Willett Hurd C.

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Hurd C.

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  • Book
    Report on an experiment in five-day weather forecasting
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1940-04) Allen, R. A. ; Fletcher, R. ; Holmboe, J. ; Namias, Jerome ; Willett, Hurd C.
    The following report is presented as a statement of progress made at the Massachusetts Institute of Technology (M.I.T.) in the investigation into the possibility of extending the range of reliable weather forecasts. This project has been supported at M.I.T. and other private institutions by Bankhead-Jones appropriations since September, 1937. This report is concerned only with the work completed or in progress at M.I.T. The complementary program now in progress at the Weather Bureau in Washington is referred to only in so far as it has contributed directly to these investigations. Furthermore, the following report refers only to the last two years of the M.I.T. project. The first year of the three-year project was given over principally to the study of the results obtained by long range forecast methods already in use, and to the establishment of a northern hemisphere synoptic weather map procedure as a necessary precedent to the preparation of weekly forecasts on a synoptic basis. The results of the M.I.T. study of certain long range forecast methods already in practice are included in a general survey of such methods already published. The synoptic charts prepared at M.I.T. during that first year of the investigation are listed in an appendix to this report, together with those of the last two years. The preparation of weekly forecasts carried on during a part of that first year was so experimental in nature, and the procedure was so much changed the following year, that the results obtained were considered neither suffciently significant nor comparable enough with the later forecast results to merit any discussion. The present report is divided into three principal sections. Section I presents in condensed form our present conception of the essential nature of the general circulation, and discusses briefly the background of one or two of Professor Rossby's theoretical considerations concerning the general circulation which have found statistical and synoptic application in this investigation. Section II contains in brief form the results of synoptic and statistical checks of a large number of hypothetical relationships which might be assumed to hold in the earth's atmosphere. These include possible relationships in the large scale features of the general circulation, relationships between the general circulation and its different branches or centers of action, between the different branches or centers of action of the general circulation, between characteristics of the general circulation or its branches and anomalies of the meteorological elements in certain regions, between anomalies of the meteorological elements in one region and those in another region, and even between solar activity (sunspots) and characteristics of the general circulation or anomalies of the meteorological elements. The aim was to investigate possible interrelationships of all kinds, either with or without lag, in order to detect as many interaction principles or points as possible in the earth's atmosphere, whether they had direct or only the most indirect bearing on the forecast problem. The relationships investigated applied to daily, weekly, monthly, seasonal, or annual mean conditions. They were selected for investigation either from theoretical or practical considerations of the nature of the general circulation as outlined in Section I, or on the basis of popular beliefs which have long been current among meteorologists, or on the basis of direct observation of data which looked promising. The majority of these hypothetical relationships are found to be quite weak when subjected to rigid statistical checks, but all such results, whether positive or negative, are summarized in this report. Section III outlines the five-day forecast routine practice which has been carried on at M.I.T. during the greater part of the past two years on a weekly basis. It includes a statistical analysis of the verification results. In the conclusion are summarized the results of the investigation which thus far appear significant enough to justify their consideration in five-day or longer range forecasts. Suggestions are offered as to further steps which might profitably be taken if the investigation is to be continued. Finally there is an appendix in which are listed all the daily synoptic maps and mean charts and diagrams of surface and upper air data which have been plotted and analyzed at M.I.T. in connection with this project during the past three years. The importance of such a list is apparent when it is realized that inevitably in an investigation of this kind much the greater part of the time and effort expended is consumed in the routine or semiroutine duties involved in the preparation of such charts.
  • 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
    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
    Discussion and illustration of problems suggested by the analysis of atmospheric cross-sections
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1935-07) Willett, Hurd C.
    The preparation of atmospheric cross-sections, in which the fields of the various meteorological elements are represented in the vertical plane containing a number of synoptic aerological soundings, has long been a part of the technique applied to the investigation of problems in synoptic meteorology. However, owing to the lack of adequate observational material, the number of such cross-sections prepared in the past has been very small. The method was applied only in a few cases chosen for careful analysis and study. Consequently no uniform technique of analysis of such cross-sections has been developed, nor have the possibilities of this method of synoptic investigation received much attention. In the fall of 1933 the author decided that the possibilities of the cross-section method of synoptic representation warranted the systematic preparation and analysis of a large number of cross-sections. For this purpose a number of periods during which the synoptic maps seemed to indicate interesting atmospheric developments, and for which numerous aerological observations were available, were chosen from the maps of the preceding two or three years for detailed cross-sectional study. In all, ten periods of from two to six days each were chosen, a total of 36 days, entailing the preparation of about 90 cross-sections, and the use of about 400 aerological soundings.
  • Book
    Report of the five-day forecasting procedure, verification and research as conducted between July 1940 and August 1941
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1941-11) Willett, Hurd C. ; Allen, R. A. ; Namias, Jerome
    The present report is intended to cover fully the activities of the long-range forecast project both at the Massachusetts Institute of Technology and at the U. S. Weather Bureau in Washington, between July 1, 1940, and August 1, 1941. It includes all material bearing on the activities of the current fiscal year which has appeared in the three progress reports that were written during the year. The report is in four sections. Section I outlines the administrative set-up of the project and its transfer from the Massachusetts Institute of Technology to the U. S. Weather Bureau in Washington, indicates the general purpose of the project, outlines the program of routine synoptic and statistical work which is maintained as a necessary part of the five-day forecast service, and lists the personnel which has been available to carry on the project. Section II covers in some detail the five-day forecast procedure as practiced during the past year, including one illustrative case selected and discussed by Mr. Namias. The discussion of the five-day forecast procedure is concluded with some remarks on the significance of the results obtained by the basic method and a summary by Mr. Allen of the success of the forecasts as shown by the statistical verification of the forecast temperature and precipitation anomalies. Section III contains a brief discussion of each of the special investigations made during the past year which bear on the five-day forecast problem. For the most part, the results of these investigations were not obtained soon enough to be incorporated in the forecast procedure outlined in Section II. Section IV sets forth recommendations for further theoretical, synoptic and statistical research which is needed to develop and extend the five-day forecasting technique which has been developed by this project.