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This paper considers climate prediction from the perspective of the experimental, physical sciences, and discusses three ways in which the two differ. First, the construction of long-term climate series requires benchmark measurements, i.e., measurements calibrated in situ against international standards. An instrument capable of accurate, benchmark measurements of thermal, spectral radiances from space is available but has yet to be used. Second, objective criteria are needed to evaluate measurements for the purpose of improving climate predictions. Techniques based on Bayesian inference are now available. Third is the question of how to use suitable data to improve a climate prediction, when they are available. A method based on the Bayesian Evidence Function is, in principle, available, but has yet to be exploited. None of these three aspects are considered in current operational climate forecasting. All three are potentially capable of improving forecasts, and all are subjects of current research programs, with the likelihood of their eventual adoption.

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.

An approach to test climate models with observations is presented. In this approach, it is possible to directly observe the longwave feedbacks of the climate system in time series of annual average outgoing longwave spectra. Tropospheric temperature, stratospheric temperature, water vapor, and carbon dioxide have clear and distinctive signatures in the infrared spectrum, and it is possible to detect trends of these signals unambiguously from trends in the outgoing longwave spectrum by optimal detection techniques. This approach is applied to clear-sky data in the tropics simulated from the output of an ensemble of climate models. Estimates of the water vapor–longwave feedback by this approach agree to within estimated errors with truth, and it is likely that an uncertainty of 50% can be obtained in 20 yr of a continuous time series. The correlation of tropospheric temperature and water vapor anomalies can provide a constraint on the water vapor–longwave feedback to 5% uncertainty in 20 yr, or 7% in 10 yr. Thus, it should be possible to place a strong constraint on climate models, which currently show a range of 30% in the water vapor–longwave feedback, in just 10 yr. These results may not hold in the presence of clouds, however, and so it may be necessary to supplement time series of outgoing longwave spectra with GPS radio occultation data, which are insensitive to clouds.

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.

Sampling retrievals of high-accuracy first-moment statistics constitute a central concern for climate research. Considered here is the important case of brightness temperature retrievals from a selection of possible orbits. Three-hourly global satellite brightness temperature data are used to predict the sampling error of monthly to annual mean brightness temperature retrieved by one or more satellites in low earth orbits. A true polar orbit is found to offer substantial advantages over a sun-synchronous orbit in the retrieval of annual mean brightness temperature, since the rotation of the local time of observation through two full diurnal cycles greatly reduces the error due to imperfect sampling of diurnal variations. Thus, a single polar orbiting satellite can produce annual mean, zonal mean brightness temperatures with typical sampling errors of less than 0.1 K, while even three sun-synchronous orbiters have high-latitude errors of up to 0.4 K. The error in retrievals of the annual mean diurnal cycle of brightness temperature is also discussed. In this case, high accuracy (

Spectrally resolved thermal radiances measured from orbit with an accuracy in brightness temperature of 100 mK constitute a critical observation for climate monitoring. The design of a small, low-cost instrument capable of accuracies of better than 100 mK , demonstrated on-orbit, is presented and analyzed. It is shown that systematic and random errors inherent in observations from space can be reduced to levels commensurate with the instrumental accuracy of 100 mK . Monitoring spectrally resolved radiance, accurate to 100 mK , is feasible, and constitutes a versatile climate Benchmark observation that is needed in the national research strategy.

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.

[Figure: see text] ▪ Abstract FAUST: Ich fühl's, vergebens hab' ich alle Schätze Des Menschengeists auf mich herbeigerafft, Und wenn ich mich am Ende niedersetze, Quilt innerlich doch keine neue Kraft; Ich bin nicht um ein Haar breit höher, Bin dem Unendlichen nicht näher. Goethe's Faust, Part I, lines 1810–15. 1 A dedication to research in the physical sciences together with the circumstances of World War II, led me into theoretical and observational studies of the global physical climate. For all practical purposes, I was on my own when working in Cambridge and London, England, and I went whereever my interests led me. I organized three atmospheric observatories (two in England). I have also worked at many astronomical observatories. As time progressed, I became increasingly involved in studies of atmospheric radiation as a controlling factor for the Earth's climate. I am often taken to be a specialist in atmospheric radiation, but I have never regarded it as more than an important element in climate studies. But radiative transfer and global questions did not become important for climate science until later, and in the 1950s and 1960s I found myself drawn to studies of planetary atmospheres as an arena in which my skills were of central importance. Mars and Venus were the focus of my work for many years, and I was partly responsible for launching the Pioneer Venus mission, which placed probes into the Venus atmosphere in 1978. Much later, the experience I gained in space instrumentation and in the structure of atmospheres led me back to climate science, where I started. Then my interest was in observing the climate and testing the credibility of climate predictions. I still maintain some activity in this field. Outside these research activities, I created a Center for Earth and Planetary Physics at Harvard University to take over the activities of the Blue Hill Observatory, when that Observatory ceased to be a viable facility. The purpose of the Center was to teach earth science in the context of the discipline of physical science. The Center had some notable achievements but eventually had to give way to requirements for environmental sciences in the University, a change that I regret. During my active life in the United States, I invested a great deal of effort in support of the work of the National Research Council (NRC), including many years spent on report review. I am increasingly troubled by the postmodern view of science that appears to dominate these activities. But that may be no more than a biased rosy view of the past with its exciting early experiences and hopes.

A successful global climate monitoring system must fulfill clear societal objectives. For some aspects of climate monitoring, the societal goals are understood and are clearly stated, but long-term, decadal/centennial climate predictions have, in the past, been judged more in terms of curiosity-led criteria. A curiosity-led climate programis not, however, the effective way to achieve the required societal objective, which is to produce thebest possible long-term climate projections. In terms of the universal use of numerical models for climateprojections, this leads to the need for monitoring programs that provide data to test model output against reliable observations. This requires an operational climate model (which the United States does not now have), and observationsthat emphasize accurate and reproducible data designed to provide critical tests of model output. The priorities for specific monitoring programs can be formulated in terms of these requirements, which can also provide metrics o...

Spectral empirical orthogonal functions (EOFs) derived from the covariance of satellite radiance spectra may be interpreted in terms of the vertical distribution of the covariance of temperature, water vapor, and clouds. This has been done for four major geographic regions: the tropical oceans, midlatitude oceans, and three important land areas. The purpose of the investigation is to demonstrate the important constraints that resolved spectral radiances can place upon climate models.

The scientific merit of decadal climate projections can only be established by means of comparisons with observations. Testing of models that are used to predict climate change is of such importance that no single approach will provide the necessary basis to analyze systematic errors and to withstand critical analysis. Appropriate observing systems must be relevant, global, precise, and calibratable against absolute standards. This paper describes two systems that satisfy these criteria: spectrometers that can measure thermal brightness temperatures with an absolute accuracy of 0.1 K and a spectral resolution of 1 cm-1, and radio occultation measurements of refractivity using satellites of the GPS positioning system, which give data of similar accuracy. Comparison between observations and model predictions requires an array of carefully posed tests. There are at least two ways in which either of these data systems can be used to provide strict, objective tests of climate models. The first looks f...

The authors compare the performance of broadband radiometers with spectrally dispersed measurements. Spectrally dispersed radiometers may be more accurately calibrated than is possible with broadband filter instruments. They also have a larger information content than have filter measurements. Accuracy and information content are two important requirements for climate observations.

The motivation for this paper is to understand better the means available for testing climate models. Statistics of observed, outgoing, thermal spectra are compared with those predicted from a climate model, on the basis of data collected over a period of approximately 1 year. This is a powerful approach to testing a model with respect to processes internal to the atmosphere. These processes, which have characteristic timescales of less than a year, define the atmosphere's response to external forcing. Second-moment statistics are particularly important for testing model variability, which is key to predicting the results of forcing the atmosphere, for example, by ocean surface temperature changes, increase of greenhouse gases, etc. Comparisons are presented between statistical data from the infrared interferometer spectrometer (IRIS), an orbiting fourier transform spectrometer, and spectra calculated using the medium-resolution spectral code, MODTRAN, applied to the temperature and humidity profiles from a well-known climate model. Ten months of IRIS data are available, and we have compared means, standard deviations, skew, and kurtosis of its spectrally resolved brightness temperature in three tropical regions for individual months and for a range of timescales. Also presented are comparisons of covariances using Empirical Orthogonal Functions (EOFs) calculated in frequency space. All data that are presented are based on radiance differences from two like spectra, which eliminates many of the errors generated by the use of MODTRAN and most of the errors due to calibration uncertainties in IRIS. Important differences (i.e., residuals) between the IRIS and the GCM statistics are found in comparisons, demonstrating that the spectral data can provide a severe test of many aspects of the variability of a general circulation model. We discuss some of the residuals and how they may be used to improve model performance in the context of an adjoint formalism. In the long run the only way to have confidence in the performance of a model is to subject it to as many discriminating comparisons with data as are practicable, and we present a good candidate.

We discuss two practical issues concerning the relationship between the entropies of the atmosphere and of the radiation field. The first is whether the radiative flux of entropy can be determined from a satellite with sufficient accuracy for climate studies. We conclude that an accuracy much better than 1% is required, but that this can be achieved in the thermal spectrum with spectrometers having spectral resolutions ∼ 1 cm−1; it is also possible that the required accuracy can be achieved with a non-spectral approach. The second is whether the rate of change of the atmospheric entropy inventory can be inferred from the outgoing radiative-entropy flux. We conclude that, for clear skies in the thermal region of the spectrum, the two are directly proportional, and that the atmospheric term can be inferred with useful accuracy from an empirical relation.

In view of the cost and complexity of climate-observing systems, it is a matter of concern to know which measurements, by satellite or in situ, can best improve the accuracy and precision of long-term ensembles of climate projections. We follow a statistical procedure to evaluate the relative capabilities of a wide variety of observable data types for improving the accuracy and precision of an ensemble of Intergovernmental Panel on Climate Change (IPCC) models. Thirty-two data types are evaluated for their potential for improving a 50-y surface air temperature trend prediction with data from earlier periods, with an emphasis on 20 y. Data types can be ordered in terms of their ability to increase the precision of a forecast. Results show that important conclusions can follow from this ordering. The small size of the IPCC model ensemble (20 members) creates uncertainties in these conclusions, which need to be substantiated with the larger ensembles expected in the future. But the larger issue of whether the methodology can provide useful answers is demonstrated.

A simple inexpensive and compact Cassegrain reimaging system for scanning IR images is described. Its performance is as good as or better than a conventional scanning secondary in all important respects.

Four types of instruments for recording monochromatic astronomical images are compared: filters; slitless spectrographs; multislit spectrographs; and interferometers. Each of these instruments has been used on the sodium emission cloud of Io, with varying degrees of success. Multislit spectrographs and interferometers encode the signal, and it can be extracted with a noise level close to that for photon statistics. This is not normally the case for filters and slitless spectrographs. On balance, it is found that a Mach-Zehnder interferometer provides the best system for imaging faint monochromatic signals on a brighter continuum background.

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 were calculated. The results show that the tidal mechanism proposed by Fels and Lindzen (1974) 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.

The fundamentals of radiation calculations in planetary atmospheres have been known for a long time, but the practical problems of calculating radiation over a broad spectral range both efficiently and accurately remain an area of active research. The Goody et al. paper of 1989 [13] established a milestone in that long effort. Goody et al. highlighted attempts to formulate the problem in terms of a few absorption coefficients that could represent typically tens of thousands of coefficients in a rigorous line-by-line calculation. Here we provide a brief background, point out that the correlated-k method is a special case of a broader spectral mapping concept, and mention some new ideas that have emerged recently.

[1] Spectrally resolved outgoing radiance is a potentially powerful tool for testing climate models. To show how it can be used to evaluate the simulation of cloud variability, which is the principal uncertainty in current climate models, we apply spectral empirical orthogonal function (EOF) analysis to satellite radiance spectra and synthetic spectra derived from a general circulation model (GCM). We show that proper averaging over a correct timescale is necessary before applying spectral EOF analysis. This study focuses on the Central Pacific and the western Pacific Warm Pool. For both observation and GCM output, cloud variability is the dominant contributor to the first principal component that accounts for more than 95% of the total variance. However, the amplitude of the first principal component derived from the observations (2 � 3.4 Wm � 2 )i s 2� 6 times greater than that of the GCM simulation. This suggests that cloud variability in the GCM is significantly smaller than that in the real atmosphere. INDEX TERMS: 3359 Meterology and Atmospheric Dynamics: Radiative processes; 3360 Meterology and Atmospheric Dynamics: Remote sensing; 3337 Meterology and Atmospheric Dynamics: Numerical modeling and data assimilation; 3399 Meterology and Atmospheric Dynamics: General or miscellaneous

Richard M. Goody was awarded the William Bowie Medal at the AGU Spring Meeting Honors Ceremony, which was held on May 27, 1998, in Boston, Massachusetts. The William Bowie Medal recognizes outstanding contributions to fundamental geophysics and unselfish cooperation in research.

Limits to the recovery of planetary images by speckle imaging were investigated by means of a numerical simulation of the image-forming process. Laboratory measurements established that the numerical model correctly represented the process. With this numerical model we studied the observing conditions required to obtain useful planetary data for Neptune and Io, and we learned which factors are important for the successful recovery of images. We also showed that our methods of amplitude and phase recovery do not contribute to image degradation, which is essentially caused by photon noise alone. From this conclusion we were led to two simple models of speckle imaging that involve neither details of the recovery procedure nor of the atmospheric behavior (except for the size of the seeing disk). Both models are governed by a dimensionless ratio that involves all parameters relevant to the process of image restoration. The models can be used by any observer, and they have been used by us to predict the performance of speckle imaging for T-tauri stars and for a Mars cloud study.

The semimajor axis and the inclination are the two most important quantities presently determined from 56 well-calibrated speckle-interferometric observations of the position of Charon, which are presented in conjunction with an orbit solution that incorporates them. Both values in the best solution obtained are noted to significantly differ from earlier determinations. The new value for the semimajor axis represents a 2.7 percent increase over the previously accepted value; the mean density of the system, however, remains unaltered.

Previous calculations of zonally averaged temperature, circulation, and eddy source requirements for the Venus atmosphere are extended to include the region from the surface to 95 km, using a Curtis-matrix method for the radiation calculation. The cloud top circulation is not significantly changed from previous calculations based on a radiative-relaxation method, but large differences occur in the lower atmosphere. 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. 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. The circulation below the clouds is important compared to viscous dissipation above the lowest scale height.

The eddy source pattern required to maintain zonally averaged circulation in the solar heating and zonal wind profiles of the Venus atmosphere below 80 km has been calculated. The calculated residual meridional circulation in the cloud top region corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks, which may be due to thermal tides.

Thermal maps of Venus on 16 days during a span of 43 days just before inferior conjunction were obtained during 1973-1974 and are described. The research represents a first step towards the goal of using ground-based observations to determine the time and space scales of dynamical events taking place in the Venus clouds. The described average limb darkening differs from that reported by Ingersoll and Orton (1974). Real day-to-day changes in limb darkening, one occasion of a 4-day repetition of a thermal anomaly, solar-related anomalies, and a southern hemisphere solar-related disturbance are discussed.

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...

A review is presented of events relating polar regions to the world climate, the mechanisms of sea ice and polar ice sheets, and of two theories of the Pleistocene Ice Ages. The sea ice which varies over time scales of one or two years and the polar ice sheets with time changes measured in tens or hundreds of thousands of years introduce two distinct time constants into global time changes; the yearly Arctic sea ice variations affect northern Europe and have some effect over the entire Northern Hemisphere; the ice-albedo coupling in the polar ice sheets is involved in major climatic events such as the Pleistocene ice ages. It is concluded that climate problems require a global approach including the atmosphere, the oceans, and the cryosphere.

We inquire into the limits of validity of Priestley's 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. Ball's model of an unstable layer indicates that the critical difference between dust devil and plume conditions is that the inversion above the ...

The accuracy of the correlated-k method, which is a technique for radiation calculations with spectrally averaged data in nonhomogeneous atmospheres, is investigated. Comparisons are made for scattering and absorbing atmospheres containing CO2, H2O, and O3, and it is concluded that: (1) the errors in correlated-k are generally of order of magnitude 1 percent, (2) much larger errors occur only when a radiative quantity is very much smaller than its average value, (3) errors do not depend systematically on the gas molecule, the distributions of gases and aerosols, or on the aerosol optical properties, and (4) errors do not systematically increase with the order of differencing. It is shown that the multiplication property for transmission by overlapping bands can be incorporated into correlated-k, that temperature effects can be interpolated on a coarse grid, and that 10 quadrature points are often sufficient to average over complex spectral intervals containing thousands of lines.

We give a quantitative theory of line formation in an atmosphere above a surface with backscattering properties. Sufficiently high spatial and spectral resolution spectra of resonance lines in Io region A can yield data on the surface scattering properties as well as the number density of scattering molecules. We discuss macroscopically homogenous models of scattering from the surface of Io and conclude that multiple reflection from crystal facets is the most likely cause for the observed geometric albedo and phase variation.

The global hydrogen Lyman alpha, helium (584 angstroms), and molecular hydrogen band emissions from Saturn are qualitatively similar to those of Jupiter, but the Saturn observations emphasize that the H(2) band excitation mechanism is closely related to the solar flux. Auroras occur near 80 degrees latitude, suggesting Earth-like magnetotail activity, quite different from the dominant Io plasma torus mechanism at Jupiter. No ion emissions have been detected from the magnetosphere of Saturn, but the rings have a hydrogen atmosphere; atomic hydrogen is also present in a torus between 8 and 25 Saturn radii. Nitrogen emission excited by particles has been detected in the Titan dayglow and bright limb scans. Enhancement of the nitrogen emission is observed in the region of interaction between Titan's atmosphere and the corotating plasma in Saturn's plasmasphere. No particle-excited emission has been detected from the dark atmosphere of Titan. The absorption profile of the atmosphere determined by the solar occultation experiment, combined with constraints from the dayglow observations and temperature information, indicate that N(2) is the dominant species. A double layer structure has been detected above Titan's limb. One of the layers may be related to visible layers in the images of Titan.

The determination of the rotation rate of Uranus based on available observational evidence is discussed. Previous determinations of the rotation rate since the work of Lowell and Slipher (1912), which tended to converge on a period of 10.8 days until the mid 1970s, most likely due to mutual reinforcement between unreliable results, are reviewed. Recent independent determinations based on (1) the use of theoretical interior models together with observations of oblateness and the gravitational moment J2; (2) periodic brightness fluctuations; and (3) spectrographic measurements of Doppler shifts are then presented which yield a weighted mean value of 16.31 + or - 0.27 h for the rotational period of Uranus. It is noted that the detection of the motion of surface features across the disk by future high-resolution imaging and Voyager 2 observations may allow a direct determination of the rotational period of Uranus.

Recent Earth-based measurements and results from the first decade of space exploration have led to a new level of understanding of Mars and Venus, which permits a perspective view of some of the major issues concerning the inner solar system. The following are discussed in this review: the interiors; crustal dynamics; water, carbon dioxide and the early history of an atmosphere; life on the inner planets; comparative meteorology; photochemical processes; planetary environments.

The present study of speckle imaging technique effectiveness encompasses image reconstruction by means of a division algorithm for Fourier amplitudes, and the Knox-Thompson (1974) algorithm for Fourier phases. Results which have been obtained for Io, Titan, Pallas, Jupiter and Uranus indicate that spatial resolutions lower than the seeing limit by a factor of four are obtainable for objects brighter than Uranus. The resolutions obtained are well above the diffraction limit, due to inadequacies of the video camera employed. A photon-counting camera has been developed to overcome these difficulties, making possible the diffraction-limited resolution of objects as faint as Charon.

A numerical model of the diurnal transport of water across the Martian surface is developed. The atmospheric boundary layer is modeled in terms of local radiative-convective processes, and radiative effects of ice fogs near the surface are included. Diffusion of water in the ground is treated for the cases of adsorption and condensation. The model is applied to the diurnal variation of water vapor in the atmosphere as observed by Barker (1974). The morning rise in the amount of water vapor can be explained in terms of the evaporation of ground fogs. The evening decrease is compatible with the model if adsorption dominates in the soil. The average level of vapor concentration requires that the atmosphere above the boundary layer be relatively dry. The ground fogs persist until midmorning and should be observable. Some consequences of these conclusions are discussed.

The thermal maps of Murray and his collaborators have been analyzed statistically into solar effects, latitude variations, and limb darkening. Seeking a pole position for minimum residual variance leads to α = 7.4 ± 2.0°, δ = −68.1 ± 0.9°. The solar effect is opposite to the simple expectation of an increasing temperature from antisolar to subsolar point; this suggests that the main deposition of solar energy takes place somewhat below the levels relevant to the measured emission. Inversion of the limb-darkening curves yields a source function which, if interpreted as a thermal source function, indicates an increasing temperature with depth and cold polar regions, in agreement with microwave data. Finally, analysis of the terminator position indicates a very deep and variable scattering layer and gives some support to a predominantly scattering source function in the 10-μ region.

We have computed radiative relaxation times for temperature perturbations in CO 2 with small admixtures of water vapor under conditions which are similar to those occurring in the martian atmosphere. Certain aspects of the influence of radiative transfer on dynamical phenomena in the martian atmosphere are discussed in terms of these radiative relaxation times. It is found that: (i) diurnal changes in the temperature profile will extend to considerably greater heights in the martian atmosphere than is the case on Earth; the diurnal wave will propagate more by radiative transfer than by turbulent diffusion; (ii) a non-negligible diurnal wind system exists on Mars; (iii) non-linear interactions between the motion field and the initial state of radiative equilibrium are much smaller on Mars than on Earth; (iv) radiative de-stabilization of regions with a negative lapse rate may be important in the upper martian atmosphere.

We have made a theoretical and experimental study of the effect of radiative transfer on the onset of convection by means of comparative experiments in dry air and ammonia contained between horizontal aluminium plates maintained at different temperatures.The first effect of radiative transfer is to distort the linear, diffusive profile in the initial, pre-convective state. A non-grey theory is developed and is shown to predict the non-linear profiles profiles with satisfactory accuracy. The change of radiative flux with pressure of ammonia is also predicted and confirmed. This constitutes the first successful attempt to confirm the methods used in atmospheric studies in controlled experiment.A non-grey theory of the onset of convection is developed, separating effects associated with the distortion of the static state and the dissipative effect of radiative transfer on temperature fluctuations.Experiments indicate that the critical Rayleigh number in ammonia can be greatly increaesd over the best value for air (Rac = 1786); the maximum observed being Rac = 4870. Theory and experiment are shown to agree within reasonable limits.This work confirms the validity of methods which are of great importance to astrophysics and atmospheric physics.

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A simple approximation to the equation of radiative heating has been developed for use in dynamical calculations in the Martian atmosphere. The integral equation is reduced to a linear algebraic equation by means of a trapezoidal approximation which pays particular attention to radiation exchange with the planet's surface and with space. The accuracy of the approximation is demonstrated both for radiative equilibrium and for perturbation heating calculations in a pure carbon dioxide atmosphere.

The great Martian 1971 dust storm is described using Carrier's (1971) model of a terrestrial hurricane with a somewhat modified thermodynamic drive. The model predicts the course of development and the time elapsing in three different phases: growth, maturity, decay. All the predictions correspond reasonably well to the observed phenomena. Explanations are offered for the rarity of the storms and the time of year and location at which they most commonly commence.

An attempt has been made to detect the airglow on Venus by means of differential photometric scans across the dark limb. No airglow was detected placing an upper limit of 100 kR on individual Unes or 0·5 kR/A on the continuum. The upper limit was imposed by scattered light in the telescope optics and the wide filters (200 A) employed. A great improvement would be possible with a specially designed telescope and narrower filters. There is no difficulty in principle in going to the limit imposed by photomultiplier noise, possibly to less than 100 R.

A simple treatment of twilight refraction is presented, replacing sections of the tables of Link and Sekera (1940) by explicit formulae. The question of the scale height relevant to the twilight problem is discussed and shown to be important for accurate calculations.

The Curtis-Godson approximation for computing transmission along an inhomogeneous path is extended to include a higher moment of the density distribution. Numerical computations for typical situations indicate that the three-parameter model is a considerable improvement over the Curtis-Godson approximation, although the latter is surprisingly accurate for a wide range of conditions. The three-parameter model can be expressed in terms of an algebraic correction to the amount of absorbing matter.