The south east Australia region is influenced by the multiple drivers with all three; El Niño/Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Southern Annular Mode (SAM) affecting rainfalls in autumn, winter and spring, although their influence varies on decadal scales. In the south east Australian oceans, evidence shows ENSO affecting the Tasman Seas where there are significant signals in the subtropical gyre and south Tasman Sea and with subtropical mode water formation enhanced in the region during El Niño.
Recently, research on the influence of IOD and ENSO on the southeast Australian rainfall showed that the influence of ENSO is restricted to the subtropics during winter and spring, and that a positive IOD plays a major role in the droughts in the south eastern Australia, with El Niño playing a lesser role. However, the interaction between ENSO and the IOD is complex, with strongest rainfall anomalies observed in years where both drivers co-occur. In addition, the pattern of IOD influence in rainfall variability across southern Australia is significantly correlated to all drivers (i.e. IOD, ENSO and SAM) in most seasons, with high variance explained by IOD and ENSO in southeaster Australia in spring and SAM in western Tasmania in the same season.
The following high-level science questions will guide the Southeast Australia IMOS observing strategy in this area:
- How do ENSO, IOD and SAM affect circulation in south east Australia? What role do they play in upwelling/downwelling events in shelf currents?
- How do long-term changes in these modes of variability affect the boundary currents important to the region?
- How do severe winter storm events effect nearshore, intertidal and beach topography, wave dynamics, storm surge and coastal inundation?