Month to month changes of thermospheric neutral winds obtained from a data assimilation model

Thermospheric neutral winds play an important role in ionospheric and thermospheric dynamics and strongly affect temporal and spatial variations of ionospheric plasma.
However, direct observations of thermospheric neutral winds are historically limited both temporally and spatially.
For example, interferometric methods for measuring thermospheric winds are restricted to nighttime observations and cloudless conditions and are limited to relatively few locations.
Space-based observations made by cross-track measurements from accelerometers as well as onboard interferometers and spectrometers provide valuable information of thermospheric winds but coverage is sparse over a given location for all local times.
Radio occultation (RO) measurements obtained from satellites profile the upper atmosphere and provide critical parameters associated with ionospheric dynamics, i.e. hmF2 and NmF2.
These observations are abundant and embed information about the underlying thermosphere.
Data assimilation is a technique that combines information from observations with a physical model.
Observed data are assimilated into the model as a constraint for the physical equations that describe the dynamics of the system, which allows estimates of unobserved driving forces, e.g., the thermospheric neutral wind.

The Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model can assimilate global maps of hmF2 and NmF2 from COSMIC radio occultation measurements to estimate magnetic meridional winds at low- and mid-latitudes.
The Thermospheric Wind Assimilation Model (TWAM) combines these magnetic meridional wind estimates with the equation of motion of the neutral gas using a Kalman filter technique to provide monthly climatology estimates of the thermospheric wind components.

We will present the month-to-month progression of the TWAM thermospheric wind estimates for the year 2009 as well as comparisons with the empirical Horizontal Wind Model (HWM14) and ground- and space-based observations.