Accuracy of USU‐GAIM specifications of foF2 and M(3000)F2 for a worldwide distribution of ionosonde locations

Abstract

The Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) model has replaced the Parameterized Real‐Time Ionospheric Specification Model (PRISM) for operational use at the Air Force Weather Agency (AFWA). Validation of the model by the Air Force Research Laboratory has therefore passed from the sanity checking stage to investigations of the accuracies and limitations of the model when it is used to generate Operational Space Environment Network Display (OpSEND) products. This paper presents the results of an extensive analysis of the errors in the USU‐GAIM specifications of the key ionogram characteristics foF2 and M(3000)F2 for 21 ionosonde locations distributed around the world, 9 in Australia and 12 in other countries, for September 2006. The ground‐truth observations of foF2 are manually scaled hourly values. The ground‐truth observations of M(3000)F2 are manually scaled hourly values for the Australian ionosondes, and filtered autoscaled values for the other 12 ionosondes. The analysis provides representative latitude‐dependent median errors for both characteristics, together with errors in the values of the maximum usable frequency for the standard 3000 km HF communications circuit. In general, GAIM performs well at all locations. The errors seem to be a function of the availability of data from nearby GPS TEC sites, the accuracy of the program's background ionosphere, and the validity of the assimilated TEC data, rather than of any limitations of the assimilation technique.