Henry Ambrose Hunt

“ When very strong the anticyclone is elongated and the southern isobars are flattened. (See Chart 30) . They are very cold and dry, having all the raw feeling of the easterly winds of England, and have been known to last for several weeks without intermission; they are the most persistent winds during our winter. In heavy westerly winds the cold is very severe in Bass' Straits, between the south coast of Victoria and Tasmania, rain, hail, and sleet being very common. It is almost needless to say that on land they bring very little rain, and they rapidly dry up the soil. ”

“ The conditions leading to the fall of rain in the interior of Western Australia are by no means always of the same type. The most striking feature shown by the analysis is the persistence of one type throughout a season in one year which may not occur in the same season next year. For instance, in January and February, 1911, there was a greater distance between the low (over Condon) and the high to the south-east (south of Mt. Gambier, &c.) than usual. In June and July, 1910, and 1912, the high covered most of Eastern Australia, while the low off Albany led to rains over the gold-fields. ”

“ It is there explained that the south wind comes in front of an approaching anticyclone, and that it is felt from West to Eastern Australia, but it is only on the eastern coast, where, aided by the smaller friction of the ocean and the shelter which the mountains afford from other winds, that the southerly becomes more vigorous and rushes northwards in a squall, which happens so suddenly and with such force, that at times ships drag their anchors in Sydney harbour. ”

“ September is, perhaps, the driest month in the year; if we consider Australia as a whole. Only the extreme south-west corner of Tasmania and the Cordillera region in the south-east have a rainfall of over 2 inches. The southern rains are now moving south as the sun retraces his path from his northern limit.
In October there can hardly be said to be a rain belt, for the rain region is divided into three isolated areas. ”

“ The summer latitude is about 40° south. They are less extensive in summer than in winter, and do not so completely control our weather as they do in winter, for their southern position leaves room for the southerly extension of monsoonal low pressures, which make a great deal of our weather; but the anticyclone makes the change from hot northerly to cool southerly winds, the bursters of the east coast. ”

“ The chief feature indicating thunderstorms is the narrowness of the col [2] and somewhat congested state of isobars in the high pressures west and east of it, resulting in opposing winds. Those of the tropical tongues are hot and charged with moisture, while those of the Λ depressions are strong and dry. This type is met with during the monsoonal season. The rains resulting from this feature are not generally heavy, and though thunderstorms may be experienced over extensive areas of Queensland, New South Wales, and Northern Territory, a number of them may occur without any rain falling. ”

“ In January the sun's heat effect is greatest, and the monsoon is at its height. The cold Tibetan Plateau and warm centre of Australia act in unison to produce many on-shore northerly winds in Northern Australia, and hence an average of 1⁄2 inch of rain falls each day at Port Darwin—gradually decreasing towards the south. Alice Springs (in the centre) gets about 1 inch in the month, while south and south-west Australia receive practically no rain.
In February the rain belt is less intense at Port Darwin, the monthly fall being 10 inches instead of 15 inches ”

“ During the winter months the antiyclones are much larger than they are in summer, and their latitude about 30° S.; very commonly their area is equal to Australia, and their control of the weather more complete than it is in summer. Fine weather marks their centres, and the rains come chiefly from the low pressures between each pair of anticyclones, and the strong westerly gales are but part of the circulation about these high pressures. ”

“ In framing official predictions of the weather the daily synoptic and isobaric chart is the chief evidence relied upon.
To forecast with any degree of accuracy requires considerable experience, a knowledge of the distribution of the normal local climatic elements, and a due appreciation of the significance of the varying features of atmospheric systems and the degree to which they are affected by latitude, longitude, the seasons of the year, and, at times, even by the prevailing conditions of the land surface over which the atmospheric systems are passing. ”

“ In the dry region of Western Australia—for the most part with a rainfall of less than 10 inches per year—are three important centres of settlement. In the north is the Pilbara Gold-field, in the centre the Murchison Gold-field, and in the south the Coolgardie Gold-field. Kalgoorlie has a population of over 17,000 inhabitants, while some £112,000,000 have been won by miners from the gold-fields of Western Australia.
A special study of the rainfall of this area is justified by its economic importance and by its interest as a region which has been settled in defiance of physical control. ”

“ And just as the trade wind intensifies its northern circulation by adding force thereto, so the brave west winds of the southern ocean follow the general move of the weather systems northwards, and thus add force to the westerly circulation of the anticyclone, and its greater dimensions increase the size of the Λ depression, so much that it no longer has the sharply defined change from notherly to southerly winds, but from north-west to south-west winds ”

“ The heavy and extensive inland rain which accompanied this inland cyclone was the only good spring rain experienced in 1911, and was the salvation of the crops over South Australia, Victoria, and much of New South Wales. The chart of 1st September shows it as an ordinary Antarctic disturbance, but with an exceptionally good trough extending northwards in front of which there was a wide and unbroken flow of northerly winds from the Gulf of Carpentaria into South Australia and Victoria. ”

“ As a general rule, weather is set fine when anticyclones move rapidly, and in a straight line across Australia, i.e., at a rate exceeding five hundred miles per day. And weather is unsettled when they move slowly, and not in a straight line, i.e., in a zigzag line, especially if they show no appreciable forward motion for a day or two. When anticyclones move in low latitudes the conditions favour dry weather, in high latitudes, wet weather, especially if they rest for a time south of South Australia. ”

“ The winds though strong do not seem to have been of exceptional force. The storm continued its southward course for another day, bringing rain to the eastern parts of New South Wales, then moved off towards New Zealand. These storms may occur at any season, and are felt most severely along the coast-line between Brisbane and Sydney, where they develop a wind force and coastal rain production much beyond what their previous history while approaching oversea from the north or north-east would suggest. ”

“ The energy of wind circulation increases over South Australia, and as the whole system moves bodily eastward from the Australian Bight to the mainland, the circulation is seen to be that of a fully developed cyclone of small area, with a diameter three to five hundred miles, formed out of the southern part of the extensive monsoonal depression. ”

“ It is in respect to this thunderstorm origin that it differs from a whirlwind, the latter usually originating at ground level and not rising high enough to cause condensation in the very dry, hot air in which it occurs. The radius of action of the tornado may not be much greater than the few yards covered by an ordinary whirlwind, and rarely exceeds one-fourth of a mile, but what it lacks in area it more than makes up in intensity. From the cyclone it differs in the area affected, but, nevertheless, it is not to be regarded as a miniature cyclone. The tornado is a part of one thunderstorm ”

“ On the 25th September, the day following the gale, the weather everywhere was generally fine, while all that remained of the energetic high and low pressure systems were parallel isobars lying over the southern areas of Australia with very shallow gradients. This gale was very destructive and did much damage to property in Sydney; in some instances houses were unroofed, and the wind and sea on the coast were very heavy. ”

“ It completely wrecked a farmhouse which lay in its track, killing two of its inmates, carried large pieces of furniture for over half-a-mile, tore up trees by the roots and transported them for considerable distances, and demolished all of an orchard over which it passed. ”

“ The force of wind is often sufficient to break off growing trees, two and even three feet in diameter, and the reason there is so little damage to life and property is not the want of power, but the sparse population and the very small number of towns.
Chart 20, March 20th, 1894. An extensive anticyclone lies south of Australia, giving way in its central parts to an extensive monsoonal dip. The isobars are generally uniform and of even gradients, though a suspicious interval exists to the west of New South Wales between the 30•0 and 29•9 curves. ”

“ The storm has plenty of wind energy, the barometer falling rapidly southwards over Victoria and Tasmania, but the unbroken belt of high pressure lying east and west over the Continent to northward shows that in rain production it is not aided by any flow of air from the tropical belt. ”

“ Antarctic Depression favorable to Inland Rains (Winter Type) .—18th August, 1910. In this storm the wide trough between 30.0 isobars extending northwards favoured northerly winds and large cloud development as far north as Alice Springs. Rain as far inland as William Creek was recorded next day, and over the whole drainage area of the Darling River within the next two days. Rain production was probably aided considerably by the flow of air southward in front of the trough from well within the tropical belt, the cooling due to increase of latitude favouring condensation. ”

“ Along the west coast of Tasmania is a region, unique in Australia, where a superabundance of rain has almost prohibited settlement. There are practically no inhabitants in the south-west region, which is very rugged country covered with an almost impenetrable scrub. ”