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Fog, in the form of a cloud, descends upon a High Desert community in the Western United States, while leaving the mountain exposed. High Desert Fog.jpg
Fog, in the form of a cloud, descends upon a High Desert community in the Western United States, while leaving the mountain exposed.
Heavy fog over Koblenz dissipates into a beautiful sky near the Moselle river.

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. [1] Fog can be considered a type of low-lying cloud, usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.

Aerosol colloid of fine solid particles or liquid droplets, in air or another gas

An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog, dust, forest exudates and geyser steam. Examples of anthropogenic aerosols are haze, particulate air pollutants and smoke. The liquid or solid particles have diameters typically <1 μm; larger particles with a significant settling speed make the mixture a suspension, but the distinction is not clear-cut. In general conversation, aerosol usually refers to an aerosol spray that delivers a consumer product from a can or similar container. Other technological applications of aerosols include dispersal of pesticides, medical treatment of respiratory illnesses, and convincing technology. Diseases can also spread by means of small droplets in the breath, also called aerosols.

Water chemical compound

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

Drop (liquid) small unit of liquid

A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Drops may also be formed by the condensation of a vapor or by atomization of a larger mass of liquid.



The term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes). [2]

By definition, fog reduces visibility to less than 1 kilometre (0.62 mi), whereas mist causes lesser impairment of visibility. [3]

In meteorology, visibility is a measure of the distance at which an object or light can be clearly discerned. It is reported within surface weather observations and METAR code either in meters or statute miles, depending upon the country. Visibility affects all forms of traffic: roads, sailing and aviation. Meteorological visibility refers to transparency of air: in dark, meteorological visibility is still the same as in daylight for the same air.

Mist phenomenon caused by small droplets of water suspended in air

Mist is a phenomenon caused by small droplets of water suspended in air. Physically, it is an example of a dispersion. It is most commonly seen where warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing water onto the hot stove of a sauna. It can be created artificially with aerosol canisters if the humidity and temperature conditions are right. It can also occur as part of natural weather, when humid air cools rapidly, for example when the air comes into contact with surfaces that are much cooler than the air.

For aviation purposes in the UK, a visibility of less than 5 kilometres (3.1 mi) but greater than 999 metres (3,278 ft) is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported. [4] [ full citation needed ]

Relative humidity

Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air. A related parameter is that of dewpoint.

Haze atmospheric phenomenon in which dust, smoke, and other dry particulates obscure the clarity of the sky

Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand, and snow. Sources for haze particles include farming, traffic, industry, and wildfires.


Minute droplets of water constitute this after-dark radiation fog, with the ambient temperature -2 degC (28 degF) FogParticles.jpg
Minute droplets of water constitute this after-dark radiation fog, with the ambient temperature −2  °C (28  °F )
Up-close view of water particles forming fog FogParticlesHighSpeed.jpg
Up-close view of water particles forming fog

Fog forms when the difference between air temperature and dew point is less than 2.5  °C (4.5  °F ). [5]

Dew point temperature at which air becomes saturated with water vapor

The dew point is the temperature to which air must be cooled to become saturated with water vapor. When further cooled, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface. When the temperature is below the freezing point of water, the dew point is called the frost point, as frost is formed rather than dew. The measurement of the dew point is related to humidity. A higher dew point means there will be more moisture in the air.

Celsius Scale and unit of measurement for temperature

The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI). As an SI derived unit, it is used by all countries except the United States, the Bahamas, Belize, the Cayman Islands and Liberia. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps.

Fahrenheit unit of temperature

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt. Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature. The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.

Fog begins to form when water vapor condenses into tiny liquid water droplets that are suspended in the air. Six examples of ways that water vapor is added to the air are by wind convergence into areas of upward motion; [6] precipitation or virga falling from above; [7] daytime heating evaporating water from the surface of oceans, water bodies, or wet land; [8] transpiration from plants; [9] cool or dry air moving over warmer water; [10] and lifting air over mountains. [11] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. [12] [13] Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. [14]

Water vapor gaseous phase of water; unlike other forms of water, water vapor is invisible

Water vapor, water vapour or aqueous vapor is the gaseous 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. Unlike other forms of water, water vapor is invisible. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. It is less dense than air and triggers convection currents that can lead to clouds.

Condensation change of the physical state of matter from gas phase into liquid phase; reverse of evaporation

Condensation is the change of the physical state of matter from the gas phase into the liquid phase, and is the reverse of vaporisation. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapour to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition.

Virga clouds supplementary feature; precipitation that doesnt reach the ground

In meteorology, a virga is an observable streak or shaft of precipitation falling from a cloud that evaporates or sublimates before reaching the ground. A shaft of precipitation that does not evaporate before reaching the ground is a precipitation shaft. At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is often due to compressional heating, because the air pressure increases closer to the ground. It is very common in deserts and temperate climates. In North America, it is commonly seen in the Western United States and the Canadian Prairies. It is also very common in the Middle East, Australia, and North Africa.

Fog normally occurs at a relative humidity near 100%. [15] This occurs from either added moisture in the air, or falling ambient air temperature. [15] However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.

Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets. [16] This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.

The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fogbank it may contain, will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.


Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred.

Radiation fog is formed by the cooling of land after sunset by infrared thermal radiation in calm conditions with a clear sky. The cooling ground then cools adjacent air by conduction, causing the air temperature to fall and reach the dew point, forming fog. In perfect calm, the fog layer can be less than a meter thick, but turbulence can promote a thicker layer. Radiation fog occurs at night, and usually does not last long after sunrise, but it can persist all day in the winter months, especially in areas bounded by high ground. Radiation fog is most common in autumn and early winter. Examples of this phenomenon include the Tule fog. [17]

Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds. [18] However, the term is usually a synonym for shallow radiation fog; in some cases the depth of the fog is on the order of tens of centimeters over certain kinds of terrain with the absence of wind.

Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background San francisco in fog with rays.jpg
Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background

Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. [19] It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog). A strong enough temperature difference over water or bare ground can also cause advection fog.

Although strong winds often mix the air and can disperse, fragment, or prevent many kinds of fog, markedly warmer and humid air blowing over a snowpack can continue to generate advection fog at elevated velocities up to 80 km/h (50 mph) or more – this fog will be in a turbulent, rapidly moving, and comparatively shallow layer, observed as a few centimeters/inches in depth over flat farm fields, flat urban terrain and the like, and/or form more complex forms where the terrain is different such as rotating areas in the lee of hills or large buildings and so on.

Fog formed by advection along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coast-ward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline; a phenomenon known as a "southerly surge", typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain. Moderate turbulence will typically transform a fog bank, lifting it and breaking it up into shallow convective clouds called stratocumulus.

Evaporation fog or steam fog forms over bodies of water overlain by much colder air; this situation can also lead to the formation of steam devils, which look like dust counterparts. Lake effect fog is of this type, sometimes in combination with other causes like radiation fog. It tends to differ from most advective fog formed over land in that it is, like lake-effect snow, a convective phenomenon, resulting in fog that can be very dense and deep and looks fluffy from above.

Frontal fog forms in much the same way as stratus cloud near a front when raindrops, falling from relatively warm air above a frontal surface, evaporate into cooler air close to the Earth's surface and cause it to become saturated. This type of fog can be the result of a very low frontal stratus cloud subsiding to surface level in the absence of any lifting agent after the front passes.

Ice fog forms in very low temperatures and can be the result of other mechanisms mentioned here, as well as the exhalation of moist warm air by herds of animals. It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions, which can cause many types of halos and other results of refraction of sunlight by the airborne crystals.

Freezing fog, which deposits rime, is composed of droplets of supercooled water that freeze to surfaces on contact.

Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms.

Hail fog sometimes occurs in the vicinity of significant hail accumulations due to decreased temperature and increased moisture leading to saturation in a very shallow layer near the surface. It most often occurs when there is a warm, humid layer atop the hail and when wind is light. This ground fog tends to be localized but can be extremely dense and abrupt. It may form shortly after the hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating. [20]

Upslope fog forms when moist air is going up the slope of a mountain or hill (orographic lifting) which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.

Freezing conditions

Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime. [21] This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is super-cooled, filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful".

Aerial Video of freezing fog in the Okanagan Highlands

In the western United States, freezing fog may be referred to as pogonip. [22] It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip is derived from the Shoshone word paγi̵nappi̵h, which means "cloud". [23] [24] In The Old Farmer's Almanac, in the calendar for December, the phrase "Beware the Pogonip" regularly appears. In his anthology Smoke Bellew, Jack London described a pogonip which surrounded the main characters, killing one of them.

The phenomenon is also extremely common in the inland areas of the Pacific Northwest, with temperatures in the 10 to 30 °F (−12 to −1 °C) range. The Columbia Plateau experiences this phenomenon most years due to temperature inversions, sometimes lasting for as long as three weeks. The fog typically begins forming around the area of the Columbia River and expands, sometimes covering the land to distances as far away as LaPine, Oregon, almost 150 miles (240 km) due south of the river and into south central Washington.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below −35 °C (−31 °F), making it common only in and near the Arctic and Antarctic regions. [25] It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Utqiagvik, Alaska. Ice fog often leads to the visual phenomenon of light pillars.

Topographical influences

Nascer do sol em meio a neblina, na Pedra do Sino.jpg
Nascer do Sol no Dedo de Deus.jpg
Fog over the Pedra do Sino (Bell Rock; left) and Dedo de Deus (God's Finger; right) peaks in the Serra dos Órgãos National Park, Rio de Janeiro state, Brazil

Up-slope fog or hill fog forms when winds blow air up a slope (called orographic lift), adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.

Valley fog forms in mountain valleys, often during winter. It is essentially a radiation fog confined by local topography, and can last for several days in calm conditions. In California's Central Valley, valley fog is often referred to as tule fog.

Sea and coastal fog

Sea fog (also known as haar or fret) is heavily influenced by the presence of sea spray and microscopic airborne salt crystals. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves. Except in areas of storminess, the most common areas of breaking waves are located near coastlines, hence the greatest densities of airborne salt particles are there.

Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. Another recently discovered source of condensation nuclei for coastal fog is kelp seaweed. Researchers have found that under stress (intense sunlight, strong evaporation, etc.), kelp releases particles of iodine which in turn become nuclei for condensation of water vapor, causing fog that diffuses direct sunlight. [26]

Sea smoke , also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land. [21] It often causes freezing fog, or sometimes hoar frost.

Arctic sea smoke is similar to sea smoke, but occurs when the air is very cold. Instead of condensing into water droplets, columns of freezing, rising, and condensing water vapor is formed. The water vapor produces the sea smoke fog, and is usually misty and smoke-like. [27]

Garúa fog near the coast of Chile and Peru, [28] occurs when typical fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a "transparent mist". Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers because of deposition of liquid water on hard surfaces.

Visibility effects

Heavy fog on a road near Baden, Austria Fog near Baden, Austria.JPG
Heavy fog on a road near Baden, Austria
Light fog reduces visibility on a suburban street, rendering the cyclist very hazy at about 200 m (220 yd). The limit of visibility is about 400 m (440 yd), which is before the end of the street. 20080313 Foggy Street.jpg
Light fog reduces visibility on a suburban street, rendering the cyclist very hazy at about 200 m (220 yd). The limit of visibility is about 400 m (440 yd), which is before the end of the street.

Depending on the concentration of the droplets, visibility in fog can range from the appearance of haze, to almost zero visibility. Many lives are lost each year worldwide from accidents involving fog conditions on the highways, including multiple-vehicle collisions.

The aviation travel industry is affected by the severity of fog conditions. Even though modern auto-landing computers can put an aircraft down without the aid of a pilot, personnel manning an airport control tower must be able to see if aircraft are sitting on the runway awaiting takeoff. Safe operations are difficult in thick fog, and civilian airports may forbid takeoffs and landings until conditions improve.

A solution for landing returning military aircraft developed in World War II was called Fog Investigation and Dispersal Operation (FIDO). It involved burning enormous amounts of fuel alongside runways to evaporate fog, allowing returning fighter and bomber pilots sufficient visual cues to safely land their aircraft. The high energy demands of this method discourage its use for routine operations.


Sutro Tower casts a 3-dimensional fog shadow Fog shadow tv tower.jpg
Sutro Tower casts a 3-dimensional fog shadow

Shadows are cast through fog in three dimensions. The fog is dense enough to be illuminated by light that passes through gaps in a structure or tree, but thin enough to let a large quantity of that light pass through to illuminate points further on. As a result, object shadows appear as "beams" oriented in a direction parallel to the light source. These voluminous shadows are created the same way as crepuscular rays, which are the shadows of clouds. In fog, it is solid objects that cast shadows.

Sound propagation and acoustic effects

Sound typically travels fastest and farthest through solids, then liquids, then gases such as the atmosphere. Sound is affected during fog conditions due to the small distances between water droplets, and air temperature differences.

Molecular effect: Though fog is essentially liquid water, the many droplets are separated by small air gaps. High-pitched sounds have a high frequency, which in turn means they have a short wavelength. To transmit a high frequency wave, air must move back and forth very quickly. Short-wavelength high-pitched sound waves are reflected and refracted by many separated water droplets, partially cancelling and dissipating their energy (a process called "damping"). In contrast, low pitched notes, with a low frequency and a long wavelength, move the air less rapidly and less often, and lose less energy to interactions with small water droplets. Low-pitched notes are less affected by fog and travel further, which is why foghorns use a low-pitched tone. [29]

Temperature effect: A fog can be caused by a temperature inversion where cold air is pooled at the surface which helped to create the fog, while warmer air sits above it. The inverted boundary between cold air and warm air reflects sound waves back toward the ground, allowing sound that would normally radiate out escaping into the upper atmosphere to instead bounce back and travel near the surface. A temperature inversion increases the distance that lower frequency sounds can travel, by reflecting the sound between the ground and the inversion layer. [30]

Record extremes

The foggiest place in the world[ citation needed ] is Hamilton, New Zealand, followed closely by the Grand Banks off the coast of Newfoundland (the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south). Some of the foggiest land areas in the world include Argentia (Newfoundland) and Point Reyes (California), each with over 200 foggy days per year.[ citation needed ] Even in generally warmer southern Europe, thick fog and localized fog are often found in lowlands and valleys, such as the lower part of the Po Valley and the Arno and Tiber valleys in Italy; Ebro Valley in northeastern Spain; as well as on the Swiss plateau, especially in the Seeland area, in late autumn and winter.[ citation needed ] Other notably foggy areas include coastal Chile (in the south); coastal Namibia; Nord, Greenland; and the Severnaya Zemlya islands.

As a water source

Redwood forests in California receive approximately 30–40% of their moisture from coastal fog by way of fog drip. Change in climate patterns could result in relative drought in these areas. [31] Some animals, including insects, depend on wet fog as a principal source of water, particularly in otherwise desert climes, as along many African coastal areas. Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient.

Artificial fog

Artificial fog is man-made fog that is usually created by vaporizing a water- and glycol-based or glycerine-based fluid. The fluid is injected into a heated metal block, and evaporates quickly. The resulting pressure forces the vapor out of a vent. Upon coming into contact with cool outside air, the vapor condenses in microscopic droplets and appears as fog. [32] Such fog machines are primarily used for entertainment applications.

Historical references

The presence of fog has often played a key role in historical events, such as strategic battles. One example is the Battle of Long Island (August 27, 1776), when American general George Washington and his command were able to evade imminent capture by the British Army, using fog to conceal their escape. Another example is D-Day (June 6, 1944) during World War II, when the Allies landed on the beaches of Normandy, France during fog conditions. Both positive and negative results were reported from both sides during that battle, due to impaired visibility. [33]

See also




Related Research Articles

Evaporation Type of vaporization of a liquid that occurs from its surface; surface phenomenon

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other based on how they collide with each other. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas. When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling.

Frost coating or deposit of ice that may form in humid air in cold conditions, usually overnight

Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor to ice as the water vapor reaches the freezing point. In temperate climates, it most commonly appears on surfaces near the ground as fragile white crystals; in cold climates, it occurs in a greater variety of forms. The propagation of crystal formation occurs by the process of nucleation.

Diamond dust is a ground-level cloud composed of tiny ice crystals. This meteorological phenomenon is also referred to simply as ice crystals and is reported in the METAR code as IC. Diamond dust generally forms under otherwise clear or nearly clear skies, so it is sometimes referred to as clear-sky precipitation. Diamond dust is most commonly observed in Antarctica and the Arctic, but can occur anywhere with a temperature well below freezing. In the polar regions of Earth, diamond dust may persist for several days without interruption.

Stratus cloud genus of clouds, low-level clouds characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals

Stratus clouds are low-level clouds characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals. More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. The word "stratus" comes from the Latin prefix "strato-", meaning "layer". Stratus clouds may produce a light drizzle or a small amount of snow. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region. Some call these clouds "high fog" for the fog-like cloud. While light rain may fall, this cloud does not indicate much meteorological activity.


A dehumidifier is an electrical appliance which reduces and maintains the level of humidity in the air, usually for health or comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses.

Precipitation product of the condensation of atmospheric water vapour that falls under gravity

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates". Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."

Cloud physics Study of the physical processes in atmospheric clouds

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of atmospheric clouds. These aerosols are found in the troposphere, stratosphere, and mesosphere, which collectively make up the greatest part of the homosphere. Clouds consist of microscopic droplets of liquid water, tiny crystals of ice, or both. Cloud droplets initially form by the condensation of water vapor onto condensation nuclei when the supersaturation of air exceeds a critical value according to Köhler theory. Cloud condensation nuclei are necessary for cloud droplets formation because of the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface. At small radii, the amount of supersaturation needed for condensation to occur is so large, that it does not happen naturally. Raoult's law describes how the vapor pressure is dependent on the amount of solute in a solution. At high concentrations, when the cloud droplets are small, the supersaturation required is smaller than without the presence of a nucleus.

June Gloom

June Gloom is a Southern California term for a weather pattern that results in cloudy, overcast skies with cool temperatures during the late spring and early summer. While it is most common in the month of June, it can occur in surrounding months, giving rise to other colloquialisms, such as "May Gray", "No Sky July", and, rarely, "Fogust". Low-altitude stratus clouds form over the cool water of the California Current, and spread overnight into the coastal regions of Southern California. The overcast skies often are accompanied by fog and drizzle, though usually not rain. June Gloom usually clears up between mid-morning and early afternoon, depending on the strength of the marine layer, and gives way to sunny skies. On a strong June Gloom day, the clouds and fog may extend inland to the valleys and Inland Empire and may persist into the mid-afternoon or evening.

Rime ice

Rime ice forms when supercooled water liquid droplets freeze onto surfaces. Meteorologists distinguish between three basic types of ice forming on vertical and horizontal surfaces by deposition of supercooled water droplets. There are also intermediate formations.

The Wegener–Bergeron–Findeisen process, is a process of ice crystal growth that occurs in mixed phase clouds in regions where the ambient vapor pressure falls between the saturation vapor pressure over water and the lower saturation vapor pressure over ice. This is a subsaturated environment for liquid water but a supersaturated environment for ice resulting in rapid evaporation of liquid water and rapid ice crystal growth through vapor deposition. If the number density of ice is small compared to liquid water, the ice crystals can grow large enough to fall out of the cloud, melting into rain drops if lower level temperatures are warm enough.

Precipitation types

In meteorology, the various types of precipitation often include the character or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is generally more intense, and of shorter duration, than stratiform precipitation. Orographic precipitation occurs when moist air is forced upwards over rising terrain, such as a mountain.

Atmospheric convection

Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.

Condensation cloud

A transient condensation cloud, also called Wilson cloud, is observable at large explosions in humid air.

Glossary of meteorology Wikimedia list article

This glossary of meteorology is a list of terms and concepts relevant to meteorology and the atmospheric sciences, their sub-disciplines, and related fields.


  1. "The international definition of fog consists of a suspended collection of water droplets or ice crystal near the Earth's surface ..." Fog and Boundary Layer Clouds: Fog Visibility and Forecasting. Gultepe, Ismail, ed. Reprint from Pure and Applied Geophysics Vol 164 (2007) No. 6-7. ISBN   978-3-7643-8418-0. p. 1126; see Google Books Archived 3 September 2016 at the Wayback Machine Accessed 2010-08-01.
  2. Use of the term "fog" to mean any cloud that is at or near the Earth's surface can result in ambiguity as when, for example, a stratocumulus cloud covers a mountaintop. An observer on the mountain may say that he or she is in a fog, however, to outside observers a cloud is covering the mountain. "Standard practice for the design and operation of supercooled fog dispersal projects" Thomas, P. (2005) p. 3. ISBN   0-7844-0795-9 See Google Books. In fact, some people commonly mistake mist for fog. These two are a little bit different as mist is thinner than fog. Archived 3 September 2016 at the Wayback Machine Accessed 2010-08-01. Further distinguishing the terms, fog rarely results in rain, while clouds are the common source of rain.
  3. "Federal Meteorological Handbook Number 1: Chapter 8 – Present Weather" (PDF). Office of the Federal Coordinator for Meteorology. 1 September 2005. pp. 8–1, 8–2. Archived from the original (PDF) on 21 May 2011. Retrieved 9 October 2010.
  4. annex 3 Seventeenth Edition July 2010
  5. "Fog – AMS Glossary". Archived from the original on 27 March 2013. Retrieved 16 March 2013.
  6. Robert Penrose Pearce (2002). Meteorology at the Millennium. Academic Press. p. 66. ISBN   978-0-12-548035-2 . Retrieved 2 January 2009.
  7. National Weather Service Office, Spokane, Washington (2009). "Virga and Dry Thunderstorms". Archived from the original on 22 May 2009. Retrieved 2 January 2009.CS1 maint: Multiple names: authors list (link)
  8. Bart van den Hurk; Eleanor Blyth (2008). "Global maps of Local Land-Atmosphere coupling" (PDF). KNMI. Archived from the original (PDF) on 25 February 2009. Retrieved 2 January 2009.
  9. Krishna Ramanujan; Brad Bohlander (2002). "Landcover changes may rival greenhouse gases as cause of climate change". National Aeronautics and Space Administration Goddard Space Flight Center. Archived from the original on 3 June 2008. Retrieved 2 January 2009.
  10. National Weather Service JetStream (2008). "Air Masses". Archived from the original on 24 December 2008. Retrieved 2 January 2009.
  11. Michael Pidwirny (2008). "CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes". Physical Geography. Archived from the original on 20 December 2008. Retrieved 1 January 2009.
  12. Glossary of Meteorology (June 2000). "Front". American Meteorological Society. Archived from the original on 14 May 2011. Retrieved 29 January 2010.
  13. Roth, David M. (14 December 2006). "Unified Surface Analysis Manual" (PDF). Hydrometeorological Prediction Center. Archived (PDF) from the original on 29 September 2006. Retrieved 9 October 2010.
  14. FMI (2007). "Fog And Stratus – Meteorological Physical Background". Zentralanstalt für Meteorologie und Geodynamik. Archived from the original on 6 July 2011. Retrieved 7 February 2009.
  15. 1 2 Gleissman, Stephe (2007). Agroecology: the ecology of sustainable food systems. CRC Press. p. 73. ISBN   0849328454.
  16. Allred, Lance (2009). Enchanted Rock: A Natural and Human History. University of Texas Press. p. 99. ISBN   0292719639.
  17. Cox, Robert E. Applying Fog Forecasting Techniques using AWIPS and the Internet Archived 29 October 2007 at the Wayback Machine . National Weather Service, 2007.
  18. Climate education update: News and information about climate change for teachers and students Archived 27 May 2010 at the Wayback Machine . Atmospheric Radiation Measurement. Climate Research Facility. U.S. Department of Energy.
  19. Frost, H. (2004). Fog. Capstone Press. p. 22. ISBN   978-0-7368-2093-6.
  20. Marshall, T., Hoadley, D. (1995). Storm Talk. Tim Marshall.
  21. 1 2 Understanding Weather – Fog Archived 31 January 2009 at the Wayback Machine . BBC Weather.
  22. "Pogonip – Definition from the Merriam-Webster Online Dictionary". Archived from the original on 25 April 2009. Retrieved 14 February 2009.
  23. "Pogonip – Definition from the Merriam-Webster Online Dictionary". Archived from the original on 25 April 2009. Retrieved 14 February 2009.
  24. "Pogonip - Definition from the". Archived from the original on 22 February 2014. Retrieved 2 January 2013.
  25. Haby, Jeff. What is the difference between ice fog and freezing fog? Archived 8 January 2006 at the Wayback Machine
  26. Stressed seaweed contributes to cloudy coastal skies, study suggests Archived 11 May 2008 at the Wayback Machine ,
  27. "Arctic Sea Smoke". Archived from the original on 6 May 2016.
  28. Cowling, R. M., Richardson, D. M., Pierce, S. M. (2004). Vegetation of Southern Africa. Cambridge University Press. p. 192. ISBN   0521548012.
  29. "Does fog have a dampening effect on sounds?". Archived from the original on 16 January 2015.
  30. "How fog can play tricks on your ears?". Archived from the original on 12 April 2015.
  31. Joyce, Christopher (23 February 2010). "Fog Fluctuations Could Threaten Giant Redwoods". Archived from the original on 27 January 2016.
  32. Karukstis, K. K., Van Hecke, G. R. (2003). Chemistry connections: the basis of everyday phonemena. Academic Press. p. 23. ISBN   0124001513.
  33. "Characterizing fog and the physical mechanisms leading to its formation during precipitation in a coastal area of the northeastern United States". Archived from the original on 24 December 2014. Retrieved 31 January 2015.
  34. "Sunset Panorama at La Silla". Archived from the original on 28 November 2015.

Under "[ ^ "Federal Meteorological Handbook Number 1: Chapter 8 – Present Weather" (PDF). Office of the Federal Coordinator for Meteorology. 1 September 2005. pp. 8–1, 8–2. Retrieved 9 October 2010. ] " ….

Actually use the following link- and proceed to Chapter 8, etc.

Further reading