Dependence of radiation belt enhancements on the radial extent of Pc5 waves and the plasmapause location

Abstract:

Low-energy electrons are accelerated to relativistic energies through different mechanisms, transporting them across their drift shells to the outer radiation belt. Among the different acceleration mechanisms, radial diffusion describes the result of ULF magnetic field pulsations resonantly interacting with radiation belt electrons. In this paper, the radial positioning of the relativistic electron population during 39 intense and moderate magnetic storms is examined against that of ULF Pc5 wave power and the plasmapause location. The relativistic electron population of the outer radiation belt appeared enhanced in the 2 - 6 MeV electron flux data from SAMPEX and in > 2 MeV electron flux data from the geosynchronous GOES satellites following 27 of the magnetic storms. We compared relativistic electrons observations with concurrent radial distribution of wave power enhancements at Pc5 frequencies as detected by the IMAGE and CARISMA magnetometer arrays, as well as by additional magnetic stations collaborating in SuperMAG. We discuss the growth and decay characteristics of Pc5 waves in association with the plasmapause location, determined from IMAGE EUV observations, as the controlling factor for wave power penetration deep into the magnetosphere. We show that, during magnetic storms characterized by increased post-storm fluxes, Pc5 wave power penetrates to L shells of 4 and lower. On the other hand, magnetic storms which were characterised by loss of electrons were related to low Pc5 wave activity, which was not intensified at low L shells. These observations provide support for the hypothesis that enhanced Pc5 wave activity deep into the magnetosphere during the main and recovery phase can discriminate between storms that result in increases of electron fluxes from those that do not.

The work leading to this paper has received funding from the European Union's Seventh Framework Programme (FP7-SPACE-2011-1) under grant agreement no. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.