Author(s): Jarle Berntsen; Guttorm Alendal

Linked Author(s):

Keywords: Ekman drainage; Dense water cascading; Bottom Ekman layer; Numerical modeling; Bergen Ocean Model

Abstract: The dynamics of the overflow mixing and entrainment (DOME) has been investigated in many numerical studies. In the present study, the focus is on the representation of the bottom Ekman layer dynamics and Ekman drainage. The present study is based on the setup from DOME investigations and the use of the Bergen Ocean Model (BOM). The BOM is a terrain-following σ-coordinate ocean model. A horizontal view of the computational domain is given. The domain is 1100×700 km, the maximum depth is 3600 m, and a slope with slope steepness 0.01 connects the deep part to the coast where the depth becomes 600 m. From x = 0 km, there is a 100 km wide and 600 m deep channel through which dense water will enter the domain. The lateral boundaries to the east and to the west are open, and Neumann boundary conditions are applied to let the flow freely out of or into the computational domain. The lateral boundary to the south is closed. The initial and ambient stratification, ρ(z), is assumed to be linear. Through the channel, there is an inflow of dense water with flux Q = 5 Sv. The Coriolis parameter f is 1×10⁻⁴ s⁻¹. The horizontal grid size is 10 km. In order to investigate the sensitivity of the model outputs to vertical resolution, a sequence of vertical σ-grids is produced and the finest grids have high resolution over the bottom Ekman layer. To investigate the sensitivity of the plume dynamics to the bottom boundary condition, the experiments are performed with three choices of this condition. Firstly, a quadratic drag law is applied. Secondly, the experiments are repeated with the no-slip condition implemented as in the MITgcm. Thirdly, some experiments are performed with a quadratic drag law using a constant value of CD. As the dense water from the embayment enters the slope, the plume veers to the left looking towards the inlet due to geostrophic balance and after 40 days the front of the plume has reached the open boundary to the west. Due to the rotation of the earth and the bottom drag, the fluid parcels near the bottom will veer to the left.

DOI: https://doi.org/10.3850/978-981-11-2731-1_031-cd

Year: 2018