ATMOSPHERE STUDY

Taranaki Daily News, 22 December 1934, Page 14 (Supplement)

ATMOSPHERE STUDY

IMPROVING FORECASTING. AIR-MASS ANALYSIS MADB,:/ Every morning at 5 a.m., rain or shine, powerful small aeroplanes take off from twenty flying-fields throughout the United States. They climb swiftly to an altitude of three or four miles, and presently descend, bearing information as to the temperature, humidity, barometric pressure, and the direction and force of the. wind at the altitudes reached. Meanwhile, at other stations, free balloons are released at regular intervals, and watched closely with theodolites as they climb through higher and higher air-strata, flying this way and that when encountering winds moving in different directions at various levels. These performances, often of such a nature as to mystify persons living nearby, are parts of the new method, known as air-mass analysis, being developed by the United States Weather Bureau for the improvement of . forecasting, states the Literary Digest. The adoption of the. system is one of the first fruits of the Science Advisory Board, appointed by President Roosevelt in July, 1933, to advise the Government on scientific matters, and to suggest improvements in methods' used by its research and technical branches. ‘ • • NOT A NEW METHOD. Air-mass analysis is not a new method among weather forecasters, but it never has been put into operation on a practical scale in America.. European forecasters .have used it with excellent Results fpr some time, notably in Germany and. Sweden, where daily flights for up-per-air ’ data have. been made for five years or, more. The usefulness of the method depends on the fact 'that the atmosphere does not consist of a sjngle . homogeneous envelope l of air, but is composed of numerous masses in motion, each differing from the others in' temperature, humidity, compactness, velocity, and other characteristics. • • These-air-masses, cold and dry from the polar regions, warm and humid from the equatorial, do not mix readily, but tend to preserve their original identities, They meet along irregular, but rather sharply-marked boundaries variously known as the "discontinuity line,” the ‘*polar ’ front,”, or the “wind shift.” After collision with, one another, their relative positions, frequently are shifted. For example, when a v cold, dry air-mass meets a warm, moist one, the latter, being the lighter, is forced to rise. The cold mass possibly flattening out like a wedge, sweeps under it, moving along the ground. Having, been forced- into higher, colder regions, the humid mass becomes chilled. The moisture it carries is condensed into ‘clouds, and, finally, into rain. This is an explanation of certain kinds of stormy weather experienced in temperate zones. The chief source of these differing airmasses are the polar and tropical regions. How they rise, how and where they travel, and the laws which, control them still are but little known. On these important paints the widespread adoption of air-mass analysis is expected to. shed soma light, as well as on the more immediate mechanism by which storm’s are produced. The classical method of predicting weather, by means of the “synoptic weather map,” consists of gathering data from many points, and correlating these observatidns by means of lines on a map. The map then can be interpreted as indicating the movements of stormcentres across the country. Extremely useful,; the synoptic weather map nevertheless is only a two-dimensional pic-

ture of the condition of the atmosphere —a representation of the effects of the air-masses at the plane where they touch the earth. The daily flights are the first attempt in America to obtain regular information on a thrde-dinidnsidnal scale. Starting last July they have been continued through a co-operative arrangement between the WCather Bureau and War and Navy Departments. Twenty stations are considered tod few to give as much data as is needed, but, at present, the Weather Bureau has too little money to add new ones.