Atmospheric focusing

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image of an explosion with a labeled shock wave

Atmospheric Focusing[]

Atmospheric focusing occurs when a shock wave is produced and impacted by conditions in the atmosphere. Examples of this are seen during supersonic booms, large extraterrestrial impacts from objects like meteors, and nuclear explosions.

Shock waves are focused and refracted horizontally by density variations in the atmosphere. They can have impacts in localized areas much further away than the theoretical extent of its blast effect. 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.^[1] 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 (${\displaystyle 1/r^{2}}$falloff for weak shock or acoustic waves, as expected at large distances).  

Supersonic Booms[]

Atmospheric focusing from supersonic booms is a modern occurrence and a result of the actions of air forces across the world.^[1] When objects like planes travel faster than the speed of sound, they create sonic booms and pressure waves that can be focused.^[1] Atmospheric factors present when these waves are created can focus the waves and cause damage.^[1]

Planes can also create boom waves and explosion waves that can be focused.^[1] Consideration for atmospheric focusing in flight plans is critical. The wind and altitude during a flight can create environments for atmospheric focusing.^[1] When this is the case, the flight should not persist through these conditions. To determine this, flights consider a focusing curve. If the conditions are above the curve, atmospheric focusing can occur and there may be damage on the ground.^[1]

Meteor Impacts[]

Meteors can also cause shock waves that can be focused.^[2] As the meteor enters Earth’s atmosphere and reaches lower altitudes, it can create a shock wave.^[2] The shock wave is impacted by what the meteor is made of, temperature, and pressure.^[1] Because the meteors need to have a large size and mass, there is only a small percentage of meteors that can create these shock waves.^[2] Radar and Infrasonic methodologies are able to detect meteor shock waves. These tools are used to study these shock waves and can help create new methods of learning about meteor shock waves.^[2]

Nuclear Explosions and Bombs[]

Nuclear explosions and bombs can also lead to atmospheric focusing. The effects of focusing may be found hundreds of kilometers from the blast site. An example of this is the case of the Tsar Bomba test, where damage was caused up to approximately 1,000 km away. Atmospheric focusing can increase the damage caused by these explosions.^[3]

See also[]

• Knudsen number
• Nuclear weapons testing
• Rankine–Hugoniot conditions

References[]

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