Transient Foreshock Structures Upstream of Mars: Implications of the Small Martian Bow Shock

Madanian, Hadi; Omidi, N.; Sibeck, D. G.; Andersson, L.; Ramstad, Robin; Xu, Shaosui; Gruesbeck, J.; Schwartz, S. J.; Frahm, R. A.; Brain, David; Kajdič, Primož; Eparvier, F.; Mitchell, David; Curry, S.

doi:10.1029/2022gl101734

Cited by 4 publications

(4 citation statements)

References 56 publications

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“…Indeed, an early stage FB reported by Madanian et al. (2023, Figure 3) at the Martian bow shock compares favorably with the FB core in our simulations. Moreover, since we are not resolving the global curvature of bow shocks, any simple trajectory crossing the FB must either start or end in the foreshock.…”

Section: Resultssupporting

confidence: 85%

“…Since we are not resolving the full shock we are always going to observe the initial growth-phase of the FB, and we are therefore limited to much smaller structures than usually observed in space. Indeed, an early stage FB reported by Madanian et al (2023, Figure 3) at the Martian bow shock compares favorably with the FB core in our simulations. Moreover, since we are not resolving the global curvature of bow shocks, any simple trajectory crossing the FB must either start or end in the foreshock.…”

Section: Temporal Evolution Of Shock-rd Interactionsupporting

confidence: 77%

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The Influence of Rotational Discontinuities on the Formation of Reconnected Structures at Collisionless Shocks—Hybrid Simulations

Steinvall,

Gingell

2024

JGR Space Physics

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Recent simulations and in‐situ observations have shown that magnetic reconnection is an active dissipation mechanism in the transition region of collisionless shocks. The generation mechanisms and upstream conditions enabling reconnection have been studied numerically. However, these numerical studies have been limited to the case of a steady, uniform upstream. The effect upstream discontinuities have on shock reconnection remains poorly understood. Here, we use local hybrid (fluid electron, particle ion) simulations with time‐varying upstream conditions to study the influence upstream rotational discontinuities (RDs) have on the formation of reconnected magnetic structures in the shock transition region. Our results show that bursts of reconnection can occur when RDs interact with the shock. This effect is much more significant at initially quasi‐parallel shocks than quasi‐perpendicular shocks, as the interaction between the RDs and the foreshock (only present in the quasi‐parallel case) can lead to the generation of foreshock bubbles, in which we observe an enhanced reconnection occurrence. The enhanced fluxes of accelerated ions within the foreshock bubble are likely a contributing factor to the increased reconnection occurrence. In addition, we find that the RDs with large magnetic shear are prone to reconnect upon reaching the shock, resulting in the generation of large magnetic islands. Our findings illustrate that upstream discontinuities can significantly increase the amount of reconnected magnetic structures at the bow shock, suggesting that reconnection might be a particularly important dissipation mechanism during periods of dynamic upstream conditions.

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Section: Resultssupporting

confidence: 85%

Section: Temporal Evolution Of Shock-rd Interactionsupporting

confidence: 77%

The Influence of Rotational Discontinuities on the Formation of Reconnected Structures at Collisionless Shocks—Hybrid Simulations

Steinvall,

Gingell

2024

JGR Space Physics

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“…A weaker magnetic field in the upstream plasma corresponds to a larger foot region. For nonplanar bow shocks, the reflection point across the shock also influences the ion trajectory (Gedalin 2023;Madanian et al 2023).…”

Section: Introductionmentioning

confidence: 99%

“…Especially at high Mach numbers, where upstream magnetic perturbations change the morphology of the shock surface(Krasnoselskikh et al 2002), some ions are nonspecularly reflected or scattered upon reflection. In addition, nonlocal ion reflection and extended trajectory of RIs upstream of the shock further increases the velocity spread of RIs(Gedalin 2023;Madanian et al 2023).…”

mentioning

confidence: 99%

Drivers of Magnetic Field Amplification at Oblique Shocks: In Situ Observations

Madanian,

Gingell,

Chen

et al. 2024

ApJL

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Collisionless shocks are ubiquitous structures throughout the Universe. Shock waves in space and astrophysical plasmas convert the energy of a fast-flowing plasma to other forms of energy, including thermal and magnetic energies. Plasma turbulence and high-amplitude electric and magnetic fluctuations are necessary for effective energy conversion and particle acceleration. We survey and characterize in situ observations of reflected ions and magnetic field amplification rates at quasiperpendicular shocks under a wide range of upstream conditions. We report magnetic amplification rates as high as 25 in our current data set. Reflected ions interacting with the incoming plasma create magnetic perturbations that cause magnetic amplification in upstream and downstream regions of quasiperpendicular shocks. Our observations show that, in general, magnetic amplification increases with the fraction of reflected ions, which itself increases with Mach number. Both parameters plateau once full reflection is reached. Magnetic amplification continuously increases with the inverse of the magnetization parameter of the upstream plasma. We find that the extended foot region upstream of shocks and nonlinear processes within that region are key factors for intense magnetic amplification. Our observations at nonrelativistic shocks provide the first experimental evidence that below a certain magnetization threshold, the magnetic amplification efficiency at quasiperpendicular shocks becomes comparable to that at the quasiparallel shocks.

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