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Australian climate and Australian monsoon in coupled model projections

PI: Aurel Moise
Institution: Australian Bureau of Meteorology
Additional Investigators: Rob Colman, Huqiang Zhang, Ian Watterson
Abstract:
We propose an investigation of a range of aspects of Australian climate, as projected by the models for the SRES A1B, B1 and A2 scenarios.

Initially, we will compare the annual and monthly climate of a suite of models participating in the AR4 CMIP with those of observations and reanalyses. Emphasis will be the seasonal (monthly) variation across Australia of temperature, precipitation and surface pressure, to determine how well the observed climatologies, as well as their seasonal variations are captured by the models.

A second component of the study will address the impact of climate change on temperature and precipitation in the Australian region as projected by the models. In particular, we are interested in evaluating the evolution of the Australian component of the Asian-Australian monsoon under climate change conditions. Depending upon time, other variables (e.g. cloud cover, soil moisture, winds) may also be considered, as available, in both current climate and under climate change.

Background

The Australian continent extends from the tropics to mid latitudes, and poses a particular challenge for climate models. The Australian tropics are strongly influenced by the surrounding oceans, and are subject to a strongly varying seasonal cycle of precipitation and surface pressure, dominated by the Australian component of the Asian-Australian monsoon (e.g. McBride, 1998). Total precipitation in northern Australia is strongly influenced by ENSO, showing marked interannual variability. Winter conditions in tropical Australia, on the other hand are subject to mild, and relatively dry, southeast trades.

Southern Australian regions are subject to eastward moving mid latitudes cyclones. The mean location of the cyclone belt varies seasonally from south of the continent in summer, to the southern portion of the continent in winter, with consequent seasonality of temperature and precipitation. Central parts of the continent are predominantly dry, with occasional precipitation episodes penetrating from the north and south. Other distinctive features contribute to mid continental precipitation, such as north-west cloud bands. Topography across the continent is generally low, although the eastern ranges have a significant impact on regional temperatures and precipitation.

These patterns of precipitation: monsoonal in the north, Mediterranean in the southwest, 'mid latitude' in the southeast, and dry in the centre are important features to capture in climate models. As part of the CMIP2 subproject 54, Moise et al. (manuscript in preparation) have reported a preliminary analysis of 18 CMIP2 models in their simulations of key surface climate and surface fluxes in the Australian region. Significant model deficiencies in their simulations of rainfall and surface temperature climatologies were identified.

The AR4 model comparison offers a unique opportunity to (a) examine how the latest versions of coupled models represent basic features such as pressure, temperature and precipitation in the current Australian region climate, including their seasonal and geographical variations, and (b) investigate projected climate change under standard scenarios. Time permitting, a further study of basic features of the Australian monsoon will also be considered. This is a necessary component in the ongoing efforts of projecting future climate changes in Australia using coupled climate models. The IPCC assessment of vulnerability report (Watson et al., 1998) noted particular concern for Australia for changes to the timing, intensity and location of tropical monsoon systems, and location and intensities of mid latitude weather systems and the subtropical anti cyclone belt.

Methodology

The first stage of the study will involve a comparison of annual and monthly AR4/CMIP control simulations (20th century simulation or other ‘control’ simulations) with ‘observed’ values. ‘Observational’ data sets here include the Australian Bureau of Meteorology rainfall and temperature data sets, as well as ERA-40 and NCEP reanalyses. Comparisons will be of mean fields, as well as geographical patterns and seasonal changes of surface temperature, precipitation (including monsoon precipitation) and MSLP.

The second stage involves a comparison of patterns of future climate change projected by the AR4/CMIP models for the Australian region. This will consist of comparisons of the last 20 years of the control versus the SRES experiments, as well as comparisons of the full experiment time series.

A later part of the project will consider interannual variability, in addition to the calculation of standard deviation from multi-year model integrations in measuring the interannual climate variations simulated by the models.

To further understand the role of ENSO in affecting Australian climate interannual variations, some simple statistics, such as the correlations of surface climate variables with Nino3.4 index, will be calculated from the AR4/CMIP runs.

References

McBride, J., 1998: Indonesia, Papua New Guinea and tropical Australia: the Southern Hemisphere monsoon. In 'Meteorology of the Southern Hemisphere', Karoly, DJ and Vincent, DG (Eds), AMS Monographs, vol 27 No. 49, 89-100.

Zhang, H. and A. Henderson-Sellers, P. Irannejad, S. Sharmeen, T. Phillips, and K. McGuffie, 2002: Land-surface Modelling and Climate Simulations: Results over the Australian Region from Sixteen AMIP2 Models, Bureau of Meteorology Research Centre Report, No. 89.

Watson, R.T., Zinyowera, M.C. and Moss, R.H. 1998: The Regional Impacts of Climate Change: an Assessment of Vulnerability. Cambridge University Press.


Runs to be considered: 20th century simulations
SRES A1B
SRES B1
SRES A2

Model data requested: initially monthly data for temperature, precipitation, mslp, other variables depending on availability.
Further data: daily.
Publications:

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