Variability of GNSS PWV in global tropics over different time scales

The variability of water vapour in the global tropics has impacts on global circulation patterns through atmospheric teleconnections. Various timescales of its fluctuations strongly affect weather, including interannual to daily changes. Although traditional techniques of water vapour measurements have always been vital in understanding complex thermodynamic processes, they still face some limitations related to e.g. temporal sampling, non-automatic data collection, or cost efficiency. In light of this, global navigation satellite systems (GNSS) can state for a valuable source of precipitable water vapour (PWV) data. Taking advantage of a long time series of collected by International GNSS Service (IGS) observations, we performed an analysis of the variability of 18-year GNSS PWV over the tropics, from interannual to daily time scales. Results have proved, that the GNSS technique is capable of capturing long-term changes in PWV resulting from climate modes, such as El Nino Southern Oscillations or Indian Ocean Dipole. Additionally, analysis of diurnal GNSS variability, together with satellite-based precipitation and cloudiness data, taken from the Tropical Rainfall Measurement Mission gridded dataset (TRMM 3B42 v7) and the global, merged infrared (IR) dataset, have enabled reliable estimation of changes that are in line with various regimes of tropical deep convection.  In particular, our results show that the diurnal cycle of PWV and TB were almost entirely dominated by mono-modal distributions. The diurnal cycle of precipitation onshore (continental areas or big islands; continental regime) had a single late afternoon peak, and that offshore (small islands; oceanic regime) had both a midday and a nocturnal peak. The daily amplitude phase shift of PWV and precipitation at onshore stations with a continental regime consistently occurred at the same time, while TB maximum peaked about five hours later. Furthermore, results show that the daily mean and the amplitude of the diurnal cycle of PWV, precipitation, and TB appeared smaller on offshore stations, exhibited to an oceanic regime, than on onshore, continental stations.