Abstract
During the last 300 years, most of the poor rice harvests caused by unusual cool summers and leading to famine conditions in the Tohoku district (the northeastern part of Japan), took place just after the great volcanic eruptions.
An analysis of instrumental observations in the past century on the Kinkasan Island indicates that, though the standard deviation in the summer air temperature is 1.1°C for 1882–1985, the summer air temperature averages 1.3±0.5°C lower than normal during the summer following the great volcanic eruptions, the mid- latitudinal mean surface air temperature in the northern hemisphere decreased only about 0.2°C. This result indicates that the summer air temperature in Tohoku district tends to be particularly sensitive to such eruptions. In all the cool summers a blocking high persisted over the ocean northeast of Japan, and impeded the northward movement of the “Raiu” front (the stagnating polar front during the early summer).
Exceptionally cool summers occurred frequently without great volcanic eruptions during 1931-45. During this period, the sea water temperatures at Tohoku's coastal stations on the Pacific were lower by 1.5°C, on the average, than those of the subsequent period of 1946–79.
