WATCHING WEATHER.

Marlborough Express, Volume XLIII, Issue 116, 14 May 1909, Page 3

WATCHING WEATHER.

HOW FORECASTING IS DONE.

BAROMETER THE CHIEF

GUIDE,

Monday's Post says:—People with rheumatic joints ■ areP said to be good weather prophets, but the Government does not insist on rheumatism or gout as a qualification for a btate Meteorologist. Neither.is the official observer provided with a basin or water and a frog to assist him in his prophecies. Rough and ready estimates of impending changes in the weather may be based on the antics of animals or the twinge in a toe or knee, but the prophet who gets his knowledge in that way is not usually able to pick the direction from which the disturbance will come. Neither does -the Chief Meteorologist peer from a window by day or sit up by night to see whether the moon "comes in wet" or back to front. Wellington is not without enthusiasts who invoke the sun, moon, and stars to help them in making a hazard at the weather for a month or more ahead, but the Government office does not just yet reach so far into the heavens for its information about the wind and rain that may visit this earth. BY CYCLONES AND ANTICYCLONES. When the office of the Chief Meteorologist (the Rev. D. C. Bates) was invaded this morning he was ,cheerfully engaged with a low pressure cyclone, Which has charged down upon New Zealand from the north-west, and had its centre at Cape Egmont at 9 : o'clock. He had scores of telegrams beside him, giving the barometer readings and other conditions at the various stations throughout New Zealand, and he was mapping out the effects likely to be produced by the depressing visitor. • A cyclone is commonly understood to be a violent whirling wind, but in meteorology the term is applied to a low pressure movement, advancing like a great top, spinning from left to right, the direction traced by the hands of a watch. An anti-cyclone is a high pressure movement, in which the whirl is from right to left. Thus if a cyclone has its centre in Cook Strait the result will be westerly wind at Auckland, a northerly on the East Soast, southerly on the west, and easterly at the Bluff. An anti-cyclone, similarly centred, reverses the dispensation, giving an easterly to Auckland and a westerly to the Bluff. One has only to watch the face of a watch, to follow the range of the wind.

"The motions of the atmosphere are found to be mainly regulated by the ■distribution of barometrical pressure over the globe," states one of the weather text-books, and the pressures come in series, the cyclone, the anticyclone, the monsoonal, and the A-shaped depression, corresponding (in New Zealand) with the V-shape of Great Britain. By watching the advance of these aerial visitors, the meteorologist gives his warnings. AN EXAMPLE. This morning's cyclone of depression was a series of low-pressure circles within circles, with 1500 miles as the total diameter. A glance at the table shows that the barometer improved as the distance from Cape Egmont became greater. There "is a steady lise from 29.44 from Cape Egmont to 29.80 .at the Bluff, and 29.65 jit Cape Maria.

Places on the same curve in both Islands have, roughly, the same barometrical pressure. The line con- ■ necting such places, with the same barometrical reading, is known as an isobar, and. the isobat is to the meteorologist as a crowbar is to a navvy or a hair-pin to a woman. Aware, that the cyclone had its centre at Cape Egmont, and with some facts in the way of telegrams to assist him, the meteorologist is able to trace the probable course of the winds in the near future and indicate the places at which rain may be expected. Most of the North Island's bad weather is brought by cyclone and monsoonal depressions—chiefly cyclones —and much of the South Island's share of disagreeableness is due to" westerly waves of low pressure. The low-pressure cyclones are responsible for the numerous northerlies and the not infrequent south-casters that sweep Wellington. Cook Strait is on the boundary line of both systems, and therefore the capital may get a taste of each disturbance.. The high-pres-sure anti-cyclones generally bring bright days, and the life of this friend is generally from seven to nine days, but it may be rudely ousted by an enemy after a reign of only one day. NOTICE OF MOTION. Per electric cable the low pressure waves from the west give notice of motion. When Perth announces that it has been visited by a low pressure,

Hobart may expect a call three days later, and the Biuff may be reached in another three days. The gap between Perth and the Bluff is generally covered in five to seven days; the average is six days. However, the undesirable immigrant may be diverted, it may die away or be delayed. The cyclones manage to get a tyrannical sway for a time, but the ruling force is the anti-cyclone. For ever the high-pressure is in conflict with the low, and the high pressure wins, eventually, by superior size and strength. It is a beautiful game of balancing, and man, taking the years •through, gets the balance in his favor. GENERAL AIDS. The barometer is thus the meteorologist's chief guide; he looks on the glass for sign and portents. The Wellington office has a self-recording instrument, and, of course, keeps in close touch with outlying stations. Yet with all these aids, the careful meteorologist is not prone to jump at conclusions. Judgment is an important factor. The cyclones, the anti-cyclones, the low-pressure waves from the west, determine the gener&l character of the weather; but the wise man also studies local conditions, in conjunction with the general information given by the Meteorological office. He knows the lesson to be drawn from the humidity of the air, and he sees portents in the skies—but before all and above all, is the barometer. Yet amateurs are warned to be prudent when consulting the glass. "A rapid and unexpected rise of the barometer," says one authority, "is often the precursor of a coming depression, so that whenever we see a sudden rise we may expect an equally sudden fall, and must be on the look-out for the slightest tendency of pressure to give way."