Pacific Ocean, Not Ice Sheet, Shifted West Coast Storms South


New study: Ocean temperature patterns drive the West’s wintertime storm tracks

About 20,000 years ago, large ice sheets loomed over North America, and researchers thought the ice, itself, pushed storms south, drenching the Southwest and leaving the Pacific Northwest dry. Now, a new CIRES-led study finds that ocean temperatures are the real culprit behind the dramatic shift in atmospheric circulation. The work, published in Earth and Planetary Science Letters suggests that West Coast precipitation patterns are tightly linked to changes in Pacific Ocean temperatures.

“Although there is no chance that a 3-km-tall ice sheet will suddenly appear over North America, modern climate can produce similar changes in North Pacific ocean temperatures that could temporarily swap the climates of the Southwest and the Pacific Northwest,” said Dillon Amaya, a former CIRES Visiting Fellow and lead author on the paper.

Amaya, now a NOAA research scientist with the Physical Sciences Laboratory, and his colleagues used a climate model to evaluate the impact of Northern Hemisphere ice sheets on West Coast atmospheric dynamics during the Last Glacial Maximum, when today’s arid Southwest was moist and the wet Pacific Northwest was dry. This major shift in storm tracks is supported by geologic evidence and previous modeling work, but the underlying cause remained less clear.

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