Sensing of diurnal and semi-diurnal variability in the water vapour content in the tropics using GPS measurements

Abstract

The diurnal and semi-diurnal variability of the integrated precipitable water vapour (IPWV) was studied by using Global Positioning System (GPS) data (1998-2004) from 14 International GNSS Service (IGS) stations located between latitudes 20°S and 20°N, and longitudes 70°-170°E. The phases and amplitudes of the EPWV are compared to the corresponding estimates from two numerical weather models (NWMs). Results reveal that there are diurnal amplitudes of more than 0.4 mm for most sites, except sites on small islands in the ocean. The maximum diurnal amplitude is 3 mm at Bakosurtanal, Indonesia. The estimated semi-diurnal signals are in general small. The maximum of the IPWV typically occurs between 1200 and 2400 local solar time. The results suggest that GPS data are useful for high-temporal-resolution studies of IPWV. The accuracy of the estimated diurnal amplitudes is limited by the use of a simple model for the mean temperature of the wet refractivity, and the accuracy of the estimated semi-diurnal amplitudes is likely to be improved by a higher temporal resolution of the ground pressure data at the GPS sites. Copyright © 2007 Royal Meteorological Society.