Research sheds new light on understanding Pacific Trade Winds

Named for their ability to help sailors with trade in the 14th century, the ‘Pacific Trade Winds’, had a profound influence on political geography with captains using them to cross the world’s oceans.

However, in the late 1990s scientists observed an unprecedented strengthening of these trade winds during the observational record, which was subsequently related to the early 21st century slowdown in global surface warming, extreme sea level rise in the western tropical Pacific, and a range other substantial impacts.

While their models have been able to shed light on the timing of these recent trade wind changes, they have been unable to reproduce the magnitude.

Now a new international study, led by a Monash climate scientist, and published in the prestigious journal Nature Climate Change has for the first time been able to identify a deficiency thought to underpin this model underrepresentation of Pacific Trade Wind trends. This study was a collaboration between scientists from Australia, the US and the UK and the new finding was achieved with the help of a large number of numerical model simulations.

“Numerical models are known to have biases in their representation of the long term average climate, these same models are also known to have biases in their representation of variability, which includes the underrepresentation of decadal variability in the Pacific Ocean,” said lead study author Dr Shayne McGregor, from the Monash School of Earth, Atmosphere and Environment.

“However, these two issues have often been treated separately as there was little evidence linking the two until now,” he said.

“Our results identify biases in the representation of the model long term average appear to play a prominent role in the under representation of this recent Pacific Ocean trade wind strengthening.”

Since all of the ocean basins are connected by the atmosphere and ocean, it is not just the mean state in the Pacific Ocean that is important, according to Dr McGregor.

“Our results highlight the prominent role of the Atlantic Ocean mean state in the underrepresentation of the recent Pacific trade wind strengthening, but it would be naive to think that biases in the Indian and Pacific Ocean regions would not also have an impact,” he said.

There are two major implications of this research.

“The first is that it appears that fixing the model mean state biases should go a long way to also fixing the model representation of variability,” Dr McGregor said.

“Secondly, we now know the experimental conditions needed to examine the impact of our results on the variability of models and this can be achieved prior to fixing the mean state bias.”

The study involved Australian researchers from Monash University, the University of New South Wales, both of which are part of the ARC Centre of Excellence for Climate System Science. The study also involved international researchers from the University of Washington, Seattle, WA, USA, and the University of Exeter, Exeter, UK.

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