The Complex Space Weather Events of September 2017

Abstract

13 solar cycle 14 • Varying geomagnetic impacts of interplanetary shocks, waves, HCSs/HPSs, sheaths, 15 MCs, CIRs and HSSs are studied and explained 16 • Solar sources and interplanetary characters of the space weather events are identified 17 18 Abstract 19 20The complex magnetospheric and ionospheric events during September 2017 are studied. 21There were 4 X-class, 27 M-class and numerous C-class flares related to ~68 coronal mass 22 ejections (CMEs), 4 of which were halo CMEs. Of the 4 halo CMEs, only 3 reached the Earth. 23A fast interplanetary-CME (ICME) created an upstream sheath that caused an intense magnetic 24 storm (SYM-H peak = -146 nT). This was followed by another intense storm (SYM-H peak = 25 -115 nT) caused by the magnetic cloud (MC) portion of the ICME. Two moderate storms (with 26 SYM-H peaks of -65 nT and -74 nT) were caused by a sheath associated with another halo 27 CME and a corotating interaction region (CIR), respectively. The solar wind high-speed 28 streams (HSSs) led to continuous substorm and convection events but no magnetic storms. Fast 29 forward shocks (FSs) and reverse waves (RWs) associated with the fast CMEs and CIRs, and 30 heliospheric current sheet/heliospheric plasma sheet encounters were detected. The FSs and 31 RWs caused positive and negative sudden impulses, respectively. Half of the FSs triggered 32 substorm onsets and the RWs caused substorm recovery phases. While the FSs led to 33 magnetospheric relativistic electron decreases, electron accelerations were associated with the 34 MC and the HSSs. During main phases of the intense storms, two supersubstorms (SSSs) were 35 detected, one triggered by a FS and the other by a non-shock ram pressure pulse. The SSSs 36 caused major geomagnetically induced currents. CME propagation codes were tested with 37 errors in arrival times ranging from ~24 min to > 35 h.38 39

Long‐Term Variations of the Geomagnetic Activity: A Comparison Between the Strong and Weak Solar Activity Cycles and Implications for the Space Climate

“…When storms are separated in intensity, the solar maximum centric occurrence is most prominent for the intense storms, while the moderate storms peak during the descending phase, resulting in an overall dual‐peak occurrence pattern of the magnetic storms. These results are consistent with previous reports (e.g., Echer et al., 2008, 2011; Hajra et al., 2013) and attributed to various solar/interplanetary sources of HILDCAAs and magnetic storms (see, e.g., Du, 2011; Du & Wang, 2012; Echer et al., 2004, 2008, 2011; Gonzalez et al., 1990, 1994, 2011; Hajra et al., 2013, 2014, 2020; Kirov et al., 2013; Samsonov et al., 2019; Tsurutani & Gonzalez, 1987; Veretenenko et al., 2020, and references therein, for a more detailed discussion of this topic).…”

“…A large percentage of modern technical systems, from space communication satellites to ground‐based power grids, is vulnerable to space weather (see Cannon et al., 2013; Lakhina et al., 2020, and references therein). Space weather includes everything from variations in the Sun, solar wind to their impacts on the interplanetary space, Earth, and other solar system bodies with varying magnetic and plasma properties (e.g., Echer et al., 2005; Hajra et al., 2020, and references therein). These are strongly modulated by the ∼11‐year “Schwabe” cycle (Schwabe, 1844) when Sun's activity rises and falls.…”

The physics of space weather/solar-terrestrial physics (STP): what we know now and what the current and future challenges are

“…Modeling ICME propagation in interplanetary space during disturbed AR periods has met only limited success (Echer et al, 2009;Mostl et al, 2015;Hajra et al, 2019). Sometimes it is difficult to even identify to which flare or disappearing filament a detected ICME is related (see Tang et al, 1989).…”

Impact angle control of local intense d$B$/d$t$ variations during shock-induced substorms

“…Tsurutani and Hajra (2021) noted that all events showed shock-related GIC effects. Hajra and Tsurutani (2018) noted that supersubstorms are usually triggered by IP shocks strongly compressing the magnetosphere under extremely high solar wind ram pressure, associated with intense southward turnings of the IMF B z component. Therefore, we suggest that the nearly symmetric compression of the magnetosphere is a crucial factor for the triggering of supersubstorms due to the subsequent intensity amplification of the resulting substorm current wedge (McPherron, 1972;Pytte et al, 1976).…”