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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.

A recent analysis of winds in the upper atmosphere, as revealed by sodiumvapor trails, led its authors to the conclusion that all the observed winds could be explained on the basis of prevailing and tidal components. Irregularly varying winds were attributed to ‘phase anomalies’ in the tidal oscillations, and the thesis that they were due instead to internal atmospheric gravity waves was excluded. In the present paper the steps that led to these conclusions are examined critically. It is shown that little, if any, weight can be placed in the arguments that were presented, and that there are substantial reasons for rejecting them. The relevance of prevailing and tidal components may be readily accepted, and indeed is supported in a companion paper, but the thesis that these components account for all the winds is simply not in accordance with the available evidence.

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.

In two earlier articles the authors have shown that if atmospheric ozone is considered as existing in a photochemical steady state depending on solar radiation, calculations involving certain assumptions regarding the absorption-coefficients yield a distribution of the ozone with height which is sufficiently similar to the distribution that is deduced from experimental observations to suggest that the photochemical picture is adequate to account for atmospheric ozone. At the end of the first paper the disturbance of the steady state by atmospheric circulation was briefly discussed, and it was pointed out that the known variations in the existing vertical ozone path over any point on the Earth's surface might be explained as due to such disturbance. In order to estimate the quantitative importance of circulation in the photochemical picture, it is necessary to have some idea of the rates at which the steady state is maintained at the various heights. It is one of the purposes of the present paper to estimate the approximate values of these rates.

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.

With total ozone sensors on earth-orbitung satellites the ozone distribution over the entire earth may be measured daily. The conclusions from some of the Nimbus III measurements are discussed in this paper. A comparison of time-longitude variations of stratospheric radiance values at 60°S with values of the total ozone indicated that low (high) radiance values correspond very closely with the low (high) total ozone amounts. The speed at which these ozone ‘waves’ progress eastward is greatest in the winter hemisphere. The speed of eastward progression decreases as one approaches the lower latitudes in the winter hemisphere. In the equatorial region the progression of the ozone ‘waves’ appears to be slowly westward. In the Northern Hemisphere the waves progress slowly eastward during summer. The intensity of the ozone ‘waves’ was also observed to change with latitude. These temporal and spatial fluctuations are related mainly to the motion of dynamic tropospheric systems. The extremely tight ozone gradients, which may be seen in the winter hemisphere data, have been shown to be associated with strong baroclinic zones in the lower stratosphere and upper troposphere, which are moving eastward. Assuming uniform zonal velocity we found Rossby wavelengths that varied from 2500 to 3700 km.

In a paper by Davies and Oakes (1962) concerning the problem of formulating a model of the general atmospheric circulation, the boundary condition used at the surface of the earth involved the assumption that the surface meridional, zonal, and vertical velocities are zero. In this note the effect on the model is evaluated by using as boundary condition at the earth's surface the more realistic assumption that the Reynolds stress is proportional to the first power of the surface wind speed.

In 1900 I communicated to this Society a paper on the above subject. Since that date a great deal of information has been obtained by means of free balloons carrying instruments which recorded the temperature, humidity, and pressure of the air up to great elevations. Much of this new knowledge seems to contradict our previous ideas, and does not seem to fit into the old convectional theory that cyclones are formed by the rising of the hot, moist air from the surface of the earth; their energy being due to their temperature and to the heat liberated by the condensation of the water vapour in them. We are told by those who have studied the bearing of the new knowledge on our atmospheric circulation that the old theory is “utterly untenable.” Their reasons for this conclusion are, first, that the recent investigations show that the air is colder in cyclones than in anticyclones; second, that the isothermal layer is lower than the mean over cyclones, while it is higher than the mean over anticyclones. At first sight these discoveries seem to shatter the convectional theory, but before we come to any conclusion I should like to present certain facts which it appears to me will require to be considered before we scrap our old ideas.

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

A result from a previous paper (Priestley 1947) indicates the existence of a broad upper limit to the size of pressure systems, and a lower limit to the distance separating the centres of two significant closed pressure systems. The pressure field has thus an inherent scale of pattern which varies with latitude, imposed by the essential geometry and dynamics of atmospheric flow. Orders of magnitude deduced theoretically agree well with experience. The implications contribute to an understanding of the mechanism of the mean global circulation.

Until quite recent years meteorology was in no position to make an effective contribution to the understanding of paleoclimates. Lacking were both a theory of the general circulation of the atmosphere and the upper wind observations which have provided the essential foundation of such theoretical understanding of the circulation as we now possess. The most notable early contributions from meteorology wereSimpson's (1934) schematic construction of a presumed mean circulation at the time of the Quaternary ice age maximum andWillett's (1949) proposal of two alternative modes of the general circulation, summarized as expansions and contractions of the circumpolar vortex of upper westerly winds. Both theories lacked an observational basis, especially for their more sweeping generalizations (e.g. simultaneity of ice-ages and lowlatitude pluvials, limitation to only two main atmospheric circulation types etc.) as well as for their author's further proposals about variations of the solar radiation. Nevertheless, they marked a valuable step forward, because they stimulated workers in many fields to interpret their evidence of climatic changes as part of a world phenomenon in which the general wind circulation must be involved. A strictly empirical study of the broadest possible scope of the climatic changes observable within the last 100–1000 years was badly needed. Examination reveals that significant changes have taken place within this period. Study of them is instructive. Whatever changes (if any) of effective radiation available at the Earth's surface occur, the atmospheric and ocean circulations are the mechanism whereby the heat and moisture are distributed. As in synoptic meteorology, circulation maps have been found the most useful means of obtaining a unified view of the climatic changes of recent times. The first successful studies of this kind were byDefant (1924), who showed that the mean circulation over the North Atlantic had intensified materially from the 1880s to the present century, i.e. in part of the period of Arctic warming and increasing mildness of winters in Europe. The present paper shows how our knowledge of changes such asDefant found has been extended over more of the world and a longer period of time. This leads to some indications about the probable nature and possible origins of the phenomenon, which is revealed as rather simple and world-wide in scope. We learn some of the types of variation that actually occur. Examination of the charts indicates inter alia progressive changes of intensity and position of the mainstreams of the atmospheric circulation, and of the ocean currents and climatic zones that correspond to them, within the last 100–250 years. Consideration of the nature of the Little Ice Age epoch of 1550–1850, and comparisons with what is known of the great ice ages of the Pleistocene, appears to throw some new light on the ice age problem.

Since June 1966, results from the French Thomson-scatter bistatic sounder (SaintSantin-Nancay) have yielded a considerable amount of data for the study of ionization transports in the F-region of the ionosphere. The first section of this paper brings out the importance and scale of transports in the ionosphere, and describes the new method of measurement used at Nancay. In the second section, experimental results of about 20 diurnal variations as described by hourly values of velocities are presented. Section 3 interprets these velocities as the sum of two effects: horizontal circulation of the neutral air, and ambipolar diffusion of ionization under gravity and under its own partial pressure. The two effects can be separated, giving an evaluation of neutral atmosphere velocities.

Two Skylark sounding rockets carrying chemical seeding payloads were launched from Woomera, South Australia (31 S, 137 E) in October 1969. In conjunction with these firings, the University of Adelaide conducted ground-based experiments on the upper atmosphere using the radio meteor and spaced receiver drift methods. This paper presents the measurements of properties of the neutral atmosphere above 90 km which were obtained from these experiments.

This paper describes a study of the average contour length changes and trough developments at the 300-mb level following geomagnetic disturbances from October 1956 through March 1957. A ‘contour length index’ and a ‘trough index’ were developed to measure the degree of disturbance of the 300-mb circulation over western North America and the eastern Pacific Ocean and the intensity of troughs in this circulation. Three trough classifications were defined and the development of all troughs appearing in the Aleutian Island-Gulf of Alaska area were analyzed by class. The results suggest that troughs which appeared in the Aleutian Island-Gulf of Alaska area a few days after an abrupt increase in geomagnetic activity subsequently developed a stronger average cyclonic curvature than other troughs. The largest trough developments and the maximum contour lengths occurred, on the average, eight to nine days after the magnetic disturbance. Added studies will be needed to determine whether the suggested relationships are general ones.

There are many papers on the effects of meteorological factors on insects, but only a few state these effects in terms of large-scale weather processes. Even fewer report the logical condusion of such studies: prediction of the biological phenomena with the aid of modern methods of weather analysis and forecasting.

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.