Modeling Concepts - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 279

R = 0.2 R = 0.05 R = 0.2 R = 0.05 R = 0.2 R = 0.05

90

80

u = 0.6 m s − 1

u = 0.02 m s − 1 u = 0.1m s − 1

70

60

1 2

3

Coriolis effect in
horizontal circulation:

50

40

1 = is insignificant

= becomes significant

30

2

20

3

= is significant

10

0

1 10 100 1000

Lagoon width, km

FIGURE 6.16 Range of significant-insignificant Coriolis effects as a function of latitude and
lagoon width for three fixed characteristic velocities.

where the latitude 10 −5 s −1 and the charac-

teristic velocity is within the range of 0.05-0.10 m s −1 , the radius of inertial cycle can
be estimated as r c

ϕ is 55 ° , the Coriolis parameter f is 11.94 ⋅

0.044-0.088. In this case, the Coriolis force
is significant in the whole lagoon since the average width is 9 km.
Strictly speaking, the Coriolis force is at work in any basin at any movement.
The period of the Coriolis cycle equals 2

≈ 400-800 m, and R ϕ ≈

f −1 , which yields values of 23 h 56 min,
14 h 37 min, and 12 h and 44 min for latitudes of 30

π

, respectively.
This means that any advective movement of equivalent or longer time scales will
be affected by the Coriolis force. Since the horizontal spatial scale in a lagoon is
fixed, the slower the movement is in the lagoon, the greater the influence of Coriolis
force on water dynamics and mixing processes. Although this may seem contrary
to the idea that Coriolis acceleration is proportional to speed, this can be seen in
Figure 6.16 and Figure 6.17.
Assuming that the wind-induced water velocity in a lagoon is 0.1 m s −1 ,
Figure 6.16 shows that the Coriolis effect at a fixed latitude is insignificant when
a lagoon width L width is less than 5 · r c or R ϕ

° , 55 ° , and 70 °

> 0.2 starts to be significant (shaded

strip) when 5 · r c L width < 20 · r c , or , and dominates when L width >

20 · r c , or . Similar arguments can be made for the same lagoon width at
different latitudes. For example, the Coriolis effect is important for all lagoons with
a width of 10 km only if they are located at latitudes greater than 45

< 0.05 << R ϕ 0.

R ϕ < 005 .

. Furthermore,
considering a velocity of 0.02 m s −1 as a lower limit of natural lagoon velocities
(as measured by most oceanographic instruments), Figure 6.16 indicates that the
circulation in any lagoon with a length scale less than

°

*

L min will never be affected