Thermosphere Neutral Densities at Dusk/Dawn Derived from Space-Borne Atmospheric Density Detectors

Based on the in-situ observed mass densities derived from the space-borne atmospheric density detectors on the Atmospheric density detection and Precise Orbit Determination (APOD) and another Chinese satellite (CHN-sat), from 2008–2018, the neutral density variations of the dawn/dusk thermosphere mass density at 460 km, 630 km altitudes are presented in this paper. Our results reveal: (1) The densities observed by APOD show consistent variations with that in empirical model results, and the latitudinal- seasonal structure shows that the largest density maxima appear near equinoxes in the northern high latitudes with the higher maximum near March than that in October at solar minimum. (2) Equatorial observations of CHN-sat are in good agreement with model results, while significant differences between observations and MSISE00 densities occur at high latitudes under the very low solar activity conditions. In solstices, the measured densities by CHN-sat at high latitudes in the summer hemisphere are distinctly higher than those in the winter hemisphere, which indicates that the relative importance of the conjunct contribution from oxygen atom and temperature, and the winter helium bulge maybe should be adjusted in the empirical model. (3) The weak geomagnetic disturbance can strengthen the high-latitude density at dawn and the low-latitude density maxima at dusk at CHN-sat altitudes.