Mushroom cloud
Encyclopedia
Pyrocumulus cloud
A pyrocumulus, or literally fire cloud, is a dense cumuliform cloud associated with fire or volcanic activity.A pyrocumulus is similar dynamically in some ways to a firestorm, and the two phenomena may occur in conjunction with each other...
mushroom
Mushroom
A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
-shaped cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
of condensed water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
or debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
resulting from a very large explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
. They are most commonly associated with nuclear explosion
Nuclear explosion
A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed nuclear reaction. The driving reaction may be nuclear fission, nuclear fusion or a multistage cascading combination of the two, though to date all fusion based weapons have used a fission device...
s, but any sufficiently large blast will produce the same sort of effect. They can be caused by powerful conventional weapons like the GBU-43/B Massive Ordnance Air Blast bomb
GBU-43/B Massive Ordnance Air Blast bomb
The GBU-43/B Massive Ordnance Air Blast bomb is a large-yield conventional bomb developed for the United States military by Albert L. Weimorts, Jr. At the time of development, it was touted as the most powerful non-nuclear weapon ever designed...
. Volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
eruptions and impact event
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
s can produce natural mushroom clouds.
Mushroom clouds form as a result of the sudden formation of a large mass of hot, low-density gases near the ground creating a Rayleigh–Taylor instability. The mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a vortex ring
Vortex ring
A vortex ring, also called a toroidal vortex, is a region of rotating fluid moving through the same or different fluid where the flow pattern takes on a toroidal shape. The movement of the fluid is about the poloidal or circular axis of the doughnut, in a twisting vortex motion...
and drawing up a column of additional smoke and debris in the center to form its "stem". The mass of gas eventually reaches an altitude where it is no longer of lower density than the surrounding air and disperses, the debris drawn upward from the ground scattering and drifting back down (see fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
).
Origin of the term
Although the term itself appears to have been coined at the start of the 1950s, mushroom clouds generated by explosions were being described before the atomic era. For instance, The TimesThe Times
The Times is a British daily national newspaper, first published in London in 1785 under the title The Daily Universal Register . The Times and its sister paper The Sunday Times are published by Times Newspapers Limited, a subsidiary since 1981 of News International...
published a report on 1 October 1937 of a Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese attack on Shanghai
Shanghai
Shanghai is the largest city by population in China and the largest city proper in the world. It is one of the four province-level municipalities in the People's Republic of China, with a total population of over 23 million as of 2010...
in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
which generated "a great mushroom of smoke". The 1917 Halifax explosion
Halifax Explosion
The Halifax Explosion occurred on Thursday, December 6, 1917, when the city of Halifax, Nova Scotia, Canada, was devastated by the huge detonation of the SS Mont-Blanc, a French cargo ship, fully loaded with wartime explosives, which accidentally collided with the Norwegian SS Imo in "The Narrows"...
also produced one. During World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, descriptions of mushroom clouds were relatively common.
The atomic bomb cloud over Nagasaki, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
was described in The Times
The Times
The Times is a British daily national newspaper, first published in London in 1785 under the title The Daily Universal Register . The Times and its sister paper The Sunday Times are published by Times Newspapers Limited, a subsidiary since 1981 of News International...
of London of 13 August 1945 as a "huge mushroom of smoke and dust." On 9 September 1945, The New York Times
The New York Times
The New York Times is an American daily newspaper founded and continuously published in New York City since 1851. The New York Times has won 106 Pulitzer Prizes, the most of any news organization...
published an eyewitness account of the Nagasaki bombing, written by William L. Laurence
William L. Laurence
William Leonard Laurence was a Jewish Lithuanian born American journalist known for his science journalism writing of the 1940s and 1950s while working for the New York Times...
, the official newspaper correspondent of the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
, who accompanied one of the three aircraft that made the bombing run. He wrote of the bomb producing a "pillar of purple fire", out of the top of which came "a giant mushroom that increased the height of the pillar to a total of 45,000 feet."
Later in 1946, the Operation Crossroads
Operation Crossroads
Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. It was the first test of a nuclear weapon after the Trinity nuclear test in July 1945...
nuclear bomb tests were described as having a "cauliflower
Cauliflower
Cauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed...
" cloud, but a reporter present also spoke of "the mushroom, now the common symbol of the atomic age
Atomic Age
The Atomic Age, also known as the Atomic Era, is a phrase typically used to delineate the period of history following the detonation of the first nuclear bomb Trinity on July 16, 1945...
." Mushrooms have traditionally been associated both with life and death, food and poison, making them a more powerful symbolic connection than, say, the "cauliflower" cloud.
Physics
Blast wave
A blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localised volume. The flow field can be approximated as a lead shock wave, followed by a 'self-similar' subsonic flow field. In simpler terms, a blast wave is an area of...
. Immediately after detonation, the fireball itself begins to rise into the air, acting on the same principle as a hot-air balloon.
One way to analyze the motion, once the hot gas has cleared the ground sufficiently, is as a 'spherical cap bubble', as this gives agreement between the rate of rise and observed diameter.
As it rises, air is drawn upwards and into the cloud (similar to the updraft of a chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
), producing strong air currents known as "afterwinds", while inside the head of the cloud, the hot gases rotate in a toroidal
Vortex ring
A vortex ring, also called a toroidal vortex, is a region of rotating fluid moving through the same or different fluid where the flow pattern takes on a toroidal shape. The movement of the fluid is about the poloidal or circular axis of the doughnut, in a twisting vortex motion...
shape. When the detonation altitude is low enough, these afterwinds will draw in dirt and debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
from the ground below to form the stem of the mushroom cloud.
After the mass of hot gases reaches the equilibrium level
Equilibrium level
In meteorology, the equilibrium level , or level of neutral buoyancy , or limit of convection , is the height at which a rising parcel of air is at a temperature of equal warmth to it....
, the ascent stops and the cloud starts forming the characteristic mushroom shape.
Nuclear mushroom clouds
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
.
Detonations significantly below ground level or deep below the water (for instance, nuclear depth charges) also do not produce mushroom clouds, as the explosion causes the vaporization of a huge amount of earth and water in these instances. Detonations underwater but near the surface produce a pillar of water, which, in collapsing, forms a cauliflower-shape, which is mistaken for a mushroom cloud on many pictures (such as that seen in the well-known pictures of the Crossroads Baker
Operation Crossroads
Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. It was the first test of a nuclear weapon after the Trinity nuclear test in July 1945...
test). Underground detonations of low depth produce a mushroom cloud and a base surge, two different distinct clouds. The amount of radiation vented into the atmosphere decreases with increasing detonation depth.
With surface and air bursts, the amount of debris lofted into the air decreases rapidly with increasing burst altitude. At burst altitudes of approximately 7 meters/kiloton, a crater
Subsidence crater
A subsidence crater is a hole or depression left on the surface of an area which has had an underground explosion. Many such craters are present at the Nevada Test Site, which is no longer in use for nuclear testing....
is not formed, and correspondingly lower amounts of dust and debris are produced. The fallout-free height, above which the radioactive particles consist only of the fine fireball condensation, is approximately 55 meters/kiloton. However, even at these burst altitudes, fallout may be formed by a number of mechanisms.
At the moment of the explosion, the fireball is formed. The ascending, roughly spherical mass of hot, incandescent gases changes shape due to atmospheric friction and cools its surface by energy radiation, turning from a sphere to a violently swirling annular vortex. The vortex sucks air into its center, creating afterwinds and cooling itself. The speed of its swirling slows down as it cools, and may stop entirely during later phases. The vaporized parts of the weapon and other materials condense into visible dust, forming the cloud; the white-hot vortex core becomes yellow, then red, then loses visible incandescence. With further cooling, the bulk of the cloud grows as atmospheric moisture condenses. As the cloud ascends and cools, its buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
lessens, and its ascent slows.
If the fireball is comparable to the size of atmospheric density scale height
Scale height
In various scientific contexts, a scale height is a distance over which a quantity decreases by a factor of e...
, the movement of the cloud will be ballistic, overshooting large volume of denser air to greater altitudes. Significantly smaller fireballs produce clouds with buoyancy-governed ascent.
After reaching the tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
, the region of strong static stability, the cloud tends to slow its ascent and spread out. If it contains sufficient energy, part of it may continue rising up into stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
. A mass of air ascending from troposphere to stratosphere leads to formation of acoustic-gravity wave
Gravity wave
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media which has the restoring force of gravity or buoyancy....
s, virtually identical to those created by intense stratosphere-penetrating thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s. Smaller scale explosions generate waves of higher frequency, classified as infrasound
Infrasound
Infrasound is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high...
.
The explosion raises a large amount of moisture-laden air from lower altitudes. As the air rises, the temperature drops and the water vapor condenses as water droplets, and later freezes as ice crystals. The phase change releases latent heat
Latent heat
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a process that occurs without a change in temperature. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. The term was...
which heats the cloud, driving it to yet higher altitudes.
A mushroom cloud undergoes several phases of formation.
- Early time, the first about 20 seconds, when the fireball forms and the fission products mix with the material aspired from the ground or ejected from the crater. The condensation of evaporated ground occurs in first few seconds, most intensely during fireball temperatures between 3500–4100 K.
- Rise and stabilization phase, 10 seconds to 10 minutes, when the hot gases rise up and early fallout is deposited.
- Late time, until about 2 days later, when the airborne particles are being distributed by wind, deposited by gravity, and scavenged by precipitation.
The shape of the cloud is influenced by the atmospheric conditions and wind patterns. Fallout distribution is predominantly a downwind plume
Plume (hydrodynamics)
In hydrodynamics, a plume is a column of one fluid or gas moving through another. Several effects control the motion of the fluid, including momentum, diffusion, and buoyancy...
. However if the cloud reaches the tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
, it may spread against the wind direction, as the convection speed is higher than the ambient wind speed. The tropopause cloud shape is roughly circular and spread out.
The initial color of some radioactive clouds can be colored red or reddish brown, due to presence of nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
, formed from nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, and atmospheric moisture. In the high-temperature high-radiation environment of the blast; ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
is also formed. It is estimated that each megaton of yield produces about 5000 tons of nitrogen oxides. Yellow and orange hues are also described. The reddish hue is later obscured by the white color of water vapor, condensing in the fast-flowing air as the fireball cools, and the dark color of smoke and debris sucked into the updraft. The ozone gives the blast its characteristic corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
like smell.
The droplets of condensed water vapor gradually evaporate, leading to apparent disappearance of the cloud. The radioactive particles however remain suspended in the air, and the now invisible cloud continues depositing fallout along its path.
The stem of the cloud is gray to brown in a ground burst, as there is dust, dirt and soil sucked into the mushroom. Air bursts produce white and steamy stems. Dark mushrooms from ground bursts contain irradiated material from the ground in addition to the bomb and its casing, and therefore produce more radioactive fallout with larger particles that deposit locally.
A higher-yield detonation can carry the nitrogen oxides high enough in atmosphere to cause significant depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...
of the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...
.
A double mushroom, with two levels, can be formed under certain conditions. For example, the Buster-Jangle Sugar
Operation Buster-Jangle
Operation Buster-Jangle was a series of seven nuclear weapons tests conducted by the United States in late 1951 at the Nevada Test Site. Buster-Jangle was the first joint test program between the DOD and Los Alamos National Laboratories. 6,500 troops were involved in the Desert Rock I, II, and III...
shot formed the first head from the blast itself, followed by another one propelled by the heat from the freshly formed crater.
The fallout itself may appear as dry ash-like flakes, or as particles too small to be visible; in the latter case often deposited by rain. Higher amount of newer, more radioactive particles deposited on skin can cause beta burns, often presented as discolored spots and lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s on the backs of exposed animals. The fallout from the Castle Bravo
Castle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
test had the appearance of white dust and was nicknamed Bikini snow; the tiny white flakes resembled snowflake
Snowflake
Snowflakes are conglomerations of frozen ice crystals which fall through the Earth's atmosphere. They begin as snow crystals which develop when microscopic supercooled cloud droplets freeze. Snowflakes come in a variety of sizes and shapes. Complex shapes emerge as the flake moves through...
s, stuck to surfaces, and had salty taste. The fallout from the Operation Wigwam
Operation Wigwam
Operation Wigwam involved a single test of the Mark 90 Betty nuclear bomb. It was conducted between Operation Teapot and Operation Redwing on May 14, 1955, about 500 miles southwest of San Diego, California. 6,800 personnel aboard 30 ships were involved in Wigwam...
test consisted of 41.4% of irregular opaque particles, a bit over 25% of particles with transparent and opaque areas, about 20% were microscopic marine organisms, and 2% were microscopic radioactive threads of unknown origin.
Cloud composition
The cloud contains three main classes of material: the remains of the weapon and its fission products, the material acquired from the ground (for burst altitudes below the fallout-free altitude, which depends on the weapon yield), and water vapor. The bulk of radiation contained in the cloud consists of the nuclear fission products; neutron activationNeutron activation
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus often decays immediately by emitting particles such as neutrons, protons, or alpha...
isotopes from the weapon materials, air, and the ground debris are only a minor fraction. The neutron activation occurs during the neutron burst at the instant of the blast itself and the range of neutron reach is limited by atmospheric absorption.
Most of the radiation is created by the fission products. Thermonuclear weapons produce a significant part of their yield from nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
. Fusion products are typically non-radioactive. The degree of radiation fallout production is therefore measured in kilotons of fission. Tsar Bomba
Tsar Bomba
Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. It was also referred to as Kuz'kina Mat , in this usage meaning "something that has not been seen before"....
, which produced 97% of the 50 Mt yield from fusion, was a relatively very clean weapon, as its fusion tamper was made of lead instead of uranium-238, otherwise the yield would have been 100 Megatons, 51 Megatons from fission. The fallout would have been equal to 25% of all nuclear weapon tests.
Initially, the fireball contains a highly ionized plasma consisting of atoms of the weapon, its fission products, and atmospheric gases. As the plasma cools, the atoms react, forming fine droplets and then solid particles of oxides. The particles coalesce to larger ones, and deposit on surface of other particles. Larger particles usually originate from material aspired into the cloud. Particles aspired while the cloud is still hot enough to melt them mix with the fission products throughout their volume. Larger particles get molten radioactive materials deposited on their surface. Particles aspired into the cloud later, when its temperature is low enough, do not become significantly contaminated. Particles formed only from the weapon itself are fine enough to stay airborne for long time and become widely dispersed and diluted to non-hazardous levels. Higher-altitude blasts which do not aspire ground debris, or which aspire dust only after cooling enough and where the radioactive fraction of the particles is therefore small, cause much smaller degree of localized fallout than lower-altitude blasts with larger radioactive particles formed.
The concentration of condensation products is the same for the small particles and for the deposited surface layers of larger particles. About 100 kg of small particles par per kiloton of yield are formed. The volume, and therefore activity, of the small particles is almost three orders of magnitude lower than the volume of the deposited surface layers on larger particles.
For higher-altitude blasts, the primary particle forming processes are condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
and subsequent coagulation
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
. For lower-altitude and ground blasts, with involvement of soil particles, the primary process is deposition on the foreign particles.
A low-altitude detonation produces a cloud with dust loading of 100 tons per megaton of yield. A ground detonation produces clouds with about three times as much dust. About 200 tons per kiloton of soil, for a ground detonation, gets melted and comes in contact with radioactivity.
The fireball volume is the same for surface and atmospheric detonation. In the first case, the fireball is a hemisphere instead of a sphere, with a correspondingly larger readius.
The particle sizes range from submicrometer and micrometer sized (created by condensation of plasma in the fireball), through 10–500 micrometers (surface material agitated by the blast wave and raised by the afterwinds), to millimeter and above (crater ejecta). The size of particles together with the altitude they are carried to, determines the length of their stay in the atmosphere, as larger particles are subject to dry precipitation. Smaller particles can be also scavenged by precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
, whether of the moisture condensing in the cloud itself or by the mushroom meeting with a rain cloud. The fallout carried down by rain is known as rainout if scavenged during raincloud formation, washout if absorbed into already formed falling raindrops.
Particles from air bursts are smaller than 10–25 micrometers, usually in submicrometer range. They are composed mostly of iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
s, with smaller proportion of aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
, and uranium
Uranium oxide
Uranium oxide is an oxide of the element uranium.The metal uranium forms several oxides:* Uranium dioxide or uranium oxide * Uranium trioxide or uranium oxide...
and plutonium oxides. Particles larger than 1-2 micrometers are very spherical, corresponding to vaporized material condensing into droplets and then solidifying. The radioactivity is evenly distributed throughout the particle volume, making total activity of the particles linearly dependent on particle volume. About 80% of activity is present in more volatile elements, which condense only after the fireball cools to considerable degree. For example, strontium-90
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
will have less time to condense and coalesce into larger particles, resulting in greater degree of mixing in the volume of air and smaller particles. The particles produced immediately after the burst are small, with 90% of radiation activity present in particles below 300 nanometers. These coagulate with stratospheric aerosols. Coagulation in troposphere is more extensive, and at ground level most activity is present in particles between 300 nm and 1 micron. The coagulation offsets the fractionation processes at particle formation, evening out isotopic distribution.
Carbon particles (soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
) and smoke
Smoke
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...
from fires ignited by the blast can be sucked into the mushroom cloud. Large fires can create significant clouds of smoke on their own.
For ground and low-altitude bursts, the cloud contains also vaporized, melted and fused soil particles. The distribution of activity through the particles depends on their formation. Particles formed by vaporization-condensation have activity evenly distributed through volume as the air-burst particles. Larger molten particles have the fission products diffused through the outer layers, and fused and non-melted particles that were not heated sufficiently but came in contact with the vaporized material or scavenged droplets before their solidification have a relatively thin layer of high activity material deposited on their surface. The composition of such particles depends on the character of the soil, usually a glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
-like material formed from silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
minerals. The particle sizes do not depend on the yield but instead on the soil character, as they are based on individual grains of the soil or their clusters. Two types of particles are present, spherical, formed by complete vaporization-condensation or at least melting of the soil, with activity distributed evenly through the volume (or with a 10–30% volume of inactive core for larger particles between 0.5–2 mm), and irregular-shaped particles formed at the edges of the fireball by fusion of soil particles, with activity deposited in a thin surface layer. The amount of large irregular particles is insignificant. Particles formed from detonations above, or in, the ocean, will contain short-lived radioactive sodium isotopes, and salts from the sea water. Molten silica is a very good solvent for metal oxides and scavenges small particles easily; explosions above silica-containing soils will produce particles with isotopes mixed through their volume. In contrast, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
debris, based on calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, tends to adsorb radioactive particles on its surface.
The elements undergo fractionation
Fractionation
See also: Fractionated spacecraftFractionation is a separation process in which a certain quantity of a mixture is divided up in a number of smaller quantities in which the composition changes according to a gradient. Fractions are collected based on differences in a specific property of the...
during particle formation, due to their different volatility
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
. Refractory
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
elements (Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Pm) form oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
s with high boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
s; these precipitate the fastest and at the time of particle solidification, at temperature of 1400 °C, are considered to be fully condensed. Volatile elements (Kr, Xe, I, Br) are not condensed at that temperature. Intermediate elements have their (or their oxides) boiling points close to the solidification temperature of the particles (Rb, Cs, Mo, Ru, Rh, Tc, Sb, Te). The elements in the fireball are present as oxides, unless the temperature is above the decomposition temperature of a given oxide. Less refractory products condense on surfaces of solidified particles. Isotopes with gaseous precursors solidify on the surface of the particles as they are produced by decay.
The largest, and therefore the most radioactive particles, are deposited by fallout in the first few hours after the blast. Smaller particles are carried to higher altitudes and descend slower, reaching ground in less radioactive state as the isotopes with the shorest half-lives decay the fastest. The smallest particles can reach stratosphere and stay there for weeks, months, even years and reach an entire hemisphere via atmospheric currents. The high-danger, short-term, localized fallout is deposited primarily downwind from the blast site, in a cigar-shaped area, assuming a constant-strength, constant-direction wind. Crosswinds, wind direction changes, and precipitation greatly alter the fallout pattern.
The condensation of water droplets in the mushroom cloud depends on the amount of condensation nuclei. Too many condensation nuclei actually inhibit condensation, as the particles compete for a relatively insufficient amount of water vapor.
Chemical reactivity of the elements and their oxides, ion adsorption properties, and compound solubility influence particle distribution in the environment after deposition from the atmosphere. Bioaccumulation
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
influences the propagation of fallout radioisotopes in the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
.
Radioisotopes
The primary hazard fallout hazard is gamma radiation from short-lived radioisotopes, which represent the bulk of activity. Within 24 hours after the burst, the fallout gamma radiation level drops 60 times. Longer-life radioisotopes, typically caesium-137Caesium-137
Caesium-137 is a radioactive isotope of caesium which is formed as a fission product by nuclear fission.It has a half-life of about 30.17 years, and decays by beta emission to a metastable nuclear isomer of barium-137: barium-137m . Caesium-137 is a radioactive isotope of caesium which is formed...
and strontium-90
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
, present a long-term hazard. Intense beta radiation from the fallout particles can cause beta burns to people and animals coming in contact with the fallout shortly after the blast. Ingested or inhaled particles cause an internal dose
Internal dosimetry
Internal dosimetry provides methods for calculation of radiation dose and risks from radionuclides incorporated inside human body. The Radionuclide deposited in human body will irradiate that person and will give dose to body until excreted or completely decayed from the body.Routes of intakeThere...
of alpha and beta radiation, which may lead to long-term effects, including cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
.
The neutron irradiation of the atmosphere itself produces a small amount of activation, mainly as long-lived carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...
and short-lived argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
-41. The elements most important for induced radioactivity for sea water are sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
-24, chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
, and bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
. For ground bursts, the elements of concern are aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
-28, silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
-31, sodium-24, manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
-56, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-59, and cobalt-60
Cobalt-60
Cobalt-60, , is a synthetic radioactive isotope of cobalt. Due to its half-life of 5.27 years, is not found in nature. It is produced artificially by neutron activation of . decays by beta decay to the stable isotope nickel-60...
.
The bomb casing can be a significant sources of neutron-activated radioisotopes. The neutron flux in the bombs, especially thermonuclear devices, is sufficient for high-threshold nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
s. The induced isotopes include cobalt-60, 57 and 58, iron-59 and 55, manganese-54, zinc-65, yttrium-88, and possibly nickel-58 and 62, niobium-63, holmium-165, iridium-191, and short-lived manganese-56, sodium-24, silicon-31, and aluminium-28. Europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
-152 and 154 can be present, as well as two nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s of rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
-102. During the Operation Hardtack, tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
-185, 181 and 187 and rhenium
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
-188 were produced from elements added as tracers to the bomb casings, to allow identification of fallout produced by specific explosions. Antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
-124, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
-109, and cadmium-113m are also mentioned as tracers.
The most significant radiation sources are the fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
s from the primary fission stage, and in the case of fission-fusion-fission weapons, from the fission of the fusion stage uranium tamper. Many more neutrons per unit of energy are released in a thermonuclear explosion in comparison with a purely fission yield influencing the fission products composition. For example, the uranium-237 isotope is a unique thermonuclear explosion marker, as it is produced by a (n,2n) reaction from uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
, with the minimal neutron energy needed being about 5.9 MeV. Considerable amounts of neptunium-239 and uranium-237 are indicators of a fission-fusion-fission explosion. Minor amounts of uranium-240 are also formed, and capture of large numbers of neutrons by individual nuclei leads to formation of negligible amounts of higher transuranium element
Transuranium element
In chemistry, transuranium elements are the chemical elements with atomic numbers greater than 92...
s, e.g. einsteinium
Einsteinium
Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein...
-255 and fermium
Fermium
Fermium is a synthetic element with the symbol Fm. It is the 100th element in the periodic table and a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities,...
-255.
The radioactivity of the particles decreases with time, with different isotopes being significant at different timespans. For soil activation products, aluminium-28 is the most important contributor during the first 15 minutes. Manganese-56 and sodium-24 follow until about 200 hours. Iron-59 follows at 300 hours, and after 100–300 days, the significant contributor becomes cobalt-60.
Radioactive particles can be carried for considerable distances. Radiation from the Trinity test
Trinity test
Trinity was the code name of the first test of a nuclear weapon. This test was conducted by the United States Army on July 16, 1945, in the Jornada del Muerto desert about 35 miles southeast of Socorro, New Mexico, at the new White Sands Proving Ground, which incorporated the Alamogordo Bombing...
was washed out by a rainstorm in Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
. This was deduced, and the origin traced, when Eastman Kodak
Eastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....
found x-ray films were being fogged
Fogging (photography)
Fogging in photography is the deterioration in the quality of the image caused either by extraneous light or the effects of a processing chemical.-Taxonomy of fogging:...
by cardboard
Paperboard
Paperboard is a thick paper based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker than paper. According to ISO standards, paperboard is a paper with a basis weight above 224 g/m2, but there are exceptions. Paperboard can be single...
packaging produced in the Midwest. Unanticipated winds carried lethal doses of Castle Bravo
Castle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
fallout over the Rongelap Atoll
Rongelap Atoll
Rongelap Atoll or Namorik Atoll is a coral atoll of 61 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its total land area is only , but it encloses a lagoon with an area of...
, forcing its evacuation. The crew of Daigo Fukuryu Maru
Daigo Fukuryu Maru
was a Japanese tuna fishing boat, which was exposed to and contaminated by nuclear fallout from the United States' Castle Bravo thermonuclear device test on Bikini Atoll, on 1 March 1954....
, a Japanese fishing boat located outside of the predicted danger zone, was also affected. Strontium-90 found in worldwide fallout later led to the Partial Test Ban Treaty
Partial Test Ban Treaty
The treaty banning nuclear weapon tests in the atmosphere, in outer space and under water, often abbreviated as the Partial Test Ban Treaty , Limited Test Ban Treaty , or Nuclear Test Ban Treaty is a treaty prohibiting all test detonations of nuclear weapons...
.
Fluorescent glow
The intense radiation in the first seconds after the blast may cause an observable aura of fluorescenceFluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
, the eerie blue-violet-purple glow
Ionized air glow
The ionized-air glow is the emission of characteristic blue–purple–violet light, of color called electric blue, by air subjected to an energy flux. -Processes:...
of ionized oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
at some distance from the fireball, surrounding the forming radioactive cloud. The light is best visible during the night or weak daylight. The brightness decreases rapidly, becoming barely visible in few tens of seconds.
Condensation effects
Nuclear mushroom clouds are often also accompanied by short-lived vapor clouds, "Wilson clouds" also known as condensation clouds or vapor rings. These are created by the blast wave causing a sudden drop in the surrounding air temperatures, causing water vapor in the air to condense around the explosion cloud. When a nuclear weaponNuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
is detonated in humid air, the "negative phase" of the shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
causes rarefaction
Rarefaction
Rarefaction is the reduction of a medium's density, or the opposite of compression.A natural example of this is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.Another...
(reduction in density) in the air surrounding the explosion, but not contained within it. This results in a temporary cooling of that air, which causes a condensation of some of the water vapor contained in it. When the pressure and the temperature return to normal, the Wilson cloud dissipates. Scientists observing the Operation Crossroads
Operation Crossroads
Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. It was the first test of a nuclear weapon after the Trinity nuclear test in July 1945...
nuclear tests in 1946 at Bikini Atoll
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
named that transitory cloud a "Wilson cloud" because of its similarity to the appearance of the inside of a Wilson cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...
, an instrument they would have been familiar with. (The cloud chamber effect is caused by a tempory reduction in pressure in a closed system) and marks the track(s) of electrically charged sub-atomic particles. Analysts of later nuclear bomb tests used the more general term "condensation cloud" for the "Wilson clouds".
The same kind of condensation is sometimes seen above the wings of low-altitude jet aircraft in moist atmosphere. The top of a wing is a curved surface. The curvature (and increased air velocity) causes a reduction in air pressure, as given by Bernoulli's Law. This reduction in air pressure causes cooling, and water vapor condensation. Hence, the small, transient clouds appear. In technical terms, the "Wilson cloud" is also an example of the Prandtl–Glauert singularity in aerodynamics.
The shape of the shock wave, influenced by different speed at different altitudes, and the temperature and humidity of different atmospheric layers determines the appearance of the Wilson clouds. Condensation rings around or above the fireball are commonly observed. Rings around the fireball may become stable and form rings around the rising stem. Higher-yield explosions cause intense updrafts where the air speed can reach 300 miles per hour. The entrainment
Entrainment (meteorology)
Entrainment is a phenomenon of the atmosphere which occurs when a turbulent flow captures a non-turbulent flow. It is typically used to refer to the capture of a wind flow of high moisture content, or in the case of tropical cyclones, the capture of drier air....
of higher-humidity air together with the associated drop of pressure and temperature leads to formation of skirts and bells around the stem. If the water droplets become sufficiently large, the cloud structure they form may become heavy enough to descend. A rising stem with a descending bell around it can be formed. The layering of humidity in the atmosphere that is responsible for the appearance of the condensation rings influences the shape of the condensation artifacts along the mushroom stem, as the updraft causes laminar flow
Laminar flow
Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...
. The same effect above the top of the cloud, where the expansion of the rising cloud pushes a layer of humid air above the cloud from a lower altitude, and the lower temperature at high altitude, causes condensation of water vapor and droplet freezing, forming ice caps (or icecaps), similar in appearance, and mechanism of formation, to scarf clouds.
The resulting structures can be fairly complex. The Castle Bravo
Castle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
cloud at various phases of its development had 4 condensation rings, 3 ice caps, 2 skirts and 3 bells.
Of further note, the streaks of smoke seen to the left of the explosion at detonation are vertical smoke flares which are used to observe the shockwave.
External links
- Carey Sublette's Nuclear Weapon Archive has many photographs of mushroom clouds
- DOE Nevada Site Office has many photographs of nuclear tests conducted at the Nevada Test SiteNevada Test SiteThe Nevada National Security Site , previously the Nevada Test Site , is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about northwest of the city of Las Vegas...
and elsewhere - Burning bulbs is a set of photographs by Kevin Tieskoetter, showing fine mushroom cloud structures generated by burning lightbulb filaments in air