4:15 PM - 4:30 PM
[MAG33-08] Assessment of the Atmospheric Environment and Precipitation at the Time of the Atomic Bombing of Hiroshima
– Based on meteorological data rescue –
Keywords:Meteorological Reanalysis Data, Data Rescue, Non-hydrostatic model
Reproducing the atmospheric environment at the time of the atomic bombing on August 6, 1945 is a very challenging task. While testimonies of exposure and black rain are being archived, attempts are being made to reconstruct the environment of the time. Observation over Japan and surrounding oceans during the war are far fewer than today, but valuable meteorological observations continue to be made, which have not yet been incorporated into the reanalysis data. Digitization of these data would be significant for the verification and uncertainty evaluation of the simulation of the atmospheric environment, and for the preparation of synthetic atmospheric and surface data in the future, as the only country exposed to the atomic bombings during wartime.
We have digitized the following data.
(1) Sonde observations at Tateno, Ibaraki Prefecture (from Aoyama et al. 2013)
(2) Surface meteorological data in and around Hiroshima (from the Digital Typhoon Site).
This study reports 1) a comparison and validation of the historical reanalysis data OCADA, and ECMWF ERA5, and 2) the validation results of the explosion and urban fire experiments with WRF and ERA5 (presented by Ishikawa et al. in this session).
1) OCADA's 80 ensemble averages and ensemble spreads were compared with ERA5's 10-member ensemble averages and spreads according to (1). At Tateno, the wind speed and direction in the lower troposphere (750-900 hPa) was 4 m/s, with a northerly wind at 900 hPa and an easterly prevailing from 750-850 hPa. In the middle level (700-400hPa), wind speeds were 2-8 m/s with northwesterly winds dominant, and in the upper level (350-250hPa), wind speeds were 2-8 m/s with westerly to northwesterly winds dominant (8/6 6JST and 9JST). The ensemble averages are in good agreement with the vertical profiles of the sonde wind speeds for both OCADA and ERA5, and ensemble spread of ERA5 is smaller than that of OCADA. On the other hand, both reanalyses showed similar wind directions above 600 hPa, and both reanalyses showed westerly winds in the 300-250 hPa layer (observation was the northwest). The wind direction in the lower atmosphere was significantly different between the two reanalyses, with ERA5 showing northerly to easterly winds close to the sonde observations, while OCADA showed northwesterly winds. The center location, intensity, and pressure gradient of the Pacific High in both reanalyses are slightly different, and this difference is also responsible for the difference in wind direction over Hiroshima. ERA5 shows a west-northwestward wind direction at around 700 hPa, and therefore, it is expected that the WRF experiment using ERA5 as a boundary condition for simulating the spread of black rain in the northwestward direction from the hypocenter will show a distribution close to the actual one.
2) The simulation results of the WRF explosion and urban fire experiment using ERA5 as the initial boundary condition were verified by correcting for the bias of the barometer at that time and calculating specific humidity values from the ground meteorological observation records (wind direction, wind speed, pressure, temperature and relative humidity) at the Hiroshima weather Station (now Hiroshima city Ebayama museum of meteorology). The Hiroshima weather station is located on a hill (Mt. Eba) near the coast to the south of the hypocenter. A staff of the meteorological observatory at the time recorded that the explosion and combustion also increased wind velocity and specific humidity by drawing the surrounding lower atmosphere. Although the supply of water vapor in the lower layers is considered important for the development and organization of clouds that produce black rain, the specific humidity values from noon to afternoon underestimated the observed values in all experiments.
We have digitized the following data.
(1) Sonde observations at Tateno, Ibaraki Prefecture (from Aoyama et al. 2013)
(2) Surface meteorological data in and around Hiroshima (from the Digital Typhoon Site).
This study reports 1) a comparison and validation of the historical reanalysis data OCADA, and ECMWF ERA5, and 2) the validation results of the explosion and urban fire experiments with WRF and ERA5 (presented by Ishikawa et al. in this session).
1) OCADA's 80 ensemble averages and ensemble spreads were compared with ERA5's 10-member ensemble averages and spreads according to (1). At Tateno, the wind speed and direction in the lower troposphere (750-900 hPa) was 4 m/s, with a northerly wind at 900 hPa and an easterly prevailing from 750-850 hPa. In the middle level (700-400hPa), wind speeds were 2-8 m/s with northwesterly winds dominant, and in the upper level (350-250hPa), wind speeds were 2-8 m/s with westerly to northwesterly winds dominant (8/6 6JST and 9JST). The ensemble averages are in good agreement with the vertical profiles of the sonde wind speeds for both OCADA and ERA5, and ensemble spread of ERA5 is smaller than that of OCADA. On the other hand, both reanalyses showed similar wind directions above 600 hPa, and both reanalyses showed westerly winds in the 300-250 hPa layer (observation was the northwest). The wind direction in the lower atmosphere was significantly different between the two reanalyses, with ERA5 showing northerly to easterly winds close to the sonde observations, while OCADA showed northwesterly winds. The center location, intensity, and pressure gradient of the Pacific High in both reanalyses are slightly different, and this difference is also responsible for the difference in wind direction over Hiroshima. ERA5 shows a west-northwestward wind direction at around 700 hPa, and therefore, it is expected that the WRF experiment using ERA5 as a boundary condition for simulating the spread of black rain in the northwestward direction from the hypocenter will show a distribution close to the actual one.
2) The simulation results of the WRF explosion and urban fire experiment using ERA5 as the initial boundary condition were verified by correcting for the bias of the barometer at that time and calculating specific humidity values from the ground meteorological observation records (wind direction, wind speed, pressure, temperature and relative humidity) at the Hiroshima weather Station (now Hiroshima city Ebayama museum of meteorology). The Hiroshima weather station is located on a hill (Mt. Eba) near the coast to the south of the hypocenter. A staff of the meteorological observatory at the time recorded that the explosion and combustion also increased wind velocity and specific humidity by drawing the surrounding lower atmosphere. Although the supply of water vapor in the lower layers is considered important for the development and organization of clouds that produce black rain, the specific humidity values from noon to afternoon underestimated the observed values in all experiments.