Richard Goody

Formation and Persistence of Summertime Arctic Stratus Clouds

Abstract We have developed a numerical model which can explain the principle observed properties of the summertime stratus clouds occurring over the Arctic Basin. Warm, moist air from the surrounding land masses is modified as it passes over the melting pack ice. Motions are calculated on the basis of a fixed pressure field, but all other relevant fields (temperature, mixing, solar and terrestrial radiation, water in the liquid and vapor phase) are calculated on the basis of an internally consistent thermodynamic model which is considered to be complete in all essential physical processes. The ubiquitous occurrence of stratus clouds is explained in terms of the relative unimportance of cloud dissipative processes over the Arctic Ocean. The commonly observed layering results from the trapping of solar radiation inside a cloud which is opaque to thermal radiation. The absence of similar layering in mid-latitude stratus is probably due to the diurnal variation of solar radiation, which is largely absent in t...

Maximum Entropy Production in Climate Theory

R. D. Lorenz et al. claim that recent data on Mars and Titan show that planetary atmospheres are in unconstrained states of maximum entropy production (MEP). Their model as it applies to Venus, Earth, Mars, and Titan is reexamined, and it is shown that their claim is not justified. This does not necessarily imply that MEP is incorrect, and inapplicable to atmospheres, but it does mean that the difficult and unexplored problem of dynamical constraints on the MEP solution must be understood if it is to be of value for climate research.

Radiative Time Constants in the Atmosphere of Jupiter

Abstract We have computed radiative decay times for thermal disturbances near the cloud tops of Jupiter and conclude that they are much larger than probable dynamical time constants. Under these circumstances radiative equilibrium calculations are of little significance.

The energy balance of planetary atmospheres

Abstract We discuss the problem, of the energy balance of a planetary atmosphere: whether the atmospheric structure is under radiative control or whether it is significantly influenced by large scale fluid motions. The time constant for relaxation of the temperature by radiative transfer is shown to be largely independent of the atmospheric composition. The magnitude of the dynamical effects is obtained for a non‐rotating planet and it is shown that the lower atmosphere of Venus, where solar radiation is absorbed, is strongly dynamically controlled. It is probable, however, that a stratospheric region, under radiative control, exists above the visible cloud tops. The problem of rotating planets is more complex because free dynamical modes are known to be important. We conclude that Earth, Mars and Jupiter are all under dynamical control in their lower atmospheres: this conclusion is at least certain for Mars. Stratospheric radiative regimes may occur: close to the surface for Mars; two or three scale heig...

On the mechanical efficiency of deep, tropical convection

Abstract A heuristic model of deep, tropical convection duplicates many of the results obtained by Pauluis and Held from studies of a numerical model of a tropical convective ensemble, and offers insights into and explicit parametric relationships for the reversible and irreversible terms.

Diagnostic Requirements for the Superrotation on Venus

Abstract For the solar heating and zonal wind profiles observed in the Venus atmosphere (below 80 km) we have calculated the eddy source pattern required to maintain the zonally averaged circulation. In the cloud-top region (45-75 km) the calculated residual meridional circulation corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. For the amount of small-scale diffusion suggested by in situ measurements, the circulation is close to the nearly inviscid limit, and advections by the mean circulation must be balanced by eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks (i.e., Eliassen-Palm flux divergences or convergences), which may possibly be caused by thermal tides. Below the cloud decks, the effect of meridional motions is small, and eddy sources are required to balance diffusion (if diffusion is as large ...

Models of the Venus Clouds

Abstract This paper describes an attempt to find a self-consistent radiative-convective model of the Venus clouds, with the sun as the only external source of heat. The transfer of heat and cloud particles by thermal convection are treated by means of Priestleys theory of free convection and Kraichnans theory of a convective boundary layer. Approximate equations are used to describe solar and thermal radiative transfer. We constrain the model to give the correct planetary albedo, and suitable line-formation properties, and the cloud particles conform to Mies theory. We find that a transition region, from fully developed turbulence to radiative control, exists at the cloud tops. There is only negligible diurnal variation of temperature inside the cloud. The constraints imposed are so restrictive that no type of cloud is fully satisfactory. Dust clouds do not convect at depth. High vapor pressure condensates, such as water, cannot satisfy optical constraints. Low vapor pressure condensates do not convect...

Zonal superrotation above venus' cloud base induced by the semidiurnal tide and the mean meridional circulation

Abstract We have calculated the equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base. The results show that the tidal mechanism proposed by Fels and Lindzen can account for a substantial fraction—and possibly all—of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.

Further Studies of the Circulation of the Venus Atmosphere

Abstract We have extended our previous calculations of zonally averaged temperature, circulation, and eddy source requirements for the Venus atmosphere to include the region from the surface to 95 km, using a Curtis matrix method for the radiation calculation. We conclude: (i) The cloud top circulation is not significantly changed from our previous calculations based on a radiative-relaxation method, but large differences occur in the lower atmosphere. (ii) The physical and dynamical states of the atmospheric regions above and below the cloud base are effectively independent and are equally important for accounting for the 4-day circulation at the cloud tops. (iii) Above the cloud base, the circulation is effectively inviscid and the eddy source requirements at the low latitudes are consistent with the mean-flow forcing by the semidiurnal tide. (iv) The circulation below the clouds is important compared to viscous dissipation above the lowest scale height. We discuss possible mechanisms for satisfying the...

The Influence of Vorticity on Free Convection

Abstract We inquire into the limits of validity of Priestleys theory of free convection when vorticity influences the dynamics of the convective elements. On the assumption that plumes and vortices (dust devils) are alternative forms envolving from the same triggering process, we conclude that the replacement of plumes by vortices results in the virtual suppression of free convection as a heat transport mechanism. Reasoning from the observed properties of plumes and vortices we make the hypothesis that the transformation from plume to vortex is the result of the inhibition by rotation of lateral diffusion near the core. This leads to a transformation condition Ω02>−N2, where Ω0 is one-half the ambient vorticity and N is the imaginary Brunt-Vaisala frequency. We conclude that the inequality is satisfied most easily by the existence of a very deep unstable layer. Balls model of an unstable layer indicates that the critical difference between dust devil and plume conditions is that the inversion above the ...