Rossby Carl-Gustaf

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Rossby
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Carl-Gustaf
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  • Book
    Fluid mechanics applied to the study of atmospheric circulations. I. A study of flow patterns with the aid of isentropic analysis.
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1938-12) Rossby, Carl-Gustaf ; Namias, Jerome ; Simmers, Ritchie G.
    This paper constitutes Part I of a report on certain investigations which have been in progress at the Massachusetts Institute of Technology during the past few years and which have been supported in part with funds provided by the Weather Bureau of the U. S. Department of Agriculture under the Bankhead-Jones Special Research Fund. The ultimate purpose of these investigations is to develop a sound physical model of the general circulation of the atmosphere, in the hope that an improved understanding of this process eventually may furnish valuable clues as to how the time range of our present daily weather forecasts may be extended and their quality be improved. In the past, the interpretation of the large-scale circulations of the atmosphere with the aid of the tools of classical hydrodynamics has suffered from the fact that these tools were designed for the study of thermodynamically inactive fluids, in which, furthermore, viscous or eddy stresses could be neglected. Through the work of V. Bjerknes and his students a good start has now been made towards the development of a science of hydrodynamics applicable also to thermodynamically active fluids, in which density changes are taking place as a result of non-adiabatic temperature changes. The removal of the second restriction-i.e., the development of hydrodynamic tools adapted to the study of fluids in which eddy stresses playa dominant role-has been accomplished mainly through the investigations of the Göttingen school of fluid mechanics. As yet, no synthesis of these two modern developments has been accomplished, although it is becoming increasingly clear that such a synthesis is needed before any headway can be made with the interpretation of the behaviour of the atmosphere. There has been a tendency on the part of meteorologists to assume that the effects of eddy stresses are restricted to a layer near the ground, and that the atmosphere above this layer behaves approximately as an ideal fluid. Even fairly elementary considerations show that a real understanding of atmospheric circulations becomes absolutely impossible on the basis of this assumption. A modest first attempt towards such a synthesis of the Norwegian and German developments will be attempted in these reports. It will be shown that the movements in the free atmosphere above the ground friction layer are affected by large-scale lateral mixing processes which produce shearing stresses acting across vertical planes, and one or two examples will be given to demonstrate that reasonable steady state solutions for the atmosphere can be obtained by taking this internal stress distribution into account. It will be shown, moreover, that the distribution of cold sources and heat sources in the free atmosphere is at least in part controlled by the stress distribution, which regúlates the location of ascending and descending movements.
  • Book
  • Book
    On the momentum transfer at the sea surface. I. On the frictional force between air and water and on the occurrence of a laminar boundary layer next to the surface of the sea. II. Measurements of vertical gradient of wind over water. III. Transport of surface water due to the wind system over the North Atlantic
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1936-06) Rossby, Carl-Gustaf ; Montgomery, Raymond B.
    I. It is fairly generally assumed that the horizontal circulation of the ocean "troposphere" is maintained by the large scale permanent wind system of the atmosphere. Accurate knowledge of the tangential force exerted by the wind on the surface of the water should therefore be a prerequisite for every attempt to analyze the movements of the surface water. Very few data are available from which this shearing force may be accurately determined, although several, in principle simple, methods of attack are available. Recently some estimates of the wind force have appeared in studies not primarily concerned with the oceanographic aspects of the problem. In view of the conflicting results obtained and in view of the importance of the problem to physical oceanography it seems desirable to examine the question theoretically and to study critically the empirical determinations just referred to. II. Despite the great importance, in studies of the frictional forces between atmosphere and ocean, of wind gradient measurements next to the ocean surface, to my knowledge the only observations that have been published are those of Wüst and of Shoulejkin. Both of these are so fragmentary that one would find it very difficult to draw general conclusions from them alone. Feeling that further measurements of any sort might prove useful, and lacking time and facilities for a large program, the author felt justified in making the following simple measurements during September 1935, which may be regarded as preliminary. III. The results of Section I above and of our previous paper are here applied to the specific computation of the transport of the drift current system over the North Atlantic. Only the computation is given here, but the authors of this paper expect to discuss in later articles its significance in connection with the surface salinity distribution and with the Equatorial Current.
  • Book
    Thermodynamics applied to air mass analysis
    (Massachusetts Institute of Technology, 1932) Rossby, Carl-Gustaf
    Since the beginning of 1929 systematic work has been carried out at the Massachusetts Institute of Technology to develop practical methods for the identification and characterization of air masses with the aid of upper air soundings of pressure, temperature and humidity. A brief report on this work was published in October 1930. It was then shown that by plotting against each other two meteorological elements, which under certain well defined conditions are recognized as conservative, namely, specific humidity and potential temperature, curves are obtained which, in winter time, to a high extent remain unchanged and characteristic of the individual air masses. In view of this property the curves were named "invariant curves." Since the invariance is restricted to the winter season, but the curves always may be advantageously used to determine the vertical structure and life history of air masses, they shall, in the following, be referred to as "characteristic curves." The report also stated that by means of characteristic curves a new method had been created of indicating certain differences in stability between the principal American air masses. These differences may be expressed in terms of the variation with elevation of specific entropy, and it was therefore decided to continue the investigation and to include in it a study of the equivalent-potential temperature, which, in an easily comprehensible form, measures the specific entropy of moist air. The excellent results obtained by Robitzsch through the introduction of equivalent-potential temperature into practical meteorological work lent additional support to this decision.
  • Book
    The layer of frictional influence in wind and ocean currents
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1935-04) Rossby, Carl-Gustaf ; Montgomery, Raymond B.
    The purpose of the present paper is to analyze, in a reasonably comprehensive fashion, the principal factors controlling the mean state of turbulence and hence the mean velocity distribution in wind and ocean currents near the surface. The plan of the investigation is theoretical but efforts have been made to check each major step or result through an analysis of available measurements. The comparison of theory and observations is made diffcult by the fact that in most cases measurements have been arranged without the aid of a working hypothesis concerning the dynamics of the effect studied; thus information is often lacking concerning parameters essential to the interpretation of the data.
  • Book
    Dynamics of steady ocean currents in the light of experimental fluid mechanics
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1936-08) Rossby, Carl-Gustaf
    The present investigation may be regarded as a part of a systematic effort to introduce into meteorology and physical oceanography methods and results which for a number of years have contributed to the rapid growth and increasing practical significance of experimental fluid mechanics. This science has recognized that the exact character of the forces controlling the motion of a turbulent fluid is not known and that consequently there is very little justification for a purely theoretical attack on problems of a practical character. For this reason fluid mechanics has been forced to develop a research technique all of its own, in which the theory is developed on the basis of experiments and then used to predict the behavior of fluids in cases which are not accessible to experimentation. In oceanography it has long been regarded as an axiom that the movements of the water are controlled by three forces, the horizontal pressure gradient, the deflecting force, and the frictional force resulting from the relative motion of superimposed strata. It is significant that thirty-five years of intensive theoretical work on this basis have failed to produce a theory capable of explaining the major features of the observed oceanic circulation below the pure drift current layer. The present investigation considers a force which has been completely disregarded by theoretical investigators although its existence has been admitted implicitly by practically everyone who has approached physical oceanography from the descriptive side, namely the frictional force resulting from large-scale horizontal mixing. The intro- . duction of this force permits us to see how motion generated in the surface layers may be diffused and finally dissipated without recourse to doubtful frictional forces at the bottom of the ocean.