Geoscience Reference
In-Depth Information
Completing this long journey takes several hundred years, which is
very rapid compared to typical diffusion times, but very slow
compared to typical timescales in the atmosphere. It is thus possible to
see here the importance of the oceanic dynamics, which by a tempo
very specific to different regions, actively participate in keeping the
planet's climate in equilibrium and participate in its variability.
2.4. Some key elements for understanding the ocean's role in the
climate
2.4.1.
Typical times
To understand the behavior of the climate system, it is necessary to
contrast the different compartments that contribute to it and in
particular to analyze the two large fluids that, through their continual
motion, contribute to regulate the disparities in energy. The
atmosphere is known for its rapid reactions, but also for its weak
memory to disturbances in energy. A disturbance at mid-latitudes is
transmitted in a few days into the surrounding regions and in less than
a month to the entire hemisphere concerned. On a global scale, the
Earth is in radiative equilibrium: all the energy that it receives from
the Sun is emitted back into space. As a zonal average however, this
energy equation is not balanced: the tropical regions receive energy in
excess whereas the polar regions have a deficit. This planetary
imbalance causes a redistribution of heat in which the ocean and
atmosphere participate in equal parts (Figure 2.19). The atmosphere
participates actively in the transfer of thermal energy from the Equator
to the Poles by its average circulation in tropical regions (Hadley cell)
and by its transient motions at mid-latitudes. Equally, the ocean
participates in this transfer of energy from the Equator to the Poles
notably by its northward heat transport in the subtropical basins but at
its own speed. Moreover, in this meridional heat transport, each
basin brings a particular contribution: the Pacific Ocean transports heat
from the Equator to the Poles in a symmetrical manner; the Atlantic
Ocean guarantees a heat transport to the north from the southern
hemisphere, as far as the Arctic regions, whereas the Indian Ocean,
