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Abstract The upstream and downstream plasmas of 109 strong‐compression forward interplanetary shocks are statistically analyzed using 3‐s measurements from the WIND spacecraft. The goal is a comparison of the fluctuation properties of downstream plasmas in comparison with the fluctuation properties of upstream plasmas in the inertial range of frequencies and the magnetic‐structure range of spatial scales. The shocks all have density compression rations of ~2 or more. When possible, each shock is categorized according to the type of solar wind plasma it propagates through: 15 shocks are in coronal‐hole‐origin plasma, 42 shocks are in streamer‐belt‐origin plasma, 36 shocks are in sector‐reversal‐region plasmas, and 11 shocks are in ejecta plasma. The statistical study examines magnetic field and velocity spectral indices, the Alfvénicity, the fluctuation amplitudes, Alfvén ratios, the degree of plasma inhomogeneity, and Taylor microscales, looking in particular at (1) fluctuation values downstream that are related to fluctuation values upstream and (2) systematic differences in fluctuation values associated with the type of plasma. It is argued that inhomogeneity of the downstream plasma can be caused by spatial variations in the shock normal angleθBncaused by field direction variations in the upstream magnetic structure. The importance of determining the type of plasma that the shock propagates through is established.
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Transmission of magnetic island modes across interplanetary shocks: comparison of theory and observations
Abstract Interplanetary shock waves are observed frequently in turbulent solar wind. They naturally enhance the temperature/entropy of the plasma through which they propagate. Moreover, many studies have shown that they also act as an amplifier of the fluctuations incident on the shock front. Solar wind turbulent fluctuations can be well described as the superposition of quasi-2D and slab components, the former being energetically dominant. In this paper, we address the interaction of fast forward shocks observed by the Wind spacecraft at 1 AU and quasi-2D turbulent fluctuations in the framework of the Zank et al. (2021) transmission model and we compare model predictions with observations. Our statistical study includes 378 shocks with varying upstream conditions and Mach numbers. We estimate the average ratio of the downstream observed and theoretically predicted power spectra within the inertial range of turbulence. We find that the distributions of this ratio for the whole set and for the subset of shocks that met the assumptions of the model, are remarkably close. We argue that a large statistical spread of the distributions of this ratio is governed by the inherent variation of the upstream conditions. Our findings suggest that the model predicts the downstream fluctuations with a good accuracy and that it may be adopted for a wider class of shocks than it was originally meant for.
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- Award ID(s):
- 2148653
- PAR ID:
- 10448670
- Date Published:
- Journal Name:
- Journal of Physics: Conference Series
- Volume:
- 2544
- Issue:
- 1
- ISSN:
- 1742-6588
- Page Range / eLocation ID:
- 012009
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The acceleration of charged particles by interplanetary shocks (IPs) can drain a nonnegligible fraction of the plasma pressure. In this study, we have selected 17 IPs observed in situ at 1 au by the Advanced Composition Explorer and the Wind spacecraft, and 1 shock at 0.8 au observed by Parker Solar Probe. We have calculated the time-dependent partial pressure of suprathermal and energetic particles (smaller and greater than 50 keV for protons and 30 keV for electrons, respectively) in both the upstream and downstream regions. The particle fluxes were averaged for 1 hr before and 1 hr after the shock time to remove short timescale effects. Using the MHD Rankine–Hugoniot jump conditions, we find that the fraction of the total upstream energy flux transferred to suprathermal and energetic downstream particles is typically ≲16%, in agreement with previous observations and simulations. Notably, by accounting for errors on all measured shock parameters, we have found that for any given fast magnetosonic Mach number,Mf< 7, the angle between the shock normal and average upstream magnetic field,θBn, is not correlated with the energetic particle pressure; in particular, the partial pressure of energized particles does not decrease forθBn≳ 45°. The downstream electron-to-proton energy ratio in the range ≳ 140 eV for electrons and ≳ 70 keV for protons exceeds the expected ∼1% and nears equipartition (>0.1) for the Wind events.more » « less
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Abstract Relativistic collisionless shocks are associated with efficient particle acceleration when propagating into weakly magnetized homogeneous media; as the magnetization increases, particle acceleration becomes suppressed. We demonstrate that this changes when the upstream carries kinetic-scale inhomogeneities, as is often the case in astrophysical environments. We use fully kinetic simulations to study relativistic perpendicular shocks in magnetized pair plasmas interacting with upstream density perturbations. For amplitudes of δ ρ / ρ ≳ 0.5, the upstream fluctuations are found to corrugate the shock front and generate large-scale turbulent shear motions in the downstream, which in turn are capable of accelerating particles. This can revive relativistic magnetized shocks as viable energization sites in astrophysical systems, such as jets and accretion disks. The generation of large-scale magnetic structures also has important implications for polarization signals from blazars.more » « less
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Aims. An interplanetary coronal mass ejection (ICME) event was observed by the Solar Orbiter at 0.8 AU on 2020 April 19 and by Wind at 1 AU on 2020 April 20. Futhermore, an interplanetary shock wave was driven in front of the ICME. Here, we focus on the transmission of the magnetic fluctuations across the shock and we analyze the characteristic wave modes of solar wind turbulence in the vicinity of the shock observed by both spacecraft. Methods. The observed ICME event is characterized by a magnetic helicity-based technique. The ICME-driven shock normal was determined by magnetic coplanarity method for the Solar Orbiter and using a mixed plasma and field approach for Wind. The power spectra of magnetic field fluctuations were generated by applying both a fast Fourier transform and Morlet wavelet analysis. To understand the nature of waves observed near the shock, we used the normalized magnetic helicity as a diagnostic parameter. The wavelet-reconstructed magnetic field fluctuation hodograms were used to further study the polarization properties of waves. Results. We find that the ICME-driven shock observed by Solar Orbiter and Wind is a fast, forward oblique shock with a more perpendicular shock angle at the Wind position. After the shock crossing, the magnetic field fluctuation power increases. Most of the magnetic field fluctuation power resides in the transverse fluctuations. In the vicinity of the shock, both spacecraft observe right-hand polarized waves in the spacecraft frame. The upstream wave signatures fall within a relatively broad and low frequency band, which might be attributed to low frequency MHD waves excited by the streaming particles. For the downstream magnetic wave activity, we find oblique kinetic Alfvén waves with frequencies near the proton cyclotron frequency in the spacecraft frame. The frequency of the downstream waves increases by a factor of ∼7–10 due to the shock compression and the Doppler effect.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1742-6596/2544/1/012009
