I'm modelling the Hiroshima nuclear explosion on a real time real scale physics simulator. My initial simulations based on data accumulated from wikipedia such as temperature of the fireball the radius of it and using air pressure and air density data based on the detonation height of 600m has yielded a surprising result of the mushroom cloud reaching supersonic speeds as it rises like a balloon upward and creating a shockwave of its own that might have been the shockwave the pilots of the "Enolagay" felt 11 miles away. I also simulated drag and the change of drag coefficient of a sphere shaped object namely the fireball. Can you guys confirm if mushroom clouds reach supersonic speeds rising up? And if they make a shockwave of their own after the initial explosion that would have caused the first shockwave? Image Description: The screenshots of my simulation software shows a simplified model of the Earth with the tallest building of the world and mount Everest in view to allow players to have a sense of scale, the atmosphere also changes shades every 1km upward . The red circles are soundwaves that travel at the speed of sound based on the height they were spawned. The fireball changes color as it cools from 6,000 C and becomes invisible at 15degC. The fireball has a diameter of about 370m and expands gradually.