On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street, Liverpool, L3 5DA, UK
02 Apr 2013
Received: 15 November 2012 – Published in Ocean Sci. Discuss.: 10 December 2012 Abstract. In recent years coastal oceanographers have suggested using the "Strouhal"
number or its inverse, the "Stokes" number, to describe the effect of
bottom boundary layer turbulence on the vertical structure of both density
and currents. These are defined as the ratios of the frictional depth
(δ) to the water column depth (h) or vice versa. Although many
researchers have mentioned that the effects of the earth's rotation should
be important, they have tended to omit it. Rotation may have an important
influence on tidal currents, as the frictional depth from a fully cyclonic
to a fully anticyclonic tidal ellipse can vary by up to an order of
magnitude at mid latitudes. The Stokes number might appear smaller for
cyclonic current ellipses (larger for anticyclonic) than it is without
rotation, resulting in frictional effects being underestimated
(overestimated). Here, a way to calculate a Stokes number is proposed, in
which the effect of the earth's rotation is taken into account. 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 use
of the rotational number improves the predictions of fronts in shallow
cyclonic areas of the eastern Irish Sea. This suggests that the effect of
rotation on the water column structure will be more important in shallow
shelf seas and estuaries with strong rotational currents.
Revised: 27 February 2013 – Accepted: 12 March 2013 – Published: 02 April 2013
Citation: Souza, A. J.: On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas, Ocean Sci., 9, 391-398, doi:10.5194/os-9-391-2013, 2013.