Teleconnections Concept Map

Concept map describing the key climate drivers and teleconnections to southern Australian rainfall.

Project summary

Individual rainfall events are generally associated with the local impacts of particular synoptic weather systems. Seasonal timescale drivers such as ENSO, IOD and SAM alter the seasonal behaviour of these individual weather events to cause wetter or drier seasons. The drivers are mostly tropical (ENSO and IOD) or high-latitude (SAM) phenomena remote from the continent, whereas rainfall in SE Australia is related to local mid-latitude weather systems. Therefore the teleconnection between the mid-latitude weather systems and the remote drivers is of prime importance.

Recent research has highlighted the importance of a synoptic weather system known as a cutoff low in providing about half the total rainfall in SE Australia, and nearly all of the effective high rainfall events. It is known that climate models are capable of simulating cutoff lows, but so far they account for a much smaller proportion of the model rainfall than is observed. This appears to be related to the inability of models to accurately represent atmospheric blocking, which is observed to be an important factor in the development of cutoff lows and their subsequent slow eastwards movement. The relatively slow movement of these systems appears to partially explain how they can produce substantial rain in SE Australia.

It is not known how ENSO and the other remote drivers influence the atmospheric long waves, cutoff lows or blocking. It may be through changes in the meridional circulation (Hadley cell), or it may be through changes to the moisture inflow which is so important for trigger mechanisms such as cutoff lows to be able to produce rainfall. There is also some evidence to suggest that blocking in the Australian region may be linked to blocking in other regions of the hemisphere such as the South American region where ENSO is a known influence.

Project objectives

• Diagnose and, to the extent possible, explain the dynamical and physical processes underlying how the long timescale tropical (ENSO and IOD) and high-latitude (SAM) drivers alter the behaviour of mid-latitude rain-bearing weather systems.
• Diagnose these mechanisms in POAMA and compare to observed mechanisms.
• Identify aspects of model performance that need improvement in order to represent better the key teleconnections.