1.
Weather radar
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Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation, both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather. During World War II, radar operators discovered that weather was causing echoes on their screen, techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radars were used to detect precipitation, since then, weather radar has evolved on its own and is now used by national weather services, research departments in universities, and in television newscasts. Raw images are used and specialized software can take radar data to make short term forecasts of future positions and intensities of rain, snow, hail. Radar output is even incorporated into weather prediction models to improve analyses. During World War II, military radar operators noticed noise in returned echoes due to rain, snow, after the war, military scientists returned to civilian life or continued in the Armed Forces and pursued their work in developing a use for those echoes. In the United States, David Atlas, at first working for the Air Force and later for MIT, Marshall and R. H. Douglas formed the Stormy Weather Group in Montreal. By 1950 the UK company EKCO was demonstrating its airborne cloud, in 1953 Donald Staggs, an electrical engineer working for the Illinois State Water Survey, made the first recorded radar observation of a hook echo associated with a tornadic thunderstorm. Between 1950 and 1980, reflectivity radars, which measure position, the early meteorologists had to watch a cathode ray tube. During the 1970s, radars began to be standardized and organized into networks, the first devices to capture radar images were developed. The number of scanned angles was increased to get a view of the precipitation, so that horizontal cross-sections. Studies of the organization of thunderstorms were then possible for the Alberta Hail Project in Canada, the NSSL, created in 1964, began experimentation on dual polarization signals and on Doppler effect uses. In May 1973, a tornado devastated Union City, Oklahoma, for the first time, a Dopplerized 10 cm wavelength radar from NSSL documented the entire life cycle of the tornado. The researchers discovered a mesoscale rotation in the cloud aloft before the tornado touched the ground – the tornadic vortex signature, NSSLs research helped convince the National Weather Service that Doppler radar was a crucial forecasting tool. The Super Outbreak of tornadoes on 3–4 April 1974 and their devastating destruction might have helped to get funding for further developments, between 1980 and 2000, weather radar networks became the norm in North America, Europe, Japan and other developed countries. Conventional radars were replaced by Doppler radars, which in addition to position, in the United States, the construction of a network consisting of 10 cm radars, called NEXRAD or WSR-88D, was started in 1988 following NSSLs research. In Canada, Environment Canada constructed the King City station, with a 5 cm research Doppler radar, by 1985 and this led to a complete Canadian Doppler network between 1998 and 2004
2.
Precipitation
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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, 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 vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated, 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, moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain is occurring. A stationary front is often present near the area of freezing rain, provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. Eventually, the droplets will grow large enough to form raindrops. Lake-effect snowfall can be locally heavy, thundersnow is possible within a cyclones comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation, on the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. The movement of the trough, or intertropical convergence zone. Precipitation is a component of the water cycle, and is responsible for depositing the fresh water on the planet. Approximately 505,000 cubic kilometres of water falls as precipitation each year,398,000 cubic kilometres of it over the oceans and 107,000 cubic kilometres over land. Given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres, Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Precipitation may occur on celestial bodies, e. g. when it gets cold, Mars has precipitation which most likely takes the form of frost. Precipitation is a component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km3 of water falls as precipitation each year,398,000 km3 of it over the oceans, given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective, stratiform, and orographic rainfall, Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice
3.
Nimbostratus cloud
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This change in classification would once have made it a Family D cloud, but this style of nomenclature was discontinued by the WMO in 1956. Nimbostratus usually produces precipitation over a wide area, nimbo- is from the Latin word nimbus, which denotes precipitation. It has a cloud base generally found anywhere from near surface in the low levels. Although usually dark at its base, it often appears illuminated from within to a surface observer, Nimbostratus usually has a thickness of about 2000 m. Though found worldwide, nimbostratus occurs more commonly in the middle latitudes and it is coded CM2 on the SYNOP report. Downward-growing nimbostratus can have the vertical extent as most large upward-growing cumulus. This sometimes leads to the exclusion of nimbostratus from the group of vertical clouds by some independent meteorologists. Species and varieties, Nimbostratus is very thick, opaque, and featureless, precipitation-based supplementary features, Nimbostratus is a major precipitation cloud and produces the virga or praecipitatio features. The latter can achieve heavy intensity due to the vertical depth. Accessory cloud, Pannus frequently forms in precipitation and is coded CL7, genitus mother clouds, This genus type can form from cumulus and cumulonimbus. Mutatus mother clouds, Nimbostratus can form due to the transformation of altocumulus, altostratus and stratocumulus. Often, when an altostratus cloud thickens and descends into lower altitudes, lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it. The occurrence of cumulonimbus and nimbostratus together is uncommon, and usually only nimbostratus is found at a warm front, Nimbostratus pannus is an accessory cloud of nimbostratus that forms as a ragged layer in precipitation below the main cloud deck. Usually, nimbostratus is a sign of easily steady to powerful precipitation, however, precipitation does not occur at ground level in case of virga and accompanies other cloud types. Precipitation may last for days, depending on the speed of the warm or occluded front it accompanies. A nimbostratus virga cloud is the same as a normal nimbostratus cloud, stratus or stratocumulus usually forms when it clears. These were further divided into upper and lower types depending on altitude and it was then renamed nimbostratus, and published with the new name in the 1932 edition of the International Atlas of Clouds and of States of the Sky. This left cumulonimbus as the only nimbiform type as indicated by its root-name, national Science Digital Library - Nimbostratus Nimbostratus and Other Low Clouds
4.
Atmospheric convection
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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 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 development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes, there are a few general archetypes of atmospheric instability that correspond to convection and lack thereof. Steeper and/or positive lapse rates suggests atmospheric convection is more likely and this is because any displaced air parcels will become more buoyant, given their sign of adiabatic temperature change, in the steep lapse rate environments. Convection begins at the level of free convection, where it begins its ascent through the free convective layer, the rising parcel, if having enough momentum, will continue to rise to the maximum parcel level until negative buoyancy decelerates the parcel to a stop. Acceleration is of relevance to convection. Drag produced by the updraft creates a force to counter that from the buoyancy. This could be thought of as similar to the velocity of a falling object. This force from buoyancy can be measured by Convective Available Potential Energy, see the CAPE, buoyancy, and parcel links for a more in depth mathematical explanation of these processes. Within the atmosphere, this means from the surface to above the 500 hPa level, oceanic deep convection only occurs at a few locations. While less dynamically important than in the atmosphere, it is responsible for the spreading of cold water through the low layers of the ocean, as such, it is important for the large-scale temperature structure of the whole ocean. A thermal column is a section of rising air in the lower altitudes of the Earths atmosphere. Thermals are created by the heating of the Earths surface from solar radiation. The Sun warms the ground, which in turn warms the air directly above it, the warmer air expands, becoming less dense than the surrounding air mass, and creating a thermal low. The mass of air rises, and as it does. It stops rising when it has cooled to the temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column, the downward moving exterior is caused by colder air being displaced at the top of the thermal
5.
Tropical cyclone
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Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane, typhoon /taɪˈfuːn/, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface and this energy source differs from that of mid-latitude cyclonic storms, such as noreasters and European windstorms, which are fueled primarily by horizontal temperature contrasts. The strong rotating winds of a tropical cyclone are a result of the conservation of momentum imparted by the Earths rotation as air flows inwards toward the axis of rotation. As a result, they form within 5° of the equator. Tropical cyclones are typically between 100 and 2,000 km in diameter, Tropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas. Cyclone refers to their nature, with wind blowing counterclockwise in the Northern Hemisphere. The opposite direction of circulation is due to the Coriolis effect, in addition to strong winds and rain, tropical cyclones are capable of generating high waves, damaging storm surge, and tornadoes. They typically weaken rapidly over land where they are cut off from their energy source. For this reason, coastal regions are vulnerable to damage from a tropical cyclone as compared to inland regions. Heavy rains, however, can cause significant flooding inland, though their effects on human populations are often devastating, tropical cyclones can relieve drought conditions. They also carry heat away from the tropics and transport it toward temperate latitudes. Tropical cyclones are areas of low pressure in the troposphere. On Earth, the pressures recorded at the centers of tropical cyclones are among the lowest ever observed at sea level, the environment near the center of tropical cyclones is warmer than the surroundings at all altitudes, thus they are characterized as warm core systems. The near-surface wind field of a cyclone is characterized by air rotating rapidly around a center of circulation while also flowing radially inwards. At the outer edge of the storm, air may be nearly calm, however, due to the Earths rotation, as air flows radially inward, it begins to rotate cyclonically in order to conserve angular momentum. At an inner radius, air begins to ascend to the top of the troposphere and this radius is typically coincident with the inner radius of the eyewall, and has the strongest near-surface winds of the storm, consequently, it is known as the radius of maximum winds. Once aloft, air flows away from the center, producing a shield of cirrus clouds
6.
Cold front
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A cold front is defined as the leading edge of a cooler mass of air, replacing at ground level a warmer mass of air, which lies within a fairly sharp surface trough of low pressure. It forms in the wake of a cyclone, at the leading edge of its cold air advection pattern. Temperature changes across the boundary can exceed 30 °C, when enough moisture is present, rain can occur along the boundary. If there is significant instability along the boundary, a line of thunderstorms can form along the frontal zone. If instability is less, a shield of rain can move in behind the front. Cold fronts are stronger in the fall and spring transition seasons, when a cold front catches up with the preceding warm front, the portion of the boundary that does so is then known as an occluded front. The cooler and denser air wedges under the less-dense warmer air and this upward motion causes lowered pressure along the cold front and can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. On weather maps, the position of the cold front is marked with the symbol of a blue line of triangles/spikes pointing in the direction of travel. Cold fronts move faster than warm fronts and can produce changes in weather. Since cold air is denser than air, it rapidly replaces the warm air preceding the boundary. Normally, cold fronts can be marked by these characteristics, *provided there is sufficient moisture, if the cold front is highly unstable, cumulonimbus clouds producing thunderstorms commonly form along the front. Anvil cirrus clouds may spread a considerable distance downwind from the thunderstorms, the other cloud types associated with a cold front depend on atmospheric conditions such as air mass stability and wind shear. With significant airmass instability, vertically developed cumulus or cumulonimbus with showers, small and unchanging amounts of cumulus or cirrus clouds in an otherwise clear sky are usually indications of continuing fair weather as long as the barometric pressure remains comparatively high. A cold front commonly brings a band of precipitation that follows along the leading edge of the cold front. These bands of precipitation are very strong in nature. In the spring, these fronts can be very strong. During the winter months, cold fronts come through an area with little or no precipitation. Wider rain bands can occur behind cold fronts tend to have more stratiform
7.
Squall line
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A squall line is a line of thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front and it contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Strong straight-line winds can occur where the line is in the shape of a bow echo. Tornadoes can occur along waves within a line echo wave pattern, some bow echoes which develop within the summer season are known as derechos, and they move quite fast through large sections of territory. On the back edge of the rain associated with mature squall lines. Polar front theory was developed by Jacob Bjerknes, derived from a network of observation sites in Scandinavia during World War I. This theory proposed that the inflow into a cyclone was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The trailing convergence zone was referred to as the line or cold front. Areas of clouds and rainfall appeared to be focused along this convergence zone, the concept of frontal zones led to the concept of air masses. The nature of the structure of the cyclone was conceptualized after the development of the upper air network during the 1940s. Organized areas of thunderstorms activity reinforce pre-existing frontal zones, and they can outrun cold fronts and this outrunning occurs within the westerlies in a pattern where the upper level jet splits into two streams. The resultant mesoscale convective system forms at the point of the upper level split in the pattern in the area of best low level inflow. The convection then moves east and toward the equator into the warm sector, when the convection is strong linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise. This feature is commonly depicted in the season across the United States on surface analyses. If squall lines form over arid regions, a known as a haboob may result from the high winds in their wake picking up dust from the desert floor. Smaller cumulus or stratocumulus clouds, along with cirrus, and, sometimes, altocumulus or cirrocumulus and these clouds are the result of former cumulonimbus clouds having disintegrated, or an area of only minor instability ahead of the main squall line. The areas of dissipating squall line thunderstorms may be regions of low CAPE, low humidity, insufficient wind shear, from here, a general thinning of a squall line will occur, with winds decaying over time, outflow boundaries weakening updrafts substantially and clouds losing their thickness. Because of the nature of updrafts and downdrafts, pressure perturbations are important
8.
Tornado
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A tornado is a rapidly rotating column of air that spins while in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Most tornadoes have wind speeds less than 110 miles per hour, are about 250 feet across, the most extreme tornadoes can attain wind speeds of more than 300 miles per hour, are more than two miles in diameter, and stay on the ground for dozens of miles. Various types of tornadoes include the multiple vortex tornado, landspout and waterspout, waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water and these spiraling columns of air frequently develop in tropical areas close to the equator, and are less common at high latitudes. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirls, downbursts are frequently confused with tornadoes, though their action is dissimilar. Tornadoes have been observed and documented on every continent except Antarctica, however, the vast majority of tornadoes occur in the Tornado Alley region of the United States, although they can occur nearly anywhere in North America. There are several scales for rating the strength of tornadoes, the Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale. An F0 or EF0 tornado, the weakest category, damages trees, an F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes, Doppler radar data, photogrammetry, and ground swirl patterns may also be analyzed to determine intensity and assign a rating. The word tornado is a form of the Spanish word tronada. This in turn was taken from the Latin tonare, meaning to thunder and it most likely reached its present form through a combination of the Spanish tronada and tornar, however, this may be a folk etymology. A tornado is also referred to as a twister, and is also sometimes referred to by the old-fashioned colloquial term cyclone. The term cyclone is used as a synonym for tornado in the often-aired 1939 film The Wizard of Oz, the term twister is also used in that film, along with being the title of the 1996 tornado-related film Twister. A tornado is a rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud. For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a definition of the word, for example. Tornado refers to the vortex of wind, not the condensation cloud and this results in the formation of a visible funnel cloud or condensation funnel. There is some disagreement over the definition of cloud and condensation funnel
9.
Jet stream
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Jet streams are fast flowing, narrow, meandering air currents found in the atmosphere of some planets, including Earth. On Earth, the jet streams are located near the altitude of the tropopause and are westerly winds. Their paths typically have a meandering shape, Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet. The strongest jet streams are the jets, at 9–12 km above sea level. The Northern Hemisphere and the Southern Hemisphere each have a polar jet, the Coriolis force is caused by the planets rotation on its axis. On other planets, internal heat rather than solar heating drives their jet streams, the Polar jet stream forms near the interface of the Polar and Ferrel circulation cells, while the subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells. During the Northern Hemisphere summer, easterly jets can form in tropical regions, low-level jets also are typical of various regions such as the central United States. Meteorologists use the location of some of the jet streams as an aid in weather forecasting, often, the airlines work to fly with the jet stream for this reason. Clear-air turbulence, a hazard to aircraft passenger safety, is often found in a jet streams vicinity. After the 1883 eruption of the Krakatoa volcano, weather watchers tracked and mapped the effects on the sky over several years and they labelled the phenomenon the equatorial smoke stream. In the 1920s, a Japanese meteorologist, Wasaburo Oishi, detected the jet stream from a site near Mount Fuji and he tracked pilot balloons, also known as pibals, as they rose into the atmosphere. Oishis work largely went unnoticed outside Japan because it was published in Esperanto, American pilot Wiley Post, the first man to fly around the world solo in 1933, is often given some credit for discovery of jet streams. Post invented a suit that let him fly above 6,200 metres. In the year before his death, Post made several attempts at a high-altitude transcontinental flight, german meteorologist Heinrich Seilkopf is credited with coining a special term, Strahlströmung, for the phenomenon in 1939. Many sources credit real understanding of the nature of jet streams to regular, flyers consistently noticed westerly tailwinds in excess of 100 mph in flights, for example, from the US to the UK. Similarly in 1944 a team of American meteorologists in Guam, including Reid Bryson, had enough observations to forecast very high west winds that would slow bombers going to Japan. Polar jet streams are located near the 250 hPa pressure level, or 7 to 12 kilometres above sea level, while the weaker subtropical jet streams are much higher. Jet streams wander laterally dramatically, and have large changes in their altitude, the Polar jets, at lower altitude, and often intruding into mid-latitudes, strongly affects weather and aviation
