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Abstract:
In this research study, Global Navigation Satellite System (GNSS) tropospheric gradients and Zenith Total Delays (ZTDs) are assimilated into the Weather Research and Forecasting (WRF) model. The WRF model has its operator already developed for the ZTDs. In our project, we are developing a new operator for the assimilation of tropospheric gradients. The assimilation of ZTDs, which are closely related to the Integrated Water Vapor (IWV) above the GNSS station, has a positive impact on weather forecasts. On the other hand, tropospheric gradients are not yet operationally assimilated by weather agencies. Our research is based on a project titled “Exploitation of GNSS tropospheric gradients for severe weather Monitoring And Prediction” (EGMAP) focusing on the impact of GNSS tropospheric gradients and how it can be effectively used for operational forecasting of severe weather. EGMAP is funded by the German Research Foundation (DFG). We will rely on a simple and fast observation operator, which is based on the closed-form expression depending on the north–south and east–west horizontal gradients of atmospheric refractivity (Davis et al., 1993). Initial testing of the operator is done on a 0.1 x 0.1-degree mesh with 50 vertical levels up to 50 hPa. Initial DA tests are being performed with an automated rapid update cycle DA framework based on a deterministic three-Dimensional Variational (3DVar) DA system for testing ZTDs and tropospheric gradients. The EGMAP project status and initial results from the impact of assimilating GNSS-ZTDs and tropospheric gradients will be presented.
