Seeking Tyge Sjöstrand

[Malenfant]

Is Tyge Sjöstrand here on CotI? (I have a suspicion that he might be Hemdian?)

If so, I'm wondering where your world generation rules have gone that used to be on your website. (which were really detailed, you had formulas for greenhouse effects and stuff. You'd covered most of the physical stuff and had started discussing climatology). I've downloaded them on my website, but I wanted to point some people to them and the link seems to be dead. Are they still available?

 

[BeRKA]

You can find Tyge Sjöstrands world generation here:
http://www.trisen.com/sol/default.asp?topic=20

 

[Malenfant]

Thanks, BeRKA - that's what I was after. Well, this specifically at least.

 

[Pompe]

Hemdian is not me (although I'm very grateful for his assistance).

 

[Malenfant]

Pompe - you're Tyge?

 

[Pompe]

That's me, yes.

 

[Malenfant]

I wondered what made you so good with worldbuilding, now I know - that's good stuff there! Ever planning to finish the rest of it at all?

 

[Pompe]

Sure, when someone pays me. No, I'm just kidding.*

Revision and eventually completion, in that order, yes. (Progress reports on occasion here )

*But considering that there seems to be a demand for detailed world gen systems and that those that have been made seem to be well liked, I'm a bit surprised the game corps don't publish more and instead leave it up to fans like you and me to occasionally put out fan stuff, but I guess they don't sell well. Has QLI made some sort of world building supplement/aide?

 

[Malenfant]

Pompe - how accurate is that equation for calculating Greenhouse Effect on your pages? I've been trying to find an accurate way of calculating GFX for ages, and that's the only equation I've ever found for it...

 

[Anthony]

Hm... the correct way to do greenhouse effect (which is not, however, particularly easy to apply) is:

1) compute albedo using a solar spectrum
2) compute albedo using a blackbody spectrum at the expected blackbody temperature of the planet.
3) If we call the first albedo As and the second one At, actual temperature should be (blackbody temperature) * ((1-As)/(1-At))^1/4.

 

[Malenfant]

1) compute albedo using a solar spectrum

I know how to do step 2. (I think. Do you mean multiply the blackbody temperature of the planet at that distance by (1-albedo^(0.25))?)

How do you do step 1 though (what do you mean "using a solar spectrum")?

 

[Anthony]

Albedo is commonly referred to as a single number, but it's not -- planets reflect different amounts of light at different wavelength, so albedo depends on the spectrum of light you're talking about.

Now, for a given wavelength, absorption and emissions are linked -- the more reflective an object is, the less it emits. So, if an object is extremely reflective at IR wavelengths, it will emit relatively little IR. The reason the greenhouse effect works is because the spectrum of incoming light isn't the same as the spectrum of outgoing light.

So, if you can figure out how reflective the planet is if using a thermal IR spectrum, you can also tell how much energy it will emit as thermal IR. Then, simply balancing the energy input and output will give a temperature.

 

[Malenfant]

which is all very well, but how do you figure out how reflective the planet is using an IR spectrum?!

I was hoping more for an approach that had a factor for the density of the atmosphere, a factor for the cloudiness, and a factor for the greenhouse gases (though even that might be too complicated). You tot those up to get a multiplier between 1.0 and 3.0 or 4.0 and you apply that to your albedo-modified blackbody temperature.

That's kinda what Pompe did, but I wondered if he got that formula on his pages from somewhere.

 

[Pompe]

Pompe - how accurate is that equation for calculating Greenhouse Effect on your pages? I've been trying to find an accurate way of calculating GFX for ages, and that's the only equation I've ever found for it...

On of the first things I write is that I _don't_ claim the system is scientifically accurate (unlike say a system which certainly isn't scientifically accurate but claim to be). It is based upon science, yes, but it is as virtually all world generation systems a random-generation mathod which simplifies and extrapolates things in order to give what might be perceieved as realistic results.

So in this case (which is an excellent example), it is simply a simulation to give a somewhat decent result (thus the 1D10-factor, as an example, which means sheer randomness might have quite an impact) based upon how greenhouse effects tend to stack up and with what I perceive as the appropriate complexity level for the document. (And it is _not_ done the same in the revision, no).

I mean, in reality different greenhouse gasses are of different effectiveness, you can't just add them together, and the net effect depends on how the atmosphere is structured. And so on. It is all easy if you know the relevant albedos, but usually in RPG world building you don't know them but you have instead generated a world with a certain base temperature and a certain atmosphere - probably more intuitive than going the other way, I think.

However, if want to do a heavier model, you should check out how different gasses absorb in different wavelengths. I have a book on atmosphere physics aomewhere which I did use and I can't find right now, but I'll notify you when I dig it up.