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We have tested the response of certain versions of atmospheric general circulation models (GCM's) to random perturbations in initial conditions while leaving external and boundary conditions unaltered. By means of time averaging and global space averaging, we have investigated the reduction of the level of noise inherent in the models. In this way, comparisons of the magnitude of the models' response to random perturbations with their response to advertent changes can be used to determine the significance of prescribed (non-random) perturbation experiments. This paper is intended to present preliminary results from two GCM's (NCAR and Rand) and may be useful for those contemplating using GCM's for climate or perturbation experiments.

This paper presents results of experiments designed to test the importance of arithmetic precision in short-term forecasts and long-term climate simulations with the NCAR global circulation model. It is expected that the next-generation computers will have a sizable speed gain when using lower-precision arithmetic. To determine how precision affects the model results, we compare several short- and long-term experiments using 48-bit mantissa arithmetic (normal for the CDC 6600 and 7600 computers) with corresponding experiments using 24- and 21-bit mantissa arithmetic. The errors due to the lower precision are much smaller than typical observational errors. In addition, it appears that in the short-term experiments the rapid error growth of the model dominates the round-off error accumulation resulting from the lower-precision arithmetic. Therefore, the lower precision used by the next-generation computers should not have a detrimental effect on short-term forecast accuracy. The long-term climate s...

This paper summarizes certain facts of observation, as reported by a number of investigators, concerning the nature of climatic variations on the earth's surface during observational time, during postglacial or historical time, and during the geological past. Particular emphasis is placed on possible interpretations or explanations of these changes. The discussion of the secular variations of the world weather patterns during observational time stresses on the one hand apparent relationships between these variations and solar activity, as indicated by sunspots, and on the other hand the essential similarity of these secular variations to those which occur from week to week and month to month in the fluctuation of the general-circulation pattern between more zonal (high index) and more cellular (low index) characteristics. The discussion of the variations of world climate during geological time is concerned primarily with the relative merits of the three principal theories which currently attempt ...

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...

A frontal contour chart is one portraying the topography of frontal surfaces by means of contour lines. The method of constructing the charts is briefly indicated. Frontal contour charts have been prepared on a routine basis for about a year; a close study of these charts has revealed a number of interesting features. Isolated or semi-isolated domes of cold air and pockets of warm air are found at intervals. The characteristics, motion, and manner of formation of these are described briefly. Upper fronts, both cold and warm, take on a fresh significance when studied by means of frontal contour charts. The paper ends with a discussion of the role of cold domes and warm pockets in the mechanism of the general circulation.

In 1947 a suggestion was made by one of the authors that the existence of fast narrow currents in the upper troposphere was due to the bringing together, or confluence, of warm and cold air masses from northerly and southerly regions. In the present paper an attempt is made to extend this theory by a somewhat more detailed examination of the dynamics of confluence. It is suggested that the energy of the jet is derived from a direct transformation of potential into kinetic energy. This source of energy is independent of stability in the usual sense, a fact which may be of some importance in understanding the general circulation. A comparison is made between this theory and the known behavior of the jet stream. Here extensive use is made of recent synoptic studies by Palmen and his co-workers and of charts showing the normal appearance of the hemispheric jet stream (which are shown for the first time). It is concluded that these observational studies tend to confirm the theory of confluence.

SYNOPSIS In the first part of the paper effort is made to discover to what extent periods of abnormally high or abnormally low temperature in the United States synchronize and also as to whether or not there is evidence of a periodicity in the occurrence and recurrence of these phenomena. The basic material for the study was 12-month consecutive or overlapping monthly means of the temperature for fairly large geographic districts. The districts used are (1) the New England States, (2) Minnesota, (3) Colorado, (4) Washington, and (5) Louisiana. The monthly mean temperature for each of these districts was originally computed from the means of all of the individual stations therein. The period 1888–1919 furnished the data for the study. As was to have been expected, the control of the changes in temperature of the various parts of the United States is clearly that of the general circulation of the atmosphere, as modified, of course, by the secondary circulation due to the movement of cyclones and an...

This paper reviews the literature on the main aspects of marine air invasion on the Pacific coast. In particular, it considers the sea breeze, Pacific coast monsoon, and airflow over coastal mountains. The major problems associated with marine air invasion are: 1) the relationship of microscale convection, waves, and banded convection- waves to the sea-breeze energetics and sea-breeze front, 2) the interaction of energy forming and dissipating processes from the general circulation down to the micrometeorological scale, 3) the climatology and dynamics of the monsoon, and 4) the mechanism of the lee waves observed in the lee of the heated coastal mountains. Lee waves often form in a statically unstable atmosphere.

Since the motions of the atmosphere involve the presence of external heat sources and heat sinks, it is important to incorporate these effects into the hydrodynamical theory of air motions. In the discussion contained in this paper a method for accomplishing such a synthesis of hydrodynamics and thermodynamics is formulated for the case of two-dimensional motion. The use of the method is illustrated by an exact integration of the equations for the case of a circular vortex. Possible further elaborations of the method are discussed with a view of throwing light upon the fundamental nature of the general circulation of the atmosphere.

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.

We describe in this paper a set of general circulation model experiments on possible climate changes caused by man's generation of thermal energy or pollution. Three experiments were carried out: one in which we introduced only a small initial error, one in which we added the expected ultimate levels of thermal energy generation, and one in which we added a negative amount of thermal energy. In an three experiments, we obtained the same results, indicating that the thermal pollution effect is probably small compared to the natural fluctuations of the model. We also discuss some limitations of the present model for inferring the proper climatic-change response.

The concept of primary singularities extant in the general circulation, and their relation to secondary singularities in local and regional weather are examined through analysis of the walls Walla, Wash., daily records of January temperature and June precipitation. The results underline the influence of the hemispheric circulation upon local weather. I The traditionally accepted January thaw in New Eng- land and elsewhere on the east coast holds a strong place in the folklore. Slocum (l) in a study of temperature records for Washington, D. C., and Wahl 121, in investi- gating the New England thaw within the Boston records, presented results that bear on the question of the existence of such a singularity. Both of these studies point up the anomalous warming on the east coast for the period January 20-23. That this tendency is aligned with a change in the synoptic conditions was shown by Wahl with mean maps for the 20th and 27th of January which delineated a change from a westerly circulation pattern t'o one predominantly northwesterly. A further stride forward was made by Wahl (3) in a second paper in which the January thaw was related to the mean features of the general circulation by judicious application of the total zonal index of the westerlies to the Boston records. The existence of primary singularities, representing distinct changes in the hemispheric flow pattern and affecting the local or secondary singularities, was reflected in the monthly mean index. It was found that separation of the Boston record into high and low index years led to mean temperahre curves with pro- nounced accentuation of the thaw in the specific low-index singularity curve. In view of these interesting results it was decided to examine the daily maximum temperature during January and precipitation occurrences during June at Walla Walla, Wash., for evidence of such a primary-secondary singular- ity relationship in this region. The local climatological conditions suggested that the maximum temperature is more representative of the air-mass regime here than is the mean.