Preprints
https://doi.org/10.5194/egusphere-2025-19
https://doi.org/10.5194/egusphere-2025-19
07 Feb 2025
 | 07 Feb 2025

Assimilation of GNSS Zenith Delays and Tropospheric Gradients: A Sensitivity Study utilizing sparse and dense station networks

Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert

Abstract. The assimilation of Global Navigation Satellite System (GNSS) zenith total delays (ZTDs) into numerical weather models improves weather forecasts. In addition, the GNSS tropospheric gradient (TG) estimates provide valuable insight into the moisture distribution in the lower troposphere. In this study, we utilize a newly developed forward operator for TGs to investigate the sensitivity effects of incorporating TGs into the Weather Research and Forecasting model at varying station network densities. We assimilated ZTD and TGs from sparse and dense station networks (0.5 and 1-degree). Through this study, we found that the improvement in the humidity field with the assimilation of ZTD and TGs from the sparse station network (1-degree resolution) is comparable to the improvement achieved by assimilating ZTD only from the dense station network (0.5-degree resolution). These results encourage the assimilation of TGs alongside ZTDs in operational weather forecasting agencies, especially in regions with few GNSS stations. Conversely, assimilating TGs alongside ZTDs from sparse GNSS networks can be a cost-effective way to enhance the accuracy of the model fields and subsequent forecast quality.

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Journal article(s) based on this preprint

30 Sep 2025
Assimilation of global navigation satellite system (GNSS) zenith delays and tropospheric gradients: a sensitivity study utilizing sparse and dense station networks
Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert
Atmos. Meas. Tech., 18, 4907–4922, https://doi.org/10.5194/amt-18-4907-2025,https://doi.org/10.5194/amt-18-4907-2025, 2025
Short summary
Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-19', Anonymous Referee #1, 08 Apr 2025
  • RC2: 'Comment on egusphere-2025-19', Anonymous Referee #2, 23 Apr 2025
  • RC3: 'Comment on egusphere-2025-19', Anonymous Referee #3, 23 Apr 2025
  • RC4: 'Comment on egusphere-2025-19', Anonymous Referee #4, 24 Apr 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-19', Anonymous Referee #1, 08 Apr 2025
  • RC2: 'Comment on egusphere-2025-19', Anonymous Referee #2, 23 Apr 2025
  • RC3: 'Comment on egusphere-2025-19', Anonymous Referee #3, 23 Apr 2025
  • RC4: 'Comment on egusphere-2025-19', Anonymous Referee #4, 24 Apr 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Rohith Muraleedharan Thundathil on behalf of the Authors (20 May 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (03 Jun 2025) by Roeland Van Malderen
RR by Anonymous Referee #4 (23 Jun 2025)
RR by Anonymous Referee #3 (24 Jun 2025)
ED: Publish subject to technical corrections (08 Jul 2025) by Roeland Van Malderen
AR by Rohith Muraleedharan Thundathil on behalf of the Authors (08 Jul 2025)  Author's response   Manuscript 

Journal article(s) based on this preprint

30 Sep 2025
Assimilation of global navigation satellite system (GNSS) zenith delays and tropospheric gradients: a sensitivity study utilizing sparse and dense station networks
Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert
Atmos. Meas. Tech., 18, 4907–4922, https://doi.org/10.5194/amt-18-4907-2025,https://doi.org/10.5194/amt-18-4907-2025, 2025
Short summary
Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert

Data sets

Assimilation of GNSS Zenith Delays and Tropospheric Gradients: A Sensitivity Study utilizing sparse and dense station networks Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert https://zenodo.org/records/13734635

Rohith Thundathil, Florian Zus, Galina Dick, and Jens Wickert

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Latest update: 30 Sep 2025
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Short summary
Tropospheric gradients provide information on the moisture distribution, whereas ZTDs provide the absolute amount of moisture through integrated water vapor. When TGs are assimilated with ZTDs, it helps the model actuate the moisture fields, correcting its dynamics. In our research, we show evidence that in particular regions with very few GNSS stations, the assimilation of gradients on top of ZTDs can provide the same impact as the assimilation of only ZTDs with dense coverage of GNSS stations.
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