The 16 August 1999 EUV brightenings are numerically simulated by a third-order upwind compact scheme,basing on the TRACE observation.The present simulation can give a possible explanation to its formation and evolution.The numerical results show that the initial reconnection jets at around X-point are responsible for the occurrence of EUV brightening.The strong and superposed ejections caused by the first and second coalescence of magnetic islands are possibly related to the lifted material which initially appeared as absorption features and Later EUV-emitting structures respectively.The bi-directional reconnection jets may correspond to the lifted material that either continued to move upward along the apparently open field lines or fell down to the surface.
A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.
A three-dimensional MHD simulation is conducted to study the steady solar wind in Carrington Rotation (CR) 1935 by using the three-dimensional numerical magnetohydrodynamic (MHD) model introduced by Feng et al The numerical results demonstrate that the neutral current sheet has two peaks and two valleys, which is consistent with the result of PFSS model at Wilcox Solar Observatory (WSO). The obtained proton number density at 2.5 Rs is of the same order of magnitude as the result estimated from K-coronal brightness during the CRs 1733-1742 in 1983 made by Wei et al. The radial velocity profile along heliocentric distance is consistent with that of low solar wind speed deduced by Sheeley and Wang et al. However, it is not able to reproduce the fast-speed flow in coronal holes and slow solar wind in streamers because of oversimplified energy equation adopted in our model. Future efforts must be made to remedy this deficiency.
An asynchronous and parallel time-marching method for three-dimensional (3D) time-dependent magnetohydrodynamic (MHD) simulation is used for large-scale solar wind simulation. It uses different local time steps in the corona and the heliosphere according to the local Courant-Friedrichs-Levy (CFL) conditions. The solar wind background with observed solar photospheric magnetic field as input is first presented. The simulation time for the background solar wind by using the asynchronous method is <1/6 of that by using the normal synchronous time-marching method with the same computation precision. Then, we choose the coronal mass ejection (CME) event of 13 November, 2003 as a test case. The time-dependent variations of the pressure and the velocity configured from a CME model at the inner boundary are applied to generate transient structures in order to study the dynamical interaction of a CME with the background solar wind flow between 1 and 230 Rs. This time-marching method is very effective in terms of computation time for large-scale 3D time-dependent numerical MHD problem. In this validation study, we find that this 3D MHD model, with the asynchronous and parallel time-marching method, provides a relatively satisfactory comparison with the ACE spacecraft obser- vations at L1 point.
