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Chapter 2 Heating Earth’s Surface and Atmosphere The Atmosphere 9e Lutgens & Tarbuck Power Point by Michael C. LoPresto PowerPoint PPT Presentation


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Chapter 2 Heating Earth’s Surface and Atmosphere The Atmosphere 9e Lutgens & Tarbuck Power Point by Michael C. LoPresto. Earth’s Motions. Earth has two principle motions Rotation – the spinning of Earth about its axis Revolution – the movement in orbit around the sun.

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Chapter 2 Heating Earth’s Surface and Atmosphere The Atmosphere 9e Lutgens & Tarbuck Power Point by Michael C. LoPresto

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Chapter 2Heating Earth’s Surface and AtmosphereThe Atmosphere 9eLutgens & TarbuckPower Point by Michael C. LoPresto


Earth’s Motions

  • Earth has two principle motions

    • Rotation – the spinning of Earth about its axis

    • Revolution – the movement in orbit around the sun


  • Distance between Earth and Sun averages 150 million km.

    • Distance varies during the year

  • Perihelion: point in orbit of a planet closet to the sun.

  • Aphelion: point in orbit of a planet farthest from the sun.


The Seasons

  • Earth’s Orientation-Inclination of the Axis


The Seasons

  • The gradual change in day length accounts for some of the difference between winter and summer

  • The seasonal changes in the angle of the Sun above the horizon accounts for most of the difference

    • When the sun is directly above, the rays are more concentrated

    • When the sun is at an angle, the rays are spread out over a larger area


Earth-Sun Relations


  • The four days each year given special significance based on the annual migration of the direct rays of the Sun and its importance to the yearly cycle of weather are:


  • Solstices and Equinoxes


Solstices and Equinoxes

  • Winter Solstice – shortest day, first day of winter (December 21 or 22)

  • when the vertical rays of the Sun are striking 23.5° south latitude (Tropic of Capricorn


  • Summer Solstice – longest day, “official” first day of summer (June 21 or 22)

  • when the vertical rays of the Sun are striking 23.5° north latitude (Tropic of Cancer)


  • Equinoxes – Half way between the solstices, equal days and nights

    • Autumnal equinox – Sept. 22 or 23

    • Vernal (spring) equinox – March 21 or 22

    • when the vertical rays of the Sun strike the equator


Energy and Temperature

  • Energy – the capacity to do work

  • Kinetic Energy – energy associated with and object by virtue of its motion (swinging a hammer)

  • Potential Energy – has the potential to do work (food, hail suspended in a storm)

  • Temperature – how warm or cold an object is OR a measure of the average (not total) kinetic energy of the atoms or molecules in a substance


Heat

  • Heat – the transfer of energy into or out of an object and its surroundings.

  • Flows from region of higher temperature to one of lower temperature.

  • Once equal, flow stops.


  • Mechanisms of Energy Transfer


Mechanisms of Heat Transfer

  • Conduction – transfer of heat from one object to another through electron and molecular collisions (ex. Metals)

  • Convection – heat transfer that involves the actual movement or circulation of a substance

    • Thermals – examples of convection that involve upward movement of warm, less dense air

      - advection – the horizontal component of convection, common name “wind”


  • Radiation – does not need a medium, can travel through the vacuum of space

    • The sun is the ultimate source of energy that drives the weather

    • Electromagnetic Spectrum

      • Gamma, X-ray, UV, Visible Spectrum, IR, Micro, Radio

    • All electromagnetic waves travel at 300,000 km/s

    • It is the wavelength that changes

    • Most of the sun’s waves is concentrated in the visible to near visible range (43%), IR (49%), and <1% x-ray, gamma, and radio


Electromagnetic Radiation

Electromagnetic Spectrum


Laws of Radiation

  • 1. all objects emit radiant energy

  • 2. hotter objects radiate more total energy per unit area than colder objects

  • 3. the hotter the radiating body, the shorter is the wavelength of maximum radiation

  • 4. objects that are good absorbers of radiation are also good emitters


Radiation from Sun & Earth


Incoming Solar Radiation

  • Some energy absorbed

    • Object gets warmer

  • Some energy transmitted

    • Object transparent to certain wavelengths

  • Some radiation bounces off object

    • Reflection: bounces back @ same angle and intensity

    • Scattered: larger # of weaker rays in many directions


Reflection

Scattering


Incoming Solar Radiation

  • About 50% of the solar energy hits the Earth’s surface

  • 30% is reflected back to space

  • The remaining 20% is absorbed by clouds and atmospheric gases

  • Albedo – the fraction of radiation reflected by a surface


What Happens to Radiation?


  • Radiation Emitted by Earth

Atmospheric Window


Radiation Emitted by Earth

  • Radiant energy absorbed is eventually reradiated skyward

  • This radiation is in the form of long wave infrared radiation

  • Because atmospheric gases are more efficient absorbers of long wave radiation, the atmosphere is heated from the ground up


  • The general drop in temperature with increased altitude in the troposphere (about 6.5°C/kilometer, a figure called the normal lapse rate) supports the fact that the atmosphere is heated from below.


Heat Budget


Heat Budget

  • The annual balance that exists between incoming and outgoing radiation is called the heat budget.

  • Earth’s average temperature remains relatively constant despite seasonal cold spells and heat waves.

  • This holds for the entire planet but not at each latitude.


Sun Angles at Different Latitudes


Latitudinal Heat Balance


  • Averaged over the year, a zone between 38°N and 38°S receives more solar radiation than is lost to space.

  • The opposite is true for higher latitudes, where more heat is lost through radiation than is received.

  • It is this energy imbalance between the low and high latitudes that drives the global winds and ocean currents, which transfers surplus heat from the tropics poleward.


  • Also, the radiation balance of a given place fluctuates with changes in cloud cover, atmospheric composition, and most important, Sun angle and length of daylight.

  • Thus, areas of radiation surplus and deficit migrate seasonally as the Sun angle and length of daylightchange.


Temperature Data at Different Latitudes


Calculating Sun Angles


Chapter 2

END


The Greenhouse Effect


Reflection and Earth’s Albedo


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