Gurps Space. Axial tilt and Climate

[pro100kostya]

So.. I've built a world. I've got axial tilt and Average surface temperature. But how to get temperatures at different latitudes and time of year depending on axial tilt?

I know there are no such rules. I'd like to know what you guys think. Maybe some of you did such computations.

[David Johnston2]

Originally Posted by pro100kostya

So.. I've built a world. I've got axial tilt and Average surface temperature. But how to get temperatures at different latitudes and time of year depending on axial tilt?

I know there are no such rules. I'd like to know what you guys think. Maybe some of you did such computations.

The span between equator and pole is 90 degrees. For Earth the climate type at 45 degrees is Normal. The climate type at the north pole is Chilly. The climate type at the south pole is Cold. The climate type inland at sea level at the equator is Tropical. Near the ocean or at higher altitudes it's Warm. The temperature moderating effects of oceans are important and not to be neglected.

Shift the average temperature for the planet and you shift the average temperature at every latitude. For example if the planet is Tropical at 45 degrees, then that means it will probably be Very Hot at 0 degrees away from the ocean and and Cool to Normal at the poles. Axial tilt on the other hand changes where the climate zones are over the course of the year. A 15 degree axial tilt means that on the equator during the depth of winter an equator that is normally Tropical may drop down to warm while during the hottest days of the year it averages Hot.

Local ocean and wind pattern mean that precise calculation is worthless. You just have to guesstimate local conditions bearing these general guidelines in mind.

[Astromancer]

Extreme axial tilts get extreme results. On Earth, the Tropic of Cancer (the Northern limit of the tropics) is 23.5 degrees. The Artic circle is at 66.5 degrees. This leaves a forty-three degrees temperate zone between them. A world with a forty-seven degree axial tilt, would have the northern limit of the tropics, four degrees further north than the artic circle. The climate would be wild.

[Alden Loveshade]

The first GURPS campaign I ran was science fiction/space which was centered in a galaxy I created for science fiction stories. I worked to design worlds realistically--which proved very difficult, even though GURPS Space helped a great deal.

Axial tilt is an important factor in climate, but there are many others. There's the planet's atmosphere, its rotation rate (how many times does it rotate in one of its years), how eccentric is its orbit, etc.

NASA has an article that might help at https://www.nasa.gov/audience/foredu...t_Seasons.html

[pro100kostya]

Thanks to all of you guys. I already know what you say. I wanted something more precise. So I found a climatology book and I read it now.

So I've got an idea.

I've found insolation formula which shows how much energy get to a certain point on earth depending on time of year, latitude, axial tilt, day longevity and so on. I can't copy the formula unfortunately.

But it's in kWt/m2.

I think I can get insolations for latitudes (not every latitude, 0, 10, 20 and so on should be enough). Then I get approximate insolation for a planet. Then I get latitude/approximate insolation ratio. And I assume latitude/approximate insolation ratio will be equal to latitude/approximate temperature ratio. And I know approximate temperature from Gurps Space computations already. Thus I can get approximate temperatures for any period of time at any latitude.

[doctorevilbrain]

What does m2 mean?

[David Johnston2]

Originally Posted by doctorevilbrain

What does m2 mean?

Square meters.

[Agemegos]

Originally Posted by pro100kostya

I think I can get insolations for latitudes (not every latitude, 0, 10, 20 and so on should be enough). Then I get approximate insolation for a planet. Then I get latitude/approximate insolation ratio. And I assume latitude/approximate insolation ratio will be equal to latitude/approximate temperature ratio. And I know approximate temperature from Gurps Space computations already. Thus I can get approximate temperatures for any period of time at any latitude.

You are going to have to take into account thermal inertia and the meridional transport of heat in the atmosphere and oceans. Insolation alone would give far too great a variation of temperature with latitude and season.

Furthermore, for an isolated black-body radiator, equilibrium temperature would go with the fourth root of insolation, not in proportion with insolation.

[pro100kostya]

Originally Posted by Agemegos

You are going to have to take into account thermal inertia and the meridional transport of heat in the atmosphere and oceans. Insolation alone would give far too great a variation of temperature with latitude and season.

Furthermore, for an isolated black-body radiator, equilibrium temperature would go with the fourth root of insolation, not in proportion with insolation.

Yes. I should consider all this. But I think air and oceanic currents make way more impact on heat transportation than thermal inertia and the latter is negligible.

[ericthered]

Originally Posted by pro100kostya

Yes. I should consider all this. But I think air and oceanic currents make way more impact on heat transportation than thermal inertia and the latter is negligible.

I think thermal inertia drives the air and oceanic currents.



Observe that two months on each side of the summer solstice each receive the same amount of sun. The 20th of april and the 20th of august have the same amount of sun, but radically different weather. This is because in april its been cold all winter and spring and the heat goes into warming the place up, while in august things have already been hot for a while. The greatest amount of sun is received in late June, but the average temperature doesn't start dipping until the amount of sun starts approaching average again.