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Overview of Climate

Overview of Climate. V. Ramaswamy (“Ram”) U.S. National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory Princeton University [USA]. Lecture # 1. Energy balance of the planetary surface-atmosphere system. Factors governing the global-mean energy balance.

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Overview of Climate

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  1. Overview of Climate V. Ramaswamy (“Ram”) U.S. National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory Princeton University [USA]

  2. Lecture # 1 • Energy balance of the planetary surface-atmosphere system. • Factors governing the global-mean energy balance. • Radiative and Radiative-Convective Equilibria.

  3. Temperatures of Planets Planet Dist. S0 A Te Tm Tsfc GHE from (W/ (K) (K) (K) (K) Sun m2) (AU) VENUS 0.72 2640 0.75 232 235 730 495 EARTH 1.0 1366 0.30 255 254 288 34 MARS 1.52 570 0.15 217 218 223 5 AU = Astronomical unit = 1,5 x 108 km S0 = Solar irradiance at planet GHE = GreenHouse Effect

  4. Can you estimate a “WhiteHouse Effect” viz., how much the Earth is kept ‘cool’ owing to its reflecting abilities ?

  5. Factors involved in the Global Heat Balance • Gradients in Temperature • Amount and location of species (gases, aerosols and clouds) • Radiative (absorption, emission, reflection) properties of species in the electromagnetic spectrum • Radiative properties of the surface • Convection (arising due to differential heating of surface and atmosphere) • Large-scale dynamical flows caused by planetary rotation, topography, and land-sea contrast

  6. Solar blackbody fn. Earth’s “effective” blackbody fn. CFCs Clouds, Aerosols active throughout spectra Methane Nitrous oxide Oxygen; Ozone Carbon dioxide Water vapor uv vis near-ir longwave

  7. Curve of growth of absorption by gases CO2 (15 micron Band CH4, N2O CFCs

  8. Note: Radiances (represented through brightness temperatures) are in the unit of Kelvin. GCM vs. AIRS –Global annual mean spectra Clear-sky Total-sky [Huang et al. 2007 GRL]

  9. CLEAR Sky (over Oceans) E = surface emitted flux (goes as T4) F = Longwave flux at TOA (E – F) = a measure of “greenhouse effect” Raval and Ramanathan (1989)

  10. Total Outgoing LW radiation ~ 240 W/m2

  11. VIS Near- IR

  12. 100 Gas Depth 0.01 0.9 Cloud SS alb. 0.999

  13. Water clouds can usually be treated as “blackbody” radiative agents in the longwave, just like the surface.

  14. Aqua CERES Measurement 256 128 0 350 250 150 Reflected shortwave radiation (W m-2) Outgoing longwave radiation (W m-2) Global, annual-mean Net SW = Net LW = 240 W/m2

  15. Vertical profile of temperature(RE and RCE conditions) • SW and LW components only  Radiative Equilibrium (RE), BUT this is not the real story • Balance against the radiative cooling of atmosphere • Considerations for the global,annual-mean • Horizontal- and time-averaging  a compensating ‘force’ acting in the vertical • This ‘force’ acts to redistribute heat in the vertical • This ‘force’ is  CONVECTION  Radiative-Convective Equilibrium (RCE)

  16. Strictly speaking, an assumption is that contributions from large-scale dynamics is negligible. • Concept of ‘lapse rate’  the gradient of temperature with respect to height (or pressure).

  17. Question If the solar irradiance available to the Earth were to change by 2% from the present-day value, what would be the response in the effective planetary temperature? [The solution is the same as that for doubling of carbon dioxide in the absence of feedbacks]

  18. Principal Sources • “Physics of Climate” by A. OORT and J. PEIXOTO • “Global Physical Climatology” by D. HARTMANN • Radiation notes [JOS LELIEVELD, MPI-Mainz] • Atmospheric Radiation lectures [Boulder, 1986] • Intergovernmental Panel on Climate Change, 2001 and 2007, Working Group I (The Physical Science Basis) • Y. Huang, Ph. D. thesis (Princeton University, 2008)

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