Measuring the magnetic origins of solar flares, coronal mass ejections, and space weather

With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near-UV (NUV) part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, the Hubble Space Telescope, and SKYLAB, along with 1D computations of the NUV spectrum and numerical experiments based on the MURaM radiation-magnetohydrodynamic and HanleRT radiative transfer codes, we address multiple challenges.

These challenges are best met through a combination of NUV lines of bright Mg ii, and lines of Fe ii and Fe i (mostly within the 4s-4p transition array) which form in the chromosphere up to 2 x 10(4) K. Both Hanle and Zeeman effects can in principle be used to derive vector magnetic fields. However, for any given spectral line the tau = 1 surfaces are generally geometrically corrugated owing to fine structure such as fibrils and spicules.