Looking for Evidence of Wind‐Shear Disconnections of the Earth's Magnetotail: GEOTAIL Measurements and LFM MHD Simulations

Borovsky, Joseph E.

doi:10.1029/2018ja025456

Cited by 6 publications

(4 citation statements)

References 71 publications

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“…This is unusual for ICMEs (see [39]). In accordance with the windsock effect, we expect a deflected tail [40][41][42][43]. 2) Close to the red vertical guideline at ~10:10 UT, there are clear field and flow gradient discontinuities near maximum B.…”

Section: Interplanetary and Far Tail Observationssupporting

confidence: 62%

Effects from dayside magnetosphere to distant tail unleashed by a bifurcated, non-reconnecting interplanetary current sheet

et al. 2022

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Global magnetospheric effects resulting from the passage at Earth of large-scale structures have been well studied. The effects of common and short-term features, such as discontinuities and current sheets (CSs), have not been studied in the same depth. Herein we show how a seemingly unremarkable interplanetary feature can cause widespread effects in the magnetosheath-magnetosphere system. The feature was observed by Advanced Composition Explorer inside an interplanetary coronal mass ejection on 10 January 2004. It contained 1) a magnetic field dip bounded by directional discontinuities in field and flows, occurring together with 2) a density peak in what we identify as a bifurcated, non-reconnecting current sheet. Data from an array of spacecraft in key regions of the magnetosheath/magnetosphere (Geotail, Cluster, Polar, and Defense Meteorological Satellite Program) provide context for Wind’s observations of flapping of the distant (R ∼ −226 RE) magnetotail. In particular, just before the flapping began, Wind observed a hot and tenuous plasma in a magnetic field structure with enhanced field strength, with the By and Bz components rotating in a fast tailward flow burst. Closer inspection reveals a large flux rope (plasmoid) containing lobe plasma in a tail strongly deflected and twisted by interplanetary non-radial flows and magnetic field By. We try to identify the origin of this ‘precursor to flapping’ by looking at data from the various spacecraft. Working back towards the dayside, we discover a chain of effects which we argue were set in motion by the interplanetary CS and its interaction with the bow shock. These effects include 1) a compression and dilation of the magnetosphere, 2) a local deformation of the postnoon magnetopause, and, 3) at the poleward edge of the oval in an otherwise quiet polar cap flow, a strong (3 km/s) sunward flow burst in a double vortex-like structure flanked by two sets of field-aligned currents. Clearly, an intertwined set of phenomena was occurring at the same time. We learn that multi-spacecraft analysis can give us great insight into the magnetospheric response to transient changes in the solar wind.

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Section: Interplanetary and Far Tail Observationssupporting

confidence: 62%

Effects from dayside magnetosphere to distant tail unleashed by a bifurcated, non-reconnecting interplanetary current sheet

et al. 2022

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“…Figure 12 of Borovsky and Denton (2010)]. The impacts of intense velocity shears on the magnetosphere have been investigated by Borovsky (2012a), Borovsky (2018c) via data analysis and global MHD computer simulations. A common feature seen in the global simulations are comet-like disconnections of the Earth's magnetotail, although these are not likely to produce an enhanced coupling as seen in geomagnetic indices.…”

Section: Solar-wind Current Sheets and Velocity Shearsmentioning

confidence: 99%

Further investigation of the effect of upstream solar-wind fluctuations on solar-wind/magnetosphere coupling: Is the effect real?

Borovsky

2023

Front. Astron. Space Sci.

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There is a general consensus that fluctuations in the solar wind magnetic field and/or the Alfvenicity of the solar wind drive a solar wind-magnetosphere interaction. 11 years of hourly-averaged solar wind and magnetospheric geomagnetic indices are used to further examine this hypothesis in detail, confirming that geomagnetic activity statistically increases with the amplitude of upstream fluctuations and with the Alfvénicity, even when solar-wind reconnection driver functions are weak and reconnection on the dayside magnetopause should vanish. A comparison finds that the fluctuation-amplitude effect appears to be stronger than the Alfvénicity effect. In contradiction to the generally accepted hypothesis of driving an interaction, it is also demonstrated that many solar wind parameters are correlated with the fluctuation amplitude and the Alfvénicity. As a result, we caution against immediately concluding that the latter two parameters physically drive the overall solar-wind/magnetosphere interaction: the fluctuation amplitude and Alfvénicity could be acting as proxies for other more-relevant variables. More decisive studies are needed, perhaps focusing on the roles of ubiquitous solar-wind strong current sheets and velocity shears, which drive the measured amplitudes and Alfvénicities of the upstream solar-wind fluctuations.

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“…There is also a velocity structure associated with the magnetic structure (De Keyser et al, 1998;Denskat & Burlaga, 1977;Neugebauer, 1985), which will be explored in the present study. The Earth's magnetotail can be disrupted by the strong velocity shears in the solar wind associated with magnetic current sheets (Borovsky, 2012a(Borovsky, , 2018b.…”

Section: Introductionmentioning

confidence: 99%

On the Motion of the Heliospheric Magnetic Structure Through the Solar Wind Plasma

Borovsky

2020

JGR Space Physics

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A reference frame in the solar wind can often be found wherein the flow vector v is everywhere approximately parallel to the magnetic field vector B. This is the frame of the heliospheric magnetic structure moving relative to the plasma. Since v⊥ is very small in this reference frame, the magnetic structure appears to have little temporal evolution. The structure moves outward away from the Sun faster than the plasma flow. Even for highly Alfvénic plasma, the structure does not move at the Alfvén speed relative to the proton plasma, rather it moves at ~0.7 vA. This may be caused by the spread in the vector directions of the local magnetic field. The degree of inhomogeneity of the plasma is hypothesized to control the motion of the magnetic structure through the plasma. If so, non‐Alfvénicity may be owed to an inability of Alfvénic perturbations to coherently propagate from Alfvénic injections at the Sun. Schemes that mathematically advect magnetic and plasma structure from upstream solar wind monitors to the Earth may be improved by calculating and including the motion of the structure relative to the solar wind velocity vector.

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Looking for Evidence of Wind‐Shear Disconnections of the Earth's Magnetotail: GEOTAIL Measurements and LFM MHD Simulations

Cited by 6 publications

References 71 publications

Effects from dayside magnetosphere to distant tail unleashed by a bifurcated, non-reconnecting interplanetary current sheet

Effects from dayside magnetosphere to distant tail unleashed by a bifurcated, non-reconnecting interplanetary current sheet

Further investigation of the effect of upstream solar-wind fluctuations on solar-wind/magnetosphere coupling: Is the effect real?

On the Motion of the Heliospheric Magnetic Structure Through the Solar Wind Plasma

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