The High‐Latitude Workbox for the Ionosphere (HAWK‐I): A New Toolkit for Real‐Time Specification of the Arctic Ionosphere

Abstract The high‐latitude ionosphere exhibits rapid spatial and temporal variability during geomagnetically active periods, creating persistent challenges for accurate nowcasts. The High‐latitude Workbox for the Ionosphere (HAWK‐I) is a real‐time ionosphere nowcast and specification system designed for operational deployment to address these challenges. HAWK‐I employs the Ionospheric Data Assimilation Four‐Dimensional (IDA4D) framework, implemented as a three‐dimensional variational (3DVar) algorithm, to update a log‐electron‐density state and produce three‐dimensional electron density specifications from GNSS and radio occultation observations at 5‐min cadence. Performance is evaluated during the May 2024 geomagnetic storm using ground‐based GNSS Total Electron Content and incoherent scatter radar measurements. Results demonstrate substantial reductions in TEC error and improved representation of storm‐time ionospheric structure relative to background models, with complementary strengths of empirical and physics‐based models. Assimilation of Radio Occulation (RO) observations further improves performance in regions distant from ground‐based receivers, highlighting their importance for high‐latitude ionospheric specification.