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The Role of Clouds and Convection in Earth’s Energy Balance

The Role of Clouds and Convection in Earth’s Energy Balance. Lisa Goddard goddard@iri.columbia.edu. Interaction of atmospheric processes. (from Arakawa 2004, J. Climate). OUTLINE. Ideal Gas Law & vertical structure of atmosphere Effect of clouds on energy balance

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The Role of Clouds and Convection in Earth’s Energy Balance

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  1. The Role of Clouds and Convection in Earth’s Energy Balance Lisa Goddard goddard@iri.columbia.edu EESC W4400x

  2. Interaction of atmospheric processes (from Arakawa 2004, J. Climate) EESC W4400x

  3. OUTLINE • Ideal Gas Law & vertical structure of atmosphere • Effect of clouds on energy balance • Lapse Rate & Atmospheric stability • Starting to form the “big picture”: temperature, pressure, clouds & OLR • Parameterization of convection & cloud physics Main Points • Troposphere heated from below  CONVECTION - primary mechanism for transporting heat from surface to mid-troposphere - thoroughly mixes atmospheric constituents • Radiative-convective equilibrium is consequence of energy balance in atmosphere, and sets criterion of vertical stability EESC W4400x

  4. Ideal Gas Law Where, p = pressure (N/m2=kg/m.s2) V = volume (m3) m = mass (kg)  ρ = m/V = density R = gas constant (depends on particular gas) T = temperature (oK) EESC W4400x

  5. Vertical Profile of Atmosphere Temperature decreases w/ altitude to ~15km (w/i troposphere)then starts to increase again (w/i stratosphere) … Pressure decreases w/ altitude Mesoopause Stratopause Tropopause EESC W4400x

  6. Clouds & The Greenhouse Effect More transparent to solar radiationRadiate at cooler temperatures  Net effect = Warming Less transparent to solar radiationRadiate at warmer temperatures  Net effect = Cooling EESC W4400x

  7. S (=net solar in) F+(z=) Atmosphere Fah Fv(z=0) Foh Ocean Example: Energy budget of column of atmosphere-ocean system S = absorbed solar radiation F+() = outgoing infrared flux (outgoing longwave radiation, OLR) Fah = horizontal energy flux in atmos. Foh = horizontal energy flux in ocean Fv(0) = atmos. to ocean energy flux EESC W4400x

  8. Effect of [simplified] clouds. Effect of greenhouse gasses in atmos. Estimating Temperature Profiles using RCMs EESC W4400x

  9. S (=net solar in) F+(z=) Atmosphere Fah Fv(z=0) Foh Ocean Example: Energy budget of column of atmosphere-ocean system • S = Sc - Cs • F+() = F+c() – Cl • Cs = cloud shortwave forcing • Cl = cloud longwave forcing • Sc = estimate of absorbed solar radiation in absence of clouds • F+c() = estimate of OLR in absence of clouds • Fv() = Sc - F+c() - (Cs - Cl) EESC W4400x

  10. Earth’s Globally Averaged Atmospheric Energy Budget All fluxes are normalized relative to 100 arbitrary units of incident radiation. Values are approximate. EESC W4400x

  11. Sensible Heat Flux Latent Heat Flux Radiative Heat Flux Surface Energy Budget How is energy/temperature transferred from surface to atmosphere? GH Effect(LW) Net Solar Radiation(SW) Atmos. Ground EESC W4400x

  12. Atmospheric Stability EESC W4400x

  13. 1st Law of Thermodynamics dEint = dQ – dW The internal energy Eintof a system tends to increase if energy is added as heat Q and tends to decrease if energy is lost as work W done by the system. The First Law of Thermodynamics: Four Special Cases EESC W4400x

  14. Stability of Dry Air EESC W4400x

  15. Example: Stability of Moist Air EESC W4400x

  16. Lapse Rate Changes Through the Day • What time of day is atmosphere most stable near the ground? Why? • How might time of year be affecting this graph? EESC W4400x

  17. Outgoing Longwave Radiation (OLR) Recent week – 9/4/2006 – 9/10/2006 Recent season – 6/13/2006 – 9/10/2006 EESC W4400x

  18. Sea Surface Temperatures Recent season – 6/13/06 – 9/10/06 EESC W4400x

  19. Sea Level Pressure Recent season – 6/2006 – 9/2006 EESC W4400x

  20. Example: Convective Parameterization Open arrows indicate convective dynamicsClosed arrows indicate ‘large-scale’ dynamics EESC W4400x

  21. Uncertainties in Formulating Cloud & Associated Processes (from Arakawa 2004, J. Climate) EESC W4400x

  22. Radiation Imbalance The annual mean, average around latitude circles, of the balance between the solar radiation absorbed at the ground (in blue) and the outgoing infrared radiation from Earth into space (in red). The two curves must balance completely over the entire globe, but not at every single latitude. In the tropics, there is an access of radiation (solar radiation absorbed exceeds outgoing terrestrial radiation) in middle and high latitudes all the way to the poles, there is a deficit (Earth is radiating into space more than it receives from the sun). The atmosphere and ocean systems are forced to move about by this imbalance, and bring heat by convection and advection from equator to the poles. EESC W4400x

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