The How and Why of Weather Knowledge

Climate and Man • Yearbook of Agriculture • 1941 The How and Why of Weather Knowledge BY F. W. R ErCIiELDEKFER ' GLliVIATE AND VVE/VI HKR are basic natural resources, but they must be understood if they are to be turned to good advantage. No one has better reason to know this than the fanner. As civiUzation has become more complex, our depend- ence on intimate and accurate knowledge of climate and weather has increased. Today this knowledge is so indispensable that every civilized country has an elaborate weather service. In the United States this service functions 24 hours a day and endeavors to bring up-to-date information to every individual in the land who needs it. For 50 years the service was part of the T3epartment of Agriculture, and it is still closely associated with aojricultural activities. What does it do? How docs it work? How can we make the best use of its activities? The Director of the service explains. i.K. W. li(.MC!hol<l(>rffr is Direcior, fniu-ii ShUcs \\'vu\]u'\- iUnv.ui. (12ÍÍ' The How and Why of W eather Knowledge • 129 WEATHEK AND CLi:\rATE ùi'o as vital to liiiman life as tht> soil itself. They ar-e amoiig our most valuable natural resources. If the weather is too dry or too wet, crops fail, aiul the farmer suffers— but not the farmer aJone. Permanent changes in climate could bring ruin to our entire business structure and make our continent practically unin- habitable. Fortunately the supply of weather, unlike the reserves of some natural resoui'ces, appears to be inexhaustible. Although there are fluctuations in rainfall, temperature, and other atmospheric elements from day to day, month to month, and year to year, ^'permanent^' changes in climate within the records of civilized man have been small. But even the yearly fluctuations have such profound influence on man's livelihood and pursuit of happiness that no matter what his occupation - -farmer, aviator, engineer, industrialist, laborer, merchant, clerk- he daily takes keen interest in the weather. It is usually the first thing he thinks of when he lays his plans for the day's work and decides w^hat clothes to wear. In this country 2 million businessmen every morning turn at once to the weather report when they pick up the daily paper. More than a million people listen for the weathei' forecast by radio once or more each day, and a hundred thousand, desiring more than is given in the press or over the radio, telephone or visit Weather Bureau offices daily to obtain further information. The Nation-wide meteorological service of the Weather Bureau provides reports and advices of value to almost every kind of business and profession and probably ranks close to the postal service in universal interest and application.^ In a recent survey of the utilization of weather service in the united States, it was found that the protection to property afforded by the weather reports and forecasts of the Weather Bureau, and the increased profits through reduction in loss or increase in production from use of weathci' information, account for savings and profits totaling more than 3 billion dollars annually. Large as this sum is, it does not represent the fullest practicable utilization of the weathei* service available to agi'iculture, commerce, and industry. In view of the fundamental influence of weather and climate on man^s food, clothing, and shelter, and therefore on his health and happiness, it is not surprising to find that from the earhest times he has taki^n notice of seasonal variatioiis and that long ago he lookcid for signs or onK^ns that would foretell the weather, particularly the approach of storms. In an attempt to court supernatural aid in warding off unfavorable weather he made supplication to meteorological deities. Some of the weatluu' signs picked up by man through the ages contain an element of truth; others were mere superstitions. A surprisingly large number of these superstitious notions about tlit^. weather still persist. These are slowdy giving way to a more scientific viewpoint and a bettej' understanding of how a modei*n weather service functions, its possibilities, and its limitations. - All acl, of C'oiigrcss dated Ocl.ohor 1, 1890, created the Weailjfir Bureau and iriadt; it n^sponsible for the general wcûher service of the XatioTi. SubseciuoHt líígislation and Executive dccisioDH extended the Bu- reau's responsibilities in the sci(ince of weathiT and climate until its service now applies to civil aeroTiautics and other modern fields as well as to general agricultural, comnu^cial, industrial, and transportation interests. The I'ourth Plan of Government Keorganization, 1940, transferred the Weather Bureau from the ])epartment of Agriculture to the Department of Commerce, ciïcctive June 30, \04(}. 'J'his transfer has not modified the Weather Bureau's service to any of the general interests of the country, including agriculture. H. Doc. 602, 7Gth ('ong., 3d sess., states that tiie transfer "will permit better coordination of Government activities relating to aviation and to commerce generally, without in any way lessening the bureau's contribution lo agriculture." 130 • Yearbook of Agriciiliure, 1911 THE DEVELOPMENT OF MODERN WEATHER SCIENCE Although mim's obscu'vatioiis of the weather began with the dawn of consciousness^ rneteoi'ology,'^ or weather science, is still a com- paratively young niembei- of tíie family of modern sciences. Accmâte observations, truly representative of open-air conditions—that is, immodified by purely local or accidental influences—are not easy to obtain. Prior to the invention of meteorological instruments, it was impossible to measure accurately atmospheric pressure, temperature, humidity, wind velocity, and other elements. The barometer and thermometei' were developed during the seventeenth centur}^. There- after weather recor(ls became more accurate, but daily weather service as it is now known could not be estal)lished until tlie telegraph was invented and a WLdes¡)i*ead system of dail\' synoptic reporting was organized. Sv\()PTic WEATKEK RRPOKïS A synoptic weather- r(^porl is a concise^ synopsis, or sunuruuy, usually in a simple code for brevity, describiug th(^ weather conditions in a locality at a certain time. (The word ''synoptic^- comes from two Greek words meaning ''general view.'') It is important to under- stand the role of the synoptic report in modern meteorology. The stud}^ of daily synoptic reports as represented on tlu^ weather map is the basis of our understandhig of weather changes. A single isolated weatlier observation tells little of the general state of the atmosphere or of the changes that are about to take place in it. Experienced outdoor observers like farmers and mariners may recog- nize the approach of a storm from a single observation of clouds or the appearance of the sky, but such an observation does not enable them to describe the weather in detail or for a large area each day. As may be seen from the article on The Scientific Basis of Modern Meteor- ology, page 599, the moisture that falls as rain is usually transported by ail" from some distant ocean. Vast bodies of air, technicallj^ known as air masses, come together from widely separated j-egions and by their contrasting characteristics produce changes in weather. Clouds and rain usually occur alottg the boundai'ies of air masses and are the result of theii- overlapping. An air mass is frequently composed of millions of cul)ic miles of air mor-e or less homogeneous in character, and it may pass over many lands and seas before encountering an air mass of opposite characteiistics, interaction with which causes clouds and rain. In order to have a comprehensive understanding of weather and climate, it is necessary to view a major portion of the atmos])here as a whole, such as a polar hemisphere or the quadrant or octant encompassitig the region mider consideration. The state of tlie atmos])here at an}' instant may be likened to a great jigsaw puzzle in which one local weather observation is a single pi(^ce that reveals little or nothing of the whole picture. The synoptic s The word "meteorology" comes from the ancieiit Greek term for the atmosphere. Ooneral meteoroloííy iuchulos the subjects weather and elimale. It does not include the ¡study of nLeleo^t^ and oilier heavenly hodies, which properly belongs to astronomy. In the popular mind meteorology is ol'ton confused with astronomy and sometimes with metrology, which deals with wêights and measures. Meteorology has lirtle to do with the heavenly bodies except for the sun as a source of radiant energy. The How and Why of Weather Knowledge • 131 weather reports from well-distributed observing points make up the numerous pieces of the weather puzzle. Many simultaneous observations are necessary to reveal the pattern. Pieced together in the form of the daily weather map, they give the complete view of the weather as seen by observers on the ground. This branch of weather science is called synoptic meteorology. It is the foundation of the modern weather service. THE DAILY WEATHER MAP The daily weather map of the United States, made possible by synchronized observations throughout the country collected quickly by telegraph, was first published by the United States Government in 1871.^ This was a great step toward modern meteorology. How- ever, the surface map represents the weather conditions over a portion of the globe as viewed from the ground, and except for cloudiness it gives little direct information of conditions in the air high above. Since some of the most important processes of weather formation take place in the upper air, the surface weather map obviously cannot give a complete understanding of weather.

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