Page:Hunt - The climate and weather of Australia - 1913.djvu/47

Rh In conclusion it may be noted that there is each day a noteworthy change in wind direction near noon. During the first half of the year (February-July) this occurs just after noon; in the latter half of the year (August-January) just before noon. In Adelaide, much the same phenomena can be noticed. (Fig. 37.)

The normal winds of this region (deduced from the average throughout the month) are— Here the coastline has much the same direction as at Perth. So that the land breeze is E.N.E. and the sea breeze W.S.W. as before.

It will be noticed that the land wind is very strong in the months of May and June. It also deflects the normal wind appreciably, but not very greatly in other months. The sea breeze is not strong in winter, but all the rest of the year is very important in the afternoon, exercising a strong deflection in January, February, and March.

 V.—RAINFALL.

Australia and Tasmania cover 2,974,581 square miles. Of this total area, 1,045,073 square miles have less than 10 inches per annum on the average; 651,961 square miles have from 10 to 15 inches; 416,135 from 15 to 20 inches; 502,929 square miles from 20 to 30 inches; 198,608 square miles from 30 to 40 inches; and 159,875 square miles have an annual average rainfall of over 40 inches.

The rains of Australia fall mainly in connexion with two storm types, viz., tropical depressions and southern depressions, the latter locally known as Antarctic depressions.

The former rain-bearing factor operates over two-thirds of the continent, roughly, over that portion of Australia lying to the north of a line extending approximately from Cossack on the North-west Coast to Sydney on the south-east coast, the rainy season being from December to March inclusive, and the wettest month, January. The remaining third of Australia's area receives its rain principally through the southern depressions which operate during the autumn, winter, and spring months, with the heaviest monthly totals in June. 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. A considerable amount of anti-cyclonic rain falls over the eastern coastal districts of the continent at any time of the year, when the recurring high-pressures pass in high latitudes and are actually centred to the west of Tasmania.

In a map showing the annual rainfall of the continent the isohyets form approximately concentric ovals around the arid centre of the continent. This arrangement does not, however, mean that the coastal regions are always 