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Atmosphere
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Turbulence and Energy Dissipation in Solar System Plasmas
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Turbulence and Energy Dissipation in Solar System Plasmas

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Upper Atmosphere".

Deadline for manuscript submissions: closed (15 November 2021) | Viewed by 14359

Special Issue Editors

Dr. Luca Franci

E-Mail Website
Guest Editor
Astronomy Unit - School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London E1 4NS, UK
Interests: plasma; solar wind; numerical simulations; data analysis; turbulence
Dr. Julia E. Stawarz

E-Mail Website
Guest Editor
Imperial College London, South Kensington Campus, London SW7 2AZ, 6M71Huxley BuildingSouth, Kensington Campus, London SW7 2AZ, UK
Interests: spacecraft observations; plasma turbulence; magnetosphere; solar wind

Special Issue Information

Dear Colleagues,

Highly nonlinear turbulent dynamics play a fundamental role in cross-scale energy transfer and particle energization in astrophysical plasmas. Unlike the turbulence observed in terrestrial fluids, where collisional viscosity accounts for energy dissipation from turbulent fluctuations, the lack of collisions in many space and astrophysical plasmas leaves the question of how turbulent fluctuations are ultimately dissipated a major open area of research. A wide array of turbulent plasmas are found within our own solar system – ranging from the solar corona and solar wind to the terrestrial and planetary magnetospheres. These systems can be directly probed by a range of spacecraft missions, including Magnetospheric Multiscale, Parker Solar Probe, Solar Orbiter, BepiColombo, Juno, and many more, making these some of the best regions for exploring plasma turbulence in the collisionless regime. Furthermore, the comparison of these systems provides access to a variety of different plasma regimes, driving mechanisms, and boundary conditions, thus potentially providing access to a range of different turbulence behaviours and dissipation mechanisms. In this Special Issue, we invite both observational and numerical studies focused on examining the turbulence within the varied systems in the solar system, with the aim of assembling a body of work that highlights the similarities and differences in turbulent dynamics and dissipation within the different environments. This collection will thus help to consolidate the knowledge of plasma turbulence gleaned from these systems and guide future research into astrophysical turbulence.

Dr. Luca Franci
Dr. Julia E. Stawarz
Guest Editors

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Keywords

  • turbulence
  • solar wind
  • numerical simulations
  • magnetic field
  • energy dissipation

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Published Papers (5 papers)

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Research

18 pages, 4889 KiB  
Article
Properties of Magnetic Field Fluctuations in Long-Lasting Radial IMF Events from Wind Observation
by Gilbert Pi, Alexander Pitňa, Guo-Qing Zhao, Zdeněk Němeček, Jana Šafránková and Tsung-Che Tsai
Atmosphere 2022, 13(2), 173; https://doi.org/10.3390/atmos13020173 - 21 Jan 2022
Cited by 4 | Viewed by 2878
Abstract
Long-lasting radial interplanetary magnetic field (IMF) intervals in which IMF points along the solar wind velocity for several hours have many interesting properties. We investigate the average parameters and the behavior of magnetic field fluctuations within 419 such radial intervals. The power spectral [...] Read more.
Long-lasting radial interplanetary magnetic field (IMF) intervals in which IMF points along the solar wind velocity for several hours have many interesting properties. We investigate the average parameters and the behavior of magnetic field fluctuations within 419 such radial intervals. The power spectral density (PSD) calculated over 1-h intervals of a radial IMF is compared with PSDs in adjacent regions prior to and after the radial IMF. We concentrate on (1) the power of IMF fluctuations, (2) the median slopes of PSDs in both inertial and kinetic ranges, (3) the proton temperature and its anisotropy, and (4) the occurrence rate of wavy structures and their polarization. We have shown that the fluctuation amplitude is low in the radial IMF intervals in both magnetohydrodynamic (MHD) and kinetic ranges, and the spectral power increases with the cone angle in the MHD range. We discuss this effect in the light of present knowledge on plasma turbulence and peculiarities of observations of magnetic field variations under the radial background magnetic field. We found that in the radial IMF events, the proton temperature is more isotropic, the occurrence rate of waves is higher, and the waves have no preferred polarization in the frequency range from 0.1 to 1 Hz. It suggests that the radial IMF structure leads to a different development of turbulence than the typical Parker-spiral structure. Full article
(This article belongs to the Special Issue Turbulence and Energy Dissipation in Solar System Plasmas)
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12 pages, 2962 KiB  
Article
Properties of Hall-MHD Turbulence at Sub-Ion Scales: Spectral Transfer Analysis
by Emanuele Papini, Petr Hellinger, Andrea Verdini, Simone Landi, Luca Franci, Victor Montagud-Camps and Lorenzo Matteini
Atmosphere 2021, 12(12), 1632; https://doi.org/10.3390/atmos12121632 - 7 Dec 2021
Cited by 7 | Viewed by 3480
Abstract
We present results of a multiscale study of Hall-magnetohydrodynamic (MHD) turbulence, carried out on a dataset of compressible nonlinear 2D Hall-MHD numerical simulations of decaying Alfvénic turbulence. For the first time, we identify two distinct regimes of fully developed turbulence. In the first [...] Read more.
We present results of a multiscale study of Hall-magnetohydrodynamic (MHD) turbulence, carried out on a dataset of compressible nonlinear 2D Hall-MHD numerical simulations of decaying Alfvénic turbulence. For the first time, we identify two distinct regimes of fully developed turbulence. In the first one, the power spectrum of the turbulent magnetic fluctuations at sub-ion scales exhibits a power law with a slope of ∼−2.9, typically observed both in solar wind and in magnetosheath turbulence. The second regime, instead, shows a slope of −7/3, in agreement with classical theoretical models of Hall-MHD turbulence. A spectral-transfer analysis reveals that the latter regime occurs when the energy transfer rate at sub-ion scales is dominated by the Hall term, whereas in the former regime, the governing process is the dissipation (and the system exhibits large intermittency). Results of this work are relevant to the space plasma community, as they may potentially reconcile predictions from theoretical models with results from numerical simulations and spacecraft observations. Full article
(This article belongs to the Special Issue Turbulence and Energy Dissipation in Solar System Plasmas)
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21 pages, 4232 KiB  
Article
A Novel Method for Estimating the Intrinsic Magnetic Field Spectrum of Kinetic-Range Turbulence
by Alexander Pitňa, Jana Šafránková, Zdeněk Němeček, Luca Franci and Gilbert Pi
Atmosphere 2021, 12(12), 1547; https://doi.org/10.3390/atmos12121547 - 24 Nov 2021
Cited by 9 | Viewed by 2084
Abstract
Understanding plasma turbulence below the ion characteristic scales is one of the key open problems of solar wind physics. The bulk of our knowledge about the nature of the kinetic-scale fluctuations comes from the high-cadence measurements of the magnetic field. The spacecraft frame [...] Read more.
Understanding plasma turbulence below the ion characteristic scales is one of the key open problems of solar wind physics. The bulk of our knowledge about the nature of the kinetic-scale fluctuations comes from the high-cadence measurements of the magnetic field. The spacecraft frame frequencies of the sub-ion scale fluctuations are frequently around the Nyquist frequencies of the magnetic field sampling rate. Thus, the resulting ‘measured’ time series may significantly differ from the ‘true’ ones. It follows that second-order moments (e.g., power spectral density, PSD) of the signal may also be highly affected in both their amplitude and their slope. In this paper, we focus on the estimation of the PSD slope for finitely sampled data and we unambiguously define a so-called local slope in the framework of Continuous Wavelet Transform. Employing Monte Carlo simulations, we derive an empirical formula that assesses the statistical error of the local slope estimation. We illustrate the theoretical results by analyzing measurements of the magnetic field instrument (MFI) on board the Wind spacecraft. Our analysis shows that the trace power spectra of magnetic field measurements of MFI can be modeled as the sum of PSD of an uncorrelated noise and an intrinsic signal. We show that the local slope strongly depends on the signal-to-noise (S/N) ratio, stressing that noise can significantly affect the slope even for S/N around 10. Furthermore, we show that the local slopes below the frequency corresponding to proton inertial length, 5≳kλpi>1, depend on the level of the magnetic field fluctuations in the inertial range (Pin), exhibiting a gradual flattening from about −11/3 for high Pin toward about −8/3 for low Pin. Full article
(This article belongs to the Special Issue Turbulence and Energy Dissipation in Solar System Plasmas)
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16 pages, 1489 KiB  
Article
Spectra of Temperature Fluctuations in the Solar Wind
by Zdeněk Němeček, Jana Šafránková, František Němec, Tereza Ďurovcová, Alexander Pitňa, Benjamin L. Alterman, Yuriy M. Voitenko, Jiří Pavlů and Michael L. Stevens
Atmosphere 2021, 12(10), 1277; https://doi.org/10.3390/atmos12101277 - 30 Sep 2021
Cited by 4 | Viewed by 2331
Abstract
Turbulent cascade transferring the free energy contained within the large scale fluctuations of the magnetic field, velocity and density into the smaller ones is probably one of the most important mechanisms responsible for heating of the solar corona and solar wind, thus the [...] Read more.
Turbulent cascade transferring the free energy contained within the large scale fluctuations of the magnetic field, velocity and density into the smaller ones is probably one of the most important mechanisms responsible for heating of the solar corona and solar wind, thus the turbulent behavior of these quantities is intensively studied. The temperature is also highly fluctuating quantity but its variations are studied only rarely. There are probably two reasons, first the temperature is tensor and, second, an experimental determination of temperature variations requires knowledge of the full velocity distribution with an appropriate time resolution but such measurements are scarce. To overcome this problem, the Bright Monitor of the Solar Wind (BMSW) on board Spektr-R used the Maxwellian approximation and provided the thermal velocity with a 32 ms resolution, investigating factors influencing the temperature power spectral density shape. We discuss the question whether the temperature spectra determined from Faraday cups are real or apparent and analyze mutual relations of power spectral densities of parameters like the density, parallel and perpendicular components of the velocity and magnetic field fluctuations. Finally, we compare their spectral slopes with the slopes of the thermal velocity in both inertial and kinetic ranges and their evolution in course of solar wind expansion. Full article
(This article belongs to the Special Issue Turbulence and Energy Dissipation in Solar System Plasmas)
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17 pages, 1049 KiB  
Article
Flattening of the Density Spectrum in Compressible Hall-MHD Simulations
by Victor Montagud-Camps, František Němec, Jana Šafránková, Zdeněk Němeček, Andrea Verdini, Roland Grappin, Emanuele Papini and Luca Franci
Atmosphere 2021, 12(9), 1162; https://doi.org/10.3390/atmos12091162 - 10 Sep 2021
Cited by 2 | Viewed by 2031
Abstract
Observations of proton density fluctuations of the solar wind at 1 au have shown the presence of a decade-long transition region of the density spectrum above sub-ion scales, characterized by a flattening of the spectral slope. We use the proton density fluctuations data [...] Read more.
Observations of proton density fluctuations of the solar wind at 1 au have shown the presence of a decade-long transition region of the density spectrum above sub-ion scales, characterized by a flattening of the spectral slope. We use the proton density fluctuations data collected by the BMSW instrument on-board the Spektr-R satellite in order to delimit the plasma parameters under which the transition region can be observed. Under similar plasma conditions to those in observations, we carry out 3D compressible magnetohydrodynamics (MHD) and Hall-MHD numerical simulations and find that Hall physics is necessary to generate the transition region. The analysis of the kω power spectrum in the Hall-MHD simulation indicates that the flattening of the density spectrum is associated with fluctuations having frequencies smaller than the ion cyclotron frequency. Full article
(This article belongs to the Special Issue Turbulence and Energy Dissipation in Solar System Plasmas)
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