Global simulation of extremely fast coronal mass ejection on 23 July 2012

摘要

The July 23, 2012 CME was an extremely fast backside event, reaching similar to 1 AU (STEREO-A) within 20 h as compared to similar to 3-6 days for typical CME events. Here, we present results from a simulation study of the CME and its driven shock using a combined kinematic and magnetohydrodynamic (MHD) simulation model, H3DMHD. In general, the model results match well with in situ measurements in the arrival time of the CME-driven shock and the total magnetic field strength, assuming an initial CME speed of 3100 km/s. Based on extrapolation of an empirical model, the fast CME and its large magnetic field (I vertical bar B vertical bar similar to 120 nT) are capable of producing an extremely large geomagnetic storm (Dst similar to - 545 nT), comparable to the well-known Halloween storm in 2003, if the CME had made a direct impact to the Earth. We investigated the effect of the adiabatic index (gamma). It is found that the shock tends to arrive slightly later for a smaller gamma value, and gamma=5/3 provides the best agreement for the shock arrival time. We also demonstrate that the strength (the Mach number) of the CME-driven fast-mode shock is not the largest at the "nose" of the CME. This is mainly due to the manifestation of fast-mode wave speed upstream of the shock. (C) 2014 Elsevier Ltd. All rights reserved.