Ionospheric and Thermospheric Responses to the Recent Strong Solar Flares on 6 September 2017

Abstract

Two solar flares X2.2 and X9.3 erupted over the active region 2673 on 6 September 2017, and the second flare is the strongest since 2005. In order to investigate the ionospheric and thermospheric responses to the two solar flares, the global total electron content and the critical frequency of F2 layer obtained from GPS stations and ionosondes are used. The results indicate that the ionosphere in the sunlit hemisphere increased significantly with magnitudes of 0.1 and 0.5 total electron content units for the X2.2 and X9.3 solar flares, respectively. The electron density, thermospheric neutral density, and neutral temperature simulated by the Thermosphere-Ionosphere Electrodynamics Global Circulation Model show that the behavior of ionospheric and thermospheric responses is different. The ionospheric disturbances occurred at the altitude ranges of 150À300 km, and the thermospheric responses occurred at the altitudes of 250À400 km are caused by solar extreme ultraviolet and ultraviolet photons, respectively. Both ionospheric and thermospheric responses are proportional to the height within their corresponding altitude ranges. Observations and simulations reveal that the ionospheric and thermospheric responses are nonlinearly dependent on the solar zenith angle. The disturbances caused by the X2.2 solar flare are symmetric, but the X9.3 solar flare are not. The O/N 2 density ratio simulated by Thermosphere-Ionosphere Electrodynamics Global Circulation Model increases from lev0 to lev5.0 pressure surface with a magnitude of 0.1-1.8, while the ratio decreases in the American sector with a magnitude of À0.6 to À0.3. The longitudinal asymmetry of O/N 2 density ratio is a major contributor to the longitudinal asymmetry of ionospheric and thermospheric responses. (CMD = 83°) was smaller than that caused by the X17.2 flare on 28 October 2003 (CMD = 8°), which was

Ionospheric Response at Conjugate Locations During the 7–8 September 2017 Geomagnetic Storm Over the Europe‐African Longitude Sector

“…In general, the solar and geomagnetic activity conditions for 4-11 September 2017 have been described as complex largely due to the occurrence of multiple solar flares of different classes (e.g., Curto et al, 2018;Mosna et al, 2020;Yasyukevich et al, 2018) and storm-related activity that led to two consecutive Dst minima separated by about 13 hr on the same day (e.g., Aa et al, 2019;Lei et al, 2018). Figure 2 shows changes in (a) solar wind velocity, V sw (m/s), and B z component of the interplanetary magnetic field, IMF B z (nT); (b) auroral electrojet, AE (nT) index and SYM-H (nT) index equivalent to high-resolution Dst index (Wanliss & Showalter, 2006); and (c) the interplanetary electric field, The black vertical straight lines on Figure 3a show the occurrence time of the two solar flares X2.2 and X9.3 at 0910 UT and 1158 UT, respectively, on the 6 September 2017 (e.g., Curto et al, 2018;Li et al, 2018;Mosna et al, 2020;Yasyukevich et al, 2018). As indicated in Figure 2, the first sudden storm commencement occurred on 6 September 2017 at 2343 UT, while both main and recovery phases were on 8 September 2017.…”

“…The first X2.2 solar flare at 0910 UT on 6 September 2017 did not generate clearly visible changes in TEC as seen in Figure 6a. The global ionospheric response (including using data over Europe and South Africa) to solar flares on 6 September 2017 has been reported in Li et al (2018) highlighting an increase in TEC and foF2 for the X9.3 flare occurrence which peaked at 1202 UT compared to the less intense X2.2 that had its peak at 0910 UT. Therefore, Figure 6a demonstrates the importance of utilizing different parameterization when studying different ionospheric phenomena.…”

Ionospheric Current Variations Induced by the Solar Flares of 6 and 10 September 2017

“…When a solar flare erupts, short‐period changes often called the sudden ionospheric disturbances are observed in the D region (Ogunmodimu et al, 2018), E layer (Curto et al, 1994; Li et al, 2018; Rastogi et al, 1999; Yamazaki et al, 2009) and occasionally in the F 2 region (Scherliess, 2016; Thome & Wagner, 1971). These sudden ionospheric disturbances are due to the sudden increase in the X‐ray and EUV irradiance (Le et al, 2007; Tsurutani et al, 2005).…”

Advanced Machine Learning Optimized by The Genetic Algorithm in Ionospheric Models Using Long-Term Multi-Instrument Observations

“…The global foF2 and hmF2 maps provided by IZMIRAN can be regarded as new GIM-TEC products [32]. The GIM-TECs are estimated by the dual-frequency observations obtained from hundreds of International GNSS Service (IGS) stations with spherical harmonics and have been widely applied in scientific research and practical productions [33][34][35][36]. Therefore, the IZMIRAN maps were capable of meeting the requirements of this study.…”