Magnetic reconnection and coronal transients

Abstract

Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts -the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered -one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light.Since major flares are usually associated with a filament eruption about 10-15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.

Two types of flare-associated coronal mass ejections

“…Probably in the case of the slowest events, the reconnection does not generate such jets but only reduces the magnetic tension and diminishes the erupting-flux rope acceleration (e.g. Anzer & Pneuman 1982;Cheng & Krall 2003;Lin et al 2004). These events tend to be decelerated even if they are slow (Fig.…”

The CME-flare relationship: Are there really two types of CMEs?

“…There are two effects of reconnection process which may play an important role in the CME dynamics. Firstly, the reconnection reduces the net tension of the overlaying arcade field and increases the magnetic pressure below the erupting flux-rope (e.g., Van Tend & Kuperus 1978;Anzer & Pneuman 1982;Forbes 1990;Cheng et al 2003;Lin et al 2004). Secondly, the upward-directed reconnection jet carries the reconnected field lines to the erupting fluxrope, supplying it with a "fresh" poloidal flux.…”

Processes and mechanisms governing the initiation and propagation of CMEs

“…Firstly, the reconnection reduces the net tension of the overlying arcade field and increases the magnetic pressure below the flux-rope, which certainly plays a significant role in the CME dynamics (e.g., van Tend and Kuperus, 1978;Anzer and Pneuman, 1982;Lin, 2002). Secondly, the upward-directed reconnection jet carries the reconnected field lines to the erupting flux-rope, supplying it with a "fresh" poloidal flux.…”