Step 1 basic elevation map
The first step is to make the elevation map. I made one level of elevation for each 1000m above sea level.
I added several others layers of elevation under 1000m but they are mostly aesthetical.
And by the way, it will also help a lot if you have latitude/longitude lines since we will refer to them all the time.
elevation map legend.png
color altitude.png
Step 2 oceanic circulation, surface currents:
Reference maps:
A simple one:
0908B.jpg
And another, more detailed: https://upload.wikimedia.org/wikiped...erless%293.png
Color signification:
- · Blue: Polar currents are cold between the poles and the polar circle. Currents flowing toward the equator are cold if they originate from these regions.
- · Red: Equatorial currents are hot, including those flowing from the equator toward the poles.
- · White: Mid latitudes currents are mild. Hot current flowing poleward eventually get mild. And cold current become mild when they get closer to the equator. Mild currents also happen when cold and hot water are mixed.
Close to the equator, you can omit the transition to mild because at this latitude, water temperature has little impact unless it’s very cold.
Mapping the currents:
1. Close to the equator there are two currents flowing westwards.
2. As these two currents meet a large landmass they diverge away from the equator, toward the poles.
They will stick to the eastern coast of that continent approximately until 40ş to 45ş of latitude. They are hot: draw them in red.
3. At about 45ş, the Westerlies (West -> East winds) are strong enough to create an eastward current. It gradually shift direction toward the east.
As it cross the ocean it can sometimes be tilted a little toward the north east. Draw in red and use white if the current drifts far enough from the continent.
4. When this current meets continental shores, it spreads north and south following the coasts.
The currents moving back to equator will get slowly warmer. The part that flows north continues to cool slowly.
5. Poles: If you have polar oceans, you need to close the loops.
Cold current flowing back to mid latitudes tends to stick to the coast until they encounter the hot currents mentioned at point 2.
They fill the void left by the north-eastward movement of this hot current and then turn abruptly to the east. In the current map: see the Labrador Current east of New England.
Near the poles, the currents are flowing from the east to the west. This only happens at very high latitudes (over 70 degrees approximately), where the polar easterlies are the dominant winds.
oceanic currents new.png
Step 3 : Atmospheric pressure systems
The hottest place is near the equator. It’s the Intertropical convergence zone, ITCZ for short. The air rises.
The poles are the coldest, and the cold air sinks.
The position of the pressure systems changes over the course of the year, with the ITCZ roughly located where the planet receive the most energy from the star. It should be close to the tropic n the summer but the position is influenced by the actual temperatures. Land heat up more than water and large landmasses will pull it to them. This mechanism is the main engine of the atmospheric circulation.
Look here for a detailed explanation of atmospheric circulation: https://en.wikipedia.org/wiki/Atmospheric_circulation
The ITCZ, a low pressure system
Close to 10-15° normally. During the summer, the movement of the ITCZ is strong in Asia but limited elsewhere. In order to have an impact, continents need to be large, hot, with significant landmasses around the tropics.
The position of the ITCZ is not always clearly defined. The Intertropical latitudes are always hot and therefore, there is a consistent low pressure system.
A. High pressure center
Oversea:
Cold season: 30° in a more or less continuous line
Hot season 35° separated, mostly on the eastern side of the oceans
Tend to be located on the eastern side, close to the continents because it’s where the cold currents are flowing.
In summer, the high pressure system breaks apart as the continents are affected by low pressure systems due to hotter temperatures.
Inland:
Cold season: high pressure systems develop over the continents (including the poles). Larger continent = higher pressure.
Hot season: hot temperatures prevent the formation of high pressure systems.
The inland systems tends to be poleward of the high pressure systems that are over the ocean.
Areas between the tropics are not cold enough to become high pressure but it does not mean that the pressure is low.
B. Low pressure systems:
Oversea:
Cold season: Centered around 55°
Hot season: Move 5 to 10° closer to the poles
They tend to disappear over the land.
Inland:
Cold season: No low pressure overland.
Hot season: large landmasses become hot and the low pressure can cover most of the continent.
January
jan pressure.jpg
July
jul pressure.jpg
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