Iselin Columbus O’Donnell

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Columbus O’Donnell

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  • Technical Report
    Preliminary report on the prediction of "afternoon effect"
    (Woods Hole Oceanographic Institution, 1942-07-25) Iselin, Columbus O’Donnell ; Woodcock, A. H.
    Please see for appendix information. With moderate or light winds and a clear sky the diurnal heating which occurs near the sea surface can cause a serious reduction in the range of submarine detection, especially on shallow targets. This has usually been called the "afternoon effect", although as will be noticed below the ranges often remain short long after sun down. The heating of surface waters which causes such sharp downward refraction can of course be noted on a bathythermograph record, provided pen vibration does not confuse the upper part of the trace. Unfortunately it is the upper 20 or 30 feet of a bathythermograph curve which in the case of ships moving faster than 12 knots is often somewhat difficult to read with sufficient certainty. Moreover, in planning a days operations it is clearly desirable to know in advance how much reduction in range may be expected from diurnal warming. Unfortunately it has turned out that five, more or less independent variables are involved. Listed in the order of their importance these are as follows: the altitude of the sun, the degree of cloud coverage, the strength of the wind, the difference in temperature between air and water, and the humidity of the air. It was at first thought that wind and cloud observations alone would be sufficient in most cases for a rough prediction of the seriousness of diurnal warming to echo ranging conditions. Thus it has been previously reported that with winds of force 4 or greater it can be expected that turbulence will prevent thermal stability from developing at depths critical to sound ranging, while with lighter winds ranges will be more or less reduced in the afternoon, except during cloudy weather. But the problem is considerably more complex than this and such simplification is not always justified.
  • Book
    A study of the circulation of the western North Atlantic
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1936-08) Iselin, Columbus O’Donnell
    With the opening of the Woods Hole Oceanographic Institution in July 1931, there was inaugurated a program of investigations in the deep waters of the western North Atlantic for which there had long been a great need. In contrast to most deep-sea investigations, which have had to be planned as single expeditions, the Institution was able to initiate a general program which could be carried out gradually in order to take advantage of knowledge gained during the course of the work. Suffcient funds having been provided for the continuous operation of its research vessel "Atlantis," work could be planned for all seasons of the year. Although these investigations have not been in progress for long and new data are continually being brought in by the "Atlantis," there are several reasons that make it seem desirable at this time to publish a preliminary report based on the completed temperature and salinity observations. In the first place, the problem of oceanic circulation is such that we cannot hope for a satisfactory solution for a long time to come. Moreover, it would be unwise to allow too much data to accumulate, because several years may pass before we can arrive at more important conclusions. Secondly, both the chemical and biological programs undertaken at the same time, require as a background the general scheme of circulation in the western North Atlantic as well as the distribution of temperature and salinity. It is, in fact, the necessity of taking into consideration the movements of the sea water which ties together the whole subject of oceanography. Therefore, it is the duty of those interested in ocean circulation to make available their findings as soon as possible for investigators of other problems in the same area. The "Atlantis" temperature and salinity observations discussed in these pages were planned with two main purposes in view. The first objective was an intensive study of seasonal changes along sections running from the southwestern corner of Nova Scotia to Bermuda and from Bermuda to the mouth of Chesapeake Bay.! This, of course, included an examination of fluctuations in the Gulf Stream, as well as of the variations in the water masses on each side of it. Second, there has been planned and partly carried out, a more general survey of the western North Atlantic, where accurate, deep stations have been sadly lacking.
  • Book
    Preliminary report on long-period variations in the transport of the Gulf Stream system
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1940-07) Iselin, Columbus O’Donnell
    In 1937 the Woods Hole Oceanographic Institution and the Bermuda Biological Station for Research agreed to cooperate on a five year program of observations. This was designed to throw light on the general problem of long-period fluctuations in the transport of the Gulf Stream, and their possible significance for fisheries research and for meteorology. The investigation originated at the suggestion of the Bermuda Oceanographic Committee of the Royal Society of London, which also arranged for a generous grant of money to enable the Bermuda laboratory to undertake part of the field work. A summary of the ideas on which the original program was based has already been published (Iselin, 1938a) and more recently two short papers (Iselin, 1938b, 1939) have emphasized certain aspects of the theoretical considerations on which it rests. Although the primary objective has been a study of long-period trends in the strength of the Gulf Stream and only two and a half years have elapsed since the work at sea began, nevertheless it now seems desirable to set forth some of the preliminary results and to discuss further the underlying assumptions. It is hoped that in this way we can gain the benefits of criticism and thus be more wisely guided during the remainder of the five years for which continued field work is now planned. In preparing this report I have had the assistance and advice of the staff of the Woods Hole Oceanographic Institution. I am especially indebted to Dr. Sidney C. T. Hsiao who prepared the final drawing of the diagrams and carried through the necessary computations. In addition, I have worked in close cooperation with Dr. E. F. Thompson of the Bermuda Bio.logical Station and Mr. H. B. Hachey of the Atlantic Biological Station. It is most gratifying to have taken part in an investigation with so many willing and helpful participants.