Solar Surface Boundary Research Articles

Effects of negative ions on equilibrium solar plasmas in the fabric of gravito-electrostatic sheath model

The gravito-electrostatic sheath (GES) model, exploring the solar wind plasma (SWP) origin from the solar interior plasma (SIP) via the solar surface boundary (SSB), is revaluated by including realistic negative ionic species. A constructive numerical analysis of the structuring equations shows that the SIP volume shrinks with an increase in the negative ion concentration. This shrinking nature is independent of ion mass and plasma temperature. The electric potential is insensitive to the negative ion concentration, mass, and plasma temperature. The solar plasma flow dynamics is studied with the Mach number and current density profiles. The sonic transition of the SWP depends on the Ti/Te-ratio. The current density responds to the negative ion density and Ti/Te−ratio in both the SIP and SWP. A deviation from the local quasi-neutrality state is observed in the SIP. The GES model equations result in a modified GES-Bohm sheath criterion in a well justifiable and validated form. The obtained results are then compared with the various observed outcomes and previous GES-based predictions. The relevance of this multi-parametric solar plasma analysis is lastly emphasized on the basis of the current solar research progressions.

A theoretic analysis of magnetoactive GES-based turbulent solar plasma instability

ABSTRACT A recently reported gravito-electrostatic sheath (GES) model is procedurally applied to study the turbumagnetoactive helioseismic oscillation features in the entire bi-fluidic solar plasma system. The bounded solar interior plasma (SIP, internally self-gravitating), and the unbounded solar wind plasma (SWP, externally point-gravitating) are coupled through the interfacial diffused solar surface boundary (SSB) due to an exact gravito-electrostatic interplay. A numerical platform on the developed theoretic formalism reveals the evolution of both dispersive and non-dispersive features of the modified GES mode fluctuations in new parametric windows. Different colourspectral profiles exhibit important features of the GES-based SIP–SWP perturbations elaborately. It is illustratively shown that the thermostatistical GES stability depends mainly on the radial distance, magnetic field, equilibrium plasma density, and plasma temperature. We see that their dispersive features are more pertinently pronounced in the self-gravitational domains (SIP) than the electrostatic counterparts (SWP). Besides, different characteristic parameters with accelerating (or decelerating) and stabilizing (or destabilizing) effects influencing the entire solar plasma stability are illustratively portrayed. We speculate that, in the SIP, the long-wave (gravitational-like) helioseismic fluctuations become highly dispersive showing more propagatory nature than the shorter ones (acoustic-like). The short waves show more propagatory propensity than the longer ones in the SSB and SWP regime. The reliability of our proposed investigation is bolstered along with the tentative applicability and future scope in light of the current solar observational scenarios, such as SOHO, STEREO, SDO, PSP, and SolO.

Solar plasma characterization in Kappa (κ)-modified polytropic turbomagnetic GES-model perspective

ABSTRACT The gravitoelectrostatic sheath (GES) model for exploring the surface emission mechanism of the solar wind plasma (SWP), transformed from the solar interior plasma (SIP) via the solar surface boundary (SSB), has recently been reformulated in different conditions. It considers the realistic plasma key factors previously remaining unaddressed. This continued study elaborately explores the diverse GES-microphysical features influenced mainly by the plasma non-thermality, bulk polytropicity, magneto-activity, logatropicity, etc. It shows that, in the SIP (SWP), the electric potential is κ-insensitive, the Mach number is κ-sensitive, and the current density is κ-sensitive (insensitive). The Mach number is insensitive and the current density is insensitive (sensitive) to the relative temperature, Te/Ti, in the SIP (SWP). The inhomogeneity-induced GES properties are illuminated with the gradient-scale behaviours of the relevant physical variables on both SIP and SWP scales. The self-organization of the bi-scaled solar plasma system is well confirmed by mapping the electric and gravity field gradients in a defined colour phase space illustratively alongside reliability check-ups. A judicious application of the newly derived model-structuring equations results in a non-thermally modified form of the equivalent κ-Bohm sheath criterion featuring the GES formation alongside electric current-flow analyses. Its reliability is validated with a sensible comparison with the extremal cases in fair corroboration with the previous sheath scenarios extensively reported elsewhere. The relevancy of our investigation on the solar multiparametric variations in the GES fabric is lastly bolstered in light of the recent solar astronomic scenarios, such as SolO and PSP.

Athermal GES-based solar plasma stability with sphero-logabarotropic special effects

A model formalism for the small-scale radial fluctuations excitable in the athermal (non-thermal) solar plasma system on the basis of the non-extensive gravito-electrostatic sheath (GES) model fabric is reported. A unique speciality here is that it intercouples the solar interior plasma (SIP) and the solar wind plasma (SWP) gravito-electrostatically via the interfacial diffused solar surface boundary (SSB). The constitutive electrons are thermostatistically framed in the κ-distribution laws via the Tsallis thermostatistics. In contrast, the heavier ions are treated as an inhomogeneous fluid. The turbulent degrees of freedom are accounted through the Larson nonlinear logabarotropic equation of state in curved geometry. A spherically symmetric wave analysis over the perturbed GES structure results in a unique pair of distinct linear dispersion laws (SIP plus SWP) without any typical quasi-classic approximation. A numerical illustrative platform for the dispersion analysis specifically shows that an antikink-type (kink-type) impulsive rarefactive (compressive) propagatory boost due to irregular dispersion is experienced by the fluctuations at the heliospheric core (photospheric SSB). We see that the thermostatistical parameter (Tsallis power-law tail index κ) acts as a unique form of acceleration agency for both the SIP and SWP instabilities to proliferate. At the last, the explorative semi-analytic results are contextually compared with the realistic domains of the collective excitation of the helioseismic waves and SSB oscillations.

Non-planar magnetoactive GES-based solar plasma stability

A laboratory plasma-wall interaction-based astrophysical gravito-electrostatic sheath (GES) model is methodologically applied to study the dynamic stability of the magnetoactive bi-fluidic solar plasma system in the presence of turbulence effect. The spherically symmetric GES-model formalism couples the solar interior plasma (SIP, internally self-gravitating, bounded) and the solar wind plasma (SWP, externally point-gravitating, unbounded) through the diffused solar surface boundary (SSB). A normal spherical mode ansatz results in a generalized linear quadratic dispersion relation depicting the modal fluctuations on both the SIP and SWP scales. A constructive numerical platform reveals the evolution of both dispersive and non-dispersive modal features of the modified-GES mode excitations. The reliability of the derived non-planar dispersion laws is concretized with the help of an exact analytic shape matching the previously reported results founded on the plane-wave approximation. It is found that the thermo-statistical GES stability depends mainly on the magnetic field, equilibrium plasma density, and plasma temperature. It is speculated that the dispersive features are more pronounced in the self-gravitational domains against the electrostatic ones. The magneto-thermal interplay introduces decelerating (accelerating) and destabilizing (stabilizing) influences on the SIP (SWP), and so forth. At last, we briefly indicate the applicability of the proposed analysis to understand diverse helioseismic activities from the collective plasma dynamical viewpoint in accordance with the recent astronomical observational scenarios reported in the literature.

Magnetohydrodynamic Simulations for Solar Active Regions using Time-series Data of Surface Plasma Flow and Electric Field Inferred from Helioseismic Magnetic Imager Vector Magnetic Field Measurements

Abstract Temporal evolution of magnetic structures of the solar active region (AR) NOAA AR 11158, is simulated with our magnetohydrodynamic (MHD) simulation models using time-dependent solar-surface electric field or plasma flow data. Using the Solar Dynamics Observatory/Helioseismic Magnetic Imager vector magnetogram data, the solar-surface boundary electric field maps are derived with our recently developed algorithm to reproduce the temporal evolution of solar-surface vector magnetic field as observed. The plasma motion velocity maps are calculated through the Differential Affine Velocity Estimator for Vector Magnetograms. In both data-driven models, the simulated evolutionary magnetic field structures at strong-field low-beta regions appear near force-free state, as the current helicity density ( ) are roughly constant along each field line. Although the magnetic energy simulated with the newly developed plasma-velocity-driven model is about 10% of that by the electric-field driven model, the plasma-velocity-driven model can maintain the frozen-in condition, and evolution of current and free energy generated by the solar-surface plasma motions can be spatially and temporally traced. The present MHD simulation models for AR system can be a step toward better, more realistic data-driven evolutionary modeling, in particular, establishing boundary treatments for introducing the time-dependent observation data in a physically and mathematically consistent manner.

Nonextensive GES instability with nonlinear pressure effects

Abstract We herein analyze the instability dynamics associated with the nonextensive nonthermal gravito-electrostatic sheath (GES) model for the perturbed solar plasma portraiture. The usual neutral gas approximation is herewith judiciously relaxed and the laboratory plasma-wall interaction physics is procedurally incorporated amid barotropic nonlinearity. The main motivation here stems from the true nature of the solar plasma system as a set of concentric nonlocal nonthermal sub-layers as evidenced from different multi-space satellite probes and missions. The formalism couples the solar interior plasma (SIP, bounded) and solar wind plasma (SWP, unbounded) via the diffused solar surface boundary (SSB) formed due to an exact long-range gravito-electrostatic force-equilibration. A linear normal mode ansatz reveals both dispersive and non-dispersive features of the modified GES collective wave excitations. It is seen that the thermostatistical GES stability depends solely on the electron-to-ion temperature ratio. The damping behavior on both the scales is more pronounced in the acoustic domain, K → ∞ , than the gravitational domain, K → 0 ; where, K is the Jeans-normalized angular wave number. It offers a unique quasi-linear coupling of the gravitational and acoustic fluctuations amid the GES force action. The results may be useful to see the excitation dynamics of natural normal modes in bounded nonextensive astero-environs from a new viewpoint of the plasma-wall coupling mechanism.

Turbulent Gravito-Electrostatic Sheath (GES) Structure with Kappa-Distributed Electrons for Solar Plasma Characterization

We report on new characteristic features of the plasma-based gravito-electrostatic sheath (GES) model for solar plasma equilibrium characterization through nonthermal ( $\kappa$ -distributed) electrons composed of both a thermal halo (low-speed) and a suprathermal (high-speed) energy tail. The constituent ions are treated collectively as inertial species. The presence of intrinsic fluid turbulence is included with the help of a proper logatropic equation of state in the ionic momentum conservation law. The analysis is based on the basic physics of space-charge polarization effects, collectively evolving as a plasma sheath, but previously known only for laboratory plasma-scales. We show that the radial location of the solar surface boundary (SSB, inner boundary, diffused), formed by the counteracting GES force balancing, becomes slightly enhanced (by 0.5 on the Jeans scale). The net electric current densities, in both the solar interior and exterior, confirm the universal law of total charge conservation in the presence of geometrical curvature effects. The relevant properties of the new $\kappa$ -modified equilibrium GES structure are numerically illustrated and discussed. The results are finally compared in the light of existing reports based on the Maxwell–Boltzmann electron distribution. The new outcomes can be extensively expanded to analyze the realistic thermostatistical dynamics of the Sun and its ambient atmosphere, as predicted earlier from various space-based observations.

Modified gravito-electrostatic sheath in the presence of turbu-magnetic pressure effects

The gravito-electrostatic sheath (GES) model, previously formulated to investigate the equilibrium properties of the Sun and its unbounded atmosphere coupled via the interfacial solar surface boundary (SSB) under the gravito-electrostatic interplay, is re-examined. It is modified, for the first time, with the self-consistent inclusion of turbu-magnetic pressure effects originating from intrinsic continuous instability processes. The role of the new effects is interestingly realized through considerable changes in the dynamic properties of the solar plasma system on both the bounded and unbounded scales. The SSB, as a result of the outward turbu-magnetic action relative to the inward self-gravitating one, is found to shift radially outwards by 5.71% relative to the sheer GES model, and by 7.50% inwards relative to the pure uniformly magnetized counterpart. The sonic point moves inwards by 30% in the former, and by 24% in the latter; respectively. It is further found that the floating surface and floating potential increase by 47% each relative to the GES; and by 27% and 160% relative to the pure magnetic case; respectively. The implications and applications are discussed in the panoptical light of real astronomical observations alongside the facts, faults and future refinements.

GPU-accelerated computing of three-dimensional solar wind background

High-performance computational models are required to make the real-time or faster than real-time numerical prediction of adverse space weather events and their influence on the geospace environment. The main objective in this article is to explore the application of programmable graphic processing units (GPUs) to the numerical space weather modeling for the study of solar wind background that is a crucial part in the numerical space weather modeling. GPU programming is realized for our Solar-Interplanetary-CESE MHD model (SIP-CESE MHD model) by numerically studying the solar corona/interplanetary solar wind. The global solar wind structures are obtained by the established GPU model with the magnetic field synoptic data as input. Meanwhile, the time-dependent solar surface boundary conditions derived from the method of characteristics and the mass flux limit are incorporated to couple the observation and the three-dimensional (3D) MHD model. The simulated evolution of the global structures for two Carrington rotations 2058 and 2062 is compared with solar observations and solar wind measurements from spacecraft near the Earth. The MHD model is also validated by comparison with the standard potential field source surface (PFSS) model. Comparisons show that the MHD results are in good overall agreement with coronal and interplanetary structures, including the size and distribution of coronal holes, the position and shape of the streamer belts, and the transition of the solar wind speeds and magnetic field polarities.

Time‐dependent MHD modeling of the global solar corona for year 2007: Driven by daily‐updated magnetic field synoptic data

In this paper, we develop a time‐dependent MHD model driven by the daily‐updated synoptic magnetograms (MHD‐DUSM) to study the dynamic evolution of the global corona with the help of the 3D Solar‐Interplanetary (SIP) adaptive mesh refinement (AMR) space‐time conservation element and solution element (CESE) MHD model (SIP‐AMR‐CESE MHD Model). To accommodate the observations, the tangential component of the electric field at the lower boundary is specified to allow the flux evolution to match the observed changes of magnetic field. Meanwhile, the time‐dependent solar surface boundary conditions derived from the method of characteristics and the mass flux limit are incorporated to couple the observation and the 3D MHD model. The simulated evolution of the global coronal structure during 2007 is compared with solar observations and solar wind measurements from both Ulysses and spacecrafts near the Earth. The MHD‐DUSM model is also validated by comparisons with the standard potential field source surface (PFSS) model, the newly improved Wang‐Sheeley‐Arge (WSA) empirical formula, and the MHD simulation with a monthly synoptic magnetogram (MHD‐MSM). Comparisons show that the MHD‐DUSM results have good overall agreement with coronal and interplanetary structures, including the sizes and distributions of coronal holes, the positions and shapes of the streamer belts, and the transitions of the solar wind speeds and magnetic field polarities. The MHD‐DUSM results also display many features different from those of the PFSS, the WSA, and the MHD‐MSM models.

A Numerical Characterization of the Gravito-Electrostatic Sheath Equilibrium Structure in Solar Plasma

This article describes the equilibrium structure of the solar interior plasma (SIP) and solar wind plasma (SWP) in detail under the framework of the gravito-electrostatic sheath (GES) model. This model gives a precise definition of the solar surface boundary (SSB), surface origin mechanism of the subsonic SWP, and its supersonic acceleration. Equilibrium parameters like plasma potential, self-gravity, population density, flow, their gradients, and all the relevant inhomogeneity scale lengths are numerically calculated and analyzed as an initial value problem. Physical significance of the structure condition for the SSB is discussed. The plasma oscillation and Jeans time scales are also plotted and compared. In addition, different coupling parameters, and electric current profiles are also numerically studied. The current profiles exhibit an important behavior of directional reversibility, i.e., an electrodynamical transition from negative to positive value. It occurs beyond a few Jeans lengths away from the SSB. The virtual spherical surface lying at the current reversal point, where the net current becomes zero, has the property of a floating surface behavior of the real physical wall. Our investigation indicates that the SWP behaves as an ion current-carrying plasma system. The basic mechanism behind the GES formation and its distinctions from conventional plasma sheath are discussed. The electromagnetic properties of the Sun derived from our model with the most accurate available inputs are compared with those of others. These results are useful as an input element to study the properties of the linear and nonlinear dynamics of various solar plasma waves, oscillations and instabilities.

A numerical investigation of electric current conservation associated with solar wind plasma under GES-model approach

A plasma-based Gravito-Electrostatic Sheath (GES) model for theoretical description of the basic physics of the surface emission mechanism of the quasi-neutral Solar Interior Plasma (SIP) on a bounded scale, and subsequently, its transonic transition into Solar Wind Plasma (SWP) on an unbounded scale with a simplified field-free fluid model approach has already been proposed. An autonomous closed set of self-consistently coupled nonlinear eigenvalue equations for analyzing the dynamical stability of the steady GES model on both the scales is developed. The focussed aim of the present contribution is only to study the electric current profiles associated with the SIP as well as SWP, and hence to investigate conservative dynamical features thereof. Applying the developed set of coupled nonlinear dynamical evolution equations, the profiles of electric currents associated with both SIP as well as SWP have been obtained numerically under a wide range spectrum of initial values of relevant physical parameters (by nonlinear stability analysis). Interestingly, it is conjectured that the dynamical evolution of solar electric currents is found fairly to be conservative (divergence-free) in nature except some deviations near the defined solar surface boundary. Results, discussions and conclusions on the basis of the obtained numerical results are presented in brief.

A Gravito‐electrostatic Sheath Model for Surface Origin of Subsonic Solar Wind Plasma

Parker's model prediction of an unbounded solution for the supersonic solar wind plasma (SWP) requires a subsonic origin at the solar surface. The transition to supersonic SWP flow is well understood by analogy with the de Laval nozzle. The basic physics, however, of the self-consistent solar surface emission of subsonic SWP is still not very clear. We propose a theoretical model based on a gravito-electrostatic plasma sheath (GES) to investigate the surface emission mechanism of the quasi-neutral SWP. The basic equations for the interior steady state description are solved numerically as an initial-value problem under spherical geometry. A bounded solution for the solar self-gravity distribution is found to exist, meaning that a global quasi-hydrostatic equilibrium is formed at some distance from the heliocentric origin. This defines the solar surface boundary in our model, which lies at radius ξ ~ 3.5 (in units of the Jeans length). A minimum speed of ~3.0 cm s-1, corresponding to Mach number ~10-7, is obtained at this location. Consequently, a subsonic origin of the solar interior plasma flowing radially outward becomes a physical reality. Our model requires a mean electron temperature Te ~ 107 K (=1 keV) for the numerical results to match the standard solar values. The boundary is found to be negatively biased, with a normalized value of the electrostatic potential θs ~ -1 (=1 kV). It is conjectured that our model provides an interesting new physical basis for understanding the collective dynamical coupling processes of solar interior and exterior (heliosphere) regions through local, as well as global, modes of GES-induced collective waves, instabilities, and oscillations.

Modeling the coronal magnetic field, with a new method for obtaining boundary conditions on the farside of the Sun

A novel technique is presented that aids the reconstruction of solar coronal magnetic fields by augmenting the visible solar surface boundary conditions with an estimate of the simultaneous conditions on the far side of the Sun. In converting from line‐of‐sight measurements, two alternative assumptions are considered: (1) ignore the plasma beta differences between corona and photosphere and so find a radial field component that is consistent with an overlying potential (or force free) field corona; and (2) characterize the change in beta by a boundary layer, matching the coronal field to the photosphere where the field, seen in projection, is taken to be wholly radial. The radial magnetic field (or radial field component) over the unseen hemisphere of the Sun is deduced from information held within a time series of the Solar and Heliospheric Observatory Michelson Doppler imager photospheric magnetograms centered on the time of interest and combined with a full disc of visible data for that time. Comparison is made with the more usual synoptic map boundary conditions to test the time sensitivity of the problem. Several methods of extrapolation to the far side are assessed using data centered on an observation at the end of August 1996, when a large equatorial coronal hole was present on one side of the Sun. The corresponding magnetic field equilibrium in the corona is found, assuming a simple potential approximation, which employs an outer “source surface” in addition to the derived inner boundary condition. Together with the inherent assumption that the evolution of the global field is slow, the validity of the technique is confirmed by the self‐consistency of the results.

The solar-surface boundary conditions of coronal magnetic loops

The dynamical properties of a realisticthermal-structure interface between a coronal loop and the chromosphere/photosphere are investigated by numerical simulations using acoustic and Alfvenic excitations. These properties are relevant to the end conditions seen by coronal MHD perturbations (e.g., waves or instabilities), in the absence of much slower energetics effects. Analytic studies of coronal-loop hydromagnetics have often made simplifying assumptions about the boundary conditions at the loop base in order to make their calculations tractable. However, in the presence of a transition region and chromosphere with rapidly varying plasma conditions, it is not clear how valid these heuristic assumptions are. In this study, we find that the discontinuous fluid-density model approximately represents the reflection/ transmission scaling with respect to varying transition-region density and temperature (i.e., dynamic impedance) ratios, although it does not quantitatively predict the chromospheric response to wave-like coronal activity. This disagreement is partially due to the finite width of the corona-to-photosphere transition.