Extending Global and Regional Near Real-Time GNSS ZTD Solutions Using BSW5.4 at the University of Luxembourg: Contributions to E-GVAP

The University of Luxembourg (UL), in collaboration with the United Kingdom Met Office, continues to advance the provision of global and regional near real-time (NRT) Zenith Total Delays (ZTDs) from GNSS ground networks to support operational meteorological products within the EUMETNET EIG GNSS Water Vapour Programme (E-GVAP). E-GVAP facilitates coordination and uptake of NRT GNSS-based atmospheric monitoring, which is indispensable for assimilation in Numerical Weather Prediction (NWP) models across Europe, including at the Met Office, where high-temporal-resolution data enhance mesoscale weather forecasting. This study highlights the collaborative efforts of the Met Office and UL in delivering accurate, timely meteorological data from GNSS. The partnership has resulted in the development and enhancement of NRT processing systems using the state-of-the-art Bernese GNSS software version 5.4 (BSW5.4), generating ZTD products at both UL and the Met Office at 1-hour intervals globally and regionally, and at sub-hourly intervals regionally. Over the past year, UL has focused on developing hourly NRT ZTD solutions for global and regional networks, and more recently extending them to sub-hourly intervals (down to 15 minutes) for regional coverage, thereby refining the temporal resolution for E-GVAP users. In particular, we are now prepared to provide NRT products in the form of a global hourly product (ULGH), a regional hourly product (ULRH), and a regional sub-hourly product (ULRS) to E-GVAP. As part of the system's development, we validate our latest global, regional, and sub-hourly ZTD solutions against established NRT outputs from E-GVAP and benchmark post-processed Double-Difference Network (DDN) products, while also verifying Integrated Water Vapour (IWV) estimates against ECMWF Reanalysis v5 (ERA5). Finally, we highlight how higher-frequency updates can positively influence NWP assimilation in rapidly evolving weather situations, detailing data flow and latency management that ensure reliable NRT ZTD delivery to E-GVAP participants and the Met Office. By extending temporal coverage from hourly to sub-hourly in regional networks and continuing our global solutions, we advance the utility of GNSS-based atmospheric sensing for short-term weather forecasting, providing consistent, high-quality NRT GNSS products for meteorological operations in Europe and beyond.