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© N ASA
perature can
At the Equator, the sea tem
1. Solar radiation at its strongest
reach 28°C!
Solar radiation is at its maximum in the tropics. It is stored in the ocean in the form of heat.
A portion of these warm oceanic waters evaporates and condenses at altitude, forming
heavy clouds. Another part is taken away by ocean currents to higher latitudes. At the
Equator, however, some highly particular phenomena occur.
2. A heated pool !
At the Equator, the Earth’s rotation generates fast currents, mainly from East to West.
These currents rapidly move great quantities of water from one border to the other of the
Pacific and the Atlantic. These warm waters accumulate especially to the West of these
ocean basins. Their depth sometimes reaches nearly 200 m and they are the ocean’s main reservoir of energy. For the Pacific,
this body of water is known as the “warm pool” and has an average temperature of 28°C.
The Indian Ocean is subjected to the particular climate regime of the monsoon. In summer (May-October),
the winds blow from the ocean towards the Asian continent generating rainfall as far as the foothills of
the Himalaya. In winter (November-April), the winds switch direction, to sweep down from Asia towards
the ocean. They then create equatorial currents going East-West similar to those observed in the Pacific or
the Atlantic.
3. Highly mobile warm water masses
Ocean structure at the Equator
East
West
The ocean waters in the tropics are heated from above. The natural stratification
0,4 m
of the ocean is then reinforced because the warm surface waters are lighter
0m
than the deeper water masses, colder and more dense. This layering impedes
50 m
Wind moderat
e
0m
Warm water
Th
the heat absorbed in the surface masses from spreading down into the depths.
line
ermoc
Owing to this, but also because of strong equatorial currents, the only way
50 m
Cold deep
water
200 m
the warm surface waters can go is to move horizontally from East to West,
but sometimes they switch to go from West to East when El Niño episodes
0,4 m
200 m
The ocean’s water is warm at the surface and cold at depth. The thermocline marks the abrupt,
are in force. The shifting to and fro of these huge masses of warm water
vertical thermal transition between these two water types, warm and cold. At the Equator winds
exerts a major influence on the climate of the whole globe.
a depth of 200 m; to the East, they go down only to about 50 m.
force the warm surface waters to accumulate at the West of the ocean basin, where they can reach
When their surface temperature is high, the oceans liberate heat and
water vapour. This hot, humid air condenses at high altitude to form clouds
and sometimes intense rainfall. In the particularly warm areas of tropical
oceans, this rise of air can generate violent depressions and cyclones. The
warming of the ocean water linked to that of the global climate is currently
accentuating the probability of extreme meteorological events.
110 °
100 °
90 °
© NASA
The on-going climate change affecting ocean waters is bringing more frequent
extreme climatic events.