The impact of tropical precipitation on summertime euro-Atlantic circulation via a circumglobal wave train

Christopher H. O'Reilly, Tim Woollings, Laure Zanna, Antje Weisheimer

Research output: Contribution to journalArticle

Abstract

The influence of tropical precipitation variability on summertime seasonal circulation anomalies in the Euro-Atlantic sector is investigated. The dominant mode of the maximum covariance analysis (MCA) between the Euro-Atlantic circulation and tropical precipitation reveals a cyclonic anomaly over the extratropical North Atlantic, contributing to anomalously wet conditions over western Europe and dry conditions over eastern Europe and Scandinavia (in the positive phase). The related mode of tropical precipitation variability is associated with tropical Pacific SST anomalies and is closely linked to the El Niño-Southern Oscillation (ENSO). The second MCA mode consists of weaker tropical precipitation anomalies but with a stronger extratropical signal that reflects internal atmospheric variability. The teleconnection mechanism is tested in barotropic model simulations, which indicate that the observed link between the dominant mode of tropical precipitation and the Euro-Atlantic circulation anomalies is largely consistent with linear Rossby wave dynamics. The barotropic model response consists of a circumglobal wave train in the extratropics that is primarily forced by divergence anomalies in the eastern tropical Pacific. Both the eastward and westward group propagation of the Rossby waves are found to be important in determining the circulation response over the Euro-Atlantic sector. The mechanism was also analyzed in an operational seasonal forecasting system, ECMWF's System 4. While System 4 is well able to reproduce and skillfully forecast the tropical precipitation, the extratropical circulation response is absent over the Euro-Atlantic region, which is likely related to biases in the Asian jet stream.

Original languageEnglish (US)
Pages (from-to)6481-6504
Number of pages24
JournalJournal of Climate
Volume31
Issue number16
DOIs
StatePublished - Aug 1 2018

Keywords

  • Atmosphere-ocean interaction
  • Atmospheric circulation
  • Diabatic heating
  • Rainfall
  • Rossby waves
  • Teleconnections

ASJC Scopus subject areas

  • Atmospheric Science

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