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A Simple Analytical Model of the Diurnal Ekman Layer

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  • 1 Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington
  • | 2 NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington
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Abstract

The effects of time-varying turbulent viscosity on horizontal currents in the ocean surface boundary layer are considered using a simple, theoretical model that can be solved analytically. This model reproduces major aspects of the near-surface ocean diurnal cycle in velocity and shear, while retaining direct parallels to the steady-state Ekman solution. The parameter dependence of the solution is explored, and quantitative measures of the low-frequency rectification of velocity and shear are derived. Results demonstrate that time variability in eddy viscosity leads to significant changes to the time-averaged velocity and shear fields, with important implications for the interpretation of observations and modeling of the near-surface ocean. These findings mirror those of more complete numerical modeling studies, suggesting that some of the rectification mechanisms active in those studies may be independent of the details of the boundary layer turbulence.

Current affiliation: Department of Environmental Earth System Science, Stanford University, Stanford, California.

Joint Institute for the Study of the Atmosphere and Ocean Contribution Number 2495 and Pacific Marine Environmental Laboratory Contribution Number 4418.

Corresponding author address: Jacob O. Wenegrat, Department of Environmental Earth System Science, Stanford University, 473 Via Ortega, Stanford, CA 94305. E-mail: jwenegrat@stanford.edu

Abstract

The effects of time-varying turbulent viscosity on horizontal currents in the ocean surface boundary layer are considered using a simple, theoretical model that can be solved analytically. This model reproduces major aspects of the near-surface ocean diurnal cycle in velocity and shear, while retaining direct parallels to the steady-state Ekman solution. The parameter dependence of the solution is explored, and quantitative measures of the low-frequency rectification of velocity and shear are derived. Results demonstrate that time variability in eddy viscosity leads to significant changes to the time-averaged velocity and shear fields, with important implications for the interpretation of observations and modeling of the near-surface ocean. These findings mirror those of more complete numerical modeling studies, suggesting that some of the rectification mechanisms active in those studies may be independent of the details of the boundary layer turbulence.

Current affiliation: Department of Environmental Earth System Science, Stanford University, Stanford, California.

Joint Institute for the Study of the Atmosphere and Ocean Contribution Number 2495 and Pacific Marine Environmental Laboratory Contribution Number 4418.

Corresponding author address: Jacob O. Wenegrat, Department of Environmental Earth System Science, Stanford University, 473 Via Ortega, Stanford, CA 94305. E-mail: jwenegrat@stanford.edu
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