Data-constrained Modeling of the Flaring Solar Chromosphere

The Sun, our nearest star, has a profound influence on all life on Earth. As we become more and more reliant upon technology, understanding how the Sun's radiative output varies, and the impact of that variability on planetary atmospheres, is becoming ever more important through the emerging field of space weather research. The Sun's output can vary on a range of timescales, from seconds to minutes (during solar flares), to weeks and months (due to sunspot rotation), and years and decades (over solar cycles). Solar flares are the most energetic explosions in the solar system resulting from rapid restructuring of the Sun's coronal magnetic field. This accelerates particles to extremely high energies which ultimately collide with the dense, underlying chromosphere, causing it to heat and expand. The resulting increase in ultraviolet and X-ray radiation can significantly impact the upper layers of Earth's atmosphere, as well as those of other planets. On Earth this can have implications for GPS accuracy, the propagation of radio signals, and atmospheric drag on orbiting spacecraft. This radiation also allows us to diagnose the plasma conditions within the flaring chromosphere itself and put constraints on various flare heating models, as the underlying physical mechanisms are not yet fully understood. The study of solar flares is also important to help us understand flares on other stars, and how they may impact the search for potentially habitable exoplanets.

As Solar Cycle 24 draws to a close, a considerable amount of solar flare data has been amassed from a wealth of space-based solar observatories over the past decade. Numerical simulations of solar flare heating have also become more sophisticated thanks to advances in computation. These two factors make this an opportune time to make significant strives in our understanding of what drives increases in ultraviolet radiation during solar flares, how this contributes to the solar irradiance, and what impact this has on planetary atmospheres. As we look ahead to Solar Cycle 25 this research will also be crucial for the interpretation of observations from newly-launched and upcoming space missions that will study the Sun in greater detail than ever before.