Steepening of waves at the duskside magnetopause

Plaschke, Ferdinand; Kahr, N.; Fischer, D.; Nakamura, R.; Baumjohann, W.; Magnes, W.; Burch, J. L.; Torbert, R. B.; Russell, C. T.; Giles, B. L.; Strangeway, R. J.; Leinweber, H. K.; Bromund, K. R.; Anderson, B. J.; Le, G.; Chutter, M.; Slavin, J. A.; Kepko, E. L.

doi:10.1002/2016gl070003

Cited by 15 publications

(25 citation statements)

References 48 publications

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“…To obtain the velocity

{\overset{V}{true}}_{s}

of structures/fluctuations in the magnetic field and thereby the propagation velocity of waves and/or current sheets, we perform a timing analysis with the method detailed in Plaschke, Kahr, et al (), using 3 s long sliding intervals. This interval length allows for a good time resolution of

{\overset{V}{true}}_{s}

while keeping its noise low.…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

“…The averages of the components are subtracted from the magnetic field data, yielding modified vector time series

{\overset{\overset{B}{true}}{true}}_{1}

{\overset{\overset{B}{true}}{true}}_{2}

{\overset{\overset{B}{true}}{true}}_{3}

, and

{\overset{\overset{B}{true}}{true}}_{4}

for MMS 1, 2, 3, and 4. For each spacecraft pair MMS 1 and 2, 1 and 3, and 1 and 4, we compute the cross‐correlation P ( τ ), for instance (equation (2) in Plaschke, Kahr, et al, ):

P_{12} (τ) = \frac{\sum_{t} ((), {\overset{\overset{B}{true}}{true}}_{1} (t + τ) \cdot {\overset{\overset{B}{true}}{true}}_{2} (t))}{\sqrt{((), \sum_{t} {\overset{\overset{B}{true}}{true}}_{1}^{2} (t + τ)) ((), \sum_{t} {\overset{\overset{B}{true}}{true}}_{2}^{2} (t))}}

P 12 , P 13 , and P 14 are computed for each possible value of τ , which ranges between ±2 s in steps of Δ τ = (1/128) s, which is the burst FGM data sampling period. By using

\overset{\overset{B}{true}}{true}

instead of

\overset{B}{true}

, we ensure that magnetic field fluctuations in all directions contribute equally to the cross‐correlations P 12 , P 13 , and P 14 .…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

“…All the maxima of the cross‐correlation functions P (equation ) are above 0.78 within the jet interval. The maximal angular uncertainty of the velocity computations can be estimated with equation (1) of Plaschke, Kahr, et al ():

\arcsin (V_{s} Δt / s)

, where V s ≤400 km/s is the structure velocity, Δ t is the error in timing, which we assume to be the burst data sampling period and resolution of τ of Δ τ = (1/128) s, and s ≈35 km is a measure of the spacecraft separation distance. With these numbers, we obtain an upper limit for the angular uncertainty of approximately 5°.…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

“…The averages of the components are subtracted from the magnetic field data, yielding modified vector time series⃗ B 1 ,⃗ B 2 ,⃗ B 3 , and⃗ B 4 for MMS 1, 2, 3, and 4. For each spacecraft pair MMS 1 and 2, 1 and 3, and 1 and 4, we compute the cross-correlation P( ), for instance (equation (2) in Plaschke, Kahr, et al, 2016):…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

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Magnetosheath High‐Speed Jets: Internal Structure and Interaction With Ambient Plasma

et al. 2017

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For the first time, we have studied the rich internal structure of a magnetosheath high‐speed jet. Measurements by the Magnetospheric Multiscale (MMS) spacecraft reveal large‐amplitude density, temperature, and magnetic field variations inside the jet. The propagation velocity and normal direction of planar magnetic field structures (i.e., current sheets and waves) are investigated via four‐spacecraft timing. We find structures to mainly convect with the jet plasma. There are indications of the presence of a tangential discontinuity. At other times, there are small cross‐structure flows. Where this is the case, current sheets and waves overtake the plasma in the jet's core region; ahead and behind that core region, along the jet's path, current sheets are overtaken by the plasma; that is, they move in opposite direction to the jet in the plasma rest frame. Jet structures are found to be mainly thermal and magnetic pressure balance structures, notwithstanding that the dynamic pressure dominates by far. Although the jet is supermagnetosonic in the Earth's frame of reference, it is submagnetosonic with respect to the plasma ahead. Consequently, we find no fast shock. Instead, we find some evidence for (a series of) jets pushing ambient plasma out of their way, thereby stirring the magnetosheath and causing anomalous sunward flows in the subsolar magnetosheath. Furthermore, we find that jets modify the magnetic field in the magnetosheath, aligning it with their propagation direction.

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“…To obtain the velocity

{\overset{V}{true}}_{s}

{\overset{V}{true}}_{s}

while keeping its noise low.…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

“…The averages of the components are subtracted from the magnetic field data, yielding modified vector time series

{\overset{\overset{B}{true}}{true}}_{1}

{\overset{\overset{B}{true}}{true}}_{2}

{\overset{\overset{B}{true}}{true}}_{3}

, and

{\overset{\overset{B}{true}}{true}}_{4}

for MMS 1, 2, 3, and 4. For each spacecraft pair MMS 1 and 2, 1 and 3, and 1 and 4, we compute the cross‐correlation P ( τ ), for instance (equation (2) in Plaschke, Kahr, et al, ):

P_{12} (τ) = \frac{\sum_{t} ((), {\overset{\overset{B}{true}}{true}}_{1} (t + τ) \cdot {\overset{\overset{B}{true}}{true}}_{2} (t))}{\sqrt{((), \sum_{t} {\overset{\overset{B}{true}}{true}}_{1}^{2} (t + τ)) ((), \sum_{t} {\overset{\overset{B}{true}}{true}}_{2}^{2} (t))}}

P 12 , P 13 , and P 14 are computed for each possible value of τ , which ranges between ±2 s in steps of Δ τ = (1/128) s, which is the burst FGM data sampling period. By using

\overset{\overset{B}{true}}{true}

instead of

\overset{B}{true}

, we ensure that magnetic field fluctuations in all directions contribute equally to the cross‐correlations P 12 , P 13 , and P 14 .…”

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

\arcsin (V_{s} Δt / s)

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

Section: Timing Analysis Of Magnetic Structuresmentioning

confidence: 99%

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Magnetosheath High‐Speed Jets: Internal Structure and Interaction With Ambient Plasma

et al. 2017

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“…Hereinafter, we denote this modified MVA (MMVA) coordinate system as MMVA coordinate system. To determine the time difference between the S/C and thus the DF normal direction from the timing method precisely, we first linear interpolate the 16 Hz magnetic field data to 128 Hz and obtain the time differences between the S/C by cross-correlating their magnetic field measurements between [t Bzmin , t Bzmax ] in the same way as Plaschke et al (2016, Sergeev et al, 2006). • The difference between the estimated DF normal direction from the timing method (n tim ) and the minimum variance direction of MMS1 (n MVA ) is smaller than 10 • .…”

Section: Data and Event Selectionmentioning

confidence: 99%

Dipolarization Fronts: Tangential Discontinuities? On the Spatial Range of Validity of the MHD Jump Conditions

et al. 2019

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Magnetotail dipolarization fronts (DFs) are referred as the sharp increase of the northward magnetic field component, embedded in bursts of fast earthward moving plasma flows, so called bursty bulk flows. Earlier studies often considered DFs as tangential discontinuities (TDs), which can be understood as thin vertical current layers of earthward moving flux tubes, so called dipolarzing flux bundles (DFBs), which separate the ambient plasma sheet plasma from the low entropy plasma within the DFB. Here we present a statistical study of 23 DFs observed by the Magnetospheric Multiscale mission during 2017 and 2018 when the apogee was at 25 R E in the magnetotail. We perform a test of the Walén relation to distinguish whether the observed DFs have rather a TD or rotational discontinuity character and evaluate the plasma flow across the DFs in detail. The results show that on MHD large scales, all 23 DFs can be considered as TD like, but sometimes may have a significant normal plasma flow across it: for 16 events (∼ 70%), the plasma flows mainly tangential to the DFs, while for seven events (∼ 30%), the plasma flows mainly across the DFs. Based on the findings present in this study, we further hypothesize that the DF structure becomes more distorted and unstable in a (locally) more dipolarized background magnetic field region, which may additionally facilitate the plasma flow across the front.sides of this type of discontinuity. For RDs, on the other hand, all field and plasma quantities are continuous across it and only a rotation of the tangential velocity and magnetic field vectors within the discontinuity take place. This implies that for RDs, a change of the plasma velocity and the Alfvén velocity across the discontinuity must change accordingly. This relation is called the Walén relation (e.g. Hudson, 1970) and is valid for linear and nonlinear Alfvén waves (RDs are nonlinear Alfvénic waves). Note that the alignment between the plasma and Alfvén velocity alone is not sufficient to discriminate TDs from RDs, since such an alignment would be also present, for example, for Alfvénic surface waves traveling along a TDs Denskat and Burlaga (1977). The ratio of the magnitude changes of plasma and Alfvén velocity, however, may be a distinctive feature. Previous studies often used this Walén relation as a criteria to distinguish RDs and TDs in the solar wind (e.g. Neugebauer et al., 1984) or at the magnetopause (e.g. Paschmann et al., 1986).

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Four‐Spacecraft Magnetic Curvature and Vorticity Analyses on Kelvin‐Helmholtz Waves in MHD Simulations

2018

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Four‐spacecraft missions are probing the Earth's magnetospheric environment with high potential for revealing spatial and temporal scales of a variety of in situ phenomena. The techniques allowed by these four spacecraft include the calculation of vorticity and the magnetic curvature analysis (MCA), both of which have been used in the study of various plasma structures. Motivated by curved magnetic field and vortical structures induced by Kelvin‐ Helmholtz (KH) waves, we investigate the robustness of the MCA and vorticity techniques when increasing (regular) tetrahedron sizes, to interpret real data. Here for the first time, we test both techniques on a 2.5‐D MHD simulation of KH waves at the magnetopause. We investigate, in particular, the curvature and flow vorticity across KH vortices and produce time series for static spacecraft in the boundary layers. The combined results of magnetic curvature and vorticity further help us to understand the development of KH waves. In particular, first, in the trailing edge, the magnetic curvature across the magnetopause points in opposite directions, in the wave propagation direction on the magnetosheath side and against it on the magnetospheric side. Second, the existence of a “turnover layer” in the magnetospheric side, defined by negative vorticity for the duskside magnetopause, which persists in the saturation phase, is reminiscent of roll‐up history. We found significant variations in the MCA measures depending on the size of the tetrahedron. This study lends support for cross‐scale observations to better understand the nature of curvature and its role in plasma phenomena.

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Steepening of waves at the duskside magnetopause

Cited by 15 publications

References 48 publications

Magnetosheath High‐Speed Jets: Internal Structure and Interaction With Ambient Plasma

Magnetosheath High‐Speed Jets: Internal Structure and Interaction With Ambient Plasma

Dipolarization Fronts: Tangential Discontinuities? On the Spatial Range of Validity of the MHD Jump Conditions

Four‐Spacecraft Magnetic Curvature and Vorticity Analyses on Kelvin‐Helmholtz Waves in MHD Simulations

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