The dominant large-scale features of the atmosphere are summarized
by the /tricellular model/ i.e. the Hadley cell, the Ferrel, cell,
and the polar cell.
Roughly speaking, this explains why (generally speaking) you are not
surprised to see
-- lots of rainfall near 0 degrees and 55 degrees latitude, and
-- very dry conditions near 25 degrees and 90 degrees latitude.
Also the Britannica has a nice article on atmosphere, weather and
climate: readable and informative.
I find this a fascinating subject. It can be presented at a qualitative
level. The tricellular model allows a unified view of many phenomena,
including horse latitudes, doldrums, trade winds, prevailing westerlies,
jungles, deserts, et cetera.
IMHO it is not, however, something students can be expected to figure out
on their own. It doesn't fit the spirit of yesterday's "good questions"
thread.
Students -- if they have thought about weather patterns at all -- have
seen 2D /plan view/ weather maps, more-or-less exclusively. It is unlikely
that they will figure out on their own that they should take a 3D view of
the weather, including the /side view/ necessary to make sense of global
circulation patterns.
This is in some ways an example of an "AHA!" problem. If you ask students
"what about 3D circulation" they might figure out that there is rising air
at the equator and descending air at the poles... but left to their own
devices, it is unlikely they will ask themselves the 3D question. The
troposphere is, after all, very thin compared to its horizontal extent
... so treating it as two-dimensional is not an unreasonable idea, and
in fact it is a deeply-ingrained idea.
As always, there is a psychological barrier against moving beyond a familiar
approximation. The better an approximation works in familiar cases, the
harder people must struggle to move beyond it.
==========
As to why there are /three/ big cells in each hemisphere, as opposed to
one, or five, or some other number ... I have no idea how to deduce that.
It must depend on the size of the earth, the thickness of the atmosphere,
the viscosity of the air, the rotation-rate of the earth, the brigtness of
the sun, et cetera. Personally I am content to take the number of cells
as an empirically-observed fact and leave it at that.
Extra credit question: Can you give a nice simple qualitatively-correct
explanation for the observed fact that there is tremendously low barometric
pressure at the south pole?