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What is the simplest simulatable model giving our rotating earth its 3 circulati

ID: 1384230 • Letter: W

Question

What is the simplest simulatable model giving our rotating earth its 3 circulation cells (Hadley, Ferrel, Polar)? The model should also show 1 circulation cell if the earth's rotation were stopped (or in a case like Venus), and no circulation at all if radiation were somehow uniform to/from the earth (instead of true equator-heating due to the sun's point source). By the way, it would be nice if the same model could show 8 circulation cells in a case like Jupiter.

I expect the earth's 23? tilt can be ignored. The important parameters seem to be the planet's radius, the planet's rotation speed, the planet's mass, the atmosphere's mass, the atmosphere's molar density (treated as an ideal gas with energy absorption from the earth's surface, but not directly from the sun's rays), and the atmosphere's viscosity. I hope the earth's surface could simply be modelled with a constant temperature profile, increasing from the pole to the equator (or, I wonder if daily thermal cycling of this surface temperature profile might be needed to generate multiple circulation cells).

Anyway, using parameters like these, I'm hoping to see a justifiable formula giving 3 (I can't yet accept the qualitative "Hadley cell air falls with inertia and friction" explanations on the internet).

Explanation / Answer

It is based on the constructal law. Constructal law promoted by Bejan&al, belongs to the family of variational principles but deals with macroscopic flow distributions. According to Bejan, the constructal law belongs to the laws of nature close to but different from the 2nd law of thermodynamics.

The constructal law says that in any flow system, the flow will be organised in such a way that the access of every part of the system to the flow configuration will be maximized. This looks close to ideas about maximum/minimum entropy production but is in reality different.

To be complete, the existence of a constructal law as a law of nature is generally not accepted by fluid mechanics specialists. Personally I stay agnostic - the law status is not demonstrated yet the results obtained by applying this principle are correct in most cases.

To summarize this paper which is fairly long and deals also with diurnal heat transfer betweeen the hot daily half and cold night half, I highlight :

the number of cells depends on rotation speed and on the equator-pole temperature difference. For slow rotations (> 144 h) a single cell develops. For fast rotations (< 24 h) 3 cells develop. For fixed rotation speed the number of cells is farther modulated by the temperature difference. At 24 hours and 20

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