How To Make Wind and Influence Climate
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Hey, Porklet. I'm no climatologist, nor do I play one on TV. Nonetheless, like you, I'm interested. A few questions that may steer your wind planning & climates: what's your axial tilt? Is it the 23 degrees you refer to as a break point? Does your world have enough orbital eccentricity to accentuate or mute the summer/winter effects from tilt? Are these the only landmasses?
I have started a tutorial ( I need to apologize to Slipguard every time I mention it til I get it finished :-) ) on figuring wind and ocean currents. Some others here have written up how they figured things - in particular I recall seeing Naeddyr's amazing Ysi Earth II - that's the Featured Map page for it; follow the link to the WIP thread. It is an amazing stream-of-cartography lesson. Note that in the heat of battling climate issues, Naeddr swore off ever doing another such thoroughly rationalized climate map.... don't pay that too much heed.
A significant issue in figuring rain shadow effects is that with an axial tilt, those nice generalized wind patterns are going to oscillate north-south between summer and winter. So really, the only "reliably shaded" area would be one where both summer and winter general winds go the same way. Or same-ish way... Too, you won't get neat bands, unless you have a cue ball of a planet (or a mostly gaseous one - see Jupiter's and Saturn's banding). Instead, you get general highs and lows, with attendant clockwise and counterclockwise flow (flipping once you cross the equator) (and here one means "heat equator", roughly the latitude at which the sun at noon is straight overhead) (BUT strongly modified N-S by large land and sea masses). Also, any such pattern is the general airflow. There'll be plenty of weather activity that differs from time to time.
Got a used bookstore nearby? Grab a college climatology / weather textbook. A well-spent five to ten bucks. There's a wealth of info on the web too, but it helps to know the terms to search for. There's NOT many treatments of generalized arbitrary worlds - most understandably are Terra-centric.
"Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies" ( Wikipedia ) . Here's a map of one of my worlds showing general cyclone tracks.
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That planet has its own wiki (many people's work!) where I have a Cyclone distribution article that might give you ideas. A similar coverage of Earth's cyclones shows graphically the curving effects and where they spawn. You can see they just don't cross the equator.
So that's Q3. Q2 I'd wait to figure til you work out likely (or just plausible - there ARE no climatology police here :-) ) summer/winter patterns. Q1 - yep, you could get rain dumped on the upwind side of a range, and some of the rainfall running "around the corner" across the resulting dryer area, or maybe through a pass in the range. Remember if there's much of a cleft in a barrier range, the wet air will seep through too, muting the rain shadow effect. Or a continent-spanning river (cf: Nile) could catch rain in a wet area and run across unrelated dry areas.
Have you read Redrobes' river location tutorial? Ascension put a mini-tutorial in a post in a thread about where to place stuff. njordys put up a nice climate zone / rainfall map pair - you can infer the prevailing winds, but you need a January vs. July pair, which by the way shows what drives the ocean currents. Here's a prettier view - kind of the average of those seasonal prevailing winds. If you're used to thinking in terms of high and low pressures and what they do to weather, this pair are useful. The rules of thumb about what forms over a large-ish landmass or large-ish ocean in which season, will let you guess something like this for your world. Reason I asked if these were the only landmasses is that the behavior over an uninterrupted hemisphere-size ocean would lean more toward the ideal than our "continental high in winter" thought.
Not complex enough? Well, those are the surface winds. Another big driver in climate & weather is the jet streams, as you can see in many weather maps. They're pretty dynamic, so maybe less use in predicting average patterns. But if you're using your world for anything other than a pretty map, knowing when and where the storms run could be hugely important. this site has jetstream maps down at the bottom - there's more golden info all up and down it too. Such as a clue why some latitudes have much more of wet season / dry season, than what we temperate-zone folks think of as summer and winter. Then once you get all that air and water moving, it transports the very heat that drove the motion in the first place. THe mundane example is the 'abnormal' warmness of the northeast Atlantic thanks to the Gulf Stream. Generalized, that becomes a world map showing where heat gets shoved around.
Waldronate posted a couple of awesome links that go into more detail about the other factors driving currents, including deep-water ones.
Yeah, the forum's image-attacher thingamwhoozit sometimes glitches. For me a link is fine, 'stead of a thumbnail.
That's a decent progression of rain & wind, then currents & climate. Just be willing to iterate it a bit, as for instance the ocean currents influence the temperatures which goes back and affects the rainfall, etc. Or stop the thinking at any point you like and just MAP.... it's all your set of judgements, and the rare person who decides to nitpick your exact climate can feel free to redo it to suit himself :-). Me; I look forward to seeing your process in action, so do please keep us posted.
Originally Posted by jbgibson
Your planet would also rotate somewhat more slowly since it doesn't need to go as far to get that 24 hour day, resulting in much decreased wind patterns, weather, and climate. Also, I'm not sure a lot of Earth climatology models would be comparable with a planet with that much decreased surface area.
