Download Energy: Warming the earth and Atmosphere

Energy: Warming the earth
and Atmosphere
Chapter 2
Energy, Temperature, & Heat
• Energy is the ability to do work (push, pull,
lift) on some form of matter.
• Potential energy is the potential for work
(mass x gravity x height)(PE=mgh)
• Kinetic energy is energy of a moving
object (half of mass x velocity
squared)(KE=1/2mv2)
• Temperature is the average speed of
atoms and molecules
Energy, Temperature, & Heat
• Which has more energy?
– A lake or a cup of hot tea?
• Heat is energy in the process of being
transferred from one object to another
because of a difference in temperature.
• Energy cannot be destroyed or created;
First Law of Thermodynamics
(Conservation of Energy)
Temperature Scales
• Kelvin scale
– or absolute; 0K = -273°C
– Lord Kelvin (1824-1907)
• Fahrenheit scale
– Water : 32 freeze, 212 boil
• Celsius scale
– Water : 0 freeze, 100 boil
• C=5/9(F-32) or F= 9/5C +32
• K=C+273
Specific Heat
• Heat capacity is the heat energy absorbed
to raise a substance to a given
temperature
• Specific heat is the heat capacity divided
by mass or the amount of energy required
to raise one gram of a substance 1°C
• High specific heat equates to slow
warming and vice versa
Latent Heat (vs sensible heat)
Change of state or phase change
represents change between solid, gas,
and liquid.
Latent heat is the energy involved in the
change of state.
Stepped Art
Fig. 2-3, p. 33
Water Phase Changes
The hot burner warms the bottom of the pot by conduction. The warm pot, in turn, warms the water in contact with it. The
warm water rises, settings up convection currents. The pot, water, burner, and everything else constantly emit radiant energy
(orange arrows) in all directions.
Heat Transfer in the Atmosphere
• Conduction: transfer heat from one
molecule to another in a substance
– Energy travels from hot to cold
– Air is a poor conductor, metal a good conductor
• Convection: transfer of heat by the mass
movement of a fluid (water or air)
• Convection circulation: warm air expands
and rises then cools and sinks; thermal cell
• Horizontal component
– wind
• Carries properties
– advection
• Special Topic: Rising and Sinking Air
– As air rises part of its energy is lost as it expands
and cools and when the air sinks it is compressed
and the energy of molecules increase causing
temperature to increase.
• Radiant energy from the sun travels through the
space and the atmosphere in the form of a
wave (electromagnetic waves) and is called
radiation.
• Units of measure
– 1 micrometer (μm) =0.000001 m = 10-6m
ects with a temperature greater than 0K radiate energy.
Radiant Energy is governed by basic laws
Hotter objects radiate more total energy per unit
area than do cooler objects (Stefan-Boltzmann
Law)
The hotter the radiating body, the shorter the
wavelength of maximum radiation (Wien’s
Displacement Law)
Objects that are good absorbers of radiation are
good emitters as well (Kirchoff’s Law)
Stefan-Boltzmann Law
• Hotter objects radiate more total energy
per unit area than do cooler objects
• The hotter the radiating body, the shorter the
wavelength of maximum radiation
The hotter sun not only radiates more energy than that of the cooler earth (the area
under the curve), but it also radiates the majority of its energy at much shorter
wavelengths. (The area under the curves is equal to the total energy emitted, and the
scales for the two curves differ by a factor of 100,000.)
The sun’s electromagnetic spectrum and some of the descriptive names of each region.
The numbers underneath the curve approximate the percent of energy the sun radiates
in various regions.
– UV index is a weather forecast product that indicates the
potential for sun burn due to high energy or short
wavelengths emitted by the sun.
Balancing Act
• If the Earth is radiating energy all the time, why is it
not very cold?
–
–
–
–
Earth is in Radiative Equilibrium
Radiative Equilibrium Temperature = 255 K (-18C, 0F)
Why is the average surface temperature 288K, 15C, 59F?
Our atmosphere absorbs and emits infrared radiation
• Does not behave as blackbody
– Gases act as Selective Absorbers
• GoodSelective
absorbers are
good emitters at a
Absorbers
particular wavelength and vice versa.
– Kirchoff’s Law
The melting of snow
outward from the
trees causes small
depressions to form.
The melting is caused
mainly by the snow’s
absorption of the
infrared energy being
emitted from the
warmer tree and its
branches. The trees
are warmer because
they are better
absorbers of sunlight
than is the snow.
Absorption of radiation
by gases in the
atmosphere. The
shaded area
represents the percent
of radiation absorbed
by each gas. The
strongest absorbers of
infrared radiation are
water vapor and
carbon dioxide. The
bottom figure
represents the percent
of radiation absorbed
by all of the
atmospheric gases.
FIGURE 2.13 (a) Near the surface in an atmosphere with little or no greenhouse gases, the earth’s surface would constantly
emit infrared (IR) radiation upward, both during the day and at night. Incoming energy from the sun would equal
outgoing energy from the surface, but the surface would receive virtually no IR radiation from its lower atmosphere. (No
atmospheric greenhouse effect.) The earth’s surface air temperature would be quite low, and small amounts of water found
on the planet would be in the form of ice.
(b) In an atmosphere with greenhouse gases, the earth’s surface not only receives
energy from the sun but also infrared energy from the atmosphere. Incoming energy still equals outgoing energy, but the
added IR energy from the greenhouse gases raises the earth’s average surface temperature to a more habitable level.
Greenhouse Enhancement
• Global warming is occurring due to an increase
in greenhouse gases
– Carbon dioxide
– Methane
– Nitrogen Oxide
– Chlorofluorocarbons
• Positive feedbacks continue the warming trend.
– Rising sea temps, increase evaporation add water
vapor
• Negative feedbacks decrease warming.
– Increasing clouds, cooling effect
Incoming Solar Radiation
(INSOLATION)
• Solar constant – about 2c/cm2/min. or 1367
W/m2
• What happens to the INSOLATION?
– Scattered
– Reflected
– Absorbed
• The scattering of light by air molecules. Air molecules tend to
selectively scatter the shorter (violet, green, and blue)
wavelengths of visible white light more effectively than the
longer (orange, yellow, and red) wavelengths.
Blue skies, red skies, and white clouds
– Selective scattering of incoming solar radiation causes
reflectance in portion of the electromagnetic spectrum that
correspond with the colors our eyes detect.
At noon, the sun usually
appears a bright white. At
sunrise and at sunset,
sunlight must pass
through a thick portion of
the atmosphere. Much of
the blue light is scattered
out of the beam, causing
the sun to appear more
red.
Cloud droplets scatter all wavelengths of visible white light about equally. This type of
scattering by millions of tiny cloud droplets makes clouds appear white.
Reflected - energy sent back
Albedo - % reflected
On the average, of all the solar energy that reaches the earth’s atmosphere annually,
about 30 percent (30⁄100) is reflected and scattered back to space, giving the earth and
its atmosphere an albedo of 30 percent. Of the remaining solar energy, about 19 percent
is absorbed by the atmosphere and clouds, and 51 percent is absorbed at the surface.
Stepped Art
Fig. 2-17, p. 49
The average annual incoming solar radiation (yellow
lines) absorbed by the earth and the atmosphere
along with the average annual infrared radiation (red
lines) emitted by the earth and the atmosphere
Particles and Aurora
• Solar wind or plasma - charged particles
traveling through space from sun to Earth.
• Solar wind interacts with Earth’s
magnetosphere and creates auroras
– Aurora borealis
– Aurora australis
The stream of charged particles from the sun—called the solar wind—distorts the
earth’s magnetic field into a teardrop shape known as the magnetosphere
When an excited atom, ion, or molecule de-excites, it can emit visible light.
(a) The electron in its normal orbit becomes excited by a charged particle and
(b) jumps into a higher energy level. When the electron returns to its normal orbit, it
(c) emits a photon of light.
The aurora borealis is a
phenomenon that forms
as energetic particles
from the sun interact
with the earth’s
atmosphere.
The aurora belt (solid red line) represents the region where you would most likely
observe the aurora on a clear night. (The numbers represent the average number of
nights per year on which you might see an aurora if the sky were clear.) The flag MN
denotes the magnetic North Pole, where the earth’s magnetic field lines emerge from the
earth. The flag NP denotes the geographic North Pole, about which the earth rotates.