Saturday, December 29, 2018

Reliable Tropical Weather Pattern to Change in a Warming Climate

The Madden-Julian Oscillation's precipitation variations are likely to increase in intensity under a warmer climate, while wind variations are likely to increase at a slower rate

Every month or two, a massive pulse of clouds, rainfall and wind moves eastward around the Earth near the equator, providing the tropics their famous thunderstorms.

This band of recurring weather, first described by scientists in 1971, is called the Madden-Julian Oscillation. It has profound effects on weather in distant places, including the United States. Atmospheric scientists have long studied how the Madden-Julian Oscillation modulates extreme weather events across the globe, from hurricanes to floods to droughts.

Current climate is represented in (a), and a warmer climate in (b). As the climate warms, the mean vertical gradient in water vapor (blue) increases. Tropospheric temperature (orange shading) will also increase more than the lower atmosphere.

Credit: Eric Maloney/Colorado State University

As human activities cause the Earth's temperature to increase, reliable, well-studied weather patterns like the Madden-Julian Oscillation will change too, say researchers at Colorado State University.

Eric Maloney, professor in the Department of Atmospheric Science, has led a new study published in Nature Climate Change that attributes future changes in the behavior of the Madden-Julian Oscillation to anthropogenic global warming. Maloney and co-authors used data from six existing climate models to synthesize current views of such changes projected for the years 2080-2100.

Their analysis reveals that while the Madden-Julian Oscillation's precipitation variations are likely to increase in intensity under a warmer climate, wind variations are likely to increase at a slower rate, or even decrease. That's in contrast to the conventional wisdom of a warming climate producing a more intense Madden-Julian Oscillation, and thus an across-the-board increase in extreme weather.

"In just looking at precipitation changes, the Madden-Julian Oscillation is supposed to increase in strength in a future climate," Maloney said. "But one of the interesting things from our study is that we don't think this can be generalized to wind as well."

Atmospheric science relies on weather patterns like the Madden-Julian Oscillation to inform weather prediction in other areas of Earth. For example, atmospheric rivers, which are plumes of high atmospheric water vapor that can cause severe flooding on the U.S. west coast, are strongly modulated by certain phases of the Madden-Julian Oscillation.

According to Maloney's work, the Madden-Julian Oscillation's impact on remote areas may gradually decrease. Degradation in the oscillation's wind signal may thus diminish meteorologists' ability to predict extreme weather events. In particular, preferential warming of the upper troposphere in a future, warmer climate is expected to reduce the strength of the Madden-Julian Oscillation circulation.

Maloney and colleagues hope to continue studying the Madden-Julian Oscillation using a broader set of climate models to be used in the next Intergovernmental Panel on Climate Change assessment.

Contacts and sources:
Anne Manning
Colorado State University

Citation:  Madden–Julian oscillation changes under anthropogenic warming Eric D. Maloney, Ángel F. Adames & Hien X. Bui Nature Climate Change volume 9, pages 26–33 (2019)

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