Analysis of Alfvénic flows with Solar Orbiter: particle and magnetic observations down to kinetic scales.

2021 ◽  
Author(s):  
Philippe Louarn ◽  
Andrei fedorov ◽  
alexis Rouillard ◽  
Benoit Lavraud ◽  
Vincent Génot ◽  
...  
Keyword(s):  
Solar Wind ◽  
Fine Structure ◽  
Time Resolution ◽  
Time Scale ◽  
Residual Energy ◽  
Distribution Functions ◽  
Strongly Correlated ◽  
Temperature Anisotropy ◽  
Velocity Fluctuations ◽  
Turbulence Parameters

<p>The magnetic and velocity fluctuations of the solar wind may be strongly correlated. This characterizes the  ‘Alfvenic’ flows. Using the observations of the Proton Alfa sensor (PAS/SWA) and the magnetometer (MAG) onboard Solar Orbiter, we analyze a period of 100 hours of such alfvenic flows, at different scales. Several parameters of the turbulence are computed (V-B correlation, various spectral indexes, cross-helicity, residual energy). We explore how these parameters may vary with time and characterize different turbulent states of the flow. More specifically, using the unprecedented time resolution of PAS during burst mode, especially its capability to measure 3D distribution functions at time scale below the proton gyroperiod, we study the connection of the turbulence to the dissipation domain and analyze the fine structure of the distribution functions and their evolutions at sub-second scales. The goal is to investigate whether some characteristics of the distributions, as their more or less pronounced temperature anisotropy, may be related to the turbulence parameters and the degree of V-B correlation.</p>

scholarly journals A short-lived flare of EV Lacertae

1990 ◽  
Vol 137 ◽  
pp. 35-36
Author(s):  
B. E. Zhilyaev ◽  
Ya. O. Romanjuk ◽  
O. A. Svyatogorov
Keyword(s):  
Fine Structure ◽  
Light Curve ◽  
Time Resolution ◽  
Time Scale ◽  
High Time ◽  
High Time Resolution ◽  
Decay Times ◽  
Ev Lac

Flare events on a time scale of the order of one second were observed on EV Lac by Gershberg and Petrov [1], Zalinian and Tovmassian [2], Tsvetkov, Antov and Tsvetkova [3]. The nature of such phenomena is very mysterious. We hope that monitoring of EV Lac with high time resolution will yield the information about growing and decay times as well as fine structure of the light curve and color one. A short-lived flare of EV Lac was recorded in U and V bands in 1989, September 3 2h 14m 30s UT. The duration of the event was about 150 milliseconds.

Fine structure of the interplanetary shock front according to measurements of the ion flux of the solar wind with high time resolution

2017 ◽  
Vol 55 (1) ◽  
pp. 30-45 ◽  
Author(s):  
V. G. Eselevich ◽  
N. L. Borodkova ◽  
M. V. Eselevich ◽  
G. N. Zastenker ◽  
Y. Šafránkova ◽  
...  
Keyword(s):  
Solar Wind ◽  
Fine Structure ◽  
Shock Front ◽  
Time Resolution ◽  
Interplanetary Shock ◽  
Ion Flux ◽  
High Time ◽  
High Time Resolution

scholarly journals Combined electron firehose and electromagnetic ion cyclotron instabilities: quasilinear approach

2020 ◽  
Vol 499 (1) ◽  
pp. 659-667
Author(s):  
Z Ali ◽  
M Sarfraz ◽  
P H Yoon
Keyword(s):  
Solar Wind ◽  
Dynamical Evolution ◽  
Solar Wind Plasma ◽  
Distribution Functions ◽  
Temperature Anisotropy ◽  
Spatial And Temporal Scales ◽  
Proton Temperature ◽  
Ion Cyclotron ◽  
Velocity Distribution Functions ◽  
High Beta

ABSTRACT Various plasma waves and instabilities are abundantly present in the solar wind plasma, as evidenced by spacecraft observations. Among these, propagating modes and instabilities driven by temperature anisotropies are known to play a significant role in the solar wind dynamics. In situ measurements reveal that the threshold conditions for these instabilities adequately explain the solar wind conditions at large heliocentric distances. This paper pays attention to the combined effects of electron firehose instability driven by excessive parallel electron temperature anisotropy (T⊥e < T∥e) at high beta conditions, and electromagnetic ion cyclotron instability driven by excessive perpendicular proton temperature anisotropy (T⊥i > T∥i). By employing quasilinear kinetic theory based upon the assumption of bi-Maxwellian velocity distribution functions for protons and electrons, the dynamical evolution of the combined instabilities and their mutual interactions mediated by the particles is explored in depth. It is found that while in some cases, the two unstable modes are excited and saturated at distinct spatial and temporal scales, in other cases, the two unstable modes are intermingled such that a straightforward interpretation is not so easy. This shows that when the dynamics of protons and electrons are mutually coupled and when multiple unstable modes are excited in the system, the dynamical consequences can be quite complex.

scholarly journals Adaptive Critical Balance and Firehose Instability in an Expanding, Turbulent, Collisionless Plasma

2021 ◽  
Vol 922 (2) ◽  
pp. L35
Author(s):  
A. F. A. Bott ◽  
L. Arzamasskiy ◽  
M. W. Kunz ◽  
E. Quataert ◽  
J. Squire
Keyword(s):  
Collisionless Plasma ◽  
Residual Energy ◽  
Distribution Functions ◽  
Magnetized Plasma ◽  
Marginal Stability ◽  
Anomalous Scattering ◽  
Magnetic Fluctuations ◽  
Temperature Anisotropy ◽  
Ion Distribution ◽  
Spatial Anisotropy

Abstract Using a hybrid-kinetic particle-in-cell simulation, we study the evolution of an expanding, collisionless, magnetized plasma in which strong Alfvénic turbulence is persistently driven. Temperature anisotropy generated adiabatically by the plasma expansion (and consequent decrease in the mean magnetic-field strength) gradually reduces the effective elasticity of the field lines, causing reductions in the linear frequency and residual energy of the Alfvénic fluctuations. In response, these fluctuations modify their interactions and spatial anisotropy to maintain a scale-by-scale “critical balance” between their characteristic linear and nonlinear frequencies. Eventually the plasma becomes unstable to kinetic firehose instabilities, which excite rapidly growing magnetic fluctuations at ion-Larmor scales. The consequent pitch-angle scattering of particles maintains the temperature anisotropy near marginal stability, even as the turbulent plasma continues to expand. The resulting evolution of parallel and perpendicular temperatures does not satisfy double-adiabatic conservation laws, but is described accurately by a simple model that includes anomalous scattering. Our results have implications for understanding the complex interplay between macro- and microscale physics in various hot, dilute, astrophysical plasmas, and offer predictions concerning power spectra, residual energy, ion-Larmor-scale spectral breaks, and non-Maxwellian features in ion distribution functions that may be tested by measurements taken in high-beta regions of the solar wind.

scholarly journals Magnetic and Velocity Fluctuations in the Near-Sun Region from 0.1−0.3 au Observed by Parker Solar Probe

2021 ◽  
Vol 922 (2) ◽  
pp. 92
Author(s):  
Honghong Wu ◽  
Chuanyi Tu ◽  
Xin Wang ◽  
Liping Yang
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Component ◽  
Residual Energy ◽  
Slow Solar Wind ◽  
Magnetic Fluctuations ◽  
Velocity Fluctuations ◽  
Observational Uncertainty ◽  
Wind Spacecraft ◽  
Alignment Structure

Abstract The fluctuations observed in the slow solar wind at 1 au by the WIND spacecraft are shown by recent studies to consist of mainly magnetic-field directional turning and magnetic-velocity alignment structure (MVAS). How these structures are created has been a question because the nature of the fluctuations in the near-Sun region remains unknown. Here, we present an analysis of the measurements in the slow solar wind from 0.1−0.3 au by Parker Solar Probe during its first six orbits. We present the distributions in the C vb ′ – σ r plane of both the occurrence and average amplitudes of the fluctuations, including the magnetic field, the velocity, and the Elsässer variables, where C vb ′ is the correlation coefficient between the magnetic and velocity fluctuations multiplied by the opposite sign of the radial component of the mean magnetic field and σ r is the normalized residual energy. We find that the dominant composition is the outward-propagating Alfvénic fluctuations. We find Alfvénic fluctuations with C vb ′ > 0.95 , in which the amplitudes of z + reach 60 km s−1 and those of z − are close to the observational uncertainty. We also find a region with high C vb ′ and moderate minus σ r in which the fluctuations are considered MVAS being magnetic dominated with the amplitude of magnetic fluctuations reaching 60 km s−1. We provide empirical relations between the velocity fluctuation amplitude and C vb ′ . The comparison between these results and those observed at 1 au may provide some clues as to the nature and evolution of the fluctuations.

scholarly journals Fine Structure and Dynamics of the Inner Corona

1977 ◽  
Vol 43 ◽  
pp. 9-9
Author(s):  
G.E. Brueckner ◽  
J.D.F. Bartoe ◽  
M.E. VanHoosier
Keyword(s):  
Solar Wind ◽  
Fine Structure ◽  
Thermal Energy ◽  
Column Density ◽  
Line Profiles ◽  
Quiet Sun ◽  
Structure And Dynamics ◽  
Fine Structures ◽  
The Doppler Effect ◽  
Average Size

High spectral (0,05 Å) and spatial (⋍ 1000 km) resolution spectra of the Fe XII line 1349.4 Å reveal the existence of coronal fine structures in the quiet sun against the solar disk. These coronal bright elements have an average size of 2000-3000 km; their column density can be 3 x 1017 cm –2 . In the quiet sun, outward streaming velocities of 10-15 km sec –1 can be measured by means of the Doppler effect. The total kinetic and thermal energy of the outstreaming gas can be estimated to be larger than 1 x 10 5 ergs cm –2 sec –1, enough to account for the heating of the corona and the losses of the solar wind. At the outer limb (cos θ ⋍0.1) line profiles show a strong blue asymmetry, which could be caused by expanding material in a piston-driven shock, whereby the opaque, cool piston causes the asymmetry of the line profile.

Tsallis Distribution Functions in the Solar Wind: Magnetic Field and Velocity Observations

2007 ◽  
Author(s):  
Leonard F. Burlaga ◽  
Adolfo F. Viñas ◽  
Sumiyoshi Abe ◽  
Hans Herrmann ◽  
Piero Quarati ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Distribution Functions ◽  
Solar Wind Magnetic Field ◽  
Tsallis Distribution

scholarly journals Uncertainties of the solar wind in-situ velocity measurements

2020 ◽  
pp. 193-197
Author(s):  
G. Gogoberidze ◽  
E. Gorgaslidze
Keyword(s):  
Solar Wind ◽  
Independent Method ◽  
Inertial Range ◽  
Velocity Measurements ◽  
Fast Solar Wind ◽  
Magnetohydrodynamic Turbulence ◽  
Velocity Fluctuations ◽  
Measurement Uncertainties ◽  
General Instrument

We study spectral features of Alfvénic turbulence in fast solar wind. We propose a general, instrument independent method to estimate the uncertainty in velocity fluctuations obtained by in-situ satellite observations in the solar wind. We show that when the measurement uncertainties of the velocity fluctuations are taken into account the less energetic Elsasser spectrum obeys a unique power law scaling throughout the inertial range as prevailing theories of magnetohydrodynamic turbulence predict.

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