A magnetospheric specification model validation study: Geosynchronous electrons

The Rice University Magnetospheric Specification Model (MSM) is an operatio nal space environment model of the inner and middle magnetosphere designed to specify charged particle fluxes up to 100 keV. Validation test data take n 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 measur e the particle environment and surface potential monitors to track differen tial charging between various materials and vehicle ground. While typical R MS 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 s tate is probable. In this validation study, differential charging states ob served by DSCS are used to determine several threshold fluxes for the assoc iated 20 -50 keV electrons and joint probability distributions are construc ted to determine Hit, Miss, and False Alarm rates for the models. An MSM ru n covering the two and one-half year interval is performed using the minimu m required input parameter set, consisting of only the magnetic activity in dex Kp, in order to statistically examine the model's seasonal and yearly p erformance. In addition, the relative merits of the input parameter, i.e., Kp, Dst, the equatorward boundary of diffuse aurora at midnight, cross-pola r cap potential, solar wind density and velocity, and interplanetary magnet ic field values, are evaluated as drivers of shorter model runs of 100 d ea ch. In an effort to develop operational tools that can address spacecraft c harging issues, we also identify temporal features in the model output that can be directly linked to input parameter variations and model boundary co nditions. All model output is interpreted using the full three-dimensional, dipole tilt-dependent algorithms currently in operational use at the Air F orce 55th Space Weather Squadron (55 SWXS). Results indicate that both diur nal and seasonal activity related variations in geosynchronous electrons ar e reproduced in a regular and consistent manner regardless of the input par ameter used as drivers. The ability of the MSM to specify DSCS electrons in relation to thresholds indicative of spacecraft charging varies with the c ombination of input parameters used. The input parameter of greatest benefi t to the MSM, after the required Kp index, is the polar cap potential drop as determined by DMSP spacecraft. Regarding the highest electron flux thres hold, the model typically achieves high HIT rates paired with both high Fal se Alarm rates and higher RMS error. Suggestions are made regarding the uti lization of proxy values for the polar cap potential parameter and Kp-depen dent model boundary conditions. The importance of generating accurate real- time proxy input data for operational use is stressed. Published by Elsevie r Science Ltd.