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Abstract The cold, dense plasma of the plasmasphere is sourced by outflows from the ionosphere, but the refilling process is still poorly understood. Refilling may occur in stages, and studying this process is important to understanding how the ionosphere couples to the magnetosphere. This study examines the two‐stage refilling process of the plasmasphere using data from 42 geomagnetic storms observed during the Van Allen Probes era. We find that two‐stage refilling is characterized by an initial stage of low density plasma which refills slowly, followed by a second stage where the density increases and shows very high variation. We observe two‐stage refilling 40% of the time in events where the plasmasphere was significantly depleted. We find that two‐stage refilling is not strongly correlated with global geomagnetic indices (DST, AE, and Kp), but it is highly dependent on local time and rarely occurs in the noon and afternoon sectors.
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This content will become publicly available on December 16, 2026
Bridging the Gap Between the Earth's Ionosphere and Plasmasphere
Abstract Cold plasma distribution in the ionosphere‐plasmasphere system governs wave‐particle interactions, plasma energization and loss, and radio wave propagation. A longstanding observational gap at altitudes 800–8,000 km has largely prevented studying the coupled dynamics of the two regions. Here, we show that observations by JAXA's Arase mission can bridge this gap. Electron densities inferred from the upper hybrid resonance frequencies measured by Arase are highly consistent with radio occultation profiles from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) mission, with a median difference of 5%. Using the combined COSMIC‐Arase data set, we provide a convenient way to reconcile the two regions in empirical models based on the analytical Chapman function inversion for scale height. Our results enable studying fundamental questions about the ionosphere‐plasmasphere coupling, their transition, and life cycle of cold plasma in near‐Earth space.
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- Award ID(s):
- 2054356
- PAR ID:
- 10700196
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 23
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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