Migrating and Nonmigrating Neutral Mass Density Tides From GRACE‐FO Observations for Solar Minimum Conditions

Abstract This study presents the migrating and nonmigrating thermospheric neutral mass density tides from the Gravity Recovery And Climate Experiment Follow‐On (GRACE‐FO) observations under solar minimum conditions (year 2020). The observed densities are first mapped to a reference altitude of 500 km using an empirical model (NRLMSIS 2.0) to remove the impact of the elliptical orbit. To address incomplete local solar time sampling due to the slow orbit precession and to achieve full local solar time coverage, 161‐day composite windows centered on each analysis day are constructed. A two‐dimensional fast Fourier transform is then applied in time and longitude to extract the amplitudes and phases of migrating tides, including DW1, SW2, TW3, and QW4, as well as nonmigrating tides such as DE3, DW2, and SE2. The retrieved tides show distinct seasonal‐latitudinal variability. Migrating DW1 and SW2 are the dominant contributors to the density tidal spectrum, while higher‐order migrating components such as TW3 and QW4 also produce significant variability at 500 km. A consistency check is also performed using the independent CHAllenging Minisatellite Payload (CHAMP) relative density tidal data set under comparable solar minimum conditions. The GRACE‐FO tidal structures show good agreement with CHAMP relative density tides, supporting the reliability of the tidal diagnostics. These results provide new observational constraints on upper‐atmospheric tidal dynamics and establish a framework for using GRACE‐FO neutral density measurements to study vertical coupling and thermospheric variability, with important implications for satellite orbit‐drag prediction.