A magnetospheric specification model validation study: Geosynchronous electrons

The Rice University Magnetospheric Specification Model (MSM) is an operational space environment model of the inner and middle magnetosphere designed to specify charged particle fluxes up to 100 keV. Validation test data taken between January 1996 and June 1998 consist of electron fluxes measured by a charge control system (CCS) on a defense satellite communications system (DSCS) spacecraft. The CCS includes both electrostatic analyzers to measure the particle environment and surface potential monitors to track differential charging between various materials and vehicle ground. While typical RMS error analysis methods provide a sense of the models overall abilities, they do not specifically address physical situations critical to operations, i.e., how well does the model specify when a high differential charging state is probable. In this validation study, differential charging states observed by DSCS are used to determine several threshold fluxes for the associated 20–50 keV electrons and joint probability distributions are constructed to determine Hit, Miss, and False Alarm rates for the models. An MSM run covering the two and one-half year interval is performed using the minimum required input parameter set, consisting of only the magnetic activity index Kp, in order to statistically examine the model's seasonal and yearly performance. In addition, the relative merits of the input parameter, i.e., Kp, Dst, the equatorward boundary of diffuse aurora at midnight, cross-polar cap potential, solar wind density and velocity, and interplanetary magnetic field values, are evaluated as drivers of shorter model runs of 100 d each. In an effort to develop operational tools that can address spacecraft charging issues, we also identify temporal features in the model output that can be directly linked to input parameter variations and model boundary conditions. All model output is interpreted using the full three-dimensional, dipole tilt-dependent algorithms currently in operational use at the Air Force 55th Space Weather Squadron (55 SWXS). Results indicate that both diurnal and seasonal activity related variations in geosynchronous electrons are reproduced in a regular and consistent manner regardless of the input parameter used as drivers. The ability of the MSM to specify DSCS electrons in relation to thresholds indicative of spacecraft charging varies with the combination of input parameters used. The input parameter of greatest benefit to the MSM, after the required Kp index, is the polar cap potential drop as determined by DMSP spacecraft. Regarding the highest electron flux threshold, the model typically achieves high HIT rates paired with both high False Alarm rates and higher RMS error. Suggestions are made regarding the utilization of proxy values for the polar cap potential parameter and Kp-dependent model boundary conditions. The importance of generating accurate real-time proxy input data for operational use is stressed.