Modeling the deep penetration of outer belt electrons during the “Halloween” magnetic storm in 2003

Abstract

Radiation belt electrons are a natural hazard to satellites and humans in space, and they can be quickly enhanced and redistributed in the magnetosphere. Specification and advanced warning of such a reconfiguration of the electron distribution will be valuable to spacecraft designers, operators, and astronauts. Here we report our modeling results and discuss a feasible forecast procedure on such an extreme event. During the geomagnetic storm of October/November 2003, the intensity peak of the outer radiation belt electron moved from its nominal position of L ≈ 4 to L ≈ 2.5 in a day. This event was correlated with extremely high solar wind speeds and enhanced ULF wave power through out the inner magnetosphere, both are known to be associated with enhanced radial transport of radiation belt electrons. A radial diffusion model is developed, using the measurements of relativistic electrons at geosynchronous orbit as the source population and making the radial diffusion coefficient a function of solar wind parameters and L. We found that the deep penetration of 4.5 MeV electrons down to L ≈ 2.5 measured by Polar High Energy Space Telescope can be modeled by the fast inward radial transport mechanism. The practical significance of this model is that the inputs are solely from measurements of current solar wind and energetic electrons at geosynchronous orbit. Thus the model can be operated in real time to forecast the multiple MeV electron fluxes inside geosynchronous orbit and down to L ≈ 2.5 in such an extreme storm event.