... airburst: 20 kiloton

... this illustration by famed artist Chesley Bonestell depicts a Hiroshima sized atomic bomb detonating at several thousand feet above a major American city. Detonating the weapon at an altitude above the target maximized blast damage. Illustrations like this, in major publications, helped to personalize the specter of atomic war. Producing both anti-war sentiment and anti-communist paranoia.

... here is a depressing British documentary about the effects of a bomb 500 times larger detonated over London- http://www.youtube.com/watch?v=7AYMS1po0L8