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Information regarding small-scale turbulence in the Venus atmosphere is important and desirable because it contributes to understanding of the atmosphere's circulation. It is demonstrated that the radio occultation data of a flyby spacecraft such as Mariner 5 can provide valuable information on turbulence in the Venus atmosphere. Unlike previous studies of the Mariner 5 data, this paper is based on the frequency spectrum rather than the variance of the log-amplitude fluctuations. The excellent agreement between the processed and previously derived theoretical spectra furnishes strong evidence that the Mariner 5 fluctuations are primarily turbulence-induced. It is seen that, above 35 km, turbulence is strongest in the vicinity of 45 and 60 km, and that the outer scale of turbulence is of the order of 100 m. Comparison with the results obtained from the Venera missions is also discussed.

Recent studies have revealed a relationship between variations in gravitational tidal forces and rainfall. A possible mode of interaction of the tidal forces on atmospheric processes is suggested to explain how the tidal forces which are small may induce detectable effects on atmospheric circulation, considering both synoptic-scale and short-period processes in the atmosphere. The variability of gravitational tidal forces is compared with variations in precipitation as revealed by statistical studies. The interrelation between thermal and tidal forces is brought out to account for the anomalous distribution of maximum precipitation in the United States during the synodic month when classified according to seasons, geographical areas, and periods of high versus low solar activity. The model suggested in this paper is based on an intuitional approach to the problem. Its usefulness or validity can be ascertained only by further investigations of rainfall variations; in addition there is the need to ...

The growth of small errors in numerical models of the atmospheric circulation destroys the detailed predictive capability of those models within a few days. Despite the failure of the models to produce accurate local predictions, it was hypothesized that a change in the equator-to-pole temperature gradient would produce discernible effects in average conditions. This paper presents the results of an experiment to test this hypothesis. The Mintz-Arakawa model was started with a standard set of initial conditions and was run 60 days. The experiment was then replicated twice, with two independent sets of random temperature variations superposed on the temperatures at the σ = 0.25 and σ = 0.75 levels. At this point, the ice of the Arctic Ocean was replaced with water at the freezing temperature. Again the model was run, starting once with the standard initial conditions (other than the ice removal) and once each with the two sets of temperature “errors” added. For the four replications with temperatu...

The future observing system of the global atmosphere which has been contemplated for the Global Atmospheric Research Program (GARP) is a combination of various observing subsystems including satellites, constant-level balloons, automatic ocean buoys, etc., as well as conventional upper-air and surface networks. All observing subsystems are neither perfect nor ideal. Numerical experiments (with global circulation models) are needed to evaluate the subsystems in terms of the accuracy, density, and frequency of observations. They are called Observing Systems Simulation Experiments (OSSE). The purpose of this report is to describe the present activities in OSSE. Most useful up-to-date information was obtained from the oral presentation of papers at the International Symposium on Four-Dimensional Data Assimilation, Princeton, N. J., 19–22 April 1971. Since a global circulation model is used as an integrator and analyzer of observed data in three-dimensional space and time taken from various observing subsystems, the question of error growth of the prediction model in relation to the accuracy of observation is discussed as the predictability experiment. Another important property of the model atmosphere is the ability to adjust the model's variables for forced prescription of incomplete observed data. This adjustment property is used to assimilate observed data in four dimensions. The method of direct substitution is used to determine the basic data requirements for observation of wind, temperature, and surface pressure. Various methods of four-dimensional data assimilation are reviewed for the purpose of optimum design for OSSE. Finally, questions concerning the reference level information are reviewed and results of some numerical experiments conducted at the National Center for Atmospheric Research are presented.