ES 1110 Chapter 2

1
ES 1110 Chapter 2

• The Energy Cycle

2
Scalars and Vectors

• A scalar quantity has just a magnitude. Examples
  are temperature, age, and mass
• A vector quantity has both a magnitude and a
  direction. Examples are velocity, force, and
  acceleration.
• Velocity 10 miles per hour towards North
• Speed is just the magnitude part of the
  velocity vector there is no direction

3
Forces

• A force is in simple terms a push or pull
• Mathematically, F m x a
• where F force
• m mass
• a acceleration
• When a force is exerted on an object,
  acceleration results

4
Acceleration

• Acceleration is a change to an objects velocity
  vector
• Remember, the velocity vector includes the
  magnitude and a direction
• Acceleration could be when an object moves faster
  or slower (change in magnitude), when an object
  moves in a different direction, or both

5
Work and Energy

• In physics, work is performed when a force exerts
  a push or pull an object over a distance
• In order to do work, energy is required
• Energy is defined as the capacity to do work
• There are four kinds of energy heat,
  electrical, kinetic, and potential
• Energy can be converted from one form to another,
  but the total amount of energy is always
  conserved (the Conservation of Energy)

6
Kinetic Energy

• Kinetic energy is the work that a body can do by
  virtue of its motion
• Kinetic energy depends on the mass of the object
  and how fast a mass is moving (KE ½ m x v2,
  where m is mass and v is velocity)

7
Potential Energy

• Potential energy is the work an object can do as
  a result of its relative position
• Lifting a book off the floor requires work (force
  over a distance)
• Placing it on a desk, the book now has potential
  energy
• The higher the book is lifted, the more potential
  energy the book has
• Once pushed off the edge, potential energy
  converts to kinetic energy

8
Air Parcels

• An air parcel is a hypothetical balloon-like blob
  of air that we will move around the atmosphere
• Inside a stationary parcel, variables such as
  pressure, temperature, and moisture are a
  constant throughout
• Rule 1 No energy exchange happens between the
  parcel and the environment outside (parcel is
  insulated)
• Rule 2 No mass exchange happens between the
  parcel and the environment outside (the molecules
  we start with in the parcel, we keep)
• Rule 3 The parcel does not have fixed
  dimensions (the parcel can expand and contract as
  needed)
• You may want to think of a balloon rather than a
  box when envisioning a parcel

9
Temperature

• Temperature is defined as the average kinetic
  energy of a substance
• The higher the temperature of a gas, the faster
  the gas molecules are moving (on average)
• It is an average because some molecules are
  moving very fast, some are moving more slowly
• Air molecules that move at different speeds
  collide with the bulb of a thermometer
• What we see on the thermometer is an average
  result of the kinetic energy of the molecules

10
Temperature Scales

• Fahrenheit is only used in the United States and
  a few other countries
• Celsius is used by the majority of countries
• Kelvin is used in mathematical equations
• (For Water at Sea Level) Freezing point
  Boiling Point
• Fahrenheit 32 212
• Celsius 0
  100
• Kelvin (273 C) 273 373

11
Temperature Scales

• Figure 2.1, Page 29

12
Calories, Joules, Power, and Watts

• A calorie is the amount of energy required to
  raise the temperature of 1 gram of water 1 degree
  Celsius
• The food Calorie 1000 calories
• Joule another unit to measure energy (1 Joule
  0.2389 calories)
• Power is the rate at which energy is transferred,
  received, or released
• A unit of power is the watt, which is one joule
  of energy per second

13
Heat

• Heat is energy produced by the random motions of
  molecules and atoms
• Heat is defined as the total kinetic energy of a
  substance
• Recall temperature was the average kinetic energy
  of a substance
• Therefore, heat is computed by adding up the
  kinetic energy of every molecule in a substance

14
Heat vs. Temperature

• To highlight the difference between heat and
  temperature another way, picture a very large
  iceberg and an Eskimo on top
• In terms of temperature (average kinetic energy),
  the Eskimo has a higher temperature (98.6 F vs.
  32 F at most)
• In terms of heat, the iceberg has more
• While the molecules in the iceberg are all moving
  more slowly than the Eskimos molecules, the
  iceberg has many, many more molecules to add up
  the total kinetic energy

15
Specific Heat

• Specific heat is the amount of heat required to
  increase the temperature of one gram of that
  substance one degree Celsius
• Sound familiar? The specific heat of water is 1
  calorie
• The lower the specific heat of a substance, the
  substance will heat up and cool down faster
  (requiring little energy)

16
Specific Heat of Substances

• Table 2.1, Page 30

17
Temperature Changes

• The temperature change of an object depends on
• How much heat is being added to the object
• The amount of matter of the object
• The specific heat of the substance

18
Means of Energy Transfer

• Energy can move from one object to another in the
  following three ways
• Conduction molecule-to-molecule transfer
• Convection transfer by fluid motions
• Radiation transfer by electromagnetic waves
• Energy always travels from regions of more energy
  to regions of low energy

19
Conduction

• Requires two objects to be in contact
• More important means in solids
• Not important in the atmosphere except near the
  ground
• The air is not heated directly by the Sun, but it
  gets its energy from the heated ground below (and
  gets the energy by conduction)
• Amount of heat transferred depends on
• Temperature difference between two objects
• Thermal conductivity of the two objects
• Water is a good conductor
• Air is a poor conductor (we use it as insulation)

20
Conduction

• Figure 2.2, Page 30

21
Convection

• Air is heated at the surface by conduction
• A heated air parcel rises vertically upward
• Cooler parcels replace the rising parcel
• Rising thermals and thunderstorms are two
  examples of convection in the atmosphere
• Convection is strongest over deserts and the low
  latitudes, weakest at the poles

22
Convection

• Figure 2.3, Page 31

23
Other Means in the Book

• The text also mentions advection, latent heating,
  and adiabatic cooling as means of energy transfer
• In reality, only conduction, convection and
  radiation are a means of energy transfer
• The above processes are important, but they are
  not means of energy transfer (as I will detail as
  we get to each point)

24
Advection

• Advection is the horizontal transport of heat
  energy by the wind
• Rather than a process in and of itself, advection
  is really the horizontal portion of convective
  circulation
• One can see hot or cold air advection when the
  wind is blowing perpendicular to the isotherms

25
Cold Air Advection

• Figure 2.4, Page 31

26
Phases of Water

• There are three phases of any substance solid,
  liquid, and gas
• Each phase has a different relationship amongst
  the molecules of that substance
• Solid (ice) molecules are arranged in a
  crystalline lattice (each molecule is fixed in
  space, kinetic motion of the molecules are only
  vibrations)
• Liquid (water) molecules are free to move
  about, but are connected to each other in a
  linear fashion
• Gas (water vapor) each water molecule is
  independent and not connected to another water
  vapor molecule kinetic energy is the highest of
  any phase

27
Phases of Water

• Figure taken from different text showing the
  relationship between water molecules in each of
  the three phases

28
Phase Changes and Energy

• Figure 2.5, Page 34

29
Heating of Water

• As we saw earlier, it takes 1 calorie of heat to
  raise the temperature of 1 gram of liquid water 1
  degree Celsius
• If we have one gram of liquid water at 20 degrees
  Celsius, how much energy would we need to
  vaporize the water into a gas?
• By adding 80 calories, we should end up with 1
  gram of liquid water at a temperature of 100
  degree Celsius
• If we were to add 1 more calorie, nothing
  happens!
• If we add 10 more calories, nothing happens (we
  still have 1 gram of liquid water at a
  temperature of 100 C)
• If we add 100 more calories, still nothing
  happens!!!
• In fact, we wouldnt see the water vaporize until
  540 calories were added after reaching 100
  degrees Celsius!
• Where did all that heat go?!

30
Latent Heat

• In our previous discussion of trying to vaporize
  water, we saw that heat was disappearing (no
  increase in temperature)
• This hidden heat is not changing the temperature,
  but the energy is being expended in order to
  break the molecular bonds between water molecules
• Only after the molecular bonds are broken can a
  water molecule fly away independently as a water
  vapor molecule
• Latent means hidden
• Latent heat must be added to water or removed
  from water in order to have a change of phase

31
Latent Heat of Water

• To go from a solid to a liquid, latent heat of
  melting (80 calories per gram) must be added to
  the water
• To go back from a liquid to a solid, latent heat
  of fusion (80 calories per gram) must be removed
  from the water
• To go from a liquid to a gas, latent heat of
  vaporization (540-600 calories) must be added to
  the water
• To go from a gas back to a liquid, latent heat of
  condensation (540-600 calories) must be removed
  from the water
• To go directly from a solid to a gas, latent heat
  of sublimation (680 calories) must be added to
  the water
• To go directly from a gas back to a solid, latent
  heat of deposition (680 calories) must be removed
  from the water

32
Latent Heat

• The evaporation of sweat involves latent heat,
  and explains why we cool off nicely when it
  happens
• Water has an extremely high latent heat of
  vaporization/condensation (600 calories!)
• When water vapor condenses (forms cloud
  droplets), a large amount of heat is released
  into the environment
• Latent heat is the fuel of a hurricane

33
Latent Heat as a Means of Transfer

• The book mentions that latent heat is a means of
  energy transfer
• Latent heat is indeed a way to transfer energy
  from one region to another
• However, when latent heat is released by water
  vapor during condensation, the surroundings warm
  up due to conduction, convection, and radiation
  of that heat

34
Lifting of an Air Parcel

• Imagine creating an air parcel at the surface
• The temperature, dew point, and pressure of the
  parcel will be the same as that of the
  surrounding air
• If were to lift that parcel up one mile, what do
  we know will be different up there?
• Air pressure always decreases with height
• At 1 mile, the pressure will be about 850 mb
• The air pressure in the parcel will be about 1000
  mb
• What will happen to the air parcel when we lift
  it up there?
• The parcel will expand in size because the
  pressure inside is greater than the pressure
  outside

35
Lifting of an Air Parcel

• What does an air parcel do when it expands?
• Because it pushes out against the environment
  (and expands a certain distance), work is
  performed by the parcel
• What do we need to do work?
• Energy is required to do work
• What energy does the parcel have to do work?
• The parcel has the kinetic energy of the
  molecules inside as a form of energy to expend to
  do the work
• As the kinetic energy of the molecules decreases
  as it does work, what happens to the temperature
  of the parcel?
• The temperature of the air in the parcel
  decreases as a result of the parcel being lifted
  and expanding

36
Dry Adiabatic Lapse Rate

• Notice that the air parcels temperature
  decreased, but a parcel can not exchange heat
  with the environment (Parcel Rule 1)
• Adiabatic means without heat
• The parcel had an adiabatic temperature change
• This is called a dry process because no phase
  change of water occurred
• The amount of cooling that a parcel will
  experience when lifted is called the dry
  adiabatic lapse rate
• The dry adiabatic lapse rate is a constant 10
  degrees Celsius for every kilometer of lifting

37
Dry Adiabatic Lapse Rate

• Figure 2.6, Page 34

38
Adiabatic Processes as a Means of Energy Transfer

• The book calls an adiabatic process a means of
  heat transfer, but as we have seen, no heat was
  transferred!
• The temperature decreased because the kinetic
  energy of the molecules was used up to do the
  work of expansion
• When a parcel is lowered in the atmosphere, the
  parcel will warm at the dry adiabatic lapse rate
• Therefore, no heat energy has been transferred

39
Moist Adiabatic Lapse Rate

• As we have seen, phase changes of water can
  involve a lot of heat energy
• A moist parcel is a parcel in which water vapor
  molecules are changing phase from a vapor to a
  liquid or ice
• Because of the phase changes, latent heat is
  released by the water vapor into the parcel
• As a result, will the parcel cool more or less
  than the dry parcel when lifted?
• A moist parcel will cool less than the dry
  adiabatic lapse rate because the latent heat
  being released will offset the cooling due to
  expansion
• The rate that a moist parcel cools is called the
  moist adiabatic lapse rate
• Unlike the dry adiabatic lapse rate, the moist
  adiabatic lapse rate is not a constant (depends
  on the amount of water vapor present)
• The book assumes a 6 degree Celsius per kilometer
  lapse rate for a moist parcel, but please
  remember this is not a constant value!

40
A Lifted Moist Parcel

• Figure 2.7, Page 36

41
Radiation

• Radiation was the third and final means of heat
  transfer
• Radiant energy is energy in the form of waves it
  is also called radiation or electromagnetic
  energy
• Radiation is able to travel through a complete
  vacuum (no matter needed)
• Energy from the Sun reaches the Earth by radiation

42
Waves

• Waves have two properties
• Wavelength The distance between two wave crests
  (or between two corresponding points)
• Amplitude Half the height from the peak of the
  wave crest to the lowest point of the wave trough
• We can categorize different types of
  electromagnetic radiation on the basis of
  wavelength
• The shorter the wavelength, the more energy the
  wave will have

43
Electromagnetic Spectrum

• Figure 2.9, Page 38

44
Electromagnetic Radiation

• From shortest to longest wavelengths
• Gamma rays
• X-rays
• Ultraviolet
• Visible (VIBGYOR)
• Infrared
• Radio

45
Radiation Types

• Shortwave Radiation Emitted by the Sun (UV,
  Visible, Near-IR)
• Ultraviolet (UV) light is responsible for tanning
  our skin and can lead to skin cancer
• Longwave Radiation Emitted by the Earth (mostly
  IR)
• Longwave Radiation is also called Terrestrial
  Radiation

46
Radiation Laws

• All objects with a temperature above absolute
  zero (0 Kelvin) emit radiation
• Stefan-Boltzmann Law The amount of radiation
  emitted by an object depends on the fourth power
  of temperature (E s x T4, where s is a constant
  and T is temperature)
• If the temperature doubles, the amount of energy
  emitted is 16 times more!
• Wiens Law The peak wavelength of energy
  emitted by an object depends on the temperature
  of the emitting body (?max constant/T)
• Because temperature is on the bottom, an increase
  in temperature results in a shorter peak
  wavelength

47
Radiation Curves

• Figure 2.10, Page 39

48
Radiation Interacting with an Object

• When radiation interacts with an object, it can
  be
• Absorbed the radiant energy ceases to be and
  goes into increasing the energy of the absorbing
  molecule
• Reflected the radiation is sent back out
• Transmitted the radiation passes through
  (transparent)
• The initials of the three spells ART

49
Albedo

• Albedo is the percentage of light that is
  reflected off an object
• The higher the albedo, the whiter the object
• The average planetary albedo for Earth is 30
• The energy that is not reflected is either
  absorbed or transmitted

50
Absorption

• If a molecule absorbs high-energy radiation, it
  may alter the molecule
• Photodissociation The absorption of UV can
  break apart chemical bonds between atoms (such as
  Oxygen and Ozone)
• Absorption of IR will result in a molecule
  vibrating or spinning more (increasing the
  temperature)

51
Absorption of Radiant Energy

• The amount of radiant energy absorbed by an
  object depends on
• The radiative properties of the material (some
  substance only absorb certain wavelengths)
• The amount of time the object is exposed to the
  emitted energy (longer time, more absorption)
• The amount of material (increasing thickness
  results in more absorption)
• How close the object is to the source of energy
  (the closer it is, the more energy reaches it to
  be absorbed)
• The angle at which the radiation is striking the
  object (radiation striking an object directly
  results in a more concentrated beam and more
  absorption)

52
Other Radiation Issues

• Blackbody an object that absorbs all the
  electromagnetic radiation that it encounters
  regardless of wavelength
• No object is a perfect blackbody
• Kirchoffs Law A good absorber of radiation is
  also a good emitter of radiation at that same
  wavelength

53
The Ozone Layer

• Ultraviolet light strikes an oxygen molecule (two
  atoms of oxygen bonded together)
• Photodissociation of the oxygen molecule results
  in two single oxygen atoms after the UV light is
  absorbed
• The single oxygen wishes to bond with the next
  oxygen it finds, which is usually an oxygen
  molecule
• Therefore, UV radiation creates ozone
• UV radiation also destroys ozone
• The creation and destruction of ozone has been a
  steady process for millions of years

54
Destruction of the Ozone Layer

• Normal photodissociation is not destroying the
  ozone layer
• Chlorofluorocarbons are molecules that contain
  chlorine, fluorine, and carbon
• CFCs break down in the stratosphere
• Chlorine reacts with ozone to produce chlorine
  monoxide and molecular oxygen
• When a stray oxygen atom strikes the chlorine
  monoxide, the oxygen bonds together and the
  chlorine is free again
• Because chlorine is free to react with ozone
  many, many times, the ozone is destroyed more
  than it is created
• The ozone hole is found over Antarctica because
  of meteorological factors that exist solely over
  Antarctica
• Elsewhere on the planet, there is a thinning of
  the ozone layer
• With less ozone, more ultraviolet light can reach
  the surface and result in more skin cancer for
  humans

55
Earth-Sun Relationships

• The Earth orbits the Sun in one year
• The orbit is elliptical
• Aphelion Earth farthest from the Sun (on or
  about July 3)
• Perihelion Earth closest to the Sun (on or
  about January 3)
• The Earth spins on its axis once in 24 hours
• The axis of rotation is tilted 23 ½ with
  respect to the orbital path, called the angle of
  inclination
• The North Pole always points in the same
  direction (towards Polaris the North Star)

56
Earth-Sun Relationships

• Figure 2.13, Page 44

57
Important Dates of the Year

• Summer Solstice (on or about June 21) Noon Sun
  directly over Tropic of Cancer (23 ½ N)
• Winter Solstice (on or about December 21) Noon
  Sun directly over Tropic of Capricorn (23 ½ S)
• Vernal Equinox (on or about March 21) Noon Sun
  directly over the Equator, equal hours of
  daylight and darkness everywhere
• Autumnal Equinox (on or about September 22)
  Noon Sun directly over the Equator

58
Seasons

• The reason we experience seasons is the tilt of
  the Earths axis (and the location of the noon
  Sun changing over the year)
• The greater the tilt of the axis, the greater the
  difference between the seasons
• The variation of solar energy by latitude is
  caused by
• Changes in the angle that the Suns rays hit the
  Earth
• The amount of atmosphere the Suns rays have to
  pass through
• The number of daylight hours

59
Solar Energy Changes in a Year

• Figure 2.14, Page 45

60
Suns Location by Latitude

• Figure 2.16, Page 46

61
Solar Energy Changes by Latitude

• Figure 2.17, Page 47

62
Solar Changes

• Solar Constant the average amount of solar
  energy that reaches the outer limits of our
  atmosphere is about 1368 watts per square meter
• This constant can fluctuate by as much as 0.4
  in a week
• This constant also changes regularly with solar
  cycles on an 11 year period

63
Radiative Properties of the Atmosphere

• Each gas in the atmosphere is not a blackbody,
  but is a selective absorber
• Oxygen and Ozone absorb shortwave radiation
• The atmosphere is mostly transparent for visible
  light
• Methane, carbon dioxide, and water vapor absorb
  infrared radiation
• Water vapor absorbs more infrared radiation than
  any other gas in the atmosphere
• Atmospheric Window The atmosphere is relatively
  transparent between 10-12 µm

64
Absorption by the Atmosphere

• Figure 2.18, Page 48

65
The Greenhouse Effect

• The selective nature of radiation absorption by
  atmospheric gases is the fundamental cause of the
  greenhouse effect
• Shortwave energy largely passes through the
  atmosphere
• Longwave energy is absorbed by the atmosphere
• After absorption of longwave energy, the
  atmosphere emits the longwave energy in all
  directions
• Some of the longwave radiation is absorbed by the
  surface, keeping our surface temperature warmer
• The greenhouse effect is a GOOD thing our
  planet is 60 degrees Fahrenheit warmer (we would
  be an ice planet otherwise)

66
The Misnomer

• Greenhouse Effect is a poor choice of words to
  describe this process
• It used to be thought that a greenhouse becomes
  warmer because the glass transmits shortwave
  energy but blocks longwave energy from leaving
  the greenhouse
• The glass does not block longwave energy
• The greenhouse becomes warm because the glass
  prevents convective motions of the air
• Therefore, the two processes are not the same

67
Greenhouse Warming

• Greenhouse warming, also called global warming or
  the enhanced greenhouse effect, attempts to
  explain the increase in surface temperatures
  lately with an increase in the greenhouse gases
• Therefore, the greenhouse effect and global
  warming are two different things
• Greenhouse gases water vapor, carbon dioxide,
  methane, ozone, and CFCs)
• Water vapor is the most important greenhouse gas

68
Global Energy Budget

• We can calculate energy gains and losses at three
  points
• At the surface
• In the atmosphere
• At the top of the atmosphere

69
Global Energy Budget

• Including shortwave, longwave, and other forms of
  energy gains and losses, we discover that there
  is a balance at all three locations, averaged
  over the entire year and over the entire globe
• Other forms of energy gains and losses that must
  be included are
• Sensible heating processes of conduction and
  convection
• Latent heating

70
Global Energy Budget

• Figure 2.20, Page 51

71
Latitudinal Imbalances

• There is a long-term, global energy balance
• At any given latitude, however, there are some
  locations with energy surpluses and some with
  energy deficits
• The tropics have an energy surplus (more solar
  energy received than terrestrial energy lost)
• The mid-to-upper latitudes have an energy deficit
  (less solar energy received than terrestrial
  energy lost
• These latitudinal imbalances drive the global
  circulation of the oceans and the atmosphere

72
Latitudinal Imbalances

• Figure 2.21, Page 53