It is all a matter of the angle the sun
makes with a pole struck in the ground at local
time of noon, when the sun is highest in the sky.
Near the equator, the sun's rays are coming in
at a steep angle close to 90 degrees. This means
that the sun's rays are concentrated. On the
other hand at high latitudes , the sun's rays are
coming in at a relatively shallow angle...so the
rays get spread out over a larger area. Hence
the heat per unit area is HIGHER at low
latitude compared to HIGH latitude.
The effect of this uneven heating, caused
ultimately by the tilt of the Earth's own axis, is
to give rise to what is called Hadley
Hadley circulation. Hot air rises in
equatorial regions and then moves north and south
(towards the poles). As it moves it gives up its
heat and eventually sinks down near the poles and
flows south or north (depends on hemisphere)
towards the equator to pick up more of the
concentrated heat from the sun.
A simple way to imagine this is to get a
basketball and shine a flash light at it along its
equator...up near the pole, the light rays will
come in almost parallel to the surface! very weak
light! But near the equator, the light will be
concentrated, because the rays are perpendicular
to the (local) surface.
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