Structure and Dynamics of the Outer Radiation Belt

Since the early 1990s a series of spacecraft missions have completely transformed our view of the electron radiation belts. This paper summarizes a number of new results on the structure and dynamics of the belts obtained from those measurements. First, the structure of the outer electron belt is discussed with emphasis on the regions (P0-P2) distinguished on the basis of the time variations of the electron flux. Each region is characterized by distinct set of acceleration and loss processes. While these processes are traditionally represented by diffusion models, new empirical models have emerged in the last decade. These models are developed from the observed dynamics of the flux as a function of L shell and energy. We have developed such models in each P_i region, and introduce methods of writing them as empirical diffusion-convection models. Since any realistic space weather model must be driven by interplanetary activity parameters, we discuss the development of input-output models (filters) focusing on those driven by the solar wind velocity. In addition to the plasma velocity, other solar wind and IMF parameters are important for each outer-belt region. Taken together, these parameters describe geoeffective solar wind structures. This precursor information can be used to advance the forecast lead time. The expected impact of these modeling approaches to radiation belt forecasting is discussed.