Three-dimensional Magnetohydrodynamic Model Research Articles

MHD Simulations for the Origin and Magnetic Topology of Solar3He Events

The origin and magnetic topology of impulsive solar energetic particle (SEP) events (also called solar 3He-rich events) are numerically investigated by using a three-dimensional axisymmetric time-dependent self-consistent magnetohydrodynamic (MHD) model. The results indicate that when a counterclockwise (or normal) magnetic flux rope is emerged from the photosphere at the open field region near the closed magnetic field lines, the magnetic topology produced by the MHD simulation is that proposed by Reames to lead to impulsive SEP events. The flux emergence initiates the magnetic configuration which produces the magnetic reconfiguration and reconnection at the coronal base. The magnetic reconnection at the coronal base strongly disturbs the magnetic fields in the solar corona and interplanetary space, and generates fast jetlike plasma outflows (or non-flux-rope coronal mass ejections). The magnetic field line disturbances could scatter charged particles and therefore accelerate them to high energies through the Fermi acceleration mechanism.

An optimal, parallel, fully implicit Newton–Krylov solver for three-dimensional viscoresistive magnetohydrodynamics

The conceptual development and implementation of a scalable nonlinear solver for the time-dependent three-dimensional (3D) compressible resistive magnetohydrodynamics model (MHD) is discussed. The approach is based on Jacobian-free Newton–Krylov technology, preconditioned with multigrid methods for algorithmic scalability. The key to the approach is the reformulation of the hyperbolic MHD system into a parabolic one, which is amenable to multigrid techniques. Such reformulation (parabolization) aims to render the modified system block diagonally dominant (unlike the original MHD system, which is diagonally submissive for implicit time steps Δt larger than the explicit Courant–Friedrichs–Lewy time step). The algorithm has been tested on a variety of 2D and 3D configurations which demonstrate its excellent algorithmic scalability properties. In particular, it is shown that, serially, the CPU time for a given simulation scales linearly with the number of unknowns, and that large CPU gains (∼30) are attainable with respect to an explicit approach even for moderate grids (256×256). In parallel, the algorithm features excellent scalability properties up to thousands of processors (4096) and millions of unknowns (∼1.3×108).

Multi-fluid model of comet 1P/Halley

A new three-dimensional magnetohydrodynamic model of the coma of a comet has been developed and applied to simulations of a Halley-class coma using the solar-wind conditions of the Giotto flyby of Halley in 1986. The code developed for high-performance parallel processing computers, combines the high spatial resolution of smaller than 1 km grid spacing near the nucleus, with a large computational domain that enables structures nearly 10 million km down the comet tail to be modeled. Ions, neutrals, and electrons are considered as separate interacting fluids. Significant physical processes treated by the model include both photo and electron impact ionization of neutrals, recombination of ions, charge exchange between solar-wind ions and cometary neutrals, and frictional interactions between the three fluids considered in the model. A variety of plasma structures and physical parameters that are the output of this model are compared with relevant Giotto data from the 1986 Halley flyby.

Nonlinear wave modulation in a quantum magnetoplasma

Amplitude modulation of ion-acoustic waves (IAW) in a magnetized electron-ion quantum plasma is investigated. For this purpose, a three-dimensional (3D) quantum magnetohydrodynamic model is considered in the limit of small mass ratio of the charged particles. By using the standard reductive perturbation technique, a 3D nonlinear Schrödinger equation containing the magnetic field and the quantum effects is derived. The importance of quantum corrections is described through a nondimensional parameter H which is proportional to quantum diffraction effects. Some important and new modulational instability criteria of 3D IAW, quite distinct from the classical one, are obtained and analyzed.

Modeling the Radiative Signatures of Turbulent Heating in Coronal Loops

The statistical properties of the radiative signature of a coronal loop subject to turbulent heating obtained from a three-dimensional (3D) magnetohydrodynamics (MHD) model are studied. The heating and cooling of a multistrand loop is modeled and synthetic spectra for Fe XII 195.12, Fe XV 284.163, and Fe XIX 1118.06 ? are calculated, covering a wide temperature range. The results show that the statistical properties of the thermal and radiative energies partially reflect those of the heating function in that power-law distributions are transmitted, but with very significant changes in the power-law indices. There is a strong dependence on the subloop geometry. Only high-temperature radiation (?107 K) preserves reasonably precise information on the heating function.

The Possibly Remnant Massive Outflow in G5.89‐0.39. I. Observations and Initial Magnetohydrodynamic Simulations

We have obtained maps of the large-scale outflow associated with the UC H II region G5.89-0.39 in CO and 13CO (J = 3-2), SiO (J = 8-7, J = 5-4), SO2 (J = 132,12-131,13),13 and H13CO+(J = 4-3). From these maps we have been able to determine the mass (3.3 M☉), momentum (96 M☉ km s-1), energy (3.5 × 1046 ergs), mechanical luminosity (141 L☉), and mass-loss rate (~ 1 × 10-3 M☉ yr-1) in the large-scale outflow. The observationally derived parameters were used to guide three-dimensional magnetohydrodynamic models of the jet-entrained outflow. Through the combination of observations and simulations, we suggest that the large-scale outflow may be inclined by approximately 45° to the line of sight, and that the jet entraining the observed molecular outflow may have been active for as little as 1000 years, half the kinematic age of the outflow.

The Partial Expulsion of a Magnetic Flux Rope

We demonstrate the partial expulsion of a three-dimensional magnetic flux rope, in which an upper, escaping rope is separated from a lower, surviving rope by cusped, reconnecting loop field lines. We use the three-dimensional magnetohydrodynamic model recently presented by Fan, extended to examine the erupting rope's end state. As in that work, the modeled flux rope in spherical coordinates erupts when enough twist has emerged to induce a loss of equilibrium. After multiple reconnections at current sheets that form during the eruption, the rope breaks in two, so that only a part of it escapes. We consider the details of how this separation occurs and discuss the observational significance of such a partially expelled flux rope for partially erupting filaments and re-forming X-ray sigmoids.

Modeling the Sun-to-Earth propagation of a very fast CME

We present a three-dimensional (3-D) numerical ideal magnetohydrodynamics (MHD) model describing the time-dependent propagation of a CME from the solar corona to Earth in just 18 h. The simulations are performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind Scheme) code. We begin by developing a global steady-state model of the corona that possesses high-latitude coronal holes and a helmet streamer structure with a current sheet at the equator. The Archimedian spiral topology of the interplanetary magnetic field is reproduced along with fast and slow speed solar wind. Within this model system, we drive a CME to erupt by the introduction of a Gibson–Low magnetic flux rope that is embedded in the helmet streamer in an initial state of force imbalance. The flux rope rapidly expands, driving a very fast CME with an initial speed of in excess of 4000 km/s and slowing to a speed of nearly 2000 km/s at Earth. We find our model predicts a thin sheath around the flux rope, passing the earth in only 2 h. Shocked solar wind temperatures at 1 astronomical unit (AU) are in excess of 10 million degrees. Physics based AMR allows us to capture the structure of the CME focused on a particular Sun–Earth line with high spatial resolution given to the bow shock ahead of the flux rope.

Numerical Simulation of the Interaction of Two Coronal Mass Ejections from Sun to Earth

We present a three-dimensional compressible magnetohydrodynamics (MHD) model of the interaction of two coronal mass ejections (CMEs). Two identical CMEs are launched in the exact same direction into a preexisting solar wind, the second one 10 hr after the first one. Our global steady state coronal model possesses high-latitude coronal holes and a helmet streamer structure with a current sheet near the equator, reminiscent of near-solar minimum conditions. Within this model system, we drive the CMEs to erupt by the introduction of two three-dimensional magnetic flux ropes embedded in the helmet streamer. After an initial phase, when the trailing shock and the second CME propagate into the disturbed solar wind medium, they reach the edge of the first magnetic cloud, leading to complex magnetic interactions and a steep acceleration of the shock. Later, the trailing shock reaches the dense sheath of plasma associated with the leading shock, where it decelerates to a speed about 100 km s-1 larger than the speed of the leading shock. Eventually, the two shocks merge and a stronger, faster shock forms in association with a contact discontinuity between the old and new downstream regions. We find that the trailing shock always remains a fast-mode shock. A reverse shock is driven after the collision of the two magnetic clouds due to the difference in speed within the reconnection region. At Earth, the two magnetic clouds can still be distinguished, with a compressed and heated first cloud and a second overexpanded cloud. The transit time of this complex ejecta is reduced by about 6 hr compared to the case of the first CME without interaction. Our simulation is able to reproduce and explain some of the general features observed in satellite data for multiple magnetic clouds.

Simulation of the Effects of Several Factors on Arc Plasma Behavior in Low Voltage Circuit Breaker

Taking into account the properties of the arc plasma and the electromagnetic, heat and rediative phenomena, commercial computational fluid dynamics software PHOENICS has been adapted and modified to develop the three-dimensional magneto-hydrodynamic (MHD) model of arc in a low voltage circuit breaker. The effects of the arc ignition location, venting size and gassing material on arc behavior have been investigated. The analysis of the results show that the arc velocity accelerates with the increase in the distance between arc ignition location and of the venting size, and the existence of the gassing material is beneficial to improving the arc voltage and reducing the arc temperature.

A Three-Dimensional Magnetohydrodynamic (MHD) Model of Active Region Evolution

A three-dimensional, time-dependent, magnetohydrodynamic (MHD) model is constructed for the study of active region (AR) evolution. The new physics included in this model is differential rotation, meridional flow, effective diffusion and cyclonic turbulence effects, which means, that the photospheric shear is automatically generated instead of prescribed as is usually done for modeling. To benchmark this newly developed model, we have used observed active region NOAA/AR-8100 (October 29 - November 3, 1997) to verify the model by computation of the total magnetic flux and magnetic field maps of that active region. Then, we apply this model to compute the non-potentiality magnetic field parameters for possible coronal mass ejection production. These parameters are: (i) magnetic flux content (). These parameters are compared with the measured values which showed remarkable agreement.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Solar Observation-Based Model for Multiday Predictions of Interplanetary Shock and CME Arrivals at Earth

We present the design, implementation, present status, and preliminary use of an operational forecaster-friendly solar wind prediction system. We have tested this architecture in our real-time fearless prediction study of interplanetary shock arrival time (SAT) at Earth. This study has progressed on a continuous basis since 1997, near the rise of Solar Cycle 23. Comparisons of predicted SAT with observed SAT provide a measure of model forecast skill. We present our kinematic model's forecast skill statistics as compared with several other SAT models and propose important reference metrics for evaluating this and any other interplanetary modeling system. Our prediction system is presently being extended, via a hybrid approach, to include a three-dimensional magnetohydrodynamic (MHD) model. This procedure will accommodate proxy inputs for simulating interplanetary disturbances that are associated with various forms of solar activity (flares, disappearing filaments, coronal mass ejection imagery, shocks). The objective is to provide a capability in the near term to predict, shortly after the launch of large-scale structures at the Sun, the time-dependent interplanetary magnetic field vector (including the north-south component, Bz) at Earth. This is a key requirement for predicting geomagnetic storms.

Three-Dimensional Magnetohydrodynamic Modeling of Plasma Jets in the North Star Space Experiment

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Coronal Mass Ejection: Initiation, Magnetic Helicity, and Flux Ropes. I. Boundary Motion–driven Evolution

In this paper we study a class of three-dimensional magnetohydrodynamic model problems that may be useful to understand the role of twisted flux ropes in coronal mass ejections. We construct in a half-space a series of force-free bipolar configurations with different helicity contents and bring them into an evolution by imposing to their footpoints on the boundary slow motions converging toward the inversion line. For all the cases that have been computed, this process leads, after a phase of quasi-static evolution, to the formation of a twisted flux rope by a reconnection process and to the global disruption of the configuration. In contrast with the results of some previous studies, however, the rope is never in equilibrium. It thus appears that the presence of a rope in the preeruptive phase is not a necessary condition for the disruption but may be the product of the disruption itself. Moreover, the helicity keeps an almost constant value during the evolution, and the problem of the origin of the helicity content of an eruptive configuration appears to be that of the initial force-free state. In addition to these numerical simulations, we report some new relations for the time variations of the energy and the magnetic helicity and develop a simple analytical model in which the magnetic field evolution exhibits essential features quite similar to those observed during the quasi-static phase in the numerics.

A Coupled Model for the Emergence of Active Region Magnetic Flux into the Solar Corona

We present a set of numerical simulations that model the emergence of active region magnetic flux into an initially field-free model corona. We simulate the buoyant rise of twisted magnetic flux tubes initially positioned near the base of a stable stratified model convection zone and use the results of these calculations to drive a three-dimensional magnetohydrodynamic model corona. The simulations show that time-dependent subsurface flows are an important component of the dynamic evolution and subsequent morphology of an emerging magnetic structure. During the initial stages of the flux emergence process, the overlying magnetic field differs significantly from a force-free state. However, as the runs progress and boundary flows adjust, most of the coronal field—with the exception of those structures located relatively close to the model photosphere—relaxes to a more force-free configuration. Potential field extrapolations do not adequately represent the magnetic structure when emerging active region fields are twisted. In the dynamic models, if arched flux ropes emerge with nonzero helicity, the overlying field readily forms sigmoid-shaped structures. However, the chirality of the sigmoid and other details of its structure depend on the observer's vantage point and the location within a given loop of emitting plasma. Thus, sigmoids may be an unreliable signature of the sign and magnitude of magnetic twist.

Pickup ions near Mars associated with escaping oxygen atoms

Ions produced by ionization of Martian neutral atoms or molecules and picked up by the solar wind flow are expected to be an important ingredient of the Martian plasma environment. Significant fluxes of energetic (55–72 keV) oxygen ions were recorded in the wake of Mars and near the bow shock by the solar low‐energy detector (SLED) charged particle detector onboard the Phobos 2 spacecraft. Also, copious fluxes of oxygen ions in the ranges 0.5–25 and 0.01–6 keV/q were detected in the Martian wake by the Automatic Space Plasma Experiment with Rotating Analyzer (ASPERA) instrument on Phobos 2. This paper provides a quantitative analysis of the SLED energetic ion data using a test particle model in which one million ion trajectories were numerically calculated. These trajectories were used to determine the ion flux as a function of energy in the vicinity of Mars for conditions appropriate for Circular Orbit 42 of Phobos 2. The electric and magnetic fields required by the test particle model were taken from a three‐dimensional magnetohydrodynamic (MHD) model of the solar wind interaction with Mars. The ions were started at rest with a probability proportional to the density expected for exospheric hot oxygen. The test particle model supports the identification of the ions observed in channel 1 of the SLED instrument as pick‐up oxygen ions that are created by the ionization of oxygen atoms in the distant part of the exosphere. The flux of 55–72 keV oxygen ions near the orbit of the Phobos 2 should be proportional to the oxygen density at radial distances from Mars of about 10 Rm (Martian radii) and hence proportional to the direct oxygen escape rate from Mars that is an important part of the overall oxygen loss rate at Mars. The modeled energetic oxygen fluxes also exhibit a spin modulation as did the SLED fluxes during Circular Orbit 42.

Three‐dimensional Model of the Structure and Evolution of Coronal Mass Ejections

We present a new three-dimensional magnetohydrodynamic (MHD) model that describes the evolution of coronal magnetic arcades in response to photospheric flows. The dynamics of the system is discussed, and it is shown that the model reproduces a number of features characteristic of coronal mass ejection (CME) observations. In particular, we propose explanations for the three-part structure of CMEs observed at the solar limb and the formation and evolution of sigmoids and overlaying arcades. The model includes the effects of finite resistivity in the system and morphological changes induced by reconnection are studied. Reconnection is found to prevent the formation of highly twisted magnetic structures if the magnitude of photospheric velocity is close to the observed values. In addition, we suggest a novel explanation for the splitting of the CME's core prominence material observed in some eruptions. The distinguishing features of the model are the novel numerical methods used to evolve the MHD system and the formulation of the boundary conditions. The stiffness of the resistive MHD equations constitutes a major difficulty for numerical simulations. Calculations in our model are performed using recently introduced exponential propagation techniques that allow efficient integration of the equations with time steps far exceeding the CFL bound that constrains explicit schemes.

One-, two-, and three-dimensional modeling of the different phases of wire array Z-pinch evolution

A series of one-, two-, and three-dimensional (1-D, 2-D, and 3-D) resistive magnetohydrodynamic models are used to build up a composite model of the different phases of wire array Z-pinch implosions. 1-D(r) and 2-D(r,z) “cold-start” simulations of single wire experiments are used to illustrate some of the important processes in the plasma formation phase of wire arrays. Detailed comparison of the simulation results with data from single wire experiments provides an excellent method of code verification. 2-D simulations in the r–θ or x–y plane show how the combination of the core–corona structure of the wire plasmas and the magnetic field topology result in the formation of radial plasma streams and a precursor plasma on axis well before the implosion phase commences. The same 2-D(x–y) model is also used to illustrate how the implosion trajectories of nested wire arrays are controlled by the levels of momentum, energy, and magnetic flux which are transferred during their collision. Preliminary results showing the evolution of a single wire in the array in 3-D are presented. These results suggest that the dynamics and structure of imploding wire arrays at Imperial College can potentially be explained in terms of the current breaking through the wire cores rather than in terms of the Rayleigh–Taylor instability.

Ion trajectories in Saturn's magnetosphere near Titan

Abstract We numerically determine the trajectories of several ions in the vicinity of Titan using for the required electric and magnetic fields the output from a three-dimensional magnetohydrodynamic model of Titan. These trajectories are analyzed to provide insight into the external plasma interaction with that satellite as well as to make predictions for the Cassini Orbiter particle experiments (Young et al. , 1998).

Magnetohydrodynamic modeling of the global solar corona

A three-dimensional magnetohydrodynamic model of the global solar corona is described. The model uses observed photospheric magnetic fields as a boundary condition. A version of the model with a polytropic energy equation is used to interpret solar observations, including eclipse images of the corona, Ulysses spacecraft measurements of the interplanetary magnetic field, and coronal hole boundaries from Kitt Peak He 10 830 Å maps and extreme ultraviolet images from the Solar Heliospheric Observatory. Observed magnetic fields are used as a boundary condition to model the evolution of the solar corona during the period February 1997–March 1998. A model with an improved energy equation and Alfvén waves that is better able to model the solar wind is also presented.