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Assume an Earth-Clone, that has an axial tilt of 90°. How would the circulation of the atmosphere look like? Would there still be three convection cells?

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  • $\begingroup$ Earth clone also in the orbital period? $\endgroup$ – L.Dutch - Reinstate Monica Sep 15 at 13:28
  • $\begingroup$ @L.Dutch Earth clone in everything but axial tilt. $\endgroup$ – TheDyingOfLight Sep 15 at 14:53
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So the axial tilt doesn't actually influence the number of convection cells very much, afaik. It does, however, affect their position. You might also want to note that a world with a 90° axial tilt would essentially present on side to its star half the year and the other half the rest of the year. That means a long day which is summer and a long night which is winter. This leads to some EXTREME weather patterns that until recently were though impossible to overcome (well, at the very least it was thought to be the case for tidally locked planets, but recent simulations show a fast enough spin can compensate that effect). In the case of a 90° planet, the spin will have no effect on spreading the extra heat from the day side though, because the axis faces towards or against the sun for roughly half of the year (and it faces perpendicular the other half). This means that half of the year, you'd have heat trapped in the day cycle either on one side or the other depending if you take the winter or summer quarter. This could be mitigated if you have a short enough year but then you'd run into problems of star size with instability that features coronal ejections and lethal rays so… maybe not a good idea (red dwarves are extremely unstable).

What would affect the number of cells is the rotation speed.

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    $\begingroup$ "A world with a 90° axial tilt would essentially present on side to its star half the year and the other half the rest of the year": how so? All the area between 45° latitude south and 45° latitude north (that's 70% of the total area) will get at least some sunlight for 50% of the year. (And all the area between 30° latitude south and 30° latitude north will get some sunlight for two thirds of the year.) $\endgroup$ – AlexP Sep 15 at 20:03
  • $\begingroup$ @AlexP I'm not sure what you're saying here. A world with a 90° axial tilt is like Uranus. Basically, its pole is facing the sun. Then, as the planet moves around its orbit, the axial tilt remains in place facing (for example) towards the centre of the galaxy, while the sun is on the left, if you were looking at the centre of the galaxy. This is the autumn equivalent where all the planet would get some sunlight. Then the other pole would get all the sun and that'd be winter. Etc. $\endgroup$ – Nierninwa Sep 15 at 20:15

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