Characteristics Of Plasma Turbulence Research Articles

Exploring the influence of the ‘Smiley Sun’ on the dynamics of inner solar corona and near-Earth space environment

ABSTRACT The image captured by SDO/AIA (Solar Dynamics Observatory) in the 193 Å ultraviolet channel from 2022 October 25–27, unveiled a remarkable trio of dark coronal holes near the heliocentric equator, forming a distinctive smiling face. Serendipitously, during that period, coronal radio science experiments were being conducted using the Akatsuki spacecraft to investigate turbulence regimes in the inner-middle corona and track the acceleration of solar wind streams. By analysing Doppler frequency residuals, we derived valuable insights into plasma turbulence characteristics, estimated electron density fluctuations and flow speeds using isotropic quasi-static turbulence methods. The analysis consistently unveiled a shallow turbulence spectrum and flow speeds ranging from 180 to 400 km s−1 at heliocentric distances of 3–9 Rs. During this period, the solar wind flow speed, recorded at the L1 point near Earth, was of the order of 600–650 km s−1. This presented a unique opportunity to delve into turbulence within the inner corona and explore the mechanisms responsible for energizing and accelerating high-speed streams emanating from these trans-equatorial coronal holes. The study also suggests the innovative use of spacecraft signals as radio beacons for enhanced forecasting of potential space weather events triggered by Earth-directed high-speed solar wind streams.

Dependence of the Properties of a Turbulent Cascade behind the Bow Shock on the Dynamics of the Solar Wind Parameters

The magnetosheath is an integral element of solar–terrestrial relations. The paper analyzes the influence of the solar wind parameters and their variability, as well as the topology of the bow shock on the characteristics of plasma turbulence in the magnetosheath on scales corresponding to the transition from the inertial region of a turbulent cascade to the dissipative one. The analysis is based on extensive statistics of measurements of the BMSW instrument with high time resolution on board the Spektr-R satellite in the magnetosheath in 2011–2018. It is shown that the variability of the solar wind plasma density and the interplanetary magnetic field magnitude, as well as the angle between the normal to the bow shock and the interplanetary magnetic field has the greatest influence on the form of the turbulent cascade directly behind the bow shock.

Plasma Turbulence in the Local Bubble

Turbulence in the Local Bubble could play an important role in the thermodynamics of the gas that is there. This turbulence could also determine the transport of cosmic rays and perhaps heat flow through this phase of the interstellar medium. The best astronomical technique for measuring turbulence in astrophysical plasmas is radio scintillation. Scintillation measurements yield information on the intensity and spectral characteristics of plasma turbulence between the source of the radio waves and the observer. Measurements of the level of scattering to the nearby pulsar B0950+08 by Philips and Clegg in 1992 showed a markedly lower value for the line-of-sight averaged turbulent intensity parameter 〈C N 2 〉 than is observed for other pulsars, qualitatively consistent with radio wave propagation through a highly rarefied plasma. In this paper, we discuss the observational progress that has been made since that time. The main development has been improved measurements of pulsar parallaxes with the Very Long Baseline Array. This provides better knowledge of the media along the lines of sight. At present, there are four pulsars (B0950+08, B1133+16, J0437-4715, and B0809+74) whose lines of sight seem to lie mainly within the local bubble. The mean densities and line of sight components of the interstellar magnetic field along these lines of sight are smaller than nominal values for pulsars, but not by as large a factor as might be expected. Three of the four pulsars also have measurements of interstellar scintillation. The value of the parameter 〈C N 2 〉 is smaller than normal for two of them, but is completely nominal for the third. This inconclusive status of affairs could be improved by measurements and analysis of “arcs” in “secondary spectra” of pulsars, which contain information on the location and intensity of localized screens of turbulence along the lines of sight. Similar data could be obtained from observations of highly compact extragalactic radio sources which show the “intraday variability” phenomenon.

Characteristics of plasma turbulence and radio emission from an interplanetary shock wave

Aims. We investigate the characteristics of energetic electron beams, plasma turbulence and radio emission from interplanetary shock waves. Methods. Numerical calculations of spectra and Landau damping of hot plasma eigen oscillations in the magnetic field are used. Results. It is shown that the longitudinal wave spectrum, excited in the solar wind plasma, extends with the increase of the refractive index n over range of values n >10. This result allows us to explain the broad band of emission, the constant value of the average ratio of frequency-band to radio emission frequency from interplanetary shock wave fronts, and to estimate the electron beam density and amplitude of Langmuir waves at the shock. It is shown that a spectrum of radio emission is determined by the spectrum of Langmuir waves excited upstream of the interplanetary shock wave by heated electrons escaping from the shock wave front.

Properties of solar wind turbulence near the Sun as deduced from coronal radio sounding experiments

The characteristics of plasma turbulence in the inner solar wind, as deduced from radio frequency fluctuation measurements recorded during solar conjunction, are reviewed. Special emphasis is placed on results from the radio occultation experiments performed with the Galileo and Ulysses spacecraft in the interval 1991–2000. Estimates of the power spectral index are obtained over the range of heliocentric distances 5 R ⊙ < R < 80 R ⊙ and the radial evolution of this parameter is discussed. Low-heliolatitude data from Galileo are compared with high-heliolatitude data from Ulysses during the period of solar activity minimum. Unusual power spectra with a sharp break at high fluctuation frequencies are detected for the first time in the solar wind acceleration region. The observations are interpreted within the framework of a theoretical model based on local generation of density fluctuations via nonlinear interactions of Alfvén waves propagating away from the Sun.

Non-dimensional scaling of turbulence characteristics and turbulent diffusivity

Plasma turbulence characteristics, including radialcorrelation lengths, decorrelation times, amplitude profile and flowvelocity, have been measured during a ρ* scan on DIII-D while allother transport relevant dimensionless quantities (e.g., β, ν*, κ, q,Te/Ti) are held nearly constant. The turbulence is measured byexamining the correlation properties of the local long wavelength(k⊥ρi ⩽ 1) density fluctuations, measured with beam emissionspectroscopy. The radial correlation length of the turbulence Lc,ris shown to scale with the local ion gyroradius, Lc,r ≈ 5ρi,while the decorrelation times scale with the local acoustic velocityas τc∼a/cs. The turbulent diffusivity parameter, D∼(Lc,r2/τc), scalesin a roughly gyro-Bohm-like fashion, as predicted by the gyrokineticequations governing turbulent transport. The experimental one fluidpower balance heat diffusivity scaling and that from GLF23 modellingcompare reasonably well.