Regional Precipitation Variability Associated with Zonal Movement of Indian Ocean High Pressure System

Abstract

Several studies have linked ongoing austral winter drying conditions in southwest Western Australia (SWWA) to changes in regional and large scale sea level pressure. As the region bounded by SWWA occupies limited observation of a typical global climate model (GCM), it is not easy to infer the influence of global climate change during the drought in SWWA. In this study, we explore the relationships between early winter (May-Aug) rainfall in Kent river catchment (KRC), Southwestern Australia and Indian Ocean High Pressure system. We construct two objective indices of Indian Ocean High Pressure system (IOHPS), viz., (i) the intensity of Indian Ocean High Pressure (IOHP) and, (ii) the Indian Ocean High Longitude (IOHLN) using National Center of Environmental Prediction mean sea-level pressure (MSLP) reanalysis data. The station data of seasonal rainfall is obtained from Australian Bureau of Meteorology. A representative rainfall index for the KRC was built by averaging the seasonal rainfall three major stations for the period of 1951–2016. Significant inverse relationship is found between early wintertime precipitation in KRC, Southwestern Australia and the IOHP and IOHLN. The IOHPS accounts for more of the early winter (May–August) precipitation variation in KRC than the Southern Oscillation Index (SOI), Southern Annular mode (SAM) and Indian Ocean Dipole (IOD). Our significant findings suggest that strengthening of IOHP and zonal movement of IOHPS has a major contribution in decline of early winter precipitation in KRC.