CYCLONIC STORMS.

Auckland Star, Volume LXIX, Issue 142, 18 June 1938, Page 8

CYCLONIC STORMS.

THE ENEMY OF SAILORS

flty TiXU.I

Tiny cruising yacht and ocean mammoth alike must constantly steer warily of the cyclone, violent killer of men and >hi|is. For the cyclone, known t.> mariners for close on 000 years, but still an enigma to the landsman, always has been one of the -shipmasters most feared enemies. Jn its relentless, whirling curvature through the oceans it. takes compassion neither on ship nor crew, and woe betide the mariner who ignores its warning. For hydrographical purposes, the world is geometrically divided into dcT'ees of latitude and longitude over which there are clearly defined areas of consistent prevailing winds (sometimes subject to seasonal change) and variable winds. All winds, however, irrespective of location or direction, are created by variations in barometric pressure. Numerous oliscrvat ions under normal conditions have shown that the world is ringed by two ridges of high pressure, approximately on latitude .'ls degrees in the northern hemisphere and .'{o degrees in the southern hemisphere. From the ]>eak of these ridges pressure falls away towards the equator and more rapidly towards the Poles. The unequal distribution of land masses and oceans create discrepancies, but generally speaking there is a continual flowing of surface air [away from the high ridges constituting the trades towards the equator, and the westerlies in the opposite direction. 1 The rapid rotation of the earth has a | bearing on direction. Air flowing from a high ridge towards the equator, which has a greater distance to go in its daily circuit, is apparently left behind by the earth, and draws more and more from the east to the west, forming the nor'-cast and sou'-east trade winds. As opposed to that, air spilling from the ridge in the middle latitudes towards the Poles, and having the velocity of that ridge, draws steadily to where the earth's velocity is less, so that the wind hauls more and more into the west. The general circulation of winds, therefore, is from east to west in the tropics and from west to cast in the middle and high latitudes. Pressure Differences. Where, at any point in .that system, there oecurs a local area of low pressure, the air from the surrounding regions of high pressure is deflected inwards, not towards the centre, but in a spiral around it. The velocity of the revolving wind depends on the rapidity of pressure changes. The inward flow is converted into a clockwise whirl in the southern hemisphere and a counter-clock wise whirl in the northern hemisphere. To these revolving winds has been given the name of cyclone. The different ty[«'s of cyclone are too numerous to discuss in detail, but are either tropical or extra-tropical. Although the tropical cyclone, as it,i name connotes, in tropic in origin and henee restricted in area, it swirls with terrible fury, creating havoc on land and at sea. The extra-tropical cyclone is so vast that it may encompass a diameter as great as 1500 to 2000 miles, but an average is 500 to 1000 miles. These, almost invariably, curve to the eastward, but may have a north or south component. True to the old adage, certain phenomena forewarn the mariner of a cyclone's approach, usually long before it hits the ship at sea. During the seasons of such depressions, or "lows," as meteorology succinctly describes them, the sailor knows full well tluit any barometric irregularity apart from the diurnal oscillations, is a warning of a weather change. While not infallible, the rate of fall of the mercury level should give an indication of the rate of approach of the disturbance, and the distance from its centre. An oppressive atmosphere' accompanied by unusually clear visibility and the cirrus effect of 'the skv will confirm any doubts. These conditions may also he accompanied by a higher than normal "glass," but it will quaver and pump uncertainly. 'Ware the Storm Centre. Following oliservations taken at intervals, the sailor will estimate approximatelv when he will be engulfed in the storm and in what sectors, or quadrant, he will be. On occasions he will out-manoeuvre the cyclone, but if that be impossible, he will immcdiatelv set about preparing for the combat. On ' its line of progress, the cyclone is divided into dangerous and navigable semi-circles, and the shipmaster who finds himself in the former may well l>e worried. inhere his craft will be in danger of being drawn into the damaging, shrieking vortex, or storm centre, whereas in the navigable semi-circle hi' ma\ gradually edge away. Should all endeavours to elude the vortexfail, the ship will experience a short period of calm when in the storm centre, but the seas will be high, confused and in a dangerous state. Before long, the wind will burst with hurricane force from a point directly opposite to that from which it was blowing. It is during that time the ship is likely to suffer the greatest harm On account of the extremely intricate nature of the cyclone, its peculiarities and the methods of dealing with it. the landsman must find difficulty in endeavouring to appreciate it in near-technical language. The best and most lasting manner of impressing the meaning of a cyclone on the mind is. therefore, to experience one at sea, and preferably undo/ sail.