Modeling magnetic flux ropes in the solar atmosphere

Coronal flux ropes are highly sheared or twisted magnetic fields overlying polarity inversion lines on the solar photosphere. The formation of such flux ropes is briefly discussed. A coronal flux rope can be stable for many days and then suddenly lose equilibrium and erupt, producing a coronal mass ejection (CME). To understand what causes such eruptions, we need to determine the 3D magnetic structure of observed active regions prior to CMEs. This requires constructing nonlinear force free field models of active regions based on observed photospheric vector fields, Hα filaments, or coronal loop structures. We describe a new method for constructing models containing flux ropes.