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SUMMARY:Climate entropy production based on AOGCM diagnostics - Gregory\, 
 J (University of Reading)
DTSTART:20100826T130000Z
DTEND:20100826T140000Z
UID:TALK25882@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Most investigations of the MEP hypothesis have used climate mo
 dels which do not explicitly simulate the physics and dynamics of the clim
 ate system (such as Paltridge's model)\, or in which they are radically si
 mplified (such as a dry GCM). We have instead concentrated on entropy anal
 ysis of the HadCM3 atmosphere-ocean general circulation model (AOGCM)\, th
 e kind of model used for prediction of 21st-century global climate change.
  In the AOGCM\, we diagnose the entropy sources and sinks directly from th
 e diabatic heating terms. The rate of material entropy production of the c
 limate system (i.e. not including thermal equilibration of radiation) is a
 bout 50 mW m-2 K-1. The largest part of the material EP (about 38 mW m-2 K
 -1)\, is due to sensible and latent heat transport. When we vary parameter
 s in the physical formulation of the AOGCM\, MEP might suggest that the mo
 st realistic version is the one with the largest EP. However\, in the AOGC
 M there is no maximum in EP\, for two reasons. First\, the strongest influ
 ence on EP is the throughput of energy from the net shortwave absorption\,
  which is very sensitive to model parametrisation\, rather than the antico
 rrelation of heat flux and temperature gradient seen in simple models when
  net shortwave absorption is fixed. This dependence comes particularly fro
 m the dominance of EP by the hydrological cycle\, which intensifies monoto
 nically with the global average temperature. Second\, the EP predominantly
  comes from vertical heat transport\, and to achieve a maximum with fixed 
 shortwave heating implies an unrealistic vertical temperature gradient and
 /or unphysical longwave emissivity. There is\, however\, a maximum in KE d
 issipation in the atmosphere\, similar to Lorenz's (1960) conjecture\, ass
 ociated with a smaller part of the material EP (about 13 mW m-2 K-1).
LOCATION:Seminar Room 1\, Newton Institute
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