Atmospheric drag provides an indirect approach for evaluating atmospheric mass density, which can be derived from the Precise Orbit Determination (POD) of Low Earth Orbit (LEO) satellites. A method was developed to estimate nongravitational acceleration, which includes the drag acceleration of the thermospheric density model and empirical force acceleration in the velocity direction from the centimeter-level reduced-dynamic POD. The main research achievements include the study of atmospheric responses to geomagnetic storms, especially after the launch of the spherical Qiu Qiu (QQ)-Satellite (QQ-Satellite) with the global navigation system satellite (GNSS) receiver onboard tracking the Global Positioning System (GPS) and Beidou System (BDS) data. Using this derivation method, the high-accuracy POD atmospheric density was determined from these data, resulting in better agreement among the QQ-Satellite-derived densities and the NRLMSISE-00 model densities. In addition, the POD-derived density exhibited a more sensitive response to magnetic storms. Improved accuracy of short-term orbit predictions using derived density was one of the aims of this study. Preliminary experiments using densities derived from the QQ-Satellite showed promising and encouraging results in reducing orbit propagation errors within 24 h, especially during periods of geomagnetic activity.

The polar-orbiting spherical experimental satellite of China for atmospheric density detection with an altitude of ~520 km was successfully launched on 14 October 2021. Based on the dynamic inversion method for atmospheric density and the precise orbit determination data obtained by its GNSS, we inverted the orbital atmospheric density during the severe geomagnetic storm in early November 2021. In this paper, we compared the atmospheric density data obtained by the spherical satellite with the simulations of the MSISE00 and the DTM, evaluated their error distribution, and analyzed the response of the atmospheric density during the severe geomagnetic storm in the dawn–dusk orbit of 520 km altitude. The properties and the physical processes for the atmospheric density of the time evolutions in different latitudes and the global distributions during the severe geomagnetic storm were obtained. We found that the substantial disturbance enhancement and recovery of the atmospheric density of the dawn–dusk orbit have a close correlation with the geomagnetic indexes Kp and Dst. The elevation extends from the poles to the equator, and the relative variation in two hemispheres demonstrates a bimodal nearly symmetric growth structure. The maximum relative variation of the two hemispheres both occurred in the middle latitude, and, for this case, the enhancement of atmospheric density in the mid-latitude region accounted for a larger proportion. The asymmetry between the northern and southern hemispheres is demonstrated by the fact that the absolute value and absolute change in the southern hemisphere in summer are larger than those in the northern hemisphere, and the bimodal structure of the relative variation is inclined to the northern hemisphere.

This article proposes a single-frequency occultation method whose core is the reconstruction of a second frequency measurement. We process the actual received Galileo E1 single-frequency occultation observation data of FengYun3E to meet the urgent need for single-frequency Galileo occultation inversion of FengYun3 E/F/G/H satellites. Galileo single-frequency occultation events are globally distributed evenly and have stable quantities. The refractive index products and dry temperature products inverted from the single-frequency occultation data are reliable at altitudes of 5–30 km. The Galileo E1 single-frequency occultation process can effectively improve the output of FengYun3E/GNOS occultation products. These results validate the feasibility and correctness of using FengYun3/GNOS for the actual Galileo single-frequency occultation process. The atmospheric occultation products of Galileo single-frequency occultation increase the quantity of global occultation products and serve as a beneficial supplement to global numerical weather prediction data sources.

High-resolution thermospheric mass density (TMD) measurements from Low Earth Orbit (LEO) Satellites are valuable to accurately estimate the short-term atmosphere abrupt disturbances, triggered by magnetospheric forcing. A good characterization of TMD variation ahead of the arrival geomagnetic storms can benefit LEO operations and crucial for both orbit propagation and collision avoidance. In this contribution, we will reveal the most probable feature of TMD variation during the initial stage of solar cycle 25, at the same time, we proved Wygant function as a better geomagnetic events indicator.In this study, GRACE-FO 10s accelerometer-derived TMD measurements were employed and normalized at altitude of 505km by the NRLMSISE-00 (Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Exosphere 2000) empirical atmosphere model to investigate the status of solar cycle 25 between September 1 and December 31, 2020. With the high-inclination orbit global coverage, three magnetic latitude regions were separated and divided into day and nighttime using magnetic local times (MLT). 4-month enhancing disturbances observations suggest solar activities will shift from its relatively quiet condition to a much more active behavior, which reveal unexpected dependencies on the temporal and spatial characteries. Our detailed analysis shows that (1) TMD spreads from high latitudes to low latitudes and as same as time lag, (2) TMD enhancement in the Southern hemisphere is more intense than in the Northern one, reaching peak value around 15:00 MLT; geomagnetic activities cause TMD to increase up to 0.86×10-13 kg/m3 at night side, 3.4×10-13 kg/m3 at day side, and (3) the TMD enhancement was symmetric in both N- and S- hemispheres before the equinox. In general, thermospheric mass density analysis reveals the significant impact of solar and geomagnetic activities, providing the most relevant and probable characteristic of the TMD disturbances driven by solar wind.Additionally, we try to use different geomagnetic indices for a complete description of geomagnetic storms and their phases. The S10.7 index is used as a proxy for solar irradiation. These indicators show high correlation with the TMD variation during recurrent geomagnetic activities. What’s more, the cross-correlation analysis reflects a high correlation of to the Wygant function EWAV found both at three latitude bins.Even thought our study is considered a minor to moderate geomagnetic storm of the upcoming solar cycle 25 maximum, the high-speed stream injection into the thermosphere still caused thermosphere expansion that significantly enhanced the neutral density in the LEO environment. Therefore, all these findings provide a possibility to improve our understanding of LEO orbital drag.