Chapter2

ES 1110 – Chapter 2: 

ES 1110 – Chapter 2 The Energy Cycle

Scalars and Vectors: 

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

Forces: 

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

Acceleration: 

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

Work and Energy: 

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)

Kinetic Energy: 

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)

Potential Energy: 

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

Air Parcels: 

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

Temperature: 

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

Temperature Scales: 

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

Temperature Scales: 

Temperature Scales Figure 2.1, Page 29

Calories, Joules, Power, and Watts: 

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

Heat: 

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

Heat vs. Temperature: 

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 Eskimo’s molecules, the iceberg has many, many more molecules to add up the total kinetic energy

Specific Heat: 

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)

Specific Heat of Substances: 

Specific Heat of Substances Table 2.1, Page 30

Temperature Changes: 

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

Means of Energy Transfer: 

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

Conduction: 

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)

Conduction: 

Conduction Figure 2.2, Page 30

Convection: 

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

Convection: 

Convection Figure 2.3, Page 31

Other Means in the Book: 

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)

Advection: 

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

Cold Air Advection: 

Cold Air Advection Figure 2.4, Page 31

Phases of Water: 

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

Phases of Water: 

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

Phase Changes and Energy: 

Phase Changes and Energy Figure 2.5, Page 34

Heating of Water: 

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 wouldn’t see the water vaporize until 540 calories were added after reaching 100 degrees Celsius! Where did all that heat go?!

Latent Heat: 

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

Latent Heat of Water: 

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

Latent Heat: 

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

Latent Heat as a Means of Transfer: 

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

Lifting of an Air Parcel: 

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

Lifting of an Air Parcel: 

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

Dry Adiabatic Lapse Rate: 

Dry Adiabatic Lapse Rate Notice that the air parcel’s 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

Dry Adiabatic Lapse Rate: 

Dry Adiabatic Lapse Rate Figure 2.6, Page 34

Adiabatic Processes as a Means of Energy Transfer: 

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

Moist Adiabatic Lapse Rate: 

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!

A Lifted Moist Parcel: 

A Lifted Moist Parcel Figure 2.7, Page 36

Radiation: 

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

Waves: 

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

Electromagnetic Spectrum: 

Electromagnetic Spectrum Figure 2.9, Page 38

Electromagnetic Radiation: 

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

Radiation Types: 

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

Radiation Laws: 

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 = σ x T4, where σ is a constant and T is temperature) If the temperature doubles, the amount of energy emitted is 16 times more! Wien’s Law: The peak wavelength of energy emitted by an object depends on the temperature of the emitting body (λmax = constant/T) Because temperature is on the bottom, an increase in temperature results in a shorter peak wavelength

Radiation Curves: 

Radiation Curves Figure 2.10, Page 39

Radiation Interacting with an Object: 

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”

Albedo: 

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

Absorption: 

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)

Absorption of Radiant Energy: 

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)

Other Radiation Issues: 

Other Radiation Issues Blackbody – an object that absorbs all the electromagnetic radiation that it encounters regardless of wavelength No object is a perfect blackbody Kirchoff’s Law: A good absorber of radiation is also a good emitter of radiation at that same wavelength

The Ozone Layer: 

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

Destruction of the Ozone Layer: 

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

Earth-Sun Relationships: 

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)

Earth-Sun Relationships: 

Earth-Sun Relationships Figure 2.13, Page 44

Important Dates of the Year: 

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

Seasons: 

Seasons The reason we experience seasons is the tilt of the Earth’s 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 Sun’s rays hit the Earth The amount of atmosphere the Sun’s rays have to pass through The number of daylight hours

Solar Energy Changes in a Year: 

Solar Energy Changes in a Year Figure 2.14, Page 45

Sun’s Location by Latitude: 

Sun’s Location by Latitude Figure 2.16, Page 46

Solar Energy Changes by Latitude: 

Solar Energy Changes by Latitude Figure 2.17, Page 47

Solar Changes: 

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

Radiative Properties of the Atmosphere: 

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

Absorption by the Atmosphere: 

Absorption by the Atmosphere Figure 2.18, Page 48

The Greenhouse Effect: 

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)

The Misnomer: 

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

Greenhouse Warming: 

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

Global Energy Budget: 

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

Global Energy Budget: 

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

Global Energy Budget: 

Global Energy Budget Figure 2.20, Page 51

Latitudinal Imbalances: 

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

Latitudinal Imbalances: 

Latitudinal Imbalances Figure 2.21, Page 53