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(Received 1974 January 24)* Summary In an earlier paper (Lambeck & Cazenave, Part I) we investigated the seasonal variations in the Earth’s rotation and their relation to the global wind circulation. In this paper we consider mainly the high frequency part of the length-of-day spectrum. A month-by-month evaluation of the zonal wind excitation function shows that these rotational variations are all of zonal wind origin for frequencies up to at least 6 cycles per year. The zonal winds also contribute to frequencies greater than 6 cpy in the Earth’s rotation and will degrade the results for the Love numbers k2 estimated from the tidal terms near 13 and 26 cpy. Rapid changes of as much as during 5 days have been observed in the length of day on several occasions and these are also caused by meteorological disturbances. Any study of other possible excitation functions will require that these meteorological contributions are first evaluated. There does not appear to be any single wind pattern that is responsible for the observed high frequency variations in the length of day and it does not seem possible to use these observations as an indication of the nature of the zonal wind pattern other than as a global zonal wind index. There is some evidence that the zonal winds will contribute to those long-period variations in the Earth‘s rotation that are usually attributed to core-mantle coupling, In a previous paper (Lambeck & Cazenave 1973; referred to hereafter as Paper I) we discussed the relation between the annual, semi-annual and biennial variations in the Earth’s rate of rotation and the atmospheric circulation. We concluded that these observed periodic fluctuations in the rotation are largely due to the zonal winds and, on the basis of the astronomical evidence, we were able to draw some conclusions concerning the extent and variability of the downward propagation and the period of the global quasi-biennial circulation. We concluded, for example, that for the years 1965-1969 the period of this oscillation was closer to 3 years than to two but that by 1970 the period was again close to 2 years. The recent time-height zonal wind section at the Canal Zone and Kawajalein given by Wallace (1973) confirms such changes in the period. In this paper we are primarily concerned with the non-seasonal changes in the Earth’s rotation and their relation to variations in the zonal wind circulation. Short duration irregular variations in the length of day (lod) have been observed since

In the early times of the Boyal Society (a little more than 200 years ago) a spirit of inquiry and of speculation as to the causes of the Trade Winds arose among its members. The papers which we may presume to have first brought the subject into special notice in the Society, and which were published in the * Transactions,’ offered views which, in the light of subsequent knowledge and theory, show themselves as being untenable, and in part even grotesque. But those papers were soon followed by, and probably had an effect in leading to, a much more important paper by the eminent astronomer Edmund Halley; and this was followed 49 years later by one, more important still, by George Hadley, in which we may with confidence judge that a substantially true theory of a large part of the system of Atmospheric Circulation in its grandest and most dominant conditions was for the first time offered to the world through the pages of the ‘ Philosophical Transactions.’ Further speculations on the subject and advances in our knowledge of it have been made in later times and have been brought into notice in various ways. I believe that I have myself arrived at some improved considerations which are to a large extent trustworthy and go far towards completing the true theory of the grand currents of atmospheric circulation, and I entertain the ambition to have my views placed on record by this Society—the Society in which the subject had its most important beginnings.

In the early times of the Boyal Society (a little more than 200 years ago) a spirit of inquiry and of speculation as to the causes of the Trade Winds arose among its members. The papers which we may presume to have first brought the subject into special notice in the Society, and which were published in the * Transactions,’ offered views which, in the light of subsequent knowledge and theory, show themselves as being untenable, and in part even grotesque. But those papers were soon followed by, and probably had an effect in leading to, a much more important paper by the eminent astronomer Edmund Halley; and this was followed 49 years later by one, more important still, by George Hadley, in which we may with confidence judge that a substantially true theory of a large part of the system of Atmospheric Circulation in its grandest and most dominant conditions was for the first time offered to the world through the pages of the ‘ Philosophical Transactions.’ Further speculations on the subject and advances in our knowledge of it have been made in later times and have been brought into notice in various ways. I believe that I have myself arrived at some improved considerations which are to a large extent trustworthy and go far towards completing the true theory of the grand currents of atmospheric circulation, and I entertain the ambition to have my views placed on record by this Society—the Society in which the subject had its most important beginnings.

To many of us the virtues of our day-to-day changeable weather are manifest. Seventy years of standardized meteorological records give us a good idea of the limits within which any day's events are likely to fall. In the southern English lowlands a fall of two feet of snow, a shade temperature of 970, or a month with 70 per cent. of the possible sunshine, represent extremes unlikely to be surpassed. Superimposed upon our day-to-day weather how? ever we now recognize that small but definite fluctuations of climate exist and that since about 1925 an appreciable amelioration has set in round the North Atlantic. Professor Ahlmann has recently reviewed the many associated events.1 It remains for us to consider the possible amplitude of the variation of our climate in Britain, as distinct from the weather. I shall first comment on the magnitude of the present fluctuation in Britain, in terms of overall mean temperature. I shall follow with some evidence for past fluctuations provided by the instrumental records since 1700, relating them to the earlier climatic recessions demanded by the pollenanalysts in historic and prehistoric time. In the second part of the paper I shall address myself more to those technical experts who are acquainted with the geological and botanical background, and I shall give estimates for the temperature of the various phases since the last Glacial maximum in order to compare the range of variation over which our climate appears at intervals to have changed. In my view it is high time such estimates of the mean tem? perature of summer and winter were made, and an opportunity of doing this for Late Glacial times is now provided by using Professor Ahlmann's relationships between the height of the snow-line, the amount of accumulated pre? cipitation and the mean temperature of the ablation season. Comparisons between present-day fluctuations and past changes may throw light on the possible causes of climatic variation; some will be led to consider whether the present amelioration in north-west Europe will con? tinue, and for how long. Throughout this paper I shall largely confine atten? tion to the mean temperature of January and July as a sufficient initial indication of winter and summer characteristics. Periods of disturbed weather when the oceanic influence is greater are characterized by a diminished January-July range; in quieter and more "continental" phases the range increases. Meteorological aspects of this "varying vigour of the atmospheric circulation" are discussed by Angstrom * and Willett.3 1 H. W:son Ahlmann, "The present climatic fluctuation," Geogr.J. 112 (1948) 165-95. 3 A. Angstrom, "The change in the temperature climate in present time," Geogr. Ann. 21 (1939) 119. 3 H. C. Willett, "Long-period fluctuations of the general circulation of the atmo? sphere," Journ. Met., 6, 1949, pp. 34-50; "Solar-variability as a factor in the fluctua? tions of climate," Geogr. Ann. 31 (1949) 295. See also Q. J. R. Met. S., Centenary Proceedings, 1950.

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...

Recurrence of precipitation during weekends—and of precipitation-free weekdays—was especially prominent over the southeastern quarter of the United States during much of the 1964-65 winter. This paper, with the help of maps averaged by day of the week, points out the relation of the weekly precipitation periodicity to interactive cyclone-scale and long wave systems over North America and the Pacific. Despite the averaging, the continuity in these maps is surprisingly clear. For example, an upper trough over west-central portions of the country in mid-week progresses to a position off the Atlantic Seaboard at the beginning of the week. This progression is associated with periodic (largely diabatic) development of the Gulf of Alaska Cyclone, which, in turn, can be traced to the periodic establishment of a ridge in the Bering Sea and occurrence of cyclogenesis in middle and lower latitudes of the North Pacific. An increase in hemispheric wave number, provided periodically by development of the Gulf of Alaska trough, leads to eastward motion of downstream features over the U.S., but when the Gulf trough fills abrupt retrogression sets in until its redeepening reestablishes the eastward motion. One of the primary circulation forcing elements, cyclogenesis in the Pacific, appears to be related to abnormal sea-surface temperature fields established during the preceding fall and maintained by the overlying atmospheric circulation during winter. While this interaction may offer a clue to the sequence of downstream events, it does not imply a weekly periodicity. Not even the transmission of the periodicity downstream is suggested by present numerical forecasts, but this failure can be attributed to typical errors in these forecasts. Further empirical studies, detecting weather periodicities and relating them to the time-averaged circulations or regimes in which they occur, might help in understanding and eventually predicting the occurrence of the periodicities. DOI: 10.1111/j.2153-3490.1966.tb00294.x

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.

(Abstract.)In these papers the meteorological observations taken during the voyage of the “Challenger ” are discussed; and, from data collected from all parts of the world, fifty-two maps have been prepared, showing for each month of the year the distribution of temperature and pressure over the globe and the prevailing winds. Part I. deals with the diurnal, and Part II. with the seasonal phenomena of meteorology.

Photosynthesis of leafy shoots was determined under a range of CO2 concentrations that spanned past and likely future levels of atmospheric CO2. The temperature regime was also manipulated. Response of photosynthesis to CO2 was pronounced, and differed markedly among species. A substantial rise in atmospheric CO2 is likely to produce shifts in species composition of southern California mountain and foothill vegetation, with several conifer species being disadvantaged. INTRODUCTION How much has the well-advertised increase in atmospheric CO2 affected photosynthesis of land plants? What sorts of response can we expect from further increases in CO2? What might be the outcome in a forest? These questions are explored in this paper. In the late 1800's, concentration of atmospheric CO2 was ca. 285 ppm (Callendar, 1958). According to recent careful measurements (Keeling, 1970), the current mean world CO2 level is close to 324 ppm. Annual rate of CO2 increase is approaching 1 ppm and is rising. Levels of 400 ppm by the year 2000, and 500 ppm by 2020, are predicted (Peterson, 1969). Increased burning of fossil fuel is at the root of this increase. Carbon that was gradually withdrawn from global circulation over several hundred million years is suddenly being returned to the carbon cycle. It can be absorbed by sea water, or even contribute to deposition of new fossil fuel, but such processes take thousands to millions of years (Bolin, 1970). If the earth's fossil fuels are fully exploited over the next several hundred years, we face a precipitous rise in atmospheric C02, followed by an almost equally precipitous drop (Revelle, 1965). It is well known that CO2 is one of the principal limiting factors governing rates of photosynthesis on land. A number of studies have shown that plants respond to increased CO2 up to several thousand ppm (Hesketh, 1963; Madsen, 1968; Gordon and Gatherum, 1969). Enhancement of CO2 in greenhouses by artificial means is now accepted practice in many places. However, little is recorded concerning the response of native vegetation to small increments in atmospheric C02, such as have been experienced in the past 100 years or may be expected in the 50 years to come. A field study in the oak-pine forest on Long Island, New York, indicated that enhancement of CO2 up to about 100 ppm above ambient levels produced a sharp linear rise in photosynthesis of leafy twigs (Wright and Woodwell, 1970). The present study was designed to explore the response of a number of western species to modest CO2 enhancement, and to assess the relation of CO2 response to composition of the vegetation.