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Climate Dynamics

, Volume 23, Issue 1, pp 17–28 | Cite as

Climate impact of the European winter blocking episodes from the NCEP/NCAR Reanalyses

  • R. M. Trigo
  • I. F. Trigo
  • C. C. DaCamara
  • T. J. Osborn
Article

Abstract

A comprehensive multivariable characterisation of the climatic impacts of winter blocking and strong zonal-flow (non-blocking) episodes over the Euro-Atlantic sector is presented here, using a 40-year (1958–97) consistent dataset from NCEP/NCAR. Anomaly fields of surface or low troposphere climate variables are then interpreted based on large-scale physical mechanisms, namely, the anomalous mean flow (characterised by the 500 hPa geopotential height and the surface wind) and the anomalous eddy activity (characterised by the surface vorticity and cyclonic activity). It is shown that the lower troposphere (850 hPa) temperature patterns are mainly controlled by the advection of heat by the anomalous mean flow. However, at the surface level, the anomaly patterns obtained for maximum and minimum temperatures present important asymmetries, associated with a different control mechanism, namely the modulation of shortwave and longwave radiation by cloud cover variations. It is shown that blocking and non-blocking episodes are typically associated with important meridional shifts in the location of maximum activity of transient eddies. The influence of persistent anomaly events in precipitable water is strongly related to the corresponding anomaly fields of lower troposphere temperature. The precipitation rate, however, appears to be essentially controlled by the surface vorticity field and preferred locations of associated cyclones.

Keywords

Cyclone Precipitable Water Vorticity Field Anomaly Field Transient Eddy 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The Reanalyses data have been produced by the NCEP and NCAR DSS. The window (30°N–80°N, 60°E–70°W) has been extracted and kindly provided by Ian Harris and David Viner (CRU). The authors would like to acknowledge Dr. Jean Palutikof and Ms. Célia Gouveia for their helpful suggestions.

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Copyright information

© Springer-Verlag  2004

Authors and Affiliations

  • R. M. Trigo
    • 1
    • 2
  • I. F. Trigo
    • 1
    • 3
  • C. C. DaCamara
    • 1
    • 3
  • T. J. Osborn
    • 4
  1. 1.Centro de Geofísica da Universidade de LisboaDepartamento de Física, Faculdade de Cièncias Campo GrandeLisbonPortugal
  2. 2.Departamento de Eng. Civil da Universidade LusófonaLisbonPortugal
  3. 3.Instituto de MeteorologiaLisbonPortugal
  4. 4.Climatic Research UnitUniversity of East AngliaNorwichUK

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