Download Radiation (Electromagnetic Energy)

Solar Radiation: The driving factor
• Radiative Energy (energy transmitted as waves,
rays and particles)
released, absorbed &
reflected by all things
• travels as both a particle and
a wave
• is affected by
- gravity, magnetism, and
atmosphere composition,
distance, angle of incidence
• provides Earth with an
external source of energy - EXOSPHERE
The sun produces most of its
electromagnetic energy in
intermediate wavelengths /
frequencies.
A. True
B. False
Sources of radiation
• Sun and other stars are dominant source
- Sun is closest so it has a greater influence
• Earth emits some energy as well
- Solar radiation is absorbed by Earth and
transformed into longwave radiation
• Many other planets emit radiation as well
- e.g., Jupiter and Saturn
- source is from the planet itself
not all is absorbed and re-emitted like Earth
The Sun
• 93 million miles from Earth
• It rotates once every 600 hrs (25 days)
• Has hot spots and "cool" spots
- sunspots are relatively "cool"
Produces electro•
magnetic radiative
energy
- concentrated in
UV, Visible &
IR spectral
classes
Energy
output from
the sun
Variable
Changes with time
Changes over
long term billions of years
short term –
11 year cycles
The earth receives a
small percentage of
the total output of
energy from the sun
Sunspots - cyclical magnetic “storms” that occur in 11
year cycles are lower in temperature, but increase
solar output.
Solar Max = lots of sunspots and increased energy output
Solar Min = few to no sunspots and decreased energy output
Electromagnetic Spectrum
Long
Short
(l)
Frequency (mHz) refers to vibration of particles
Wavelength ( l) = distance between wave crests
Position affects amount radiation we receive
radiation; Closer=more radiation
• Far away=less radiation
away=lessmore
radiation;
Tilted toward = more
radiation
• Titled toward=
perihelion
aphelion
Our seasons on Earth are NOT related to
distance from the Sun
Earth is at Aphelion during the northern hemisphere
summer months (our warm months)
“Aphelion” means farthest away from the Sun
farther away means less energy reaches the surface
but that change is very small compared to those
related to tilt
Earth’s seasons are due to the tilt of our axis
of rotation!
changes the length of the day; and
changes the angle of incidence for incoming solar energy
The northern hemisphere experiences winter because
the Earth is farther away from the Sun than it is
during the summer months.
A. True
B. False
Milankovitch Orbital Variations
Eccentricity – orbit around the Sun changes
from a circle to an ellipse over a 100,000
year cycle
Obliquity-Earth’s axis of rotation changes
from 22.5 to 24.5°over a 41,000 year
cycle
Precession of equinox- earth wobbles very
slowly as it spins, changing the timing of
seasons with respect to perihelion and
aphelion 22 to 25 kyr
All three are independent of one another. Change
in energy reaching the Earth is small and requires
amplification by Earth systems to initiate climate
change
Eccentricity
100 kyr cycle
aphelion
Earth’s orbit
Obliquity
41 kyr cycle
Axis 20 kyr ago
Axis at present
Axis at 20 kyr in future
Perpendicular to the ecliptic
Precession of Equinox
22-25 kyr cycle
Conditions 11 kyr ago
sun
Earth at
perihelion
Earth at
aphelion
sun
Path of Earth’s orbit around the sun
Conditions now
Precession
22 -25 kyr cycle
Milankovitch cycles- pacemaker to the ice ages
*
fromO18 ice and deep sea sediment cores
The atmosphere acts as a mirror, prism and a trap
• Scatters some of the radiation
- why the sky is blue
• Reflects some of the radiation
- clouds, snow, water etc.
• Absorbs some of the radiation
- ground, ozone, dust, etc.
Ozone & dust
prism
Dust & clouds
mirror
Clouds & gases
trap
Albedo
radiation
Albedo = reflected
________________
incident radiation
･ A measure of the amount of reflected radiation
･ Some things reflect radiation better than others
- "dry" or "cold" Snow & Ice = high albedo
- water = moderate for visible, low for infrared
- plants= moderate for visible
･ Land absorbs and releases radiative energy
quicker than water
Albedo of land surfaces on Earth
Warm colors are higher; cool are lower; white no data available
Data collected by NASA’s MODIS satellite, April 2002
IR output from Earth
K
Effects of cloud type on radiation budget
• different types of interference have
different effects on Earth's energy budget