Dear Forum, Hadley Cells have not had a topic in awhile, so it recommended I start a new topic instead of reactivating an old one.
My understanding of planetary circulation systems like Hadley Cells changed today. I would appreciate your feedback. Am I on the right track or further from it?
I used to think the number of cells was changeable. We currently have 3 cells, Hadley, Ferrel, and Polar. Lower the temperature enough and the Polar would grow and the Hadley would fade until you had just two. Lower it still more and you would have just one, a Polar cell over a snowball earth. And by the same thinking, raise the temperature from our current arrangement enough and the Polar cell goes away. Raise it still more, and we get to a hot house world with just one cell, the Hadley cell which would stretch from the equator to the pole.
But today my understanding shifted. I'm now thinking that these cells are not interchangeable. You can't replace one with another. Because of a bunch of math and physics and things like planetary rotation and axle tilt, you will always have 3 cells, or at least the potential for 3 cells.
They are more like a series of buckets. There will always be 3 buckets. You always start by filling the first bucket. When the first bucket gets full enough it starts spilling over into the second bucket. Fill the first and second buckets enough and it will start spilling over into the third.
Even a low energy/low heat planet (like a snowball Earth or current conditions on Mars) would still have a Hadley cell. (It would have the potential for the others, there just would not be enough heat/energy to activate them). Meaning as soon as a planet gets enough atmosphere and enough solar heat/energy the first cell, the Hadley cell would start up.
As the heat/energy rises, and the original Hadley cell raises its territory above freezing, the heat/energy starts to spill over into the 2nd cell (Ferrel). Moisture from this 2nd cell would still travel north and rise up near its northern boundary, which would most likely be over the edge of the great ice sheet. The rising air would dump its precipitation just beyond the edge, which would fall as snow and help build the ice sheet. But beyond that there would be little heat/energy conveyed.
Raise the heat/energy enough and the 2nd cell fills up enough to start spilling over into the third cell. Now the polar cell is receiving enough heat/energy that the great ice sheets pull way back and the ground may melt free of snow in the summer.
Raise the heat/energy still more and the 3rd cell fills up enough for its annual average to stay above freezing. Oh it may still form ice and snow in the winter, but it will all melt out in the summer, there will be no permafrost or permanent ice sheet.
Raise the heat/energy still more, and all the cells will stay above freezing all year long.
Then no matter how much you raise the heat/energy. As long as there is still atmosphere, there will still be 3 cells. As I read today, even Venus with its extreme heat/energy still has 3 cells. There is a huge Hadley cell. There is a narrow “Polar Rim” as they call it. And then there is a Polar Vortex, a split polar vortex with two permanent (?) centers.
So once there is enough heat/energy to activate 3 cells, there will always be 3 cells in some form or another. The 1st cell can expand farther from the equator. The 2nd and 3rd cells can be compressed into a smaller space. The 2nd and 3rd cells can heat up and become more energetic. But it is not the case of one cell being consumed by another.
