Introduction to Climatology GEOGAPHY 300 Dipoition of Solar adiation at Earth Surface Tom Giambelluca Univerity of Hawai i at Mānoa eflection: Albedo i a key property of urface controlling the urface energy balance Aborbed radiation: ued to Heat the oil: oil heat flux (G) Heat the air: enible heat flux (H) Evaporation water: latent heat flux (LE) Energy Balance and ALBEDO K α = K where : α = albedo K = reflectedhortwave radiation K = downward hortwave radiation Typical Albedo Land cover type Albedo Foret 0.12-0.14 Graland 0.16-0.25 Crop 0.16-0.22 Bare oil (wet) 0.08-0.10 Bare oil (dry) 0.15-0.25 Burned vegetation 0.06-0.10 Snow 0.80-0.90 Ocean (calm; high zenith 0.08 angle) Pla Earth 0.30 1
GLOBAL ALBEDO PATTEN Influence on Albedo Denity, LAI, and height of vegetation Soil color and moiture content Sun angle and lope/apect of land urface elative amount of direct and diffue light Albedo v. LAI Longwave adiation Surface emit longwave radiation a a function of it temperature and emiivity Atmophere aborb mot longwave radiation from the urface: Greenhoue Effect Surface alo receive longwave radiation from the atmophere Hale et al. 2004. Senitivity of tropical land climate to leaf area index: role of urface conductance veru albedo. J. Clim. 17: 1459-1473 2
Greenhoue Effect Exchange of adiation Between the Surface and the Atmophere Of the hortwave radiation reaching the urface, a certain amount i reflected, depending on the albedo of the urface, the ret i aborbed. Once aborbed, that energy i converted to other form. One reult of aborbing olar radiation i that the urface become warmer. Thi increae the emiion of longwave radiation by the urface (Stefan-Boltzmann Eq.). LONGWAVE EXCHANGE adiation Balance Longwave radiation by the urface i trongly aborbed by greenhoue gae in the atmophere. The atmophere i warmed a a reult of aborbing longwave radiation, and hence emit more radiation. Atmopheric radiation goe in all direction, ome warming the layer of air above, and ome warming the urface. Thi re-radiation by the atmophere to the urface i reponible for the greenhoue effect. 3
SUFACE NET ADIATION where : = K K + A L = radiation A = downward longwave radiation aborbed by the urface L = upward longwave radiation emitted by the urface SUFACE NET ADIATION = K K + A L = (1 α) K + A ε σt = (1 α) K + ε ( L σt where α = albedo ε = urfaceemiivity T = urface temperature L = downward longwave radiation from atmophere 4 4 ) adiation Meaurement Shortwave radiation Eppley 8-48 black & white adiation Meaurement Direct hortwave radiation NIP: Normal incidence pyrheliometer Eppley PSP: preciion pectral pyranometer Kipp & Zonen CM11 Diffue hade band hade dik 4
adiation Meaurement Surface temperature (upward LW): infrared thermometer Apogee ITS-P adiation Meaurement Net radiation: radiometer EBS Q*7.1 adiation Meaurement Net radiation: radiometer Kipp & Zonen CN1 All-Wave adiation Shortwave adiation Longwave adiation 5
Solar contant: 1367 W m -2 Area intercepting radiation (dik area): πr 2 Surface area of earth (urface of phere): 4πr 2 Solar contant per unit urface area of earth = 1367 W m -2 x πr 2 / 4πr 2 = 1367/4 = 341.75 W m -2 Aume earth maintain energy equilibrium Aume exchange of energy into and out of the earth plaary ytem are only in the form of radiation Earth receive 341.75 W m -2 of olar energy To maintain energy equilibrium, Earth mut give up 341.75 W m -2 Plaary albedo: 30% Therefore, the earth aborb 70% of 341.75 W m -2 = 239.23 W m -2 To maintain balance earth mut emit 239.23 W m -2 What i the radiative equilibrium temperature of earth (temp. neceary to emit 239.23 W m -2 )? Ue the Stefan-Boltzmann equation: earranging I = σt 4 we get: T = (I/σ) 0.25 T = (239.23/ 5.67 x 10-8 ) 0.25 = 254.86 K = -18.3 C ß adiative Equilibrium of Earth adiative Equilibrium of Earth = -18.3 C Actual mean urface temperature of earth: 20 th Century Mean: 13.9 C (57.0 F) 2010 Mean: 14.5 C (58.12 F) Quetion 1: Why i the actual urface temperature 32.8 C higher than the radiative equilibrium temperature? Quetion 2: I the radiative equilibrium temperature of the earth changing due to increaing greenhoue gae? Quetion 3: Why i the urface temperature of the earth increaing? 6
Sytem Component Plaary Sytem: for plaary ytem = 0 Atmophere: for plaary ytem < 0 Surface: for plaary ytem > 0 Why no radiative equilibrium for atmophere or urface? Becaue of other (non-radiation) energy exchange between urface and atmophere Senible and latent energy flux move energy derived from radiation urplu at urface to make up the radiation deficit in the atmophere Why no radiative equilibrium for atmophere or urface? Energy balance equation: = LE + H + G + P Surface Energy Balance where: LE = latent energy flux to the atmophere, H = enible energy flux to the atmophere, G = enible energy conduction into the oil, and P = photoythei G i poitive during the day and negative at night; on a 24-hour bai G can be ignored Fundamental Influence on Air cloudine, urface characteritic P i mall relative to other energy balance term and can alo be ignored Simplified Energy Balance Equation = LE + H Thi ay that the energy derived from radiation at the urface goe primarily into to thing: energy for evaporation of water and energy for heating the air. Surface characteritic control the partitioning of radiation into LE and H. 7
Fundamental Influence on Air cloudine, urface characteritic partitioning of radiation: urface characteritic (vegetation cover, moiture availability) = LE + H Fundamental Influence on Air cloudine, urface characteritic partitioning of radiation: urface characteritic (vegetation cover, moiture availability) = LE + H energy advection: horizontal tranfer of energy via ocean current and atmopheric circulation Fundamental Influence on Air cloudine, urface characteritic partitioning of radiation: urface characteritic (vegetation cover, moiture availability) = LE + H energy advection: horizontal tranfer of energy via ocean current and atmopheric circulation land or ocean: pecific heat, evaporation, mixing, tranparency Fundamental Influence on Air cloudine, urface characteritic partitioning of radiation: urface characteritic (vegetation cover, moiture availability) = LE + H energy advection: horizontal tranfer of energy via ocean current and atmopheric circulation land or ocean: pecific heat, evaporation, mixing, tranparency altitude-elevation: air i primarily heated by the urface-- ditance from the ource; reduced downward longwave radiation with elevation; riing air cool by expanion. 8
Global Ditribution Continentality 9