[Award Winner] Where does the wind blow?

[jbgibson]

That said, how about prevailing winds like so in northern summer:

[jbgibson]

Stare at that a while and think - does it follow all the rules of thumb? Mmmmm - no, one I left out is that when the ITCZ migrates away from the equator, the inflow on the equator-ward side of it tends to switch direction. Think of it as the same as the way the southern lows have air spiraling in one way, while in the northern hemisphere it spirals the other. If there's a pronounced low *spot*, the spiraling bit holds, whereas if it's a trough, the 'ideal shifted ITCZ behavior' rules. So that means my two seasonal ideals need slight revisions, like so:

[jbgibson]

Yeah, my Aurora wind maps don't show that back-curving when the wind crosses the equator. Call them Version 0...

So that makes the 'completed' northern summer pattern look like:

[jbgibson]

Well, phooey. Now that makes SE Paidixira wetter in Summer. Dryish air sourced from that high to the SE, but it passes over ocean before it crosses The Cusp. The area's still pretty dry in winter, based on the location of the high. If this was my planet, I'd evaluate whether I needed The Cusp to be desert. If I was intent upon it being seriously dry, I'd think if I could plant a set of coastal mountains across the very south coast of The Cusp. If it was a pretty strong set of mountains, it would dry out the air on the lee side.

If you DO want The Cusp to be desert, hmmmmm.... I could probably consoldate the two summer highs south of Paidixira into one, that hangs near The Cusp. Of maybe strengthen the leftmost and drag it near The Cusp, and shove the right one out in the ocean a bit to the right of where it sits now. <shrug> What do you think, Slipguard?


Before I go on to the northern winter, does this make sense? I have further explanation in mind related to this atmospheric circulation stuff, such as the rain shadow effect, how these surface winds drive ocean currents, and typical tracks of tropical cyclones.

[Slipguard]

This all clears the waters, yes. I think the direction you're going in is clearly defined, and I think I want to follow it. The Cusp simply has to be impenetrable for an invading force. It could definitely work as a dense tropical jungle story-wise. Summer precipitation gets my green light, sir!

P.S.If the Cusp goes that direction could those kinds or densities of jungle show up elsewhere in Paidixira, like say, in Valpyra or Komagi, or would the Cusp's biome be unique compared to the rest of the continent?

P.P.S. What do you know about how the placement of trade winds and pressure centers effect sailing routes?

[cantab]

I'm working on a planet that's rather different to Earth, and I'm unsure how that will affect the atmospheric circulation. It's rather smaller (5716 km equatorial radius), but has higher surface gravity (1.1g) due to having a big core. Its day length is 11 hrs 32 minutes, and the axial tilt's about 10 degrees. I'm wondering if that increased rotation speed will result in there being more than three circulation cells.

[jbgibson]

I've read that with faster rotation, the cells can "tear" into more - five N and five S next, I assume. Look at Jupiter and Saturn for a "many bands" effect. Of course their parameters are WAY different from Earth or your planet. My gut feeling is doubling the speed won't spawn more circulation bands, but that's based on no expertise whatsoever.

Hmmmm... but in looking up books on the subject of planetary circulation, I ran across a guy I work with as a reviewer.... let me ask him if he knows useful texts on the subject, or if he has one I can borrow.

Small world....

[Cookierobber]

Wow, this is a great tutorial, really informative. I was wondering though, how can you tell what latitudes the high pressure (30 degree-ish) areas and low pressure (60 degree-ish) troughs will move to during the summer/winter? I understand that the ITCZ will move to the tropics of cancer and capricorn, and will bend away from the equator while over landmasses, but how do you tell how far these areas will move?

[jbgibson]

How far? Insanely wild guesswork, tempered by a look at what happens on Earth. Honestly, any of this wind & climate work is so far into pure fantasy that I should be drawing dragons on all the updrafts, and fairies on the downdrafts -- it's plausibility built on a duct-tape and baling wire foundation that I'm shooting for. Nobody, absolutely nobody (excerpt internet-type trolls) will question your work, but will instead be blinded by your science and will marvel in awe at the pretty winds. Don't tell yourself your suppositions are tissue-paper constructs, but rather repeat to yourself that this is how it IS on this world, because you SAY SO. If you are male, do this in a manly growl, thumping your tankard of ale on the table authoritatively. If female... I dunno - some aspiring female climatologist tell us how to be assertive in one's head, ok?

My goal in adding complexity to a world this way is to get all the delightful odd turns and unexpected revelations that I wouldn't have thought of in a vacuum. "Oh, so over here would be an eddy, huh? That's cool." "and over there the rain would be monsoon-crazy for two months then would be missing for ten... " and from that starts to grow in my head a picture of the culture, the people, the social geography.

Back to your question - how far will the ITCZ move poleward over landmasses? As far as suits you. Figuring that these curved winds can't plausibly make right angle turns... maybe letting how the parallel circulation lines 'want' to fill in gaps be the driver. If the ITCZ is the 'heat equator' and vertical circulation is dumping wetness thereabouts, then let your imagination paint jungles and rain forests and swamps as far poleward as that line wanders -- if imagination is intrigued by a certain peninsula maybe being heavily treed and populated by more Holliphants than lawyers, then tell imagination "imagination, good job. that's right where physics says the ITCZ line goes." Then look over at nearby people and lift an eyebrow, with a firm "What?!". What business is it of theirs if you voice both parts in a dialogue between Reason and Imagination?

Then based on that 'seasonal heat equator' I'd shift highs and lows to be somewhat evenly distributed. If that pushes two highs rather close together, I'll squint and make a snap decision that maybe those would coalesce into one larger high. Or I'll take a less snappy tack and say some years one gets two weak highs, vs. other years a stronger single, with consequently differing weather driven by the climate generalities. SO all of a sudden my mariners have a reason to be unsure WHICH year they'll return to port, since favorable winds happen only one year out of three across this certain stretch. And ashore, the wheat crop fails for that one year in three, when rains are too heavy for optimum growth. More autogenerated details, like the fractals beneath the terrain generation I started with, or genning character traits for roleplaying with dice.

[Jalyha]

Don't tell yourself your suppositions are tissue-paper constructs, but rather repeat to yourself that this is how it IS on this world, because you SAY SO. If you are male, do this in a manly growl, thumping your tankard of ale on the table authoritatively. If female... I dunno - some aspiring female climatologist tell us how to be assertive in one's head, ok?

If you are female, do this in an only-dogs-can-hear-this high pitched shriek, thumping your broom against the head of anyone who questions your god-like world-building authority. ...Authoritatively.