Solar flares are the result of magnetic reconnection in the solar corona which converts magnetic energy into kinetic energy resulting in the rapid heating of solar plasma. Characterizing how this hot plasma subsequently cools is important for understanding the evolution of flares and the corresponding heating of the quiescent corona. Because the flare soft x-ray and EUV emission spectra are dependent on the source plasma temperature, understanding flare cooling is also important for understanding how solar flares impact planetary atmospheres.
Solar flare cooling has been studied extensively with hydrodynamic simulations that model the temperature, pressure and velocity evolution of a flaring loop. In this seminar, I present a simple new framework in which to study flare cooling which does not involve solving the hydrodynamic equations. Instead, I use a novel Lumped Element Thermal Model (LETM) for describing cooling flare plasma. LETM analysis is frequently used in science and engineering to simplify a complex multi-dimensional thermal system by reducing it to a 0-D thermal circuit. For example, a structure that conducts heat out of a system is simplified with a resistive element and a structure that allows a system to store heat is simplified with a capacitive element. A major advantage of LETM analysis is that the specific geometry of a system can be ignored, allowing for an intuitive analysis the major thermal processes.
I will show that LETM analysis is able to accurately reproduce the temporal evolution of cooler flare emission lines based on hotter emission line evolution. The LETM framework also results in a number of interesting analytical expressions relating flare plasma properties. I will show that these expressions are consistent with those approximated from hydrodynamic analysis, but also provide new insight such as a closed-form expression for the decay-phase heating function as a function of temperature and density, and a relation for the flare cooling time based on the peak electron density measured early in the flare. I will present observational evidence supporting the LETM framework, motivating its use as a new tool for investigating solar flare evolution.