OSD Ocean Science Discussions OSD 1812-0822 Copernicus GmbH Göttingen, Germany 10.5194/osd-9-3723-2012 On the use of the Strouhal/Stokes number to explain the dynamics and water column structure on shelf seas Souza A. J. 1 National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street, Liverpool, L3 5DA, UK 10 12 2012 9 6 3723 3738 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ocean-sci-discuss.net/9/3723/2012/osd-9-3723-2012.html The full text article is available as a PDF file from http://www.ocean-sci-discuss.net/9/3723/2012/osd-9-3723-2012.pdf

In recent years coastal oceanographers have suggested the use of the "Strouhal" number or it's inverse the "Stokes" number, which have been defined as the ratios of the frictional depth (δ) to the water column depth (<i>h</i>) or vice versa, to describe the effect of bottom boundary layer turbulence on the vertical structure of both density and currents. Although they have mention that the effects of rotation should be important, they have tended to omit it. This omission may be important when talking about tidal currents as the frictional depth from a fully cyclonic to a fully anticyclonic tidal ellipse can vary up to an order of magnitude in the mid latitudes; so that the stokes number might appear smaller (larger) than it is resulting in frictional effects being underestimated (overestimated). Here a way to calculate a Stokes number, in which the effect of the Earth's rotation is taken into account, is suggested. Then the standard Stokes and the rotational Stokes numbers are used as predictors for the position of the tidal mixing fronts in the Irish Sea. Results show that the rotational number improves prediction of the front in shallow cyclonic areas of the eastern Irish Sea. This suggest that the effect of rotation on the water column structure will be more important in shallow shelf seas and estuaries with strong rotational currents.

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