Advanced Ocean Modelling: Using Open-Source Software

4.2 Exercise 16: Geostrophic Adjustment 105Fig. 4.5 Exercise 16 (with Coriolis force). Evolution of the density distribution (shading) atselected times of the simulation. Lines are contours of v with a contour interval of 0.05 m/s. Solid(broken) lines denote positive (negative) speeds0.35 ± 15 cm/s. The time-averaged flow speed is slightly lower that the theoreticalvalue of 49 cm/s, derived from Eq. (4.13), presumably because of artificial lateraldiffusive smoothing of steep gradients in the sea level.Interestingly, initial water-column stretching creates deep flows running oppositeto those establishing in the surface layer. This feature is important to remember forstudies of rotational exchange flows through oceanic straits, to be investigated inExercise 22.It is obvious that temporal variations of flow speeds are the signature of inertialoscillations. These oscillations lead to an oscillatory pattern alternating betweenlateral stretching and shrinking of the low-density surface lens. The Coriolis parameterused corresponds to an inertial period is 17.5 hrs, which agrees well with theprediction (not shown). The reader is encouraged to verify the latter statement. Overall,the 2.5d vertical ocean-slice model appears capable of successfully simulatingrotational effects incurred by the Coriolis force.4.2.4 Additional Exercise for the ReaderRepeat this exercise, but place an isolated layer of denser water on the sea floor.Explore the resultant evolution of the density field for different values (includingzero) of the bottom friction parameter.