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The Premise

The Earth rotates on its own axis, which is tilted by about 23 degrees. I am imagining a situation where such an axial tilt does not exist.

From general reading, it appears the largest impact of removing an axial tilt would be on seasonal change, in the sense that there wouldn't be any changes whatsoever. Every latitudinal belt would have its own set season all year round, with some minimal changes depending on the earth's distance from the sun in its usual orbit (ranging basically from 91.4 million miles in January compared to 91.5 million miles in July - which is less than 1%).

The Question

What would be the implication on rain cycles if the Earth had no Axial Tilt? It appears to me that rain carrying clouds move to the dictates of wind blowing to an area with a different air pressure. If our planet had no axial tilt, the Equator would get extremely hot all year round, causing water to evaporate and move north or south towards cooler areas - at least that's my understanding.

What parts of earth would receive the most rainfall if such a change were to occur?

arkaia
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Ambarish Sathianathan
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  • You have already cross posted this on worldbuilding twice. http://worldbuilding.stackexchange.com/questions/13318/what-if-an-earth-like-planet-had-no-axial-tilt-climate-and-technology. So I presume this question relates to the atmospheric part of what if the earth did not have an axial tilt. –  Apr 07 '15 at 11:24
  • Not quite an answer b/c I don't want to bother with references: The Earth would likely be uninhabitable. Low latitudes would be far hotter than they are now, high latitudes regions far colder than they are now. There might be a thin strip of inhabitable space somewhere in between. – David Hammen Apr 07 '15 at 16:36
  • Would the equator be less habitable? – gerrit Apr 07 '15 at 17:31
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    @gansub, Spot on. Those questions were with regard to impact on technology and ecosystems (flora/fauna). This one is specifically for cimate. – Ambarish Sathianathan Apr 07 '15 at 17:57
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    As with these other hypothetical question, I suggest placing them on [worldbuilding.se], with the tag [reality-check] – Jan Doggen Oct 30 '15 at 14:17
  • @JanDoggen and Ambarish Sathianathan, as written now, this looks like a Worldbuilding Q, though still topical here. With just the slightest of editing, you can make this into a Q about exoplanets, therefore unambiguously topical here. Give that a try. – Eubie Drew Oct 30 '15 at 15:35
  • Seems fitting for this site. Would think it's best for a meteorologist or climatologist would be needed, not just a general theorizing. Ironically, questions like these are very common meteorology finals in advanced courses in my experience, to show that you understand\can work with the dynamics if the equations change. Other common ones: how would Earth's weather change with different rotation rates, or if the freezing point of water changed. So I'd think an earth scientist is the best chance of an answer. – JeopardyTempest Sep 01 '16 at 07:43
  • I don't believe thermodynamically, there wouldn't be a huge change if the axis were near vertical. The net insolation at all locations would be the same (aside from small adjustments due to atmosphere thickness). The absorption would slightly vary due to ground\cloud cover differences, but no biggy. The main energy movement on earth isn't pumping from one pole to the other, but between equator and poles. – JeopardyTempest Sep 01 '16 at 07:49
  • Weather, whether it's wind blowing or thunderstorms building, is the result of the imbalance in energy, all moving towards balance and dissipation of energy [thanks to friction] (see 2nd Law of Thermodynamics). Rotation helps prevents fairly quick balancing, though continued imbalanced input must continue for weather to continue. But it will on a vertical earth. Basically, it'd line up a lot like spring\fall, and a system continually in that state has no problems. There'd still be jets and fronts and a Hadley Circulation to diffuse warmth poleward. – JeopardyTempest Sep 01 '16 at 07:54
  • I'm thinking weather might become a little more stable compared to what we see in spring\fall, as over time the global features\positions of longterm highs and lows would probably become even more entrenched due to continual feedback. Likewise, that could even lead to more occasional and violent swings... as typical blocking patterns perpetuate more without the destabilization that seasonal changes bring... such that when energy finally builds up high enough to break them down, things just go nuts. – JeopardyTempest Sep 01 '16 at 08:03
  • But most of all, you'd likely see a greater disparity between locations. Places right near the equator would be wetter yet as the ITCZ parks there all year long. The bands nearer the subtropics (about 20-40 N and S) would become much drier yet. The subarctic (think 50-70 N and S) would become get more wet\snowy. And the Poles would become even drier (Antarctica is already the largest desert)! Just because there wouldn't be the variation there is now. – JeopardyTempest Sep 01 '16 at 08:09
  • Just perhaps a few less hurricanes (since there'd be no peak heating to get the ocean real hot), though they might recurve less as there probably wouldn't be as many deep intrusions if the pattern were more stable than our typical spring\summer. So they might last longer at latitudes if there's fairly minimal land (such as there is in the northern Hemisphere, really... with only the African Sahel as a fairly great landmass). Even continuing around the globe repeatedly perhaps. – JeopardyTempest Sep 01 '16 at 08:19
  • And you know where all this takes me??? In a word: http://www.space-pictures.com/images/full-size/Planet_Jupiter_2009.jpg Indeed, it turns out Jupiter has a 3 degree tilt (as does Venus). And you'd likely get a very stratified, stable pattern (even as that pattern is continually very violent in places) as in its image. A lot less variation. A lot more boring. No leaves falling in autumn, no great bloom in the spring. Perpetual spring\fall, except a lot more stable. People might like the new temperatures in the US\Europe, but they'd probably hate the storms (or lack, depending on location). – JeopardyTempest Sep 01 '16 at 08:23

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Just throwing some thought on the subject, it is easy to me to understand that there is a big pump moving large amount of water from one pole to the opposite one along the year, that is during summer in north hemisphere the ice melts at Arctic and mix to the sea; at the same time water start precipitating more and more on the Antarctica, piling up as snow and ice. During the other six months the pump reverts, moving water from Antarctica to the Arctic.

In this hypothetical situation this pump will behave differently. The water will evaporate from the sea, and precipitate towards the poles. Those rain in midway to the pole would provide vegetation life, erosion, and all sort of things rain water does. That water falling in the north and south pole would have no reason, in principle, to melt and reinsert in the oceans.

If the rain started to fall mostly on high latitudes, possibly the region around equator would be more exposed and deserter, increasing the heat, evaporation, and the convection of the air at high speed. Possibly very intense winds blowing everything, moving quickly the clouds and vapor to higher latitudes, where the rain would fall. Anyway, the hotter atmosphere should increase the loss of the lighter gases to the space due to kinetic energy gain, decreasing the atmosphere pressure little by little while becoming hotter. In this loss there could be even some water vapor.

Then I think that in the long run the water would tend to move all the way to the poles draining drastically the remaining of the planet. If we think of an ocean as salty (3.5%) as ours, possibly there would be deposition of large layers of salt, most of it sodium chloride. I don't really know if there would be a "life zone" around some high latitude. Certainly tropic would have no meaning in this configuration.

That is the "big picture", but not all the story.

We have different wind flow in atmosphere and water flow in the oceans due to others factors. One of those being the tides that move water in waves half circumference of the planet. The main component being that from the moon, but we have other of smaller intensities like the solar influence. Other factors are the convection due difference temperatures and pressures, and Coriolis force making it go round in its trip across latitudes.

Another factor is that we have a non homogeneous distribution of mass on planet surface, the removal of large amount of water, moved to the poles, possibly would increase the amount of wobbling, then the precession ( https://en.wikipedia.org/wiki/Axial_precession) of the planet. Perhaps this wobbling would be responsible to a certain amount of melting at the poles, keeping the pumping working longer and, who knows, preserving some life in the planet.

A hotter atmosphere could increase the amount of clouds, if it covers all the planet we could have a very long freezing of the planet.

If we think on a dry planet with water moved to poles as ice, we could perhaps include sublimation of ice in the figure, adding the loss of water to space due to heating of the atmosphere. I don't think we would become a Mars, our gravity is about three times Mar's gravity.

HTH

Roxo
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