Plasma Physical Parameters Along Cme-Driven Shocks. Ii. Observation–simulation Comparison

Abstract

In this work, we compare the spatial distribution of the plasma parameters along the 1999 June 11 coronal mass ejection (CME)-driven shock front with the results obtained from a CME-like event simulated with the FLIPMHD3D code, based on the FLIP-MHD particle-in-cell method. The observational data are retrieved from the combination of white-light coronagraphic data (for the upstream values) and the application of the RankineHugoniot equations (for the downstream values). The comparison shows a higher compression ratio X and Alfvénic Mach number M A at the shock nose, and a stronger magnetic field deflection d toward the flanks, in agreement with observations. Then, we compare the spatial distribution of M A with the profiles obtained from the solutions of the shock adiabatic equation relating M A , X, and Bn q (the angle between the upstream magnetic field and the shock front normal) for the special cases of parallel and perpendicular shock, and with a semi-empirical expression for a generically oblique shock. The semi-empirical curve approximates the actual values of M A very well, if the effects of a non-negligible shock thickness sh d and plasma-to magnetic pressure ratio u b are taken into account throughout the computation. Moreover, the simulated shock turns out to be supercritical at the nose and sub-critical at the flanks. Finally, we develop a new one-dimensional Lagrangian ideal MHD method based on the GrAALE code, to simulate the ion-electron temperature decoupling due to the shock transit. Two models are used, a simple solar wind model and a variable-γ model. Both produce results in agreement with observations, the second one being capable of introducing the physics responsible for the additional electron heating due to secondary effects (collisions, Alfvén waves, etc.).

Physical Conditions of Coronal Plasma at the Transit of a Shock Driven by a Coronal Mass Ejection

“…These are not strong assumptions, as discussed in Bemporad & Mancuso (2011), and can be considered fairly verified also in our case. Under these hypotheses, as we verified observationally in Bemporad, Susino, & Lapenta (2014) and theoretically in Bacchini et al (2015), the Alfvénic Mach number is well approximated in the general case of oblique shock by the following semi-empirical formula:…”

“…The validity of Eq. ( 4) has been confirmed by the analysis of Bemporad, Susino, & Lapenta (2014) which takes advantage of both white-light and ultraviolet data from the Ultra-Violet Coronagraph Spectrometer (UVCS) on board SOHO (see discussion therein) and has been recently tested with MHD numerical simulations by Bacchini et al (2015). This equation allowed us to derive, from different values of X and θ sh parameters, 2D polar maps of M A∠ values, as shown in Figure 7 (top right panel).…”

Division E Commission 49: Interplanetary Plasma and Heliosphere

“…Bemporad et al (2014)). Simulations and theories of particle acceleration have confirmed that the low corona is an environment that supports the conditions necessary for particle acceleration to high energies (Kozarev et al (2011), Bacchini et al (2015)). Several modeling efforts of particle acceleration at coronal shocks have been developed (e.g., Battarbee et al (2013), Gargaté et al (2014), Schwadron et al (2015), and references therein).…”

Corrugated Features in Coronal-mass-ejection-driven Shocks: A Discussion on the Predisposition to Particle Acceleration

“…This deflection is also mentioned in Liu et al (2011) as the rotation of the magnetic field in the downstream. This deflection is explained by the shock transit on the magnetic field that drape the CME (e.g., Bacchini et al 2015). Additionally, some MHD numerical shock studies show the magnetic field amplification in downstream region and parallel upstream magnetic field disposition explained through that perpendicular downstream magnetic field is not advected (e.g., Falceta-Gonçalves & Abraham 2012;Rocha da Silva et al 2015).…”