Molecular ion upflow observed by the EISCAT radar in conjunction with the Arase (ERG) satellite during the September 7, 2017 magnetic storm
Abstract
Molecular ions (O2+/NO+/N2+) originating from the ionosphere have been observed in the magnetosphere during the magnetic storms [e.g., Klecker et al., 1986; Christon et al., 1994] and also recently observed by Arase satellite even during weak geomagnetic disturbance periods [Seki et al., 2019]. It suggests that the molecular ions are commonly supplied from the ionosphere. However, it is not revealed how these molecular ions are transported from the low-altitude (<300 km) ionosphere where molecular ions usually exist. These molecular ions are considered to be transported upward by some heating mechanisms such as ion frictional heating, ion resonance heating and local plasma instabilities. However, previous observations indicate that those mechanisms are not efficient enough to transport molecular ions by overcoming loss due to the dissociative recombination [Peterson et al., 1994].
In this study, we aim at quantitative assessment of the ion upflow process for the molecular ions from the low-altitude ionosphere based on the conjugate observations by the EISCAT radar and the Arase (ERG) satellite on September 8, 2017. The results show: (1) Arase observed molecular ions in the ring current layer during a magnetic storm with the minimum Dst of -124 nT. (2) EISCAT observed the molecular ions' upflow (Vi~100 m/s) together with enhancements of the electric field and ion pressure gradient in the low-altitude ionosphere. The results suggest that the fast upflow caused by the ion frictional heating enables molecular ions to escape against dissociative recombination. We also estimated the flux decrease of molecular ions due to dissociative recombination. The O2+ (NO+ ) flux decreased to ~1 (~0.001) % at 350 km compared with 280 km. The estimated upflow flux of O2+ (NO+ ) at 350 km is at least ~1010 (~107) m-2 s-1. These results indicate that the strong ion frictional heating during magnetic storms enabled molecular ions to be transported upward from the low-altitude ionosphere and provided a source of molecular ion outflows into the magnetosphere. References: Klecker et al., Geophys. Res. Lett., Vol. 13, 632-635, 1986. Peterson et al., J. Geophys. Res., Vol. 99, 23257-23274, 1994. Christon et al., Geophys. Res. Lett., Vol. 21, 3023-3026, 1994. Seki et al., Geophys. Res. Lett., Vol. 46, doi:10.1029/2019GL084163, 2019.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSA41B3183T
- Keywords:
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- 2407 Auroral ionosphere;
- IONOSPHERE;
- 2431 Ionosphere/magnetosphere interactions;
- IONOSPHERE;
- 2475 Polar cap ionosphere;
- IONOSPHERE;
- 2752 MHD waves and instabilities;
- MAGNETOSPHERIC PHYSICS