Equatorial ocean circulation
259
equatorial at about 1.33λ o from the equator. This distance increases (Fig. 11.12)
for higher Rossby waves, i.e., larger j.F o rc o =2ms −1 , the dimensional values of
-0.2
-0.1
0
0.1
0.2
0.3
-4
-2
0
2
4
j = 1
j = 2
j = 3
j = 5
j = 4
y
amplitude
Figure 11.12. Meridional structure of the dimensionless thermocline field ˆ
hj (see e.g., (11.46c)
below) associated with the first 5 (long) free Rossby waves (j =1, ..., 5).
the meridional locations at which Rossby wave thermocline amplitudes have their
maximum are shown in Table 11.1 for the long waves with j =1 , ..., 5 together
with dimensional crossing times for a basin of 15,000 km.
Wave type
y max
θ max
τ d (days)
Kelvin
0.00 .08 7
Rossby, j =1
1.22
±3.31
260
Rossby, j =2
1.75
±4.75
434
Rossby, j =3
2.17
±5.88
608
Rossby, j =4
2.50
±6.77
781
Rossby, j =5
2.83
±7.67
955
Table 11.1. Typical quantities of free equatorial waves for co =2m/s, and β0 =2 .2 ×
10
−11 (ms)
−1 , such that λo = 301.5 km. The dimensionless quantity ymax is the position of
the maximum amplitude of the thermocline depth as seen in Fig. 11.12; θmax is the latitude of this
position. The travel time τd is based on the time it takes for the wave to cross a basin of 15,000 km.
The Kelvin wave travels from west to east whereas all Rossby waves travel from east to west.