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Climatology and ENSO-related variability of North American extratropical cyclone activity

TitleClimatology and ENSO-related variability of North American extratropical cyclone activity
Publication TypeManual Entry
Year of Publication2006
AuthorsEichler, T., and W. Higgins
Journal of Climate
Volume19
Pagination2076-2093
Abstract

The climatology and interannual variability of North American extratropical cyclones are examined using 6-hourly sea level pressure data from the NCEP-NCAR reanalysis for the period 1950-2002 and ECMWF 40-yr Re-Analysis (ERA-40) data from 1971 to 2000. The climatology includes an evaluation of the seasonal frequency and intensity of storms as well as an analysis of extreme event intensity. ENSO variability is evaluated by ENSO phase with emphasis on boreal winter. Results show an enhanced East Coast storm track during El Nino as well as an equatorward shift in storm tracks in the North Pacific for storms generated from both the NCEP-NCAR reanalysis and ERA-40 datasets. Observed precipitation close to a storm's center is used to determine which phase of the ENSO cycle is associated with the most productive storms and where they occur. During El Nino winters, a precipitation maximum is located east of the Appalachians and is associated with an enhanced East Coast storm track. During La Nina winters, the precipitation maximum shifts to the Ohio Valley and is associated with an enhanced Great Lakes storm track. Along the U.S. west coast, there is a precipitation maximum in the Pacific Northwest during La Nina winters, which is due to a storm track west of Washington State.

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Study Findings:

  • Frequeny maxima of storm tracks during winter (JFM) occur in the Great Lakes
  • these storms originate from Alberta clippers or from lee Rocky cyclogenesis
  • as La Nina strength increases, the frequency of GL storms becomes more pronounced.
  • there is a negative correlation between GL storm-track frequency and El Nino
  • "the Great Lakes storm track remains a major contributor to the precipitation during weak/moerate La Nina events although the precipitation is less for strong La Nina events likely due to the poleward shift of the jet stream."

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