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 Diamagnetic structures as a basis of quasi-stationary slow solar wind

2019 ◽  
Vol 5 (3) ◽  
pp. 36-49
Author(s):  
Виктор Еселевич ◽  
Viktor Eselevich
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Plasma Density ◽  
Neutral Line ◽  
Angular Size ◽  
Radial Component ◽  
Slow Solar Wind ◽  
Small Scale ◽  
The Sun ◽  
Streamer Belt

The results presented in this review reflect the fundamentals of the modern understanding of the nature of the structure of the slow solar wind (SW) along the entire length from the Sun to the Earth's orbit. It is known that the source of the slow quasi-stationary SW on the Sun is the belt and the chains of coronal streamers The streamer belt encircles the entire Sun as a wave-like surface (skirt), representing a sequence of pairs of rays with increased brightness (plasma density) or two lines of rays located close to each other. Neutral line of the radial component of the solar global magnetic field goes along the belt between the rays of each of these pairs. The streamer belt extends in the heliosphere is as the heliospheric plasma sheet (HPS). Detailed analysis of data from Wind and IMP-8 satellites showed that HPS sections on the Earth orbit are registered as a sequence of diamagnetic tubes with high density plasma and low interplanetary magnetic field. They represent an extension of rays with increased brightness of the streamer belt near the Sun. Their angular size remains the same over the entire way from the Sun to the Earth's orbit. Each HPS diamagnetic tube has a fine internal structure on several scales, or fractality. In other words, diamagnetic tube is a set of nested diamagnetic tubes, whose angular size can vary by almost two orders of magnitude. These sequences of diamagnetic tubes that form the base of slow SW on the Earth's orbit has a more general name — diamagnetic structures (DS). In the final part of this article, a comparative analysis of several events was made, based on the results of this review. He made it possible to find out the morphology and nature of the origin of the new term “diamagnetic plasmoids” SW (local amplifications of plasma density), which appeared in several articles published during 2012–2018. The analysis carried out at the end of this article, for the first time, showed that the diamagnetic plasmoids SW are the small-scale component of the fractal diamagnetic structures of the slow SW, considered in this review.

Nature of Elsässer Variables in the slow solar wind turbulence

2020 ◽  
Author(s):  
Xin Wang ◽  
Chuanyi Tu ◽  
Jiansen He
Keyword(s):  
Solar Wind ◽  
Residual Energy ◽  
Slow Solar Wind ◽  
Cascade Process ◽  
Convective Structures ◽  
Solar Wind Turbulence ◽  
Horizontal Stratification ◽  
Wind Turbulence ◽  
Wind Spacecraft ◽  
Energy Plane

<p>Elsässer Variables z± are widely considered as outward and inward propagating Alfvén waves in the solar wind turbulence study. It is believed that they can interact nonlinearly with each other to generate energy cascade. However, z− variations sometimes show a feature of convective structures or a combination of white noise and pseudo-structures. Here we present the amplitude of z± in σc (normalized cross helicity) - σr (normalized residual energy) plane in order to get some information on the nature of z±. Measurements from the WIND spacecraft in the slow solar wind during 2007-2009 are used for analysis. In each interval with length of 20 min, we calculate σc, σr, and consider the variance of z± as the amplitude of them for the given interval. We find that in the σc-σr plane, the level contours of the average z- amplitude present a feature of nearly horizontal stratification, which means that the amplitude of z- is independent of the value of σc, and is just related to σr. The horizontal-stratification feature suggests that z- could be convective structures. While the level contours of the average amplitude of z+ are approximately concentric semicircles, and the circle with larger radius corresponds to larger z+ amplitude. It indicates that z+ represents Alfvén waves. The nature of z± in the slow wind here will help us to understand more about the cascade process in the solar wind turbulence.</p>

On the direction of the velocity and magnetic field fluctuations in undisturbed solar wind

2021 ◽  
Vol 30 (1) ◽  
pp. 184-190
Author(s):  
Dmitry V. Erofeev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Alfven Waves ◽  
High Solar Activity ◽  
Slow Solar Wind ◽  
Alfvén Waves ◽  
Velocity Fluctuations ◽  
Field Fluctuations

Abstract Measurements of velocity and magnetic field in near-Earth heliosphere is analized in order to investigate systematical deflection from transversality of the velocity and magnetic field fluctuations in undisturbed solar wind. Fluctuations occurred in the meridional plain of heliosphere (RN plain of the RTN reference system) are transversal with respect to mean magnetic field during periods of high solar activity, but they become non-transversal close to solar cycle minima. This phenomenon is investigated focusing on a role of Alfvén waves. It is shown that deflections from transversality is mostly expressed by fluctuations in slow solar wind streams with low contribution of Alfvén waves, whereas strongly Alfvénic turbulence undergo such deflection in a less degree. In addition, we consider orientation of velocity fluctuations in the azimuthal (RT) plain of heliosphere, which also indicates some interesting features.

scholarly journals Highly Alfvénic slow solar wind at 0.3 au during a solar minimum: Helios insights for Parker Solar Probe and Solar Orbiter

2020 ◽  
Vol 633 ◽  
pp. A166 ◽  
Author(s):  
D. Perrone ◽  
R. D’Amicis ◽  
R. De Marco ◽  
L. Matteini ◽  
D. Stansby ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Low Frequency ◽  
Intrinsic Property ◽  
Flow Speed ◽  
Local Magnetic Field ◽  
Slow Solar Wind ◽  
Magnetic Fluctuations ◽  
Origin And Evolution ◽  
Slow Wind

Alfvénic fluctuations in solar wind are an intrinsic property of fast streams, while slow intervals typically have a very low degree of Alfvénicity, with much more variable parameters. However, sometimes a slow wind can be highly Alfvénic. Here we compare three different regimes of solar wind, in terms of Alfvénic content and spectral properties, during a minimum phase of the solar activity and at 0.3 au. We show that fast and Alfvénic slow intervals share some common characteristics. This would suggest a similar solar origin, with the latter coming from over-expanded magnetic field lines, in agreement with observations at 1 au and at the maximum of the solar cycle. Due to the Alfvénic nature of the fluctuations in both fast and Alfvénic slow winds, we observe a well-defined correlation between the flow speed and the angle between magnetic field vector and radial direction. The high level of Alfvénicity is also responsible of intermittent enhancements (i.e. spikes), in plasma speed. Moreover, only for the Alfvénic intervals do we observe a break between the inertial range and large scales, on about the timescale typical of the Alfvénic fluctuations and where the magnetic fluctuations saturate, limited by the magnitude of the local magnetic field. In agreement with this, we recover a characteristic low-frequency 1/f scaling, as expected for fluctuations that are scale-independent. This work is directly relevant for the next solar missions, Parker Solar Probe and Solar Orbiter. One of the goals of these two missions is to study the origin and evolution of slow solar wind. In particular, Parker Solar Probe will give information about the Alfvénic slow wind in the unexplored region much closer to the Sun and Solar Orbiter will allow us to connect the observed physics to the source of the plasma.

Reversibility of Turbulent and Non-Collisional Plasmas: Solar Wind

2019 ◽  
Vol 15 (S354) ◽  
pp. 363-366
Author(s):  
Belén Acosta ◽  
Denisse Pastén ◽  
Pablo S. Moya
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
Solar Wind ◽  
Solar Wind Plasma ◽  
Magnetized Plasma ◽  
Slow Solar Wind ◽  
Magnetic Fluctuations ◽  
Particle In Cell ◽  
Leibler Divergence ◽  
Fast Wind

AbstractWe have studied turbulent plasma as a complex system applying the method known as Horizontal Visibility Graph (HVG) to obtain the Kullback-Leibler Divergence (KLD) as a first approach to characterize the reversibility of the time series of the magnetic fluctuations. For this, we have developed the method on Particle In Cell (PIC) simulations for a magnetized plasma and on solar wind magnetic time series, considering slow and fast wind. Our numerical results show that low irreversibility values are verified for magnetic field time series associated with Maxwellian distributions. In addition, considering the solar wind plasma, our preliminary results seem to indicate that greater irreversibility degrees are reached by the magnetic field associated with slow solar wind.

scholarly journals Diamagnetic structures as a basis of quasi-stationary slow solar wind

2019 ◽  
Vol 5 (3) ◽  
pp. 29-41 ◽  
Author(s):  
Виктор Еселевич ◽  
Viktor Eselevich
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Plasma Density ◽  
Neutral Line ◽  
Angular Size ◽  
Radial Component ◽  
Slow Solar Wind ◽  
Small Scale ◽  
The Sun ◽  
Streamer Belt

The results presented in this review reflect the fundamentals of the modern understanding of the nature of the structure of the slow solar wind (SW) along the entire length from the Sun to the Earth's orbit. It is known that the source of the slow quasi-stationary SW on the Sun is the belt and the chains of coronal streamers The streamer belt encircles the entire Sun as a wave-like surface (skirt), representing a sequence of pairs of rays with increased brightness (plasma density) or two lines of rays located close to each other. Neutral line of the radial component of the solar global magnetic field goes along the belt between the rays of each of these pairs. The streamer belt extends in the heliosphere is as the heliospheric plasma sheet (HPS). Detailed analysis of data from Wind and IMP-8 satellites showed that HPS sections on the Earth orbit are registered as a sequence of diamagnetic tubes with high density plasma and low interplanetary magnetic field. They represent an extension of rays with increased brightness of the streamer belt near the Sun. Their angular size remains the same over the entire way from the Sun to the Earth's orbit. Each HPS diamagnetic tube has a fine internal structure on several scales, or fractality. In other words, diamagnetic tube is a set of nested diamagnetic tubes, whose angular size can vary by almost two orders of magnitude. These sequences of diamagnetic tubes that form the base of slow SW on the Earth's orbit has a more general name — diamagnetic structures (DS). In the final part of this article, a comparative analysis of several events was made, based on the results of this review. He made it possible to find out the morphology and nature of the origin of the new term “diamagnetic plasmoids” SW (local amplifications of plasma density), which appeared in several articles published during 2012–2018. The analysis carried out at the end of this article, for the first time, showed that the diamagnetic plasmoids SW are the small-scale component of the fractal diamagnetic structures of the slow SW, considered in this review.

scholarly journals Experimental and numerical investigation of plasma parameters in the magnetosheath

2018 ◽  
Vol 145 ◽  
pp. 03003
Author(s):  
Polya Dobreva ◽  
Monio Kartalev ◽  
Olga Nitcheva ◽  
Natalia Borodkova ◽  
Georgy Zastenker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Numerical Investigation ◽  
Euler Equations ◽  
Ideal Gas ◽  
Bow Shock ◽  
Plasma Parameters ◽  
Wind Spacecraft ◽  
The Magnetic Field ◽  
Good Agreement

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.

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>

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