Storm-time fingerprints and global profiles of ULF wave power at geosynchronous orbit

We examine the relationship between long-period (Pc4 and Pc5) ULF wave power and the rapid increase in relativistic electron fluxes observed during some magnetic storms. A qualitative comparison of the ULF dynamic power spectra of the total field magnitude (compressional component) during two major storms indicates a sustained, broadband enhancement of ULF power beginning in the main phase and extending well into the recovery phase for the storm with relativistic electrons. The ULF compressional power increase appears more narrowband and not as sustained during the storm without such electrons. A statistical study using a database of 42 isolated storms indicates that an extended period of elevated Pc5 power throughout the recovery phase may be necessary for electron energization. A similar, albeit weaker effect is observed for Pc4 waves. Finally, the average local-time profiles of Pc4 and Pc5 wave power at geosynchronous orbit are calculated for the early, intermediate, and late stages of the recovery phase for our storm database. A clear difference in the local-time distribution of Pc5 power during the early recovery phase between storms with relativistic electrons and those without is observed. In both cases, there is a Pc5 power peak in the afternoon. However, there are also comparable levels of wave power in the morning sector for storms during which electrons are accelerated to relativistic speeds. This may indicate that high Pc5 power levels occurring on both the dawn and dusk flanks are necessary to “kickstart” the electron acceleration and are one of the factors in differentiating between magnetic storms with enhanced relativistic electron fluxes and those without.