Application of satellite altimetry for studying the water vapour variability over the tropical Indian Ocean

Satellite altimetry was originally intended for oceanographic and geodetic applications. An uncommon application of satellite altimetry data, demonstrated in this paper, is for atmospheric study by utilising the onboard microwave radiometer. The Wet Tropospheric Correction (WTC) data from the Topex/Jason altimetry mission series (Topex/Poseidon, Jason-1, Jason-2/OSTM and Jason-3) are used, which have spanned nearly 30 years, making them sufficient for climate study. Precipitable Water Vapour (PWV) is derived from the WTC and used to study the atmospheric water vapour variability over the tropical Indian Ocean (TIO). Preliminary analysis is performed by comparing the generated PWV data with the PWV from a dedicated meteorological satellite Aqua, which was found to be comparable with a correlation coefficient of 0.94 for the monthly mean data and 0.74 for the anomaly component. Using standard empirical orthogonal function and composite analysis, the interannual variability of the tropospheric water vapour in TIO is thoroughly analysed. The mechanics and impacts of the two leading modes, the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are characterised. Furthermore, the modulation of the atmospheric circulation cell can be monitored. A distinct characteristic is found for the spurious IOD event in 2017 and 2018, which is the forming of a PWV anomaly meridional gradient in the Indian Ocean during June due to the activity of the Southern Indian Ocean Dipole mode. This showcases the potential of using altimetry satellite data for atmospheric study and opens up the possibility of further utilisation.