Advanced Ocean Modelling: Using Open-Source Software

3.20 Exercise 12: Double-Diffusive Layering 77three-dimensional nature. The result of the double-diffusive instability is a slightlystratified water column characterised by a stability frequency of N =4×10 −3 s −1 .This weak residual density stratification is caused by the initial outburst of convectiveplumes moving density anomalies away from the initial density interface.In due course of the double-diffusive instability process, the Turner angle remainsclose to a value of 90 ◦ while the temperature and salinity contrasts between thelayers gradually become weaker (Fig. 3.44).Fig. 3.44 Exercise 11. Evolution of temperature and salinity contrasts between the layers (arrow)expressed in equivalent density units. The open circle denotes the initial value. The arrow headpoints to the final value after 60 min of simulation3.20 Exercise 12: Double-Diffusive Layering3.20.1 AimThe aim of this exercise is to explore the double-diffusive layering process in a watercolumn which is initially uniform in density, but displays sharp vertical contrasts intemperature and salinity.3.20.2 Task DescriptionThis exercise is a repeat of Exercise 11 except for a vertical swap of the layers.The warm, saline layer is located this time below a layer of colder, freshersurface water. The temperature difference between the layers is 10 ◦ C and thesalinity contrast is chosen such that density is spatially uniform. The initial gradient