Solar Magnetic Topologies and Reconnection

Abstract

A review is presented on the topology and eruption of twisted magnetic configurations in connection with eruptive flares, dynamical disparition brusque of prominences, and coronal mass ejections. A classical view of magnetic reconnection is mainly based on the MHD physics of 2-D configurations with an X-type neutral point, or on the extension of it to 3-D, and it is thought to be accompanied by flux transport across separatrices (places where the field-line mapping is discontinuous). This view is too restrictive because energy release can also occur in configurations without a magnetic null point both in the corona and terrestrial magnetosphere. These configurations have continuous field-line linkage; it implies that the classical picture of reconnecting field lines at the intersection of separatrices should be revised. We present here such an attempt applied to twisted configurations. We define a function N that gives a quantitative estimate of the field line linkage. While the field line linkage is continous, there are extremely thin layers, called quasi-separatrix layers (QSLs), where the gradient of the field-line linkage from one part of a boundary to another exeeds its typical value by many orders of magnitude. Even for highly conductive media these extremely thin layers behave like separatrices. Thus reconnection without null points can occur in QSLs with a breakdown of ideal MHD and a change in connectivity of plasma elements.