Physics-based assimilative atmospheric modeling for satellite drag specification and forecasts

We describe ongoing work to build a comprehensive nowcast and forecast system for specifying orbital drag conditions. The system outputs include neutral density, winds, temperature, composition, and the satellite drag derived from these parameters. This modeling tool is called the Atmospheric Density Assimilation Model or ADAM. ADAM is based on three state-of-the-art coupled models of the thermosphere-ionosphere running in real-time and uses assimilative techniques to produce a thermospheric nowcast. ADAM will also produce 72 hour predictions of the global thermosphere-ionosphere system using the now-cast as the initial condition and using near real-time and predicted space weather data and indices as the inputs. We show here that the model drag nowcast is comparable to the current state-of-the-art empirical models even in a non-assimilative mode. We also show preliminary results of lower-boundary assimilation in the atmospheric model as well as the improvements from using an assimilative specification of storm-time energy inputs. With additional assimilation and tuning, we expect model performance to exceed the performance of current atmospheric models thus lowering the in-track orbit errors associated with Low Earth Orbit predictions.