A model study of spin-down and circulation in a cold water dome

Abstract

A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction, mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial temperature distribution characteristic of the dome, and an associated along frontal flow. The spindown of the dome is found to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography, suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes.

Cyclonic versus Anticyclonic Circulation in Lakes and Inland Seas

“…As a result of these latter efforts, various processes contributing to the crossshore density difference have been elucidated. Moreover, Hill (1993Hill ( , 1996, Xing and Davies (2005), and Davies and Xing (2006) focused on an inland sea after the onset of stratification, with the cold water remaining trapped beneath the thermocline in the open sea and the warm water being subjected to strong tidal mixing in the shallow coastal area. Huang additionally paid attention to the case when in a whole lake the temperature is lower than the temperature of maximum density, with the shallow coastal area being relatively cold due to the controlling influence of vertical mixing.…”

“…The studies, however, are strongly polarized when it comes to the circulation of bottom waters: some predict cyclonic flow that extends to the bottom (Heaps 1972;Hill 1993Hill , 1996Davidson et al 1998;Lazar et al 2007), while others obtain anticyclonic circulation in the bottom layer as opposed to cyclonic circulation in the surface layer (Huang 1971;Oonishi 1975;Orlić 1996;Xing and Davies 2005;Davies and Xing 2006). The studies, however, are strongly polarized when it comes to the circulation of bottom waters: some predict cyclonic flow that extends to the bottom (Heaps 1972;Hill 1993Hill , 1996Davidson et al 1998;Lazar et al 2007), while others obtain anticyclonic circulation in the bottom layer as opposed to cyclonic circulation in the surface layer (Huang 1971;Oonishi 1975;Orlić 1996;Xing and Davies 2005;Davies and Xing 2006).…”

“…The studies, however, are strongly polarized when it comes to the circulation of bottom waters: some predict cyclonic flow that extends to the bottom (Heaps 1972;Hill 1993Hill , 1996Davidson et al 1998;Lazar et al 2007), while others obtain anticyclonic circulation in the bottom layer as opposed to cyclonic circulation in the surface layer (Huang 1971;Oonishi 1975;Orlić 1996;Xing and Davies 2005;Davies and Xing 2006). Internal friction is either not considered (Hill 1993) or is allowed for by employing a Rayleightype parameterization (Orlić 1996), a Boussinesq-type parameterization [vertical-Heaps (1972);Hill (1996), vertical andlateral-Huang (1971); Oonishi (1975); Davidson et al (1998);Lazar et al (2007)], or a turbulent closure scheme (Xing and Davies 2005;Davies and Xing 2006). Transverse sections of most basins have dimensions close to 100 km 3 100 m, but in one paper the basin considered is much shallower (Heaps 1972) and in another it is both narrower and shallower (Oonishi 1975).…”

“…It is rather difficult to interpret the diversity of results because the authors consider different basins and take widely differing dynamics into account. As for the bottom, the authors impose various conditions there: free slip (Orlić 1996), linear slip (Heaps 1972;Lazar et al 2007), quadratic slip (Davidson et al 1998;Xing and Davies 2005;Davies and Xing 2006), and no slip (Huang 1971;Oonishi 1975;Hill 1993Hill , 1996. Internal friction is either not considered (Hill 1993) or is allowed for by employing a Rayleightype parameterization (Orlić 1996), a Boussinesq-type parameterization [vertical-Heaps (1972);Hill (1996), vertical andlateral-Huang (1971); Oonishi (1975); Davidson et al (1998);Lazar et al (2007)], or a turbulent closure scheme (Xing and Davies 2005;Davies and Xing 2006).…”

“…Transverse sections of most basins have dimensions close to 100 km 3 100 m, but in one paper the basin considered is much shallower (Heaps 1972) and in another it is both narrower and shallower (Oonishi 1975). Most authors consider steadystate conditions, and some (Oonishi 1975;Hill 1996;Xing and Davies 2005;Davies and Xing 2006) address transients. As for the bottom, the authors impose various conditions there: free slip (Orlić 1996), linear slip (Heaps 1972;Lazar et al 2007), quadratic slip (Davidson et al 1998;Xing and Davies 2005;Davies and Xing 2006), and no slip (Huang 1971;Oonishi 1975;Hill 1993Hill , 1996.…”