Hisashi Ozawa

Thermodynamics of a Global-Mean State of the Atmosphere—A State of Maximum Entropy Increase

Abstract Vertical heat transport through thermal convection of the earth’s atmosphere is investigated from a thermodynamic viewpoint. The postulate for convection considered here is that the global-mean state of the atmosphere is stabilized at a state of maximum entropy increase in a whole system through convective transport of sensible and latent heat from the earth’s surface into outer space. Results of an investigation using a simple vertical gray atmosphere show the existence of a unique set of vertical distributions of air temperature and of convective and radiative heat fluxes that represents a state of maximum entropy increase and that resembles the present earth. It is suggested that the global-mean state of the atmospheric convection of the earth, and that of other planets, is stabilized so as to increase entropy in the universe at a possible maximum rate.

On the thermodynamics of the oceanic general circulation: Irreversible transition to a state with higher rate of entropy production

The mechanism of transitions among multiple steady states of thermohaline circulation is investigated from a thermodynamic viewpoint. An oceanic general-circulation model is used to obtain the multiple steady states under the same set of wind forcing and mixed boundary conditions, and the rate of entropy production is calculated during time integration. Three states with northern sinking and four states with southern sinking are shown to exist in the model by perturbing the high-latitude salinity. It is found that for transitions among southern sinkings the transition tends to occur from a state with a lower rate of entropy production to a state with a higher rate of entropy production, but the transition in the inverse direction does not occur. These transitions can thus be said to be irreversible or directional, in the direction of the increase of the rate of entropy production. For transitions between northern sinking and southern sinking, the rate of entropy production can either increase or decrease depending on the direction of the perturbation. The decrease is found to be associated with a collapse of the northern sinking circulation by a certain amount of negative salt (positive fresh water) perturbation to the northern hemisphere. After this collapse, a new southern sinking circulation develops, and the corresponding rate of entropy production increases. All these results tend to support the hypothesis that a nonlinear system is likely to move to a state with maximum entropy production by perturbation. Copyright

On the thermodynamics of the oceanic general circulation : entropy increase rate of an open dissipative system and its surroundings

The role of thermodynamics in the oceanic general circulation is investigated. The ocean isregarded as an open dissipative system that exchanges heat and salt with the surroundingsystem. A new quantitative method is presented to express the rate of entropy increase for alarge-scale open system and its surroundings by the transports of heat and matter. This methodis based on Clausius’s definition of thermodynamic entropy, and is independent of explicitexpressions of small-scale dissipation processes. This method is applied to an oceanic generalcirculation model, and the entropy increase rate is calculated during the spin-up period of themodel. It is found that, in a steady-state, the entropy increase rate of the ocean system is zero, whereas that of the surroundings shows positive values, for both heat and salt transports. Thezero entropy increase rate of the ocean system represents the fact that the system is in a steadystate, while the positive entropy increase rate in the surroundings is caused by irreversibletransports of heat and salt through the steady-state circulation. The calculated entropy increaserate in the surroundings is 1.9×1011WK-1, and is primarily due to the heat transport. It issuggested that the existence of a steady-state dissipative system on the Earth, from a livingsystem to the oceanic circulation, has a certain contribution to the entropy increase in itsnonequilibrium surroundings.

Cirriform Rotor Cloud Observed on a Canadian Arctic Ice Cap

Abstract A thin rotor cloud was observed on the lee side of Penny Ice Cap in the Canadian Arctic on 21 April 1996. The cloud consisted of thin cirriform layers, so that its motion was clearly observed. By means of time-lapse camera photography, the velocity of the cloud rotation was estimated to be around 2 m s−1. It is suggested that the existence of a high humidity layer at the bottom of an inversion layer is a key factor for the formation of the thin rotor cloud.

The Time Evolution of Entropy Production in Nonlinear Dynamic Systems

General characteristics of entropy production in a fluid system are investigated from a thermodynamic viewpoint. A basic expression for entropy production due to irreversible transport of heat or momentum is formulated together with balance equations of energy and momentum in a fluid system. It is shown that entropy production always decreases with time when the system is of a pure diffusion type without advection of heat or momentum. The minimum entropy production (MinEP) property is thus intrinsic to a pure diffusion-type system. However, this MinEP property disappears when the system is subject to advection of heat or momentum due to dynamic motion. When the rate of advection exceeds the rate of diffusion of heat or momentum, entropy production tends to increase over time. The maximum entropy production (MaxEP), suggested as a selection principle for steady states of nonlinear non-equilibrium systems, can therefore be understood as a characteristic feature of systems with dynamic instability. The observed mean state of vertical convection of the atmosphere is consistent with the condition for MaxEP presented in this study.

Entropy Production in Planetary Atmospheres and Its Applications

Distributions of temperature and longwave radiation are predicted from a state of maximum entropy production (MaxEP) due to meridional heat flux in the atmospheres of the Earth, Mars, Titan and Venus, and the predicted distributions are compared with observational results. In the predictions, we use a multi-box energy balance model that takes into account the effects of obliquity and latitudinal variation of albedo on shortwave absorption. It is found that the predicted distributions are generally in agreement with observations of the Earth, Titan and Venus, suggesting the validity of the MaxEP state for these planets. In the case of Mars, the predicted distributions do not agree well with the observations when compared with those predicted from a state of no meridional heat flux. A simple analysis on advective heat flux using a two-box model shows that the Martian atmosphere is so scant that it cannot carry the heat energy that is necessary for the MaxEP state by advection. These results suggest that the validity of the MaxEP state for a planetary atmosphere is limited when the total amount of atmosphere is not enough to sustain the advective heat flux that is necessary for the MaxEP state.

Thermodynamics of the Oceanic General Circulation – Is the Abyssal Circulation a Heat Engine or a Mechanical Pump?

The oceanic general circulation has been investigated mainly from a dynamic perspective. Nevertheless, some important contributions to the field have been made also from a thermodynamic viewpoint. This chapter presents description of the thermodynamics of the oceanic general circulation. Particularly, we examine entropy production of the oceanic general circulation and discuss its relation to a thermodynamic postulate of a steady closed circulation such as the oceanic general circulation: Sandstrom’s theorem. Also in this section, we refer to another important thermodynamic postulate of an open non-equilibrium system such as the oceanic general circulation: the principle of Maximum Entropy Production.