The beneficial impact of radio occultation observations on Australian region forecasts

The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) was launched in April 2006. This system provides a new observation type for operational meteorology that has been shown to provide significant information on the thermodynamic state of the atmosphere and to allow improvements in atmospheric analysis and prognosis. A month of COSMIC radio occultation observations, together with a smaller number of radio occultation observations from the Meteorological Operational satellite (MetOp) and Gravity Recovery and Climate Experiment (GRACE) spacecraft, have been assimilated into the global ACCESS (Australian Community Climate Earth System Simulator) system, which is being employed at the Australian Bureau of Meteorology to provide real-time operational forecasts. In this study, four-dimensional variational assimilation (4DVAR) has been used to assimilate the radio occultation and other data into the global ACCESS system (ACCESS-G), which has been used to provide forecasts to five days ahead. For the period studied, the accuracy of these forecasts has been compared to forecasts generated without the use of the radio occultation data. The forecasts using radio occultation data have been found to be improved in the lower, middle and upper troposphere. These results, combined with the relatively unbiased nature of the radio occultation observations indicate their use has the potential to improve operational analysis and forecasting in the Australian Region and also to assist in important tasks such as a regional reanalysis and climate monitoring.