chapter 2 heating earth’s surface and atmospherefbuon/pgeog_130/lecture_pdfs/chapter2.pdfii....

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Chapter 2Heating Earth’s Surface and Atmosphere

I. Earth–Sun RelationshipsA. Earth’s 2 Principal Motions

1. Rotation : spinning about the axis2. Revolution : orbit around the sun

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Revolution

a. Perihelion :earth closest to sunb. Aphelion :earth farthest from sun

B. The seasons- result from variations in the intensity (or amount) of solar radiation striking the earth

-Height of noon sun changes

-Length of day changes


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Sun Angle-influence intensity of solar radiation

Sun Angle-influence distance traveled through atmosphere


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C. Earth’s Orientation1. Plane of the ecliptic = plane of earth’s orbit around the sun2. Inclination of the axis = tilted 23.5 degrees

C. Earth’s Orientation

Circle of illumination


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D. Solstices and equinoxes

Circle of illumination


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Temperature Data at Different Latitudes

- annual temperature range increases with latitude

- earth-sun geometry is not the only control

II. Energy, Heat, and Temperature

Universe = composed of matter and energy

Energy = the capacity to do work (move matter)

A. Forms of energy1. Kinetic energy: energy of motion (1/2 mv2), atomic level

2. Potential energy: potential to do work (ρρρρgh)


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II. Energy, Heat, and Temperature

B. Temperature: a measure of the average kinetic energy of the atoms or molecules in a substance

- Fahrenheit, Celsius, and Kelvin (-273)

C. Heat: refers to the transfer of energy between substances due to temperature differences

- heat flow stopswhen temperatures are equal

III. Mechanisms of Energy Transfer

A. Conduction: transfer of heat through electron and molecular collision

- poor conductors = insulators- air = poor conductor- metal = good conductor


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B. Convection:heat transfer involving movement or circulation of a substance (liquids & gasses)

- thermals= convective cells in atmosphere- convection = up-down movement- advection = horizontal movement

Convection Cell Examples


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C. Radiation: energy emitted in the form of waves or particles

Solar Radiation = electromagneticradiation- self-propagatingwave that can travel through the void of space - classified into types according to the wavelength


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electromagnetic radiation

- order of increasing wavelength: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, radio waves

2. Laws of radiation

- All objects continually emit radiant energy over a range of wavelengths

- Hotter objects radiate more total energy per unit area than do colder objects

Stefan-Boltzman LawE = σσσσT4 σ = 5.67x10-8 W/m2K4

Sun = 6000 K Earth = 300 KE(S)= 73,483,200 W/m2 E(E) = 459 W/m2


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- The hotter the radiating body, the shorter the wavelength of maximum radiation

Wien’s Displacement Lawλλλλmax = C/T C = 2898 µmKλλλλsun = 0.483 λλλλearth = 9.66


- Objects that are good absorbers of radiation are also good emitters

Blackbody = 100% efficientAtmospheric Gasses= selective absorbers


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III. What Happens to Radiation?- absorbed = observed increase in kinetic energy- transmitted = transparent to solar radiation- redirected = reflection and scattering

A. Reflection and scattering

diffused light = scattered solar radiation

albedo= fraction of radiation that is reflected by a surface


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Scattering & Diffused Light

Crepuscular rays

IV. Radiation Emitted by Earth

A. Earth radiates energy as a longwave (infrared band, 95%)

B. Selective absorption by gasses


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The Greenhouse Effect

CO2

H2O

C. Role of clouds in heating Earth

-clouds at nightabsorb infrared radiation and re-radiate it back to surface

-low thick clouds during the dayreflect solar radiation, cool the surface


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V. Heat Budget

VI. Latitudinal Heat Balance


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Electromagnetic radiation is generally described as a self-propagating wavein space with electric and magneticcomponents. These components oscillateat right angles to each other and to the direction of propagation, and are in phasewith each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, infrared radiation , visible light, ultraviolet radiation, X-rays and gamma rays. In some technical contexts the entire range is referred to as just 'light

Classically, the electromagnetic field is a physical influence (a field) that permeates through all of space, and which arises from electrically chargedobjects and describes one of the four fundamental forcesof nature - electromagnetism. It can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by non-moving charges and the magnetic field by moving charges (currents); these two are often described as the sources of the field.


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