XI: Meteorological Observations
The Hiroshima Meteorological Observatory is situated 2.3 miles from the hypocenter, and nearly 1000 feet high on Mr. Eba. When the shock wave struck, more than half of the doors were wrenched off and iron window sashes twisted like toffee. Glass darted about, piercing human bodies and the concrete wall with equal force. The twenty-five workers at the station suffered other injuries as well, including legs broken by flying wooden screens, and burns received out of doors. The seismograph inside the building was destroyed, but instruments housed in special shelters in the lee of the building continued to function. The staff, after applying rough first aid to wounded and blood-covered bodies, went on with their work.
Before dawn, the sky had been beautifully clear, but around six it grew slightly cloudy. High tide came at 8:05 and the wind was just shifting inland when at 8:15 the bomb exploded. On seeing the flash, the men began to count, out of habit. Five seconds later, the shock wave struck the station, indicating it had travelled about 2,300 feet per second, more than twice the speed of sound. A radioactive atomic bomb cloud boiled upward, writhing and twisting.
Some five minutes later, the crew saw smoke rising from fires here and there in the city, and in half an hour there was general conflagration, which reached its peak about two in the afternoon. Between ten and eleven in the morning thunder sounded and heavy showers fell in the northwest section of the city and as far as 18 miles away, but blue skies were visible over the southern half of Hiroshima all day.
By evening, the fires were dying down and the radioactive cloud had shifted from cumulo-nimbus to stratocumulus, but was not dispelled until the following morning.
The average temperature of the day was 81.4° with a peak of 87.8°. Humidity averaged 77.8%. It was unbearably sultry.
With the high tide, the rivers ran deep and over the heads of the people who had jumped in to escape the fire. Women and children who could not swim, and people weak to keep afloat were drowned. Then, as the tide fell and the rivers flowed more swiftly, countless victims swept out to sea.
Black Rain
At the time of the burst, dust, soot and earth had been thrown upward in a black cloud. Mingling with radioactive particles and cooling water vapor, they fell again as a heavily radioactive, sticky, black rain, between 8:30 A.M. and 12:45 P.M. The temperature dropped and naked victims shook with the cold. Gradually turning to ordinary rain, the showers lasted in some places for two hours. Toward the southeast the duration of the fall was less, and Ujina, Hijiyama and Senda Machi had none. None fell on the Meteorological Station, but at Koi, Yokogawa and Takasu there were downpours, with drops like huge hailstones.
Fifty or more days later, the earth where the black rain had fallen was tested and found many times more radioactive than earth directly below the burst. As a result of this strange rain, carp in ponds and river catfish and eels died and floated to the surface, but shrimps and crabs survived. Cattle that ate that ate grass contaminated with it became diarrhetic. Most of the people living in areas where it fell were still suffering diarrhea even three months later, probably because water pipes being broken, they drank from wells into which the black rain had seeped.
One case is recorded of a child who had not been exposed to the bomb, but slept with his head toward a wooden shutter that had been soaked by the black rain. His hair fell out. The insects that infested the rice fields were killed, but the rice that was not burned grew lushly, as though some special fertilizer had been applied. The farmers had a brief time to enjoy the prospects of a fine harvest, before typhoons and floods in September and October burst the bubble of their hopes.
Whirlwind
Strong whirlwinds developed here and there in the northern half of the city between eleven in the morning and two in the afternoon. The three rivers of Ota, Kyobashi and Kanda seemed to produce whirlwinds when cool air over the water met air heated by fires on both sides.
Oil drums whirled and tin roofing was peeled off and thrown aloft near Tokiwa Bridge. Steel plates over an inch thick circled through the air beside Ota River. A straw hamper filled with kimono danced upward near Yanagi Bridge. Adults and children, too, though the number is not known, were whirled up in the winds at Sakae Bridge.
At Hiroshima Station, a passenger car started to roll of itself, and at Yokogawa Station, burning timbers were thrown into the air. From one spot on the Kanda River, the water - rose six to eight feet in the air. These reports were gathered later by the tireless efforts of the meteorological staff.