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- Title
Low‐Altitude Ion Upflow Observed by EISCAT and its Effects on Supply of Molecular Ions in the Ring Current Detected by Arase (ERG).
- Authors
Takada, M.; Seki, K.; Ogawa, Y.; Keika, K.; Kasahara, S.; Yokota, S.; Hori, T.; Asamura, K.; Miyoshi, Y.; Shinohara, I.
- Abstract
During the magnetic storm starting on September 7, 2017, the MEP‐i instrument onboard the Arase (ERG) satellite observed molecular ions (O2+/NO+/N2+) in the ring current. The molecular ions were observed by Arase in four orbits during this magnetic storm. This indicates that there was a continuous molecular ion supply from the ionosphere. During the storm main phase around the second Dst minimum (∼−100 nT) on September 8, 2017, the European Incoherent Scatter (EISCAT) radar observed the ion upflow (∼50–150 m s−1) in the low‐altitude (250–350 km) ionosphere together with strong ion heating up to >2,000 K. The convective electric field derived from the electron heating observed by EISCAT at an altitude of approximately 110 km was also enhanced by a factor of 2. The observations suggest that the additional ion heating at low altitudes helps to cause the fast upflow and transport molecular ions upward. The flux decreases from 280 to 350 km altitudes due to the dissociative recombination was estimated to be approximately two orders of magnitude. This resulted in significant molecular ion flux remaining at 350 km altitude. These results suggest that the low‐altitude ion upflow caused by the ion frictional heating enables molecular ions to escape to space against rapid loss by the dissociative recombination. Plain Language Summary: Molecular ions (O2+/NO+/N2+) in the ring current are sometimes observed during magnetic storms. These molecular ions come from the deep ionosphere and considered good tracers of escape mechanisms from the Earth's ionosphere to the magnetosphere. However, it has not been revealed how these molecular ions are transported upward, especially by ion upflows in the low‐altitude ionosphere (∼250–350 km). It is difficult to transport sufficient flux of molecular ions due to deceleration by the strong gravitational force and rapid decrease by dissociative recombination even during magnetic storms. In this paper, we report the analysis results of the fast ion upflow (∼100 m s−1) event in the low‐altitude ionosphere observed by the European Incoherent Scatter (EISCAT) radar, while the Arase (ERG) satellite observed molecular ions in the inner magnetosphere during the magnetic storm starting on September 7, 2017. The results suggest that ion frictional heating created the ion upflow and could be a source of outflows at higher altitudes in the ionosphere to supply the molecular ions into the magnetosphere. Key Points: Arase satellite observed molecular ions in the ring current during the magnetic storm starting on September 7, 2017An ion upflow from the deep ionosphere was observed with enhancements of electric field and ion temperature by EISCATThe fast upflow caused by the ion frictional heating enables molecular ions to escape to space against dissociative recombination
- Subjects
MAGNETIC storms; RING currents; MAGNETOSPHERIC currents; IONS; IONOSPHERE
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 5, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2020JA028951