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宮原 (2014), pp.109,110
古日記などの文書の記録を用いた気候復元方法もあります。
日々の気象の状態が記録されている場合もありますし、花の開花日や紅葉などの日付が残されている場合があります(図3-2)。
植物生理学に照らし合わせることによって、開花や紅葉の日付から気温などの情報を得ることができるのです。
たとえば、何℃以上の気温の日が何日以上続くと開花する、というような規則性を使います。
それ以外に、果実の収穫日などの記録が残されている場合などもあります。
フランスのブルゴーニュ地方のワイナリーに残されたブドウの収穫日から気温の変動を復元した例もあります。
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青野・数井 (2007)
Changes in springtime temperature in Kyoto, Japan, since the 9th century were reconstructed, using the phenological data series for cherry tree (Prunus jamasakura), deduced from old diaries and chronicles.
Phenological data for 732 years was made available by combining data from previous studies.
The full-flowering date of cherry trees fluctuates in accordance with temperature conditions during February and March.
Full-flowering dates were closely related to the March mean temperature by means of a temperature accumulation index, in which plant growth is considered to be an exponential function of temperature.
Calibration enabled accurate estimation of temperatures in the instrumental period, after 1880; the root mean square error (RMSE) of temperature estimates was determined to be within 0.1 °C, after smoothing by local linear regression over time spans of 31 years.
The results suggested the existence of four cold periods, 1330–1350, 1520–1550, 1670–1700, and 1825–1830, during which periods the estimated March mean temperature was 4–5 °C, about 3–4 °C lower than the present normal temperature.
These cold periods coincided with the less extreme periods, known as the Wolf, Spoerer, Maunder, and Dalton minima, in the long-term solar variation cycle, which has a periodicity of 150–250 years.
The sunspot cycle length, a short-term solar variation cycle, was also compared with the temperature estimates, with the result that a time lag of about 15 years was detected in the climatic temperature response to short-term solar variation.
| Inter-annual variation of the full-flowering dates of the cherry tree, P.Jamasakura, at Kyoto, acquired from old diaries and chronicles
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引用/参考文献
宮原ひろ子 (2014) :
『地球の変動はどこまで宇宙で解明できるか』, 化学同人 (DOJIN選書), 2014.
青野靖之, 数井敬子 (2007) :
Phenological data series of cherry tree flowering in Kyoto, Japan, and its application to reconstruction of springtime temperatures since the 9th century
International Journal of Climatology, vol.28(7), 2007. pp.905-914
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