Geoscience Reference
In-Depth Information
Solar radiation and the global
energy budget
Learning objectives
When you have read this chapter you will:
Know the characteristics of solar radiation and the electromagnetic spectrum,
Know the effects of the atmosphere on solar and terrestrial radiation,
Understand the cause of the atmospheric greenhouse effect,
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 long-wave (infra-red) 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.
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'
(~6000 K) outer surface layer called the
photosphere
.
Temperatures rise again in the outer chromosphere
(10,000 K) 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 amount emanating from the radioactive
decay of earth minerals). The amount of energy received
10
6
km hr
-1
), interact with the
earth's magnetic field and upper atmosphere. The earth
intercepts both the normal electromagnetic radiation and
energetic particles emitted during solar flares.
The sun behaves virtually as a
black body
; i.e. it
absorbs all energy received and in turn radiates energy
