Advanced Ocean Modelling: Using Open-Source Software

4.5 Exercise 18: Coastal Upwelling and Downwelling 1134.4.4 The Upwelling IndexThe upwelling index can be used as an indicator and measure of coastal upwellingevents. This index is an estimate of the magnitude of offshore transport in the surfaceEkman layer and it is calculated from:∣∣τ wind∣ ∣ cos (α ∗ )Upwelling index =(4.20)| f | ρ owhere τ wind is the wind-stress magnitude, and α ∗ is the relative angle betweenwind direction and coastline orientation. The upwelling index carries units of squaremetres per second, which refers to a volume transport in cubic metres per second perunit length of the coastline. In contrast to coastal upwelling, coastal downwellingrefers to a situation in which the Ekman drift pushes surface water against the coastand which corresponds to negative values of the upwelling index.4.5 Exercise 18: Coastal Upwelling and Downwelling4.5.1 AimThe aim of this study is to explore the wind-driven coastal upwelling process in astratified water column with the 2.5d vertical-ocean slice model.4.5.2 Task DescriptionThe model domain is 50 km in length, resolved by a horizontal grid spacingof Δx = 500 m, and has a maximum depth of 100 m, resolved by a vertical gridspacing of Δz = 5 m (Fig. 4.12). The water depth decreases from 100 to 50 m alongthe length of the model domain. Shallow water is bounded by a coast. The offshorelateral boundary is treated as an open boundary using zero-gradient conditions forall variables except for sea-level elevation. To avoid that the model domain emptiesFig. 4.12 Initial configuration for Exercise 18