4.5 Exercise 18: Coastal Upwelling and Downwelling
113
4.4.4 The Upwelling Index
The upwelling index can be used as an indicator and measure of coastal upwelling
events. This index is an estimate of the magnitude of offshore transport in the surface
Ekman layer and it is calculated from:
Upwelling index =
τ
wind
cos (α
∗ )
| f | ρ o
(4.20)
where τ
wind is the wind-stress magnitude, and α
∗ is the relative angle between
wind direction and coastline orientation. The upwelling index carries units of square
metres per second, which refers to a volume transport in cubic metres per second per
unit length of the coastline. In contrast to coastal upwelling, coastal downwelling
refers to a situation in which the Ekman drift pushes surface water against the coast
and which corresponds to negative values of the upwelling index.
4.5 Exercise 18: Coastal Upwelling and Downwelling
4.5.1 Aim
The aim of this study is to explore the wind-driven coastal upwelling process in a
stratified water column with the 2.5d vertical-ocean slice model.
4.5.2 Task Description
The model domain is 50 km in length, resolved by a horizontal grid spacing
of Δx = 500 m, and has a maximum depth of 100 m, resolved by a vertical grid
spacing of Δz = 5 m (Fig. 4.12). The water depth decreases from 100 to 50 m along
the length of the model domain. Shallow water is bounded by a coast. The offshore
lateral boundary is treated as an open boundary using zero-gradient conditions for
all variables except for sea-level elevation. To avoid that the model domain empties
Fig. 4.12 Initial configuration for Exercise 18
113
4.4.4 The Upwelling Index
The upwelling index can be used as an indicator and measure of coastal upwelling
events. This index is an estimate of the magnitude of offshore transport in the surface
Ekman layer and it is calculated from:
Upwelling index =
τ
wind
cos (α
∗ )
| f | ρ o
(4.20)
where τ
wind is the wind-stress magnitude, and α
∗ is the relative angle between
wind direction and coastline orientation. The upwelling index carries units of square
metres per second, which refers to a volume transport in cubic metres per second per
unit length of the coastline. In contrast to coastal upwelling, coastal downwelling
refers to a situation in which the Ekman drift pushes surface water against the coast
and which corresponds to negative values of the upwelling index.
4.5 Exercise 18: Coastal Upwelling and Downwelling
4.5.1 Aim
The aim of this study is to explore the wind-driven coastal upwelling process in a
stratified water column with the 2.5d vertical-ocean slice model.
4.5.2 Task Description
The model domain is 50 km in length, resolved by a horizontal grid spacing
of Δx = 500 m, and has a maximum depth of 100 m, resolved by a vertical grid
spacing of Δz = 5 m (Fig. 4.12). The water depth decreases from 100 to 50 m along
the length of the model domain. Shallow water is bounded by a coast. The offshore
lateral boundary is treated as an open boundary using zero-gradient conditions for
all variables except for sea-level elevation. To avoid that the model domain empties
Fig. 4.12 Initial configuration for Exercise 18