This paper investigates ionospheric response characteristics from multiple perspectives based on globally distributed GNSS data and products, ionosonde data, FORMOSAT-7/COSMIC-2 occultation data, and Swarm satellite observations caused by the total solar eclipse of 8 April 2024 across North and Central America. The results show that both GNSS-derived TEC products have detected the ionospheric TEC degradation triggered by the total solar eclipse, with the maximum degradation exceeding 10 TECU. The TEC data from nine GNSS stations in the path of the maximum eclipse reveal that the intensity of ionospheric TEC degradation is related to the spatial location, with the maximum degradation value of the ionospheric TEC being about 14~23 min behind the moment of the maximum eclipse. Additionally, a negative anomaly of foF2 with a maximum of more than 2.7 MHz is detected by ionosonde. In the eclipse region, NmF2 and hmF2 show trends of decrease and increase, with percentages of variation of 40~70% and 4~16%, respectively. The Ne profile of the Swarm-A satellite is significantly lower than the reference value during the eclipse period, with the maximum negative anomaly value reaching 11.2 × 10⁵ el/cm³, and it failed to show the equatorial ionization anomaly.

With the improvement in GNSS data processing accuracies, selection of optimal asymmetric troposphere delay modeling method becomes essential, especially during the period of severe weather events and with the development of LEO constellation augmented GNSS (LeGNSS). In this research, we compare the performances of several troposphere gradient models in describing the asymmetrical troposphere delays. Using simulation data during the stable and severe periods, we find that high-order horizontal gradient models exhibit higher accuracy in the experiments. In the LeGNSS Precision Point Positioning (PPP) solutions, the second-order gradient model performs optimally, with accuracies of up to 1.1/3.8/0.8 mm during the stable period and 0.9/2.5/1.0 mm during the severe period for the horizontal component, vertical component, and Zenith Total Delay (ZTD) parameters. In comparison, the analysis of Slant Path Delays (SPD) accuracy for elevation below 10° shows that the directional model is more suitable for low elevation observations, but the introduction of too many redundant parameters leads to a decrease in the accuracy at high elevation angles. The LEO constellation can bring maximum 32.9%, 12.6% and 27.9% accuracy improvement for the horizontal component, vertical component and ZTD parameters during the stable period, while 26.5%, 31.8% and 34.9% during the severe period. The estimation of high-temporal resolution gradient parameters instead of traditional daily gradient parameters can significantly improve the accuracy of ZTD in the extreme weather events. Therefore, this research underscores the spatial and temporal resolution of horizontal gradient models, which meets the growing demand for GNSS/LeGNSS data processing during the severe weather events.

Clock offset constitutes a major error source for Global Navigation Satellite System (GNSS) radio occultation (RO) products, particularly for stratospheric observations. The adoption of high-rate clock correction strategy can effectively mitigate clock offset induced errors. In this study, high-rate (1-s) undifferenced (UD) Low Earth Orbit (LEO) clock corrections are used to retrieve RO observations from the Fengyun-3E (FY-3E) satellite. The retrieval results are compared with those derived from the conventional 30-s clock correction scheme and the single-difference (SD) scheme currently adopted in the official data processing. The results demonstrate that the 1-s LEO clock correction scheme improves the overall quality of FY-3E RO retrievals. For bending angle, the most prominent improvements are found in the altitude range of 40-60 km. Globally, its systematic difference is roughly 3% smaller than that of the 30-s scheme and 1% smaller than the SD scheme. Such superiority further propagates downward to refractivity and dry temperature. For refractivity, the largest improvements are also found in the altitude range of 40-60 km with systematic differences for the 1-s UD scheme reduced by approximately 0.5% relative to the other two schemes. Standard deviations of the 1-s scheme remain consistently smaller across the complete height range. Standard deviations of dry temperature are also improved with standard deviations about 0.5% smaller than SD and 1% to 2% smaller than the 30-s scheme in the altitude range from 0-40 km. The results in this study demonstrate the capability of using 1-s clock correction scheme for further promoting Fengyun GNSS Occultation Sounder-II (GNOS-II) RO observations. The results here can provide support for future operational processing and archive reprocessing of all Fengyun GNSS occultation datasets.

Clock offset constitutes a major error source for Global Navigation Satellite System (GNSS) radio occultation (RO) products, particularly for stratospheric observations. The adoption of high-rate clock correction strategy can effectively mitigate clock offset induced errors. In this study, high-rate (1-s) undifferenced (UD) Low Earth Orbit (LEO) clock corrections are used to retrieve RO observations from the Fengyun-3E (FY-3E) satellite. The retrieval results are compared with those derived from the conventional 30-s clock correction scheme and the single-difference (SD) scheme currently adopted in the official data processing. The results demonstrate that the 1-s LEO clock correction scheme improves the overall quality of FY-3E RO retrievals. For bending angle, the most prominent improvements are found in the altitude range of 40-60 km. Globally, its systematic difference is roughly 3% smaller than that of the 30-s scheme and 1% smaller than the SD scheme. Such superiority further propagates downward to refractivity and dry temperature. For refractivity, the largest improvements are also found in the altitude range of 40-60 km with systematic differences for the 1-s UD scheme reduced by approximately 0.5% relative to the other two schemes. Standard deviations of the 1-s scheme remain consistently smaller across the complete height range. Standard deviations of dry temperature are also improved with standard deviations about 0.5% smaller than SD and 1% to 2% smaller than the 30-s scheme in the altitude range from 0-40 km. The results in this study demonstrate the capability of using 1-s clock correction scheme for further promoting Fengyun GNSS Occultation Sounder-II (GNOS-II) RO observations. The results here can provide support for future operational processing and archive reprocessing of all Fengyun GNSS occultation datasets.