Application of an optimal estimation inverse method to GPS/MET bending angle observations

Palmer et al. [2000] describes an optimal estimation inverse method for radio occultation (RO) bending angle measurements to retrieve simultaneously temperature, humidity, and surface pressure, outlines quality control procedures for retrieved profiles; and investigates the results from numerical simulations. Here we present retrievals that use bending angle observations from the Global Positioning System Meteorology (GPS/MET) satellite instrument and a priori information from the European Centre for Medium-Range Weather Forecasts analyses. Retrieved profiles are compared with correlative radiosondes, United Kingdom Meterological Office UKMO) model analyses, and retrievals from the conventional inverse method, Retrieved temperature profiles are generally colder than analyses but agree with the conventional inverse method to within I K. Water vapor retrievals are generally drier than the UKMO analyses and wetter than the radiosonde profiles. Quality of retrieved surface pressure values are related to the extent to which RO observations reach into the troposphere. Low-latitude retrievals make large adjustments to surface pressure and tropospheric temperatures, which are directly linked to the lack of water vapor above 300 hPa in the inverse model, consistent with previous studies. A study of individual occultations at low and high latitude shows that the optimal retrievals are able to resolve small-scale atmospheric structure exhibited by the conventional inverse method and collocated radiosondes, not shown by analyses.