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.