Geoscience Reference
In-Depth Information
3
CHAPTER THREE
Solar radiation and the
global energy budget
LEARNING OBJECTIVES
When you have read this chapter you will:
n
know the characteristics of solar radiation and the electromagnetic spectrum
n
know the effects of the atmosphere on solar and terrestrial radiation
n
understand the cause of the atmospheric greenhouse effect
n
understand the earth's heat budget and the importance of horizontal transfers of energy as
sensible and latent heat.
This chapter describes how radiation from the
sun enters the atmosphere and reaches the surface.
The effects on solar radiation of absorbing gases
and the scattering effects of aerosols are examined.
Then terrestrial longwave (infrared) radiation
is discussed in order to explain the radiation
balance. At the surface, an energy balance exists
due to the additional transfers of sensible and
latent heat to the atmosphere. The effects of
heating on surface temperature characteristics are
then presented.
amount emanating from the radioactive decay of
earth minerals). The amount of energy received
at the top of the atmosphere is affected by four
factors: solar output, the sun-earth distance, the
altitude of the sun, and day length.
1 Solar output
Solar energy originates from nuclear reactions
within the sun's hot core (16
10
6
K), and is
transmitted to the sun's surface by radiation and
hydrogen convection. Visible solar radiation
(light) comes from a 'cool' (~ 6000K) outer surface
layer called the
photosphere
. Temperatures rise
again in the outer chromosphere (10,000K) and
corona (10
6
K), which is continually expanding
into space. The outflowing hot gases (plasma)
from the sun, referred to as the
solar wind
(with a
speed of 1.5
×
A
SOLAR RADIATION
The source of the energy injected into our
atmosphere is the sun, which is continually
shedding part of its mass by radiating waves of
electromagnetic energy and high-energy particles
into space. This constant emission represents all
the energy available to the earth (except for a small
10
6
km hr
-1
), interact with the earth's
magnetic field and upper atmosphere. The earth
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