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°F freeze, 212°F boil
• Celsius scale
– Water : 0°C freeze, 100°C 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.
•
•
Ice or liquid to vapor: absorbs energy and cools
environment (melt, evaporation, sublimation)
Vapor or liquid to ice: releases energy and heats
environment (freeze, condense, deposition)
Stepped Art
Fig. 2-3, p. 33
Water Phase Changes
Heat Transfer
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
The rising of hot air and the sinking of cool air sets up a convective circulation.
Normally, the vertical part of the circulation is called convection, whereas the horizontal
part is called wind. Near the surface the wind is advecting smoke from one region to
another.
• Special Topic: Rising and Sinking Air
– As air rises part of its energy is lost as it expands and cools
– When the air sinks it is compressed and the energy of
molecules increase causing temperature to increase.
• RADIATION
• 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
• Radiation and Temperature
– All objects with a temperature greater than 0K
radiate energy.
– As the temperature of an object increases, more
total radiant energy is emitted by an object
(Stefan Boltzmann Constant).
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
• Radiation of the Sun and Earth
– Sun at 6000 K
– Earth at 288 K
– Shortwave radiation (high energy) from the Sun
– Longwave radiation (low energy) from the Earth
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.
A 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
Selective Absorbers
• Good absorbers are good emitters at a
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.
(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 and add
water vapor to the atmosphere
• Negative feedbacks decrease warming.
– Increasing clouds would reflect light, 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 - 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 earth-atmosphere energy balance. Numbers represent approximations based
on surface observations and satellite data. While the actual value of each process may
vary by several percent, it is the relative size of the numbers that is important
Summary of Annual Energy Budget
• 50% of insolation reaches the Earth’s surface.
• The Earth’s surface and atmosphere absorb
energy from the sun and each other
• And a balance is maintained
– Essentially no yearly total gain/loss of energy
– Average temp of earth and atmosphere fairly constant from
one year to next
– But, over time it can! 1°F increase in last century
• But a balance is not maintained at each latitude
• Tropics have a surplus of energy .
– Why?
The average annual incoming solar radiation (yellow lines) absorbed by the
earth and atmosphere
The average annual infrared radiation (red lines) emitted by the earth and
the atmosphere
Particles and Aurora
Characteristics of the Sun
–
–
–
–
Nearest star, 150 million km
Earth receives one 2 billionth’s of sun’s energy
Giant celestial furnace 15 million degrees C
Core, photosphere, sunspots, chromosphere, corona,
prominence, flares
– Magnetic storm
– CME
• Coronal Mass Ejection
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.