Improvement in thermospheric neutral density estimations of the numerical TIE-GCM by incorporating helium data from the empirical NRLMSISE-00 model

The total atmospheric neutral densities derived from the CHAMP (CHAllenging Minisatellite Payload) and the GRACE (Gravity Recovery And Climate Experiment) accelerometer data are used to investigate the accuracy of the empirical as well as numerical thermospheric neutral density models during the solar maximum (year 2002) through the solar minimum (year 2007). The models used in this thesis include the empirical models of the Jacchia-Bowman models (JB2006 and JB2008) and the MSIS (Mass Spectrometer Incoherent Scatter)-class model, and the numerical model of the NCAR's TIE-GCM (National Center for Atmospheric Research's Thermosphere Ionosphere Electrodynamics General Circulation Model). The thermospheric neutral density models show good agreement to the variations of neutral densities from the accelerometer data, but still had uncertainties which should be taken into account for better prediction of satellites' position in orbit. The TIE-GCM shows larger uncertainties in the root mean square (RMS) in percent deviations at 400 km compared to the empirical models: 47.1% for the TIE-GCM compared to 15.7%, 10.3%, and 20.3% for the JB2006, JB2008, and NRLMSISE-00 models, respectively. The errors gradually increase with the decline in the solar activity. The partial pressures of helium obtained from the Naval Research Laboratory's MSIS Extension 2000 (NRLMSISE-00) model are incorporated into the TIE-GCM to reflect the helium effect in calculating the molecular viscosity, the thermal conductivity, and the specific heat. As a result, the secular increases of the percent deviations are eliminated and the RMS of the TIE-GCM is improved to 21.4% and 22.8% for the densities from the CHAMP and the GRACE-A accelerometer data, respectively, with the incorporation of 71% partial pressures of helium from the NRLMSISE-00 model.