“The Little Ice Age” started in the 17th century and ended in the middleof the 19th century in Central Japan. The reconstruction of climatic conditions during the Little Ice Age was attempted, based on old documentary records. There are many old documents in which daily weather conditions were recorded. Those records were collected and arranged according to the order of dates. Through the works, weather diagrams were compiled for the historical times in Central Japan. By analyzing the diagrams, some climatic conditions during the historical times (from the end of the 18 th century to the middle of the 19 th century) were reconstructed for Central Japan. The main results are shown as follows.
(1) Winter season temperatures were very low in the 1810's and the 1820's. After that it tended to become warmer gradually.(2) Precipitation amounts in winter on the Pacific coastal region is small. However after the 1830's, it increased to the present level.(3) Frequency of the appearance of the winter monsoonal flow pattern was higher in the 1810's and 1820's, and it became lower in the 1830's.(4) The end of the Bai-u season was delayed in the 1780's, 1830's and 1890's. In those periods, cool summers appeared in northern Japan frequently.(5) Heavy rainfalls frequently occurred during the Bai-u season in the middle of the 19th century. On the contrary, rainfall amounts during the Bai-u season were very small in the beginning of the 19th century.(6) In the beginning of the 19th cent ury, climatic condition of summer season was dry with little rain. Conversely, it is wet and much rain in the middle of the 19th century.
There were some differences in climatic conditions between the early period and th e middle period of the 19th century. The main causes that bring these differences may have been the changes in general circulation patterns over East Asia. By comparing the climatic conditions in several different regions, the relationship between climatic changes andgeneral circulation patterns will be clarified.
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