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PostPosted: Mon Jul 12, 2010 2:26 am 
Sanci
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Torco wrote:
Shihali wrote:
Could somebody outline the conditions for a relevant monsoon pattern to form? I have a con-continent in the tropics shaped vaguely like Africa, and I'm not sure whether it should have an important monsoon.


From what I know, strong seasonal patterns [so a big axial tilt, I guess, or some other seasonal cause, like eccentricity] and a big enough continent makes sufficiently low pressure areas in the center of the continent in the summer to draw in a lot of moist air from some nearby sea. As this wet air rises it cools and no longer can hold moisture, which falls. This means summer rain.

Thanks. Does crossing the equator matter?

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PostPosted: Mon Jul 12, 2010 2:47 am 
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Shihali wrote:
Torco wrote:
Shihali wrote:
Could somebody outline the conditions for a relevant monsoon pattern to form? I have a con-continent in the tropics shaped vaguely like Africa, and I'm not sure whether it should have an important monsoon.


From what I know, strong seasonal patterns [so a big axial tilt, I guess, or some other seasonal cause, like eccentricity] and a big enough continent makes sufficiently low pressure areas in the center of the continent in the summer to draw in a lot of moist air from some nearby sea. As this wet air rises it cools and no longer can hold moisture, which falls. This means summer rain.

Thanks. Does crossing the equator matter?


I figure it does; the Indic Occean is, after all, right over the equator, so it might be that it's pretty hot by the time summer comes, and with all that vapor running around, and a huge low pressure area right above India and whatever, it's kind of a recepy for monsoons.

I imagine bigger axial tilt would make monsoons more likely ?


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PostPosted: Mon Jul 12, 2010 2:52 am 
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Anguipes wrote:
The moving ICTZ causes the specific latitudes and absolute sizes of the cells to expand and contract, but not these proportions. The presence or absence of land also does not significantly affect these boundaries [confirmation needed].

I remember reading something once (can I find it now? Of course not!) that argued that the Mediterranean was an example of how really extenuating circumstances can slightly modify the proportions. IIRC, it was a perfect storm, so to speak between the Gulf Stream artificially warming European winters along with the really large amount of inland seas in the area preventing too much cooling (not just the Mediterranean, but also the Black Sea to a limited extent), and on the other end of the spectrum the Sahara (for reasons seemingly mostly unknown) has started to discourage the ICTZ from heading north. That said, the difference from what it would have been anyway (again IIRC, and from looking now at a map) was less than ten degrees, if not stunningly small.

Thinking about it now, it seems more like the temperate zone is merely more concentrated, having a sharper transition zone in the Maghreb (for comparison wiki the climates of San Francisco and Lisbon). Meanwhile, for reasons unclear, the ICTZ actually is having difficulties extending as far north as it should into Africa.

So, yes, almost all of the time, things should be proportionate, roughly.

@ Shihali: Monsoons are the part of climates that I am weakest on, but (assuming you mean the continent is cut by the equator) I don't think that would work. Monsoons work best where the continent can become seasonally cooler than the surrounding waters, which just can't happen in the tropics (but can and does in the subtropics). I could see an equatorial supercontinent with the highest elevations in its northernmost and southernmost areas perhaps having slight monsoon patterns, but nothing like Asia, let alone North America.

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PostPosted: Mon Jul 12, 2010 5:56 am 
Sanno
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Monsoons are complicated, and nobody understands them.

There are five distinct things going on in a monsoon climate:

- ordinary seasonal variation is at a peak. Ideally, the ICTZ is over a region in one season and a long way away for another season, so you get strongly seasonal rainfall.

- rainshadow effects. Mountains can cause the heavy rainy season to be even heavier, exagerating the difference. Even more exceptionally, if seasonal variations cause the direction of winds to change considerably, seasonally, this can become very important when there's a mountain range involved - the rain can fall on one side in the wet season and the other in the dry season (when there isn't much to fall anyway), which further exagerates the difference.

- big blobs of land. These result in stronger pressure fluctuations between seasons, which results in air being pulled onto or off the land. The differences are higher on the eastern sides of continents.

- mountains! As well as creating rainshadows, mountains also exagerate pressure differentials - high mountains have low pressure air which helps suck up wet water from the ocean.

-longitudinal effects. We easily understand latitudinal circulations, but longitudinal effects are a lot harder to work out. Basically, there's a big pressure differential between eastern asia and the western pacific, which causes wind to move between them - but this interacts in a complex way with normal latitudinal pressure differences, through mechanisms such as counter-currents and ocean heights. In essence: when you've got an ocean with an equatorial current, warm water is moved from east to west. This makes the sea higher in the west. This causes water to move away - partly in the powerful western boundary currents, but also partly in a counter-current that slips between the two main equatorial currents, in the opposite direction. The relative balance of these currents is vital. Strong boundary currents reduce the warm peaks, but disperse warm water poleward, bringing rain further from the equator; strong counter-currents move warm water back to the east. If the counter-currents are very weak compared to the equatorial currents, there is a huge mass of very warm, wet, high-pressure water in the west. In summer, this combines with the low pressure over land to create lots and lots of rain. Eg China. But if the counter-current is strong, there is less warm water, so the monsoon effect is weaker. But we don't know exactly what governs the strength of the currents. AND the currents change over time - hence 'El Nino'. AND in the Indian ocean we have complications because the basin isn't big enough for a nice symmetrical current system.


----

Also, I don't think 'monsoon' is that helpful a term. It's nothing unique, just an exageration of normal processes - a dividing line will be artificial.

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PostPosted: Mon Jul 12, 2010 3:14 pm 
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So, Sal, to bring it back to the original question, the first requirement on your list makes it impossible (or at least very, very difficult) for an equatorial continent to have a Monsoon, right? If the ICTZ is crossing the continent at the equinoxes (roughly, in theory) as well as caught on either end of the continent at the solstices (again, this is assuming somethings about size of the continent and other landmasses nearby, but still), then the continent will always experience roughly similar equatorial weather (with some locally-defined seasonal changes in rainfall with minor temperature changes, but the opposite of a continent-wide seasonal shift).

A quick comparison helps - northern South America or central Africa are more like what you'd see in that situation than India or China.

And that is why you need to have a continent that is (at most) subtropical in order for it to attract the ICTZ from a distance as it's in the tropics.

EDIT: Yes, I'm using monsoon, but just as a shorthand for particularly strong seasonal ICTZ rainfall patterns. Imprecise, but concise.

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PostPosted: Mon Jul 12, 2010 5:30 pm 
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I'm not sure, actually. A big continent can make for pretty big deflections of the ITCZ. And then you've got to take the longitudinal and altitudinal effects into account.


Also: do you mean monsoon climate or monsoon winds/rainfall? West Africa is said to have monsoon winds and rain, since it's based on complete reversals of wind direction, but it doesn't have a 'monsoon climate'.

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PostPosted: Sat Aug 07, 2010 9:24 pm 
Lebom
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Back to the first page with you!

And I do have a question: How do you determine the climate of small islands? I'm assuming if they're close to shore, they'll share the climate of the mainland, but how far out do they have to be to lose that influence? How about remote oceanic islands like Hawaii, what factors affect their climate?


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PostPosted: Mon Aug 09, 2010 3:05 am 
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Really like this! The GIMP hints are really useful for a GIMP noob. Hope you're still on this and that we'll see something about oceanic currents.

Some questions though:

1) What would be the overall effect of massive patches of ocean and relatively few, compact patches of continents? For instance on Mogna there's nearly no land in the northern hemisphere and half of the southern one is a huge system of islands and continents.

2) Any idea how a (fantasy) floating continent would affect climate, pressure and the like? Well, at least I 'know' (rather 'decided') that floating continents on Mogna have their crust producing some kind of dense cloud from which a lot of water falls on the surface, although this water has some properties making the land below a dense jungle with very tall trees; and that area is pretty much like ocean when talking about heat capacity. But then, if anyone has any idea...

(More on the soft-science side for me)


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PostPosted: Tue Aug 17, 2010 7:22 am 
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I fully intend to get back to this :wink: And a quick reminder: DO NOT TRUST WHAT I SAY. I KNOW NOTHING THAT CANNOT BE GLEANED FROM A COMBINATION OF THE INTERNET AND TOO MUCH TIME. NOTHING!

Quote:
1) What would be the overall effect of massive patches of ocean and relatively few, compact patches of continents? For instance on Mogna there's nearly no land in the northern hemisphere and half of the southern one is a huge system of islands and continents.

In very rough terms, the more concentrated land and water areas are the greater their relative effects and the more extreme the climates produced. Lots of scattered islands produces more moderate climates.

Quote:
2) Any idea how a (fantasy) floating continent would affect climate, pressure and the like?

Addressing generally, the factors to determine are elevation (both of the land itself and how far between the continent and the ground level) and size of the continent, whether it is over land or sea, and whether or not it moves significantly. A short cut would be to just treat the area as have exceptional elevation and leave it at that. More interesting is what happens underneath a floating landmass - the sun is blocked, creating low temperatures and high pressures directly underneath. If the continent is large and stationary this could go as far as to lead to an extreme arctic area underneath it. An area of high pressure would probably form under any size of floating continent/island, strength depending on size, which would affect the winds of the surrounding area if not the continent itself. (And from there, surface sea currents, at least potentially).

Up high enough a floating continent would also bugger up upper atsmophere workings, but I haven't yet looked into that.

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PostPosted: Tue Oct 19, 2010 4:42 pm 
Sanci
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Oh, I missed that reply.

About the floating continent, high pressure is what I expected, although I really forgot about it possibly blocking sunlight... So yeah, I have to know at which elevation it is. In any case, I like the idea...

Then, floating continents work in such a way that they rain below. Their rain is peculiar in that it has a high density of samri, an element toxic in high doses for organisms not evolved to live with such doses. The region under that floating continent (which is mostly land) would have very unusual fauna & flora.

Anyway, you should get back to this! There's a lot to tell :P

Edit: Oh, just saw your other post about your issues coming up with rainfall and all. Good luck figuring it out then.

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PostPosted: Tue Oct 19, 2010 4:48 pm 
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I was wondering what happened to this thread.

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PostPosted: Wed Oct 20, 2010 1:29 am 
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It's a surprisingly hard subject. I suspect a lot of people are looking back at things they've said(at least I have) and said, "Wait, is that right?" There are a lot of complicated feedbacks in climatology and it's not always clear which will dominate in any given situation.

For my part, I'd like to see a lot more discussion on this, but I'm kind of blank till I get further along on my current crop of conworlds.

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PostPosted: Wed Oct 20, 2010 5:33 am 
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pwanlai wrote:
I was wondering what happened to this thread.

I got a life.

The two major problems I have with continuing for the moment are ocean currents and rainfall. Ocean currents always look like they should be easy, but once you take away the year-round oceanic high pressure areas that Earth has it gets complicated. Rain is a bastard because there are so many factors involved, and they all affect each other.

I am very maybe possibly if I can find the time, equations, code snippets and support, thinking of writing a program* to automate some of this crap.

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PostPosted: Wed Oct 20, 2010 8:55 am 
Avisaru
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Anguipes wrote:
Rain is a bastard because there are so many factors involved, and they all affect each other.

I am very maybe possibly if I can find the time, equations, code snippets and support, thinking of writing a program* to automate some of this crap.


A chat or two with a geography teacher or university staff member might help, too; every so often I've thought about approaching such higher sources of knowledge with the intention of writing a program myself, but I've always lacked sufficient round tuits.

However, you can still divide-and-conquer by taking advantage of some special cases, for example:

Code:
def probabilityOfRain(location, time):
    if location == "Manchester": return 1.0

    # rest of function

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PostPosted: Wed Oct 20, 2010 10:11 pm 
Lebom
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bricka wrote:
Code:
def probabilityOfRain(location, time):
    if location == "Manchester": return 1.0

    # rest of function


A suggested addendum:

Code:
def probabilityOfRain(location, time):
    if location == "Manchester": return 1.0
    if location == "Texas" and getMonth(time) >= 6 and getMonth(time) <= 9: return 0.0000000001

    # rest of function

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PostPosted: Thu Oct 21, 2010 12:39 pm 
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Incidentally, Bricka, I'm unable to access your website anymore! Did I miss where it got taken down or moved or something?


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PostPosted: Thu Oct 21, 2010 12:42 pm 
Sanci
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Whimemsz wrote:
Incidentally, Bricka, I'm unable to access your website anymore! Did I miss where it got taken down or moved or something?
Think his host terminated its domain or something like that. I still have the Climate Cookbook printed though... without the pictures :P But I did get a sad face when I tried to access his survey of vowel inventories; I really liked it to get ideas.

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PostPosted: Thu Oct 21, 2010 1:37 pm 
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Opera wrote:
Whimemsz wrote:
Incidentally, Bricka, I'm unable to access your website anymore! Did I miss where it got taken down or moved or something?
Think his host terminated its domain or something like that. I still have the Climate Cookbook printed though... without the pictures :P But I did get a sad face when I tried to access his survey of vowel inventories; I really liked it to get ideas.


Actually, I got tired of paying for it every month.

In case you don't know, some nice ZBB members offered to mirror the pages I wanted to keep; here are the links of those which are still around:

http://bricka.penguindeskjob.com/
http://jc.tech-galaxy.com/bricka
http://zbbarchive.freehostia.com/bricka/

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PostPosted: Thu Oct 21, 2010 2:10 pm 
Sanci
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Oh, neat, thanks for those links!

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PostPosted: Tue Nov 02, 2010 9:31 am 
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Writing some software to handle various climate-related calculations has gone from "pipe-dream" to "looking possible". I've started on a library of temperature-related functions, and once they're done I should have a program capable of taking a greyscale heightmap image (plus some variables) and outputting land, sea and air temperature maps for any time of year.

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PostPosted: Tue Nov 02, 2010 12:07 pm 
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Exciting! I look forward to seeing that.

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PostPosted: Tue Nov 02, 2010 2:39 pm 
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Oh yes!!!

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PostPosted: Wed Nov 03, 2010 8:19 am 
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I *really* like the sound of this app. Really really :D

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PostPosted: Wed Nov 03, 2010 8:46 am 
Lebom
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Anguipes wrote:
Writing some software to handle various climate-related calculations has gone from "pipe-dream" to "looking possible". I've started on a library of temperature-related functions, and once they're done I should have a program capable of taking a greyscale heightmap image (plus some variables) and outputting land, sea and air temperature maps for any time of year.


Well that is some good news well recieved today. :)

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PostPosted: Fri Nov 05, 2010 3:31 pm 
Sanci
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Any chance of your exposing the source code?

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