Transcript GEO210 Atmospheric Processes

Atmospheric Processes
The sun as a source of Energy
Key questions…
1. What is the importance of the sun for life
on Earth?
2. What forms of radiation are emitted from
the sun?
3. What are the characteristics of insolation
and factors which causes it to change?
The Sun
•
•
•
•
Yellow star – radiating
energy for approximately 5
billion years
70% Hydrogen, 28% Helium,
2% heavier ‘metals’
(oxygen, carbon, neon, iron)
Nuclear fusion – heat and
light the earth
Sole input to energy flows
within the atmosphere is
electromagnetic radiation
emitted from the Sun
Nuclear Fusion
atmosphere
Sun
Surface temp = 6000°C
Hydrogen atoms
fuse → Helium +
energy =
Nuclear Fusion
99% released as
short-wave
radiation –
travelling at
297,600 km s
Earth
– surface temp
= 14°C
148,800,000 km
Note: protons overcome their mutual electric repulsion releasing energy – further
reading: Nuclear force
Other inputs of heat
energy to the atmosphere
•
Negligible inputs of heat
energy are supplied from:
– geothermal sources
• volcanic eruptions
• hot springs
– anthropogenic sources
• domestic heating
• industry
Electromagnetic
spectrum
•
All objects with a temperature
above absolute zero (–273o C
or 0 K) emit radiation in all
directions as electromagnetic
waves travelling at the speed
of light (3 x 108 m s-1)
•
Electromagnetic waves are
spread across a range of
wavelengths – the
electromagnetic spectrum
•
Wavelengths vary in size from
<0.0001 µm (gamma rays) to
several km (long-wave radio)
•
1 µm (micron) = 1/1000th mm
Electromagnetic
spectrum
Hotter
object
Colder
object
X-axis = Wavelength
Y-axis = Amount of radiation
•
Amount and type of
radiation emitted by an
object is dependent on the
object’s temperature
•
A hotter object will emit a
greater amount of radiation
and at a shorter wavelength
than a colder object
Solar radiation
•
Emitted over a wide range of wavelengths – solar spectrum
•
99% - short-wave radiation with maximum output within the visible
part of solar spectrum
•
Total amount of solar radiation reaching top of atmosphere = 1366 W
m-2, but amount reaching Earth’s surface = c.338 W m-2 (c.25%)
Absorption of
solar radiation by
atmosphere
•
UV radiation
– Almost completely
absorbed by ozone (O3)
in stratosphere
•
Visible light
– Atmosphere is largely
transparent
•
Solar radiation passing
through troposphere is
– Scattered
– Reflected
– Absorbed
Terrestrial
radiation
•
Earth emits radiation – long-wave radiation
•
Maximum output within the infrared part of spectrum
Absorption of
terrestrial radiation
by atmosphere
•
Atmosphere is only partially
transparent to long-wave
radiation from Earth’s
surface
•
c.94% is absorbed
atmosphere, including:
–
Water vapour (H2O)
–
Carbon dioxide (CO2)
•
Part of this is radiated back
to Earth’s surface (counterradiation) – raising surface
temperature by c.38OC
•
c.6% escapes directly to
space
Earth’s Energy Budget – Effect of cloud cover
The Greenhouse Effect
Earth’s Energy Budget – Variations with latitude
•
Equator to 35O N & S – Incoming short-wave radiation (solar radiation)
exceeds outgoing long-wave radiation (terrestrial radiation)
•
Polewards of 35O N & S – Long-wave exceeds short-wave radiation
•
Continual poleward transfer of energy from area of excess to area of
deficit via general circulation of atmosphere (70%-90%), ocean
currents (10%-30%) and storms.
Earth’s Energy
Budget – Variations
with time of year
Green Flash
Green Flash
Green Flash
•
Rare optical phenomena
that occur at sunset and
sunrise
•
Appears as green spot
visible for 1-2 seconds
•
Observed at low altitudes
with unobstructed view of
horizon (e.g. ocean)
•
Caused by refraction of
light – blue light is
dispersed and only green
light remains visible
Laws of electromagnetic radiation
•
“The radiation flux (amount
of radiation emitted per unit
surface area) of an object is
proportional to the 4th power
of its absolute temperature”
•
E =  x T4
Stefan-Boltzman Law
E = Radiation flux
(amount of radiation emitted)
 = 5.67 x 10-8 W m-2 K-4
(Stefan-Boltzman constant)
T = Absolute temperature of
an object
•
Hotter objects emit more
electromagnetic radiation per
unit surface area
•
“The wavelength of peak
intensity of radiation
emitted by an object is
inversely proportional to its
absolute temperature”
•
peak =  ÷ T
Laws of electromagnetic radiation
Wien’s Displacement Law
peak = Wavelength of
maximum intensity of
radiation emitted
 = 2898 (Wien constant)
T = Absolute temperature of
an object
•
Wavelength of peak
intensity of solar radiation
is within visible part of
electromagnetic spectrum:
T = 6000 K
peak = 0.483 μm (483 nm)
Sun v. Earth
Laws of electromagnetic radiation
•
“The amount of radiation
reaching an object is inversely
proportional to the square of
the distance of that object
from the radiation source”
•
1 ÷ d2
Inverse square Law
d = Distance between radiation
source and object receiving
that radiation
•
Amount of solar radiation
received at the top of Earth’s
atmosphere (150 million km
from Sun) = 1366 W m-2
•
Known as the solar constant
Changes in the Solar Constant
“The number of polar bears, the
length of women's skirts, the stock
market: Everything imaginable has
been correlated with the solar
cycle”
29 Mar 2001
16 Jan 2009
14 May 2013
RMetS Presidential
Address 15 May 2013