So Earth has an axial tilt and that creates weather regions. For example, approximately 23 degrees north and south, approximately the same as the planets axial tilt, will give you the tropics. This creates a band around the Earth of warm wet climate. But then there are these climate cells as well. The Hadley cell occurs at 30 degrees north and south. This apparently creates low pressure and high pressure zones of hot air rising, condensing with rain, falling and cooling, etc.

So what the difference between the 23 degrees and the 30 degrees? I thought that tropics are created because of at 23 degrees tilt which also causes seasons? But then they are also created because of Hadley cells? They seem to have the same effect with 2 completely different systems. Why are there both? And what happens between 23 and 30 degrees?

  • $\begingroup$ @DefinitelyAHuman, welcome: Not clear to me what you're asking. Looks like your standing in front of a drawing of the global atmospheric circulation and loosing directions :-) Maybe it helps understanding that it's not only the axis tilt, but also the arrangement of continents, sea currents, vegetation, ... and so on, and seasonal wanderings e.g. of the ITCZ, monsoons created by temp. differences of huge landmasses ... or, in short, not only the axis tilt influences global curculation. Is that what you're after ? $\endgroup$ – user20217 Jun 23 '20 at 8:39
  • $\begingroup$ @a_donda , okay i'll try to clarify. I guess my question is more about the actual lines of longitude of climate regions and weather cells, and how they relate to one another. So the hadley cells are from 0 to 30 degs. Then you've got the high pressure to low pressure cycling in the cell. okay that makes sense. But then what is the significance of the 0 to 23 deg that creates the tropics lines? why bother having those tropics lines at all? what is the significance of 0 to 23 deg that cant be explained by the hadley cell at 30 deg? I thought that the tropic lines explained a climate zone but... $\endgroup$ – DefinitelyAHuman Jun 23 '20 at 23:29
  • $\begingroup$ @a_donda ...from looking at the weather cells those seem to be a much better explanation of climate zones. so how do the lines of longitude (23 deg and 67 deg) relate to climate zones? what do they bring to the table that cant be explained by weather cells and everything else youve mentioned (vegetation, ocean current, tech plates, etc)? $\endgroup$ – DefinitelyAHuman Jun 23 '20 at 23:32
  • $\begingroup$ Climate zones are a different thing. They are recorded and documented also to have a comparison to the past and see the change over time (see: Köppen classification). Nature does not obey a general circulation model, even if the earth was an ideal lambertian sphere with a smooth grey surface (how boring :-)). The weather doesn't change principally when one crosses 30°N. I think you understood the principle (energy from the sun and all that), now go for the details. $\endgroup$ – user20217 Jun 24 '20 at 10:26
  • $\begingroup$ The number of hadley cells on a planet is determined not by its axial tilt, but by the strength of the coriolis force, i.e. planetary rotation speed and radius: earthscience.stackexchange.com/questions/992/… $\endgroup$ – AtmosphericPrisonEscape Jun 24 '20 at 13:15

Generally speaking, the tropics are a geographical term. It's the area on the surface of the planet where at least once a year the Sun passes directly overhead.

It has relation to climate, but even then within the tropical region you have a variety of climate zones from rain-forests all the way to savannas and deserts. Being in tropical region only ensures that it's generally warm all year round, other parameters define the actual climate type. Take a look here at the range of climate types available in the tropics.

Now, coming to Hadley cells and how they relate to tropics - they are not directly related to one another, i.e. one of them is not used to define the other.

In Hadley cell the humid air rises and moves north or south depending whether it started north or south of the equator and then sinks to the surface at around 30 degrees north and south of equator. So they are both dependent on the same factors, namely the simple fact that it's generally hot in the tropical region.

What happens between 23 and 30 degrees really depends on where in the world you are. If you're between 23 and 30 degrees in North Africa, it's very unpleasant, because Sahara is right there. Other places are different depending on their own geographical and climate parameters.

  • $\begingroup$ thanks @pavel appreciate the response but its still not completely clear to me. Yes i was looking at the Köppen classification before but that didnt really clarify anything for me. Maybe lets talk about a specific example like Africa and the tropic of cancer. if i change the axial tilt of earth ill move the tropic of cancer to 15 degrees. My understanding is that much more sun reaches the equator and it gets much hotter. This makes the tropics smaller and the subtropics larger because more heat creates larger deserts. Im obviously over simplifying but please still correct me on... $\endgroup$ – DefinitelyAHuman Jun 26 '20 at 2:55
  • $\begingroup$ any of this if i have it wrong. but even changing the degree of the tropic of cancer the hadley cell doesnt change. its still from 0 to 30 degrees. you mentioned that the cells and climate regions arent related to one another. that makes a bit more sense. But what does one do that the other doesnt? from your description it seems like hadley cells and coriolis are to explain air flow but the tropic of cancer explains temperature. Is that more accurate? if not, why do we even have lines like the tropic of cancer? what is it even telling us that other factors cannot?whats the significance? $\endgroup$ – DefinitelyAHuman Jun 26 '20 at 2:57
  • $\begingroup$ Speaking of northern Africa, parts of it changed from hosting neolithic farmers to a serious desert in a few thousand years without any nudge to earth's axis. The tropic of cancer is the northern latitude where people living north of it will a long time to wait for the sun to get directly overhead. $\endgroup$ – user20217 Jun 26 '20 at 9:56

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