Diagnosing Australia-Asian monsoon onset/retreat using large-scale wind and moisture indices |
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| Authors: | Huqiang Zhang |
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| Institution: | (1) Centre for Australian Weather and Climate Research, A partnership between Australian Bureau of Meteorology and CSIRO, GPO Box 1289K, Melbourne, VIC, 3001, Australia |
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| Abstract: | Using large-scale variables, in this study we have developed a method for defining monsoon onset/retreat in the Australia-Asian
region and used this method to study monsoon activities simulated by global climate models. For this purpose, the method needs
to capture fundamental characteristics of monsoon rainfall and circulation seasonal variations and at the same time it can
be reasonably simulated by current climate models. We develop the method by using both atmospheric precipitable water and
wind conditions in our definition and compared our results using 44-year ERA-40 reanalysis data with some published results
in the region. Our results offer similar features to several observational studies, including features in Australia-Asian
summer monsoon temporal and spatial evolutions and their interannual variations. Results further show that the observed significant
increase in summer rainfall in northwest Australia corresponds to earlier onset and much longer duration of its summer monsoon,
with its duration significantly increased. Prolonged summer monsoon duration is also seen in central-east China where upward
rainfall trend is observed. Furthermore, the Australian summer monsoon appears to be more affected by ENSO than the Asian
monsoon, with delayed onsets and shortened durations during El Nino years. Finally, by analyzing results from an IPCC AR4
model, we have shown that using the two large-scale variables simulated by climate models, it is possible to conduct some
detailed studies on monsoon activities in current and future climate. Results from this particular model suggest that global
warming could potentially modify some of the monsoon characteristics, including earlier onset in most of the region but different
features for changes in duration. In the Australian region, it also displays further southward penetration of its summer monsoon. |
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