Statistical Analysis of Impulsiveness and Rise Phase Duration of Solar
Flares in the He II 304 Angstrom Chromospheric Line
Abstract
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.