KEIKA, Kunihiro

Assistant Professor
Space and Planetary Science Group

Office: -809
TEL: +81-3-5841-4593
FAX: +81-3-5841-8321


Research Field

Planetary magnetospheric plasma physics, Interplanetary plasma physics

Current Research

We study how planets- or moons-origin plasma are transported/heated/accelerated in planetary magnetospheres, how those ions affect the magnetospheric system, and how they respond to solar wind variations such as CMEs.
Particularly, we perform observational studies on protons and oxygen ions (of atmospheric origin) that make a significant contribution to plasma pressure in the Earth’s inner magnetosphere. It remains open questions when and where atmospheric ions preferably escape from the ionosphere and how they are selectively energized/transported in the magnetosphere. The relative importance of proposed processes is still a controversial issue. We utilize multi-spacecraft in-situ/remote-sensing observations of magnetospheric plasma such as Arase (ERG), Van Allen Probes, and MMS to address those unresolved issues.
We believe that insights gained into heavy ion dynamics in the Earth’s magnetosphere yield important clues in better understanding selective acceleration/heating in space plasma and heavy ion environments in the magnetosphere of other planets.

Representative Publications

1. Keika, K. et al. (2018), Ion energies dominating energy density in the inner magnetosphere: Spatial distributions and composition, observed by Arase/MEP-i. Geophysical Research Letters, 45. 10.1029/2018GL080047
2. Keika, K. et al. (2018), Three-step buildup of the 17 March 2015 storm ring current: Implication for the cause of the unexpected storm intensification. Journal of Geophysical Research: Space Physics, 123. 2017JA024462.
3. Keika, K., L. M. Kistler, and P. C. Brandt (2013), Energization of O+ ions in the Earth’s inner magnetosphere and the effects on ring current buildup: A review of previous observations and possible mechanisms, J. Geophys. Res. Space Physics, 118, 4441–4464, doi:10.1002/jgra.50371.