Statistical Study of Favorable Foreshock Ion Properties for the Formation of Hot Flow Anomalies and Foreshock Bubbles

Liu, Zixu; Zhang, H.; Turner, D. L.; Vu, Andrew; Angelopoulos, Vassilis

doi:10.1029/2022ja030273

Cited by 13 publications

(25 citation statements)

References 76 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, a recent statistical study by T. Z. Liu et al. (2022) shows that larger density ratios and higher kinetic energies of the foreshock ions favor the formation of FBs and HFAs, consistent with our simulation results. As for the thermal speed, however, T. Z. Liu et al.…”

Section: Discussionsupporting

confidence: 92%

“…As for the thermal speed, however, T. Z. Liu et al. (2022) show that a larger gyroradius calculated from the perpendicular thermal speed is a favorable condition, instead of the thermal speed. It is more likely the foreshock ion gyroradius relative to the discontinuity parameters that determines the early formation; but this requires further tests in the future.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

Liu

Zhang

et al. 2023

JGR Space Physics

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

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

Liu

Zhang

et al. 2023

JGR Space Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…In the downstream background foreshock, the ion distribution function indicates that backstreaming foreshock ions are in the anti‐parallel direction (Figure 6h) and have bunched gyrophases (Figure 6i, perpendicular cut at V para = −1,000 km/s) corresponding to the narrow yellow beam in Figure 6d. After we remove the solar wind ion beam from the ion distributions (see detailed methods in Liu, Angelopoulos et al., 2017; Liu et al., 2022), we calculate the foreshock ion moments. Figure 6e shows that the ratio of foreshock ion density to total density is 2%–4%.…”

Section: Observationsmentioning

confidence: 99%

“…As a result, a foreshock bubble (FB) shock and FB sheath form at its boundary. In the core, the solar wind density (black) is nearly 0, whereas foreshock ion density (orange) is enhanced as they are trapped in the core (e.g., Liu, An, et al., 2020; Liu, Angelopoulos et al., 2017; Liu et al., 2022). So, the ion moments, there, are strongly affected by the foreshock ions.…”

Section: Introductionmentioning

confidence: 99%

Modeling the Expansion Speed of Foreshock Bubbles

Liu

Zhang

et al. 2023

JGR Space Physics

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…However, as we discuss below, this method typically fails to fully remove the background population since the thermal velocity is typically quite large in the MSH region and even when two populations co-exist they correspond to measurements closer than one Vth to each other in velocity space. It should be noted that this technique could work well when applied to foreshock events, since in that case, the reflected particles and the SW-beam like population are well separated from each other (e.g., Liu et al, 2017Liu et al, , 2022.…”

Section: Jet Moment Derivationmentioning

confidence: 99%

On Magnetosheath Jet Kinetic Structure and Plasma Properties

Raptis

Karlsson

Vaivads

et al. 2022

Geophysical Research Letters

View full text Add to dashboard Cite

As the supersonic solar wind (SW) approaches Earth, it interacts with the planet's magnetic field, forming a bow shock. Downstream of the shock, the magnetosheath (MSH) region forms, which is a highly turbulent plasma environment where several phenomena co-exist. One of these phenomena is the so called MSH jets and during the last two decades, they have drawn considerable attention (Plaschke et al., 2018). These jets are transient dynamic pressure enhancement with respect to the downstream ambient background plasma. The dynamic pressure enhancements can be due to either a velocity and/or density increase (Archer et al., 2012).One of the most important features that determines the properties of jets is whether they are found in the so called Quasi-parallel (Qpar) or Quasi-perpendicular (Qperp) MSH. These regions are, respectively, the plasma downstream of a Qpar or a Qperp shock crossing. Typically, the distinction between Qpar and Qperp shock crossings is based on the angle between the upstream Interplanetary Magnetic Field vector and the bow shock normal vector. If the angle is less than 45°, we call the crossing Qpar, while if it is greater, we call it Qperp. The downstream MSH of the Qpar shocks is more turbulent, exhibits lower temperature anisotropy, and contains more high-energy particles (Fuselier, 1994;Karlsson et al., 2021;. The complexity of Qpar shocks also extends upstream of the shock to the foreshock region where non-linear ULF waves, field-aligned beams and wave-particle interaction regions are observed (

show abstract

Statistical Study of Favorable Foreshock Ion Properties for the Formation of Hot Flow Anomalies and Foreshock Bubbles

Cited by 13 publications

References 76 publications

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

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

Modeling the Expansion Speed of Foreshock Bubbles

On Magnetosheath Jet Kinetic Structure and Plasma Properties

Contact Info

Product

Resources

About