Climate Variability and Weather Extremes
One of the key research areas of the Q-IMOS Node is investigating the modes of climate variability and extreme weather events impacting Queensland’s coastal and marine ecosystems.
Interannual climate variability over the Pacific is dominated by the El Niño–Southern Oscillation (ENSO) cycle, which is a quasi-periodic climate pattern across the tropical Pacific Ocean. The extreme states of this coupled atmosphere-ocean system are when the warm pool in the ocean and the major uplifting convection cell in the atmosphere are in the western Pacific (known as La Niña) and the opposite condition when both have moved to their extreme position in the central Pacific (know as El Niño). El Niño episodes are characterised in the eastern Pacific by warmer surface waters that depress the thermocline shutting off the coastal upwelling that normally supports productive scale fisheries in the Americas. La Niña episodes represent the opposite state, where the thermocline in the western Pacific is depressed at the same time as it rises to the surface in the eastern Pacific. This cycle has strong and opposite influences on a range of variables (temperature, rainfall, wind, storminess, upwelling etc.) on both sides of the oceanic basin so that ENSO is a major source of climate variation impacting on ecosystems and economies.
Differences in the strength of the summer monsoon circulation over northern Australia correlated with ENSO cycles also result in marked differences in the occurrence of tropical cyclones along the Great Barrier Reef. While the immediate impacts of tropical cyclones (destructive winds and waves, storm surges) are typically sustained in northern Queensland, their effects can be felt as far away as southern Queensland (e.g. the 1974 Brisbane flood caused by Tropical Cyclone Wanda that came from the Coral Sea during a strong La Nina). Observations of sea surface height gained by satellite altimetry have shown that slow moving tropical cyclones can impart substantial momentum to the upper water column. There are suggestions there is the potential for at least some cyclonic episodes to have a lasting influence on mixing processes in the upper water column well beyond the life of the event that created them.
Most of the physical phenomena to be captured by an Integrated Ocean Observing System have annual cycles, which are driven ultimately by the seasonal patterns of global surface heating due to the earth’s orbit. For example, in the Coral Sea, the bifurcation of the South Equatorial Current at the surface moves south during the season of south-east trade winds (April-November). During the summer monsoon, southerly flows contributing to the East Australian Current (EAC) start near 15°S.
In the winter, the coastal bifurcation is found nearer to 18°S. Given the implied influence of the wind fields, this displacement is likely to vary among years.
Key Science Questions
El Nino-Southern Oscillation
- Does the bifurcation of the South Equatorial Current in the Coral Sea change between ENSO extremes?
- Do any attributes of the EAC in Queensland change with the sign of the Southern Oscillation Index?
- Do any attributes of the North Queensland Current change with the sign of the Southern Oscillation Index?
- Do longshore currents in the Great Barrier Reef Lagoon contain an ENSO signal?
Intra-seasonal variability and severe weather
- How does interannual variability in the Coral Sea influence the risks from tropical cyclones?
- How does interannual variability in the Coral Sea influence the risks from east coast lows in South East Queensland?