Winter severity in the Great Lakes region: a tale of two oscillations

Abstract

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 24:19-31 (2003) - doi:10.3354/cr024019 Winter severity in the Great Lakes region: a tale of two oscillations Sergei Rodionov1, Raymond A. Assel2,* 1Department of Computer Science, Campus Box 430, University of Colorado, Boulder, Colorado 80309-0430, USA 2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan 48105-2945, USA *Corresponding author. Email: assel@glerl.noaa.gov ABSTRACT: The effects of Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO) on Laurentian Great Lakes regional winter air temperature and, more generally, surface-air temperatures (SAT) over North America are examined. The relationship between ENSO and winter severity in the Great Lakes is highly nonlinear and depends on the strength of El Niño events. Significant positive correlation between the winter severity and ENSO indices noted in earlier works is limited to strong El Niño events and is associated with an expansion of positive temperature anomalies in NW North America inland toward the Great Lakes. Although both ENSO and PDO are positively correlated with the Pacific-North American (PNA) teleconnection index, a closer look at the large-scale atmospheric circulation associated with the 2 oscillations reveals a substantial difference. During warm PDO phases (not coincident with strong El Niño events), atmospheric circulation resembles the classical PNA pattern, with a strong Aleutian Low at the surface and amplified ridges and troughs in the mid-troposphere. During strong El Niño events the Aleutian Low is also stronger than normal, but shifted eastward, to the Gulf of Alaska. Over North America, an upper atmospheric ridge on the west is not accompanied with a deep trough on the east as in the classical PNA pattern. As a result, outbreaks of cold Arctic air over the eastern US are rare and winters in the Great Lakes region are abnormally mild. KEY WORDS: Great Lakes · Pacific Decadal Oscillation · El Niño-Southern Oscillation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 24, No. 1. Online publication date: June 10, 2003 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2003 Inter-Research.