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48-556: Robert Henry McIntosh (23 September 1894–1983), also known as All-Weather Mac for his ability to fly in foggy and difficult conditions, was one of Imperial Airways ' 16 original pilots. In 1927, he made unsuccessful attempts to fly at first across the Atlantic with James Fitzmaurice and then to fly to India and back with Bert Hinkler , both on the aircraft Princess Xenia , a Dutch Fokker F.VIIa . A road in Roundshaw , McIntosh Close,

96-452: 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

144-466: A convective phenomenon, resulting in fog that can be very dense and deep and looks fluffy from above. 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. Garúa fog near the coast of Chile and Peru occurs when typical fog produced by

192-435: A marine layer when the water-saturated air is cooled and reaches a humidity of 100%, where it will then condense and turn into water droplets. Stratus and stratocumulus can form at the top of a marine layer in the presence of these conditions. A marine layer can often be dispersed by sufficiently strong winds, which essentially blow it away. The sun can also evaporate the marine layer, as it warms air and land which decreases

240-452: 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. Fog can be of different type according to climatic conditions. Artificial fog is man-made fog that is usually created by vaporizing a water- and glycol - or glycerine -based fluid. The fluid

288-534: 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

336-466: 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 centimetres/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

384-436: Is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. Fog normally occurs at a relative humidity near 100%. This occurs from either added moisture in the air, or falling ambient air temperature. 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

432-549: 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. 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

480-513: 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 . 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

528-422: Is created by cold air passing over warmer water or moist land. It may cause freezing fog or sometimes hoar frost . This situation can also lead to the formation of steam devils , which look like their 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 )

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576-409: 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

624-568: Is derived from the Shoshone word paγi̵nappi̵h , which means "cloud". 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 describes a pogonip which surrounded the main characters, killing one of them. The phenomenon is common in the inland areas of the Pacific Northwest, with temperatures in

672-406: Is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds. 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 centimetres over certain kinds of terrain with the absence of wind. Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It

720-415: Is injected into a heated metal block which 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. Such fog machines are primarily used for entertainment applications . The presence of fog has often played a key role in historical events, such as strategic battles. One example

768-752: Is named after him. This biographical article related to aviation is a stub . You can help Misplaced Pages by expanding it . Fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth 's surface. 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 affects many human activities, such as shipping, travel, and warfare. Fog appears when water vapor (water in its gaseous form) condenses. During condensation , molecules of water vapor combine to make tiny water droplets that hang in

816-447: 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". In the western United States , freezing fog may be referred to as pogonip . It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip

864-405: Is often referred to as tule 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,

912-437: Is solid objects that cast shadows. 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. 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

960-652: Is the 1776 Battle of Long Island 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 (6 June 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. Under "[ ^ "Federal Meteorological Handbook Number 1: Chapter 8 – Present Weather" (PDF). Office of

1008-413: Is why foghorns use a low-pitched tone. 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

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1056-546: The Seeland area, in late autumn and winter. Other notably foggy areas include coastal Chile (in the south); coastal Namibia ; Nord, Greenland ; and the Severnaya Zemlya islands. 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. Some animals, including insects, depend on wet fog as

1104-535: The 10 to 30 °F (−12 to −1 °C) range. The Columbia Plateau experiences this phenomenon most years during 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 La Pine, Oregon , almost 150 miles (240 km) due south of the river and into south central Washington. Frozen fog (also known as ice fog )

1152-442: 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

1200-844: The Federal Coordinator for Meteorology. 1 September 2005. pp. 8–1, 8–2. Retrieved 9 October 2010. ] " …. Actually use the following link- http://www.ofcm.gov/publications/fmh/FMH1/FMH1.pdf and proceed to Chapter 8, etc. Marine layer A marine layer can come in a number of different forms depending on the atmospheric conditions. It may manifest itself as merely a cool, humid air mass without any cloud cover, or it may be accompanied by clouds. In many cases, marine layers can consist of dense fog. Often associated with marine layers are stratus clouds , which are lumpy, often uniform clouds that form at low elevations (less than 3000 feet). Since marine layers are pushed ashore by westward winds, wind will almost always be present in one. Ultimately,

1248-489: The United Kingdom, a visibility of less than 5 km (3.1 mi) but greater than 999 m (3,278 ft) is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported. Fog forms when the difference between air temperature and dew point is less than 2.5  °C (4.5  °F ). Fog begins to form when water vapor condenses into tiny water droplets that are suspended in

1296-442: 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 attains 100% and the minute cloud droplets begin to coalesce into larger droplets. 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

1344-595: The air. Sea fog , which shows up near bodies of saline water , is formed as water vapor condenses on bits of salt. Fog is similar to, but less transparent than, mist . 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 ocean, or from nearby moist ground or marshes ). By definition, fog reduces visibility to less than 1 km (0.62 mi), whereas mist causes lesser impairment of visibility. For aviation purposes in

1392-518: The air. Some examples of ways that water vapor is condensed include wind convergence into areas of upward motion; precipitation or virga falling from above; daytime heating evaporating water from the surface of oceans, water bodies, or wet land; transpiration from plants; cool or dry air moving over warmer water; and lifting air over mountains. Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. Fog, like its elevated cousin stratus ,

1440-454: 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

1488-514: 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. Sea smoke , also called steam fog or evaporation fog ,

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1536-424: 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 tule fog . Ground fog

1584-411: The front passes. 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

1632-404: The hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating. Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime ice . 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

1680-496: The latitude of California, and causes a strong temperature inversion. Surface waters in coastal California are kept cold through a process called upwelling, which involves cooler, deeper waters rising to the top of a water column. Occasionally the marine layer becomes particularly deep, and the clouds on land can persist all day. This can happen at any time of the year, inspiring colloquialisms such as "May Gray" or " June Gloom ". An approaching frontal system or trough can also drive

1728-502: The marine layer is a medium within which clouds may form under the right conditions; it is not the layers of clouds themselves. As air cools in a temperature inversion , the surface air becomes denser than the warmer air above it, and thus becomes trapped below it. The lower layer will also gradually increase its humidity by evaporation of the surface water, as well as by the effect of the cooling itself, since cooler air holds more moisture. Clouds and potentially fog can form within

1776-465: The marine layer onshore. Though California is a notable example of the marine layer, these atmospheric phenomena exist in several other places around the world. Marine layers often form on the west coasts of continents, where upwelling usually occurs, and where there is a relatively warm air mass moving over a cool body of water. They can also form on the coasts of cool lakes, such as the Great Lakes in

1824-402: 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

1872-433: The pressure is high and conversely may expand upwards when the pressure above it is lowering. Fog can form multiple ways, depending on how the cooling occurred that caused the condensation. 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

1920-622: The relative humidity and causes marine layer clouds to evaporate. In the case of coastal California , the offshore marine layer is enabled by the cold relative sea surface temperatures of the Pacific Ocean. California receives this unusually cold water through a process called the California Current , where cool polar water is transported from the Gulf of Alaska to the California coast. This process creates anomalously cool water temperatures given

1968-672: 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. Shadows are cast through fog in three dimensions. The fog

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2016-463: 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. The water vapor cools and at the dewpoint it condenses and fog forms. 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

2064-415: 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 condensation onto cooler hard surfaces. Camanchaca is a similar dense fog. Depending on the concentration of the droplets, visibility in fog can range from

2112-506: 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 . Frontal fog forms in much

2160-425: 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. Particularly foggy places include Hamilton, New Zealand and 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 very foggy land areas in

2208-506: 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 fog-bank it may contain, will be "squashed" when

2256-425: The temperature rises. 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. Ice fog often leads to the visual phenomenon of light pillars . Up-slope fog or hill fog forms when winds blow air up

2304-592: The world include Argentia (Newfoundland) and Point Reyes (California), each with over 200 foggy days per year. 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

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