Page:Hunt - The climate and weather of Australia - 1913.djvu/48

Rh wet; although unfortunately it is true that the interior is nearly always dry. As we shall see, in each month the region with over 1 inch of rainfall forms a somewhat "crescent" shaped area, whose concavity lies toward the centre. These "crescents" slowly swing round from north, through east to south, and then back again during the year.

Let us now consider the months in some detail.

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 ½ 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; but otherwise the distribution over the continent is much the same.

In March the summer rains have retreated still further north, and the southern limb of the "crescent" is beginning to cover the south-west coast. (The S.E. Trades have given the Queensland coast near Cairns over 20 inches during each of the three months considered.)

In April the winter rains are beginning to be felt along the whole south coast, though only to the extent of an inch or so during the month.

In May the southern type of rainfall is in full swing and no rain falls in the north. The "crescent" has now tilted round to face the south and its two limbs cover the east and west coastal areas.

In June, July, and August, similar conditions obtain; the rain belt (over 1 inch) having still the shape of a crescent, and covering the coast from North-west Cape around the south and up the east coast to Cooktown.

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 northward bulge of the Southern Ocean in the Bight has severed the winter rain area in two, while in Northern Territory the summer rains are again creeping southward and are giving that settlement over 2 inches. For six months (since April) the north-west coast and York Peninsula have had practically no rain.

In November the winter rains are over. The "crescent" faces toward the N.E. again, and the monsoonal rains are dominating the north of the continent. In December the summer rain has reached Alice Springs in the centre of the continent and over an inch has fallen in that region.

Many interesting points in connexion with the origin of the rainfall are brought out by these monthly charts. They will be discussed briefly in the next chapter. It will have been noticed that the "crescents" face north in summer (Figs. 50, 39, 40), east in autumn (Figs. 41, 42, 43), and south in winter (Figs. 44, 45, 46), but never occupy the west coast; while the centre also is never covered by the crescentic monthly rain areas.