Hybrid Simulations of a Tangential Discontinuity‐Driven Foreshock Bubble Formation in Comparison With a Hot Flow Anomaly Formation

Vu, Andrew; Liu, Zixu; Zhang, H.; Delamere, P. A.

doi:10.1029/2021ja029973

Cited by 10 publications

(32 citation statements)

References 58 publications

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“…More events are located near position = 1 versus position = 0, mainly due to the following reason: the trailing boundary (at 1 region) is usually stronger (with higher magnetic field strength) than the leading one for foreshock transients. This feature has been shown in previous observations and simulation studies (Liu et al 2016;Vu et al 2022), and Figure 1 is also an example. As a result, the change of the magnetic field strength is sharp at the region around 1 but smoother around 0.…”

Section: Statistical Resultssupporting

confidence: 84%

Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave−Particle Resonant Interaction

Shi¹,

Liu²,

Artemyev

et al. 2023

ApJ

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Thermalization and heating of plasma flows at shocks result in unstable charged-particle distributions that generate a wide range of electromagnetic waves. These waves, in turn, can further accelerate and scatter energetic particles. Thus, the properties of the waves and their implication for wave−particle interactions are critically important for modeling energetic particle dynamics in shock environments. Whistler-mode waves, excited by the electron heat flux or a temperature anisotropy, arise naturally near shocks and foreshock transients. As a result, they can often interact with suprathermal electrons. The low background magnetic field typical at the core of such transients and the large wave amplitudes may cause such interactions to enter the nonlinear regime. In this study, we present a statistical characterization of whistler-mode waves at foreshock transients around Earth’s bow shock, as they are observed under a wide range of upstream conditions. We find that a significant portion of them are sufficiently intense and coherent (narrowband) to warrant nonlinear treatment. Copious observations of background magnetic field gradients and intense whistler wave amplitudes suggest that phase trapping, a very effective mechanism for electron acceleration in inhomogeneous plasmas, may be the cause. We discuss the implications of our findings for electron acceleration in planetary and astrophysical shock environments.

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Section: Statistical Resultssupporting

confidence: 84%

Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave−Particle Resonant Interaction

Shi¹,

Liu²,

Artemyev

et al. 2023

ApJ

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“…This paper, which is a continuation of previous simulation work by Vu et al. (2022), focuses on the effects of differing solar wind and foreshock ion parameters on the early formation of TD‐driven FBs.…”

Section: Introductionmentioning

confidence: 82%

“…In recent hybrid simulations confirming the kinetic formation model, Vu et al. (2022) find that the early formation differences between TD‐driven FBs and HFAs are dependent on the relative scales of the foreshock ion gyroradii and the TD thicknesses. This paper, which is a continuation of previous simulation work by Vu et al.…”

Section: Introductionmentioning

confidence: 90%

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Parameter Dependencies of Early‐Stage Tangential Discontinuity‐Driven Foreshock Bubbles in Local Hybrid Simulations

Liu

Zhang

et al. 2023

JGR Space Physics

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Foreshock bubbles (FBs) are significant foreshock transients that can accelerate particles and disturb the magnetosphere‐ionosphere system. In the kinetic formation model, foreshock ions interact with the discontinuity by performing partial gyrations to generate currents that change the magnetic field topology around the discontinuity. However, how different foreshock ion properties affect the growth of the field variations is not well understood. Therefore, we use 2‐D local hybrid simulations to study the effects of different foreshock ion distributions and properties on the growth of tangential discontinuity (TD)‐driven FBs. We discover that for a gyrophase‐bunched distribution with an initial phase where the guiding center is on the other side of the TD, the foreshock ions gyrate together across the TD, causing more foreshock ions to cross the TD and leading to a faster expansion of the structure than for a Maxwellian distribution. A ring distribution also yields higher expansion speeds because of the higher projected velocity into the new perpendicular direction. For Maxwellian distributions, there are positive and linear correlations of the FB expansion speeds with the initial foreshock ion densities, thermal speeds, parallel speeds, and sine of the TD magnetic shear angles. These parameter dependencies grow in strength as the structures evolve with time. The foreshock ion distributions and properties that lead to stronger currents produce more significant magnetic field variations and higher expansion speeds. Our study helps quantify the formation and expansion of FBs to forecast their space weather effects and contribution to shock acceleration.

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“…The initial simulation setup is the same as Vu et al. (2022), in that the solar wind particles are injected from left boundary in the earthward direction, and the foreshock particles are injected from right boundary (that acts as the bow shock) in the sunward direction. In the middle of the simulation box, there is a TD with its normal tangential to the solar wind direction.…”

Section: Datamentioning

confidence: 99%

Modeling the Expansion Speed of Foreshock Bubbles

Liu

Zhang

et al. 2023

JGR Space Physics

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Foreshock transients, including hot flow anomalies (HFAs) and foreshock bubbles (FBs), are frequently observed in the ion foreshock. Their significant dynamic pressure perturbations can disturb the bow shock, resulting in disturbances in the magnetosphere and ionosphere. They can also contribute to particle acceleration at their parent bow shock. These disturbances and particle acceleration caused by the foreshock transients are not yet predictable, however. In this study, we take the first step in establishing a first‐order predictive expansion speed model for FBs (which are simpler than HFAs). Starting with energy conversion from foreshock ions to solar wind ions, we derive the FB expansion speed in the FB's early formation stage and late expansion stage as a function of foreshock and solar wind parameters. We use local hybrid simulations with varying parameters to fit and improve the early stage model and 1D particle‐in‐cell simulations to test the late‐stage model. By comparing model results with Magnetospheric Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations, we adjust the late‐stage model and show that it can predict the FB expansion speed. Our study provides a foundation for predictive models of foreshock transient formation and expansion, so that we can eventually forecast their space weather effects and particle acceleration at shocks.

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Hybrid Simulations of a Tangential Discontinuity‐Driven Foreshock Bubble Formation in Comparison With a Hot Flow Anomaly Formation

Cited by 10 publications

References 58 publications

Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave−Particle Resonant Interaction

Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave−Particle Resonant Interaction

Parameter Dependencies of Early‐Stage Tangential Discontinuity‐Driven Foreshock Bubbles in Local Hybrid Simulations

Modeling the Expansion Speed of Foreshock Bubbles

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