We
will check the various parts of the complex figure to be sure they are
in energy balance. We
will start with the atmosphere. Click here to download these notes in a more
printer friendly version.
The atmosphere is emitting 160 units of energy.
64 units
go up and into space, 96 units go down and are absorbed by the
ground. How would you explain the difference between the amounts
being emitted upward and downward. One explanation might be
temperature. The upper atmosphere might be colder than the lower
atmosphere. Colder air would emit less EM radiation than warm
air. The air density at high altitude is lower than at low
altitude. With less air it makes sense that there would be less
emitted light.
19 units of sunlight energy are being absorbed by the
atmosphere. 111 units of IR radiation emitted by the ground are
absorbed by the atmosphere. The 23 units at left is energy
transported in the form of latent heat (water in the lake evaporates,
heat is released into the atmosphere when the water vapor condenses and
forms the cloud). Together conduction and convection transport 7
units of energy from the ground to the atmosphere. That is a
total of 160 units and balances the 160 units of energy being emited by
the air.
Next
energy loss and gain at the ground
The ground is absorbing 147 units of energy. Surprisingly
the ground gets almost twice as much energy (96 units) from the
atmosphere as it gets from the sun (51 units). This is partly due
to the fact that the sun is shining on any particular area for part of
the day while the atmosphere is emitting IR radiation downward toward
the ground all the time.
The ground is losing 147 units of energy, so
everything is in
balance at the ground. Next we'll
check energy arriving at the top of the atmosphere from space and
energy leaving the atmosphere and going back out into space.
The earth and atmosphere send 70 units out into space. This
is balanced by 70 units of sunlight arriving at the earth shown in the
figure below.
