The complex nature of storm‐time ion dynamics: Transport and local acceleration

• Published in: Geophysical research letters Vol. 43; no. 19; pp. 10,059 - 10,067
• Main Authors: Denton, M. H., Reeves, G. D., Thomsen, M. F., Henderson, M. G., Friedel, R. H. W., Larsen, B., Skoug, R. M., Funsten, H. O., Spence, H. E., Kletzing, C. A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.10.2016; American Geophysical Union
• Subjects: Acceleration; Activation; Arrivals; ASTRONOMY AND ASTROPHYSICS; Drift; Dynamics; Free energy; Helium; inner magnetosphere; Ion dynamics; Ionosphere; Ionospheric plasma; Ionospherics; magnetic storms and substorms; Magnetosphere; magnetosphere/ionosphere interactions; Magnetospheres; Magnetotails; Oxygen; Particle physics; Plasma; plasma sheet; Plasmas (physics); Regions; Spectrometers; Storms; Transport; trapped energetic particles; Wave power
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL070878

Data from the Van Allen Probes Helium, Oxygen, Proton, and Electron (HOPE) spectrometers reveal hitherto unresolved spatial structure and dynamics in ion populations. Complex regions of O+ dominance, at energies from a few eV to >10 keV, are observed throughout the magnetosphere. Isolated regions on the dayside that are rich in energetic O+ might easily be interpreted as strong energization of ionospheric plasma. We demonstrate, however, that both the energy spectrum and the limited magnetic local time extent of these features can be explained by energy‐dependent drift of particles injected on the nightside 24 h earlier. Particle tracing simulations show that the energetic O+ can originate in the magnetotail, not in the ionosphere. Enhanced wave activity is colocated with the heavy ion‐rich plasma, and we further conclude that the waves were not a source of free energy for accelerating ionospheric plasma but rather the consequence of the arrival of substorm‐injected plasma. Key Points Enhanced O+ fluxes mimic local acceleration—shown to result from plasma transport from an injection 24 h earlier Enhanced wave power is colocated with the enhanced O+—the wave power is enhanced due to arrival of drifting plasma Time history of previous injections must be accounted for when interpreting in situ observations