Responses of Thermospheric Mass Densities to the October 2016 and September 2017 Geomagnetic Storms Revealed From Multiple Satellite Observations
In this study, the thermospheric mass densities based on satellite Precise Orbit Determination (POD) data from Gravity Recovery and Climate Experiment (GRACE), Swarm A, and Swarm B were used to explore the thermospheric variations in response to the October 2016 and September 2017 geomagnetic storms which occurred around the equinox. Two of the three satellites were nearly coplanar and the third one flew at a separated orbital plane. Based on the nearly coplanar observations of GRACE and Swarm, the thermospheric mass densities showed different hemispheric asymmetries depending on altitudes. The observations from different local times (LTs) revealed that the density enhancements were similar between the two hemispheres when the LTs were 8-10/20-22 LTs. However, the enhancements were stronger in the southern hemisphere than those in the northern hemisphere at around 16 LT. Moreover, the density enhancements at low latitudes underwent significant day night variation as the daytime densities at low latitudes increased more rapidly and strongly than the nightside. Our results demonstrated that the satellite POD data could be used to retrieve high cadence thermospheric density to study the variations of the upper atmosphere.