Slide 1Slide 2Slide 3Slide 4Eccentricity: Earth’s orbit around the sunObliquity: Tilt of the Earth’s rotational axisPrecession: positions of solstices and equinoxes in the eccentric orbit slowly changeSlide 8Slide 9Slide 10Slide 11Blackbody Radiation CurvesSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Absorption, Scattering and Reflectance (Albedo)Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Radiation, Convection and ConductionBasic Energy and Mass Transfers in the AtmosphereBasic Energy and Mass Transfers in the Atmosphere (Cont’d)Slide 41Slide 42Slide 43Chapter 2: Global Energy BalanceChapter 2: Global Energy BalanceThis chapter discusses:This chapter discusses:1.1.Earth’s emission temperatureEarth’s emission temperature2.2.Greenhouse effectsGreenhouse effects3.3.Global radiative energy balance and its Global radiative energy balance and its distributionsdistributionsWhy do we have seasons?Why do we have seasons?Earth’s Tilt and Seasonal RadiationEarth’s Tilt and Seasonal Radiation Orbit around Sun: slightly elliptical Tilt of spin axis at 23.5°Rotation on axis (day&night) in 24 hrsSpeed (eq 1038 mi/hr, 0 at axis)Axis points toward North Star (Polaris) Summer Solstice (NH) on June 21/22Axis toward SunVertical rays on Tropic of Cancer (23.5°N Lat)24-hr day above Arctic Circle (66.5°N Lat)24-hr night below Antarctic Circle (66.5°S Lat) Winter Solstice (NH) on Dec. 21/22Axis away from SunVertical rays on Tropic of Capricorn (23.5°S Lat)24-hr night above Arctic Circle (66.5°N Lat)24-hr day below Antarctic Circle (66.5°S Lat) Fall Equinox (NH) on Sept 22/23 (day = night length at all points) Spring Equinox (NH) on March 20/21 (day=night length at all points)Earth’s Orbit Today and the SeasonsEarth’s Orbit ParametersEccentricity (shape of the orbit: varies from being elliptical to almost circular)Obliquity (tilt of the axis of rotation)Precession (wobbling of the axis of rotation)Eccentricity: Earth’s orbit around the sunOrbit = Circle(Eccentricity = 0)Orbit = Ellipse (Eccentricity = 0.05 shown0.0167 today0.0605 maximum)Varies from near circle to ellipse with a period of 100,000 yearsDistance to Sun changes  insolation changesObliquity: Tilt of the Earth’s rotational axis• Cycle of ~ 41,000 years• Varies from 22.2 to 24.5°(The current axial tilt is 23.5°)If Earth’s orbit were circular,No tilt = no seasons90° tilt = largest seasonal differences at the poles (6 mon. darkness, 6 mon. overhead sun)• Greater tilt = more intense seasonsPrecession: positions of solstices and equinoxes in the eccentric orbit slowly changePeriod of about 23,000 yearsWobbling of the axisTurning of the ellipseEarth’s Orbit Changes Through TimeChanges in Insolation Received on Earth• Precession dominates at low and middle latitudes• Tilt is more evident at higher mid-latitudes.• Eccentricity is not significant directly, but modulates the amplitude of the precession cycle.• Summer changes dominate over winter at polar latitudes.Energy from the SunEnergy from the Sun1. Characteristics Travels through space (vacuum) in a speed of light3. Importance to climate and climate change In the form of waves:In stream of particlesElectromagnetic waves(Photons)Primary driving force of Earth’s climate Primary driving force of Earth’s climate engineengine2. Electromagnetic spectrum From short wavelength, high energy, gamma rays to long wavelength, low energy, radio waves Releases heat when absorbedUltraviolet, Visible, InfraredUltraviolet, Visible, InfraredSun’s Electromagnetic SpectrumSun’s Electromagnetic SpectrumSolar radiation has peak intensities in the Solar radiation has peak intensities in the shorter wavelengthsshorter wavelengths, , dominant in the region we know as dominant in the region we know as visiblevisible, thus , thus shortwave shortwave radiationradiationBlackbody Radiation Curves Any object above Any object above absolute zero absolute zero radiates heat, radiates heat, as as proportional to proportional to TT44Longwave & Shortwave RadiationLongwave & Shortwave RadiationThe The hot sunhot sun radiates at radiates at shortershorter wavelengths wavelengths that carry that carry more more energyenergy, and the , and the fraction fraction absorbed by the absorbed by the cooler earthcooler earth is is then re-radiated then re-radiated at at longer longer wavelengths.wavelengths.Incoming Solar Radiation (Insolation)Incoming Solar Radiation (Insolation) At the top of the At the top of the atmosphereatmosphereWarming Earth's AtmosphereWarming Earth's AtmosphereSolar radiation passes first through the upper atmosphere, but only Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwave energy.warm the ground and generate longwave energy.This heat and energy at the surface then warms the atmosphere This heat and energy at the surface then warms the atmosphere from below.from below.Earth’s Radiation Budget (Global Annual Average)Earth’s Radiation Budget (Global Annual Average)Earth reflects 30% directly back to space, absorbs Earth reflects 30% directly back to space, absorbs about 20% in the atmosphere, and absorbs about 50% about 20% in the atmosphere, and absorbs about 50% at the surface.at the surface.Earth’s lower atmosphere is warmed by radiation, Earth’s lower atmosphere is warmed by radiation, conduction, convection of sensible heat and latent conduction, convection of sensible heat and latent heat.heat. Kiehl and Trenberth (1997) BAMS Kiehl and Trenberth (1997) BAMS (Fig. 7)(Fig. 7)Comparison of Different EstimatesComparison of Different Estimates Kiehl and Trenberth (1997) BAMS Kiehl and Trenberth (1997) BAMS (Fig. 7)(Fig. 7)Incoming Solar RadiationIncoming Solar RadiationSolar radiation is scattered and reflected by the atmosphere, clouds, Solar radiation is scattered and reflected by the atmosphere, clouds, and earth's surface, creating an average albedo of 30%.and earth's surface, creating an average albedo of 30%.Atmospheric gases and clouds absorb another 19 units, leaving 51 Atmospheric gases and clouds absorb another 19 units, leaving 51 units of shortwave absorbed by the earth's surface.units of shortwave absorbed by the