Abstract
Reanalysis products have played an important role in space geodetic tropospheric delay retrieval and modeling in the past two decades. As the release of the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA5), with improved temporal-spatial resolutions compared to its predecessor, ECMWF Re-Analysis Interim (ERAI), the performance of ERA5 in tropospheric delay retrieval was comprehensively investigated in this study. Hourly tropospheric delays in zenith and 5° elevation directions at 312 International GNSS Service (IGS) stations covering the year of 2018 from ERA5 and ERAI were ray-traced. Taking IGS Zenith Total Delay (ZTD) as reference, the reanalysis-derived ZTDs were evaluated in annual, seasonal and diurnal scales, and superior performances of ERA5 ZTD to ERAI ZTD in all scales were revealed, with bias, Root Mean Square (RMS) and standard deviation of 1.6, 11.0 and 10.1 mm for ERA5, and of 3.1, 13.8 and 12.6 mm for ERAI, respectively. Due to the absence of reliable Slant Path Delay (SPD) references, the SPDs as well as the mapping factors derived from ERA5 and ERAI were directly compared and converted to equivalent station height errors at these stations. Obvious differences were also found for SPDs and mapping factors, especially for the wet component, with slant wet delay and wet mapping factor difference RMSs of 51.9 mm and 146.1 × 10−3, respectively, corresponding to equivalent station height RMSs of about 10.4 mm. Tropospheric delays and models (e.g., mapping functions) derived from ERA5, with improved performance and temporal resolution (e.g., to support potential tropospheric parameter diurnal variation study), therefore can be expected for space geodetic applications.
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Data availability
IGS and CODE ZTD products were available through IGS FTP (cddis.gsfc.nasa.gov/) and CODE FTP (ftp.aiub.unibe.ch/). ERA5 and ERAI were downloaded from Copernicus Climate Data Store (https://cds.climate.copernicus.eu/) and ECMWF (https://www.ecmwf.int/), respectively.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (41774036; 41804023; 41961144015), the Fundamental Research Funds for the Central Universities (2042020kf0020), the China Postdoctoral Science Foundation funded Project (2017M622518), and the Natural Science Foundation of Hubei Province of China (2018CFB193). Authors would like to thank IGS, CODE, Copernicus Climate Data Store and ECMWF for providing the research datasets, and acknowledge Higher Geodesy team of Technische Universität Wien for developing the open-source ray-tracing package RADIATE. Authors also would like to appreciate Supercomputing Center of Wuhan University for the global tropospheric delay ray-tracing calculations from 0.25° ERA5 products.
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YDL and WXZ proposed the initial ideas. YZZ and WXZ designed and performed the specific experiments, as well as wrote the manuscript with support from YDL. CLK, WXL and JNB participated in the experiments, and also provided some helpful suggestions for shaping the research, analysis and manuscript.
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Zhou, Y., Lou, Y., Zhang, W. et al. Improved performance of ERA5 in global tropospheric delay retrieval. J Geod 94, 103 (2020). https://doi.org/10.1007/s00190-020-01422-3
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DOI: https://doi.org/10.1007/s00190-020-01422-3