The Impact of GPS Radio Occultation Measurements in Numerical Weather Prediction (Invited Presentation)

GPS radio occultation (GPS-RO) measurements have now been assimilated operationally at the major international numerical weather prediction (NWP) centres since around 2006. This is a direct result of the pioneering GPS/MET “proof of concept” mission, performed by the United States in the mid 1990’s. Despite the relatively low observation numbers, the GPS-RO measurements are now considered to be an important component of the Global Observing System (GOS), because they complement the information provided by satellite radiance measurements. This is primarily because the measurements have good vertical resolution, and they can be assimilated without bias correction to the NWP model, meaning they are used as “anchor measurements” in the satellite radiance bias correction systems. This talk will explain why the GPS-RO measurements provide high information content to the GOS, describe how they are assimilated at ECMWF currently, and where they have the largest impact on the NWP forecasts. New ideas for improving the forward modelling of the GPS-RO measurements will be presented, and areas where the assimilation and impact of GPS-RO can be improved will be discussed. The impact of GPS-RO on the consistency of climate reanalyses in the lower/middle stratosphere will also be noted.