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Edit: ITCZ: https://en.wikipedia.org/wiki/Intertropical_Convergence_Zone As pointed out in comments.

I'm trying to figure out where exactly the ITCZ in my world will go (at least during its July-equivalent and January-equivalent peaks), and one thing I noticed when reading about it on Wikipedia is that it sort of "clings to" landmasses when there are landmasses present near a path that it would otherwise take over water.

Why does it do this? And, if it's passing over an area that is basically all land, how does it behave?

In the case of my January-equivalent ITCZ, when the star is closer to the southern tropic, I have some relatively small landmasses in water that it can easily cling to. But for the July-equivalent ITCZ, when the star is closer to the northern tropic, it's less clear - at the main continent, from 10 degrees north to 30 degrees north is all solidly far inland, with the bulk of landmass starting around the equator and not really easing off until 50 degrees north.

If the ITCZ's movement is influenced by elevation then there are some paths it could follow, but, the problem is that I don't actually know why it moves the way it does - does it "prefer" being over land because the land has greater elevation (which would make sense given that our July ITCZ has its biggest distortion at the Himalayas), or is there some other reason? I want to make sure I'm not misunderstanding why it acts the way it does so that when I add mine, it won't be based on completely incorrect premises.

Included is a map of the world with current placement of the July-equivalent (in red) and January-equivalent (in blue) ITCZ positions, as best I could estimate. Lighter areas on the map represent oceans.

ITCZ Tentative

I do apologize if this is something that is easily researched - perhaps I used the wrong search engine queries but while I could find plenty on the ITCZ's effect on prevailing winds and climates, I couldn't find anything that explained why landmasses affect its shape.

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    $\begingroup$ For clarity, could you tell us what ITCZ is, and what the (oddly blank except a few lines) picture represents. $\endgroup$ Jan 29, 2022 at 7:29
  • $\begingroup$ en.wikipedia.org/wiki/Intertropical_Convergence_Zone $\endgroup$
    – Monty Wild
    Jan 29, 2022 at 7:43
  • $\begingroup$ Thanks for pointing that out, I have added the link to the question. Regarding the picture, if you click and open it up at full size it should be more clearly visible and match the description given to it above, although it might not display well on mobile devices. $\endgroup$ Jan 29, 2022 at 8:20
  • $\begingroup$ Land and water respond very differently to the heat of the sun in daytime and to the cold of the night -- land is much more easy to warm up or to cool down than water. Land and water have almost always different temperatures, so that there is almost always some wind on the sea shore. But where exactly the ITCZ would be on your world cannot be answered without actually modelling and simulating the atmosphere. $\endgroup$
    – AlexP
    Jan 29, 2022 at 10:50
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    $\begingroup$ I've replaced the previous image & description with one which shows what I've currently tried, and will hopefully display properly. $\endgroup$ Jan 30, 2022 at 13:11

2 Answers 2

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It's where hot air rises

The ITCZ is a "convergence zone" because winds from north and south come together there. And then what? They go up, because they are hot. From there they spread out at high elevation and continue the Hadley Cell cycle.

The heat of land or sea drives the ICTZ, so it follows the hottest part of the summer from north to south and back over the course of the year. Note this depends on having an axial tilt something like Earth. (I have no idea what happens if a planet has an extreme inclination like Uranus, but if it has a zero inclination like Mercury the ICTZ will surely stay nailed to the Equator like a painted ship on a painted ocean)

The land "attracts" the ICTZ because at the peak of summer it can be hotter than the sea nearby in any direction. The air rising there sucks in the converging winds like a fire in a fireplace.

In your world, think about the surface temperatures when the Sun shines straight overhead. Think about the albedo and the heat capacity. If the sunlight is absorbed by black mats of floating autotrophs that become as hot and sticky as fresh roofing tar in the summer, maybe your oceans will pull in the ICTZ. If your deserts are covered in mirror-silvered grains of sand, perhaps they stay cool and the ICTZ skips rapidly from north to south there. It's impossible to give any one answer for all possible terrain, but if a world is Earth-like enough, it will have the same phenomena as Earth.

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I am not an expert but from all I have been researching lately Itcz doesn't climb on land but its pushed and deformed by pressure zones of high level and this reflects in by climbing land but not all. The ITCZ is a low pressure zone so it follows the thermal equator and low pressure areas and repulsed by high ones . Example Himalaya and the low on bottom of that during summer and the massive high zone beyond that during winter that pushes the Itcz away causing massive monsoon please correct me if I am wrong.

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