With the aid of examples, assess the extent to which albedo is the most important factor in
determining the diurnal energy budget. [15]
Albedo is the most important factor in determining the diurnal energy budget to a great
extent as it determines the amount of energy the surface can both absorb and therefore re
radiated and reflected into the atmosphere. Cloud cover is also a factor in determining the
diurnal energy budget, but closely ties in with albedo. However, albedo is not the only factor
which influence the diurnal energy as there are other methods of heat transfer which result
in the loss of energy, such as latent heat transfers.
Albedo is the percentage of radiation that is reflected by the surface. On lighter coloured
surfaces, such as glaciers and fresh snow, 95% of incoming solar radiation is reflected,
compared with only 10-25% in urban areas, covered in darker, man-made materials such as
tarmac and concrete.. This means that a much greater amount of the incoming solar
radiation in absorbed by the earth surface in these urban areas. This, therefore, means a
greater amount can be re-radiated in the form or long-wave radiation and sensible heat
transfer throughout the night. If only 5% of that insolation is absorbed, far less heat can be
reradiated from the surface, meaning the nights in places like antarctica will be much colder
than in urban areas. This huge difference in the amount that is absorbed by the surface
demonstrates how crucial albedo is in determining the diurnal energy budget and is
therefore the most important factor to a great extent.
The albedo of the surface is also crucial as it determines how deep the energy absorbed by
the ground can be transferred. Conduction is the process by which some of the energy
absorbed into the surface is transferred a short depth into the ground. Darker rocks at the
surface, such as granite, conduct heat better than lighter rocks, such as limestone, meaning
heat is transferred deeper in the darker rock. This causes the heat to be given off at a
greater rate on lighter rocks and soils than darker, as they cannot retain as much heat as the
energy is held in the surface and is unable to travel deeper into the rock. This will in turn
reduce the amount of heat energy that has been absorbed by the ground, meaning less can
be re radiated in the form of long wave radiation or sensible heat transfer to the air around.
Cloud cover is also a crucial factor in determining the diurnal energy budget but is closely
related to albedo. High, thin clouds such as cirrus allow incoming solar radiation to pass
through but absorb some of the long wave radiation, warming the earth's surface. Low thick
clouds such as stratus and stratocumulus can reflect up to 80% of solar radiation, therefore
cooling the earth's surface. This means that the type of cloud cover influences the amount
of incoming solar radiation reaching the earth's surface and the amount of long wave
radiation that can be reabsorbed, impacting the diurnal energy budget. However, albedo
makes cloud cover a more significant impact, as clouds typically have higher albedos than
the surface below them, meaning more short-wave radiation is reflected to space than
would be if there were no clouds. This demonstrates how the type of cloud cover present
can affect the diurnal energy budget, but how it is still albedo as a factor which causes this
to be significant.
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