Page:Types of Australian weather.djvu/6

 Ordinary symbols have been used, except the circle half filled for thunderstorms, and the straight line shading; parallel lines indicate the area of rainfall under one inch, crossed shading over one inch.

TYPE I.—MOVING ANTICYCLONES.

One of the best marked features of Australian weather is the steady easterly progression of all the types, and the governing type, that in fact about which all the other types seem to congregate, is the anticyclone; it has therefore been placed first in the series, with three charts to show the progress made by a quick moving one in forty-eight hours. The average daily progress of anticyclones is four hundred miles per day, but the speed at times rises to one thousand miles.

Investigation so far leaves no room to doubt that in these latitudes a series of anticyclones surround the globe; the latitude of the average one varies with the season, being farther south in summer than in winter. The normal circulation about an anticyclone brings southerly winds in front of them, and northerly winds in the rear, hence our cold and our hot winds.

Chart No. 1 shows the position, on 15th August, 1893, of the eastern half of an incoming anticyclone; it rests over Western Australia, while the departing one is seen over the Tasman Sea; between these is seen the usual depression, which is of average intensity, and a dormant tropical low pressure to the north. In Chart No. 2 the anticyclone has moved nearly nine hundred miles in the twenty-four hours, the centre being located near Fowler's Bay, north of the Australian Bight; the antarctic depression is well across the Tasman Sea, while the tropical or monsoonal isobar depicted in the previous chart has apparently merged into the high pressure system, a curious and not unusual kink being formed to the north-east of it, following the contour of the Gulf of Carpentaria. On Chart No. 3 the anticyclone is shown to have moved a further seven hundred and fifty miles, or a total of