Identifying the sources and variability of solar F10.7 with differential emission measures

The solar corona emits high-energy Extreme Ultraviolet (EUV) light that is absorbed in the Earth's upper atmosphere. creating the ionosphere. Understanding how changes in the Suns EUV emission influence the terrestrial atmosphere is important. but, due to the absorption. EUV can not be observed from the ground. Instead. a common proxy measurement is F10.7. the 10.7 cm (2.8 GHz) solar microwave flux density measured at 1 W. F10.7 is produced in the same coronal plasma as EUV and they correlate well over solar cycle tinlescales. However. F10.7 is typically averaged over 81 days when used as a proxy because there are known short-terns discrepancies in its relationship with EUV: it varies much more over a typical solar rotation than does EUV. This is due to the presence of two different coronal F10.7 emission mechanisms. bremsstrahlung that correlates extremely well with EUV. and gyroresonance that has no direct relationship with EUV emission. The purpose of this research is to determine the contribution of each of these mechanisms to the F 10.7 flux and variability. A test study is performed using a set of EUV images from the Atmospheric Imaging Assembly to compute differential emission measures (DEMs, a measure of the plasma thermal content) that are used to predict an F10.7 bremsstrahlung image. This is compared with an imaging observation of F 10.7 taken with the Very Large Array and proves the ability to identify both bremsstrahlung and gyroresonance emission with DEMs. Using the lessons from this initial analysis, four years of full-Sun DEMs are computed from EUV Variability Experiment spectra. This reveals an unexpected temporal bimodality in the coronal thermal structure. These DEMs are used to predict the bremsstrahlung emission at five microwave frequencies including F10.7 and then the relative contribution of bremsstrahlung and gyroresonance emission is determined both spectroscopically and using the DELI predictions. Breunsstrahlung emission is found to dominate the coronal F10.7 except during short periods of intense activity near solar maximum. A bremsstrahlung correction to F10.7 is calculated and compared to the traditional F10.7 proxy. revealing the fundamental limitation of its efficacy as a single-input EUV proxy.