Fluctuations of Global Solar Radiation in Japan during the First Half of the 19th Century as Estimated from Historical Weather Records

Abstract

 Many historical documents in Japan include daily weather records. To reconstruct historical climates from daily weather records, Ichino et al. (2001) constructed a method for estimating global solar radiation based on daily weather conditions. Presented is an attempt to reconstruct monthly mean solar radiation during the first part of the 19th century based on weather records found in 11 historical documents, with special attention to records in the year 1836, when a famine occurred. Global solar radiation is an important factor in the energy balance of the Earth, and is also fundamental to the hydrological cycle and agricultural productivity. This implies that reconstructing global solar radiation involves investigations into climatic physics and historical human societies. The estimated monthly means of global solar radiation in 1836 are compared to average estimations for 30 years (1821-1850), including the 1830s, at 11 points in Japan where data are generally available. According to our estimation, the values of solar radiation in July and August 1836 were smaller than their provisional normal values, which is the average for 30 years (1821-1850), at all points except those in Tohoku and southern Kyushu, although these differences were not extreme. On the other hand, fluctuations during the 1830s were larger than other decades before and afterwards. Moreover, the estimations in spring (February, March, and April) and autumn (September, October, and November) were no smaller than the average estimations. These results show an anomalously low solar radiation in July and August, which might have been a key climatic condition affecting society in the famine year.