Variation of Molecular Ions in the Inner Magnetosphere Observed by the Arase Satellite

• Published in: Geophysical research letters Vol. 51; no. 18
• Main Authors: Nagatani, A., Miyoshi, Y., Asamura, K., Kistler, L. M., Nakamura, S., Seki, K., Ogawa, Y., Shinohara, I.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-09-2024
• Subjects: Arase satellite; Charged particles; Dynamic pressure; inner magnetosphere; ion outflow; Ionosphere; Ions; Low altitude; Magnetospheres; mass spectrometer; molecular ion; Molecular ions; Pressure; Satellite observation; Satellites; Solar wind; Temporal variations
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108340

We analyzed time‐of‐flight (TOF) data from the Arase satellite to investigate temporal variations of the molecular ion group (O2+, NO+, and N2+) at 19.2 keV/q in the inner magnetosphere for 6 years from the solar declining to rising phase. The molecular ions counts were estimated by subtracting the background contamination of oxygen counts. While the number of clear molecular ion events was small, the estimated counts exhibited good correlation with the solar wind dynamic pressure and SYM‐H index. Long‐term variations of the molecular ions differed from those of counts of the O+ and N+ group. Additionally, we discuss the importance of the solar wind dynamic pressure in causing variations of molecular ions in the inner magnetosphere.
Plain Language Summary
Molecular ions (O2+, NO+, and N2+) have been observed in the magnetosphere. Molecular ions in the ionosphere are required to obtain energy through short‐lived reactions with electrons to escape from low altitudes to the magnetosphere. The escaping mechanisms of molecular ions are not fully understood. This study analyzed 6 years of data from the Arase satellite to investigate long‐term variations of molecular ion group in the inner magnetosphere. We discuss the importance of the solar wind dynamic pressure in causing variations of molecular ions in the inner magnetosphere.
Key Points
Continuous molecular ion group observations in the inner magnetosphere for 6 years
Counts of molecular ion group increase following enhancements in the solar wind dynamic pressure
The ratio of molecular ion group to O+ and N+ was lower in the rising phase of the solar cycle than that during the solar minimum