It is generally believed that the magnetic free energy accumulated in thecorona serves as a main energy source for solar explosions such as coronal massejections (CMEs). In the framework of the flux rope catastrophe model for CMEs,the energy may be abruptly released either by an ideal magnetohydrodynamic(MHD) catastrophe, which belongs to a global magnetic topological instabilityof the system, or by a fast magnetic reconnection across preexisting orrapidly-developing electric current sheets. Both ways of magnetic energyrelease are thought to be important to CME dynamics. To disentangle theircontributions, we construct a flux rope catastrophe model in the corona andsolar wind and compare different cases in which we either prohibit or allowmagnetic reconnection to take place across rapidly-growing current sheetsduring the eruption. It is demonstrated that CMEs, even fast ones, can beproduced taking the ideal MHD catastrophe as the only process of magneticenergy release. Nevertheless, the eruptive speed can be significantly enhancedafter magnetic reconnection sets in. In addition, a smooth transition from slowto fast eruptions is observed when increasing the strength of the backgroundmagnetic field, simply because in a stronger field there is more free magneticenergy at the catastrophic point available to be released during an eruption.This suggests that fast and slow CMEs may have an identical driving mechanism.
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