Atmospheric focusing is a type of wave interaction causing

shock waves In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...

to affect areas at a greater distance than otherwise expected. Variations in the atmosphere create distortions in the wavefront by

refracting In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

a segment, allowing it to converge at certain points and constructively interfere. In the case of destructive shock waves, this may result in areas of damage far beyond the theoretical extent of its blast effect. Examples of this are seen during supersonic booms, large extraterrestrial impacts from objects like

meteors A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mic ...

, and

nuclear explosion A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, t ...

Density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

variations in the atmosphere (e.g. due to temperature variations), or airspeed variations cause refraction along the shock wave, allowing the uniform wavefront to separate and eventually interfere, dispersing the wave at some points and focusing it at others. A similar effect occurs in water when a wave travels through a patch of different density fluid, causing it to diverge over a large distance. For powerful shock waves this can cause damage farther than expected; the shock wave

energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extract ...

will decrease beyond expected values based on uniform geometry (

1/r^2

falloff for weak shock or acoustic waves, as expected at large distances).

Types of atmospheric focusing

Supersonic booms

Atmospheric focusing from supersonic booms is a modern occurrence and a result of the actions of

air force An air force – in the broadest sense – is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an a ...

s across the world. When objects like planes travel faster than the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...

, they create sonic booms and pressure waves that can be focused. Atmospheric factors present when these waves are created can focus the waves and cause damage. Planes can also create boom waves and explosion waves that can be focused. Consideration for atmospheric focusing in

flight plan Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service Provider (e.g. the FAA in the United States) prior to departure which indicate the plane's planned route or flight path. Flight plan format is ...

s is critical. The

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...

and

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

during a flight can create environments for atmospheric focusing. 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.

Meteor impacts

Meteors can also cause shock waves that can be focused. As the meteor enters Earth’s atmosphere and reaches lower altitudes, it can create a shock wave. The shock wave is impacted by what the meteor is made of, temperature, and pressure. Because the meteors need to have a large size and

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

, there is only a small percentage of meteors that can create these shock waves.

Radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

and

Infrasonic Infrasound, sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perce ...

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.

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 The Tsar Bomba () ( code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation "AN602", was a thermonuclear aerial bomb, and the most powerful nuclear weapon ever created and tested. Overall, the Soviet physicist Andrei Sa ...

test, where damage was caused up to approximately 1,000 km away. Atmospheric focusing can increase the damage caused by these explosions.

References

Shock waves Nuclear weapons {{Climate-stub

Types of atmospheric focusing

Supersonic booms

Meteor impacts

Nuclear explosions and bombs

See also

References