I'm currently designing a large scale D&D based campaign, magic is based on winds and weather coming from two points, the 'northern pole' and the 'southern pole'.

Currently the "world" is a centralised giant continent (hypothetically oval) with a spread of mount ranges through the middle, splitting it. This is taking into account two smaller continents clashing in tectonic fashion and volcanic regions around the equator in the early stages of the planets development.

However within this "world" is a clearly defined North and South pole, in which magic flows; 'dark' from north, 'light' from south. However to keep the campaign as realistic as possible I need a way of determining the flows of a current/weather patterns around this entire "oval"-like continent. Does anyone know of ways I could work this out, or even ideas on how the currents would work? Northern/southern hemisphere weather taken into account as well? Season wise the world follows a regular pattern of change, with Spring, Summer, Autumn and Winter. I was very unsure of how the centre of the "super-continent" would work, would winds/weather reach this far down, and in such a strong mountain range? However most rivers would flow from these ranges, and gather in lakes and streams the more out of the continent centre they flow.

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    I'm currently in the process of asking a series of questions that will help with this, although we haven't yet reached weather patterns. The first one is here: worldbuilding.stackexchange.com/questions/581/… – Tim B Oct 8 '14 at 15:41
  • There are no four seasons near the equator, so your continent cannot be both centered and have four seasons. – celtschk Oct 8 '14 at 16:43
  • how far is your continent stretching north-south in latitudes? what is the axial tilt (inclination) of the planet? How big is your planet? How fast does it rotate on itself? – Vincent Oct 8 '14 at 18:02
up vote 6 down vote accepted

Short answer: (really!)

Ocean: it depends on how big your continent is but normally, the ocean currents are influenced by 3 things: the winds, the Coriolis Effect and the landmasses

  1. Winds are influenced by the difference of pressure between the different regions.

    The equator and its surroundings is typically a low pressure zone. This is because it is the hottest place on Earth. Hot air rises and the surrounding air masses converge there to fill the gap. It's a convection movement. The air rise and then moves toward the poles. It cool off with time and eventually the pressure increase is dragging the air mass down near the 30th of latitude. This is know as the Hadley cell.

    On the poles, it is very cold. Here, the air is not ascending but descending since it's a high pressure area. The air moves toward the equator and is getting warmer until it reaches the 60th latitude. At that latitude, the air movement is ascending. This is the Polar cell.

    It the middle, you have the mid latitude cell, or Ferrel cell. The dynamic is mostly imposed by the other 2 cells and it just follows a logical continuation of the same convection movement. At 60th of latitude you have ascending air from the pole and from the mid latitude. The air converge there.

    At the 30th of latitude, you have descending air. The air in this cell rise at 60th and sink back at 30th. If your a visual person like me, take a look at this if it's still not clear: http://en.wikipedia.org/wiki/File:AtmosphCirc2.png

    to summarize

    Poles : sinking air= dry

    latitude 60: rising air= humid

    latitude 30: sinking air= dry

    Equator: rising air=humid

    *This is just a general rule. These areas are always moving on Earth according to the seasons and are influenced by different factors including the landmasses.

    Rising air, this is when you have the precipitations. Other factors also generate precipitations but this is the most important. Rising air is hot near the land but cools off when ascending in the atmosphere. The colder air cannot contain as much humidity as hot air and this water needs to fall down. The sinking air is always dry since it already got rid of most if not all the humidity it once had.

Wind interaction with land: As I mentioned earlier, hot areas will generate low pressure. Your continent will always be hot since it sits on the equator. If it is large enough, it might trigger the mega monsoon mentioned by Ivy_lynx. It is not easy to extrapolate what we know to an extreme case. Asia is dragging the low pressure area of the equator up north as far as Shangdong China and even beyond. This is because the northern hemisphere gets really hot. I'm speculating a bit here, but in your case the continent (unless it is stretching far from the equator), would probably not have this dragging effect. The low pressure zone would move north and south but not enough to meet the low pressure of the 60th latitude.

2- Coriolis effect: it tends to deflect the currents in a clockwise manner in the northern hemisphere and counter clockwise in the southern hemisphere. By itself, it doesn't make the currents, it really just deflects them. http://en.wikipedia.org/wiki/Coriolis_effect

Coriolis+wind= it's the same result as with water. At the equator and at the mid latitudes, you have a low pressure area that is drawing the air in. Near the equator, the Coriolis effect is directing the winds and water currents toward the west but towards the east in the mid latitudes.

3-Interaction: water+land+Coriolis: the water currents will converge at the equator. At this latitude, the water flows east to west. Then, when it reaches the coasts of the continent, the water will be deflected toward each poles.

The next step depends on the size of the continent. Normally, it would flow towards the pole until the mid latitudes between 30th and 60th and then be pushed toward the east by the dominant winds. One part of the water will probably go poleward of the continent following the dominant winds (west to east). Then, my guess is that without any other landmass, most of the water will reach the opposite shore of the continent and will be deflected back toward the equator.

At the poles, water would just spin around like it does around Antarctica. I made you a very nice image :http://sketchtoy.com/63277181

I think I've covered all the bases. I just need to know the specific information to give a more precise answer. But I might not be able to

  • I was waiting for Tim B to write a question about the weather to write my answer. Weather would need to be divided in at least 3 questions to make it more manageable. winds, ocean currents and precipitations. Here I have been rough around the edges a little. – Vincent Oct 9 '14 at 1:27
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    Yeah, I'm trying to post the questions one at a time in case one needs to build on the answers from the previous one and while the erosion one has a good answer it could still use more. I'll be posting the next question soon though. – Tim B Oct 9 '14 at 7:03
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    The third question can be found here: worldbuilding.stackexchange.com/questions/1353/… – Tim B Oct 9 '14 at 12:21

Going by the example of the theorized Pangea and what weather is assumed would exist for it (Pangean Megamonsoon) it seems there could be serious problems caused by the weather.

Pangea is also assumed to be elongated in the direction perpendicular to your island, which prevented most of it from becoming a desert, assuming the theory is correct of course.

I'm no meteorologist, but going by this theory, the north and southern coasts should be the only temperate areas. I don't think the mountain range in the middle will have a huge effect, since the primary expected effect would be a rain shadow, but it's in the arid region anyway. It could however change how storm systems form but I'd expect them to be quite large and violent since there's lots of ocean for them to form over and grow on.

I don't have the expertise to make any assumptions about how closely your island would follow standard island meteorology, nor what the total effect of the huge ocean would be, but I'd expect things to be extreme.

  • I have not heard of the Pangean Megamonsoon and brings to light problems and solutions to continue with the "mega-continent" idea. Surprisingly completely forgot about our own planet being one landmass! – FirstCape Oct 8 '14 at 16:01

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