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I noticed on google maps today that the earth has two very distinct regions on which the majority of deserts are located. These fall on the tropic of capricorn and cancer. Illustrated here:

 from https://sites.google.com/site/fourbiomes/home/deserts

What causes this?

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  • $\begingroup$ Congratulations. That is a great discovery! It was explained to us in the school, at geography lessons. The teacher told however that the deserts are located in the sub tropical rather than tropical belt. Please see the difference. $\endgroup$ – Little Alien Aug 21 '16 at 12:24
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    $\begingroup$ Shawn and Little Alien are both referring to the distribution of Hadley cells, major convective features of the Earth's atmospheric circulation. You may also note that the Hadley cells are not quite symmetrically disposed around the equator. The unequal distribution of land masses between northern and southern hemispheres shifts the climatic equator to a few degrees south of the geographic equator. $\endgroup$ – Gordon Stanger Aug 21 '16 at 13:37
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    $\begingroup$ @LittleAlien I can't tell if you're being sarcastic. I apologize if my question was too stupid, i didn't do much geography at school and what i did do was many many years ago. This question literally stems from zooming out on Google maps and noticing that the worlds deserts occur in this pattern. $\endgroup$ – user2687 Aug 21 '16 at 19:56
  • $\begingroup$ @GordonStranger thank you, I'll research Hadley cells further online. $\endgroup$ – user2687 Aug 21 '16 at 19:58
  • $\begingroup$ @stanri IMHO it's a good question. You've been given enough information to read about the answer yourself, but I hope that somebody will have time to write a good one here. $\endgroup$ – Semidiurnal Simon Aug 29 '16 at 22:23
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At thirty to thirty-eight degrees north and south of the equator are the so-called Horse Latitudes, regions with constant high-pressure systems. These regions inhibit precipitation. The phenomenon is quite well described and illustrated on Wikipedia: https://en.wikipedia.org/wiki/Horse_latitudes

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  • $\begingroup$ "Constant high pressure systems" is not really correct. These regions have a higher average pressure than the surrounding regions. They still have high and low pressure systems. $\endgroup$ – naught101 Sep 2 '16 at 1:02
  • $\begingroup$ Also, it's worth noting that the deserts are generally on the western side of the continents at these latitudes because the prevailing winds are easterly, blowing moisture away from the coast. See en.wikipedia.org/wiki/Trade_winds $\endgroup$ – naught101 Sep 2 '16 at 2:15
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    $\begingroup$ @naught101: Coastal upwelling at the eastern coast leading to cold surface waters is the main reason that deserts are located on the western part of the continents. And cold surface waters inhibits evaporation and thus leads to less rainfall in these regions. $\endgroup$ – makra Sep 7 '16 at 8:15
  • $\begingroup$ @makra: did you mean to say western coast? Also, surely the off-shore winds are one of the driving factors for that cold upwelling... $\endgroup$ – naught101 Sep 8 '16 at 0:58
  • $\begingroup$ @naught101, thanks. Good catch! Of course, I meant western coast. $\endgroup$ – makra Sep 8 '16 at 14:46

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