A comparison of precipitable water values from GNSS ground-based, GPS radio occultation and reanalysis above oceanic regions

BURGOS FONSECA, Y.; ALEXANDER, P.; DE LA TORRE, A.; HIERRO, R.; LLAMEDO, P.; CALORI, A.; SCHMIDT, T.

Kyoto

Congreso; SPARC; 2018

Precipitable water (PW)inferred from GPS (Global Positioning System) radio occultation (RO) andground-based (GB) Global Navigation Satellite System (GNSS) retrievals arecompared for years 2007-2014. Previous studies were mainly performed over continentalareas, so we now focus over ocean-dominated geographical zones. As RO soundingsusually are not able to obtain observations at the lowest heights above theground, we also assess different methods to complete the lacking data. We found47 terrestrial stations that lie in islands small and far away from continentalareas where the weather might be governed by the sea conditions. Fromcomparisons of almost 5000 collocated samples, PW from RO and GB exhibit aglobal mean difference around 1 mm, root-mean-square deviation about 5 mm and acorrelation above 0.9. The 2007-2014 timeseries and the monthly mean RO and GBPW were also compared to reanalyses per hemisphere, latitude regions andoceans. In each zone it was found that PW from RO, GB and reanalyses allexhibit in general consistent seasonal qualitative behavior. However,quantitative differences exist between reanalyses on one side and RO and GB onthe other side. It is shown that PW from reanalyses lacks reliability in areaswhere the island topography is poorly represented by them. This problem may beclearly extended to continental areas. In addition, we find that RO and GB seemto be more sensitive than reanalyses for the detection of features that departfrom the regular annual cycle.