Spatial distribution of rolled up Kelvin-Helmholtz vortices at Earth's dayside and flank magnetopause

Taylor, M. G. G. T.; Hasegawa, Hiroshi; Lavraud, B.; Phan, T. D.; Escoubet, C. P.; Dunlop, M. W.; Bogdanova, Y. V.; Borg, A. L.; Volwerk, M.; Berchem, Guy; Constantinescu, Dragoş; Eastwood, J. P.; Masson, A.; Laakso, H.; Souček, J; Fazakerley, A. N.; Frey, H. U.; Panov, E. V.; Ji, Yong; Shi, Jian; Sibeck, D. G.; Pu, Z. Y.; Wang, J.; Wild, J. A.

doi:10.5194/angeo-30-1025-2012

Cited by 66 publications

(75 citation statements)

References 56 publications

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“…For example, toroidal mode plasma waves on the dawn side of the magnetosphere, as reported by Anderson et al 23 and Takahashi et al 24 , have been attributed to the KHI. On the other hand, Taylor et al 25 have suggested that the KHI is more prevalent around dusk, which is in agreement with observations of Mercury. Global simulations similar to those performed by Claudpierre et al 26 , but incorporating northward (rather than southward), IMF can potentially answer questions about asymmetry at Earth.…”

Section: Discussionsupporting

confidence: 88%

Dawn–dusk asymmetry in the Kelvin–Helmholtz instability at Mercury

Paral

Rankin

2013

Nat Commun

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The NASA MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft entered orbital phase around Mercury on 18 March 2011. A surprising consistent feature in the data returned is large-scale vortices that form exclusively on the dusk side of the magnetosphere. Here we present global kinetic hybrid simulations that explain these observations. It is shown that vortices are excited by a Kelvin-Helmholtz instability near the subsolar point, which grows convectively along the dusk-side magnetopause. Virtual time series along a track approximating a flyby of the MESSENGER show correspondence with the satellite data; the data contain sawtooth oscillations in plasma density, flow and magnetic field, and exhibit the observed dawn-dusk asymmetry. It is shown that asymmetry between dawn and dusk at Mercury is controlled by the finite gyroradius of ions and by convection electric fields. Mercury's magnetosphere offers a natural laboratory for studying plasma regimes not present in other planetary magnetospheres or the laboratory.

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Section: Discussionsupporting

confidence: 88%

Dawn–dusk asymmetry in the Kelvin–Helmholtz instability at Mercury

Paral

Rankin

2013

Nat Commun

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“…This result also took into account the faster magnetosheath flow (and enhanced velocity shear) on the dusk-flank (Longmore et al, 2005;Walsh et al, 2012;Dimmock and Nykyri, 2013) during these conditions. Interestingly, Taylor et al (2012) reported Cluster observations showing that the occurrence of the KHI was larger on the dusk-flank when observations were limited to the dayside. The results of Nykyri (2013) are relevant close to the terminator and on the nightside.…”

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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“…next paragraph), and their intermittent observation may be due to small-scale changes in the distance from the magnetopause to the spacecraft not accounted for in the MHD simulation. The reader is referred to Lavraud and Borovsky [2008] for aspects related to enhanced flows and associated magnetopause wave activity during low M A (see also Chen et al [1993], Lavraud et al [2009] and Taylor et al [2012]). However, this topic is beyond the focus of the present study.…”

Section: Magnetosheath Flows and Magnetopause Shape: Case Studymentioning

confidence: 99%

Asymmetry of magnetosheath flows and magnetopause shape during low Alfvén Mach number solar wind

et al. 2013

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[1] Previous works have emphasized the significant influence of the solar wind Alfvén Mach number (M A ) on magnetospheric dynamics. Here we report statistical, observational results that pertain to changes in the magnetosheath flow distribution and magnetopause shape as a function of solar wind M A and interplanetary magnetic field (IMF) clock angle orientation. We use all Cluster 1 data in the magnetosheath during the period 2001-2010, using an appropriate spatial superposition procedure, to produce magnetosheath flow distributions as a function of location in the magnetosheath relative to the IMF and other parameters. The results demonstrate that enhanced flows in the magnetosheath are expected at locations quasi-perpendicular to the IMF direction in the plane perpendicular to the Sun-Earth line; in other words, for the special case of a northward IMF, enhanced flows are observed on the dawn and dusk flanks of the magnetosphere, while much lower flows are observed above the poles. The largest flows are adjacent to the magnetopause. Using appropriate magnetopause crossing lists (for both high and low M A ), we also investigate the changes in magnetopause shape as a function of solar wind M A and IMF orientation. Comparing observed magnetopause crossings with predicted positions from an axisymmetric semi-empirical model, we statistically show that the magnetopause is generally circular during high M A , while is it elongated (albeit with moderate statistical significance) along the direction of the IMF during low M A . These findings are consistent with enhanced magnetic forces that prevail in the magnetosheath during low M A . The component of the magnetic forces parallel to the magnetopause produces the enhanced flows along and adjacent to the magnetopause, while the component normal to the magnetopause exerts an asymmetric pressure on the magnetopause that deforms it into an elongated shape.

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Spatial distribution of rolled up Kelvin-Helmholtz vortices at Earth's dayside and flank magnetopause

Cited by 66 publications

References 56 publications

Dawn–dusk asymmetry in the Kelvin–Helmholtz instability at Mercury

Dawn–dusk asymmetry in the Kelvin–Helmholtz instability at Mercury

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

Asymmetry of magnetosheath flows and magnetopause shape during low Alfvén Mach number solar wind

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