The bottom Ekman layer and the apparent violation of the maximum principle

Hezi Gildor*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The solution for the bottom Ekman layer has a somewhat counter intuitive character, which seems to violate the maximum principle: at a certain level the velocity within the Ekman layer is higher than the velocity in the geostrophic layer above. I explain this character by looking at an analogous problem in an inertial frame of reference and show that it is the result of observing the flow from a rotating frame of reference (i.e. within a system that is not in steady state). The flow in the bottom Ekman layer is a superposition of the flow that results from the force exerted on the fluid by the rotating Earth and of the flow that results from the pressure-gradient term. Therefore, at a certain level the speed is higher than the speed of the geostrophic layer above which results from the pressure gradient alone.

Original languageAmerican English
Pages (from-to)593-599
Number of pages7
JournalGeophysical and Astrophysical Fluid Dynamics
Issue number6
StatePublished - 2008
Externally publishedYes

Bibliographical note

Funding Information:
I enjoyed fruitful discussion on the subject of this manuscript with Alex Kostinski, Francois Lekien, Eli Tziperman, Laure Zanna, Eyal Heifetz, Mark Cane, Michael Ghil, Yossi Ashkeanzy, Doron Nof, and Gidon Eshel. However, the content of this manuscript may not necessarily represent their personal opinion of the matters discussed. This work was supported by THE ISRAEL SCIENCE FOUNDATION (grant No. 781/04). HG is the Incumbent of the Rowland and Sylvia Schaefer Career Development Chair.


  • Boundary layer
  • Ekman layer
  • Maximum principle


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