Initial-Condition Influences on CME Expansion and Propagation

A general-purpose melon-seed-overpressure-expansion (MSOE) model is used to examine the dependence of the expansion and propagation of fast CMEs on average initial values of the magnetic field inside the CME, the magnetic field outside the CME, and the CME mass. The MSOE model extracts from the real situation only features that are essential in determining the expansion and propagation processes and idealizes them to obtain an adaptable “minimalist” set of equations that governs these processes yet retains enough relevant physics to give useful results. This minimalist set is used to carry out a systematic comparison of solutions against four sets of observed correlations between CME and ICME parameters in which the input parameters to the MSOE model are varied to achieve simultaneous fits to all four correlations. The fits impose relations between the three independent input variables: initial internal field strength, initial external field strength, and initial density. For example, light CMEs (e.g., those with no prominences) require the external field strength to nearly equal the internal field strength. However, heavy CMEs (e.g., those with prominences) require the external field strength to be much weaker than the internal field strength.