A Tale of Two Chromospheres

Han Uitenbroek

Traditionally, the presence of emission lines in the solar UV spectrum, as well as the appearance of emission reversals in the cores of strong optical lines like the calcium H and K lines has been modeled with the assumption of an omnipresent chromospheric temperature rise. Recent observations of vibration-rotation transitions of the CO molecule stipulate however that the chromosphere cannot be hot everywhere and all the time. I will show some of the relevant observations and discuss how the different pictures of the chromospheric that emerge from analyzing these different diagnostics reach very different conclusions about its structure, even though they model the same spatially and temporally averaged spectrum.