Multi-sensors study of precipitable water vapour over mainland China

Water vapour, an important greenhouse gas in the atmosphere, is crucial for hydrological, atmospheric, and meteorological processes. This study first compared five precipitable water vapour (PWV) products from multi-sensors including radiosonde, AERosol RObotic NETwork (AERONET) sunphotometer, Global Positioning System (GPS) and MODerate resolution Imaging Spectroradiometer (MODIS), and then characterized the spatial and temporal trends of PWV in mainland China. Intercomparison results indicate good agreements among PWV products with correlation coefficients ranging from 0.775 to 0.937. As for spatial analysis, 13 years of MODIS MOD05 products were investigated and the spatial distribution of PWV is closely correlated with the topography, e.g. latitude and altitude, in mainland China. A monotonically increasing annual trend was detected in some radiosonde sites in China between 1976 and 1999, but a decreasing trend was observed between 2000 and 2012. Analysis of the differences in PWV between weekdays and weekends indicated a marked weekend effect, suggesting the influence of anthropogenic activities. Diurnal variations in PWV were also studied from 1999 to 2009 using GPS data. A pronounced diurnal cycle of PWV was observed in most of the sites during summer and spring seasons.