1!Lecture Ch. 12!• Review of simplified climate model!• Revisiting: Kiehl and Trenberth!• Overview of “atmospheric heat engine”!• Current research on clouds-climate!Curry and Webster, Ch. 12!For Tuesday: Read Ch. 13!ROAST review comments due Nov. 23 at 11:59pm PT!Simplified Climate Model!• Atmosphere described as one layer!– Albedo αp~0.31: reflectance by surface, clouds, aerosols, gases !– Shortwave flux absorbed at surface!• Earth behaves as a black body!– Temperature Te: equivalent black-body temperature of earth!– Longwave flux emitted from surface!Curry and Webster, Ch. 12 pp. 331-337; also Liou, 1992!FS=0.25*S0(1- αp) FL=σTe4 FL Emitted from sphere surface 4πr2 FS Incident on projected disc πr2 FS = FL Simplified Climate Model!• Incoming shortwave = Outgoing longwave!• Energy absorbed = Energy emitted!FS = 0.25*S0(1- αp) FL = σTe4 Solar Constant!• Luminosity of the sun !• Irradiance at earth S0 = L0/(4πd2) = 1.4x103 W/m2!€ d = 1.5 ×1011m (p.437)€ Area = 4πd 2L0 ~ 3.9x1026 W (p. 331)!Simplified Climate Model!• At thermal equilibrium (why?)!• Observed surface temperature T = 288K!• What’s missing?!FS = FL 0.25*S0(1- αp) = σTe4 Te = [0.25*S0(1- αp)/σ]0.25$Te ~ 255K Sensitivity to Albedo!• What if albedo changes?!• 1% decrease in albedo warms temperature 1K!• 1% increase in albedo cools temperature 1K!Te = [0.25*S0(1- αp)/σ]0.25$αp=0.31, Te ~ 255K αp=0.30, Te ~ ?2!Add an Atmosphere!!• Atmosphere is transparent to non-reflected portion of the solar beam!• Atmosphere in radiative equilibrium with surface!• Atmosphere absorbs all the IR emission!Fsurf FS TOA: FS = Fatm 0.25*S0(1- αp) = σTatm4 Tatm = 255K Fatm Fatm Atmos: Fsurf = 2Fatm σTsurf4 = 2σTatm4 Tsurf = 303K What’s wrong?!• With no atmosphere, Tsurf = 255K • With “atmosphere”, Tsurf = 303K • From observations, Tsurf = 288K • Real atmosphere: !– Not perfectly transparent to incoming solar!– Not perfectly opaque to infrared!– Not in pure radiative equilibrium with surface!• Three assumptions were wrong!!Atmospheric Heat Engine!• Latitudinal and meridional heat transfer!• Walker circulation and Aus-Asia monsoons!• Efficiency, irreversibility, entropy!• Hydrological cycle!Curry and Webster, Ch. 12!The Atmospheric “Heat Engine”!3!Atmospheric Heat Engine!Atmospheric Entropy!• Difference between energy and entropy flux!• Irreversible processes!Atmospheric Entropy!• Internal production of entropy by Earth!Hydrological Cycle!• Definition!• Residence times!4!Latitudinal Heating Distribution!• Net heating at equator!• Net cooling at poles!Heating and Circulation!• Fluid motion from vertical density gradient!5!Meridional Heat Transfer!• Equator-to-pole heat transport!Zonal Heat Transfer!• Walker circulation!• Asian-Australian
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