Variations of Energetic Particle Fluxes Around Significant Geomagnetic Storms Observed by the Low-altitude DEMETER Spacecraft
Abstract
A superposed epoch analysis is conducted for four geomagnetic storms in the year 2005 with the aim to understand energetic particle flux variations (70 keV to 2.34 MeV) as a function of L-shell, energy, and time from the Dst minimum. Data measured by the low-altitude DEMETER spacecraft are used for this purpose.
The storms are identified by a Dst index below -100 nT, as well as being isolated events in a seven-day time window. It is shown that they can be categorized into two types.
The first type shows significant variations in the energetic particle fluxes around the Dst minimum and increased fluxes at high energies (> 1.5 MeV), while the second type only shows increased fluxes around the Dst minimum without the increased fluxes at high energies. The first type of storms is related to more sudden but shorter-lasting changes in the solar wind parameters than the second type.