Global variation of COSMIC precipitable water over land: Comparisons with ground-based GPS measurements and NCEP reanalyses

Radio occultation (RO) observations of precipitable water (PW) from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) are compared with ground-based Global Positioning System (GPS) PW for 6 years (2007-2012). From comparisons of more than 120,000 collocated samples, differences in PW between RO and GPS exhibit a standard deviation of less than 3 mm with a global correlation of 0.96 to 0.97. The monthly mean RO PW is also compared to the National Centers for Environmental Prediction (NCEP) reanalyses. PWs over land for RO, GPS, and reanalyses are highly correlated in each hemisphere. We also used the RO data to explore the variation of the monthly mean PW in four regions (Tibetan Plateau, central Australia, Amazon Basin, and central Africa) where ground stations are few. This study highlights the characteristics of these PW climatologies, suggesting that the RO data are useful complements to global reanalyses and other data sets.