Cone angle control of the interaction of magnetic clouds with the Earth's bow shock

Turc, Lucile; Escoubet, C. P.; Fontaine, Dominique; Kilpua, Emilia; Enestam, S.

doi:10.1002/2016gl068818

Cited by 13 publications

(14 citation statements)

References 75 publications

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“…For a purely radial IMF, the magnetosheath asymmetries due to the bow shock configuration should completely disappear, as the θ Bn values are then distributed symmetrically about the Sun-Earth line (see e.g. Turc et al, 2016). Therefore, there should be a value of the cone angle at which the magnetosheath asymmetries maximise, before decreasing when further reducing the cone angle to finally reach the symmetrical configuration for a purely radial IMF.…”

Section: Discussionmentioning

confidence: 99%

“…This is why we did not compare our numerical results concerning M A with observations in Section 3.4. Low Alfvén Mach numbers are encountered only occasionally at Earth, but they are of great importance for solar wind-magnetosphere coupling because they are associated with extreme solar wind disturbances such as magnetic clouds (Turc et al, 2016) and they result in atypical conditions in the magnetosheath (Lavraud et al, 2013). Other studies have suggested that the Alfvén Mach number plays a role in the asymmetry (Walsh et al, 2012;Dimmock et al, 2017) but it is difficult to make a direct and meaningful comparison between all of these studies since there are extensive differences across methodologies, models, and datasets.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Turc¹,

Tarvus²,

Dimmock³

et al. 2020

Preprint

View full text Add to dashboard Cite

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“…Additionally, the bow shock and magnetosheath properties can be significantly modified during low Alfvén Mach number conditions, which are often associated with ICMEs and magnetic clouds. This may alter the solar wind-magnetosphere coupling during extreme space weather events (Lopez et al 2004(Lopez et al , 2011Lavraud et al 2007;Lavraud and Borovsky 2008;Farrugia et al 2013;Turc et al 2016).…”

Section: Influence Of the Magnetosheathmentioning

confidence: 99%

The Scientific Foundations of Forecasting Magnetospheric Space Weather

et al. 2017

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The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth's magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.

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“…This study is based on the MC catalog introduced in Turc et al [], which lists the MCs observed near the Sun‐Earth L 1 libration point from 2000 to 2014. For each of these MCs, our list also indicates in which region (i.e., solar wind, magnetosheath or magnetosphere) the following spacecraft can be found: Cluster [ Escoubet et al , ], the Time History of Events and Macroscale Interactions during Substorms (THEMIS) [ Angelopoulos , ], the Geomagnetic Tail Lab (GEOTAIL) [ Nishida , ], Interball‐Tail [ Galeev et al , ], and Double‐Star TC1 [ Liu et al , ].…”

Section: Data Set and Methodologymentioning

confidence: 99%

“…The MCs' properties, and in particular their magnetic field direction, are expected to be significantly altered through these regions, as is the case for the regular solar wind. Furthermore, we note that MCs are characterized by a low Alfvén Mach number ( M A ), generally below 5 [ Lavraud and Borovsky , ; Turc et al , ]. These low M A conditions in the solar wind alter the volume of the magnetosheath, which becomes much larger than usual as the bow shock moves outward, but also how energy is processed at the bow shock [e.g., Treumann , ], the magnetosheath flows [ Lavraud et al , ; Farrugia et al , ], the current systems in the Earth's environment [ Lopez et al , ], and more generally, the solar wind‐magnetospheric coupling during MC events [ Lopez et al , ; Lavraud and Borovsky , ; Farrugia et al , ; Myllys et al , ].…”

Section: Introductionmentioning

confidence: 99%

Statistical study of the alteration of the magnetic structure of magnetic clouds in the Earth's magnetosheath

et al. 2017

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The magnetosheath plays a central role in the solar wind‐magnetospheric coupling. Yet the effects of its crossing on solar wind structures such as magnetic clouds (MCs) are generally overlooked when assessing their geoeffectivity. Using 82 MCs observed simultaneously in the solar wind and the magnetosheath, we carry out the first statistical study of the alteration of their magnetic structure in the magnetosheath. For each event, the bow shock properties are obtained from a magnetosheath model. The comparison between the model results and observations shows that in 80% of cases, the MHD‐based model captures well the magnetosheath transition; the other events are discussed separately. We find that just downstream of the bow shock the variation of the magnetic field direction shows a very good anticorrelation (r =− 0.91) with the angle between the upstream magnetic field and the shock normal. We then focus on the magnetic field north‐south component Bz because of its importance for geoeffectivity. Although the sign of Bz is generally preserved in the magnetosheath, we also find evidence of long‐lasting intervals of opposite Bz signs in the solar wind and the magnetosheath during some events, with a |Bz| reversal >10 nT at the magnetopause. We find that these reversals are due to the draping of the field lines and are associated with predominant upstream By. In those cases, the estimated position of the regions of antiparallel fields along the magnetopause is independent of the sign of the upstream Bz. This may have strong implications in terms of reconnection.

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Cone angle control of the interaction of magnetic clouds with the Earth's bow shock

Cited by 13 publications

References 75 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

The Scientific Foundations of Forecasting Magnetospheric Space Weather

Statistical study of the alteration of the magnetic structure of magnetic clouds in the Earth's magnetosheath

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