Understanding the Evolution of He II Emission in Solar Flares

In this work, we describe a method to construct a global model of a solar flare arcade. We derive a method to empirically recreate the changing geometry of the flare, in particular the ribbon expansion and loop lengths with time. We then validate the model by comparing against SDO/AIA and MinXSS soft X-ray spectra for a set of five well-observed flares. With this validated model, we then synthesize the optically-thick He II 256 A line emission as might be seen by Hinode-EIS, as well as SDO/AIA 304 He II emission, that we then contrast with actual observed quantities seen by those instruments for a large flare. We demonstrate that the quantities can be used to tightly constrain the properties of the energy deposition in the chromosphere.