Simulated and projected summer rainfall in tropical Australia: links to atmospheric circulation using the CSIRO-Mk3.6 climate model

Abstract

Simulations of mean climate characteristics and atmospheric circulation patterns in the tropical region of Australia during the austral summer (December to February) are assessed by comparing against observations. An examination of the observed climatologies of mean sea level pressure, winds at lower and upper levels and rainfall with simulated climatologies show that the model captures the spatial structures of observed patterns fairly well. However, there are some discrepancies in the magnitudes between observed and modelled parameters. The model can reasonably reproduce the observed link between tropical Australian rainfall variability and the atmospheric circulation patterns. Changes in circulation patterns and rainfall are investigated for Representative Concentration Pathways (RCPs) 4.5 and 8.5. Spatial patterns of changes in circulation parameters and rainfall are very similar for both RCP 4.5 and RCP 8.5, but the magnitudes are larger for the RCP 8.5. Under anthropogenic climate change conditions, the CSIRO-Mk3.6 climate model simulates an atmospheric circulation pattern reflecting weaker monsoon conditions in the Australian region, and hence, reduced rainfall over tropical Australia. A slightly increased pressure over northwest Australia and slightly decreased pressure over north Asia is simulated. Winds at lower and upper tropospheric levels indicate opposing anomalies and reduced rainfall over a broader region that encompasses northern Australia, parts of Indonesia and around the Philippines. However, an increase in rainfall is simulated for the region east of Papua New Guinea.