Horizontal convective water exchange above a sloping bottom: The mechanism of its formation and an analysis of its development

The mechanism of the formation of horizontal temperature/density gradients above underwater coastal slopes of natural basins due to heating/cooling from the surface is considered. It is shown that the time required for formation of the gradients is rather small (tens of minutes for a thermocline depth of tens of meters), but the development of the corresponding flows may not be accomplished even in a day long cycle. The time dependence of the horizontal water exchange between the shallow and deep areas is analytically treated. The spatial scale of the problem is the main parameter that defines the resulting quasi-stationary value of the flow rate. The joint analysis of the published field, laboratory, and numerical data of many authors in the range of the above-slope depths of 10⁻² m < d < 3 × 10² m (d ≤ D, where D is the thickness of the upper thermally active layer of a basin) indicates that the relation between the value of the horizontal quasi-stationary volumetric flow rate and the local depth looks like Q = 0.00l3 × d ^1.37 (R ² = 0.96). The horizontal convective water exchange is shown to be generally two-layered, ageostrophic, and exhibits its maximum flow rate at the end of the slope. The inferences agree well with the field data and conclusions of other authors.