Annual-mean TOA radiation (ERBE, W/m 2 ) Absorbed SW Outgoing LW

Surface temp (NCEP, o C) January July

Surface wind (NCEP, m/s) January July

Temperature ( o C) and zonal wind (m/s) (NCEP) January July

km 10 4 –2 –8 – –4 – T decreases by 6 o C/kmincreases by 4 o C/km Temperature and potential temperature surfaces

Potential temperature (K) and zonal wind (m/s) (NCEP) January July

The “bare rock” temperature In steady state, E in = E out E in = π R 2 S (1–  ) E out = 4π R 2  T 4 R =radius  =albedo Putting it all together:

Radiative-convective equilibrium (Manabe & Strickler, 1964)

Cloud–SW interaction

Cloud–LW interaction

Net cloud forcing from simple model (Hartmann, p. 74)

Annual-mean cloud water path (g m –2 )

Annual-mean total cloud amount (%)

Annual mean low cloud amount

Annual mean middle cloud amount

Annual mean high cloud amount

Annual mean SW cloud forcing (ERBE, W m –2 )

Annual mean LW cloud forcing (ERBE, W m –2 )

Annual mean net cloud forcing (ERBE, W m –2 )

Climate feedback: the general idea What happens if we perturb the climate away from its equilibrium, for instance by increasing CO 2 concentration? +++ CO 2 positive feedback TX + CO 2 negative feedback TY – +++

In the real world, both positive and negative feedbacks act simultaneously Overall, the negative feedbacks win: otherwise temperature would run away to very high values (runaway greenhouse) However, the presence of positive feedbacks means that the temperature increase we get for a given increase in CO2 is greater than we would get in their absence: more bang for the buck Dominant feedbacks: –Negative: Planck (radiative) feedback Lapse rate feedback –Positive : Surface albedo feedback Water vapour feedback Cloud feedback?

Ice albedo feedback As surface temperature increases, some of the ice in the polar ice caps melts, exposing ocean or boreal forest Ice is much more reflective to sunlight than ocean or forest So the feedback goes like this: Increased CO 2 —› raises T —› melts some ice —› decreases reflectivity —› more insolation is absorbed —› raises T even further

Water vapour feedback Relative humidity stays roughly constant as climate warms Since RH = w/w s (T) and w s (T) increases exponentially with T, then humidity increases rapidly with T So the feedback goes like this: Increased CO 2 —› raises emission level —› raises T —› raises humidity —› raises emission level even further —› raises T even further

Feedback strengths in climate models (Soden&Held, 2006)

Insolation at TOA Absorbed insolation

Insolation at TOA Absorbed insolation

SHF into ground!

The moist equations of motion latent heat evap condensation evaporation water vapour mixing temperature mixing momentum mixing (friction)

Energetics Total energy per unit mass: Rate of change of: kinetic energy: potential energy: thermal internal energy: latent internal energy:

Energetics Rate of change of total energy per unit volume: but: Finally: Note that: moist static energysmall

AB A B Seasonal cycle of surface temperature Temp ( o C) Amplitude of seasonal cycle ( o C)