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The energy cascade associated with daily variability of the North Atlantic Oscillation
Author(s) -
Castanheira José M.,
Marques Carlos A. F.
Publication year - 2018
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.3422
Subject(s) - baroclinity , barotropic fluid , eddy , climatology , energy cascade , geology , kinetic energy , mean flow , environmental science , atmospheric sciences , meteorology , physics , turbulence , classical mechanics
An analysis of anomalies of the energy cascade associated with daily fluctuations of the North Atlantic Oscillation (NAO) is presented here. The analysis consists of a detailed version of the Lorenz energy cycle, which decomposes the energy flows into baroclinic and barotropic terms and into zonal mean and eddy components, and was applied to the 6‐hourly ERA‐Interim reanalysis for the period of 1979–2016. The obtained results show that the positive NAO phase is preceded by a significant increase of synoptic baroclinic eddy activity. The eddy available potential energy is converted into kinetic energy and transferred to barotropic synoptic eddies. Then, the kinetic energy is transferred upscale into the barotropic planetary waves, which produce the NAO pattern. Immediately after the positive NAO peak, there is a significant reduction of baroclinic activity, and no indication of an anomalous increase of the global‐mean baroclinic eddy activity in the 10‐day period after the peak was found. At longer lags, between 10 and 20 days, the kinetic energy of barotropic eddies shows positive anomalies consistent with the eddy–zonal mean flow feedback. We conclude that the synoptic baroclinic eddy activity forces the NAO variability, and no modulating role of the NAO in the global‐mean baroclinic eddy activity (storminess) occurs.