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My question is what similarities do you think there are in how water and air move around Earth?
Answer 1:

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 it can.

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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