A Lower Bound on the Altitude of the Hiroshima Firestorm Plume From Ray Optics

Abstract Projections of nuclear winter are critically sensitive to the height of soot lofted by firestorms, yet direct observations of firestorm plumes are scarce. Here, a lower bound is established for the height of the Hiroshima firestorm plume 97 min after detonation. This bound is obtained via a ray‐optics calculation using the Enola Gay 's flight log, which gives the location and time when the plume was last visible. Profiles of the atmosphere's refractive index are taken from three reanalyses (ERA5, CERA‐20C, and 20CR), and uncertainties in the aircraft's distance, altitude, and the atmospheric profile are propagated via Monte Carlo. With 95% confidence, the firestorm plume top exceeded km, which means that soot was lofted well into the upper troposphere, consistent with nuclear‐winter scenarios.