94 
The N.Z. Journal of Science and Technology. 
[Mar. 
The centre, shown in the chart south of New Zealand, was only one of 
several existing in this anticyclone, which proved to be an exceptionally 
extensive one and reached over almost the whole of Australia. After the 
front had moved farther eastward conditions improved in the eastern 
districts, the centre following taking apparently a more northerly track over 
the Dominion. 
Variation in Annual Rainfall. 
When referring to fig. 2 it was pointed out that the normal position 
of the east-west axis of anticyclones is different in summer and winter. In 
summer the mean track is a little south of Auckland, while in winter it is 
along the latitude of the Kermadec Islands. In some years, however, the 
movement of these “ highs ” is much farther north or south of the normal 
path, and this extreme migration has an important bearing on the climate 
of certain portions of New Zealand, especially with regard to the annual 
amount of rainfall. The effect is particularly noticeable in the case of the 
North Auckland district, and the annual rainfall records of the city of 
Auckland present some interesting features in years when the anticyclonic 
track has been abnormal. For instance, in 1914, which was a year when the 
high-pressure belt was in more northern latitudes than usual, the fall was 
only 28-42 in. (— 35 per cent, of mean), while in 1916 and 1917, when the belt 
had receded south of its normal track, the total falls were 66-36 in. (+ 52 per 
cent, of mean) and 74-15 in. (+ 70 per cent, of mean) respectively. 
The district of Canterbury is affected chiefly by the more northern 
position of the belt, and the rainfall does not show any marked effect from 
the southern extension. In 1914 the total year’s fall at Christchurch was 
19-90 in. (— 21 per cent, of mean). In 1916 and 1917, however, the rain¬ 
fall was about the average, but slightly above it in the latter year. The 
rainfall returns for Dunedin, which may be taken as representative of the 
southern districts, in some cases show a fall below the average when that 
at Auckland in the same year of abnormal anticyclonic movement is above 
it; but this rule is by no means consistent in the records, and so it would 
appear that the extreme south is not greatly affected by the variation from 
the normal of the anticyclonic track in any year. 
The excessive rainfall in the northern districts when the high-pressure 
systems move in higher latitudes is brought about by the greater number 
of extra-tropical cyclones, which are then able to approach within effective 
range of the northernmost portion of New Zealand. On the other hand, 
when the high-pressure areas are in lower latitudes, Antarctic or westerly 
depressions extend farther north, and the west-coast and southern districts 
of the South Island receive heavy rains. The conclusion to be drawn is 
that in years when extra-tropical cyclones are more numerous Antarctic or 
westerly areas of low pressure are less in evidence, and vice versa , and this 
the records have generally proved. 
Since the annual rainfall at Auckland shows a marked relationship to 
the abnormal positions of these anticyclonic belts, it might be expected to 
show evidences of any cyclical movement if any such existed, but from 
records which extend back to 1864 no definite periods in the intervals of 
maximum or minimum swings of the anticyclonic belts can be deduced. 
The periods between the years of maximum rainfall, and also between the 
years of minimum rainfall, appear to be altogether irregular, ranging from 
one to ten years for the former and one to eight years for the latter. The 
mean period in both cases is 4-4 years. 
(To be continued.) 
