A gentle stroll through EP flux theory

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The celebrated 1960 paper by Eliassen & Palm (hereafter EP) put on record several brilliant discoveries in the theory of linear waves on shear flows for rotating stratified fluid systems. These discoveries opened up a new perspective on linear wave dynamics in the atmosphere and on the nascent theory of nonlinear interactions between the waves and the mean flow. Arguably, the most important discovery was that of their eponymous wave activity flux vector in the meridional plane and of the conditions under which this important flux was non-divergent. In this short paper we will retrace some of the steps of EP and explore how their path-breaking discoveries came to be understood in the light of subsequent theories. Of course, an endeavour like this runs the risk of looking patronizing, if only because of 50 years of hindsight, but this is not intended: it was the power of their original discoveries that inspired five decades of further research, with new results still coming out today.

Original languageEnglish (US)
Pages (from-to)12-15
Number of pages4
JournalEuropean Journal of Mechanics, B/Fluids
StatePublished - 2014


  • Non-accelereation conditions
  • Pseudomomentum
  • Wave activity flux

ASJC Scopus subject areas

  • Mathematical Physics
  • General Physics and Astronomy


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