Abstract: In response to the underestimation of COSMIC-2-retrieved zenith tropospheric delay (ZTD)caused by missing near-surface data,this study firstly employs elevation-based scaling factors derived from the ERA5 dataset,then applies a negative exponential model to correct the COSMIC-2 ZTD,and finally validates the correction accuracy using radiosonde measurements and GNSS ZTD data from the crustal movement observation network of China (CMONOC)across China during 2020—2022.The results indicate that,after applying the correction,the mean RMSE of the COSMIC-2 ZTD decreases by 30.95 and 32.48 cm when compared to the radiosonde and GNSS ZTD references,respectively.Moreover,a month-by-month assessment for 2022 shows that the corrected COSMIC-2 ZTD RMSE stabilizes within a range of 2～8 cm.These findings demonstrate the suitability of the negative exponential elevation model for enhancing COSMIC-2 ZTD data over China,providing reliable tropospheric delay corrections that benefit both GNSS navigation and atmospheric water-vapor monitoring.

Key words: zenith tropospheric delay, elevation scaling factor, negative exponential elevation model, COSMIC-2 radio occultation, ERA5 reanalysis data