Energy: Warming the Earth

1
Energy Warming the Earth the Atmosphere

• This chapter discusses
• The role of solar energy (e.g. short wave
  radiation) in generating temperature heat
• Earth's processes for heat transfer in the
  atmosphere, including long wave radiation, to
  maintain an energy balance

2
Energy Temperature
Figure 2.1

• When solar radiation collides with atmospheric
  gas molecules, they move.
• This produces
• temperature, defined as the moving molecules
  average speed
• kinetic energy
• Total energy increases with greater molecule
  volumes.

3
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
4
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.
5
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.
6
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
7
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.
8
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
9
Longwave Shortwave Radiation
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.
Figure 2.8
10
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.
11
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.
12
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
13
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 33C cooler than the
observed temperature.
14
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.
15
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
16
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.
17
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.
18
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.
19
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
20
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