Progress in Earth and Planetary Science

There has been a societal controversy in Japan for many years regarding the estimation of the area of the "Black Rain" that occurred soon after the atomic bombings of Hiroshima and Nagasaki in 1945. Estimates of the area have been constructed primarily on the basis of testimonies and experiences, but there is a scarcity of material evidence from which the area can be estimated. The "Black Rain" consists of a complex mixture of radioactive materials from the A-bomb, dust generated by the shock wave, and the smoke of the city fire, etc. Typically, the precipitation colored black, but some testimonies suggest that it was muddy rain, colorless, etc. We define the "Black Rain" here as a comprehensive term for fallout in the vicinity (close-in fallout), including dry deposition processes. Since January 2021, we have been conducting research focusing on the following two subjects in order to contribute to resolve the issue. In this special issue, we introduce (1) the reproduction of the "Black Rain" by using meteorological simulation models including explosion and urban fires, and (2) efforts to clarify the geographical distribution and characteristics of fallout by analyzing it, which will contribute to better understand of the affected area caused not directly by ionizing and heat radiations from nuclear explosion but by the "Black Rain". The presentation will also attempt to organize relating information on the "Black Rain".

Edited by: Koichi Takamiya, Jun Inoue, Hiromi Yamazawa, Mathew Johansen, livier Masson