Climate Change and Weather Extremes

One month lead correlations of Global Ocean Data Assimilation System (GODAS) sea level anomalies (colour shading), NCEP-DOE reanalysis-2 surface wind anomalies (vector) with Fremantle sea level anomalies (only correlations >0.3 shown) (from Feng et al. 2013)
Global Ocean Data Assimilation System (GODAS) sea level anomalies

Due to the existence of equatorial and coastal waveguides, interannual variations of sea levels and thermocline depths along the northern and western coast of Australia are strongly influenced by climate variability in the equatorial western Pacific that are induced by El Niño Southern Oscillation and Pacific Decadal Oscillation/Inter-Decadal Pacific Oscillation.

The ENSO related upper ocean variations induce strong Leeuwin Current transports during the La Niña years, and weak Leeuwin Current transports during the El Niño years.  Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are also significantly correlated with the Indian Ocean dipole (IOD) variability, while the Southern Annular Mode (SAM) has been identified to strengthen the local cyclonic atmospheric circulation off the west coast of Australia and enhance the southward advection of the Leeuwin Current. Intra-seasonal variability in the Leeuwin Current is associated with the direct forcing of the Madden-Julian Oscillation (MJO).

During the February/March 2011 Ningaloo Nino – marine heat wave, nearshore water temperatures along the Gascoyne and mid-west coast exceeded 5°C above the long-term average for that time of year. This has been attributed to both a very strong Leeuwin Current (anomalously high coastal sea levels) during an intense La Niña period and anomalously high air-sea heat flux entering the ocean. Historical occurrences of the Ningaloo Nino events are found to be associated with La Nina in the Pacific, positive phase of the Southern Annular Mode, Australian monsoon, as well as local air-sea coupling.  

The following high-level science questions will guide the Western Australia IMOS observing strategy in this area:

  • What are the relative roles of local and remote forcing driving the seasonal, inter-annual, and decadal variability of the ocean boundary current systems off WA?
  • What drives the upper ocean heat and freshwater balance in the ocean boundary current systems?
  • What are drivers of the extreme Leeuwin Current strength and marine heat wave (Ningaloo Nino) off the coast of WA and what is the predictability of Ningaloo Nino? What is the nature of local and/or regional Indian Ocean air-sea coupling and feedback?
  • How do decadal climate variations and climate change affect the marine extreme events (e.g. Ningaloo Nino) off the coast?
  • How will the climate variability in the Indo Pacific affect coastal upwelling off the Western Australia coast, and subsequently the marine ecosystem?