title: Recent amplification of the North American winter temperature dipole.
abstract: During the winters of 2013-2014 and 2014-2015, anomalously warm temperatures in western North America and anomalously cool temperatures in eastern North America resulted in substantial human and environmental impacts. Motivated by the impacts of these concurrent temperature extremes and the intrinsic atmospheric linkage between weather conditions in the western and eastern United States, we investigate the occurrence of concurrent "warm-West/cool-East" surface temperature anomalies, which we call the "North American winter temperature dipole." We find that, historically, warm-West/cool-East dipole conditions have been associated with anomalous mid-tropospheric ridging over western North America and downstream troughing over eastern North America. We also find that the occurrence and severity of warm-West/cool-East events have increased significantly between 1980 and 2015, driven largely by an increase in the frequency with which high-amplitude "ridge-trough" wave patterns result in simultaneous severe temperature conditions in both the West and East. Using a large single-model ensemble of climate simulations, we show that the observed positive trend in the warm-West/cool-East events is attributable to historical anthropogenic emissions including greenhouse gases, but that the co-occurrence of extreme western warmth and eastern cold will likely decrease in the future as winter temperatures warm dramatically across the continent, thereby reducing the occurrence of severely cold conditions in the East. Although our analysis is focused on one particular region, our analysis framework is generally transferable to the physical conditions shaping different types of extreme events around the globe.
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA; Lamont-Doherty Earth Observatory Columbia University Palisades New York USA.
authors.forename: Deepti
authors.initials: D
authors.lastname: Singh
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Swain
authors.affiliation: Lamont-Doherty Earth Observatory Columbia University Palisades New York USA; NASA Goddard Institute for Space Studies New York New York USA.
authors.forename: Justin S
authors.initials: JS
authors.lastname: Mankin
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA; Department of Earth and Planetary Sciences Northwestern University Evanston Illinois USA; Woods Institute for the Environment Stanford University Stanford California USA.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Horton
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA.
authors.forename: Leif N
authors.initials: LN
authors.lastname: Thomas
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA; Department of Statistics Stanford University Stanford California USA.
authors.forename: Bala
authors.initials: B
authors.lastname: Rajaratnam
authors.affiliation: Department of Earth System Science Stanford University Stanford California USA; Woods Institute for the Environment Stanford University Stanford California USA.
authors.forename: Noah S
authors.initials: NS
authors.lastname: Diffenbaugh
keywords: atmospheric dynamics; climate change detection; climate change impacts; extreme event attribution