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Abstract:
The diurnal cycle of tropospheric Zenith Total Delays (ZTD) is critical for refining tropospheric models and understanding key geophysical and atmospheric processes. The fifth European Centre for Medium-Range Weather Forecasts reanalysis ERA5, with its unique 1-hr temporal resolution, provides valuable data for these purposes. However, we identified obvious discontinuities in ERA5-derived ZTD at 09:00 and 21:00 UTC. A comparison with 10-year GNSS data from 6,437 stations showed that 32.8% of the stations experienced discontinuities in mean diurnal anomalies of ERA5 ZTD, with an average magnitude of 2.2 mm, far exceeding the 0.3 mm hour-to-hour variations observed by GNSS. The discontinuities are more pronounced in summer and are primarily due to errors in ERA5's humidity modeling, with a few pressure-related issues limited to Antarctica. The discontinuity is attributed to the transition between ERA5's 12-hr assimilation windows and suggest that other ERA5 variables may also be impacted, warranting caution in ERA5-based diurnal cycle studies.
