We perform statistical analysis of solar flare light curves and ribbon morphology to advance our understanding of flare impulsiveness, an important parameter to describe stellar flares. The Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE) provides “Sun-as-a-star” data corresponding to the variability of the Sun’s irradiance in the XUV and EUV wavelengths (from 0.1 to 106 nm). Using EVE light curves in the 304 Angstrom line, we study 2049 solar flares from 30 April 2010 to 26 May 2014. We present an algorithm for fitting the flare light curves in the 304 Angstrom line, emitted by He II at around 50000 K from the chromosphere and transition region and therefore representative of the dominant source of radiation in a solar flare. We use this algorithm to identify particularly high signal-to-noise flare light curves within the database, with representatives from C, M, and X flare classes. The parameters of the model associated with each flare can be used to identify notable features such as the incidence of multiple peaks in the rise phase. Identification of the rise and decay phases for each flare allows us to compare rise phase duration and flare impulsiveness to geometrical and physics-based properties of each flare, an important step in advancing our understanding of flare energy release. Specifically, using SDO Atmospheric Imaging Assembly (SDO/AIA) instrument data in the 1600 Angstrom line, we analyze the flare morphology and energy release in the context of the “impulsiveness” classification scheme for a sub-sample of the flares. We also compare this index to several solar flare properties including duration, peak X-ray flux, reconnection rate, and quasi-periodic pulsation (QPP) period, among others.

It has long been recognized that the energy source for major solar flares and coronal mass ejections (CMEs) is the solar magnetic field within active regions. Specifically, it is believed to be the release of the free magnetic energy (energy above the potential field state) stored in the field prior to eruption. For estimates of the free energy to provide a prognostic for future eruptions, we must know how much energy an active region can store – Is there a bound to this energy? The Aly-Sturrock theorem shows that the energy of a fully force-free field cannot exceed the energy of the so-called open field. If the theorem holds, this places an upper limit on the amount of free energy that can be stored. In recent simulations, we have found that the energy of a closely related field, the partially open field (POF), can place a useful bound on the energy of an eruption from real active regions, a much tighter constraint than the energy of the fully open field. A database of flare ribbons (Kazachenko et al., ApJ 845, 2017) offers us an opportunity to test this idea observationally. A flare ribbon mask is defined as the area swept out by the ribbons during the flare. It can serve as a proxy for the region of the field that opened during the eruption. In this preliminary study, we use the ribbon masks to define the POF for several large events originating in solar cycle 24 active regions, and compute the energy of the POF. We compare these energies with the X-ray fluxes and CME energies for these events. Work supported by NSF, NASA, and AFOSR.