Climate Change and Weather Extremes

Low-pass filtered (a) sea surface temperature off coastal eastern Tasmania, (b) surface salinity off coastal eastern Tasmania, (c) South Pacific regional mean wind stress curl (20–50S, 180–280E), (d) net transport through the Tasman Sea, calculated using the Island Rule [Godfrey, 1989]. Black dashed lines show the linear trend. Green dashed lines illustrate the time lag between the Maria Island time series and South Pacific winds/Tasman Sea transports [from Hill et al, 2008].
Low-pass filtered ocean variables

Three major coupled ocean-atmosphere modes account for a significant portion of Australian seasonal climate variability - El Niño/Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), with centres of action in the equatorial Pacific, equatorial Indian, and Southern Oceans, respectively.

ENSO is the globally dominant mode with strong impacts on Australia. The IOD was documented as a coupled climate mode more than a decade ago and its impacts on Australia are beginning to be recognised. The SAM has been identified largely in atmospheric observations; however a possible role for oceanic circulation in the South Pacific and Indian Oceans, in particular in the Tasman Sea, has been suggested by climate models.

It also impacts the large scale circulation and eddy properties of the Southern Ocean. While the previous three modes are drivers of seasonal climate variability, at intra-seasonal timescales the Madden Julian Oscillation (MJO) is the most prominent mode. The MJO is a key phenomenon for both weather and climate forecasting science, and it spans and links the areas in the Indian and Pacific Oceans that have greatest impact on Australian climate.

It is a propagating coupled convective disturbance that migrates from the central western tropical Indian Ocean eastwards across the maritime continent and out to near the dateline in the Pacific Ocean and it is suggested to play a role in the initiation and evolution of ENSO and IOD events, modulation of the Indonesian Throughflow, and partly accounts for the dry break events within the monsoons. 

The following high-level science questions will guide the Bluewater and Climate IMOS observing strategy in this area:

Interannual

  • How does exchange of heat, moisture and momentum between the atmosphere and the ocean surface layer affect modes of climate variability?
  • Can we improve dynamical understanding of ENSO (e.g. subtropical-tropical interaction through oceanic pathways, heat transport by tropical instability waves, dynamics of the different flavours of ENSO) and use this understanding to improve seasonal forecasts and projections of ENSO in a future climate?
  • Can we improve dynamical understanding of IOD, including the possibility of coupling between IOD and ENSO?  

Intraseasonal

  • How does the Madden Julian Oscillation (MJO) interact with other climate processes, such as ENSO, IOD and the Australian monsoon?
  • What role does air-sea interaction play in the dynamics of the MJO?
  • How is the development of weather events like tropical cyclones and East Coast Lows influenced by ocean variability such as sea surface temperature?