DAILY BALLOON

New Zealand Herald, Volume LXX, Issue 21467, 15 April 1933, Page 6

DAILY BALLOON

- METEOROLOGICAL WORK -AN AID TO FORECASTING ' .WELLINGTON OBSERVATIONS " ' Every day, weather permitting and holidays excepted, there is enacted on ' the flat roof of the Kelburn Meteoro- * logical Observatory, Wellington, a little scene which would delight • the " heart of any normal child allowed to take part in it. But children, says the Evening Post, are not admitted, " though they may watch at a respectful distance if they like, and they ' often do; neither are adults admitted -as a- rul9 to the building on the roof , 7of which things happen unless they ' 'ere members of the staff of the Mete- - orological Office. ,This daily despatch of a balloon into . ..the regions of the upper air is part of -■■" the routine which helps to provide the . .official forecasters of the weather with data upon which to base their forecasts. Without a balloon to tell him, the forecaster is at.a loss to know with - any degree of certainty what is going V on in the upper air in the way of wind currents, and without that know- - ledge he cannot be certain as to what Prill happen down below, in other , words, as to what the weather is likely to be. Hence the observation of -j upper air currents becomes a very im- | portant part of meteorological work. No Instruments Attached The first step is the filling of the balloon from a cylinder of compressed hydrogen, this being done inside the building, and then the balloon is carried outside to the roof. The balloon when inflated measures about 90in. in , circumference, or 2Jft. in diameter — quite a big one if regarded as a toy balloon. The balloon is filled until its buoyancy is sufficient to lift a weight of about 80 grammes (nearly three ounces), and then it is ready for its ' one and only flight. It carries no inV Etruments, its load being a tail something like that usually attached to a kite. This tail is 120 ft. long. At a distance of 30ft. from the balloon is attached a piece of metal foil, and another piece is fixed at the end of the .tnriU The object of these pieces of foil "is to make the tail visible as the balloon recedes into the distance. By measuring the apparent length of the tail an estimation of the height of the : balloon at anjf given moment is arrived at. The balloon's sole function is io tell the meteorologist, by its rate of movement and by its direction of "flight, the strength and direction of the various air superimposed ' on each other for thousands of feet above the earth. ■ ~ On a really clear day the balloon may be kept under observation at a distance of 20 miles or so, but the average distance at which it disappears is somewhere in the neighbourhood of ten miles. - Mathematical Calculation The balloon, once liberated, is lost. Diffusion of the hydrogen through the thin rubber envelope gradually takes place. Either of two fates awaits it. .balloon, after reaching great heights, far beyond the ken of the observers' 'instruments, may burst, and thus terminate an ephemeral, although useful, career. Or it may gradually descend owing to loss of gas, and where it ,then terminates its - career depends, of course, on the wind -direction. The balloons which go up h'om Kelb'jrn usually come down in • i: the sea The meteorologists who liberate them never expect to see them I again. There is no reward for their return, and any child who is lucky enough to find one is quite at liberty to keep it as a plaything. AJthough the balloon carries no instruments, instruments are used, but i they ar«> on the ground with the observers. In theory, the rate of the ascent of the balloon should be uni-t-r ~form; but in practice, especially in mountainous regions, this assumption —is < not borne out, owing to the pre>7 valence of vertical air currents. This £ is particularly the case in the lower 4i air levels. The balloon's height, therefore, must be determined at stated inif tervals, and this is done by theodolite observations. Ktiowing the height of t T-; "the balloon, calculated from the apparent length Of the tail, and the rate of its ascent, it is easy to those well versed in mathematics to determine the balloon's horizontal distance at any given moment after its liberation, and thus to compute the Istrength of the winds which are bearing it away. /