Comparison between GNSS ground-based and GPS radio occultation precipitable water observations over ocean-dominated regions

Abstract

Precipitable water (PW) inferred from GPS (Global Positioning System) radio occultation (RO) and ground-based (GB) Global Navigation Satellite System (GNSS) observations are compared between years 2007 and 2014. As previous studies were mainly performed over continental areas we now focus over oceandominated geographical areas. Our analysis is done in order to find out how the reliability level of RO results over oceanic areas compares to land. As RO soundings usually miss some information close to the ground, we also assess different methods to complete the lacking data. We found 47 terrestrial stations that lie in islands small and far away from continental areas where the weather might be governed by the sea conditions. From comparisons of almost 5000 collocated samples, PW from RO and GB exhibit a global mean difference around 1 mm, root-mean-square deviation about 5 mm and a correlation above 0.9. The 2007-2014 timeseries and the monthly mean RO and GB PW were also I Manuscript prepared under grants CONICET PIP 11220120100034 and ANPCYT PICT 2013-1097. P. Alexander, A. de la Torre, R. Hierro and P. Llamedo are members of CONICET. GPS RO water vapor pressure observations were downloaded from cdaac-ftp.cosmic.ucar.edu, GB GNSS PW data from rda.ucar.edu/datasets/ds721.1 and NCEP and ECMWF reanalyses respectively from www.esrl.noaa.gov/psd/data/gridded and apps.ecmwf.int/datasets.