WIP (sort of tutorial to be) : Climates, applying Geoff's Cookbook at detail (some)

[Pixie]

Back at this.. It took me a while to find a perfect system I could share (and it probably ain't perfect or that easy to follow, but I'm hopeful).
This is the first part of steps towards creating a mean-temperature map for the extreme months of July and January. Along with the wetness maps for these months, we will then be able to determine the most likely climate for each region.


Temperature has a lot of conflicting influences, so we aren't just adding layers like we did for rain. The technique is somewhat different. We first map where each kind of influence is a factor to take into account. Then we generate a temperature map as if the continent was flat and waterless. And then we start adapting it.

So, first thing is mapping what will factor in. Create separate layers for each of these influences:
- Maritime influence / July and January
- Continental influence
- Cold ocean currents / July and January
- Warm ocean currents / July and January
- High humidity / July and January
- Medium elevation
- High elevation
- Very high elevation
(Overall it's 12 layers).

We'll look at one at the time.
1. Maritime influence:
Select all your oceans, seas and reasonably sized lakes (magic wand tool is your friend here). Expand that selection a fair number of pixels. Now, make your layer with dominant winds visible (for the corresponding month) and adjust your selection. Prolong it inland where the winds blow onshore, make it shorter where winds blow away from the coast. Lastly, check your topography. Areas behind mountains don't get maritime influence, except if winds can blow around them.
Paint your resulting selection in solid white and hide the layer.
Repeat for the opposing month.

january_maritime.gif
This is an example where I made the white layer 50% transparent so you can see how the wind affects it.


2. Continental influence.
Select your land masses with the magic wand. Contract the selection a fair bit (in my 1000 pixels tall map, I contracted about 50 px). Check your topography and extend this selection to all areas cut away from the seas/lakes/oceans by mountain ranges.
Again paint in solid white (we'll always do this) and leave it.

3. Warm and cold currents, July and January.
All these four layers are done in the same way. Make winds and currents visible (for the appropriate month). Make a wide selection covering the arrows with the currents. Extend the selection in the direction of prevailing winds. Again, since this a maritime influence, the selection cannot pass over mountains, so check the topography before painting in plain solid white.

july_warmcurrent.gif
Taking winds and currents into account results in something along the lines of this (shown here is the area influenced by warm currents in july).


4. High humidity
Use your rain patterns map. Make a selection encompassing all areas that are Very Wet or Wet. That's it, it's your high humidity zones, which you paint as before.

5. Elevation
We will cover three different elevation levels. Medium elevation is the selection encompassing everything above 1000m (roughly), High elevation covers areas above 2000/2500 m and Very high elevation will be for stuff above 5000m. These are aproximate levels, just use your judgement depending on your own elevation map.

mediumelevation.gif
Showing here is the area considered medium elevation (about 1000m high or above). As you can see this is quite a "tall" continent, and that will surely influence climate a lot...


Now, the influences are mapped. We will do the baseline temperature map which accounts only for solar radiation. Solar radiation depends mostly on the angle between the sun rays and the surface. In July, the Sun is stronger in the northen tropical line at 23º (equals the tilt of Earth, if you are doing a different tilt, adjust this); and in January same happens at 23º S.

baselineradiation.gif
Here's how I got this drawn:

1. First I defined a set of colors for "Very Hot", "Hot", "Warm", "Mild", "Cold", "Very Cold" and "Extremely Cold".

2. Then I drew a small 2 px line, East-West, halfway between the tropical line and the equator using the Very Hot color.

3. Then I measured the height North Pole to South Pole, in pixels and divided that by eleven. This gave me the width of each of the areas. Then, starting with the line I had drawn, I just kept expanding the selection by the number of pixels needed.

The result was this baseline "radiative" map. Note that I didn't take into account the curving of the latitude lines in the map associated with the projection. I took this liberty because I am only using the center of the map. You may have to devise alternative ways to create the baseline temperature if your map has a different projection. The point is to have this "striped" effect, ranging from Cold to Very Hot and back to Extremely Cold.
The pole facing the sun will start at Cold, whilst the other one will be Extremely Cold. In this case, the map is for January, since it's Summer in the souther hemisphere (that's the pole facing the Sun).


Time to take a rest before the second half....

EDIT: some spelling and grammar corrected