1. Three Western Pacific Typhoons Strengthened Fire Weather in the Recent Northwest U.S. Conflagration.
- Author
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Stuivenvolt Allen, Jacob, Simon Wang, S.‐Y., LaPlante, Matthew D., and Yoon, Jin‐Ho
- Subjects
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TYPHOONS , *FIRE weather , *WEATHER forecasting , *ATMOSPHERIC waves , *JET streams , *TROPICAL cyclones - Abstract
Strong winds that accentuated a fire outbreak in the western United States in early September of 2020 resulted from an atmospheric wave train that spanned the Pacific Ocean. Days before the atmospheric waves developed in the United States, three western Pacific tropical cyclones (typhoons) underwent an extratropical transition over Korea within an unprecedentedly short span of 12 days. Using a climate diagnostic approach and historical forecast data, it was found that the amplitude of the atmospheric waves accompanying the western U.S. fire weather would not have been so profound if not for the influence of these typhoons. Together, the recurving typhoons provided a significant source of wave activity flux directed toward North America – amplifying the ridge over the U.S. west coast while deepening the trough in central Canada. This anomalous circulation produced the severe frontal system that caused extreme winds in western Oregon, Washington and California – rapidly spreading fire. Plain Language Summary: The weather pattern that contributed to rapidly spreading fires in Oregon in early September 2020 can be traced back to an unexpected source: Three typhoons in the western Pacific that ran into the Korean Peninsula within two weeks of each other. Together, Typhoon Bavi, Typhoon Maysak, and Typhoon Haishen each contained enough energy to perturb the jet stream – creating an atmospheric wave train that enhanced the hot, dry weather of the western United States. This study uses forecast models and weather observations to show that these typhoons amplified areas of high and low pressure in North America leading to the intense winds which rapidly spread fire in Oregon, Washington, and California. While the impacts of climate change on these events were not evaluated in this study, the implication is that the effect of weather extremes that are known to be exasperated by climate warming are not always limited to the region in which those extremes occur. Key points: Three western Pacific typhoons tracked through the Korean peninsula – with sequential landfall within a two‐week period of timeThe diabatic outflow from these typhoons amplified an atmospheric wave train – increasing the pressure gradient over the western U.S.The heightened pressure gradient resulted in strong winds, a key element in the rapid spread of fires in Oregon and California [ABSTRACT FROM AUTHOR]
- Published
- 2021
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