Page:Hunt - The climate and weather of Australia - 1913.djvu/137

Rh XII..—TYPES OF WEATHER. The following series of weather charts is given in order to illustrate isobarically and otherwise some characteristic developments in our Australian weather. In connexion with each chart or sequence of charts is given an explanatory note, necessarily somewhat brief, but probably sufficient to enable the salient features in weather progression to be grasped. . 101.

Winter Anticyclones.—This is a common type of anticyclone in winter. The centre lies near Broken Hill between latitudes 32° and 33°, and anticyclonic weather obtains over almost the whole of the continent. Hence clear skies and dry air, aided by long nights, allow of great radiation of heat from the earth's surface, and frosts are general inland south from the Tropic. . 102. Summer Anticyclones.—8th January, 1913, provided an ordinary summer type of anticyclone covering the Bight and lying centrally over a point in about latitude 40° S.— it really passed later over or south from Southern Tasmania. The temperature differences induced by the passage of such systems along the south coast are fairly well illustrated in this case, the southerly winds in its front giving Melbourne a maximum temperature of 65°, and the north-easterly winds in its rear raising the temperature at Perth to 90°. . 103. Antarctic Depressions unfavorable to good Inland Rains (Winter Type).—7th July, 1913. This is a typical example of an "Antarctic" with no tropical connexion. 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 rains resulting from it were practically limited to coastal areas and inland slopes facing the westerly winds. . 104. 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.

. 105 106. Antarctic Cyclone passing through Bass Strait.—6th to 8th July, 1912.—An example of an Antarctic cyclone the centre of which passed through Bass Strait. As will be seen, the rainfall was widespread, covering practically all the country south of a line joining Streaky Bay and Brisbane, or not less than 440,000 square miles. On the Victorian highlands falls of over 1 inch were common. The slow rate of movement, about 360 miles per day, is worth noting.