Using GNSS data for real-time moisture analysis and forecasting over the Australian Region I. The system

The use of high spatial and temporal resolution data assimilation and forecasting around Australia's capital cities and rural land provides an opportunity to improve moisture analysis and forecasting. To support this endeavour, RMIT University and Geoscience Australia have worked with the Bureau of Meteorology (BoM) to provide real-time GNSS (Global Navigation Satellite System) Zenith Total Delay (ZTD) data over the Australian region, from which a high-resolution total water vapour field for SE Australia can be determined. The ZTD data can play an important role in high-resolution data assimilation by providing mesoscale moisture data coverage from existing GNSS surface stations over significant areas of the Australian continent. The data are now used by the BoM's high-resolution ACCESS-C3 capital city NWP systems, the ACCESS-G3 Global system and have been used by the ACCESS-R2-Regional NWP model. A description of the data collection and analysis system is provided. An example of the application of these local GNSS data for a heavy rainfall event over SE Australia/Victoria is shown using the 1.5km resolution ACCESS-C3 model, which is being prepared for operational use. The results from the test have been assessed qualitatively/synoptically and also have been examined quantitatively using the Fractions Skills Score which shows the reasonableness of the forecasts and demonstrates the potential for improving rainfall forecasts over south-eastern Australia by the inclusion of ZTD data in constructing the moisture field. These data have now been accepted for operational use in NWP.