Evolution of intra-annual thermospheric zonal wind reversal near dawn and dusk

Temporal and spatial variations in thermospheric neutral winds play a crucial role in shaping the ionospheric plasma dynamics. Despite their significance, observations of these winds are often limited in both temporal coverage and geographic distribution. Key atmospheric dynamics parameters, such as nmF2 and hmF2, can be effectively obtained through radio occultation (RO) observations. These parameters contain vital information about the underlying thermospheric conditions. Utilizing RO observations in data assimilation techniques allows for the integration of observed data with physical models. In this scheme, the data serve as a constraint to the equations governing the model, thereby providing estimates of unobserved driving forces, such as thermospheric neutral winds. In one of its modes, the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model can assimilate global maps of hmF2 and NmF2 derived from COSMIC radio occultation measurements. This approach enables the estimation of magnetic meridional winds at low- and mid-latitudes. Furthermore, the Thermospheric Wind Assimilation Model (TWAM) assimilates magnetic meridional wind estimates from the GAIM-FP model with the equation of motion of neutral gas using a Kalman filter technique. This integration allows for the provision of monthly climatology estimates of thermospheric wind components. In this study, we present thermospheric wind estimates from TWAM for the year 2009, along with an analysis of the intra-annual variation of the zonal wind reversal near dawn and dusk in the thermosphere.