HEATING EARTH’S
SURFACE AND
ATMOSPHERE
INTERESTING
The sun radiates to the Earth
phenomenal amounts of energy,
too much, in fact…
We term this quantity of energy
the solar constant [2.0 cal/cm2min or 3.1x1012 cal/mi2-hr]
INTERESTING, cont
To give this a context, an adult
sunbather would absorb 6000
cal/min at this rate.
In 30 minutes he/she would absorb
180,000 cal… enough energy to heat
10 cups of water from room
temperature to boiling
…. Luckily, <50% of solar radiation
reaches the Earth’s surface
It has long been recognized that the
Earth maintains an approx. 364 day
revolution around the sun as it
makes an approx. 24 hour rotation
on its axis (our day)
Additionally, the Earth is inclined
approx 23 ½o from perpendicular and
towards the plane of the ecliptic (our
seasons and our year)
Earth intersects less than two
billionths of the sun’s radiation
… even this is more than we need
… this energy is not even distributed,
being variable by:
(1) latitude-diffused from 30o
to 90o
(2) time of day/year-affects solar
intensity and volume of
atmosphere passing through
Mechanisms of Heat
Transfer
Radiation
Conduction
Convection /
Advection
Latent Heat of
Condensation
Mechanisms of Heat
Transfer

Radiation – the “laws”
(1) all objects emit energy
over a range of wavelengths
(2) hotter objects radiate
more total energy
(3) the hotter the body, the
shorter the wavelength
emitted
(4) good absorbers are good
emitters
Mechanisms of Heat
Transfer, cont
Conduction –
molecule-to-molecule energy
transfer
most efficient in densely “packed”
molecules
Convection –
energy transfer through expansion of
a substance
convection – vertical;
advection - horizontal
Mechanisms of Heat
Transfer, cont
Latent heat –
a potential heat
available for absorption
(into a substance) or release
(into the atmosphere)
What Happens to Incoming
Solar Radiation?
Reflection – direction change due to
contact with another surface
--- reflected at same angle
--- no heating of atmosphere
occurs
--- energy generally lost to Earth
use
Albedo – that portion of incoming
radiation reflected by a surface
… affected by color and
composition
What Happens to Incoming
Solar Radiation?, cont
Scattering – occurs when incoming
solar radiation is forced to change
direction by contact with gas
molecules in the atmosphere
--- wavelength does not change
--- radiation with shorter
wavelengths are most affected
… thus, blue skies and orange
at sunset and in pollution
What Happens to Incoming
Solar Radiation?, cont
Absorption:
(1) atmospheric – by gas
molecules / aerosols /
particulates
--- atmosphere in general is
not good absorber
--- visible light not well
absorbed
What Happens to Incoming
Solar Radiation?, cont
(2) terrestrial – absorbed by Earth
surface (and man-made)
- most is re-radiated as
infrared terrestrial
radiation
- Thus, the Earth heats the
atmosphere
- Most of this radiation is lost back
to space, concern of
greenhouse effect
(good and bad)
Average Breakdown of
Insolation
Absorbed by atmosphere –
19%-22%
Reflected into space –
34%
Absorbed Earth surface –
43%-47%

Factors Effecting
Insolation to the Ground
Latitude
- tropical zone
- mid-latitude zone
- polar zone
(2) Length of Day
(3) Atmospheric Conditions
(1)
Heat Budget – term for the balance
between energy gained through
insolation and lost through
radiation / reflection back to space
Heat Energy Budget

Insolation to the Ground
47% of incoming solar radiation
reaches the surface of the Earth
… ultimately returned to the
atmosphere
terrestrial radiation – 14%
conduction/convection – 10%
latent heat – 23%
Variation in the Heat
Energy Budget
Regions of Energy Surplus
--- tropical zones
--- seasonal
Regions of Energy Deficit
--- polar zones
--- seasonal
