What can Hall-MHD simulations tell us about the transition region in the solar wind proton density spectrum?

2020 ◽  
Author(s):  
Victor Montagud-Camps ◽  
František Němec ◽  
Jana Šafránková ◽  
Zdeněk Němeček ◽  
Roland Grappin ◽  
...  
Keyword(s):  
Solar Wind ◽  
Transition Region ◽  
Spectral Index ◽  
Density Fluctuations ◽  
Power Density Spectrum ◽  
Proton Density ◽  
Density Spectrum ◽  
Significant Difference ◽  
Field Fluctuations ◽  
Hall Mhd

<p>Similarly to the power density spectrum of magnetic field fluctuations in the solar wind, the spectrum of density fluctuations also shows multiple spectral slopes. Both of them present a spectral index varying between –3/2 and –5/3 in the inertial range and close to –2.8 between the proton and electron gyrofrequencies.</p><p>Despite these similarities, the spectrum of density fluctuations has a significant difference with respect to the magnetic and velocity fluctuations spectra: it shows a transition region between the inertial and the kinetic ranges with spectral index typically around –1.</p><p>We have combined the results of compressible Hall-MHD numerical simulations and measurements of the BMSW instrument onboard Spektr-R satellite to study the possible causes of the flattening in the density spectrum. Both numerical and experimental approaches point towards an important role played by Kinetic Alfvén Waves.</p>

scholarly journals Flattening of the Density Spectrum in Compressible Hall-MHD Simulations

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1162
Author(s):  
Victor Montagud-Camps ◽  
František Němec ◽  
Jana Šafránková ◽  
Zdeněk Němeček ◽  
Andrea Verdini ◽  
...  
Keyword(s):  
Transition Region ◽  
Cyclotron Frequency ◽  
Density Fluctuations ◽  
Proton Density ◽  
Spectral Slope ◽  
Plasma Parameters ◽  
Mhd Simulation ◽  
Density Spectrum ◽  
Mhd Simulations ◽  
Hall Mhd

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.

Mutual Iinformation exchange in solar wind density fluctuations

2020 ◽  
Author(s):  
Luca Sorriso-Valvo ◽  
Francesco Carbone ◽  
Daniele Telloni
Keyword(s):  
Solar Wind ◽  
Mutual Information ◽  
Information Flow ◽  
Information Exchange ◽  
Turbulent Energy ◽  
Density Fluctuations ◽  
Slow Solar Wind ◽  
Proton Density ◽  
Mode Decomposition ◽  
Turbulent Cascade

<p>The fluctuations of proton density in the slow solar wind are analyzed by means of joint Empirical Mode Decomposition (EMD) and Mutual Information (MI) analysis. The analysis reveal that, within the turbulent inertial range, the EMD modes associated with nearby scales have their phases correlated, as shown by the large information exchange. This is a qunatitative measure of the information flow occurring in the turbulent cascade. On the other hand, at scales smaller than the ion gyroscale, the information flow is lost, and the mutual information is low, suggesting that in the kinetic range the nonlinear interacions are no longer sustaining a turbulent energy cascade.</p>

scholarly journals Turbulent spectra in the solar wind plasma

2009 ◽  
Vol 76 (2) ◽  
pp. 183-191 ◽  
Author(s):  
DASTGEER SHAIKH ◽  
G. P. ZANK
Keyword(s):  
Solar Wind ◽  
Three Dimensional ◽  
Solar Wind Plasma ◽  
Density Fluctuations ◽  
Magnetized Plasma ◽  
Density Spectrum ◽  
Turbulent Spectrum ◽  
Extended Length ◽  
Turbulent Spectra ◽  
Magnetohydrodynamic Fluid

AbstractObservations of interstellar scintillations at radio wavelengths reveal a Kolmogorov-like scaling of the electron density spectrum with a spectral slope of −5/3 over six decades in wavenumber space. A similar turbulent density spectrum in the solar wind plasma has been reported. The energy transfer process in the magnetized solar wind plasma over such extended length scales remains an unresolved paradox of modern turbulence theories, raising the especially intriguing question of how a compressible magnetized solar wind exhibits a turbulent spectrum that is a characteristic of an incompressible hydrodynamic fluid. To address these questions, we have undertaken three-dimensional time-dependent numerical simulations of a compressible magnetohydrodynamic fluid describing super-Alfvénic, supersonic and strongly magnetized plasma. It is shown that the observed Kolmogorov-like (−5/3) spectrum can develop in the solar wind plasma by supersonic plasma motions that dissipate into highly subsonic motion that passively convect density fluctuations.

The power density spectrum break in an Alfven wave-driven solar wind

1994 ◽  
Vol 432 ◽  
pp. 409 ◽  
Author(s):  
V. Jatenco-Pereira ◽  
R. Opher ◽  
L. C. Yamamoto
Keyword(s):  
Solar Wind ◽  
Power Density ◽  
Alfven Wave ◽  
Power Density Spectrum ◽  
Density Spectrum

Sub-ion scale measurements of compressible turbulence in the solar wind MMS Observations

2020 ◽  
Author(s):  
Owen Roberts ◽  
Rumi Nakamura ◽  
Yasuhito Narita ◽  
Justin Holmes ◽  
Zoltan Voros ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Power Spectrum ◽  
Electron Density ◽  
Field Measurements ◽  
Small Region ◽  
Density Fluctuations ◽  
Compressible Turbulence ◽  
Density Spectrum ◽  
Spacecraft Potential

<p>Compressible plasma turbulence is investigated at sub ion scales using both the Fast Plasma Investigation instrument on the Magnetospheric MultiScale mission as well as using calibrated spacecraft potential. The data from FPI allow inertial and a small region of sub-ion scales to be investigated before the instrumental noise becomes significant near 3Hz. In this work we give a detailed description of the spacecraft potential and how it is calibrated such that it can be used the measure the electron density. The key advantage of using the calibrated spacecraft potential is that a much higher time resolution is possible when compared to the direct measurement. This allows a measurement down to 40Hz for a measurement of the electron density. This is an improvement of an additional decade in scale. Using a one hour interval of solar wind burst mode data the power spectrum of the density fluctuations is measured from the inertial range to the sub ion range. At inertial scales the density spectrum shows similarities with the magnetic field power spectrum with a characteristic Kolmogorov like power law. In between the ion inertial and kinetic scales there is a brief flattening in the spectra before steepening in the sub ion range to a spectral index comparable to the trace magnetic field fluctuations. The morphology if the density spectra can be explained by either a cascade of Alfv\'en waves and slow waves at large scales and kinetic Alfv\'en waves at sub ion scales, or by the presence of the hall effect. Using electric field measurements the two hypotheses are tested.</p>

scholarly journals Stratified Kelvin–Helmholtz turbulence of compressible shear flows

2018 ◽  
Vol 25 (2) ◽  
pp. 457-476 ◽  
Author(s):  
Omer San ◽  
Romit Maulik
Keyword(s):  
Power Density ◽  
Spatial Resolution ◽  
Shear Flows ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Compressible Turbulence ◽  
Power Density Spectrum ◽  
Two Dimensional ◽  
Density Spectrum ◽  
Significant Difference

Abstract. We study scaling laws of stratified shear flows by performing high-resolution numerical simulations of inviscid compressible turbulence induced by Kelvin–Helmholtz instability. An implicit large eddy simulation approach is adapted to solve our conservation laws for both two-dimensional (with a spatial resolution of 16 3842) and three-dimensional (with a spatial resolution of 5123) configurations utilizing different compressibility characteristics such as shocks. For three-dimensional turbulence, we find that both the kinetic energy and density-weighted energy spectra follow the classical Kolmogorov k-5/3 inertial scaling. This phenomenon is observed due to the fact that the power density spectrum of three-dimensional turbulence yields the same k-5/3 scaling. However, we demonstrate that there is a significant difference between these two spectra in two-dimensional turbulence since the power density spectrum yields a k-5/3 scaling. This difference may be assumed to be a reason for the k-7/3 scaling observed in the two-dimensional density-weight kinetic every spectra for high compressibility as compared to the k−3 scaling traditionally assumed with incompressible flows. Further inquiries are made to validate the statistical behavior of the various configurations studied through the use of the Helmholtz decomposition of both the kinetic velocity and density-weighted velocity fields. We observe that the scaling results are invariant with respect to the compressibility parameter when the density-weighted definition is used. Our two-dimensional results also confirm that a large inertial range of the solenoidal component with the k−3 scaling can be obtained when we simulate with a lower compressibility parameter; however, the compressive spectrum converges to k−2 for a larger compressibility parameter.

Electric Field Turbulence in the Solar Wind from MHD down to Electron Scales: Artemis Observations

2020 ◽  
Author(s):  
Chadi Salem ◽  
John Bonnell ◽  
Jordan Huang ◽  
Elizabeth Hanson ◽  
Christopher Chaston ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Solar Wind Speed ◽  
Theoretical Work ◽  
Density Fluctuations ◽  
Time Intervals ◽  
Reasonable Range ◽  
Field Fluctuations ◽  
Temporal And Spatial

<p>Recent observational and theoretical work on solar wind turbulence and dissipation suggests that kinetic-scale fluctuations are both heating and isotropizing the solar wind during transit to 1 AU.  The nature of these fluctuations and associated heating processes are poorly understood. Whatever the dissipative process that links the fields and particles - Landau damping, cyclotron damping, stochastic heating, or energization through coherent structures - heating and acceleration of ions and electrons occurs because of electric field fluctuations. The dissipation due to the fluctuations depends intimately upon the temporal and spatial variations of those fluctuations in the plasma frame.<span>  </span>In order to derive that distribution in the plasma frame, one must also use magnetic field and density fluctuations, in addition to electric field fluctuations, as measured in the spacecraft frame (s/c) to help constrain the type of fluctuation and dissipation mechanisms that are at play.</p><p>We present here an analysis of electromagnetic fluctuations in the solar wind from MHD scales down to electron scales based on data from the Artemis spacecraft at 1 AU. We focus on a few time intervals of pristine solar wind, covering a reasonable range of solar wind properties (temperature ratios and anisotropies; plasma beta; and solar wind speed). We analyze magnetic, electric field, and density fluctuations from the 0.01 Hz (well in the inertial range) up to 1 kHz. We compute parameters such as the electric to magnetic field ratio, the magnetic compressibility, magnetic helicity, compressibility and other relevant quantities in order to diagnose the nature of the fluctuations at those scales between the ion and electron cyclotron frequencies, extracting information on the dominant modes composing the fluctuations. We also use the linear Vlasov-Maxwell solver, PLUME, to determine the various relevant modes of the plasma with parameters from the observed solar wind intervals. We discuss the results and the relevant modes as well as the major differences between our results in the solar wind and results in the magnetosheath.</p>

scholarly journals On the ion-inertial-range density-power spectra in solar wind turbulence

2019 ◽  
Vol 37 (2) ◽  
pp. 183-199 ◽  
Author(s):  
Rudolf A. Treumann ◽  
Wolfgang Baumjohann ◽  
Yasuhito Narita
Keyword(s):  
Solar Wind ◽  
Source Region ◽  
Power Spectra ◽  
Density Fluctuations ◽  
Inertial Range ◽  
Wave Number ◽  
Mean Flow ◽  
Pressure Balance ◽  
Density Spectrum ◽  
Velocity Turbulence

Abstract. A model-independent first-principle first-order investigation of the shape of turbulent density-power spectra in the ion-inertial range of the solar wind at 1 AU is presented. Demagnetised ions in the ion-inertial range of quasi-neutral plasmas respond to Kolmogorov (K) or Iroshnikov–Kraichnan (IK) inertial-range velocity–turbulence power spectra via the spectrum of the velocity–turbulence-related random-mean-square induction–electric field. Maintenance of electrical quasi-neutrality by the ions causes deformations in the power spectral density of the turbulent density fluctuations. Assuming inertial-range K (IK) spectra in solar wind velocity turbulence and referring to observations of density-power spectra suggest that the occasionally observed scale-limited bumps in the density-power spectrum may be traced back to the electric ion response. Magnetic power spectra react passively to the density spectrum by warranting pressure balance. This approach still neglects contribution of Hall currents and is restricted to the ion-inertial-range scale. While both density and magnetic turbulence spectra in the affected range of ion-inertial scales deviate from K or IK power law shapes, the velocity turbulence preserves its inertial-range shape in the process to which spectral advection turns out to be secondary but may become observable under special external conditions. One such case observed by WIND is analysed. We discuss various aspects of this effect, including the affected wave-number scale range, dependence on the angle between mean flow velocity and wave numbers, and, for a radially expanding solar wind flow, assuming adiabatic expansion at fast solar wind speeds and a Parker dependence of the solar wind magnetic field on radius, also the presumable limitations on the radial location of the turbulent source region.

Calcium-Suppressed Technique in Dual-Layer Detector Computed Tomography to Evaluate Knee Articular Cartilage

2020 ◽  
Vol 16 ◽  
Author(s):  
Qinglin Meng ◽  
Mengqi Liu ◽  
Weiwei Deng ◽  
Ke Chen ◽  
Botao Wang ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Bone Marrow ◽  
Articular Cartilage ◽  
Bone Marrow Edema ◽  
Knee Joints ◽  
Infrapatellar Fat Pad ◽  
Proton Density ◽  
Knee Cartilage ◽  
Significant Difference ◽  
Marrow Edema

Background: Calcium-suppressed (CaSupp) technique involving spectral-based images has been used to observe bone marrow edema by removing calcium components from the image. Objective: This study aimed to evaluate the knee articular cartilage using the CaSupp technique in dual-layer detector computed tomography (DLCT). Methods: Twenty-eight healthy participants and two patients with osteoarthritis were enrolled, who underwent DLCT and magnetic resonance imaging (MRI) examination. CaSupp images were reconstructed from spectral-based images using a calcium suppression algorithm and were overlaid conventional CT images for visual evaluation. The morphology of the knee cartilage was evaluated, and the thickness of the articular cartilage was measured on sagittal proton density– weighted and CaSupp images in the patellofemoral compartment. Results: No abnormal signal or density, cartilage defect, and subjacent bone ulceration were observed in the lateral and medial femorotibial compartments and the patellofemoral compartment on MRI images and CaSupp images for the 48 normal knee joints. CaSupp images could clearly identify cartilage thinning, defect, subjacent bone marrow edema, and edema of the infrapatellar fat pad in the same way as MRI images in the three knee joints with osteoarthritis. A significant difference was found in the mean thickness of the patellar cartilage between MRI images and CaSupp images, while the femoral cartilage presented no significant difference in thickness between MRI images and CaSupp images over all 48 knee joints. Conclusion: The present study demonstrated that CaSupp images could effectively be used to perform the visual and quantitative assessment of knee cartilage.

scholarly journals Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 25
Author(s):  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Kaushik Chatterjee ◽  
Riya Bhowmick ◽  
Sujoy Kumar Nath ◽  
...  
Keyword(s):  
Black Hole ◽  
Temporal Analysis ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Telescope Array ◽  
Density Spectrum ◽  
X Ray ◽  
Black Hole Candidate ◽  
Short Period ◽  
Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

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