Papers in Physical Oceanography and Meteorology

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Published by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. Published originally as Massachusetts Institute of Technology Meteorological Papers (1930-1932), this collection contains papers from Vol .1 No. 1 to Vol. 10 No. 4 (1930-1948).

ISSN: 0198-6821

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  • Book
    The cycle of phosphorus in the western basin of the North Atlantic
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1935-04) Seiwell, Harry Richard
    The importance of phosphorus for organic production in the sea appears to have been recognized first by Brandt (1899) and the earlier determinations of this element in the coastal seas of northern Europe (Brandt, 1920; Raben, 1920; Mathews, 1917) suggested a correlation between seasonal variation of phosphate and growth of phytoplankton. These earlier determinations were later shown to be too high (Atkins, 1926, a) and did not indicate the complete exhaustion of phosphate from the water, so it was not until several years later that Atkins (1923), employing the rapid and more accurate colorimetric ceruleo-molybdate method of Deniges, illustrated the complete dependence of algal growth on phosphate (in the English Channel) and thus established the foundation for modern studies of marine chemical fertility. The beginning of our knowledge of phosphate content of the open ocean may, as far as is known to me, also be attributed to Atkins (1926, a) and even though these early results were frequently somewhat vitiated by storing of the samples before analyses, they represented the order of magnitude of phosphate concentration in the sea. Within recent years phosphate determination has become a component part of the program of most deep sea investigations and much general information on its distribution and variation in the open ocean has been brought to light.
  • 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
    The meteorological airplane ascents of the Massachusetts Institute of Technology. Part I. On the technique of meteorological airplane ascents. Part II. Aircraft instruments in meteorological flying
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1934-08) Lange, K. O. ; Draper, C. S.
    The aerological flights at Boston are part of the general research program of the Meteorological Division of Massachusetts Institute of Technology, which program since 1929 has been directed especially toward the study of American air masses and fronts. Recently, some results of these studies were published by Willett, who based his investigations on a series continuous over three years of mornìng and evening weather maps, analyzed at the Institute, together with upper air soundings from the United States Weather Bureau stations at Dallas, Omaha, Chicago, Groesbeck, Atlanta and from the United States Navy at Seattle, Anacostia, Pensacola and San Diego. These upper air data facilitated the determination of the properties of the air masses and so proved of inestimable value for the study. But the use of the data also showed that improvement both in the number of stations and in the quality of observations was highly desirable. Ascents in the northeastern part of the United States were lacking. Knowledge of the vertical structure of air masses reaching this region, however, is of special interest in forecasting for this densely populated district. For these reasons and since the direct comparison of actual local weather developments with upper air conditions is also con- sidered to be very valuable, the Institute started its own airplane station at Boston. In addition to "regular" ascents at the time of the morning surface observations, special flights were made when particularly interesting weather situations prevailed. On a number of days series of ascents were carried out to obtain cross sections through fronts passing over Boston. Other special flights were made to obtain information on atmospheric turbulence. For this same purpose and also in order to study the diurnal changes of temperature in the lowest 5,000 feet, several series are planned of a number of comparatively low altitude flights at short intervals throughout the day.
  • Book
    The distribution of oxygen in the western basin of the North Atlantic
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1934-08) Seiwell, Harry Richard
    The distribution of dissolved oxygen in the sea is controlled by a combination of its physical, chemical and biological characteristics; on the one hand, the chemical and biological activities tend to vary the content of the dissolved gas whereas, on the other, the circulatory agencies tend to redistribute the oxygen and bring about equilibrium. The fact that there is a constant consumption of dissolved oxygen in the depths and that frequent supersaturation with oxygen occurs at or near the surface of the ocean was observed on the "Challenger" expedition (Dittmar, 1884). An explanation of the cause of supersaturation of oxygen, however, was not forthcoming until 1899 when Martin Knudsen suggested that it was caused by photosynthetic activities of vegetable plankton. The original oxygen content of ocean waters has been obtained from a-thin surface layer in contact with the atmosphere and as a product of photosynthetic activity. In modern concepts of oceanography it is a generally accepted fact that the water masses of the depths of the oceans have at some time and place been at the surface where under the influence of climatic conditions they acquired distinct temperature, salinity and oxygen characteristics. The sinking of the surface layers in the so-called regions of convergence and their ultimate distribution by means of quasi-horizontal and convectional currents results in the whole of the ocean basins being filled with water which has acquired its fundamental characteristics while under the influence of atmospheric conditions. From general knowledge of oceanic circulation, based on researches of Nansen (1912), Jacobsen (1929), Wüst (1928), etc., the water of the western basin of the North Atlantic is probably of several origins and consequently of different ages and oxygen contents. Thus, the deepest part of the whole basin, up to depths of 2000-1500 meters appears to contain water which, for the most part, originated at the surface in high North Atlantic latitudes. Lying on top of this deepest water there is, in the northern half of the region, what appears to be a mixture of it and other North Atlantic water, while in the southern half of the region there is at intermediate depths a mass of water which apparently originated at the surface in high latitudes of the South Atlantic.
  • Book
    Studies of the waters on the continental shelf, Cape Cod to Chesapeake Bay. I. The cycle of temperature
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1933-12) Bigelow, Henry Bryant
    When the U. S. Bureau of Fisheries, in cooperation with the Museum of Comparative Zoology, commenced the oceanographic survey of the Gulf of Maine in the summer of 1912 (Bigelow, 1925-1927), it was in the hope that this might later be extended to the coastal waters thence southward; eventually even as far as the Gulf of Mexico. Cruises carried out in connection with investigations of the biology of the mackerel, by the Fisheries' steamer "Albatross II" from 1927 to 1932, supplemented by those of the research ship "Atlantis" of the Woods Hole Oceanographic Institution, have made it possible to extend the detailed examination of the physical oceanography of the continental shelf as far as the offing of Chesapeake Bay, and to the offing of Cape Hatteras for some of the months. The present account of the temperature of the region will, it is hoped, be followed shortly by corresponding accounts of salinity, of circulation and of the dominant planktonic communities.
  • Book
    Scientific results of the "Nautilus" expedition, 1931 under the command of Capt. Sir Hubert Wilkins. Parts IV and V
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1933-06) Villinger, B. ; Stetson, Henry C.
  • Book
    American air mass properties
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1933-06) Willett, Hurd C.
    In this paper the term Air Mass is applied to an extensive portion of the earth's atmosphere which approximates horizontal homogeneity. The formation of an air mass in this sense takes place on the earth's surface wherever the atmosphere remains at rest over an extensive area of uniform surface properties for a suffciently long time so that the properties of the atmosphere (vertical distribution of temperature and moisture) reach equilibrium with respect to the surface beneath. Such a region on the earth's surface is referred to as a source region of air masses. As examples of source regions we might cite the uniformly snow and ice covered northern portion of the continent of North America in winter, or the uniformly warm waters of the Gulf of Mexico and Caribbean Sea. Obviously the properties of an air mass in the source region will depend entirely upon the nature of the source region. The concept of the air mass is of importance not only in the source regions. Sooner or later a general movement of the air mass from the source region is certain to occur, as one of the large-scale air currents which we find continually moving across the synoptic charts. Because of the great extent of such currents and the conservatism of the air mass properties, it is usually easy to trace the movement of the air mass from day to day, while at the same time any modification of its properties by its new environment can be carefully noted. Since this modification is not likely to be uniform throughout the entire air mass, it may to a certain degree destroy the horizontal homogeneity of the mass. However, the horizontal differences produced within an air mass in this manner are small and continuous in comparison to the abrupt and discontinuous transition zones, or fronts, which mark the boundaries between air masses. Frontal discontinuities are intensified wherever there is found in the atmosphere convergent movement of air masses of different properties. Since the air masses from particular sources are found to possess at any season certain characteristic properties which undergo rather definite modification depending upon the trajectory of the air mass after leaving its source region, the investigation of the characteristic properties of the principal air mass types can be of great assistance to the synoptic meteorologist and forecaster. We owe this method of attack on the problems of synoptic meteorology to the Norwegian school of meteorologists, notably to T. Bergeron. Investigation of the properties of the principal air masses appearing in western Europe has been made in particular by O. Moese and G. Schinze. The purpose of this paper is to give the results of a similar investigation of the properties of the principal air masses of North America, and to comment on some of the striking differences which appear between conditions here and in Europe.
  • Book
    Scientific results of the "Nautilus" Expedition, 1931 : under the command of Capt. Sir Hubert Wilkins. Parts I to III
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1933-03) Sverdrup, Harald U. ; Soule, Floyd M.
    In 1930 Sir Hubert Wilkins announced his plan for exploring the Polar Sea by submarine. Thanks to the courtesy of the U. S. Navy Department and the U. S. Shipping Board the submarine 0 12 was placed at his disposal and the constructor of this vessel, Mr. Simon Lake, undertook to rebuild it and make it suitable for travelling underneath the Arctic pack-ice. After rebuilding the submarine was in the spring of 1931 named Nautilus. ... The expedition did not reach its goal and the scientific results are, therefore; small as compared to what had been hoped for. But we have shown that an extensive scientific program can be carried out under the conditions onboard a submarine, and it is hoped that the following papers will add to our knowledge of the region which was visited.
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  • 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
    Characteristic weather phenomena of California : a regional analysis based on aeronautical weather observations
    (Massachusetts Institute of Technology, 1931) Byers, Horace R.
    During the fiscal year beginning July 1, 1928, the Daniel Guggenheim Fund for the Promotion of Aeronautics maintained an experimental meteorological service for the benefit of air transportation between San Francisco and Los Angeles. The system was designed as a first approach toward a model weather reporting organization for air traffic. Its main feature was the gathering of simultaneous weather observations from about 35 stations in Southern and Central California covering an area of, roughly, 65,000 square miles. The observation hours were 6.30 a.m., 8 a.m., 9.30 a.m., 11 a.m., 12.30 p.m., and 3.30 p.m., 120th meridian time. The regular Weather Bureau observations furnished additional data for 5 a.m. and 5 p.m. A description of the organization has been published by E. H. Bowie. Since the service was organized strictly for the purpose of informing airplane pilots of weather conditions over their routes and not with a view of furnishing a fertile field for meteorological investigations, certain instrumental readings which are important in meteorological research were not provided. Thus humidity observations are lacking, except as subsequently obtained from the few but more thoroughly equipped stations of the U. S. Weather Bureau, the U. S. Navy and the University of California. A series of airplane ascents made at the Naval Air Station at San Diego provided pressure, temperature and relative humidity observations from the upper atmosphere for part of the period investigated. Three pilot balloon stations were established by the Fund to supplement those of the Government, so that ample free air wind data are available. Non-professional part-time observers were employed at most of the stations. For this reason, inaccuracies are likely to have lessened the value of the reports. These errors occurred chiefly in the determination of cloud forms. When the uncertainties of cloud classification and the diffculties it presents even to the trained meteorologist are fully appreciated, the errors in these observations are not surprising. It is the opinion of the authors that the cloud forms herein recorded are for all practical purposes correct. During the year in which this service was conducted by the Fund, some interesting data were collected to add to the knowledge of meteorological conditions in California. This applies particularly to the movement of fronts and the development, distribution and dissipation of the persistent and frequent fogs in the area. Some of these results will be presented below.
  • Book
    Synoptic studies in fog
    (Massachusetts Institute of Technology, 1930) Willett, Hurd C.
    This study of fog formations at Hadley Airport was carried out during the winter of 1928-29 with the intent of finding out how far a careful scrutiny of local records might assist in explaining and forecasting local fogs. It was meant to be supplementary to a more general discussion of fog and haze formation which had appeared previously in the Monthly Weather Review for November, 1928. This study is based on the general fog classification set forth there.
  • Book
    Observations of vertical humidity distribution above the ocean surface and their relation to evaporation
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1940-02) Montgomery, Raymond B.
    In order to obtain information on the effect of eddy viscosity and eddy diffusion at the boundary between sea and atmosphere, simultaneous measurements of humidity at two, three or four levels between 1 and 38 meters above the sea surface were made from Atlantis during its cruises off the east coast of the United States during the summer of 1935. The 340 series are published in the form of averages for 115 ten-minute intervals. It is now generally accepted that the wind speed in the lowest dekameters of the atmosphere varies as the logarithm of height, provided the lapse rate is not too far from the adiabatic (Lettau, 1939, p. 72 etc.). This is valid within the layer where the normal shearing stress may be considered constant with elevation and equal to the surface resistance. Accordingly the eddy viscosity coeffcient must increase linearly with elevation.
  • Book
    The effect of short period variations of temperature and salinity on calculations in dynamic oceanography
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1939-11) Seiwell, Harry Richard
    This paper is a discussion of possible discrepancies in computations of ocean currents (based on horizontal variations of dynamic topography calculated from arbitrary deep lying reference surfaces), because of time variations of temperature and salinity at fixed depths in the sea (illustrated for a 24-hour period at "Atlantis" Station 2639). The results contained herein, while based chiefly on information from the western North Atlantic, are of general applicability, since time variations of the same order of magnitude have been observed over extensive areas of the Atlantic ocean. In selecting material for analysis of dynamic situations in the region concerned, consideration has been given only to those favorably located stations from which the structural features could most conveniently be obtained for illustrating the points in question.
  • Book
    Fronts and frontogenesis in relation to vorticity
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1942-01) Petterssen, Sverre ; Austin, James Murdoch
    Soon after the discovery of the polar front, it was realized that fronts were subject to processes which either increased or diminished their intensity. Thus, fronts may form in fields where the distributiori of the meteorological elements is continuous; and, in other cases, fronts may dissolve and develop into a field of continuous distribution of the various elements. The processes which lead to the formation of a front or the increase in intensity of an existing front, are called jrontogenetical processes; and the processes which lead to the dissolution of fronts are calledjrontolytical processes. In theoretical treatments of fronts it has been customary to simplify the problem by assuming that a frontal surface is a mathematical discontinuity, and doubts have been raised against the validity of this simplification. Petterssen has shown that both the dynamic and the kinematic boundary conditions that hold for perfect discontinuities hold also for layers of transition of finite thickness within which the meteorological elements vary continuously. We are, therefore, justified in treating frontal surfaces and fronts as either strict discontinuities or as finite layers of transition. Frontogenesis may therefore be defined as the process that tends to create a surface of discontinuity in the atmosphere. Whether or not this process results in a strict discontinuity is immaterial.
  • 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
    On the measurement of drop size and liquid water content in fogs and clouds
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1938-11) Houghton, Henry G. ; Radford, W. H.
    A short critical review of possible methods for the measurement of the size of fog particles is presented. It is concluded that the only suitable method of obtaining the distribution of drop sizes present in a given fog consists in the microscopic measurement of large numbers of drops which have been collected on a properly surfaced slide. A method for surfacing microscope slides with a thin, uniform layer of petroleum grease is described. The important problem of obtaining a representative sample of drops on a slide is next considered. Experimental results indicate that slides no larger than 5 mm square will collect satisfactory samples if exposed facing the wind. Larger slides are found to discriminate against the smaller drops. Special fog microscopes which have been constructed for observing droplet samples are described, and typical results obtained in natural fogs are presented. Although forty sets of data have been procured in sixteen different fogs, it has not been possible to correlate the drop size data with any of the accompanying meteorological conditions. There is no evidence of mass grouping, such as Köhler observed in clouds; however, definite conclusions cannot be drawn from such a relatively small amount of data. The usefulness of fog water data is indicated and possible methods of procuring them are reviewed. An investigation of the sampling problem encountered in the operation of most fog measuring instruments is described. The method of avoiding sampling diffculties in a new fog water instrument is explained and the constructional features and operation of the apparatus are discussed.
  • Book
    On the local dissipation of natural fog
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1938-10) Houghton, Henry G. ; Radford, W. H.
    It is submitted that the hazards of landing aircraft in fog could be greatly reduced by providing relatively small clearings into which approaching planes could be safely guided by radio or other navigational aids which are now available. The same general method might also be used to facilitate the entrance of ships into fog-bound harbors or docks. In the first section of this paper the properties of fog which are of importance in the discussion of methods of fog dissipation are summarized on the basis of measurements made at Round Hill. The minimum dimensions of a cleared space of useful size are taken as 500 to 1000 meters long, 30 to 50 meters wide and 10 to 20 meters high. From extensive investigations at Round Hill it is known that in order to maintain a clearing of this size under typical wind conditions, fog must be cleared at a minimum rate of about 2000 cubic meters per second. This figure is used for all subsequent computations. It is pointed out that the known methods of fog dissipation can be divided into two general classifications: (1) those in which the fog particles, are physically removed from the air, and (2) those in which the particles are evaporated in the air. Numerous specific methods are then described and critically examined with respect to their ability to provide cleared air at a rate of 2000 cubic meters per second in a reasonably practical manner. The more important methods considered involve the use of intense sound fields, charged or uncharged falling particles, electrical precipitation, mechanical precipitation, evaporation by heating and evaporation induced by the condensation of atmospheric water vapor on hygroscopic particles. It is concluded that the evaporation methods as a class are superior to the physical removal methods because they lower the relative humidity of the cleared air and thereby greatly reduce the limiting effects of atmospheric turbulence which act to "fill in" the cleared space. The method involving the condensation of water vapor by means of calcium chloride is chosen as being probably the most practical of the fog dissipation methods considered. The second section of the paper presents a detailed examination of one application of the calcium chloride method of fog dissipation. In this method drops of a saturated solution of calcium chloride are released above the volume of fog which is to be cleared. These hygroscopic drops, which are large enough to fall fairly rapidly, condense a suffcient quantity of water vapor from the air through which they descend to effect the evaporation of the fog particles. The investigation of this method of fog dissipation is divided into three parts. The first part deals with the determination of the relative humidity required to cause the evaporation of the fog drops as a function of the time of evaporation and the size of the fog drops. The second part is concerned with the rate of condensation of water vapor on drops of calcium chloride solution as a function of the drop size and concentration. In the third part the criteria for the selection of the optimum size of the solution drops are presented and the development of spray nozzles capable of forming drops of approximately the desired size is described briefly. Finally, the quantity of calcium chloride solution required for the dissipation of fog under typical conditions is computed. It is found that, with the best available spray nozzles, fog can be dissipated at a rate of 2000 cubic meters per second (suffcient to maintain a cleared space of useful size under typical conditions) by spraying from 4 to 5 liters of saturated solution per second. It is concluded that the method is practicable on the scale proposed. The third section of the paper is an account of the design and successful operation of a fullsized experimental fog dissipator operating according to the method described in the second section. The major considerations which influenced the determination of the size and spraying capacity of the apparatus are summarized and the essential features of the actual installation are described. The test procedure is outlined and the average results of eight successful tests conducted during a period of two and one-half years are indicated. The tests were made at air temperatures ranging from 4° to 20°C and at wind velocities up to 7 meters per second. The clearings formed were usually from 500 to 700 meters long, 30 to 50 meters wide and 15 to 20 meters high. After the installation of an improved type of spray nozzle clearings of the same size were maintained by spraying only 5 liters of saturated calcium chloride solution per second. The data obtained in two typical fog dissipation tests are presented in detaiL. It is found that the experimental results are in excellent agreement with the computations presented in the second section of the paper. It is concluded that the local dissipation of natural fog by means of sprayed calcium chloride is entirely feasible. Certain practical disadvantages of the experimental installation are discussed and a new type of apparatus which has recently been constructed to overcome some of these limitations is briefly described. Methods for practically eliminating the corrosive action of the calcium chloride solution are also noted. The fourth and final section of the paper describes a new type of apparatus in which the general method of fog dissipation by means of hygroscopic particles is applied in a different manner. By substituting finely-divided calcium chloride powder for the relatively coarse spray it is possible to confine the hygroscopic material entirely within the dissipating apparatus which is constructed in the form of a short tunnel. The spent hygroscopic material is removed from suspension by means of a special eliminator and only cleared and dehumidified air is discharged. A powerful engine-driven blower facilitates proper distribution of the cleared air under all wind conditions. The advantages of this type of apparatus in comparison with that described in the third section are: the absence of an external spray of calcium chloride, its independence of wind velocity over a considerable range, and its smaller size which reduces the obstruction hazard and permits it to be made mobile. From the results of tests with the spray-type fog dissipator it was known that the new apparatus should be capable of reducing the relative humidity to 90% in 2000 cubic meters of fog per second in order to maintain a clearing of useful dimensions under typical conditions. A unit of excessive size would be required to handle this quantity of air. However, it is possible to remove a suffcient quantity of water vapor from a fraction of the air so that the required relative humidity of 90% can be produced in the total volume of air by proper admixture of the dried portion. A commercial calcium chloride powder was selected as the most suitable hygroscopic material and computations were made to determine the quantity of powder required and the time necessary for it to act. In order to check these computations, which involved several simplifying assumptions, and also to develop the essential features of the proposed apparatus, a working model was set up outdoors. Results from the tests with the model are in fairly good agreement with the computations. It was determined that the lowest practical exit relative humidity is about 50%. Since a relative humidity of 90% suffces for the dissipation of fog only one-fifth of the total volume of air to be cleared need be handled by the apparatus on this basis. The eliminator which mechanically removes the spent calcium chloride particles from the dehumidified air is an important part of the apparatus. After numerous tests on typical eliminators it was found necessary to develop a new type which would be effective at the required high flow velocities. The important problem of properly distributing the dried air was studied with the aid of a large mobile blower unit. It was concluded that, although it would be preferable to employ a number of appropriately spaced discharge ports when-possible, a satisfactory distribution could be effected from a single large opening by using a discharge velocity of from 20 to 30 meters per second. Preliminary designs for two units of the new type are presented to show that the size, weight, blower power requirements and quantity of calcium chloride required for apparatus capable of maintaining cleared spaces of useful size are not unreasonable.
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    Circulation in upper layers of southern North Atlantic deduced with use of isentropic analysis
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1938-08) Montgomery, Raymond B.
    Except for the presence in most localities of a shallow homogeneous surface layer and of a relatively homogeneous and deeper bottom layer, the oceans of the temperate and tropical regions are stratified and vertically stable at all depths. Due to the opacity of water for long-wave radiation and to the damping of vertical turbulence by the stability, there is no potent mechanism for altering the potential density of any water element below the layer of direct surface influences. Hence there can be no flow of major proportions across surfaces of constant potential density. For these reasons it is now generally accepted that flow takes place essentially parallel to these surfaces. It follows that the major sources for the water on each surface of constant potential density are to be found along its intersection with the sea surface in higher latitudes.
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    Application of the distribution of oxygen to the physical oceanography of the Caribbean sea region
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1938-09) Seiwell, Harry Richard
    Observational data for this discussion were obtained principally during the two cruises of the oceanographic research ship, "Atlantis," to the Caribbean Sea March 7 to May 5, 1933 (stations 1487-1610) and February 2 to March 2, 1934 (stations 1935-2002). The oxygen determinations, carried out on board, have been published in Bulletin Hydrographique (1934, 1935) together with other hydrographic data. The Caribbean Sea region falls into two natural bathymetric subdivisions: a western, lying between Yucatan Channel and a ridge extending from Honduras to Haiti via Jamaica, designated in this paper as the "Cayman basin," and an eastern, between this ridge and the lesser Antilles, here designated as the "Caribbean basin". "Cayman basin" has been used by Parr (1937) and by Rakestraw and Smith (1937), and, while antedated by "Yucatan basin" (Krümmel, 1907) it seems that less confusion will arise if the term "Cayman" is used in this discussion. The "Atlantis" observations supply for the first time the necessary information for a detailed study of the distribution of oxygen in the Caribbean Sea region. The 1933 and 1934 observations are here used indifferently; such a procedure seemed desirable since the data are insuffcient for determination of annual or seasonal variations, particularly in view of the disturbing effect which may be caused by short period vertical oscillations of relatively large magnitude.