magnetic Field Strengthsupporting

confidence: 73%

“…This run simulates the noon-midnight meridional plane of near-Earth space, as it was initially designed to study e.g. dayside and nightside reconnection in the presence of the foreshock (Hoilijoki et al, 2019). For an Alfvénic Mach number M A = 6.9 as in Run 1, the quasi-perpendicular portion of the bow shock lies roughly at the same distance from Earth both in the x − y and the x − z planes, while its quasi-parallel sector is found closer to Earth, according to MHD simulations (Chapman et al, 2004).…”

Section: Runs Used and Analysis Methodsmentioning

confidence: 99%

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Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

Turc¹,

Tarvus²,

Dimmock³

et al. 2020

Preprint

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Abstract. Bounded by the bow shock and the magnetopause, the magnetosheath forms the interface between solar wind and magnetospheric plasmas and regulates solar wind-magnetosphere coupling. Previous works have revealed pronounced dawn-dusk asymmetries in the magnetosheath properties. The dependence of these asymmetries on the upstream parameters remains however largely unknown. One of the main sources of these asymmetries is the bow shock configuration, which is typically quasi-parallel on the dawn side and quasi-perpendicular on the dusk side of the terrestrial magnetosheath because of the Parker spiral orientation of the interplanetary magnetic field (IMF) at Earth. Most of these previous studies rely on collections of spacecraft measurements associated with a wide range of upstream conditions which are processed in order to obtain average values of the magnetosheath parameters. In this work, we use a different approach and quantify the magnetosheath asymmetries in global hybrid-Vlasov simulations performed with the Vlasiator model. We concentrate on three parameters: the magnetic field strength, the plasma density and the flow velocity. We find that the Vlasiator model reproduces accurately the polarity of the asymmetries, but that their level tends to be higher than in spacecraft measurements, probably because the magnetosheath parameters are obtained from a single set of upstream conditions in the simulation, making the asymmetries more prominent. We investigate how the asymmetries change when the angle between the IMF and the Sun-Earth line is reduced and when the Alfven Mach number decreases. We find that a more radial IMF results in a stronger magnetic field asymmetry and a larger variability of the magnetosheath density. In contrast, a lower Alfven Mach number leads to a reduced magnetic field asymmetry and a decrease in the variability of the magnetosheath density and velocity, the latter likely due to weaker foreshock processes. Our results highlight the strong impact of the foreshock on global magnetosheath properties, in particular on the magnetosheath density, which is extremely sensitive to transient foreshock processes.

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Section: Magnetic Field Strengthsupporting

confidence: 73%

Section: Runs Used and Analysis Methodsmentioning

confidence: 99%

Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

Turc¹,

Tarvus²,

Dimmock³

et al. 2020

Preprint

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“…Global magnetohydrodynamic (MHD), kinetic, and Vlasiator simulations indicate that subsolar FTEs tend to grow larger as they travel away from the reconnection site along the magnetopause (Akhavan-Tafti et al, 2018;Dorelli & Bhattacharjee, 2009;Hoilijoki et al, 2017;Hoilijoki et al, 2019;Omidi et al, 2006;Omidi & Sibeck, 2007;Raeder, 2006). The growth slows down when the FTEs approach their lowest-energy state (i.e., "force-free"; Eastwood et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

MMS Multi‐Point Analysis of FTE Evolution: Physical Characteristics and Dynamics

et al. 2019

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Previous studies have indicated that flux transfer events (FTEs) grow as they convect away from the reconnection site along the magnetopause. This increase in FTE diameter may occur via adiabatic expansion in response to decreasing external pressure away from the subsolar region or due to a continuous supply of magnetic flux and plasma to the FTEs' outer layers by magnetic reconnection. Here we investigate an ensemble of 55 FTEs at the subsolar magnetopause using Magnetospheric Multiscale (MMS) multi‐point measurements. The FTEs are initially modeled as quasi‐force‐free flux ropes in order to infer their geometry and the spacecraft trajectory relative to their central axis. The MMS observations reveal a radially‐inward net force at the outer layers of FTEs which can accelerate plasmas and fields toward the FTE's core region. Inside the FTEs, near the central axis, plasma density is found to decrease as the axial net force increases. It is interpreted that the axial net force accelerates plasmas along the axis in the region of compressing field lines. Statistical analysis of the MMS observations of the 55 FTEs indicates that plasma pressure, Pth, decreases with increasing FTE diameter, λ, as Pth,obsv ∝ λ−0.24. Assuming that all 55 FTEs started out with similar diameters, this rate of plasma pressure decrease with increasing FTE diameter is at least an order of magnitude slower than the theoretical rate for adiabatic expansion (i.e., Pth,adiab. ∝ λ−3.3), suggesting the presence of efficient plasma heating mechanisms, such as magnetic reconnection, to facilitate FTE growth.

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“…Magnetospheric Multiscale (MMS) observations (Akhavan-Tafti et al, 2018) and simulations (Fermo et al, 2011;Hoilijoki et al, 2019;Raeder, 2006) indicate that flux transfer events (FTEs) form in the subsolar region and grow as they convect toward the flanks and high-latitude magnetopause. Internal plasma pressure is observed to decrease sub-adiabatically with increasing FTE diameter (Akhavan-Tafti et al, 2019) suggesting the presence of internal plasma acceleration and heating processes.…”

Section: Introductionmentioning

confidence: 99%

MMS Observations of Plasma Heating Associated With FTE Growth

Akhavan‐Tafti

Slavin

Sun

et al. 2019

Geophysical Research Letters

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Upon formation, flux transfer events (FTEs) in the subsolar magnetosheath have been observed to grow in diameter, λ, while convecting along the magnetopause. Plasma pressure has also been found to decrease sub‐adiabatically with increasing λ, indicating the presence of internal plasma acceleration and heating processes. Here, the Magnetospheric Multiscale (MMS) fields and plasma measurements are used to determine the relative roles of parallel electric fields, betatron, and Fermi processes in plasma heating inside an ensemble of 55 subsolar FTEs. Plasma heating is shown asymmetric inside FTEs. Parallel electric fields dominate (>75%) ion and electron heating at the leading edge of FTEs. At the trailing edge, betatron and Fermi processes overtake (>50%), resulting in ion cooling and electron heating, respectively. The observed strong net heatings inside FTEs are proportional to λ−1/2. It is concluded that reconnection‐driven heating continues inside FTEs far from the subsolar electron and ion diffusion regions.

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Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF B_x Component During Southward IMF

Cited by 40 publications

References 63 publications

Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

MMS Multi‐Point Analysis of FTE Evolution: Physical Characteristics and Dynamics

MMS Observations of Plasma Heating Associated With FTE Growth

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