Prof. Daehyun Kim’s research on Madden-Julian Oscillation (MJO)

Consider this: the U.S. West Coast has seen a decrease in rainfall between 1981-2018. UW scientists think a phenomenon called the Madden-Julian Oscillation (MJO) might be to blame. A stormy disturbance that occurs several times a year in the tropics, the MJO is similar to the El Nino Southern Oscillation, which is notorious for generating extreme winter weather in the Pacific Northwest. Both are closely tied to changes in sea surface temperatures. But while El Nino always remains off the West Coast of South America, the MJO actually moves from the Indian Ocean and across the Pacific.

Daehyun Kim, an atmospheric scientist focused on tropical weather patterns, contributed to recent research which suggests that trends in decreased rainfall here in the Pacific Northwest may be linked to warming in the Western Pacific Ocean, near Indonesia. The warming ocean affects weather patterns, increasing rainfall in the Amazon, southwest Africa and northern Australia, and reducing it in parts of Asia and Western North America.

As it travels over the tropics, the MJO affects local weather but it also impacts weather patterns thousands of miles away by changing the atmospheric currents moving around the earth. “The change in the West Coast precipitation is consistent with what we’d expect from the changes in the MJO life cycle,” said Kim. Washington, Oregon and California have less rainfall because the ocean on the other side of the globe is warming.

Researchers have drawn a link between changes in the MJO life cycle and weather events around the planet. The 2013-2014 California droughts, the 2011 east Africa drought, and major southeast Asia flooding in 2011 all occurred in years when this phenomenon spent more days than usual over Indonesia and the West Pacific. “As the climate warms, the temperature of the seawater [in the West Pacific] increases and that affects the life cycle of the MJO” said Kim. The disturbance spends less time over the Indian Ocean and more time over Indonesia and the West Pacific. This, in turn, corresponds to the decrease in rainfall that we’ve experienced over the past several decades in the Pacific Northwest.

Kim continues to research how the MJO forms and the conditions that change its formation. “There is some relationship between larger-scale circulation and the MJO. I am trying to understand which aspects of the average climate modulate the speed, size and formation of the MJO.”

How will continued warming in the West Pacific Ocean impact drought-prone areas of the U.S. West Coast? What could this mean for areas susceptible to wildfires? While we may not fully understand the details of these interactions, we do know that we can expect ongoing change to tropical disturbances, according to Kim. “We know for sure that the climate is warming and as the climate warms, the nature of the oscillation changes.”

From UW College of the Environment

Read more at Nature