9/1/14. Chapter 2: Heating Earth s Surface and Atmosphere. The Atmosphere: An Introduction to Meteorology, 12 th. Lutgens Tarbuck

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1 Chapter 2: Heating Earth s Surface and Atmosphere The Atmosphere: An Introduction to Meteorology, 12 th Lutgens Tarbuck Lectures by: Heather Gallacher, Cleveland State University! Earth s two principal motions: " Rotation is the spinning of the earth on its axis, resulting in the daily cycle of day and night. " Revolution is the movement of the Earth in an elliptical orbit around sun, producing one year.! Its perihelion, the closest point to sun occurs on about January 3.! The aphelion, which is the furthest point from sun occurs on about July 4.! What causes the seasons? 1

2 ! What causes the seasons? " The gradual change in day length accounts for some of the differences in the seasons. " A change in angle of the sun (altitude) also plays a significant role.! Earth s orientation! Solstices and Equinoxes: " The summer solstice occurs on or about June 21 or 22.! At that time, the sun s rays are vertical on the Tropic of Cancer.! It also produces the longest day in the northern hemisphere. " The winter solstice occurs on or about December 21 or 22.! The sun s rays are then vertical on the Tropic of Capricorn.! This results in the shortest day in the northern hemisphere. 2

3 ! Solstices and Equinoxes: " The autumnal (fall) equinox happens on or about September 21 or 22.! This means that the sun s rays are vertical on the equator.! The equinox also means that day and night are equal. " The vernal (spring) equinox occurs on or about March 21 or 22.! The sun s rays are vertical on the equator.! The equinox also means that day and night are equal.! Solstices and equinoxes:! Forms of energy: " Energy is the capacity to do work.! Kinetic energy describes an object in motion: the faster the motion, the greater the energy.! Potential energy means that an object is capable of motion or work. Substances such as food, gasoline, or wood contain potential energy. 3

4 ! Temperature: " Temperature is a measure of the average kinetic energy of atoms or molecules in a substance.! As temperature increases, energy is gained.! As temperature decreases, energy is lost.! Heat: " Heat is the energy transferred in or out of object due to temperature differences. " Energy absorbed but with no increase in temperature is called latent heat. " Sensible heat is heat we can feel or measure with a thermometer.! Conduction: " Conduction is the heat transferred through molecular and electron collisions from one molecule to another.! Convection: " Convection is the heat transferred via movement or circulation of a substance. " Warm air rising creates thermal currents. " Advection describes the primarily horizontal component of convective flow. 4

5 ! Radiation! Solar radiation travels through space providing light and heat energy. " Wavelength describes the length of the crest of one radio wave to the next. " Visible light, often referred to as white light, actually describes the sensitivity of the human eye to a range of wavelengths. " Infrared radiation cannot be seen by the human eye, but is detected as heat. " Ultraviolet radiation, on the opposite side of the visible range, consists of wavelengths that may cause sunburns.! Laws of radiation: " All objects continually emit radiate energy of a range of wavelengths. " Hotter objects radiate more total energy per unit than colder ones. " Hotter objects radiate more short wave radiation than cooler ones. " Objects that are good absorbers of radiation are also good emitters. 5

6 ! Reflection: " Light bounces back from an object at the same angle and intensity.! Scattering: " Scattering produces a large number of weaker rays traveling in different directions.! Backscattering: " Scattering, both backwards and forwards, is known as backscattering.! Reflection and the Earth s albedo: " Albedo is the % of radiation reflected by an object.! The albedo for Earth is about 30%.! For the moon, the albedo is about 7%. 6

7 ! Diffused light: " Diffused light is the result of dust particles and gas molecules scatter light in different directions. " This diffusion results in clear days with a bright blue sky. " A red sun on the horizon is the result of the great distance solar radiation must travel before it reaches your eyes.! Heating of the atmosphere:! The greenhouse effect: " The greenhouse effect is a natural phenomenon and is a result of the Earth s atmosphere trapping some outgoing radiation. " Carbon dioxide and water vapor absorb longwave radiation, which heats the air. " The greenhouse effect is NOT the same as global warming. 7

8 ! Annual energy balance: " Incoming and outgoing radiation account for the Earth s heat budget.! Latitudinal heat balance: " At 38, incoming radiation and outgoing radiation are equal. " Above 38, the atmosphere loses more radiation. " Below 38, the atmosphere gains more radiation. 8

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