O + Escape During the Extreme Space Weather Event of 4-10 September 2017 Audrey Schillings, Hans Nilsson, Rikard Slapak, Peter Wintoft, Masatoshi Yamauchi, Magnus Wik, Iannis Dandouras, Chris Carr To cite this version: Audrey Schillings, Hans Nilsson, Rikard Slapak, Peter Wintoft, Masatoshi Yamauchi, et al.. O + Es- cape During the Extreme Space Weather Event of 4-10 September 2017. Journal of Space Weather and Space Climate, EDP sciences, 2018, 16 (9), pp.1363-1376. 10.1029/2018SW001881. hal-02408153 HAL Id: hal-02408153 https://hal.archives-ouvertes.fr/hal-02408153 Submitted on 12 Dec 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. SPACE WEATHER, VOL. ???, XXXX, DOI:10.1002/, + 1 O escape during the extreme space weather event of 2 September 4–10, 2017 Audrey Schillings,1,2 Hans Nilsson,1,2 Rikard Slapak,3 Peter Wintoft,4 Masatoshi Yamauchi,1 Magnus Wik,4 Iannis Dandouras,5 and Chris M. Carr,6 Corresponding author: Audrey Schillings, Swedish Institute of Space Physics, Kiruna, Sweden. ([email protected]) 1Swedish Institute of Space Physics, Kiruna, Sweden. 2Division of Space Technology, Lule˚a University of Technology, Kiruna, Sweden. 3EISCAT Scientific Association, Kiruna, Sweden. 4Swedish Institute of Space Physics, Lund, Sweden. 5IRAP, Universit´ede Toulouse, CNRS, UPS, CNES, Toulouse, France. 6Imperial College, London, UK. D R A F T July 3, 2018, 7:30am D R A F T X-2 SCHILLINGS ET AL.: SEPTEMBER 2017 STORM 3 Abstract. We have investigated the consequences of extreme space weather 4 on ion outflow from the polar ionosphere by analyzing the solar storm that 5 occurred early September 2017, causing a severe geomagnetic storm. Sev- 6 eral X-flares and coronal mass ejections (CMEs) were observed between 4 7 and 10 September. The first shock – likely associated with a CME – hit the 8 Earth late on September 6, produced a storm sudden commencement (SSC) 9 and began the initial phase of the storm. It was followed by a second shock, 10 approximately 24h later, that initiated the main phase and simultaneously 11 the Dst index dropped to Dst = −142 nT and Kp index reached Kp = 8. 12 Using CODIF data onboard Cluster satellite 4, we estimated the ionospheric + 13 O outflow before and after the second shock. We found an enhancement + 14 in the polar cap by a factor of 3 for an unusually high ionospheric O out- 13 −2 −1 15 flow (mapped to an ionospheric reference altitude) of 10 m s . We sug- + 16 gest that this high ionospheric O outflow is due to a preheating of the iono- 17 sphere by the multiple X-flares. Finally, we briefly discuss the space weather + 18 consequences on the magnetosphere as a whole and the enhanced O out- 19 flow in connection with enhanced satellite drag. D R A F T July 3, 2018, 7:30am D R A F T SCHILLINGS ET AL.: SEPTEMBER 2017 STORM X-3 1. Introduction 20 Solar storms with associated flares, coronal mass ejections (CMEs), and radio bursts 21 may be hazardous to Earth, potentially affecting satellite operations through enhanced 22 satellite drag, causing electric power distribution failures due to extraordinary ground 23 induced currents (GIC), disturbing radio communications and causing radio blackouts due 24 to higher ionization rates in the lower ionosphere. Balch et al. [2004] report occurrence 25 rates of such events; extreme and severe radio blackouts occur approximately 1 day and 8 26 days per solar cycle respectively. Similarly, the planetary Kp index [Bartels et al., 1939; 27 Mayaud, 1980], widely used as a general indicator of geomagnetic disturbances for mid- 28 latitude regions and as a general geomagnetic alert and hazard scale, reaches extreme (Kp 29 = 9) and severe (Kp = 8) levels 4 and 100 days per solar cycle, respectively [Balch et al., 30 2004]. 31 In solar cycle 23, there were more than 100 X-flares, the strongest occurring in November 32 2003 (X28.0) and in April 2001 (X20.0). However for these events the solar active regions 33 were close to the solar limb, therefore no severe or extreme geomagnetic storms were ob- 34 served [Zhang et al., 2007]. At third strongest was an X17.2 flare detected on October 35 28, 2003 and due to a strong Interplanetary Coronal Mass Ejection (ICME) an extreme 36 geomagnetic storm – also known as the Halloween storm – took place [e.g Yamauchi et al., 37 2006; Rosenqvist et al., 2005; Gopalswamy et al., 2005]. It produced disturbances around 38 the world [Balch et al., 2004]. In the same solar cycle, on January 20, 2005 an outstanding 39 solar flare occurred (X7.1), followed by an ICME which was detected in the near-Earth 40 space on January 21. This ICME arrival resulted in an extreme magnetospheric com- D R A F T July 3, 2018, 7:30am D R A F T X-4 SCHILLINGS ET AL.: SEPTEMBER 2017 STORM 41 pression [Dandouras et al., 2009]. In solar cycle 24, in September 2017, several X-flares 42 occurred of which the most intense was an X9.0-flare (the largest observed since December 43 2006) which with strong CMEs produced an extreme geomagnetic storm. These extreme 44 events caused a strong response in the ionosphere and magnetosphere, for example vari- 45 ations in the total electron content (TEC) and enhanced magnetospheric convection. An 46 additional effect is the strongly enhanced ion outflow from the polar ionosphere [Schillings 47 et al., 2017]. 48 Ion outflow from the ionosphere has been widely studied, i.e. by Shelley et al. [1982]; 49 Chappell et al. [1987]; Moore et al. [1997]; Lennartsson et al. [2004]; Kronberg et al. [2014]; 50 Maes et al. [2015] and references therein. The most profound magnetospheric ion outflow 51 is usually observed in the open magnetic field line regions: the polar caps, cusps and 52 plasma mantle [Nilsson et al., 2012]. The mirror force plays a key role in the acceleration 53 of outflowing ions, with perpendicular energy converted into parallel energy as the ions 54 move into higher altitudes and weaker magnetic fields. Therefore, perpendicular heating 55 of ions causes subsequent outward acceleration. Wave particle-interaction can cause such 56 transverse ion heating, and these processes and their effects have been investigated at 57 different altitudes [e.g. Andre et al., 1990; Norqvist et al., 1996; Bouhram et al., 2005; 58 Nilsson et al., 2006; Moore and Horwitz, 2007; Slapak et al., 2011; Waara et al., 2011; 59 Nilsson et al., 2012]. If the heating is effective enough, the ions will gain sufficient velocities 60 to escape into the solar wind downstream in the tail [Nilsson et al., 2012] or even directly 61 from the cusp [Slapak et al., 2013]. 62 Ion outflow has been studied for different solar wind and geomagnetic conditions. Cully 63 et al. [2003] identified four factors that influence the ion outflow; the solar radio flux at D R A F T July 3, 2018, 7:30am D R A F T SCHILLINGS ET AL.: SEPTEMBER 2017 STORM X-5 64 10.7 cm (F10.7), the interplanetary magnetic field (IMF), the solar wind electric field and 65 the solar wind dynamic pressure. Using data in an altitude range of 1.3 to 2.0 RE, Yau 66 et al. [1988] found that ion outflow depends on the geomagnetic condition such that it 67 increases exponentially with Kp. Similarly, Slapak et al. [2017] made a statistical study 68 using high-altitude plasma mantle and magnetosheath Cluster data in order to quantify + 69 the total O escape as a function of Kp. Complementary to that study, Schillings et al. 70 [2017] presented that the escape rate during extreme geomagnetic storms could be higher 71 than what a linear extrapolation of the results of Slapak et al. [2017] would predict. As the + 72 whole magnetosphere is affected by disturbed magnetospheric conditions, the O outflow 73 that does not escape into the solar wind is transported to the lobes through the polar cap. + 74 Through reconnection in the plasma sheet, O coming from the lobe is heated and feeds 75 both the distant and near-Earth plasma sheet [Kistler et al., 2006; Mouikis et al., 2010]. 76 The consequence of space weather on ion outflow has not been well studied. Therefore, 77 it is not clear what parameter is most influential with what time scale. In this paper, 78 we first investigate the space weather during 4 to 10 September 2017, from solar storm 79 to geomagnetic storm. Thereafter we examine the effects on magnetosphere-ionosphere 80 coupling, in particular ion outflow. The goal is primarily to see the space weather effects 81 on ion outflow for this well studied storm. Despite that ion outflow in itself not causing 82 hazardous to human activity, the enhanced ion outflow and resulting escape are mainly 83 observed in the cusp, which has an important role in some hazards as discussed in Section 84 5.3. 2. Instrumentation and data D R A F T July 3, 2018, 7:30am D R A F T X-6 SCHILLINGS ET AL.: SEPTEMBER 2017 STORM 2.1. Cluster mission 85 The Cluster mission [Escoubet et al., 2001] was launched in 2000 and consists of four 86 spacecraft flying in tetrahedral formation in an elliptical polar orbit.