Impact of a priori zenith hydrostatic delay errors on ground-based GNSS tropopause height determinations

The determination of tropopause height (TPH) is crucial for atmospheric research and the improvement of Global Navigation Satellite System (GNSS) meteorological models. While TPH determination from ground-based GNSS zenith tropospheric delay (ZTD) offers high spatiotemporal resolution and all-weather continuity, it requires precise calibration of the zenith hydrostatic delay above the tropopause (ZHD TPH ). This calibration is typically derived from meteorological reanalysis products using the Saastamoinen model. However, the performance of the Saastamoinen model near the tropopause has not been studied yet, and reanalysis products are often constrained by large data volumes and latency. To address these gaps, in this work, we assessed the global accuracy of the Saastamoinen model and evaluated the ZHD TPH calibrations derived from three empirical meteorological models (i.e., UNB3m, PVoxel, and IGPZWD) at high altitudes (6–30 km), using the fifth-generation ECMWF global atmospheric reanalysis (ERA5) products during the year 2019. The impact of a priori ZHD TPH errors on TPH determinations from GNSS ZTD was also investigated, combined with datasets collected from 62 stations worldwide with GNSS and radiosonde collocated. Results indicate that the Saastamoinen model achieves millimeter-level accuracy at high altitudes, with a global mean RMSE below 1.1 mm, and the method for determining TPH from GNSS ZTD can be applied over the globe with a global mean RMSE of about 1.65 km. Among the three empirical models, the PVoxel model demonstrates the best overall performance for ZHD TPH calibrations. However, the impact of a priori ZHD TPH errors on GNSS-based TPH determinations is station-dependent. Statistically, the a priori ZHD TPH error of approximately 5 mm typically propagates to a 0.17 km error in TPH determination at low and high latitudes. For determining TPH from GNSS ZTD in the absence of reanalysis products, the PVoxel model is recommended for ZHD TPH calibrations at low latitudes, whereas the IGPZWD model performs better at high latitudes.