Dynamics of ENSO
277
In this oscillatory view, the cold phase of the 1997-1997 ENSO (the La Ni˜ naphase) occurred at the end of 1995. Between the cold and warm phase of the oscillation is a transition phase which occurred at the beginning of 1997 (Fig. 12.2a).
During this ‘transition phase’, SST anomalies are nearly zero over the basin as
are the wind-stress anomalies. However, the heat content anomaly in the western
and central Pacific is positive, since the thermocline is deepened. The latter is
consistent with the equatorial anomalies in heat content in Fig. 12.2b.
Additional Material
B: In Glantz (1996), a broad overview of the weather phenomena associated
with El Ni ˜
no is given with a description of their impact on society. Other
bedtime reading is Philander (2004).
12.2. A coupled ocean-atmosphere system
The equatorial ocean-atmosphere system is a strongly coupled system and an
impression of the whole system is given in Fig. 12.4. In this picture the mean
state is shown with its Cold Tongue in the east and its Warm Pool in the west.
The trade winds form part of a larger tropical circulation system consisting of the
Walker circulation and the Hadley circulation. The nature of the coupling between
Rossby wave
Kelvin wave
thermocline
Mixed layer
upwelling
Q
b
T
ρ
ρ + Δρ
u
v
w
T s
τ
τ ext
Walker Circulation
Hadley
circulation
Warm Pool
Cold Tongue
Q oa
x
y
z
trade winds
equator
OCEAN
ATMOSPHERE
Figure 12.4. Overview of the oceanic and atmospheric processes of the equatorial coupled
ocean-atmosphere system.
ocean and atmosphere is the following. A sea surface temperature anomaly will
277
In this oscillatory view, the cold phase of the 1997-1997 ENSO (the La Ni˜ naphase) occurred at the end of 1995. Between the cold and warm phase of the oscillation is a transition phase which occurred at the beginning of 1997 (Fig. 12.2a).
During this ‘transition phase’, SST anomalies are nearly zero over the basin as
are the wind-stress anomalies. However, the heat content anomaly in the western
and central Pacific is positive, since the thermocline is deepened. The latter is
consistent with the equatorial anomalies in heat content in Fig. 12.2b.
Additional Material
B: In Glantz (1996), a broad overview of the weather phenomena associated
with El Ni ˜
no is given with a description of their impact on society. Other
bedtime reading is Philander (2004).
12.2. A coupled ocean-atmosphere system
The equatorial ocean-atmosphere system is a strongly coupled system and an
impression of the whole system is given in Fig. 12.4. In this picture the mean
state is shown with its Cold Tongue in the east and its Warm Pool in the west.
The trade winds form part of a larger tropical circulation system consisting of the
Walker circulation and the Hadley circulation. The nature of the coupling between
Rossby wave
Kelvin wave
thermocline
Mixed layer
upwelling
Q
b
T
ρ
ρ + Δρ
u
v
w
T s
τ
τ ext
Walker Circulation
Hadley
circulation
Warm Pool
Cold Tongue
Q oa
x
y
z
trade winds
equator
OCEAN
ATMOSPHERE
Figure 12.4. Overview of the oceanic and atmospheric processes of the equatorial coupled
ocean-atmosphere system.
ocean and atmosphere is the following. A sea surface temperature anomaly will