Well, this is a good question. Basically the
similarity is that both air and water are driven
at the planetary scale by the Sun. The earth
is heated non-uniformly because its spin axis is
not 90 degrees to the plane of the earth's orbit
around Mr.SUN. Because of that, more of the Sun's
radiant energy falls on the earth between 20
degree North and 20 degree South latitude, more or
less what we call the TROPICs or sub Tropics.
Because of this unequal distribution of heat from
the Sun, the atmosphere gets heated and hence
comes to lower density (hot air rises) and
these buoyancy forces give rise to motion.
All the reasons above, plus the fact that the
earth is rotating (all these forces), ultimately
explain the motion of the atmosphere, the cause of
weather and the major climate belts on Earth.
Now, the oceans also respond to this unequal
heating, but because the ocean is a viscous
fluid (more viscous than the air), and because
it is denser, the fluid dynamics is different in
detail; but still the major ocean currents are
related to the ocean trying to more evenly
distribute the heat that comes into the ocean,
most in the low latitudes. This is an example of
the Second Law of Thermodynamics applied to
EARTH. The ocean/atmosphere system acts to even
out or redistribute the incoming heat as best as
Of course we need to take account of the earth's
spin and the configuration of the ocean basins and
continents and even the tides due to the Moon and
Sun. These are all complications as is the
presence of ice and of salty water. However,
basically the redistribution of energy is what
makes the air and oceans to move.
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