3:45 PM - 4:00 PM
[MAG33-06] Numerical Realization of the ‘Black-Rain’ event associated with Hiroshima Nuclear Bombing
Keywords:Atomic Bombing in Hiroshima, Black-rain, Numerical weather modeling, Historical reanalysis
Why did it rain, in the first place, with the explosion of the nuclear bomb? Even if an atmospheric nuclear experiment was conducted in a nuclear test site located in a desert area, it probably would not rain. This is because the atmosphere is dry and there is no "water" to produce precipitation. Precipitation is brought about by developed cumulus convection, and nuclear explosions trigger the generation of cumulus convection. The black rain in Hiroshima and Nagasaki is thought to have been triggered by the atomic bomb and subsequent city fires in the humid environment of summer in Japan. Ideal numerical experiments of supercell storms provide a bubble (positive temperature anomaly) trigger with an energy of 1014-1015 [J]. The total energy of the Hiroshima bomb is estimated to be O(1013) [J], which is not large in total amount, but is concentrated in a small area. In comparison, the energy of a city-area fire is much larger and more continuous, and is the major driving force that generates and maintains cumulus convection. In this study, downscaled calculations using the Weather Research and Forecasting (WRF) Model is used to calculate the local meteorology in the Chugoku region centering on Hiroshima, and to determine what kind of precipitation and mass deposition are caused by the atomic bomb explosion and subsequent city fires.
In 1945, upper meteorological observations were almost nonexistent, and reanalysis data had not been created to be used as input for local meteorological models. Recently, however, historical reanalysis data such as 20CRv3, ERA-20C, and OCADA, which were obtained by reanalysis using only ground pressure observations, have been released by the NOAA, the ECMWF, and the MRI/JMA, respectively. Using these data, it is now possible to perform downscaling calculations far back into the past. Historical reanalysis data are produced as ensemble averages of calculations with slightly different conditions to compensate for the paucity of input meteorological observations, so it is always necessary to take into account the range of variability of the ensemble members. On the other hand, very recently, the ECMWF has released modern reanalysis data (ERA5) dating back to 1940. Though the lack of upper-level meteorological observation data is the same in ERA5, but ERA5 utilizes the available data as possible. For surface observation data, full-specification data assimilation is performed incorporating observation elements other than surface pressure.
August 6, 1945, when the atomic bomb was dropped on Hiroshima, was a hot day with the Pacific High covering western Japan to the Korean Peninsula, where local circulation such as sea-land and mountain-valley winds dominates. Model forecasting is difficult in such a case with weak synoptic forcing. Therefore, we started with calculations to check the robustness of the model and the adequacy of the physical parameterization for similar cases in recent years, where both input and validation meteorological data are well available. In the black rain calculation for August 6, 1945, three different meteorological inputs, 20CRv3, OCADA and ERA5 are used as input. For ERA5 and OCADA, calculations with 10 and 80 ensemble members, respectively, were also performed to show the variability of the results. A summary of the calculations of the results obtained so far is below:
- Precipitation occurred with the heat sources of A-bomb Explosion and city fire
- The city fire has greater impact on the precipitation than the A-bomb
- The calculated precipitation areas are comparable in size to the previously reported distributions, but there are not a few differences in shape and direction of distribution. Especially in calculations using historical reanalysis data, there are large uncertainties in the calculation results due to the large variability among ensemble members.
In the presentation, results of calculations of diffusion and deposition of radioactive materials will also be discussed.
In 1945, upper meteorological observations were almost nonexistent, and reanalysis data had not been created to be used as input for local meteorological models. Recently, however, historical reanalysis data such as 20CRv3, ERA-20C, and OCADA, which were obtained by reanalysis using only ground pressure observations, have been released by the NOAA, the ECMWF, and the MRI/JMA, respectively. Using these data, it is now possible to perform downscaling calculations far back into the past. Historical reanalysis data are produced as ensemble averages of calculations with slightly different conditions to compensate for the paucity of input meteorological observations, so it is always necessary to take into account the range of variability of the ensemble members. On the other hand, very recently, the ECMWF has released modern reanalysis data (ERA5) dating back to 1940. Though the lack of upper-level meteorological observation data is the same in ERA5, but ERA5 utilizes the available data as possible. For surface observation data, full-specification data assimilation is performed incorporating observation elements other than surface pressure.
August 6, 1945, when the atomic bomb was dropped on Hiroshima, was a hot day with the Pacific High covering western Japan to the Korean Peninsula, where local circulation such as sea-land and mountain-valley winds dominates. Model forecasting is difficult in such a case with weak synoptic forcing. Therefore, we started with calculations to check the robustness of the model and the adequacy of the physical parameterization for similar cases in recent years, where both input and validation meteorological data are well available. In the black rain calculation for August 6, 1945, three different meteorological inputs, 20CRv3, OCADA and ERA5 are used as input. For ERA5 and OCADA, calculations with 10 and 80 ensemble members, respectively, were also performed to show the variability of the results. A summary of the calculations of the results obtained so far is below:
- Precipitation occurred with the heat sources of A-bomb Explosion and city fire
- The city fire has greater impact on the precipitation than the A-bomb
- The calculated precipitation areas are comparable in size to the previously reported distributions, but there are not a few differences in shape and direction of distribution. Especially in calculations using historical reanalysis data, there are large uncertainties in the calculation results due to the large variability among ensemble members.
In the presentation, results of calculations of diffusion and deposition of radioactive materials will also be discussed.