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.

6. Temperatures of Planets Planet Dist. S 0 A T e T m T sfc GHE from (W/ (K) (K)(K) (K) Sun m 2 ) (AU) VENUS 0.72 2640 0.75 232 235730 495 EARTH 1.0 1366 0.30 255 254288 34 MARS 1.52 570 0.15 217 218223 5 AU = Astronomical unit = 1,5 x 10 8 km S 0 = Solar irradiance at planet GHE = GreenHouse Effect

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

8. 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

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

11. CFCs CH 4, N 2 O CO 2 (15 micron Band Curve of growth of absorption by gases

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

14. E = surface emitted flux (goes as T 4 ) F = Longwave flux at TOA (E – F) = a measure of “greenhouse effect” Raval and Ramanathan (1989) CLEAR Sky (over Oceans)

15. Total Outgoing LW radiation ~ 240 W/m 2

16. VIS Near- IR

17. 0.01 100 Gas Depth Cloud SS alb. 0.999 0.9

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

22. 256 128 0 150 250 350 Reflected shortwave radiation (W m -2 ) Outgoing longwave radiation (W m -2 ) Aqua CERES Measurement Global, annual-mean Net SW = Net LW = 240 W/m 2

23. 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)

26.  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).

34. 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]

35. 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)