The application of radio occultation observations for climate monitoring and numerical weather prediction in the Australian region

Space-based GPS radio occultation observations provide significant information related to current and future atmospheric state. They also enable important activities such as examination of radiosonde performance and temperature trends. Three months of radio occultation observations have been assimilated using four dimensional variational assimilation into the global Australian Community Climate Earth Systems Simulator, ACCESS-G, which is employed at the Australian Bureau of Meteorology to provide operational forecasts. The radio occultation data was found to improve the forecasts in the lower, middle and upper troposphere. The improvement varies from small, to up to eight-hours improvement in 48-hour forecasts of mean sea level pressure. Because of the relatively unbiased nature of radio occultation observations, they have been used in a comparative study with radiosonde data to probe mean annual atmospheric temperature changes in the Australian region and the southern hemisphere. In particular, differences between radio occultation data based, area weighted annual average short-term (2007-2010) temperature trends over the Australian region and the southern hemisphere and those obtained by averaging data at radiosonde network sites were noted. In the Australian region a mid and upper tropospheric area averaged temperature increase from 2007 to 2010 was accompanied by an average cooling at radiosonde sites. The radio occultation data have also been used to probe ionospheric content. Results documented here indicate the use of radio occultation data has the potential to improve operational analysis and forecasting in the Australian region and to make a very important and unique contribution to vital tasks such as climate monitoring.