On the Origin of Seasonal Variability of the Diurnal Migrating Tide Excited In Situ in the Ionosphere‐Thermosphere System

The seasonal variability of the diurnal migrating tide (DW1) significantly impacts Earth's ionosphere‐thermosphere (I‐T) system, affecting navigation and communication systems; however, the underlying physical mechanisms are not yet fully understood. This study employs controlled numerical experiments using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM), individually varying Earth's obliquity and Earth‐Sun distance to systematically isolate their roles in modulating seasonal DW1 variations. As TIE‐GCM excludes tidal forcing originating from the lower atmosphere, the simulated DW1 represents tides excited purely within the I‐T system. Results reveal that pronounced low‐latitude DW1 seasonality can be excited within the I‐T system, and we identify a coupling mechanism that explains how Earth's obliquity controls this internally excited variability. Obliquity‐driven variations in solar zenith angle induce DW1 seasonality in tropical neutral winds and Pedersen and Hall conductivities, which together generate seasonal variations in dynamo currents and polarization electric fields. These electric fields efficiently project along geomagnetic field lines, driving significant seasonal variations in vertical plasma drifts, and consequently modulating O + density, electron density (Ne), and total electron content (TEC). In contrast, variations in Earth‐Sun distance exert a relatively minor influence. These results highlight electrodynamic coupling as a key pathway controlling DW1 seasonality within the I‐T system.