Abstract
Abstract In past decades, much progress has been achieved in understanding the origin and evolution of coronal mass ejections (CMEs). In situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these properties in an erupting CME flux rope, in particular in a preexisting flux rope. In this work, we propose a model to estimate the toroidal flux of a preexisting flux rope by subtracting the flux contributed by magnetic reconnection during the eruption from the flux measured in the MC. The flux contributed by the reconnection is derived from geometric properties of two-ribbon flares based on a quasi-2D reconnection model. We then apply the model to four CME/flare events and find that the ratio of toroidal flux in the preexisting flux rope to that in the associated MC lies in the range 0.40–0.88. This indicates that the toroidal flux of the preexisting flux rope makes an important contribution to that of the CME flux rope and is usually at least as large as the flux arising from the eruption process for the selected events.
Highlights
Coronal mass ejections (CMEs) represent rapid eruptions of magnetized plasma in the solar corona, and may be observed as structures that are brighter than the background in white-light coronagraph images (Hundhausen et al 1984)
CMEs propagating in interplanetary space are called interplanetary coronal mass ejections (ICMEs; Burlaga et al 1982; Klein & Burlaga 1982), some of which are termed “magnetic clouds” (MCs) when they possess a rotation of the magnetic field (Burlaga 1991) and a decrease in proton and electron temperature (Gosling et al 1987; Richardson & Cane 1995)
We quantify the toroidal flux of preexisting flux ropes of CMEs
Summary
Coronal mass ejections (CMEs) represent rapid eruptions of magnetized plasma in the solar corona, and may be observed as structures that are brighter than the background in white-light coronagraph images (Hundhausen et al 1984). As the reconnection occurs between two legs of field lines at higher and higher altitudes, the post-flare loops rise with their footpoints separating from each other, which is the separation motion of flare ribbons In this 2D model, the closed fluxes that are formed during the reconnection go totally to the poloidal flux of the CME flux rope (e.g., Lin et al 2004; Qiu et al 2007). Unlike the CSHKP model, both the flux rope envelope and the post-flare loops formed in the quasi-2D reconnection are anchored on the flare ribbons, and the newly formed twisting field lines that constitute the flux rope envelope are no longer self-closed.
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