This table shows (as might be expected) that the anticyclones are most numerous in winter (July and August), and least numerous in midsummer. The tropical depressions are generally unimportant in winter (May, June, July, and August), and increase in number as the sun moves south to a position over the continent. The Antarctic disturbances are somewhat less in evidence at Midsummer. At this period the southern low-pressure belt has moved southward and its accompanying eddies (the Antarctic V's or ows) do not so often influence Australian weather.
Speed of the Disturbances.
Sufficient data are not yet available for very accurate determinations of the speed of the disturbances. But one or two points of interest are obvious in any set of eddy charts.
The tropical lows show a marked tendency to "hang" about certain localities, such as the Pilbara heated area or the region south of the Gulf of Carpentaria. Examples of "hesitation" over Pilbara occur in the months of January, November, and December, and over Carpentaria in September, November, and December.
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. But these velocities vary with the months. Thus in June, 1910, the lows off the Leeuwin averaged about 360 miles per day; over the Bight about 550 miles, and over Tasmania about 600 miles per day. In November of the same year the velocity of the lows showed an average of 830 miles across the Bight, and 500 to the south of Tasmania.
It must also be noted that it is difficult to fix the position and velocity of these southern eddies. Their centres lie over water areas often and the positions can only be deduced approximately from the form of their northern isobars.
IV.—DOMINANT WINDS.
Some interesting particulars of the dominant coastal winds, which are more regular than those on land, have been collected from various publications, including the U.S.A. Pilot Charts.
The seas round Australia may be divided into the following regions:—
1. Northern or Tropical Region.
2. Queensland Coast.
3. New South Wales Coast.
4. South Australian Coast.
5. South-west Coast.
6. North-west Coast (Pearling Coast).
