View Full Version : Weather for my planet Anicca

05-24-2013, 09:15 AM
Hey there,

I'm trying to figure out the climate for my planet Anicca. I read the Climate Cookbook, jibgibsons tutorial where does the wind blow, but I'm not so good at english, at least not with technical terms, and I'm not sure if I understood everything. I tried to do two maps, July and January. The red line is supposed to be the inter-tropical convergence zone and the violet dots are low pressure areas and the turquiose dots high pressure areas. Did I do this right? I'm not sure if the line is even correct. I'm just looking for some advice to point me in the right direction.



In the end I want to place climate zones, but I think I have a long way to go there. The light green areas on the map are mountains. The map is from fractals, but I think I can somehow change the mountains, if they are not correct.

05-24-2013, 12:32 PM
Assuming you are using a three-cell model (like Earth actually has), then you would also have a region of low pressure around 60 degrees latitude. This is where the polar front lies, where cold air from the polar regions intersects with warmer air heading poleward. On Earth, this causes the semi-permanent Icelandic low and Aleutian low in the northern hemisphere but no such features in the southern becuase there is no land at that latitude.

On your world, this would probably mean two, maybe three semi-permanent lows in the northern hemisphere, one in the far northeast of the map over the ocean, another or maybe two in the sea in the top middle of the map. Probably two in the southern hemisphere as well, one in the far southwest and the other in the very bottom middle. These low pressure areas would of course migrate seasonally, just like the ITCZ.

Once you have the semi-permanent highs and lows in place, then you can work on the average wind flow patterns, because the wind will be affected by the highs and lows. Remember that air flows clockwise around highs and counter-clockwise around lows.

Here is a pretty good resource giving the basics: Observed average surface pressure and winds during January (http://apollo.lsc.vsc.edu/classes/met130/notes/chapter10/january_surface_press.html)

05-24-2013, 08:48 PM
Remember that air flows clockwise around highs and counter-clockwise around lows.

I had not known that. If you can explain it in a few words, what is the cause of this phenomenon?

05-24-2013, 10:36 PM
I had not known that. If you can explain it in a few words, what is the cause of this phenomenon?

First, I should note that this is only true in the northern hemisphere. It is the opposite in the southern. I have never had to forecast weather for the southern hemisphere so I forget about that.

Briefly, it is the combination of the pressure gradient force and the Coriolis force. The pressure gradient force causes air to flow from high pressure to low. The Coriolis force is a deflecting force caused by the rotation of the Earth. It causes moving air parcels to be deflected to the right in the northern hemisphere. Thus, air that is moving out from the center of an area of high pressure will be deflected to the right, or clockwise. Similarly, air moving into the center of an area of low pressure will also be deflected to the right, making it counterclockwise around the low in this case. In the southern hemisphere, the Coriolis force deflects parcels to the left, so clockwise and counterclockwise are reversed.

05-25-2013, 12:00 PM
Ah, thanks! I'd figured the Coriolis force played into it, but I hadn't thought through what actual effect of the pressure zones would have on the air. That makes perfect sense.

You know, for years I had access to a very good meteorologist at work, and it never occurred to me to quiz him for help on my map-making and world-building.