HAO Colloquium - Ed Thiemann, CU/LASP

Progress towards a more physics-based approach to solar flare irradiance proxy modeling

Solar flare enhancements for the largest X-class flares rival the enhancements of non-flaring irradiance seen over the 11-year solar cycle, increasing by orders of magnitude the irradiance at some of the highest energy wavelengths in minutes.  This irradiance enhancement increases the ionization and heating of Earth's upper atmosphere, which can adversely impact technologies we rely upon by interfering with communications and navigation signals, as well as influencing satellite trajectories.  Accurate estimates of solar flare irradiance are needed in order to estimate the atmospheric response to solar flares for both research and operational space weather applications.  Solar irradiance proxy models, which determine the solar flare irradiance from a spectrally-limited number of available measurements, are appealing because their computational simplicity allows for real-time estimates.  Further, proxy models have the ability to estimate spectral irradiance during any time when the proxy is available, which can span decades.  However, flare proxy modeling is relatively new, and the accuracy of current flare proxy models can still be improved, in part, by incorporating more of the underlying physical processes known to determine the flare spectrum.  

In this seminar, I summarize recent advances that will lead to a more physics-based approach to solar flare proxy modeling, while preserving their computational simplicity and long-term applicability.  These advances include results showing that the GOES XRS peak Emission Measure (EM) estimates are highly correlated with the peak intensity of many of the brightest EUV emission lines observed by SDO EVE, consistent with the theoretical relation between line intensity and emission measure.  Additionally, I show how incorporating knowledge from simple flare cooling theory can significantly improve the estimates of the time evolution of EUV light curves made by proxy models.  Finally, it is shown that by considering the opacity of various line emissions as derived from atomic physics parameters, more accurate estimates of the center-to-limb-variability of EUV flare emissions can be made.   

Date and time: 
Wednesday, October 17, 2018 - 2:00pm to 3:00pm