Yearly Patterns of Thermospheric Zonal Wind Reversal at Dawn and Dusk

The dynamics of the ionosphere and thermosphere are strongly shaped by thermospheric neutral winds, which influence both the temporal and spatial variations of ionospheric plasma. However, direct observations of these neutral winds are often spatially and temporally limited. Radio occultation (RO) is a technique used to measure key atmospheric parameters related to ionospheric dynamics, such as hmF2 and NmF2, which carry information about the underlying thermosphere. Data assimilation techniques combine observational data with physical models, where the observations are incorporated into the model to constrain the equations governing system dynamics. This approach enables the estimation of unobserved driving forces, such as thermospheric neutral winds. The Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model can assimilate global maps of hmF2 and NmF2 derived from COSMIC radio occultation data to estimate magnetic meridional winds in low- and mid-latitude regions. The Thermospheric Wind Assimilation Model (TWAM) integrates these wind estimates from GAIM-FP with the neutral gas equation of motion, using a Kalman filter technique to generate monthly climatology estimates of thermospheric wind components. This study presents the monthly progression of TWAM's thermospheric wind estimates for 2009, along with an analysis of intra-annual variations in the zonal wind reversal near dawn and dusk within the thermosphere.