RESUME / ABSTRACT

Column Integrated Water Vapour (IWV) can be retrieved from ground-based
GPS receiver measurements with accuracy similar to that of radiosondes
except in very dry conditions. An extensive network of ground-based GPS
receivers for meteorological applications (~ 360 sites) has been
developed in the United States by NOAA/Earth System Research Laboratory
(ESRL) to observe IWV. GPS IWV retrievals from this network are currently
assimilated at the NOAA National Centers for Environmental Prediction
(NCEP), with positive impact on forecast humidity and precipitation. The
Data Assimilation and Satellite Meteorology Section has been monitoring
and evaluating the NOAA/ESRL GPS data since 2004 and has recently
completed a series of data impact experiments with the MSC regional
analysis and forecast system which is a 3D-Var assimilation system. Here
the 3D-Var is run in FGAT (First Guess at Appropriate Time) mode to take
advantage of the high temporal resolutions of the GPS observations.
Results of these experiments will be presented with a focus on the
overall impact on humidity and precipitation fields. Verification of the
analyses and forecasts (up to day two) against radiosondes, rain gauge
measurements (SYNO and SHEF), and the GPS observations will be discussed.
The impact on the analyses and forecasts for case studies will also be
shown, including the impact of GPS observations on precipitation and
storm track for land-falling hurricanes Frances and Ivan in September
2004.