Reconstruction of Weather and Path of a Disastrous Typhoon that Struck Central Japan in 1742

Abstract

 To clarify the cause of heavy rains and weather related to a famous disaster that occurred in 1742, the weather sequence and its spatial distribution were investigated on the basis of local historical documents obtained from various areas of central Japan. As a result, the eastward movement of a typhoon was reconstructed in the sea off the south coast of central Japan. It was accompanied by an inflow of moist air around the eastern fringe of the typhoon, which brought about a rain zone extending from Kinki to Kanto from 27^th Jul. to 1^st Aug., according to the lunar calendar used at that time. The typhoon abruptly turned north when it reached southern Kanto and proceeded north across Honshu. It was accompanied by heavy rains and strong winds on 1^st and 2^nd Aug., which were recorded in central and western Kanto and areas further north. The abrupt change of direction seems to have been caused by a strong anticyclone that is thought to have extended to the east coast of Kanto. Although this situation around an anticyclone occurs frequently in late Summer, not enough evidence has been obtained yet on the situation at that time. The heavy rains and induced landslides caused floods particularly in the Ara, Tone, and Chikuma river basins. This is a matter of concern from the viewpoint of a fluvial geomorphic system analysis.