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EVAT 554 OCEAN-ATMOSPHERE DYNAMICS

EVAT 554 OCEAN-ATMOSPHERE DYNAMICS. LARGE-SCALE ATMOSPHERIC CIRCULATION. LECTURE 8. (Reference: Peixoto & Oort, Chapter 3,7). LARGE-SCALE ATMOSPHERIC CIRCULATION. IDEALIZED ATMOSPHERIC CIRCULATION. THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH. THERMAL PROFILE.

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EVAT 554 OCEAN-ATMOSPHERE DYNAMICS

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  1. EVAT 554OCEAN-ATMOSPHERE DYNAMICS LARGE-SCALE ATMOSPHERIC CIRCULATION LECTURE 8 (Reference: Peixoto & Oort, Chapter 3,7)

  2. LARGE-SCALE ATMOSPHERIC CIRCULATION

  3. IDEALIZED ATMOSPHERIC CIRCULATION THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

  4. THERMAL PROFILE Vertical temperature profile Temperatures increase with altitude in the stratosphere (10 - 50 km) due to absorption of UV light by ozone (O3). There is limited exchange of material between the troposphere and the stratosphere (i.e., across the tropopause)

  5. S0 = 1370 W m-2 Earth THERMAL PROFILE Simplest possible reasonable model for surface temperature steady no motion no thermal diffusion no water Ignore GHGs Consider global mean surface temperature, Ts esTS4 =(1- a0)S0/4 TS4 =(1- a0)S0/4es Tearth= [( 0.7)(343 W m-2)/(1)(5.67 x 10-8 W m-2 K-4)]1/4 = 255 K (-18 C) +33K (GHG) = 288K

  6. TS THERMAL PROFILE Simplest possible reasonable model for surface temperature steady no motion no thermal diffusion no water Ignore GHGs Consider surface temperature as a function of latitude esT4 =(1- a)S/4 T4 =(1- a)S/4es Assume small latitudinal variations about the global mean temperature linearization T4 =(1- a)S/4es 4T3DT=[(1- a)/4es] DS T3 ~TS3 DT=[1- a(f)][S0 /16es TS3] (cosf-2/p) Where: DS~S0[cosf- 2/p]

  7. THERMAL PROFILE TS DT=[1- a(f)][S0 /16es TS3] (cosf-2/p)

  8. THERMAL PROFILE TS DT=[1- a(f)][S0 /16es TS3] (cosf-2/p)

  9. GLOBAL ENERGY BALANCE 343 W/m2

  10. GLOBAL ENERGY BALANCE EOUT = esT4 EIN =S( )  (S/4)(1- a)cosf

  11. GLOBAL ENERGY BALANCE Why don’t the tropics continue to heat up and the poles continue to cool?

  12. GLOBAL ENERGY BALANCE Eout Ein

  13. GLOBAL ENERGY BALANCE Eout Ein steady no motion no thermal diffusion no water Advective heat transport

  14. THERMALLY-DRIVEN CIRCULATION

  15. THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) We will derive the circulation as a perturbation that arises in response to a mean imposed thermal gradient THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

  16. Pole Equator THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) Vertical momentum balance We will derive the circulation as a perturbation that arises in response to a mean imposed thermal gradient Boundary conditions: (1) no slip Start out assuming horizontally uniform surface pressure (2) no normal flow v’=w’=0 Meridional momentum balance v’=w’=0 v’=w’=0 v’=w’=0 THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

  17. Pole Equator THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) Continuity equation Not zero for compressible fluid! Boundary conditions: (1) no slip (2) no normal flow (linearized) v’=w’=0 v’=w’=0 v’=w’=0 zero near boundaries v’=w’=0 Implies the circulation pattern shown! THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

  18. THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) HADLEY CELL CIRCULATION v’=w’=0 v’=w’=0 v’=w’=0 v’=w’=0 Pole Equator THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

  19. HADLEY CELL CIRCULATION Hadley Cell Circulation is a thermally direct circulation that transports sensible heat poleward S N Equator

  20. Dry Adiabatic warming (rapid) Dry Adiabatic warming (rapid) Dry/Warm Dry/Warm HADLEY CELL CIRCULATION Hadley Cell Circulation also transports latent heatowing to different adiabatic lapse rates for dry and moist air Dry/Cold Moist Adiabatic cooling (gradual) Moist/Hot S N Equator

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