5:15 PM - 6:30 PM
[PEM08-P13] Comparative study of proton and oxygen ion supply into the inner magnetosphere during a geomagnetic storm
Keywords:Van Allen Probes, Oxygen ion
We calculated the first adiabatic invariant, mu, and PSD for ions with a pitch angle of about 90 degrees (We selected data of a telescope with a pitch angle which is the nearest 90 degrees in all telescopes and is in range of 70 – 110 degrees for each time.). Proton and oxygen PSDs for specific mu values (mu= 0.3, 0.5, 0.8, 1.0 keV/nT for proton, mu= 0.5, 0.8, 1.0 keV/nT for oxygen) were obtained as a function of L for each orbit of Van Allen Probes during the storm. The results show that both proton and oxygen ions penetrated directly down to L ~5 during the main phase of the magnetic storm (minimum Dst greater than -65 nT). The penetration boundary of protons were located at smaller L at dusk than at dawn. Protons with smaller mu values (mu= 0.3 and 0.5 keV/nT) penetrated earlier than those with larger mu values (mu= 0.8, 1.0 keV/nT). It seems consistent with the energy dependence of the Alfven layer. In contrast, the timing of O+ penetration is almost the same for all mu values (mu= 0.5, 0.8 and 1.0 keV/nT). The observations also show that O+ ions penetrated more deeply in L and earlier in time than H+ ions.
These results suggest that the source of the transported oxygen ions is located closer to the Earth than that of the protons (i.e., the inner edge of the plasma sheet).
Variations of the oxygen E-t diagram during the second main phase of the storm show enhancement of flux in energy over ~100 keV closer to the Earth than protons inner edges. The magnetic fluctuation with about 0.01 Hz is also enhanced during the second main phase of the storm closer to the Earth than protons inner edges. We suggest that deeper penetrations of oxygen ions are caused by interaction between oxygen ions and Pc5 magnetic fluctuations.
Our results thus demonstrate the importance of the contribution from high energy oxygen ions to the storm-time ring current.