BAD REPUTATION

Evening Post, Volume CXVIII, Issue 114, 10 November 1934, Page 9

BAD REPUTATION

WELLINGTON AND WIND

WHY DRAUGHTS ARE STRONG

THE SEASONS STATED

'Probably no Fellow of tho Royal Society of New Zealand •will rise up in scientific -wrath to deny the statement that Cook Strait, and especially that urea upon which stands the city of "Wellington, is -windy, and unpleasantly so at times. It-may be presumed that it al-ways has been windy ever since the strait -was fo'rmedj and it may equally ■well bo presumed that it always will be •windy. ' Up to about a hundred yeaTS ago it mattered little to anyone that Cook Strait -was windy, or to "any thing except the verdant forest which then clothed its shores. Any sapling which neglected to arrange a root 6ystein strong enough to counteract the draughts never achieved its aspiration ,to become va forest tree, but ' beyond ttiat the wind mattered little. To the primitive Maori it was probably of small inconvenience, although it doubtloss made him careful about his joy ridea jn hia canoes.' When the white man settled on tho shores of Cook Strait he quickly found that tiles, roofs, chimney pots, fences, and sheds wore affected by tho winds, and as civilisation progressed power poles and wireless masts weic added to the list of things that might bo damaged by the wind if duo piccautions word not taken. But in recent years the strong winds prevailing in Cook Strait' at practically all seasons of ' tho year have acquired a new importance "and significance. With the advent of aviation, winds have become an important factor, and an understanding of the causes and naturo of theso, winds be- * comes a subject of moio than academic intcirst.' ' i Iv answer to some questions put to \ him about Wellington's winds by a "Post" representative, Dr. E. Kidson, Director of Meteorological Services, 'remarked that Wellington's bad - leputatiou for windiness was unfortunately, justified. This reputation, he said, arose principally througli tho strength and gustiness of its northerly winds. "Tho reason for the unpleasant character of these winds is clear," he said, "when wo look at the map. Winds from, a ,westerly quarter aro by far the most frequent, in these latitudes. But from the ■Tararuas to beyond Taupo aid from near Cape Farewell to the extreme south, tho mountains of New Zealand offer a high barrier to these winds. The flow cannot, of course, stop dead on reaching New Zealand, but must continue over the mountains and ,tbrough Wy - available gaps. And in order to make up for the space lost owing to the mountains without reducing the total flow, jit has to move at1 increased speed over the lidges and through the gaps. Now, the only gap of any consequence is # that formed by Cook Strait, and we - have a fine large funnel leading into it between, Capo Egmont and Cape Farewell. It is not surprising, therefore, that the winds that blow through Cook Strait from tho western side are unusually strong. " "Again, owing to the configuration of the land, any. wind coming through tlie Straits from this side is practically forced to come from a north-north-westerly direction at any level below ' that of. the mountains on cither flank, or, say, 4000 feet. Tho original. direc- '", tion before it reached New Zealand .may hav6 been anywhere between * north-north-west, ,and west-south-west. vl j Due northerly to north-easterly winds are largely cut off by the mountains of the North Island, and aro seldom strong at ■ Wellington. Similarly, touth-westers - a are cut off by the South Ibland, and ' n-ben a south-wester is blowing we have our finest weather. It may be showery and blowing a- galo on both sides of the country, but Wellington generally has a light northerly or a calm and brilliantly clear weather. Winds between south-south-west and east are forced through the Straits on i tho opposite course to the north-west-erlies,r south-south-east being the most frequent direction. These also~Tend to concentrate through the Straits area, but from this side the collecting funnel , is not nearly so large and the increase in -the wind speed not so marked. VICIOUS OUSTS. "The northerly wind has "to Teach Wellington across the western - hills, over which it must come in rolling eddies ,or in vicious swoops. Not "only that, but it has been bustled and'deflected, by the mountains before it approaches Wellington. Consequently, it is a very -turbulent -wind. Indeed, from nowhere else have I seen records'1 of such gusty winds as those we get from . the'northeriies in Wellington. Perhaps the worst of all'is that which comes] , originally from almost due west. This is usually a turbulent -wind before it I reaches New, Zealand and when it arrives at Wellington it is terribly gusty, [ especially as'regards changes of direction. > The southerlies or south-easter-1 Hies gennot nearly so gusty because they '. arrive at Wellington direct from the, level surface of the ocean. ' "The flow of a wind over an. obstacle such as a mountain Tange is very ' complicated and varies with different weather conditions. The first effect of the obstacle oa a current coming from a, westerly direction is to cause the air to. pile up on the windward side. The result of this is that the lower layers^ become deflected to the right. That is, they take a -more northerly direction. Then, of course, the, air must rise in order to climb over the mountain. A certain amount of rise takes place up to great heights. This is illustrated at , Wellington by the formation of high "lenticular or whale-back clouds above each of the surrounding hills when a stTong westerly is blowing. These clouds frequently extend to 20,000 feet. On the leeward side the wind may pour down or it may continue at a high level above a cushion of more or less stagnant air. The colder the surface, the more likely is it to do this latter. For i this reason conditions aio somewhat quieter in the night than in the day til % But generally at Wellington a large pioportion. of the air pours down over tho ridge. -At Kelburn, for example, the pilot balloons by means of which wo, measure the wind in the upper air, almost always meet a downward current in the lower levete when a northerly is blowing. In coming over tho ridges, too, the wind forms tho rolling cfldies alTeady mentioned. Then, each penk and cully tends to deflect the .wind in a certain direction and the various minor currents produced in this way may impinge on each other, producing vertical eddies such as are seen in the willy . waas which skim across the harbour m a northerly gale. CLOUD, BUT PEW TOGS. "But another important action of the convergence of the air through Cook Strait in" winds from the north-westerly nuarter is the production of low cloud. This is due partly to tho effect of the ebld waters of the strait and partly to the forced uplift of the air. Unfortunately this cloud and the accelerated winds spoil much of what would otherwise be our best weather, warm and sunny. The low cloud does not usually extend far from the straits, but it may he very low. Occasionally when the air current is especially tjarm and moist a thick mistis produced, amounting sometimes almost to * fog. This low cloud

and mist is one of the most troublesome features of Wellington from the point of view of the aviator. Often, of course, it is combined with the storm or nun clouds of bad weather. Generally this cloud of local origin tends to ,bo thicker and lower on the western sido of the hills than on tho eastern. This affects such aicas as Porirua. "Our strong winds, however, have ono advantage, and that is that they tend to prevent tho formation of true fog, which is a suifaco phenomenon. We occasionally got fogs in light or moderate south-easterlies or in dead calms. In tho latter case the fog is usually confined to certain areas of the straits, associated probably with tidal currents, tho fog forming over a cold current. Such a fog may make one landing ground impossible, but alternative ones should not be difficult to find. "Strong southerly or south-easterly winds may,1 of course, produce a thick atmosphere and low cloud,"but there is \isually a certain amount of visibility. Tho southerly change may be dangerous to aviators, but anyone on- tho lookout should not .caught napping by one of these since thoy can usually bo seen gathering a long time befoie they arrive. As in'the case of the northerly, convergence and'uplift in southerly or south-easterly winds load to specially cloudy, weather, and, frequently, drizzling rain in the Cook Strait area. Conditions aro then usually much clearer on tho western side Of tho hills. Winds from a southerly quarter, also, aTe deflected to the right on reaching the land, just as are >ne northerhes, a south-easterly, for example, becoming more southerly. . "One result of the constf&ining of the wind to' flow in the channel of the Straits is that there may be considerable differences between the wind directions at the surface and in tho upper air. This is sparticularly the case when £he general >wind is south-wcstevly. Wellington, as wo have,seen, is protected from the. south-wester. Consequently,' it very frequently happens that when it is calm at Wellington or a light to. moderate north-north-west wind is blowing, the wind above about ■1500 feet is strong from between ■south-west and~wcst-south-wcst. Occasionally, also/ there may bo a .strong wind from between north and noithcast in the upper levels which is not indicated at the surface' "Apart from the influence of tho land, tho normal tendency in New Zealand is for all winds to becorao more westerly as tho altitude increases. Over a level surface, also, the speed generally increases with .altitude, but owing to the reinforcement in the Straits, which affects especially the lower levels, this increase is not very marked in, Wellington's northcrlies.-"