Validation of ANCHOR ionospheric data assimilation model using incoherent scatter radars

ANCHOR is a novel data assimilation model developed at the U.S. Naval Research Laboratory for nowcasting ionospheric parameters relevant to space weather applications. ANCHOR incorporates electron density observations from ionosondes, Abel inverted radio occultation (RO) data, and ground-based GNSS receiver data into a PyIRI-driven model background using the Kalman filter technique. The purpose of this study is to validate the estimated model parameters with parameters derived from electron density observations from incoherent scatter radars (ISR) at various levels of solar activity. Four distinct events were identified from a 6-year data set spanning from 2018 to 2024 collected from four operating ISRs located at varying latitudes west of the prime meridian: Arecibo, Jicamarca, Millstone Hill, and Poker Flat. These events span a range of solar activity levels, with two events at low solar activity, one at moderate and one at high solar activity, each with data coverage from at least two radars. Parameter extraction is achieved by fitting Epstein functions to the electron density profiles, where the peak density (NmF2), peak altitude (hmF2), and the bottomside and topside thickness parameters are simultaneously optimized to characterize the F2 layer. The ISR-extracted parameters are used to directly compare with the model outputs using the root mean square error (RMSE) analysis method. Up to 75% improvement relative to the background model for NmF2, hmF2, and thickness parameters with consistency across all latitudes is found. Additionally, the ANCHOR assimilative model was compared to PyIRTAM model, showing a good agreement between the performances of both systems.