Comparison of Tropospheric Water Vapour over Antarctica Derived from AMSU-B Data, Ground-Based GPS Data and the NCEP/NCAR Reanalysis

The extreme climate conditions and the sparse number of research stations in Antarctica limit the number of meteorological records over this area. Satellite radiometric measurements and ground-based GPS measurements can therefore improve the amount of available water vapour information. Combining the Zenith Total Delay (ZTD) time series from 6 Antarctic GPS stations and surface meteorological data, we have determined Precipitable Water Vapour (PW) variations with a 2-hour temporal resolution for a period of 5 years. Data from the Advanced Microwave Sounding Unit (AMSU-B) on board the NOAA-15 satellite cover most parts of Antarctica but with observations limited to merely few times a day. GPS and AMSU-B data sets are therefore complementary with respect to time and space. We present a cross validation between PW results from the two independent retrieval algorithms using one year data. Additionally, we compare the observed PW from AMSU-B and GPS with the National Centre for Environmental Prediction (NCEP) reanalysis. All three data sets are highly correlated. The mean differences between the three data sets are station dependent and vary from -1.7 to +1.2 mm. A large part of the bias may result from pressure uncertainties affecting the GPS PW estimates. GPS and AMSU-B as independent data sources are confirmed to be accurate methods for PW estimation for the dry Antarctic atmosphere. PW results from the NCEP analysis corresponds, in general, well to the PW observations at the investigated stations along the Antarctic coast. The results obtained at the station O’Higgins differ from those of the other station. O’Higgins is located at the Antarctic Peninsula and has a more humid environment than the coast of the main Antarctic continent, which may explain the peculiar behaviour of this station.