Transcript Document

Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy (e.g. short wave radiation)
in generating temperature & heat
2. Earth's processes for heat transfer in the
atmosphere, including long wave radiation, to
maintain an energy balance
Energy & Temperature
Figure 2.1
When solar radiation collides with atmospheric gas molecules, they
move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
Total energy increases with greater molecule volumes.
Temperature Scales
Thermometers detect the
movement of molecules to
register temperature.
Fahrenheit and Celsius scales
are calibrated to freezing and
boiling water, but the Celsius
range is 1.8 times more
compact.
Figure 2.2
Latent & Sensible Heat
Figure 2.3
Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
As water moves toward vapor it absorbs latent (e.g. not
sensed) heat to keep the molecules in rapid motion.
Heat Energy for Storms
Figure 2.4
Latent heat released from the billions of vapor droplets during
condensation and cloud formation fuels storm energy needs, warms
the air, and encourages taller cloud growth.
Conduction - Heat Transfer
Conduction of
heat energy
occurs as
warmer
molecules
transmit
vibration, and
hence heat, to
adjacent cooler
molecules.
Warm ground
surfaces heat
overlying air
by conduction.
Figure 2.5
Convection - Heat Transfer
Figure 2.6
Convection is heat energy moving as a fluid from hotter to cooler
areas.
Warm air at the ground surface rises as a thermal bubble, expends
energy to expand, and hence cools.
Radiation - Heat Transfer
Radiation
travels as waves
of photons that
release energy
when absorbed.
All objects
above 0° K
release
radiation, and
its heat energy
value increases
to the 4th
power of its
temperature.
Figure 2.7
Longwave & Shortwave Radiation
Figure 2.8
The hot sun
radiates at
shorter
wavelengths
that carry more
energy, and the
fraction
absorbed by the
cooler earth is
then re-radiated
at longer
wavelengths, as
predicted by
Wein's law.
Electromagnetic Spectrum
Figure 2.9
Solar radiation has peak intensities in the shorter wavelengths,
dominant in the region we know as visible, but extends at low
intensity into longwave regions.
Absorption & Emission
Figure 2.10
Solar radiation is selectively absorbed by earth's surface cover.
Darker objects absorb shortwave and emit longwave with high
efficiency (e.g. Kirchoff's law).
In a forest, this longwave energy melts snow.
Atmospheric Absorption
Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases
and re-radiated toward earth.
Figure 2.11
Greenhouse Effect
Figure 2.12B
Figure 2.12A
Earth's energy balance requires that absorbed solar radiation is
emitted to maintain a constant temperature.
Without natural levels of greenhouse gases absorbing and
emitting, this surface temperature would be 33°C cooler than the
observed temperature.
Warming Earth's Atmosphere
Figure 2.13
Solar radiation passes first through the upper atmosphere, but only
after absorption by earth's surface does it generate sensible heat to
warm the ground and generate longwave energy.
This heat and energy at the surface then warms the atmosphere
from below.
Scattered Light
Solar radiation
passing through
earth's
atmosphere is
scattered by
gases, aerosols,
and dust.
At the horizon
sunlight passes
through more
scatterers,
leaving longer
wavelengths
and redder
colors revealed.
Figure 2.14
Incoming Solar Radiation
Figure 2.15
Solar radiation is scattered and reflected by the atmosphere, clouds,
and earth's surface, creating an average albedo of 30%.
Atmospheric gases and clouds absorb another 19 units, leaving 51
units of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Figure 2.16
Earth's surface absorbs the 51 units of shortwave and 96 more of
longwave energy units from atmospheric gases and clouds.
These 147 units gained by earth are due to shortwave and longwave
greenhouse gas absorption and emittance.
Earth's surface loses these 147 units through conduction,
evaporation, and radiation.
Earth's Magnetic Field
Figure 2.17
Earth's molten metal core creates a magnetic field that covers earth
from the south to north pole.
Solar Wind
High energy
plasma is blown
from the sun in a
dangerous solar
wind, and the
magnetosphere
deflects this wind
to shield the earth.
Figure 2.18
Ions & Aurora Belts
Solar winds entering the
magnetosphere excite
atmospheric gas electrons.
When the electron de-excites it
emits visible radiation.
Figure 2.19A
The aurora is created by these
solar winds and de-exciting ions,
and has belts of expected
occurrence at both poles.
Figure 2.20