DAILY BALLOON

Hokitika Guardian, 19 April 1933, Page 6

DAILY BALLOON

METEOROLOGICAL WORK IX N.Z

AN AID TO FORECASTING

AVELLINGTON, April 17. Every day, weather permitting and

hc-Iklays excepted, there is enacted on

the Hat root' of the iKelburn Meteorological Observatory, AVellington. a little scene which would delight the

heart of ally normal child allowed to

take part in it. But children are not 'admitted, though they may watch at a respectful distance if they like, and they often do; neither are adults admitted as a rule to the building on the roof of which things happen unless they are members of the staff of the Meteorological Office. Thi,; daily despatch of a balloon into the regions of the upper air is part of the, routine wheih 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 on in the upper air in the way lof wind currents, and without that [ knowledge be cannot he certain a,s to what will happen down below, in other words, a s to what the weather is. likely to be. Hence the observation of upper air currents become® a very important part of meteorological work. The first step' is the filling of the j balloon from a cylinder of compres-sed i 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 2’ft. in diameter—quite a big one if regarded as a toy balloon. The balloon is filled until its buoyancy i.s 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 instruments, its ldad 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 at-

tached 1 a piece of metal foil, and another piece is fixed at the end of the tail. 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 any .giyen moment is arrived

at. The balloon's sole function is to tell the riieteqrologrist, by its rate of movement and ,by its direction of flight, the strength and: .direction of the various .air . currents superimposed on each other for thousands cf feet above the earth. - .

. On Pa really clear; day >the balloon may be keptunder observation at a db tanct of ,20 miles or so, but the average distance at: which it disappears is; somewhere in the neighbourhood of ten miles.

J The balloon, once liberated, is lost. Diffusion off the hydrogen' tbfcragh" * the thin ' rubber envelope gradually takes place. Either of two fates awaits it. ••• The haUootl, ' after b reaching . great, heights, far-beyond the ken of the abseryepsh/yinstniments, in.ay burst,, ; ancl, tlius- -Tei ; 'hlinhte an-; . ephemeral,; . - although -useful,-career. -Or it -may j 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, from Kelburn usually come down in the ' sea. 'The'Vmeteorologists who liberate' them never expect to see them 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. Although the balloon carries no instruments, instruments are used, but they are on the ground with the observers. In theory, the rate of the ascent of the balloon should be uniform ; but in practice, especially in mountainous regions, this assumption is not borne out, owing' to the prevalence of vertical air' currents. This is particularly .the case in the lower air levels. The baloon’s height, therefore, must be determined at stated in- ( aiid this is done by theodolite - observations. Knowing the height of the balloon, calculated from the ap- < parent-length of the tail, and the rate of its ascent, it is easy to those well , versed in ipathematics to determine ( the balloon’s horizontal distance at , any given moment after its libera- rj tion, . and thus' to compute the c strength of the winds which are bear- j ing it, away. t