Relationship between ULF waves and radiation belt electrons during the March 10, 1998, storm Original Research Article

Acceleration of electrons due to ULF oscillations is considered to be an explanation for the radiation electron flux enhancement during the storm. In this study, we examine the relationship between the ULF wave activity observed by the Equator-S satellite and the relativistic electron flux variation observed by POLAR satellite during a magnetic storm which commenced on March 10, 1998. The storm was associated with a 5-day high speed solar wind interval. Rapid enhancement of MeV electrons was observed in the outer radiation belt within the first half day after the storm commencement with strong pancake distribution in equatorial pitch angle, followed by a more gradual flux increase for the next several days with a more isotropic distribution. During this interval, when both rapid and gradual acceleration of electrons took place, enhanced ULF wave activity was observed in the dawnside magnetosphere extending down to L < 6 region. We compare the observations with different models considering the ULF waves. The observation generally supports the mechanisms of the electron acceleration due to interaction with ULF waves, although different mechanisms are possibly involved for acceleration during the early recovery phase and the later recovery phase.