THE CLIMATE KELPIE BLOG: Pacific Ocean temperatures and its effect on Australian climate

Posted by BCG on 7th April 2017

The Pacific Ocean plays a major role in the climatic conditions of Australia, especially for eastern Australia.

The El Niño Southern Oscillation (ENSO) is the key climate driver present in the Pacific Ocean, and has three key phases: neutral, El Niño and La Niña.

For many, the term El Niño has become strongly linked with drought because with El Niño there is an increased probability of drier and hotter conditions for many parts of eastern Australia.

The same can be said for La Niña. While the probability of cooler and wetter conditions in La Niña are higher.

At both ends of the extreme weather patterns (El Niño and La Niña) there is also a likelihood of damaging conditions resulting from dangerous storm conditions.

During a La Niña phase, warmer sea temperatures will be found in northern Australia, while cooler temperatures are found off western South America.

Figure 1. Sea surface temperature anomaly in a La Niña year, snap shot taken October 18, 2010.

While in an El Niño year the opposite is observed. Cooler temperatures are found over Northern Australia, while warmer temperatures can be found off the coast of western South America.

Figure 2. Sea surface temperature anomaly in an El Niño year, snap shot taken September 16, 2006.

There are two distinct regions of the Pacific ocean that we look at to investigate trends. The Nino 3 and Nino 3.4 are sections of the ocean along the equator that are monitored for changes in temperature. The threshold for El Niño in this area is +0.8 degrees, with current temperatures in Nino 3 being +0.7, but this is only one area to look at as temperature at depth is also important.

Figure 4. Sea surface temperature anomaly from March 30, 2017.

Measurements of ocean temperature is not only taken at the surface, but in most cases right down to the sea floor. This provides the opportunity to track the movement of ocean temperatures through the profile of the ocean.

Figure 3 demonstrates the change in ocean temperature at depth over a four-month period (December 2016 to March 2017).

As you can see the cooler (blue) water on the right side of the graph (representing ocean of the west coast of South America) gradually decreased in size over time. While warm water on the left side of the graph (representing ocean off Northern Australia) has increased and begun to displace the cool water and move east towards South America.

Figure 4. Pacific Ocean anomaly from December 2016 to March 2017.

For this movement of warm water to turn into an El Niño like pattern the trade winds would need to reverse and head in an east-west direction.

The following video demonstrates how the movement of cool and warm waters occurs showing the formation and reduction in the 2015 El Niño.

The Fast Break newsletter is produced by Agriculture Victoria and highlights what a set of models are indicating for the coming season. While models are currently sitting in the predictability barrier that occurs early in the year, there is some indication that the season may be dry and warm.

To sign up for The Fast Break newsletter visit the Agriculture Victoria website.

For further information about ENSO visit the Bureau of Meteorology ENSO wrap.

Through the Rural Industries and Research Development Corporation (RIRDC) funded ‘Improved use of seasonal forecasting to increase farmer profitability’ project, BCG is funded to facilitate a seasonal climate community of practice and extend learnings. The ‘community’ includes scientists, extension specialists, advisors and farmers from different agricultural sectors aiming to improve access to, and understanding of, forecasting information.  For a farmer, this will lead to better application of the forecasting information and improved decision-making at the seasonal scale.