Modeling and understanding coronal loop dynamics during solar flares

Abstract

Magnetic reconnection is widely considered to be the mechanism behind solar flares. Models powered by reconnection manage to explain many of the observational features seen in a flare. However, these models miss or contradict important elements of the flare. Here we consider three effects overlooked by models. First, the role played by the magnetic canopy in determining the chromospheric response in a flare. Second, how variations in magnetic field strength along the current sheet impact the evolution of are loops. Third, how flux tube interactions with the current sheet can lead to sub-Alfvenic motion, bringing dynamics in line with observations. These three effects were investigated with the use of one dimensional and thin flux tube models. This allowed for the dynamics to be considered independent of the reconnection process that generated the flux tubes. The canopy interaction revealed that the creation of an expansion followed by a constriction, a chamber in the flux tube, leads to multiple solutions. The solutions include smooth flow and standing shocks in the chamber. The standing shock increases the emission of the flow, as well as slowing it to subsonic speeds. The shocked solution shifts the ensemble of flux tubes to have a distribution that would indicate slower speeds than expected. The structure of the current sheet magnetic field leaves a signature on the flux tube. Each case leads to a difference in emission. Retraction through a constricting field creating a plug of material leading to a bright emission in the apex. This contrasts with retraction through an expanding field which generates high temperatures, but as a fainter emission. The interaction of drag in the current sheet allowed for the retraction to proceed at slower rates. The slower retraction matches observations of features in flares more accurately. The slower retraction also increases the brightness of the synthetic current sheet. This increased brightness brings the current sheet closer to the observed brightness. These investigations found that there was benefit to considering these additional effects. Each one of these effects was found to bring the models more in line to what observations note.