Advanced Ocean Modelling: Using Open-Source Software

4.5 Exercise 18: Coastal Upwelling and Downwelling 115where c 2 is a free parameter, Δz is vertical grid spacing, and A z,min is a smallbackground value. The author uses c 2 = 0.15. Additional treatment is required if thegrid spacing chosen does not resolve convective plumes created by unstable densitystratification (N 2 < 0). A conventional approach is to increase turbulence levels toa certain large value A z,max in such situations. Explicit finite-difference formulationof the diffusion terms is associated the stability condition:Δt ≤(Δz)2max(A z )4.5.4 Results: Upwelling ScenarioFull upwelling establishes in response to the wind forcing applied (Fig. 4.13). Thewind forcing produces offshore Ekman drift in the surface layer and onshore Ekmandrift in the bottom layer. Speeds these Ekman-layer currents are 10–15 cm/s. Currentsin the bottom Ekman layer move deeper water toward the coast and upwardFig. 4.13 Exercise 18. Upwelling scenario. Snapshots of the density field, and cross-shore andalong shore components of horizontal velocity after 3 days of simulation