# Weather simulation

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I have tried creating a system for large scale weather based on physical factors many times without success.

Whatever I come up with fails due to two issues.

1) Initial conditions

2) Calculation complexity

So I have come up with yet another approach that is working pretty well so far.

I allow the designers to specify a bunch of high and low pressure zones( with values and velocities) and connect them with weather fronts.

This is by no means realistic, but the results work well enough.

My problem is now I want to add more realism. At the moment I just create a bunch of clouds based on distance from the weather front and the local air pressure.

Now I want to add clouds based on terrain effects.

The problem with this is I really need to work out an ambient temperature value for each location on the map.

This runs me back into the initial value problem.

I have calculated the ETR* value of the sun for each location, but that only gives me a heating effect so I need a start temperature.

Has anyone come across a way of calculating an ambient temperature for a location based on date/time/location data?

* ETR == extraterrestrial radiation value, the intensity of the sun light in a location.

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I don't think the initial conditions are a big deal: If you know how to run your simulation forward, you should achieve plausible states quickly, even if you started with quite implausible ones (there is probably some formal statement of this using the notion of "thermal equilibrium", but I am not even going to try to go there).

That said, I don't really have any good suggestions for how to model the computation of the state from previous states. This is probably a large field of study. Perhaps this is a good starting point? http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-810-dynamics-of-the-atmosphere-spring-2008/

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Am i right in assuming your game is historical in nature?

Why not just get hold of the weather readings (if there were any) from various locations, and then simulate the weather at each location and interpolate between them?

You would know exactly when your game took place and where, weather reports from various stations would have been public knowledge? This is probably how i'd handle it... You won't have to worry about procedural generation, or having artists drawing weather fronts into your maps.

What do you think?

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First off, simulating weather for a game sounds awesome. I really like that idea.

Second, I wouldn't worry too much about being super precise and super realistic. As long as the weather patterns look reasonable and aren't doing anything crazy you should be fine. Your goal should be a weather simulation that makes the game more fun. If the weather patterns make sense to the player and can be used strategically then your simulation is good.

IMHO I wouldn't start with air temperature, pressure zones, and velocities in a tight grid and try to model it like the simulations used to predict weather. I would start by identifying what you want the weather to do and write a simulation that mimics that behavior. Edited by HappyCoder

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I don't think the initial conditions are a big deal: If you know how to run your simulation forward, you should achieve plausible states quickly, even if you started with quite implausible ones (there is probably some formal statement of this using the notion of "thermal equilibrium", but I am not even going to try to go there).

There is a lot of balance in weather on earth without time trace up, as encapsulated weather subject, without those as established, I guess really the simulation would become some sort of a furnace, like moon and earth spawned in space would just go collapse towards each other. Like, that New York is more south than Madrid, yet the weather and temperatures and ecosystem are incomparable becouse of some water stream.

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I don't think the initial conditions are a big deal: If you know how to run your simulation forward, you should achieve plausible states quickly, even if you started with quite implausible ones (there is probably some formal statement of this using the notion of "thermal equilibrium", but I am not even going to try to go there).

There is a lot of balance in weather on earth without time trace up, as encapsulated weather subject, without those as established, I guess really the simulation would become some sort of a furnace, like moon and earth spawned in space would just go collapse towards each other. Like, that New York is more south than Madrid, yet the weather and temperatures and ecosystem are incomparable becouse of some water stream.

I don't know if it's the grammar or just the punctuation, but I don't understand what you wrote.

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I don't know if it's the grammar or just the punctuation, but I don't understand what you wrote.

I wanted to stress that I think that initial conditions of a weather system are as vital as its corect behaviorals. If second is perfect, the system will not be simulated without first. Weather is a cycling system, just as orbits, without parameters of it, they cannot behave as you would expect, even if you would establish newton force of attraction, and base system on some reduced observation set up (position).

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I wanted to stress that I think that initial conditions of a weather system are as vital as its corect behaviorals. If second is perfect, the system will not be simulated without first. Weather is a cycling system, just as orbits, without parameters of it, they cannot behave as you would expect, even if you would establish newton force of attraction, and base system on some reduced observation set up (position).

I disagree. The atmosphere is a chaotic system that has little in common with orbiting masses. The atmosphere is a system that takes energy from the Sun and from the inside of the Earth and radiates it to space. If you start with initial conditions that are too cold or too hot, you'll see it gaining or losing heat. When it comes to humidity levels, if the air is really dry it will more easily grab moisture from the sea and other bodies of water; if it's too humid, rain will fix that. If the pressure difference between some parts of the atmosphere and others are too large, winds will take care of that.

I've studied dynamical systems enough to be pretty certain about this. Chaotic systems like this one tend to forget their initial state. There is a large portion of the state space that forms the basin of a chaotic attractor that is what corresponds to actual observed weather. If you start too far away from typical conditions, you may be in the basin of a different attractor (e.g., snowball Earth). But it shouldn't be too hard to get the initial conditions in the right ballpark.

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There is a large portion of the state space that forms the basin of a chaotic attractor that is what corresponds to actual observed weather. If you start too far away from typical conditions, you may be in the basin of a different attractor (e.g., snowball Earth). But it shouldn't be too hard to get the initial conditions in the right ballpark.

So then the weather is is an entropy system of chaos well defined over the rest of condition?(heat, energy, matter, chemical reorganization) And when the outside entropy is well defined, the weather will unfold in its exact form as consequnce? but to bottom-catch weather like this, is, like to simulate universe from big bang after a (few) pictures of the bang. Quite hard to manage, or not?

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