Identifying the Sources of the Variability in Thermospheric Mass Density

Recent accelerometer observations onboard Low Earth Orbit (LEO) spacecrafts have revealed considerable amount of variability in thermospheric neutral mass density on various temporal and spatial scales not only during periods of elevated geomagnetic activity but also during quiet times. Accurately predicting the upper atmosphere density is crucial for estimating the trajectory of LEO spacecrafts since satellite drag introduces errors in orbit determination solutions for the rapidly increasing number of man-made objects. The purpose of this study is to quantify the degree of variability in the neutral mass density in the thermosphere and identify the possible causes by utilizing the coupled Whole Atmosphere Model and Ionosphere-Plasmasphere-Electrodynamics (WAM-IPE) that is running in real-time development mode in preparation for operations at NOAA/SWPC. In this presentation, the mass density variations for various geophysical conditions are compared between the WAM-IPE model, accelerometer satellite observations from GOCE, and the Coupled Thermosphere, Ionosphere, Plasmasphere, and electrodynamics (CTIPe) model that has been well established by continuous validation efforts for over a decade. The results comparing WAM-IPE with GOCE and CTIPe suggest that the WAM-IPE model can capture the normal diurnal/latitude neutral density structure as well as the response and recovery to geomagnetic storms. With appropriate parameters in place, the results yield reasonable agreement across the neutral mass density and temperature comparisons. Furthermore, the neutral composition and energy drivers are validated to improve the storm-time and recovery responses. Sensitivity analysis are carried out to quantify the neutral mass density variability toward improved predictions of satellite orbits.