Anomalous aspects of magnetosheath flow and of the shape and oscillations of the magnetopause during an interval of strongly northward interplanetary magnetic field

Chen, Sheng-Hsien; Kivelson, M. G.; Gosling, J. T.; Walker, Raymond J.; Lazarus, A. J.

doi:10.1029/92ja02263

Cited by 138 publications

(140 citation statements)

References 35 publications

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“…The amplitude of KHI waves at Earth is reported to be in the range of 30-50 nT (ref. 20), whereas amplitudes at Mercury are in excess of 40 nT (refs 8,11). Mercury is also more dynamic, with the KHI characteristic timescales in the range of seconds 8 compared with minutes at Earth.…”

Section: Messenger Spacecraft Observations Of the Khi At Mercurymentioning

confidence: 99%

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: Messenger Spacecraft Observations Of the Khi At Mercurymentioning

confidence: 99%

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

Paral

Rankin

2013

Nat Commun

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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%

“…The flows along the flanks for a north-south IMF are, by contrast, much larger and have even been shown to exceed the solar wind speed itself by up to 60% in several cases [Lavraud et al, 2007;Rosenqvist et al, 2007]. Utilizing global magnetohydrodynamic (MHD) simulations, Chen et al [1993] and Lavraud et al [2007] have shown that it is indeed possible to attain magnetosheath speeds that exceed that of the solar wind thanks to increased magnetic forces in low b plasma. The process is akin to a slingshot-type effect.…”

Section: Introductionmentioning

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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“…Farther away in the nightside, using data from ISEE1 and 2, IMP 8 and IMP 7, it was found that the magnetotail ceased to flare during a 12 h northward IMF to an anti-sunward distance of 15 R E (Chen et al, 1993). As shown in our Fig.…”

Section: Impact Of Solar Wind Depression On Large Scale Structures: Tmentioning

confidence: 66%

Impact of solar wind depression on the dayside magnetosphere under northward interplanetary magnetic field

Baraka

Ben‐Jaffel

2011

Ann. Geophys.

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Abstract. We present a follow up study of the sensitivity of the Earth's magnetosphere to solar wind activity using a particles-in-cell model (Baraka and Ben Jaffel, 2007), but here during northward Interplanetary Magnetic Field (IMF). The formation of the magnetospheric cavity and its elongation around the planet is obtained with the classical structure of a magnetosphere with parallel lobes. An impulsive disturbance is then applied to the system by changing the bulk velocity of the solar wind to simulate a decrease in the solar wind dynamic pressure followed by its recovery. In response to the imposed drop in the solar wind velocity, a gap (abrupt depression) in the incoming solar wind plasma appears moving toward the Earth. The gap's size is a ∼15 R E and is comparable to the sizes previously obtained for both B z < 0 and B z = 0. During the initial phase of the disturbance along the x-axis, the dayside magnetopause (MP) expands slower than the previous cases of IMF orientations as a result of the abrupt depression. The size of the MP expands nonlinearly due to strengthening of its outer boundary by the northward IMF. Also, during the initial 100 t, the MP shrank down from 13.3 R E to ∼9.2 R E before it started expanding, a phenomenon that was also observed for southern IMF conditions but not during the no IMF case. As soon as they felt the solar wind depression, cusps widened at high altitude while dragged in an upright position. For the field's topology, the reconnection between magnetospheric and magnetosheath fields is clearly observed in both the northward and southward cusps areas. Also, the tail region in the northward Correspondence to: S. Baraka (suleiman.baraka@gmail.com) IMF condition is more confined, in contrast to the fishtailshape obtained in the southward IMF case. An X-point is formed in the tail at ∼110 R E compared to ∼103 R E and ∼80 R E for B z = 0 and B z < 0, respectively. Our findings are consistent with existing reports from many space observatories (Cluster, Geotail, Themis, etc.) for which predictions are proposed to test furthermore our simulation technique.

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Anomalous aspects of magnetosheath flow and of the shape and oscillations of the magnetopause during an interval of strongly northward interplanetary magnetic field

Cited by 138 publications

References 35 publications

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

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

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

Impact of solar wind depression on the dayside magnetosphere under northward interplanetary magnetic field

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