The Relationship Between Monsoon Onset and Synoptic Scale Features of the Australian Monsoon

Abstract:

The Australian branch of the Australian-Asian monsoon is an important feature of the Australian climate, however the ability to predict the onset and other important aspects of the Australian monsoon remains elusive. In this study the synoptic scale conditions prior to, and directly after monsoon onset are investigated. 

Differences between early and late onset years are shown using a composite analysis of key variables from reanalysis (ERA Interim). In particular the thermal structure and land-sea contrast prior to onset is investigated, with an emphasis on the behaviour throughout the troposphere rather than simply at the surface. The inter-annual variability of the Australian monsoon is investigated by considering the empirical modes of variability (EOFs) at different stages of monsoon development, as well as some important monsoon relationships, such as onset date with seasonal precipitation, temperature anomalies, Madden-Julian oscillation phase and El-Nino Southern Oscillation (Nino 3.4 Index).

Continental heat lows contribute to land-sea thermal contrast and are thought to be important in the dynamics of the pre-monsoon phase. A recently created climatology of Australian thermal lows is used to investigate the relationship between heat lows and monsoon behaviour. The congruity of the simulation of important monsoon features such as continental heat lows and land-sea contrast can be used to evaluate coupled models (e.g. CMIP5) in order to decrease uncertainty in projections of the Australian-Asian monsoon.