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I put a force field dome over my city. How would that affect the weather in the city, and outside it?

Specification of the city:

  • 10 × 40 km on the surface
  • 1 km in height
  • dome would be 2 to 3 km in height

Specification of the area around that City:

  • tundra-like area
  • about 50 km to the south lies an ocean
  • no mountains in sight

The context is the same as How could a force field dome be realized in my city?.

The Force field blocks any movement through it when it is activated. So everything that is in the dome stays in the dome.

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    $\begingroup$ "What happens in Fight Club, stays in Fight Club" - however, there is an important question here: is the dome always on? or is it on occasionally? That could dramatically change how much it influences weather and whether it has a microclimate. $\endgroup$ – mechalynx Oct 4 '14 at 23:17
  • $\begingroup$ The dome is blocking everything including air ? $\endgroup$ – Vincent Oct 5 '14 at 0:38
  • $\begingroup$ Do you want that light and other wave types are also blocked in both directions? Should field reflect or consume them? $\endgroup$ – Konstantin Petrukhnov Oct 6 '14 at 10:16
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I will make the assumption that air and water can't get into the dome. And I will also assume that this dome is feasible.

The weather from the exterior won't impact the interior except for the temperature. Since you said it is a tundra it is quite cold. According to the Köppen climate classification, the mean monthly temperature never go above 10°C. It's not a problem, there are several cities above 10 000 people with a tundra climate.

On the exterior, I doubt the dome would have any significant impact. Expect that the water falling on the dome would accumulate around it at the base. It is important to say that the ground is permafrost and cannot absorb water (or very little). Water will accumulate if there is a natural depression. Water is not always a concern in the tundra because some places receive almost no rain.

Even if the force field can be deactivated, the city still need to be self sufficient for a long period of time. There won't be any exchange of water or air with the exterior. They need to have the tools to recycle the air and water (to purify them). Otherwise they will suffocate and the water will become corrupted.

*About the weather inside the dome, I think you could have some condensation but I'm not sure since there is no difference in temperature between the exterior and interior. I'll let someone else answer on that topic.

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First of all lets see the shape of the dome:

dome shape

That's 40km in radius ( (2+2)*10 = 40km ) and 3km in height ( 0.3*10 = 3km )

link

many thanks to Liath for revealing this online gem

That's pretty flat. I used Kelly Thomas's approach and compared it to a geological feature, but a hill instead of a mountain since this is a lot less steep. However, it turns out the tallest hills are about 1km tall and still cause rain shadows despite the flatness. Here's some examples:

  • The Judaean Mountains which are 1km tall and relatively flat compared to what we think of as mountains, but cause enough of a difference to shadow the Judaean Desert and the Dead Sea. Now that's an effect.

  • The Tibetan Plateau, which again, while quite tall, is a relatively flat area, not very jagged and steep. At an average elevation of 4.5km, it creates a steppe region and funnels water down into lakes. This gives us a sense of scale - your dome is a huge mountain.

I apparently followed Kelly's footsteps again because I also found the Alaskan woody tundra mentioned in the answer and it seems to indeed be caused by rain shadowing. The question is, if it is already a tundra and then you add a rain shadow, what happens?

Looking around for a mountainless tundra, I found nothing - in fact searching for it just gave me results for mountains related to tundras. However, the arctic tundra variant that applies to the poles might be closer. The problem is, the climate there is so cold, it's like what do you expect? They also seem to have an altitude to them (maybe your area is a plateau/plains at high altitude). This page however implies that the antarctic tundra isn't really a tundra but more like a desert that is too damn cold to not be a tundra-like biome.

The problem remains - unless your dome caused the tundra in the first place - it would be cold plains or a regular desert (just not sandy). But tundra is believable enough I guess.

As Vincent mentions, you need to recycle water and air, but considering how large the dome is and how mountains in tundras tend to be the sources of rivers and lakes, why not just collect the water off the dome and create an artificial river or lake inside the dome? Best park evar. With enough rainfall, you won't need to dig for water, it'll just fall out of the sky.

Uh oh...

Here's the extra issue with the conditions within the dome. The outside will probably not be too much affected by your dome, considering it's already practically a desert. However, your dome is large enough to have its own weather :D

Take a look at this:

There's more of these I assume, but we have important information from this: the enclosed spaces are nowhere near as large as the space your dome encloses. Since its maximum depth is about 450m, we can assume the areas inside are going to be less tall and your dome is 6 times taller (or 4 if it's 2km). Since you're in a tundra it's cold enough to have vapors condense. Also, it's as long as your city but still a cave - so your city will have more enclosed space that that entire beast of a cave in total - I'd assume about 10-20 times as much, all in one area.

The question is, does sunlight change this? I'd assume not since clouds generally don't seem to care about sunlight, nor does the cave, but I'm no meteorologist. It may cause a warmer climate inside though. You could have a greenhouse effect on your hands, but the temperature (I assume) shouldn't be too high. A lot of humidity and heat will be trapped due to the people (assuming they're warmblooded) and water, but you need some filtration and conditioning for the air anyway, just in case, so that might be able to regulate things. Considering you'll have weather though, it might (again, I assume) not be as critical since there's plenty of space for circulation. Also, you might want to expect birds :P

At 10x40km (400 km^2) and considering this and this we can see that the New York metropolitan area covers about 34km^2 and your city is over 10 times as big. That's pretty big and I'd assume that its microclimate will be closer to an actual climate, who's nature will depend heavily on what activities take place within.

An interesting aside - the buckyball guy had proposed a dome for New York back in the 60s.

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The inside of the dome would need to take substantial step to avoid the Urban heat island effect.

In terrestial cities the chief cause of the heat island effect is the lower albedo due to dark building materials. - This can be avoided by using light building materials instead.

However there are two other causes that will need to be handled.

First the city you describe is more than 10 times the size of NY - and at 1 km height can be expected to have significantly higher population density. So human activities that generate waste heat will cause warming, this is already noticable in some terrestial cities. Here is an Irregular Webcomic strip describing the impact of this for a planet sized city.

Secondly, and directly caused by the field, your city is in effect a greenhouse. Trapping the air heated by the surfaces that are heated by the sun, or by waste heat from human acticity, and preventing convection from carrying that air away. Since convection is an effective way of temperature transfer preventing this will have implications for temperatures inside the dome.

I can not estimate how many degrees hotter the inside will be when compared to the outside, but expect the city designers to be very happy about the fact that they are in a naturally cold environment rather than in a hot one. Even with a outside temperature below 0 degrees Centigrade. I expect temperature control inside will stuggle with keeping people cool rather than heating.

Edit: I see from your other question that the force field should "block line of sight". This changes things above because it affects what happens with sunlight. If the force field tends to reflect light I have no idea what will happen, the inside would be quite cold if there where no people - but with people it depends on how energy efficient they are. If the force field absorbs light I suspect that the inside of the dome would be too hot to be habitable.

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A dome of 2-3 kilometers height would cause a rain shadow on its lee side.

enter image description here

At this height it is comparable with many of the worlds mountains and would push any humid air passing over up to a higher elevation. As pressure decreases the adiabatic dew point rises causing an increase in precipitation over the windward side of the dome, and a decrease in precipitation as dryer air travels downwind.

While on Earth rain shadows are more commonly seen at lower latitudes examples can be found in tundra like climates. As an example the Brooks Range in Alaska casts a rain shadow over the woody tundra located downwind.

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