INTO UPPER AIR

Evening Post, Volume CXV, Issue 85, 11 April 1933, Page 10

INTO UPPER AIR

THE DAILY BALLOON

ASCENT FROM KELBURN

AID TO-FORECASTING

"'Every.day, weather permitting and holidays excepted (which works,out on :m average at about six days per week throughout" the year), there is enacted on the flat roof of tho Kelburn Meteorological Observatory a little .scene which would delight the heart lof any normal youngster allowed to tako part iii it. But children a"re ■not admitted, though they may watch at a respectful distance if they like, and they often do; neither aro adults 'admitted as a rule to the building on •' tho roof of which things happen unless they happen to bo on the staff of the Meteorological Office. This ~ daily dispatch of a balloon into the regions of the upper air is part of tho routine which helps to provide the official forecasters of the'weather with'data upon which to baso their forecasts. Without a balloon to tell him, tho forecaster is at a loss to ■ know, with* any degree of certainty what is going on in tho upper air in the way of wind currents, and without that knowledge ho cannot be certain as to what will happen down below, in' other words, as to what tho weather is likely t& be. Hence tho observation of upper air currents be- ■ comes 'a - very important part of meteorological work. This morning "Post" representatives, literary-and photographic, were allowed a near view of the proceedings, which are .carried■ through with a precision .born of long experience. Tho first 3tep is tho 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 ninety inches in circuinJfe'rerice, or two and a half feet in 'diameter—quite a big one if regarded j'as a 'toy-foallooiu The balloon is filled until its buoyancy is sufficient to lift 'a weight of about 80 grammes (nearly jjthreo ounces), and then it is ready for ita one and only flight. It carries no instruments, 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 r 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 tho distance. By measuring tho apparent length of ' the tail an estimation of the height of the balloon at any given moment is ' arrived at. The balloon's sole f unction Is' to tell the' meteorologist, by its rate of movement and by its direction of flight, the strength and direction of the various air currents superimposed on cadi other, for thousands of feet above earth. '• ~■_ ■•• . VISIBLE FOR TWENTY. MILES. ' On a really clear day the balloon may 'be kept under observation at a distance 'of twenty miles or so, but the averago distance at which it disappears is somewhere dn the'neighbourhood of ten miles. Against axclear sky the easiest coloured jballoou to see is one that has no. colour at all, to express it as, an Irishman might. That is to say, the natural, rub- ' ber is..the best, for this is illuminated by the sun, and remains, visible like a bright star, with- two scintillating points below it (the foil on-the tail). A blue coloured balloon,- on the other hand, shows up best against an overcast sky, and if, conditions, are very cloudy a red balloon is used. If it happens ' to-be raining hard at 9.30 a.m. ao'bal- ' Boon at all'is sent up, and observations '• are either abandoned for the day or ' ■postponed until a later hour if the rain •' ceases. .■■-'■' _ ; ■ ' Ths balloon,: once liberated, is lost. '■ Diffusion of the hydrogen through the ; thin rubber: envelope-gradually takes place., Either of two fates.awaits it. : Tho 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 iit then terminates its career'depends ■of course on the' wind'direction. ) The balloons-which go up from Kelburn .usually como down in 7 the sea., . The meteorologists who liberate themnever expect to see them again. There is no reward for their return, and any young- ' eter who,is lucky, enough to find one is r .^quito at liberty to keep it as a. play- ; thing. ' , ■ WHERE MATHEMATICS COMES IN. '■■ Though the.balloon,carries, no.instruments, instruments are used, but they • f are on tho ground with the observers. ;'. In theoryj the rate1 of the ascent of the balloon sould bo'uniform; but in practice, especially Sn, mountainous reg- ! ions, this assumption is not true^ owing ; ,to the prevalence of vertical, air currents. This is patiricularly the case .in tho lower air levels. The balloon's i height, therefore, must be determined at stated intervals, arid this is done by theodolite observations. Knowing the Jieight of the balloon, calculated from '~ ( the apaprcnt length of the tail, and the : .xato of its. ascent, it is easy to those .. well versed iii mathematics to determine the balloon's horizontal distance !at any given moment after its libera- ~.\ iion, and thus to compute tho strength :of the winds which are bearing it away. ',', The balloon which is tho subject of ;" the photographs, in today's "Post" was an uncoloured one, liberated into , a clear blue sky. The direction it took was for a long time a steady one ', in a south-easterly direction, but after :it had reached a-considerable height it ■ began" to change its course to a more . southerly one. This balloon was kept under observation until it had reached a "height of. 33,000 feet. The northerly wind prevailing at high levels today is associated with a tropical cyclone lying to the north-west of New Zealand. y /WHEN DEPRESSIONS COME. ' Owing to the topography of the couu- .-. try, the winds prevailing at tho lower ", levels in the Cook Strait region give ', but little indication as to what currents there are high aloft. It is necessary to watch only one balloon ascend from Kelburn to realise this. For a ■ minute or two it; will bo affected by ; the wind which tho observer is feel- ; ing. But as the balloon gets higher ; arid higher, tho direction in which it is ' travelling will change, perhaps more ; than once, and if is these changes in direction that provide such useful data for the meteorologists. "Winds usually . increase in strength the higher the level reached, and at ■"the same time there is usually an increase in steadiness. In New Zealand, •'■ when westerly depressions approach, the •upper air currents follow a fairly regular regime. At higher levels iha( winds will ;be north-west, back- _ ing to tho south-west after the • passage of the line of lowest pressure. '.- But it frequently happens in Wellington that this change to the south-west ■is missed owing to the topography'of ; the Straits. The balloons, however, will tell the meteorologist of tho change that has taken place up above, even if there is no evidence' of it below. When, we have a week or so of westerly depressions, such as have ; been experienced : recently, moderate north-westerly winds may -persist all the; time in, the lower strata of the atmosphere, .any. southerly, change, being

poorly developed and perhaps only reaching as far north as Timaru. But the wind up above will have changed, j and this change the- balloon will indicate. . It is from tho behaviour of these upper air currents that the forecaster of the weather can, among other things, predict tho prevalence of a southerly— whether it is likely to be temporary or of longer duration. If the forecaster is wrong, as he admits he is occasionally, it is perhaps because the weather would not permit the dispatch of a balloon: to tell him what ho wanted to know,. k . _._..._-._;.,.....^.., .^j_,._.