Atmospheric focusing

Atmospheric focusing is a phenomenon occurring when a large shock wave is produced in the atmosphere, as in a nuclear explosion or large extraterrestrial object impact. The shock wave is refracted horizontally by density variations in the atmosphere so that it can have impacts in localized areas much further away than the theoretical extent of its blast effect. In large bombs, some effects may thus be found hundreds of kilometers from the blast site (such as in the case of the Tsar Bomba test, where damage was caused up to approximately 1,000 km away).

This effect operates similarly to the patterns made by sunlight on the bottom of a pool, the difference is that the light is bent at the contact point with the water while the shock wave is distorted by density variations (e.g. due to temperature variations) in the atmosphere. Variations of wind can cause a similar effect. This will disperse the shock wave at some places and focus it at others. For powerful shock waves this can cause damage farther than expected; the shock wave energy density will decrease beyond expected values based on uniform geometry ($1/r^2$ falloff for weak shock or acoustic waves, as expected at large distances).