Flare location on the solar disk: Modeling the thermosphere and ionosphere response

Most emission lines in the XUV region (~0.1 to ~25 nm) are optically thin and are weakly dependent on the location of the flare, but in the EUV region (~25 to ~120 nm), many important lines and continua are optically thick, so enhancements are relatively smaller for flares located near the solar limb, due to absorption by the solar atmosphere.

The flare irradiance spectral model (FISM) was used to illustrate these location effects, assuming two X17 flares that are identical except that one occurs near disk center and the other near the limb. FISM spectra of these two flares were used as solar input to the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) to investigate the ionosphere/thermosphere (I/T) response.