Project ISEST/MiniMax24
(International Study of Earth-affecting Solar Transients)
WG2 (Working Group on Theory)
Bojan Vrsnak
The overall aim of WG2 is to advance our comprehension of the physical background of Earth-affecting solar transients. The main goals can be summarized as follows:
- to improve the understanding of the structure and evolution of CMEs as well as their origin and their magnetic structure, including the problem of modelling the southward magnetic field component (Bs);
- to improve comprehension of the coronal and heliospheric dynamics of CMEs, including the interaction with ambient solar wind and interplanetary magnetic field, causing deceleration/acceleration and deflections;
- to get a better insight into how long does the Lorentz force dominate over the aerodynamic drag force, including the estimation of the drag parameter and/or the dimensionless drag coefficient;
- to compare the results derived by different analytic and numerical models with observations, e.g., 1 AU transit time, impact speed, impact magnetic field, etc.;
- to advance understanding of the structure and evolution of corotating interaction regions and physical relationship with coronal holes.
At this point, the WG2 operational activity is mainly directed to advancing analytic CME-propagation models that can be used for the forecasting purposes, such as the Drag Based Model (DBM, Zic et al. 2015 and references therein), the Deflection Model (DIPS; Wang et al. 2014) and Snow Plough Model (SPM; Tappin, 2006). In recent years, the DBM started to be frequently employed tool used to understand better various aspects of the heliospheric dynamics of CMEs (e.g., Wang et al. 2016 and references therein). The CME deflected propagation in the solar wind was reproduced in a 3D MHD simulation (Shiota et al. 2016). Comparisons of results based on analytical models and those based on numerical models have become another important aspect of WG2 activity, such as ENLIL, COIN-TVD, CESE, and H3DMHD (Figure 1; Vrsnak et al. 2014).
Figure 1. Comparison of numerical ENLIL code and analytic Drag-Based Model (DBM).
a) ENLIL simulation (http://iswa.gsfc.nasa.gov/iswa/iSWA.html);
b) DBM output (http://oh.geof.unizg.hr/DBM/dbm.php). Snapshots show the situation on 2012 April 26 (12 UT and 07 UT for ENLIL and DBM, respectively), representing the CME that was launched on 2012 April 23.
c) DBM-calculated vs. ENLIL-calculated Sun-1AU transit times for a sample of 50 CMEs (adopted from Vrsnak et al. 2014).
References:
Möstl, C., Rollett, T., Frahm, R. A., et al.: 2015, Nature Communications, 6, 7135.
Shiota, D., Iju, T., Hayashi, K., et al.: 2016, AGU Fall Meeting, SH22B-03.
Tappin, S. J.: 2006, Solar Phys., 233, 233.
Vrsnak, B., Zic, T., Temmer, M., et al.: 2014, ApJS, 213, 21.
Wang, Y., Wang, B., Shen, C., et al.: 2014, JGR, 119, 5117.
Wang, Y., Zhang, Q., Liu, J., et al.: 2016, JGR, 121, 7423.
Zic, T., Vrsnak, B., Temmer, M.: 2015, ApJS, 218, 32.