Climate and wind (or wind-lessness)

jwdoom · May 15, 2016

My WIP is on a terraformed planet that I have decreed for convenience to be close enough to Earth in size and mass and etc.

Thanks to a random planet generator and assorted deterministic worldbuilding techniques I've got a plain shaped roughly like a right triangle about 3 million square miles in area. The height and the base are high mountains to the east and the south respectively. The hypotenuse is an inland sea fed via marshes by an ocean up against the northern polar ice cap. The plain covers the tropics, from just north of the doldrums to the horse latitudes, although the sea itself extends north of that.

My location is down by the "point" dead in the middle of the tropical zone and what I need to know is how much wind would there be? I've been working under the assumption there would be effectively no wind because the eastern mountains block the northeasterly trade winds across the entire plain, but they're over 1500 miles away.

Would the planet's air circulation resume with that kind of distance and produce a kind of weak trade wind, or am I right in that there would be basically no wind?

Either way I'm thinking the region would be a pretty gnarly desert, but the answer makes a difference in that some wind would produce occasional orographic rain on the mountains that form the triangle's "point", which affects things in my setting.

thanks
JW

WeaselFire · May 15, 2016

You need to understand why air moves. Temperature differences cause air to rise or fall. The air the rises or falls leaves a void that is filled by air to the sides. This we call wind. In addition, at higher levels in the atmosphere, the spinning of the Earth causes the various layers of the planet to move at speeds and in directions appropriate to their medium and distance from the center of rotation. All of these effects cause patterns of weather and wind across the surface of the Earth.

Now, where wind comes from also depends on the knowledge and beliefs of the people experiencing the wind. It could be caused by the breathing of the various gods and life energies in your world. This isn't the scientific environment, but the subjective determination of your planet's inhabitants.

Besides, wind is not dependent on moisture levels in the atmosphere. Deserts have wind, as do oceans. You will likely want to keep to the basic mechanics for your planet unless you will somehow alter the physics for your world.

What does your story need? Write that and build your world to fit.

Jeff

jwdoom · May 16, 2016

I've done my basic research, I just can't find an answer to my question. It's an SF world so there's no fantasy air motivation. Wind carries moisture, which is why I'd like to know the answer rather than winging it.

blacbird · May 16, 2016

It's hard to imagine a planet with a significant atmosphere and no wind. Just not remotely realistic. And wind doesn't "carry" moisture. As Weaselfire said, air moves because of temperature differences. Heat the air, it expands and rises, cool the air, it becomes denser and sinks, and all manner of complexities of air movement develop. "Moisture" is carried as water vapor, simply part of the gaseous mix in the air along with (on Earth) nitrogen, oxygen, argon, carbon dioxide and other things. Also understand the difference between water vapor, which is invisible, and clouds, which are made of tiny liquid water droplets or ice crystals.

I think you may be overthinking this. A reader probably won't be as interested in the geographic details of the planetary mechanism of wind and rain, so much as interested in the simple observation that there is wind and rain, or deserty conditions, or whatever. But, to circle back, as a reader I would find an Earth-like planet with no wind a hard thing to accept.

caw

jwdoom · May 16, 2016

I'm not asking about an entire planet. I'm asking about the specific region described in my question.

blacbird · May 17, 2016

jwdoom said:
I'm not asking about an entire planet. I'm asking about the specific region described in my question.

I really don't think you can separate a "region" on a planet in this way, unless you enclose the whole thing under some kind of dome. No place on Planet Earth is isolated climatically from any other place, something we're finding out in a bunch of disturbing ways these days.

caw

SianaBlackwood · May 17, 2016

Maybe you could try looking at maps of the world to find a similar-looking region and then base your weather on what happens there.

Helix · May 17, 2016

Plenty of wind in Alice Springs.

hth

Roxxsmom · May 17, 2016

Helix said:
Plenty of wind in Alice Springs.

hth

But do you have chickens (um, chooks), and monterrey jack cheese, and bacon, and mushrooms...

http://www.favfamilyrecipes.com/wp-content/uploads/2013/05/Alice-Springs-Chicken.jpg

Sorry, I know Outback Steak House is about as Australian as Budweiser beer is German. But damn it, I can't hear the name of this city now without thinking of that chicken dish my husband always orders there :tongue

*End derail*

Helix · May 17, 2016

That'd be chicken Parmigiana (a.k.a. chicken Parmy) over here. It'd have mozzarella instead of that Monterrey stuff, but it's a staple of hotel fare.

In Alice, the alternatives would be steak and -- occasionally -- camel and kangaroo.

morngnstar · May 17, 2016

I'm not a super expert but I will offer what I know.

There is something you are neglecting if your planet has significant axial tilt: monsoons. Axial tilt means between the seasons, the "solar equator" moves relative to your country. In the summer, the country can be effectively in the Southern Hemisphere for purposes of Hadley cell circulation. Northeast trades shift to southwest. I guess since you have mountains to the south as well, you will still be in rain shadow.

I think you will always have some orographic rain. In a hot region, air will rise, and air has to come in from somewhere to replace it, even if Coriolis effects make it not particularly want to. On Earth, even in places like Central Asia, rivers flow down from mountains, like the Amu Darya and Tsangpo. Civilizations settle in the foothills which are still semi-arid, but not as harsh as the open plains. Only areas completely encircled by mountains are bone dry, such as the Taklamakan desert.

blacbird · May 17, 2016

morngnstar said:
Only areas completely encircled by mountains are bone dry, such as the Taklamakan desert.

Not really true. The driest place on planet Earth is the Atacama, in Chile, which is in the rain shadow of the Andes, but not "completely surrounded" by mountains. The Namib Desert in southwestern Africa is a very dry coastal desert in which massive sand dunes extend right down to the beaches.

What you need to get dry areas is atmospheric circulation producing persistent high-pressure regions in which descending air masses desiccate the landscape. On Earth, owing to Hadley Cell effects, these tend to align along the Tropics of Cancer and Capricorn, at about 23-24 degrees of latitude from the equator. Mountains clearly also affect wind circulation, but there are plenty of desert areas nowhere near mountains, as in the Sahara and central Australia.

caw

jwdoom · May 19, 2016

morngnstar said:
In a hot region, air will rise, and air has to come in from somewhere to replace it, even if Coriolis effects make it not particularly want to.

That's the answer I was looking for! Thanks, morngnstar!

meowzbark · May 26, 2016

Check out the climate for the Atacama Desert, which is in the rainshadow of the Amazon rainforest, and thus, has had no measurable rainfall in sections for millions of years. Yet it is often windy.

If you're searching for the least windy place on the earth to mimic climate, it is known as Ridge A, a 13,000 foot mountain located far inland in Antarctica. Scientists say that there is hardly ever weather or wind in the area. No human has ever been there. Apparently it would be the best place to put a telescope due to the low moisture in the air. Source

Climate and wind (or wind-lessness)

jwdoom

WeaselFire

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jwdoom

blacbird

jwdoom

blacbird

SianaBlackwood

Helix

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Roxxsmom

Beastly Fido

Helix

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morngnstar

blacbird

jwdoom

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