Instructions to the Marine Meteorological Observers of the U. S. Weather Bureau, 1st edition.
Cast your vote
You can rate an item by clicking the amount of stars they wish to award to this item.
When enough users have cast their vote on this item, the average rating will also be shown.
Your vote was cast
Thank you for your feedback
Thank you for your feedback
MetadataShow full item record
AbstractThe form of weather Report at present issued to vessels by the U. S. weather Bureau is a slight modification of that devised by the U. S. Signal Service for the purpose of its series of International Simultaneous Meteorological Observations, covering the period 1878- 1887, which form in its turn superseded the once well-known Meteorological Journal. The last-mentioned form of record, which went into effect in 1876, and which was in many respects identical with that recommended by the Maritime Conference held at Brussels in 1853, contemplated that the various meteorological observations should be entered at the end of every two hours throughout the twenty-four, or a total of twelve sets of observations per day. The new form demanded, in place of this series, a single daily observation, this, however, to be taken over the entire sea at· the same absolute instant of time, viz, mean noon on the meridian of Greenwich, the object of the change being the utilization of a principle whose value, already recognized ashore, had meanwhile been shown to be equally applicable to meteorological observations at sea. The principle in question was the study of weather changes by means of daily synoptic weather charts, i.e., charts showing the conditions of pressure, temperature, wind, etc., existing at a given instant of time over a wide extent of territory. In the days of Maury, and for some years subsequent to the period of his greatest activity, the common aim of the various institutions engaged in the study of ocean meteorology was to obtain for each unit area of the sea's surface (generally a field bounded by the even 5° parallels and meridians, 5°, 10°, 15°, etc.) a reasonable number of observations of wind, weather, etc., extending over any period of years. The observations were then assembled by months, the average for each month taken, and the result stated as the normal condition for the month, i.e., the condition which the mariner might expect to find most frequently prevailing throughout the given field or square during the given month. Sailing routes were then laid down for the successive months in accordance with these normal conditions, and shipmasters were instructed to adhere to these routes as rigidly as the winds would permit, even when convinced by their own experience of weather changes, as well as by the indications of their meteorological instruments, that better results might be attained by adapting the course of the voyage to the conditions actually encountered. With the advent of weather forecasting as a science, using as a basis the daily synoptic weather charts, a new importance was attached to the sailor's meteorological observations. It was seen that in taking them he was not only adding to the stock of general knowledge of the climatology of the sea, the value of which to him was future and problematical, but also that he was putting himself in possession of certain special knowledge, the value of which might prove absolute and immediate. His last preceding observation revealed a certain existent condition of the meteorological elements, his present observation a more or less different condition. What did the changes which had taken place during the time intervening between the observations foretell? Did the existence of adverse winds in his immediate neighborhood imply better or worse conditions elsewhere 1 If better, would he not in this instance be justified in abandoning the route which had been laid down for him as the best under average circumstances, and seeking that which his present observations led him to believe would prove more favorable. A satisfactory answer to these various questions demands, in addition to a knowledge of the general periodic changes which occur in the several meteorologic elements from season to season, and from month to month, a knowledge of what may be termed the nonperiodic or accidental changes which occur from day to day; of the relation which· exists between the simultaneous changes in the several elements, and of the effect which a decided variation of pressure, temperature, or wind in any one neighborhood has upon the conditions existing in other parts of the ocean. To obtain this latter knowledge it is requisite that we have at hand for the purposes of study a series of charts or pictures, as it were, of the weather covering the entire ocean at a given instant of time, taken at regular intervals so brief that we may be confident that no marked change can occur without appearing, in its different stages, upon several of these pictures in succession. An examination of this series will then serve to reveal what changes have taken place in the interval separating any two of them; to trace the development and progress of any disturbance of the normal conditions that may have arisen; to compare the conditions of wind and weather prevailing simultaneously at points of the sea more or less remote from each other; to determine the constant relation, if any, which exists between these conditions; to make plain the manner in which a vessel, beset by foul winds, might have been navigated with the result that these winds would have been avoided, or even been replaced by fair; and finally, to instruct the navigator as to the conclusions to be drawn from his meteorological observations, in order that this result may be accomplished. It was with a view to combining these two equally essential methods of meteorological' investigation-the old, having for its aim the collection of a large number of observations, independent as to time, to serve as a basis for the study of the climatological changes as they occur from month to month, and the new, having for its aim the collection of a large number of daily simultaneous observations, to serve as a basis for the study of the weather changes as they actually occur from day to day-that the present form of weather report was adopted. It demands but a single observation per day, instead of the twelve demanded by the Meteorological Journal, this large reduction being made in the hope that the number of observers would increase in the same ratio as the services required of them would diminish, a hope which has proved more than justified. This single observation, however, is to be taken each day over the entire globe at the same instant of time, viz, Greenwich mean noon. The local or ship's time of the observation will thus vary with the longitude; on the meridian of Greenwich it will be local or ship's noon; in longitude 60° E. it will be 4 p. m.; in longitude 60° W. it will be 8 a. m.; in 120° E. it will be 8 p. m.; in 120° W. it will be 4 a. m. On the meridian 180° it will be midnight.
Publisher or UniversityGovernment Printing Office
Series : NrU.S. Weather Bureau, Circular M, 1st edition