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A NEW AID IN WEATHER FORECASTING.

Every year reliable forecasting of the weather appeals more desirable and also* more attainable. la spite of the unreasonable disappointment of people who expect the details of their local weather to be given, for picnicking purposes three days in advance, there is a- growing conviction that a science- ef the weather is a possibility within man's reach if he will take the necessary trouble to secure it. The Americans, who require a practical return for their money, now mpSad dose- upon £300,000 a. year for their weather service. They give a, good dead of heed to the fore- . casts issued by their experts, since 600,000 copies of a day's forecasts axe issued to the public. The officeca of the American service have done useful work in starting comprehensive schemes of following the actual motion of the air as closely as it can.be mada out from the observations taken all over the earth. It ie a' big undertaking to identify, not only tie big drifts and currents .in, the air, but also the minor whirls which regulate the weather in particular districts. But the complicated task is being faced at last by meteorologists, and with promising results. It is now pretty well proved that an ascent of air is generally required to produce rainfall. The air at the surface of'the earth is seldom loaded more invisible vapour of water than: it can carry. When it docs become overcharged with, moisture, theexcess appeals in, fcbe shape of mist and fog. But the warmer the air becomes the more vapour can it pick up and hold, whereas the chilling of sir make* it less capable of retaining H& moisture, and ; finally causes it to throw out some in the form- of milt. When, the warm-, moist air at low level* rises, H cools at the same time, and throws out seme el ite vapour in- the form of cloud. From a dense enough cloud sa» Mis. Hence -raiafaJl » very largely dependent upon ascending air . Contents. Of cows*, it is- very seldom that these rise vertically. But if a prevailing wind has a slight rise in it, it may lift the air through a vertical height »f a j mile in , a «euple- of horns-, during which ! the wind may have travelled forty miles horizontally. At any centre towards which winds are blowing from different quarters, there will be a tendency for the air to rise en account of the action of the opposing streams in banking one another up. Just as ascent of the surface air is favourable to rainfall* descent of the upper air is conducive to fine weather. Now, in the past the upward or downward motion in wind has been almost ignored. It seemed of very little consequence compared to the rush of the wind over the surface. • Yet although the rise or the fall may be very gentle in comparison with the horizontal blowing of the wind, it is of the utmost importance in determining the character of the weather. Advanced meteorologists are now making, it their business to track the wind, and so keep the general circulation of the atmosphere under observation as well as possible. Hence* the desire for information albout the higher reaches of the air and the. despatch of balloons with instrument? for registering the conditions amongst. thf> clouds. ' Hence, also, the pains being taken to study -cloud heights and motiamp so « to be able to picture the flow of the air up to ten miles above the surface of the earth. , The reading of the barometer gives the meteorologist the amount of the atmospheric pressure. This to a large extent controls the distribution of the winds, but not entirely, because the wind, being partly the outcome of previously prevailing barometric conditions winch "helped to work up its motion, is not altogether dominated by the existing state of the barometer. As a role -the wind tends to blow from places of higher barometer to those of lower, but there are cases in which tire motion is from low barometer to. high, and in these the nreviously acquired momentum of the wind is sufficient to enable it to defy -the usual rufe that air w driven from places of high barometer to those of low. By allowing hoth for barometer and momentum a Trench meteorologist, M. Q. Guilbert, has worked 1 out a- useful principle to help to forecast the weather. For this discovery he was awarded a special prise by the Belgian Astronomical Society in 1905, since when his method has been, tried with, success in the chief meterelogical offices. He starts with the idea of a certain balance, or. equilibrium between the -momentum of the air along a stretch of country extending, say, 1&0 miles, and 1 the' difference of the barometer at its two ends. ' This k the normal state for steady wind and steadj weather. For each strength of steady wind there is a corresponding difference of barometer- at two- stations 100 miles apart, this difference being required to keep the wind steady. If in any district the wind is observed* to be greater than this normal wind of M. Gwilbert, the barometer will rise; if it is less, the- barometer will fall. Thus good records of the winds enable the meteorologist to prophesy whether the barometer will rise or fall, or remain steady. This, of course', is of the utmost importance in helping: to forecast ' the weather. .The main' thing is to know how a depression or centre of low barometer willmove during the next 24 hours. M. GuilI feert has found that a depression tends to [ move towards the place where the winds fall most below their normal values ; that is, where they are weakest when judged |by the normal standard. The centre of weakest winds is the district in which the most pronounced changes may be expected, for it is the point towards whish the- depression i* sweeping. By oonihining the »Mf oJ tfo T*tad» of ft lagm with that

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https://paperspast.natlib.govt.nz/newspapers/OW19071218.2.363

Bibliographic details

Otago Witness, Issue 2805, 18 December 1907, Page 79

Word Count
1,007

A NEW AID IN WEATHER FORECASTING. Otago Witness, Issue 2805, 18 December 1907, Page 79

A NEW AID IN WEATHER FORECASTING. Otago Witness, Issue 2805, 18 December 1907, Page 79

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