8/29/20101Solar Radiation and the SeasonsGE G 1001Professor Holly BarnardAugust 26, 2010IntroductionsSocial contractNo audible ringing or answering of cell phonesPlease text responsibly (do not break the golden rule)Computers to the sides and back of the room, pleasePlease raise your handMy name: Dr. Barnard, Prof. Barnard, Holly, or Dr. B!Add-dropLAST TIME in GEOG 1001!http://apod.nasa.gov/apod/M27: Not a Comet Credit & Copyright: Matthew T. RussellChapter 1Objectives1) Find your way around the universe2) Understand Earth’s orbit3) Find your way around Earth4) What does Jimmy Buffet have to do with Geography?8/29/20102Our Solar SystemFigure 2.1Dimensions and DistancesEarth’s orbitAverage distance from Earth to the Sun is 150,000,000 km (93,000,000 mi)Perihelion – closest at January 3147,255,000 km (91,500,000 mi)Aphelion – farthest at July 4152,083,000 km (94,500,000 mi)Earth is 8 minutes 20 seconds from the SunPlane of Earth’s orbit is the plane of the eclipticWhere are you on Earth?Chapter 2: Solar energy to Earth:What powers Earth and how? What causes the seasons?What is the relationship between energy and temperature?8/29/20103What powers Earth and how? Energy from Sun1) Solar wind2) Radiant or Solar energy (in portions of the electromagnetic spectrum3) Uneven intercepted energy at the top of the atmosphereEnergy from Sun to Earth1) Solar windEffects on: the Auroras (Australisand Borealis)Climate variations (~11 year cycle?) Energy from Sun to EarthFigure 2.8• 2) Radiant or Solar energy—in portions of the electromagnetic spectrum—i.e. Electromagnetic EnergySolarRadia-tionWhy is it uneven?Where is the place receiving the max insolation? What is it called?3. Uneven distribution of INtercepted SOLAr radiaTIONor also called? IN- SOLA- TION8/29/2010413Lambert’s Cosine Law•The way energy changes with angle is described by Lambert’s Cosine Law:E = EoX cosθ•Increasing angle increases area illuminated at the surface and therefore per unit area decreases.θθDistribution of InsolationTropics receive more concentrated insolation due to Earth’s curvatureTropics receive 2.5× more than polesDaily Net RadiationFigure 2.11The SeasonsSeasonalityReasons for seasons8/29/20105SeasonalitySeasonal changesSun’s altitude – angle above horizonDeclination – location of the subsolar pointDaylengthRevolution and RotationFigure 2.13Axial Tilt & ParallelismFigure 2.14Surplus of energyDeficitWhat weather phenomena occur to even the differencebetween areas with surplus and areas with deficit?(Earth) Sphericity results in uneven insolation8/29/20106Daily Net RadiationFigure 2.11Reasons for SeasonsRevolutionEarth revolves around the SunVoyage takes one yearEarth’s speed is 107,280 kmph (66,660 mph)RotationEarth rotates on its axis once every 24 hoursRotational velocity at equator is 1674 kmph (1041 mph)Reasons for SeasonsTilt of Earth’s axisAxis is tilted 23.5° from plane of eclipticAxial parallelismAxis maintains alignment during orbit around the SunSphericitySolar Energy: From Sun to EarthIntercepted energy at the top of the atmosphereElectromagnetic spectrum of radiant energy8/29/2010725Radiation, Distance, Energy at Top of AtmosphereFor earth system science we are interested in amount of energy incident at earth.Energy will decrease as we move away from the sun (or light bulb) because light is spread out over larger surface.Here E (energy) is:Etop of atmophere= Energysun/ Area of SphereEtop of atmophere= Energysun/ 4 π R2Note that R is the radius of a sphere defined by our distance from the sun.26Radiation, Distance, Energy at Top of AtmosphereQuestion: What is the incoming energy of a 100 W light bulb at a distance of 1 meter?Remember energy is:E1-meter away= Ebulb / area of a sphereArea of sphere:Area = 4πr2 = 4 X 3.14 X (1m)2 = 12.6 m2Energy (E) = 100 W / 12.6 m2= 8 W m-21 m27Radiation, Distance, Energy at Top of AtmosphereWhat if we are now 2 meters away from the 100 W light bulb?E1-meter away= Ebulb / area of a sphereArea of sphere:Area = 4πr2 = 4 X 3.14 X (2m)2 = 50 m2Energy (E) = 100 W / 50 m2= 2 W m-2by doubling our distance from 1 m to 2 m we reduced incident radiation by 75%2 m28UNITSHow did we end up with units of Watts per meter squared (W m-2) ?Energy (E) = 100 W / 25 m2= 4 W m-2Energy (E) = W / m2= W m-22 m8/29/20108Radiation and DistanceNow for earth we do the same thing except we replace sun’s energy for the light bulb and we replace the radius with Earth’s orbital radius: Etoa= 3.92x1026W / (4π X reo2)toa = top of earth atmosphereAssume earth orbital radius (reo) = 1.5 x 1011mEtoa= 3.92x1026W / (4π X (1.5x1011m)2)Etoa= 1404 W m-2EsunETOAStefan-Boltzmann Lawthe warmer the object, the greater the energy emitted by that
View Full Document
Unlocking...