A three-dimensional finite-element model of wind effects upon higher harmonics of the internal tide

Abstract

A non-linear three dimensional unstructured grid model of the M2 tide in the shelf edge area off the west coast of Scotland is used to examine the spatial distribution of the M2 internal tide and its higher harmonics in the region. In addition the spatial variability of the tidally induced turbulent kinetic energy and associated mixing in the area are considered. Initial calculations involve only tidal forcing, although subsequent calculations are performed with up-welling and down-welling favourable winds in order to examine how these influence the tidal distribution (particularly the higher harmonics) and mixing in the region. Both short and long duration winds are used in these calculations. Tidal calculations show that there is significant small scale spatial variability particularly in the higher harmonics of the internal tide in the region. In addition turbulence energy and mixing exhibit appreciable spatial variability in regions of rapidly changing topography, with increased mixing occurring above seamounts. Wind effects significantly change the distribution of the M2 internal tide and its higher harmonics, with appreciable differences found between up-and down-welling winds, and long and short duration winds due to differences in mixing and the presence of wind induced flows. The implications for model validation, particularly in terms of energy transfer to higher harmonics, and mixing are briefly discussed.

Fortnightly oscillations observed in the Adriatic Sea

“…We speculate that the Mf tide may be strongly amplified during weakly stratified season, as current oscillations in-phase with the Mf tide were mostly observed at that part of the year. Although the atmospheric forcing might be a source of some of the observed 10-to 20-day current oscillations (for example in April 2008), it is certainly not the source of all of the observed oscillations-but it may modulate the existing oscillations (Xing and Davies 1997;Hall and Davies 2007). Namely, no significant atmospheric forcing was present during the strong current oscillations which were observed in May-June 2008, and which were inphase with the Mf tide.…”

Assessing the water quality response to an alternative sewage disposal strategy at bathing sites on the east coast of Ireland

“…For the resolution of the horizontal turbulence, the Smagorinsky (1963) sub-grid scale model, with a length scale of 0.25 was chosen. The scheme is commonly used in maritime domains (see Marques et al 2009;Sato et al 2006;Hall and Davies, 2007) with large scale eddies where small vortices can be inhibited by the mesh. A Prandtl mixing length scale model with a Munk and Anderson (1948) damping function was used for the vertical turbulence closure.…”

Numerical studies of wind forced internal waves with a nonhydrostatic model

“…Excellent overviews from this area of research were recently given in Thorpe (2005) and Vlasenko et al (2005). Many studies have focused on tidally driven internal tides and internal waves over topography in the open ocean (Lamb 1994;Legg and Adcroft 2003;McPhee-Shaw 2006;Padman et al 2006;Lamb et al 2007;Hall and Davies 2007;Legg and Klymak 2008;Xing and Davies 1998a, b, 1999, 2001. There have also been many investigations of internal waves in fjords or lochs with sill (Stigebrandt and Aure 1989;Farmer and Freeland 1983;Lamb 2004;Vlasenko and Hutter 2002;Inall et al 2004;Cummins 2003;Davies and Xing 2007;Armi 1999, 2001;Klymak and Gregg 2004;Berntsen et al 2008;Davies 2006a, b, 2007).…”