Artificial Wind—A New Framework to Construct Simple and Efficient Upwind Shock-Capturing Schemes

Соколов, И. В.; Timofeev, E.; Sakai, Jun–ichi; Takayama, K.

doi:10.1006/jcph.2002.7130

Cited by 31 publications

(14 citation statements)

References 18 publications

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“…In this numerical code, which we refer to as TwoYama, the fluids are coupled predominantly through ion-neutral collisions but also through ionisation/recombination effects. TwoYama was developed using the previously proposed Artificial Wind (AW) numerical scheme (Sokolov et al 1999(Sokolov et al , 2002, which was successfully used by Sakai et al (2006) to simulate the magnetic reconnection of coalescing chromospheric current loops. The AW scheme is based on the fundamental physical invariance, Galilean (or more generally Lorentz), of the governing plasma equations.…”

Section: Numerical Schemementioning

confidence: 99%

Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops

Smith¹,

Sakai

2008

A&A

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Aims. We investigate magnetic reconnection rates during the coalescence of two current loops in the solar chromosphere, by altering the neutral-hydrogen to proton density ratio, ionisation/recombination coefficients, collision frequency, and relative helicity of the loops. Methods. We used a newly developed two-fluid (ion-neutral) numerical code to perform 2.5D simulations of coalescing chromospheric current loops. Developed from the Artificial Wind scheme, the numerical code includes the effects of ion-neutral collisions, ionisation/recombination, thermal/resistive diffusivity, and collisional/resistive heating. Results. It was found that the rates of magnetic reconnection strongly depend on the neutral-hydrogen to proton density ratio: increasing the density ratio a thousandfold decreased the rate of magnetic reconnection twentyfold. This result implies that magnetic reconnection proceeds significantly faster in the upper chromosphere, where the density of ions (protons) and neutral-hydrogen is comparable, than in the lower chromosphere, where the density of neutral-hydrogen is over a thousand times the ion density. This result also implies that jets associated with fast magnetic reconnection tends to occur in the upper chromosphere / lower corona. The inclusion of ionisation/recombination, an important physical effect in the chromosphere, increases the total reconnected magnetic flux, but does not alter the rate of magnetic reconnection. Reductions in the ion-neutral collision frequency result in small increases to the rates of magnetic reconnection. The relative helicity of the two current loops was not observed to have any significant effect on the rates of magnetic reconnection. Comparisons of two-fluid and MHD (Magnetohydrodynamic) simulations show significant differences in the measured rates of magnetic reconnection, particularly for the higher neutral density cases which represent the lower chromosphere. This demonstrates that MHD is not an appropriate model for simulating magnetic reconnection in the solar chromosphere. Conclusions. The magnetic reconnection rates of coalescing current loops are strongly affected by the inclusion of neutral-hydrogen particles. It is therefore essential that ion-neutral collisions are included in future analytical/numerical models of chromospheric magnetic reconnection.

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Section: Numerical Schemementioning

confidence: 99%

Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops

Smith¹,

Sakai

2008

A&A

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“…6,12 BATS-R-US solves the relativistic MHD equations using block-based AMR technology, finite-volume methodology with four approximate Riemann solvers (Roe, 9 Linde, 16 artificial wind, 17 and Lax-Friedrichs/Rusanov), four different divergence B control techniques (eight-wave, constrained transport, projection, and ∇ • B diffusion), and your choice of five limiters. You also can choose different timestepping methods (local, explicit, implicit, and combined explicit and implicit) depending on the type of problem you want to solve.…”

Section: Parallel Implementationmentioning

confidence: 99%

Solution-adaptive magnetohydrodynamics for space plasmas: Sun-to-Earth simulations

et al. 2004

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N umerical simulation and modeling are increasingly essential to basic and applied space-physics research for two primary reasons. First, the heliosphere and magnetosphere are vast regions of space from which we have relatively few in situ measurements. Numerical simulations let us "stitch together" observations from different regions and provide data-interpretation insight to help us understand this complex system's global behavior. Second, models have evolved to where their physical content and numerical robustness, flexibility, and improving ease of use inspire researchers to apply them to intriguing scenarios with new measures of confidence.Indeed, many shortcomings and questions remain for even the most advanced models in terms of inclusion of important physical mechanisms, the spatial and temporal domains they can address, and thorny technical numerical issues to be dispatched. Nonetheless, over the last several years, modeling has crossed a threshold, making the transition from the arcane preserves of specialists to practical tools with widespread applications. Global computational models based on firstprinciples mathematical physics descriptions are essential to understanding the solar system's plasma phenomena, including the large-scale solar corona, the solar wind's interaction with planetary magnetospheres, comets, and interstellar medium, and the initiation, structure, and evolution of solar eruptive events. Today, and for the foreseeable future, numerical models based on magnetohydrodynamics (MHD) equations are the only self-consistent mathematical descriptions that can span the enormous distances associated with large-scale space phenomena. Although providing only a relatively low-order approximation to actual plasma behavior, MHD models have successfully simulated many important space-plasma processes and provide a powerful means for significantly advancing process understanding.Space scientists have used global MHD simulations for over 25 years to simulate space plasmas. Early global-scale 3D MHD simulations focused on Space-environment simulations, particularly those involving space plasma, present significant computational challenges. Global computational models based on magnetohydrodynamics equations are essential to understanding the solar system's plasma phenomena, including the large-scale solar corona, the solar wind's interaction with planetary magnetospheres, comets, and interstellar medium, and the initiation, structure, and evolution of solar eruptive events.

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“…The BATS-R-US solves a set of (ideal) MHD equations using the Block Adaptive Tree Solar Wind Roe-type Upwind Scheme (BATS-R-US) code (Powell et al, 1999;Groth et al, 2000), in combination with the Artificial Wind approximate Riemann (AWR) solver (Sokolov et al, 2002). This is a conservative finite-volume method with shock-capturing total variation diminishing schemes, explicit/implicit time stepping, a block-adaptive mesh refinement scheme, that runs on massively parallel computers.…”

Section: Mhd Simulations Of Cmesmentioning

confidence: 99%

Theoretical modeling for the stereo mission

et al. 2006

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We summarize the theory and modeling efforts for the STEREO mission, which will be used to interpret the data of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the coronal plasma, in both open and closed magnetic structures, and the solar wind and its expansion outwards from the Sun, which defines the heliosphere. Particular emphasis is given to modeling of dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather. This review describes mostly existing models of groups that have committed their work to the STEREO mission, but is by no means exhaustive or comprehensive regarding alternative theoretical approaches.

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Artificial Wind—A New Framework to Construct Simple and Efficient Upwind Shock-Capturing Schemes

Cited by 31 publications

References 18 publications

Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops

Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops

Solution-adaptive magnetohydrodynamics for space plasmas: Sun-to-Earth simulations

Theoretical modeling for the stereo mission

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