Sources and sinks of climate entropy

A satisfactory climate model must have similar sources and sinks of entropy to those of the atmosphere itself. This paper examines some of the theoretical and numerical issues involved in entropy sources and sinks. A balance equation is developed that involves a balance between entropy destruction by emission and absorption of radiation and entropy production by irreversible molecular processes. Estimating the thermal molecular source from turbulent enthalpy fluxes is shown to be consistent with the second law of thermodynamics only for free convection. Four entropy sources connected with the dissipation of kinetic energy are discussed. Moist convection is treated in terms of the mixing of warm/dry and cool/moist air masses. Questions are raised about the validity of treating latent heat as an external heat source acting upon a dry atmosphere. Theoretical estimates of entropy sources are compared with earlier estimates by Peixoto and others, and to the sources and sinks of entropy in a Goddard Institute of Space Studies climate control run. There are many discrepancies, particularly for moist convection. Our knowledge of atmospheric sources and sinks of entropy is evidently poor and, even if they were known, it would be difficult to construct a climate model with sources and sinks as precise as Johnson considers to be necessary.