Advancing the Horizontal Wind Model (HWM): Integration of Non-Migrating Tides

The Horizontal Wind Model (HWM) is an extensively utilized empirical representation of the Earth's neutral atmospheric wind field, designed to provide a global and continuous characterization of horizontal winds extending from the surface of the Earth to the exobase. The model is parameterized by local time, location, day of year, and solar and geomagnetic activity. HWM serves as a critical benchmark for validating newly acquired wind observations, facilitating the interpretation of in-situ and remote sensing data, and refining our physical understanding of the coupled thermosphere-ionosphere system. Despite its wide adoption and success, the current version of HWM (which is HWM14) only includes wind structures associated with DW1, SW2, Wave-1, and Wave-2; it is lacking neutral wind variations associated with non-migrating atmospheric tides. These non-migrating tides are known to significantly influence the longitudinal organization of the thermosphere and ionosphere. To bridge this gap, we have recently made significant progress in integrating non-migrating tidal wind components into the HWM framework using the latest Climatological Tidal Model of the Thermosphere (CTMT). This work outlines the mathematical formulation, fitting methodology, and validation of the extended model against ground- and space-based wind measurements. Further, we assess any systematic biases among datasets and the model, discuss the scientific results, their implications for ionosphere-thermosphere dynamics, and future model developments.