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On an Earth-like planet, two roughly parallel mountain ranges run for several thousand miles across a continent, with a gap of several hundred miles in between.

enter image description here

I am aware that mountains can create a "rain shadow" on one side since atmospheric moisture will precipitate as it is blown over a mountain, leaving the far side drier.

Could such a phenomenon consistently happen on this parallel set of mountains, such that the far north and far south are wet and forested, while the middle section is more like a savanna?

It occurs to me that this that prevailing winds would have to be coming into the strip from both sides, causing a net air flow either upwards or along the strip to emerge at the sea. What would be the consequences of this in terms of weather and climate?

Main question: is such a climate possible? What other geographic features would have to be present to produce this pattern of wind and rain?

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  • $\begingroup$ Depends on the scale (maybe of the planet itself? because you likely need to be looking at the global convection currents that establish the prevailing wind patterns? which may limit "where" you can put this in a global context) .. but I suppose it might be possible if there were two seperate stable air cells either side. $\endgroup$
    – Pelinore
    Mar 4 at 16:39
  • $\begingroup$ When you ask "is this possible," how much science are you looking for? Climate is by far the most complex type of question we get here. To give you scientific certainly we'd need to know a LOT more about the oceans, the world's hydrology and geology, and atmospheric conditions. To give you an example, there's a 40cm difference between the Atlantic and Pacific sea levels. Depending on the altitude of those plains and where this is located, you might have a river. $\endgroup$
    – JBH
    Mar 4 at 16:47
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    $\begingroup$ BTW, what you're asking for isn't unbelievable (whether or not it's possible). The higher the elevation of the plains and mountains, and the narrower the gap, the more believable it gets. However, what you'll get will be more desert than anything else. $\endgroup$
    – JBH
    Mar 4 at 16:51
  • $\begingroup$ Have you looked at the orientation of mountains with respect to the rain shadows they create? There is a pattern to them... Also, how did your mountain range form? that is a very unusual configuration. $\endgroup$
    – Questor
    Mar 4 at 17:05
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    $\begingroup$ peru current + double rain shadow region + sandwiched bet andes mt and the chilean mt + el nino = atacama desert (driest place) $\endgroup$
    – user6760
    Mar 4 at 17:34

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OK, here's a potential rough answer for you.

Your strip of desert sandwiched between two green areas is located between two Hadley Cells.

Which means it's on the equator, you want warm air flowing toward your two mountain ranges from both sides (top and bottom in your map) so the equator is the only option.

enter image description here

You also want that warm air to be carrying moisture so you need large bodies of water (we're talking oceans here just in case that wasn't clear) to the north and south so this warm air can load up with that moisture.

This way you have two prevailing wind patterns of warm moisture laden air traveling from two directions towards each other to dump it out on their respective mountain ranges giving you your rain shadow desert between them.

So if your rough map is oriented with north at the top and south at the bottom it can kind of work for this, if you have oceans top and bottom of it rather than the sides.

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    $\begingroup$ +1 just for the phrase, "rough answer." $\endgroup$
    – JBH
    Mar 4 at 21:30
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    $\begingroup$ @JBH well, it is just a bodge job of cobbled together vague memory and the first useful image I found, I might have said "good enough for government work", but not sure anyone here would get that ;p $\endgroup$
    – Pelinore
    Mar 4 at 22:12
  • $\begingroup$ This looks like a good answer, thanks. A detail I forgot to add -- my planet has a greater axial tilt than Earth. Maybe about 40 degrees. Would this impact the formation of Hadley Cells? (In the limit of 90 degrees my intuition says this would all look very different.) $\endgroup$
    – spraff
    Mar 5 at 9:29
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    $\begingroup$ @spraff axial tilt doesn't impact the Hadley cells much, not till you get close to 90 degrees, the speed of the planets rotation is the major influence. $\endgroup$
    – John
    Mar 10 at 12:56
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    $\begingroup$ @spaff you should probably ask that as its own question first. Tilt, thickness of the atmosphere and temp all play a role. $\endgroup$
    – John
    Mar 10 at 23:55
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Probably.

Earthlike doesn't mean an exact replica of Earth. There are a lot of things that could change the way weather patterns work on a "New Earth" planet, even if most other things are the same. Some things to consider:

  • Volume/Mass: Either of these would offer possible changes to how weather patterns work and even how things like "rain shadows" might propogate.
  • Density/composition of atmosphere: Similar to the above, a more voluminous planet that is Earthlike may have a slightly less dense atmosphere which could potentially make it slightly dryer. That doesn't necessarily mean it isn't a blue-green planet. With a less dense atmosphere, there could be much more surface/subsurface water which would still allow for a blue-green planet, but less filtering of energy from the star could also create less cloud cover and less atmospheric moisture.
  • Then there's the way that Earthlike jet-streams and gulf-streams are an objective aspect specifically of Earth and our geography rather than a set aspect of an Earthlike planet. We know that modern deserts have been oceans, and modern rainforests have been plains. The makeup of our regional climates are specific to air and sea currents, mountain ranges, ice flows, volcanoes, land masses, CO2-O2 exchanges due to forests and sea life (algae), and numerous other things. Even minute changes to any of these could provide exactly what you're looking for, and on another Earth that was exactly the same but for small tweaks to any of these, the climate could look very different.
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    $\begingroup$ "Then there's the way that Earthlike jet-streams .. We know that modern deserts have been oceans" sure, but there's no relation between oceans and jet streams, oceans are due to elevation and nothing to do with the weather, wind patterns, climate or rainfall above them // things like volcanic activity and plate tectonics are what push land above sea level and the water just trickles from wherever it fell to the low points we call oceans. $\endgroup$
    – Pelinore
    Mar 11 at 0:49

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