Solar Ultraviolet Irradiance Observations of the Solar Flares During the Intense September 2017 Storm Period

Abstract

A large outburst of flares occurred between 4-10 September 2017 when new magnetic flux emerged into and strengthened an existing active region, National Oceanic and Atmospheric Administration Region 12673. This intense solar storm period included X9.3 (6 September) and X8.2 (10 September) flares, the largest flares that have occurred during Solar Cycle 24, as well as 39 M-class flares and three additional X-class flares. Another X-class flare from this active region was observed on the farside of the Sun from Mars Atmosphere and Volatile EvolutioN prior to the September events, along with other large M-class flares, showing the potential for how farside irradiance monitoring can improve flare prediction at Earth for 1-to 13-day forecasts. This September 2017 flare period is similar to other famous storm periods such as the 18 October to 5 November 2003 Halloween storm that produced 14 X-class flares and 137 M-class flares and the 6-10 September 2005 period that had 11 X-class and 68 M-class flares. All of these storm periods occurred in the declining phase of the solar cycle when solar activity had decreased significantly from solar maximum levels. This paper focuses on a number of solar irradiance observations at ultraviolet (0-190 nm) wavelengths during the September 2017 storm period and the advantages that an ensemble of measurements and models have for studying solar flares.A number of solar irradiance observatories were available to provide valuable data sets for storm periods prior to the September 2017 flares, although not all of these instruments were optimized to study these events because of reduced temporal cadence and duty cycle. Regardless, valuable studies looking at the evolution and energetics of solar flares as well as their space weather impact on planetary systems have been performed using these data. Chamberlin et al. (2008) used 27 flares observed with Solar EUV Experiment (SEE) to produce an empirical model, called the Flare Irradiance Spectral Model (FISM) to estimate the solar irradiance from 0.1 to 190 nm at 1-min cadence to quantify the solar spectral enhancement across the entire wavelength range due to solar flares. These SEE-based FISM results have been primarily used in numerous studies to quantify the ionospheric and thermospheric (I/T) responses to the increased UV irradiance

Solar Flare and Geomagnetic Storm Effects on the Thermosphere and Ionosphere During 6–11 September 2017

“…This created an even more dramatic reduction than the center‐to‐limb variability of these optically thick emissions. This was for the first part of the flare but eventually a footprint flare ribbon did make it over the limb and provided some enhancement of these emissions (Chamberlin et al, ). In this paper, we will refer to this X8.2 over‐the‐limb flare as the X8.2 limb flare for simplicity.…”

Observations and Impacts of the 10 September 2017 Solar Events at Mars: An Overview and Synthesis of the Initial Results

“…Solar images taken near Earth from the Solar Dynamics Observatory (SDO; Pesnell et al, 2012) Atmospheric Imaging Assembly (AIA; Lemen et al, 2012), such as Figure 1a (top panel), show that AR2673 was located around the western limb of the solar disk (∼W90 ∘ , where 0 ∘ longitude is located at the center of the solar disk) when the flare erupted. At the STA location, AR2673 was seen near the eastern limb (∼E90 ∘ ), as shown in Figure 1b Although there is no solar imager present at Mars, the Extreme Ultraviolet Monitor (EUVM; Eparvier et al, 2015) on board MAVEN did observe an increase in solar irradiance during the flare (Chamberlin et al, 2018). Located ∼0.66 AU further away, EUVM detected the flare ∼5.5 min after GOES.…”

“…Although there is no solar imager present at Mars, the Extreme Ultraviolet Monitor (EUVM; Eparvier et al, ) on board MAVEN did observe an increase in solar irradiance during the flare (Chamberlin et al, ). Located ∼0.66 AU further away, EUVM detected the flare ∼5.5 min after GOES.…”

Effects of the 10 September 2017 Solar Flare on the Density and Composition of the Thermosphere of Mars

“…Lee, Jakosky, et al, 2018;Mayyasi et al, 2018;Sánchez-Cano et al, 2019). Other flares of magnitude M and greater from same solar event were also not present at the time of or directly preceding the five baseline orbits (Chamberlin et al, 2018). Over the altitude range of valid number density measurements, each inbound periapsis pass spanned solar zenith angles of ∼65-70°, at ∼16.7-17.6 local solar time (LST).…”