Page:Hunt - The climate and weather of Australia - 1913.djvu/143

Rh. 113 AND 114.

Antarctic Cyclone passing inland.—1st and 2nd September, 1911. 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. It is possible that the condensation induced by the transfer of such a large body of air into higher latitudes was mainly responsible for the cyclonic development and heavy rains. . 115 AND 116.

Inland Winter Rains of Tropical Origin and Cyclonic ending.—During June and July, 1912, no less than four rain storms originated in the northern interior of the continent, two of which developed enormously and gave heavy rains to the whole eastern half of the continent. The charts of 22nd and 24th June show stages in the barometric development of the second of these storms, warning of which was first given on the 21st by the occurrence of thunderstorms in the far north-west of Queensland. Next day these were occurring over a much greater area, extending northwards beyond Powell's Creek and southwards to Broken Hill, the isobars at the same time dipping southwards towards the Bight, where previously barometers had read up to 30.5 inches. During this and the next day its rain production was at its maximum. By the 24th, a very symmetrical and fairly intense cyclone was centred near Adelaide. This afterwards rapidly lost energy both as regards pressure and rain production, and moved slowly eastwards over Victoria.

It is worthy of note that in this case, as in that of many other storms of tropical origin, the cloud and rain development were always in advance of the isobaric showing clearly the convectional origin of the cyclone which followed. . 117 AND 118. Tropical Rain Storm moving Southward from the Territory into South Australia.—Examples of this type of storm are not very numerous, but the fact that they occur almost as readily in the winter as in the summer months shows that they are not in any sense monsoonal. Perfect examples of this occurred on the 31st July, 1908, and 6th-8th June, 1907. They all gave splendid rains over the central parts of the continent. That of 26th February—5th March, 1910, was, however, the most remarkable in that and in every other respect.

On the 25th February heavy rain was general as far south as Powell's Creek, and this was accompanied by the formation of a definite low-pressure centre south from Port Darwin. This slowly moved due southwards, accompanied by a tremendous rainfall amounting at many inland stations to very nearly the annual average. By the 5th March, South Australia was deluged, and the storm, which then became very definitely cyclonic, moved off over Victoria towards the S.E., giving rainfalls in low-lying plain country of 4 or 5 inches, and up to 12 inches amongst the mountains.