地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
オーストラリアにおける降水量変動の長期傾向の地域差
岩崎 一孝
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ジャーナル フリー

1984 年 93 巻 1 号 p. 15-29

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Residual mass curves of annual summer and winter rainfall are examined from 52 widely spread stations in Australia to clarify the spatial difference of long-term rainfall trends. The calendar year is not used to compute the annual rainfall, because the calendar year divides a summer into two. The annual rainfall is defined as the total rainfall of 12 months from December of the year before to November. The summer rainfall is defined as the total rainfall during the 3 months of December, January and February within the defined annual cycle. The winter rainfall, of June, July and August. The quantity plotted in the graphs is given by,
Xi=100×∑in=1(rn-r/ra)-C
where rn. is the annual, summer or winter rainfall for the n th year of the record and the mean annual, summer or winter rainfall I has been computed for the standard 60-year period 1920-1979. ra is the mean annual rainfall. By dividing by the mean annual rainfall, the degree of contribution of summer and winter rainfall to annual rainfall can be made clear. The constant C is the summation extending from the beginning of the record to 1919,
C=100×∑tn=1(rn-r/ra)
where t is the years from the first record to 1919.
Residual mass curves are primarily classified into two types:
Type S: Summer rainfall curve is more similar to annual rainfall curve than winter rainfall curve (Fig. 2-a).
Type W: Winter rainfall curve is more similar to annual rainfall curve (Fig. 2.b). Each type is classified into sub-types (Fig. 3).
Type Se: The curve of annual rainfall shows downward trend in the former half of this century. This downward trend continues till 1960's in the region of Se-I. The curve shows upward trend in the latter half of this century in the region of Se-II (Figs. 4-a, b).
Type Sw: The curve shows upward trend from the end of the 19 th century up to 1920's, then downward trend up to 1960's. Each curve also shows short-term fluctuation as well as long-term trend (Fig. 4-c).
Type We: The curve shows upward trend in the 19 th century. This trend continues up to 1940's or 1950's in the regions of We-Ia and We-Ib, then the curve turns downward. In the region of We-Ib, downward trend is shown in 1920's and 1930's. The curve shows downward trend in the region of We-II in the former half of this century, then turns upward (Figs. 5-a, b).
Type Ww: The curve shows downward trend in the 19th century. Upward trend shows in the former half of this century in the region of Ww-I, downward trend again since 1950's. The curve shows upward trend in the beginning of this century then turn downward in the middle of this century, upward again in 1960's and 1970's in the region of Ww-(Figs. 5-c, d).
It is assumed that the east-west difference in long-term trends of rainfall is explained by the location of the deeper trough among the subtropical anticyclones presented in monthlymean sea-level pressure charts, and the south-north difference in the region W is explained by the difference of the origin of vapor shown in the precipitable water (1000-500 mb) distribution map (Figs. 6, 7, 8).

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