Indian Ocean Climate Initiative - Western Australia

Baselines and predictability of WA climate and attribution of climate change

The points under each project describe the first major deliverables that are currently being addressed and are by no means the full four-year research plan for IOCI Stage 3.

Project 1.1: Detection and Attribution of Changes to Weather Systems and Large Scale Circulation Drivers (Carsten Frederiksen, Jorgen Frederiksen and Meelis Zidikeri)

Planned outcomes:

• Identify and document observed changes in the mean climate of the SH circulation and their impacts on weather systems affecting WA in all seasons.
• Evaluate and use climate models to analyse projected future changes in the SH circulation and WA weather systems under different IPCC climate change senarios.
• Develop a methodology for attributing observed changes in the mean SH circulation using inverse modelling to identify a “fingerprint” of climate change forcing.

Figure 1.1.1: Shown in arbitrary units are the 300hPa streamfunction (left column) and the corresponding amplitude (right column) for the fastest growing Southern Hemisphere July storm track mode for 1949-68 (a, b) and 1975-94 (c, d). In the earlier period the major impact is over southwest WA; in the latter period it is in the central Pacific. The second fastest storm track mode for the latter period (not shown) has a similar structure to the fastest growing in the earlier period (a, b), but with a reduction of 33% in its growth rate.

References:
J.S. Frederiksen and C.S. Frederiksen, 2007: Inter-decadal Changes in Southern Hemisphere
Winter Storm Track Modes. Tellus, 59A, 599-617.
J.S. Frederiksen and C.S. Frederiksen, 2005: Decadal Changes in Southern Hemisphere Winter
Cyclogenesis . CSIRO Marine and Atmospheric Research Paper No. 002, 35pps.

Project 1.2: South West Western Australia’s Regional Surface Climate and Weather Systems (Pandora Hope and Catherine Ganter)

Planned outcomes:

• Analyse rainfall totals and intensities in the south west during the summer and transition seasons, and determine whether there are any trends. An update of the analysis of the winter season will be included also.
• Detail the different weather systems (identified by a new classification scheme) for all seasons.
• Report on how the frequency of these systems have changed in time.

For the network of stations across the wider south west region that have high-quality rainfall data, the full time-series of ten year averages for each month is displayed. This method of display clearly highlights the rainfall decrease in winter months in the southwest in the 1970s and again in the most recent decade. Click on each plot to see a high resolution version.

Project 1.3: Quantification of the Limits of Seasonal Predictability of WA Rainfall and Surface Temperature (Carsten Frederiksen)

Planned outcomes:

• Develop new techniques for identifying the upper limits to the predictability of WA surface temperature and rainfall in all seasons.
• Quantify the predictive characteristics of seasonal climate and report on the efficacy of developing better seasonal or dynamical seasonal forecast schemes.

Figure 1.3.1: The estimated long-range potential predictability of WA precipitation expressed as a percentage of the total inter-annual variability of the seasonal mean precipitation due to "slow" processes (e.g. sea surface temperature forcing, slowly varying internal dynamics). The higher the percentage, the more potentially predictable the precipitation.(Each season is denoted by first letter of each month).

Figure 1.3.2: The estimated long-range potential predictability of WA’s maximum surface temperature expressed as a percentage of the total inter-annual variability of the seasonal mean temperature due to "slow" processes.

Figure 1.3.3: The estimated long-range potential predictability of WA’s minimum surface temperature expressed as a percentage of the total inter-annual variability of the seasonal mean temperature due to "slow" processes.

Project 1.4: Regionally Specific Climate Data and Monitoring for the North West and South West to Support the Understanding of Past, Present and Future Climate (Karl Braganza, David Jones and Marco Marinelli)

Planned outcomes:

• Develop high-quality, high-resolution daily climate (rainfall, temperature) datasets extended back to at least 1900, which will feed into various other IOCI sub-projects, such as for downscaling of climate model projections.
• Develop a dedicated website for access to this data.