scholarly journals Ultrahigh-resolution model of a breakout CME embedded in the solar wind

2018 ◽  
Vol 620 ◽  
pp. A57 ◽  
Author(s):  
S. Hosteaux ◽  
E. Chané ◽  
B. Decraemer ◽  
D.-C. Talpeanu ◽  
S. Poedts
Keyword(s):  
Solar Wind ◽  
Adaptive Mesh Refinement ◽  
Flux Rope ◽  
Adaptive Mesh ◽  
Electrical Current ◽  
Substantial Effect ◽  
Small Scale ◽  
Release Process ◽  
Ultrahigh Resolution ◽  
Current Sheets

Aims. We investigate the effect of a background solar wind on breakout coronal mass ejections, in particular, the effect on the different current sheets and the flux rope formation process. Methods. We obtained numerical simulation results by solving the magnetohydrodynamics equations on a 2.5D (axisymmetric) stretched grid. Ultrahigh spatial resolution is obtained by applying a solution adaptive mesh refinement scheme by increasing the grid resolution in regions of high electrical current, that is, by focussing on the maximum resolution of the current sheets that are forming. All simulations were performed using the same initial base grid and numerical schemes; we only varied the refinement level. Results. A background wind that causes a surrounding helmet streamer has been proven to have a substantial effect on the current sheets that are forming and thus on the dynamics and topology of the breakout release process. Two distinct ejections occur: first, the top of the helmet streamer detaches, and then the central arcade is pinched off behind the top of the helmet streamer. This is different from the breakout scenario that does not take the solar wind into account, where only the central arcade is involved in the eruption. In the new ultrahigh-resolution simulations, small-scale structures are formed in the lateral current sheets, which later merge with the helmet streamer or reconnect with the solar surface. We find that magnetic reconnections that occur at the lateral breakout current sheets deliver the major kinetic energy contribution to the eruption and not the reconnection at the so-called flare current sheet, as was seen in the case without background solar wind.

High-Resolution Three-Dimensional MHD Simulations of Plasmoid Formation in Solar Flares

2020 ◽  
Author(s):  
Joel Dahlin ◽  
Spiro Antiochos ◽  
C. Richard DeVore
Keyword(s):  
Current Sheet ◽  
Adaptive Mesh Refinement ◽  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Dimensional Structure ◽  
Small Scale ◽  
Ample Evidence ◽  
Current Sheets

<p>In highly conducting plasmas, reconnecting current sheets are often unstable to the generation of plasmoids, small-scale magnetic structures that play an important role in facilitating the rapid release of magnetic energy and channeling that energy into accelerated particles. There is ample evidence for plasmoids throughout the heliosphere, from in situ observations of flux ropes in the solar wind and planetary magnetospheres to remote-sensing imaging of plasma ‘blobs’ associated with explosive solar activity such as eruptive flares and coronal jets. Accurate models for plasmoid formation and dynamics must capture the large-scale self-organization responsible for forming the reconnecting current sheet. However, due to the computational difficulty inherent in the vast separation between the global and current sheet scales, previous numerical studies have typically explored configurations with either reduced dimensionality or pre-formed current sheets. We present new three-dimensional MHD studies of an eruptive flare in which the formation of the current sheet and subsequent reconnection and plasmoid formation are captured within a single simulation. We employ Adaptive Mesh Refinement (AMR) to selectively resolve fine-scale current sheet dynamics. Reconnection in the flare current sheet generates many plasmoids that exhibit highly complex, three-dimensional structure. We show how plasmoid formation and dynamics evolve through the course of the flare, especially in response to the weakening of the reconnection “guide field” linked to the global reduction of magnetic shear. We discuss implications of our results for particle acceleration and transport in eruptive flares as well as for observations by Parker Solar Probe and the forthcoming Solar Orbiter.</p>

Tsunami modelling with adaptively refined finite volume methods

Acta Numerica ◽  
2011 ◽  
Vol 20 ◽  
pp. 211-289 ◽  
Author(s):  
Randall J. LeVeque ◽  
David L. George ◽  
Marsha J. Berger
Keyword(s):  
Finite Volume ◽  
Adaptive Mesh Refinement ◽  
Spatial Scales ◽  
Adaptive Mesh ◽  
Finite Volume Methods ◽  
Small Scale ◽  
Tsunami Propagation ◽  
Small Perturbations ◽  
Tsunami Modelling ◽  
Two Space Dimensions

Numerical modelling of transoceanic tsunami propagation, together with the detailed modelling of inundation of small-scale coastal regions, poses a number of algorithmic challenges. The depth-averaged shallow water equations can be used to reduce this to a time-dependent problem in two space dimensions, but even so it is crucial to use adaptive mesh refinement in order to efficiently handle the vast differences in spatial scales. This must be done in a ‘wellbalanced’ manner that accurately captures very small perturbations to the steady state of the ocean at rest. Inundation can be modelled by allowing cells to dynamically change from dry to wet, but this must also be done carefully near refinement boundaries. We discuss these issues in the context of Riemann-solver-based finite volume methods for tsunami modelling. Several examples are presented using the GeoClaw software, and sample codes are available to accompany the paper. The techniques discussed also apply to a variety of other geophysical flows.

Improving CME evolution and arrival predictions with AMR and grid stretching in EUHFORIA

2021 ◽  
Author(s):  
Tinatin Baratashvili ◽  
Christine Verbeke ◽  
Nicolas Wijsen ◽  
Emmanuel Chané ◽  
Stefaan Poedts
Keyword(s):  
Solar Wind ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Mhd Equations ◽  
Efficiency Gain ◽  
The European Union ◽  
Interplanetary Shocks ◽  
Horizon 2020 ◽  
Research And Innovation ◽  
Speed Up

<p>Coronal Mass Ejections (CMEs) are the main drivers of interplanetary shocks and space weather disturbances. Strong CMEs directed towards Earth can cause severe damage to our planet. Predicting the arrival time and impact of such CMEs can enable to mitigate the damage on various technological systems on Earth. </p><p>We model the inner heliospheric solar wind and the CME propagation and evolution within a new heliospheric model based on the MPI-AMRVAC code. It is crucial for such a numerical tool to be highly optimized and efficient, in order to produce timely forecasts. Our model solves the ideal MHD equations to obtain a steady state solar wind configuration in a reference frame corotating with the Sun. In addition, CMEs can be modelled by injecting a cone CME from the inner boundary (0.1 AU).</p><p>Advanced techniques, such as grid stretching and Adaptive Mesh Refinement (AMR) are employed in the simulation. Such methods allow for high(er) spatial resolution in the numerical domain, but only where necessary or wanted. As a result, we can obtain a detailed, highly resolved image at the (propagating) shock areas, without refining the whole domain.</p><p>These techniques guarantee more efficient simulations, resulting in optimised computer memory usage and a significant speed-up. The obtained speed-up, compared to the original approach with a high-resolution grid everywhere, varies between a factor of 45 - 100 depending on the domain configuration. Such efficiency gain is momentous for the mitigation of the possible damage and allows for multiple simulations with different input parameters configurations to account for the uncertainties in the measurements to determine them. The goal of the project is to reproduce the observed results, therefore, the observable variables, such as speed, density, etc., are compared to the same type of results produced by the existing (non-stretched, single grid) EUropean Heliospheric FORecasting Information Asset (EUHFORIA) model and observational data for a particular event on 12th of July, 2012. The shock features are analyzed and the results produced with the new heliospheric model are in agreement with the existing model and observations, but with a significantly better performance. </p><p> </p><p><strong>This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).</strong></p>

scholarly journals A dynamical model of plasma turbulence in the solar wind

2015 ◽  
Vol 373 (2041) ◽  
pp. 20140145 ◽  
Author(s):  
G. G. Howes
Keyword(s):  
Solar Wind ◽  
Solar Wind Plasma ◽  
Plasma Turbulence ◽  
Alfven Waves ◽  
Dynamical Model ◽  
Alfvén Waves ◽  
Small Scale ◽  
Current Sheets ◽  
Turbulent Fluctuations ◽  
Physical Mechanisms

A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic plasma turbulence. It is argued that the linear and nonlinear dynamics of Alfvén waves are responsible, at a very fundamental level, for some of the key qualitative features of plasma turbulence that distinguish it from hydrodynamic turbulence, including the anisotropic cascade of energy and the development of current sheets at small scales. The first dynamical model of kinetic turbulence in the weakly collisional solar wind plasma that combines self-consistently the physics of Alfvén waves with the development of small-scale current sheets is presented and its physical implications are discussed. This model leads to a simplified perspective on the nature of turbulence in a weakly collisional plasma: the nonlinear interactions responsible for the turbulent cascade of energy and the formation of current sheets are essentially fluid in nature, while the collisionless damping of the turbulent fluctuations and the energy injection by kinetic instabilities are essentially kinetic in nature.

scholarly journals What determines the formation and characteristics of protoplanetary discs?

2020 ◽  
Vol 635 ◽  
pp. A67 ◽  
Author(s):  
Patrick Hennebelle ◽  
Benoit Commerçon ◽  
Yueh-Ning Lee ◽  
Sébastien Charnoz
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
Small Scale ◽  
Initial Structure ◽  
Solar Mass ◽  
Central Object ◽  
The Impact ◽  
Protoplanetary Discs

Context. Planets form in protoplanetary discs. Their masses, distribution, and orbits sensitively depend on the structure of the protoplanetary discs. However, what sets the initial structure of the discs in terms of mass, radius and accretion rate is still unknown. Aims. It is therefore of great importance to understand exactly how protoplanetary discs form and what determines their physical properties. We aim to quantify the role of the initial dense core magnetisation, rotation, turbulence, and misalignment between rotation and magnetic field axis as well as the role of the accretion scheme onto the central object. Methods. We performed non-ideal magnetohydrodynamics numerical simulations using the adaptive mesh refinement code Ramses of a collapsing, one solar mass molecular core to study the disc formation and early, up to 100 kyr, evolution. We paid particular attention to the impact of numerical resolution and accretion scheme. Results. We found that the mass of the central object is almost independent of the numerical parameters such as the resolution and the accretion scheme onto the sink particle. The disc mass and to a lower extent its size, however heavily depend on the accretion scheme, which we found is itself resolution dependent. This implies that the accretion onto the star and through the disc are largely decoupled. For a relatively large domain of initial conditions (except at low magnetisation), we found that the properties of the disc do not change too significantly. In particular both the level of initial rotation and turbulence do not influence the disc properties provide the core is sufficiently magnetised. After a short relaxation phase, the disc settles in a stationary state. It then slowly grows in size but not in mass. The disc itself is weakly magnetised but its immediate surrounding on the contrary is highly magnetised. Conclusions. Our results show that the disc properties directly depend on the inner boundary condition, i.e. the accretion scheme onto the central object. This suggests that the disc mass is eventually controlled by a small-scale accretion process, possibly the star-disc interaction. Because of ambipolar diffusion and its significant resistivity, the disc diversity remains limited and except for low magnetisation, their properties are weakly sensitive to initial conditions such as rotation and turbulence.

SIP-CESE MHD model of solar wind with adaptive mesh refinement of hexahedral meshes

2014 ◽  
Vol 185 (7) ◽  
pp. 1965-1980 ◽  
Author(s):  
Xueshang Feng ◽  
Changqing Xiang ◽  
Dingkun Zhong ◽  
Yufen Zhou ◽  
Liping Yang ◽  
...  
Keyword(s):  
Solar Wind ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Hexahedral Meshes ◽  
Mhd Model

A Multi-Fluid Investigation of the Membrane Supporting Grid Effects on the Richtmyer-Meshkov Instability

2019 ◽  
Vol 390 ◽  
pp. 1-7
Author(s):  
Mohamad Al-Marouf ◽  
Ravi Samtaney
Keyword(s):  
Adaptive Mesh Refinement ◽  
Numerical Experiments ◽  
Complex Geometry ◽  
Adaptive Mesh ◽  
Circular Cylinders ◽  
Small Scale ◽  
Gas Mixture ◽  
Material Interface ◽  
Wire Grid ◽  
Thin Wires

We present results of numerical experiments performed to evaluate the effects of the material interface supporting wire grid on the Richtmyer-Meshkov instability (RMI). An air-SF6 interface initially perturbed sinusoidally supported on a number of solid circular cylinders. These cylinders are introduced along the interface to mimic the presence of the grid thin wires. The resulted mixing and growth rate of the perturbation in the presence and absence of the supporting grid were analyzed and validated with experimental measurements. The small scales perturbation imposed by the cylinders are around two orders of magnitude smaller than the interface sinusoidal perturbation wavelength requiring the adaptive mesh refinement (AMR) to adequately resolve small scale features. Furthermore, an embedded boundary technique is used to handle the complex geometry stemming from the presence of these multiple. A multi-fluid formulation is utilized to form a multi-gas species interface and compute the gas mixture properties.

Adaptive mesh refinement method based investigation of the interaction between shock wave, boundary layer, and tip vortex in a transonic compressor

2017 ◽  
Vol 232 (4) ◽  
pp. 694-715 ◽  
Author(s):  
Jinlan Gou ◽  
Xin Yuan ◽  
Xinrong Su
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Tip Vortex ◽  
Small Scale ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Mesh Convergence

Shock wave and tip leakage are important flow features at small length scales. These flow phenomena and their interactions play important roles in the performance of modern transonic fans and compressors. In most numerical predictions of these features, mesh convergence studies are conducted using overall performance data as criteria. However, less effort is made in assessing the quality of the predicted small-scale features using a mesh that yields a fairly accurate overall performance. In this work, this problem is addressed using the adaptive mesh refinement (AMR) method, which automatically refines the local mesh and provides very high resolution for the small-scale flow feature, at much less cost compared with globally refining the mesh. An accurate and robust AMR system suitable for turbomachinery applications is developed in this work and the widely studied NASA Rotor-37 case is investigated using the current AMR method. The complex interactions between the shock wave and the boundary layer, as well as those between the shock wave and the tip vortex, are accurately captured by AMR with a very high local grid resolution, and the flow mechanisms are analyzed in detail. The baseline mesh, which is considered to be “acceptable” according to the commonly used mesh convergence study, is unable to capture the detailed interaction between the shock wave and the boundary layer. Moreover, it falsely predicts the tip leakage vortex breakdown, which is a consequence of inadequate resolution in the tip region. Current work highlights the importance of a careful check of the mesh convergence, if small-scale features are the primary concern. The AMR method developed in this work successfully captures the flow details in the transonic compressor in an automatic fashion, and has been verified to be efficient compared with the globally mesh refinement or manually mesh regeneration.

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