Modeling high energy electron flux in the outer radiation belt

This dissertation is motivated by: (1) Current empirical radiation belt models are static in nature and do not capture the charged particle dynamics present in the outer radiation belt. Thus they do not have the temporal resolution for point specification or forecast. (2) There is a continuing and pressing need for an easy-to-use, easy-to-access, dynamic, global radiation belt model to fulfill both scientific and operational needs.; Knowledge of the distribution and dynamics of the radiation belt charged particle population in near-Earth space is important not only scientifically but also operationally. Scientifically, the radiation belts are integral parts of the magnetosphere, their structure and dynamics closely coupled to those of the magnetosphere. Near-Earth space is a convenient and close-by laboratory that may be used to build a clearer understanding of the dynamics of magnetically trapped magnetospheric plasma which may, in turn, lead to a greater understanding of particle acceleration processes that occur throughout the universe. Operationally, every activity outside the Earth's atmosphere must take the space radiation environment into account. Knowledge of particle flux and total radiation dose is important as spacecraft with greater complexity, reduced active volumes, and smaller, more radiation-sensitive components become more prevalent. High energy protons and electrons can degrade satellite performance in a number of ways including microstructural damage, background noise in detectors, errors in digital circuits, and electrostatic charge buildup in insulators.; It is shown that the large and accurate charged particle flux database created from in situ spacecraft observations may be used to improve radiation belt modeling. A three-dimensional empirically-based model of the radiation belt is used as a baseline. This baseline is adjusted by assimilating in situ satellite flux data and adjusting the model as necessary to more closely match reality.; As a necessary part of this process, several aspects of radiation belt modeling are examined in detail. Local time variation is examined as the major source of electron flux variability for most near-Earth spacecraft as they pass from the night side of the planet to the sunlit side, and back again. Variability among spacecraft sensor calibration is examined for two reasons. First, any variability among sensors affects the accuracy of model output; second, an analysis is important for identifying modeling goals: that is, determining the model standard. Lastly, the definition of “radiation belt condition” is examined. A good correlation does not exist between any existing geomagnetic index and outer belt charged particle activity on an hourly time scale. It is shown that a new definition for the state of the outer belt based on the location of the “heart” of the outer belt captures the state of outer belt electrons with greater fidelity than existing models. Demonstrations of modeling improvement in specification and forecast are provided.; As a result of this research, a clear linkage between meteorology and space weather is established and a better understanding is gained of how change is affected in the magnetospheric system and how coherence plays a large part. Local time variation and spacecraft sensor calibration differences are systematically quantified. A novel approach to determining radiation belt conditions is developed. Lastly, a user-oriented electron flux specification and forecast system is presented.