Implementing and testing the rigorous GNSS tropospheric gradient operator in the WRF data assimilation system

The assimilation of GNSS tropospheric gradients into Numerical Weather Prediction models requires the development of observation operators, a process constrained by a trade-off between accuracy and computational cost.  As an initial step, a computationally efficient operator, which we refer to as the fast tropospheric gradient operator, was implemented and tested within the WRF data assimilation system (Thundathil et al., 2024). This presentation details the implementation and testing of a rigorous tropospheric gradient operator. Based on a linear combination of ray-traced tropospheric delays, this operator demands greater computational resources but minimizes errors by replicating the method used in the GNSS data analysis. With both operators now implemented and freely available to WRF users, a significant obstacle has been removed for research studies and operational applications. The other major challenge, namely the provision of high-quality tropospheric gradients in (near) real-time, remains a task for GNSS data analysis.Reference:Thundathil, R., Zus, F., Dick, G., and Wickert, J.: Assimilation of GNSS tropospheric gradients into the Weather Research and Forecasting (WRF) model version 4.4.1, Geosci. Model Dev., 17, 3599–3616, https://doi.org/10.5194/gmd-17-3599-2024, 2024.