Selecting ERA5 Grid Spacing for GNSS Tropospheric Parameters over China

ERA5 is the fifth-generation atmospheric reanalysis from the European Centre for Medium-Range Weather Forecasts. It combines observations with a weather model to reconstruct past atmospheric conditions. We compared its 0.25° and 1° grids to assess tropospheric parameter errors and data requirements for Global Navigation Satellite System (GNSS) applications. Both grids were evaluated with radiosonde observations from 77 Chinese stations during 2016–2018. The finer grid reduced pooled root-mean-square (RMS) errors in zenith wet delay (ZWD) and zenith total delay (ZTD) by 12.3% and 12.2%, respectively. RMS errors in zenith hydrostatic delay (ZHD) and weighted mean atmospheric temperature (Tm) changed little or did not improve consistently. The lowest 3 km above the stations accounted for 73.7% of the reduction in total-column ZWD mean-squared error. GPT3-1 is the 1° grid version of the Global Pressure and Temperature 3 empirical model. At 1° spacing, ERA5 reduced pooled ZWD and ZTD RMS errors by 62.5% and 61.1%, relative to GPT3-1. Against precise point positioning (PPP)-derived ZTD at three GNSS stations, the ERA5 1° RMS error exceeded the 0.25° value by 0.258 mm. These results favor using 0.25° data for lower wet-delay errors. The 1° data reduce data requirements when their errors meet application needs.