Intra-annual evolution of the thermospheric zonal wind reversal near dawn and dusk

The dynamics of the ionosphere and thermosphere are significantly influenced by thermospheric neutral winds that affect temporal and spatial variations of ionospheric plasma. Observations of these neutral winds, however, are limited spatially and temporally. Radio occultation (RO) is a technique to obtain critical parameters of the atmosphere associated with ionospheric dynamics such as hmF2 and NmF2 which embed information about the underlying thermosphere. Data assimilation techniques combine information from observations with a physical model where data is assimilated into a model to provide a constraint for the physical equations that describe the dynamics of the system described by the model thus, in this case, allowing for calculated estimates of unobserved driving forces such as the thermospheric neutral wind. The Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) mode can assimilate global maps of hmF2 and NmF2 provided from COSMIC radio occultation measurements to estimate magnetic meridional winds at low- and mid-latitudes. The Thermospheric Wind Assimilation Model (TWAM) combines magnetic meridional wind estimates from the GAIM-FP model with the equation of motion of neutral gas using a Kalman filter technique to provide monthly climatology estimates of the thermospheric wind components. Presented here is the month-to-month progression of the TWAM thermospheric wind estimates for the year 2009 as well as the intra-annual change of the zonal wind reversal near dawn and dusk in the thermosphere.