The nature of entropy increase in the earth's climate system is investigated. Previous works on thermodynamics of the climate system are reviewed in the light of a thermodynamic concept presented here. It states that entropy of thermal reservoirs connected through a non-linear system, in which materials interact mutually, will increase along a path of evolution with a maximum rate of entropy increase, among a manifold of allowed paths. The region of the connected system is called a synthetic system. Some energy transport processes, which are not in mutual direction, e.g. absorption of solar radiation, are then excluded from the synthetic part of the system. Consequently, it is found that Paltridge's suggestion on maximum entropy increase by turbulent heat transport in the earth's climate system, as well as Malkus-Howard-Busse's suggestion on maximum energy dissipation in turbulent flows, is rigorously explained by the single thermodynamic concept. A general method to calculate the entropy increase rate for a synthetic system has been developed, and this method is applied to a spin-up period of an ocean circulation system. It is found that, at the steady-state, for both heat and salt transports, the entropy increase rates of the ocean system are zero, whereas those for the surrounding system show positive values. The result shows that the ocean circulation tends to be a steady-state with a flux-pattern of heat and salt favourable to entropy increase in the synthetic part of the surrounding system. It is suggested that the thermodynamic concept presented here may be applicable to time evolution of fluid dynamic systems (gas, liquid, mantle) in other planets and stars.


1.Hisashi Ozawa
Institute for Global Change Research, Frontier Research System for Global Change, 1-2-1 Shibaura,Minato-ku, Tokyo 105-6791, Japan
E-mail:
ozawa@jamstec.go.jp

2.Shinya Shimokawa
National Research Institute for Earth Science and Disaster Prevention, Tennodai 3-1, Tsukuba 305-0006, Japan

3.Hirofumi Sakuma
Institute for Global Change Research, Frontier Research System for Global Change, 1-2-1 Shibaura,Minato-ku, Tokyo 105-6791, Japan

4.Atsumu Ohmura
Department of Geography, Swiss Federal Institute of Technology, Winterthurerstr. 190, CH-8057 Zurich, Switzerland.


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