STUDY OF ATMOSPHERE

Evening Post, Volume CXVIII, Issue 145, 17 December 1934, Page 10

STUDY OF ATMOSPHERE

IMPEOVING FOEECASTING

air-mass" analysis

Every morning at 5 a.m., rain or shine, powerful. small aeroplanes take off from twenty flying-ficlcls through' out "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 ■ tho direction and force of the wind at the altitudes reached. ; Meanwhile, at other stations, f r-co 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. Theso performances, often of such a nature as to mystify persons living nearby, are parta 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 for some time, notably in.Germany and Sweden, where daily flights for upper-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 single homogeneous envelope of air, but is composed of numerous masses in motion, each differing from the others in temperature humidity, compactness, velocity, and other characteristics. Theso air-masscß, cold aad dry from the polar regions, warm and humid from the equatorial, do uot mix readily, but tend to preserve their original identities. They meet along irregular, but rather sharply-marked boundaries variously known as the "discontinuity line," tho "polar front," or the "wind shift." After collision with one another, their relative positions frequently are shifted. Tor example,- when ft cold, dry air-mass meets a warm, moist one, the latter, being tho lighter, is foreod to rise. Tho cold mass possibly flattening out like a wedge, sweeps under it, moving along the ground. Hay : ing been forced into higher, colder regions,, tho humid mas» becomes chilled. The moisture it carries is condensed into clouds, and, finally, into rain. This i» an explanation of certain kinds of Btormy weather experienced in temperate zones. SYNOPTIC WEATHER MAP... The chief source of these differing air-masses arc 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 points the widespread adoption of air-mass, analysis is expected to shed some light, as well as on'the moro immediate mechanism by which storms are produced. The classical method of predicting weather, by means of the "synoptic weather map," consists of gathering data from many points, and correlating theso observations by means of lines on a map. The map then can be interpreted as indicating the movements of etorm-centrcs across the country. Extremely useful, the. synoptic weather map nevertheless is only a two-dimen-sional picture of the condition of the atmosphere—a representation .of the effects of tho 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 three-dimensional scalo. Starting last July they have been continued through a co-operative arrangement between, the Weather Bureau and War and Navy Departments. Twenty stations are «ons;aered too few to give as much data as is ncedrid, but, at present, the Weather Bureau has too little money to add new ones.