Interaction of the bow shock with a tangential discontinuity and solar wind density decrease: Observations of predicted fast mode waves and magnetosheath merging

Maynard, N. C.; Burke, William J.; Ober, D. M.; Farrugia, C. J.; Kucharek, H.; Lester, M.; Mozer, F. S.; Russell, C. T.; Siebert, K. D.

doi:10.1029/2007ja012293

Cited by 29 publications

(42 citation statements)

References 55 publications

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“…The magnetopause crossing back into the magnetosphere at dashed line M3 was in response to the solar wind fivefold density and pressure change observed by ACE (Line D3 in Figure 1). A fast mode rarefaction wave, generated by the interaction of this structure with the upstream bow shock, propagated through the magnetosheath ahead of the decrease thus spreading the response's duration [ Maynard et al , 2007; Farrugia et al , 2009]. Between dashed lines M3 and M4 V Xi ⊥ never came close to reversing polarity to sunward, even though plasma density and B variations indicate that Cluster had reentered the magnetosphere.…”

Section: Observationsmentioning

confidence: 99%

Cluster observations of the dusk flank magnetopause near the sash: Ion dynamics and flow‐through reconnection

Maynard¹,

Farrugia²,

Burke³

et al. 2012

J. Geophys. Res.

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[1] Compared to the dayside, dynamics on the flanks of the magnetopause are poorly understood. To help bridge this knowledge gap we analyzed Cluster plasma and field measurements acquired during a 90-min period on 20 November 2003 when Cluster crossed the magnetopause four times in the vicinity of the sash. MHD simulations provide a context for Cluster observations. Crossings were between the magnetosheath and an S-shaped plasma sheet, rather than to the open-field lobes of the magnetotail. Cluster encountered two regions of MHD-breaking differences between perpendicular ion velocities and E Â B convection. Ion adiabatic expansion parameter (d i ) calculations show that ion gyrotropy was not broken during an episode of strong Alfvén wave activity in the magnetosheath. However, gyrotropy was broken (d i > 1) during the fourth magnetopause crossing. In the magnetosheath, ion guiding-center motion was maintained but inertial effects associated with temporally varying electric fields are probable sources of velocity differences. Regarding the magnetopause crossing, the generalized Ohm's law limits possible sources for breaking ion gyrotropy to inertial forces and/or electron pressure gradients associated with a nearby reconnection event. We suggest that Cluster witnessed effects of a temporally varying and spatially limited, flow-through reconnection event between open mantle field lines from the two polar caps adding new closed flux to the LLBL at the sash. Future modeling of flank dynamics must consider inertial forces as significant drivers at the magnetopause and in the adjacent magnetosheath.

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Section: Observationsmentioning

confidence: 99%

Cluster observations of the dusk flank magnetopause near the sash: Ion dynamics and flow‐through reconnection

Maynard¹,

Farrugia²,

Burke³

et al. 2012

J. Geophys. Res.

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“…The presence of fast mode perturbations at the edges, particularly on the leading edge, is consistent with theoretical expectations. The slow mode rarefaction behind the leading fast mode perturbation is not predicted by theory, but was observed in a recent study comparing ACE observations of a solar wind discontinuity far upstream with Polar magnetosheath observations [ Maynard et al , 2007].…”

Section: In‐situ Observationsmentioning

confidence: 99%

THEMIS observations of a hot flow anomaly: Solar wind, magnetosheath, and ground‐based measurements

Eastwood¹,

Sibeck²,

Angelopoulos³

et al. 2008

Geophysical Research Letters

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The THEMIS spacecraft encountered a Hot Flow Anomaly (HFA) on the dusk flank of the Earth’s bow shock on 4 July 2007, observing it on both sides of the shock. Meanwhile, the THEMIS ground magnetometers traced the progress of the associated Magnetic Impulse Event along the dawn flank of the magnetosphere, providing a unique opportunity to study the transmission of the HFA through the shock and the subsequent downstream response. THEMIS‐A, in the solar wind, observed classic HFA signatures. Isotropic electron distributions inside the upstream HFA are attributed to the action of the electron firehose instability. THEMIS‐E, just downstream, observed a much more complex disturbance with the pressure perturbation decoupled from the underlying discontinuity. Simple calculations show that the pressure perturbation would be capable of significantly changing the magnetopause location, which is confirmed by the ground‐based observations.

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“…The interaction of DDs with the Earth's magnetosphere was simulated using the Integrated Space Weather Prediction Model in the series of papers (Maynard et al , , ). These global MHD simulations agree well with observational results.…”

Section: Introductionmentioning

confidence: 99%

What Happens Before a Southward IMF Turning Reaches the Magnetopause?

Samsonov

Sibeck

Dmitrieva

et al. 2017

Geophysical Research Letters

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Previous observations have shown a ∼10–15 min time delay in the ionospheric response to solar wind directional discontinuities marked by either southward or northward interplanetary magnetic field (IMF) turnings. We have studied one southward IMF turning observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) and GOES in the dayside magnetosphere. Using a global MHD model, we have reproduced the magnetopause motion in this event. We find that the observed delay in the ground response can be completely explained by deceleration of the directional discontinuity in the subsolar magnetosheath. We show that the speed of the discontinuity significantly decreases in the vicinity of the magnetopause where the magnetic barrier formed during the previous northward IMF interval. The southward turning can reach the magnetopause only after complete disruption of the magnetic barrier. The disruption or dissipation occurs via magnetosheath reconnection, as confirmed by high‐speed jets in the magnetosheath. The magnetopause moves sunward as the directional discontinuity transits the magnetosheath. This sunward motion is followed by the earthward motion when the discontinuity strikes the magnetopause and magnetopause reconnection begins.

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Interaction of the bow shock with a tangential discontinuity and solar wind density decrease: Observations of predicted fast mode waves and magnetosheath merging

Cited by 29 publications

References 55 publications

Cluster observations of the dusk flank magnetopause near the sash: Ion dynamics and flow‐through reconnection

Cluster observations of the dusk flank magnetopause near the sash: Ion dynamics and flow‐through reconnection

THEMIS observations of a hot flow anomaly: Solar wind, magnetosheath, and ground‐based measurements

What Happens Before a Southward IMF Turning Reaches the Magnetopause?

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