Global Storm-Time Losses and Radial Transport of the Outer Belt Electrons at Earth

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During geomagnetic storms relativistic electron fluxes of the outer radiation belt exhibit highly dynamic behavior. The two basic processes controlling the variability of electron fluxes are radial transport of electrons across their drift shells and large-scale reconfigurations of the magnetic field due to the storm-time ring current. This project will address the following science questions: (1) What is the role of magnetic field distortions and inductive electric fields produced by the storm-time ring current on the global loss of radiation belt electron populations? (2) How do ULF oscillations induced by fluctuations of the solar wind dynamic pressure influence the global structure of the outer electron belt? The research is based on a series of controlled numerical experiments of electron transport and losses. It uses a 3D test-particle model which provides a kinetic description of global evolution of the radiation belt in the guiding-center approximation. The following features of the model are especially important for addressing the role of global mechanisms: (1) it is based on the Tsyganenko-Sitnov magnetic field model with inductive electric fields. The model accounts for realistic dynamic reconfigurations of the inner magnetospheric fields which can produce rapid electron losses during storm main phase; (2) it includes ULF fluctuations that are directly induced by variations in the solar wind dynamic; (3) it will use a newly developed model that resolves the three dimensional drift-bounce electron motion and therefore accounts for the features such as the drift shell splitting and orbit bifurcations, which are not described by two dimensional models. The project will determine the relative contributions of the adiabatic response and permanent losses during storm-time variability of the belt as a function of the solar wind and geomagnetic conditions; (2) it will quantify the degree of adiabaticity of the belt during storm recovery phase; (3) it will determine where and under what conditions radial transport in the outer belt can be described as radial diffusion; and (4) it will quantify the average transport rates as a function of the solar wind and geomagnetic conditions. The primary goal of the proposed project is to understand global variability of Earth's radiation belt. This has great relevance to space weather and phenomena that can create hazards for spacecraft and astronauts. The average radial transport rates derived in this study will be provided for the modeling community to use in diffusion and data-assimilation models of the outer bet electron fluxes. The work will also provide research training for student summer interns via a summer intern program.