Flare Irradiance Spectral Model (FISM): Flare component algorithms and results

Abstract

The Flare Irradiance Spectral Model (FISM) is an empirical model developed for space weather applications that estimates the solar irradiance at wavelengths from 0.1 to 190 nm at 1 nm resolution with a time cadence of 60 s. This is a high enough temporal resolution to model variations due to solar flares, where few accurate measurements at these wavelengths exist, as well as the solar cycle and solar rotation variations. The FISM modeling of the daily component variations, including variations from the solar cycle and solar rotation, was the topic of the first FISM paper (Chamberlin et al., 2007). The modeling of the FISM flare component that includes the solar irradiance variations from both the impulsive and gradual phases of solar flares is the topic of this paper. The flare component algorithms and results are discussed, and comparisons show that FISM estimates agree within the stated uncertainties with measurements of the solar vacuum ultraviolet (VUV; 0.1–200 nm) irradiance. Results from FISM show that the relative change of the solar irradiance during flares for some wavelengths can exceed those of the solar cycle relative changes, ranging from factors of 60 times the quiet Sun irradiance during the gradual phase for emissions originating in the solar corona to factors of 10 in the transition region emissions during the flare's impulsive phase. FISM fully quantifies, on all timescales, the changes in the solar VUV irradiance directly affecting satellite drag, radio communications, as well as the accuracy in the Global Positioning System (GPS).