Henry Ambrose Hunt

“ 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. ”

“ 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 ”

“ 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. ”

“ 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 ”

“ 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. ”

“ The velocity of the highs and lows across Southern Australia is also often very irregular. Their rate across the Australian Bight is greater than that they exhibit over South-western Australia, or over the Bass Straits area. Probably the frictional resistance is less over the water which in the Bight is thrust well northward across their path, than over the highlands in South-eastern Australia and Tasmania. ”

“ 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 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ The North-west Coast, from North-west Cape to Cambridge Gulf.—This region agrees fairly closely with the northern region. It is dominated by the south-east trade for eight months, but during midsummer the almost permanent "low" covering the hot Pilbara region in Western Australia gives rise to a "monsoon" and the coastal winds swing round from south-east to south-west. The south-east wind is, however, not so constant as that off the Queensland Coast, and in autumn (March, &c.) the winds are very variable. In the north calms are common, and except for the "willy-willies" storms are rare. ”

“ As regards the influence of the Kosciusko Ranges, it may be premised that they have a greater retarding influence upon the "highs" than the "lows," since the increase of atmospheric density downwards near the surface is greater in "highs" than in "lows," and this may cause the change to anticyclonic high pressures along the New South Wales coast to be delayed slightly, and then to be more sudden than elsewhere, causing a temporarily steep barometric gradient on the rear side of the trough with corresponding wind force. ”

“ The tornado is always associated with thunder and hail storms of extremely violent type. If we regard a thunderstorm as due to the uprushing of a column of air, from, say, the 4,000 to the 20,000 or even 30,000 feet level this giving rise to, and in turn being maintained by, the condensation of aqueous vapour, with the resulting phenomena of rain, hail, electric discharge, &c., and this column of air to take on a rapid spiral movement, which it naturally does, then the downward extension of this spiral movement to the ground provides the tornado. ”

“ Hot Spells in Southern Australia.—In the southern parts of the continent or, say, within 200 or 300 miles of the south coast-line, spells of heat unpleasantly great are usually of short duration. The immediate cause is a low-pressure trough connected with an Antarctic disturbance, and as the average rate of summer Antarctics is about 800 miles per day the northerly winds in advance of the trough rarely last more than 24 hours. ”

“ They occur nearly always when a low lies off North-west Cape—the high being to the south-east, either over the Bight or further east. The wind is generally from the north—east, but if the southern high is rather to the west then south winds also bring rain to the fields. ”

“ Our study of the chief weather elements has shown us that Australia has not one general climate, but contains within its vast area several types of climate. They may be classified according to many factors ”

“ It is for the latter type that the word "trough" is here used. In the case of a col, the isobars of the two "highs" are decidedly convex to one another along their common axis; in the case of a trough the rear isobars of the preceding "high" or the front isobars of the following "high", or both, tend to straighten and the convexity is more apparent in the isobars of the adjacent low pressure systems, producing often an hour glass appearance. The chart of 31st May, 1909, shows the straightening of the rear isobars of the preceding high very well. ”

“ We have noticed the dry belt in the Omeo region, and the similar but, larger dry belt in the Cooma Valley (The Rift) . Behind Sydney is a very interesting patch extending from Picton to the Emu Plains, with less than 30 inches. This area lies between the Blue Mountains and the highlands about Bowral and Moss Vale. The former intercept the westerly rains, the latter those coming from the south-east.
The volcanic ranges of the Warrumbungles and Nandewars also give rise to considerable increase in the rainfall in the vicinity. ”

“ It nearly always happens that the anticyclone is centred to southward. The effect of this is obvious. The gentle outflow of air from the high along the earth's surface reaches Melbourne from points between south and east, having just passed over a water surface, and so carrying a fair amount of moisture. The fact also that a cyclonic depression has very frequently been operative just before off the New South Wales coast and driven masses of humid air into Bass Strait would aid in this result. ”

“ They travel at first in a south-westerly direction, the centre keeping well out to sea; and their pressure and movement are shown by an easterly wind gradually veering north and west, accompanied by heavy rainfall. When they reach latitude 20° or thereabouts, their course alters and they recurve and commence to travel in a southerly or south-easterly direction, striking the coast generally between Condon and Fortescue, and frequently bring a "willy-willy" to wreck whatever happens to be in the way. ”

“ The rains in the north (Pilbara) usually accompany north winds in front of the low, and those in the south south or south-east winds in front of the high. There is a strong tendency for the low to "sit" over the north of the high in this month, when rain is probable. ”

“ The driest region so far furnished with rain-gauges lies east and north-east from Lake Eyre, where less than 5 inches is the average annual rainfall. This minimum rainfall is coincident with the lowest elevation, Lake Eyre being actually below sea-level, 39 feet.
In the northern moiety of the dry region the temperatures are of course much more severe than in the southern, for, as we have seen, the hottest portion of Australia lies between the Peak Hill and Pilbara Gold-Fields. ”

“ The chart of the 10th, with its cyclonic centre off Gabo Island and steep gradients, indicates very unsettled and rough weather conditions, which were sufficiently illustrated in Melbourne during the early morning by heavy hail storms, vivid lightning, and sharp peals of thunder. Moreover, the great length of north and south isobars which overlay Eastern Australia and extended through at least 30° latitude favoured great transference of cold air from Antarctic seas, even into tropical Queensland. ”

“ The large monsoonal storm system which crossed the continent in the early part of the month, the continued monsoonal disturbance and heavy rains in Queensland later, and the development of the Fiji hurricane, are evidence of unusual activity in the southern monsoonal low pressure belt during March, and it would be interesting to ascertain whether a similar activity was shown in other parts of the Southern Hemisphere. ”

“ Surrounding the central dry area of Australia, the isohyets describe almost concentric curves, any modifications being almost entirely due to variations in elevation. Thus, the Darling Ranges to a great degree account for the excellent rainfall of the south-west corner of Australia. The Flinders Range (South Australia) and Australian Alps in the south-east have heavier rainfalls than the surrounding tracts owing to their cooling effect on the air currents. Along the eastern elevated margin of Australia every ridge between large river valleys accounts for a somewhat greater rainfall. ”

“ Convectional rains may occur at any season in the interior, and cyclonic rains visit the east coast in northern parts during the summer months, and in the winter and spring months on the Southern or New South Wales coastal regions. ”

“ The result upon storm systems approaching from the west was generally disastrous; some were deflected too far south to affect Eastern Australia; some seemed to die out before arrival, and some were converted into feeble cyclonic circulations, which had little rain-producing effect. ”

“ In the first column the average for the month is given. (Here we tend to get the diurnal extremes neutralizing each other so that the normal wind of the region is shown.)
Regional Winds at Perth—
In this locality the invigorating sea-breeze—called the "Doctor"—blows from the W.S.W. during the afternoon, while a land wind (E.N.E.) sets in when the land has cooled below sea temperatures in the early morning.
The sea-breeze is most active when the land is much warmer than the sea, i.e., in the summer. The land breeze is most active for similar reasons in winter. ”