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Plasma velocity correlation with various indices of solar, cosmic ray and terrestrial activity measured during several solar rotations, using Mariner II spacecraft
There continue to be open questions regarding the solar wind and coronal mass ejections (CMEs). For example: how do magnetic fields within CMEs and corotating/stream interaction regions (CIRs/SIRs) evolve in the inner heliosphere? What is the radially distributed magnetic profile of shock-driving CMEs? What is the internal magnetic structure of CMEs that cause magnetic storms? It is clear that these questions involve the magnetic configurations of solar wind and transient interplanetary plasma structures, for which we have limited knowledge. In order to better understand the origin of the magnetic field variability in steady-state structures and transient events, it is necessary to probe the magnetic field in Earth-directed structures/disturbances. This is the goal of the Multiview Observatory for Solar Terrestrial Science (MOST) mission (Gopalswamy et al., 2022). For MOST to answer the aforementioned questions, we propose the instrument concept of the Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a simultaneous quad-line-of-sight polarization radio remote-sensing instrument. With FETCH, spacecraft radio beams passing through the Sun–Earth line offer the possibility of obtaining information of plasma conditions via analysis of radio propagation effects such as Faraday rotation and wave dispersion, which provide information of the magnetic field and total electron content (TEC). This is the goal of the FETCH instrument, one of ten instruments proposed to be hosted on the MOST mission. The MOST mission will provide an unprecedented opportunity to achieve NASA’s heliophysics science goal to “explore and characterize the physical processes in the space environment from the Sun” (Gopalswamy et al., 2022).
A general study of the structure and stability of intermediate shocks (IS) in an isotropic plasma is presented using a hybrid as well as a resistive Hall MHD code. Special emphasis is put on the question of whether the rotational layers observed at the magnetopause can be intermediate shocks. The shocks are formed dynamically by the interaction between a flowing plasma and a stationary piston. Coplanar ISs (both strong and weak) are found to be stable in a collisionless plasma. The existence of slow shocks in a high beta plasma is also established for the first time. Noncoplanar ISs are found to be time-dependent, evolving toward a rotational discontinuity (RD) after some characteristic time tau which can be quite long (1000 Omega(exp -1), where Omega is the ion gyrofrequency). The value tau is larger the closer the rotation angle is to 180 deg. Rotations larger than 180 deg are found to be unstable, decaying into a state of minimum shear (i.e., rotation angle less than 180 deg). There are various length scales associated with an IS in the kinetic regime. The shortest scale is found to be the length scale over which rotation of the transverse component of the magnetic field takes place. This scale can have a half width as small as one ion inertial length (c/omega(sub p)) for electron sense rotations and 3c/omega(sub p) for ion sense rotations, for an upstream ion beta of unity. Both of these scales are consistent with the observed thickness at the magnetopause and identical to the corresponding RD scales. A detailed study of the mode conversion of the Alfven ion cyclotron waves (A/IC) waves across both slow and intermediate shocks and the resulting downstream wave spectrum are presented. The possibility that the large number of relfected ions observed at the magnetopause may be due to the presence of strong ISs is considered. The identification of strong ISs and their distinction from RDs should be possible in observations due to significant differences that exist between jump conditions and overall structure of the two discontinuities. The jumps in the plasma parameters across a weak IS are typically small. This together with the fact that the weak ISs and RDs have very similar thickness and other overall properties makes the distinction between weak ISs and RDs in the observations largely inconsequential. However, at large noncoplanarity angles the weak IS approaches the RD limit in a relatively short time (approximately less than 100 Omega (exp -1)). Thus, magnetopause rotations with large noncoplanarity angles are most likely either RDs or strong ISs. Finally, direct comparisons between fluid (resistive Hall MHD) and kinetic simulations show that fluid theory is not applicable to study of ISs in a collisionless plasma.
We reinvestigate the generation and accumulation of magnetic flux in optically thin accretion flows around active gravitating objects. The source of the magnetic field is the azimuthal electric current associated with the Poynting-Robertson drag on the electrons of the accreting plasma. This current generates magnetic field loops which open up because of the differential rotation of the flow. We show through simple numerical simulations that what regulates the generation and accumulation of magnetic flux near the center is the value of the plasma conductivity. Although the conductivity is usually considered to be effectively infinite for the fully ionized plasmas expected near the inner edge of accretion disks, the turbulence of those plasmas may actually render them much less conducting due to the presence of anomalous resistivity. We have discovered that if the resistivity is sufficiently high throughout the turbulent disk while it is suppressed interior to its inner edge, an interesting steady-state process is established: accretion carries and accumulates magnetic flux of one polarity inside the inner edge of the disk, whereas magnetic diffusion releases magnetic flux of the opposite polarity to large distances. In this scenario, magnetic flux of one polarity grows and accumulates at a steady rate in the region inside the inner edge and up to the point of equipartition when it becomes dynamically important. We argue that this inward growth and outward expulsion of oppositely-directed magnetic fields that we propose may account for the approx. 30 min cyclic variability observed in the galactic microquasar GRS1915+105.
An investigation of the buoyancy of diffuse magnetic fields has shown that in the presence of rotation, static equilibrium configurations of the toroidal magnetic field and ambient plasma can exist. In that case, the escape of toroidal magnetic flux from the solar interior may be determined by the growth of instabilities which the equilibrium configuration may be subject to. In connection with the present investigation, it is assumed that in the region of toroidal magnetic flux amplification, the magnetic field has not as yet filamented into flux ropes, and is therefore 'diffuse'. A study is conducted of the MHD stability of an electrically conducting and differentially rotating gas in the presence of a toroidal magnetic field, an external constant gravitational field, and radiance pressure. The full dispersion relation for the magnetic buoyancy problem is developed, and the solutions of the dispersion relation are discussed.
Faraday rotation measurement of 13 cm telemetry carrier wave interacting with plasma and magnetic field in solar corona
The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.
The recurrent flow and field patterns observed by HELIOS 1, and the relation between these patterns and coronal holes are discussed. Four types of recurrent patterns were observed: a large recurrent stream, a recurrent slow (quiet) flow, a rapidly evolving flow, and a recurrent compound stream. There recurrent streams were not stationary, for although the sources recurred at approximately the same longitudes on successive rotations, the shapes and latitudinal patterns changed from one rotation to the next. A type of magnetic field and plasma structure characterized by a low ion temperature and a high magnetic field intensity is described as well as the structures of stream boundaries between the sun at approximately 0.3 AU.
A model is presented in which a plasma boundary layer of Jupiter is formed from plasma of internal origin. It is proposed that, unlike the Earth's boundary layer, which is thought to consist principally of solar wind plasma, Jupiter's boundary layer consists principally of sulphur and oxygen from the Io plasma torus, plus a small component of hydrogen from Jupiter's ionosphere. Fresh plasma is supplied to the boundary layer once each planetary rotation period by a convection pattern that rotates with Jupiter.
Recent work on the observation and theory of solar and stellar magnetic field activity and its relation to stellar activity is reviewed, emphasizing those aspects relevant to the problem of activity of red dwarf stars. New observational facts relevant to understanding the root cause of stellar surface activity are summarized and theoretical questions concerning the underlying physical basis for the observed correlations between stellar activity, rotation, and magnetic fields are addressed. These include dyanamo theory and the rotation-activity connection as well as flux tube dynamics and plasma heating.
The magnetic field control of Venus plasma 'clouds' relative to the planet has been analyzed by rotating the observed locations of the clouds into a coordinate system in which all of the transverse upstream magnetic fields were aligned. The results indicate that clouds are scattered around the periphery of the planet in the terminator plane. There is no evidence of a concentration of clouds where the magnetosheath magnetic field is most strongly 'draped'. On the other hand, statistics show that the change in the orientation of the transverse upstream magnetic field between the inbound and outbound bow shock crossings, for the orbits where clouds are seen is about 30 deg greater than the average upstream change at Venus over the same time intervals.
New observations of Jovian narrow-band kilometric (nKOM) radio emissions were made by the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft during the Ulysses-Jupiter encounter in early February 1992. These observations have demonstrated the unique capability of the URAP instrument for determining both the direction and polarization of nKOM radio sources. An important result is the discovery that nKOM radio emission originates from a number of distinct sources located at different Jovian longitudes and at the inner and outermost regions of the Io plasma torus. These sources have been tracked for several Jovian rotations, yielding their corotational lags, their spatial and temporal evolution, and their radiation characteristics at both low latitudes far from Jupiter and at high latitudes near the planet. Both right-hand and left-hand circularly polarized nKOM sources were observed. The polarizations observed for sources in the outermost regions of the torus seem to favor extraordinary mode emission.
We have studied the dynamics of a coalescence of current loops using three-dimensional electromagnetic (EM) particle simulation code. Our focus is the investigation of such kinetic processes as energy trasnfer, heating particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After the coalescence of two helical loops, tilting motions can be observed in the direction of left-hand rotation, and the helical structure will relax resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field. It is also shown that high-frequency electromagnetic waves can be emitted from the region where the two loops coalesce and propagate strongly in the direction of the electron drift velocity. These processes may be important in understanding heating mechansims for coronal loops as well as radio wave emission mechanisms from active regions of solar plasmas.
We examine the response of the high-latitude ionosphere in the prenoon sector to a northward turning of the IMF. The event was observed in the 11-13 UT interval on June 1, 1987, in the course of a multiday SUNDIAL campaign. The transition in the IMF was observed by the IMP-8 satellite which was located upstream of the earth at a distance of 36 Re. The ionospheric response in the 70-80 deg invariant latitude interval was monitored by two radars. The preexisting plasma convection observed by the radars exhibited large velocities (500-1000 m/s) and stable longterm trends, consistent with the inertial rotation of the convection pattern expected of the conditions then prevailing, B(z) less than 0, B(y) greater than 0. The plasma flow rapidly abated in response to the IMF transition. The electron density measurements made by radar in the meridional plane showed that the ionosphere had been rich in structure with the active deposition of ionization by particle precipitation. Subsequently it resembled an inactive, unstructured mid-latitude configuration. There was a dramatic decrease in the amount of backscatter observed by the HF radar. We analyze the times of transition in the various data sets and show that the ionosphere began to show the effects of the IMF transition about 2 min after its probable arrival at the magnetopause boundary.
The Voyager 1 plasma wave instrument detected many familiar types of plasma waves during the encounter with Saturn, including ion-acoustic waves and electron plasma oscillations upstream of the bow shock, an intense burst of electrostatic noise at the shock, and chorus, hiss, electrostatic electron cyclotron waves, and upper hybrid resonance emissions in the inner magnetosphere. A clocklike Saturn rotational control of low-frequency radio emissions was observed, and evidence was obtained of possible control by the moon Dione. Strong plasma wave emissions were detected at the Titan encounter indicating the presence of a turbulent sheath extending around Titan, and upper hybrid resonance measurements of the electron density show the existence of a dense plume of plasma being carried downstream of Titan by the interaction with the rapidly rotating magnetosphere of Saturn.
In the self-consistent model of the tangential magnetopause, formulated in the present paper on the basis of the Vlasov-Maxwell equations, the plasmas on both sides are magnetized and the magnetic field is everywhere parallel to the magnetopause (i.e., the normal field component is zero) and rotates through an arbitrary angle across the magnetopause. It is shown that the thickness of the magnetopause is greater than the gyroradius of the plasma ions. The presence of a trapped particle population within the magnetopause is shown to be required to allow the magnetic field to rotate more than a certain critical angle (-90 degrees). The model proposed can reproduce the observed features of the tangential magnetopause structure by specifying boundary conditions on both sides of the magnetopause.
The phenomenon of Faraday rotation of linearly polarized synchrotron emission in a magneto-ionized medium has been understood and studied for decades. But since the sense of the rotation itself is irrelevant in most contexts, some uncertainty and inconsistencies have arisen in the literature about this detail. Here, we start from basic plasma theory to describe the propagation of polarized emission from a background radio source through a magnetized, ionized medium in order to rederive the correct sense of Faraday rotation. We present simple graphics to illustrate the decomposition of a linearly polarized wave into right and left circularly polarized modes, the temporal and spatial propagation of the phases of those modes, and the resulting physical rotation of the polarization orientation. We then re-examine the case of a medium that both Faraday-rotates and emits polarized radiation and show how a helical magnetic field can construct or destruct the Faraday rotation. This paper aims to resolve a source of confusion that has arisen between the plasma physics and radio astronomy communities and to help avoid common pitfalls when working with this unintuitive phenomenon.
An axisymmetric hydrodynamic model of the sun consisting of a core at radiant equilibrium and a convective envelope is studied with consideration of gravitational forces, rotation, turbulence effects, and electromagnetic forces. The dimensionless parameters that control the equations of plasma motion within the sun and the boundary conditions are investigated; estimates are given for these parameters on the basis of experimental data and the existing theoretical models. Stability conditions are derived for convective equilibrium, developed cellular convection, and developed turbulent convection with consideration of rotation and turbulent Reynolds stresses. These conditions characterize the possible physical state of the matter in the convective envelope. Using estimates of the dimensionless parameters and models of some of them, a method of successive approximations is proposed for solution of the problem as a whole.