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
10.
Sea breeze
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As such sea breezes are more localised than prevailing winds. Because land absorbs solar radiation far more quickly than water, a sea breeze is an occurrence along coasts after sunrise. Sea breezes and land breezes are important factors in coastal regions prevailing winds. The term offshore wind may refer to any wind over open water, wind farms are often situated near a coast to take advantage of the normal daily fluctuations of wind speed resulting from sea or land breezes. The sea has a heat capacity than land, so the surface of the sea warms up more slowly than the lands surface. As the temperature of the surface of the land rises, the heats the air above it by conduction. The warm air is less dense and so it expands, decreasing the pressure over the land near the coast, the air above the sea has a relatively higher pressure, causing air near the coast to flow towards the lower pressure over land. The strength of the sea breeze is directly proportional to the difference between the land and the sea. If a strong wind is present, that is, a wind greater than 8 knots and opposing the direction of a possible sea breeze. A sea-breeze front is a front created by a sea breeze. The cold air from the sea meets the air from the land. When powerful this front creates cumulus clouds, and if the air is humid and unstable, the front can sometimes trigger thunderstorms. If the flow aloft is aligned with the direction of the sea breeze, places experiencing the sea breeze frontal passage will have benign, or fair, weather for the remainder of the day. At the front warm air continues to flow upward and cold air moves in to replace it. Its speed depends on whether it is assisted or hampered by the wind. At night, the sea breeze usually changes to a land breeze, thunderstorms caused by powerful sea breeze fronts frequently occur in Florida, a peninsula surrounded on both the east and west by the Atlantic Ocean and Gulf of Mexico, respectively. These storms also can produce significant hail due to the tremendous updraft it causes in the atmosphere especially during times when the atmosphere is cooler such as during the spring or fall. On calm summer afternoons with little prevailing wind, sea breezes from both coasts may collide in the middle, creating severe storms down the center of the state
11.
Land breeze
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As such sea breezes are more localised than prevailing winds. Because land absorbs solar radiation far more quickly than water, a sea breeze is an occurrence along coasts after sunrise. Sea breezes and land breezes are important factors in coastal regions prevailing winds. The term offshore wind may refer to any wind over open water, wind farms are often situated near a coast to take advantage of the normal daily fluctuations of wind speed resulting from sea or land breezes. The sea has a heat capacity than land, so the surface of the sea warms up more slowly than the lands surface. As the temperature of the surface of the land rises, the heats the air above it by conduction. The warm air is less dense and so it expands, decreasing the pressure over the land near the coast, the air above the sea has a relatively higher pressure, causing air near the coast to flow towards the lower pressure over land. The strength of the sea breeze is directly proportional to the difference between the land and the sea. If a strong wind is present, that is, a wind greater than 8 knots and opposing the direction of a possible sea breeze. A sea-breeze front is a front created by a sea breeze. The cold air from the sea meets the air from the land. When powerful this front creates cumulus clouds, and if the air is humid and unstable, the front can sometimes trigger thunderstorms. If the flow aloft is aligned with the direction of the sea breeze, places experiencing the sea breeze frontal passage will have benign, or fair, weather for the remainder of the day. At the front warm air continues to flow upward and cold air moves in to replace it. Its speed depends on whether it is assisted or hampered by the wind. At night, the sea breeze usually changes to a land breeze, thunderstorms caused by powerful sea breeze fronts frequently occur in Florida, a peninsula surrounded on both the east and west by the Atlantic Ocean and Gulf of Mexico, respectively. These storms also can produce significant hail due to the tremendous updraft it causes in the atmosphere especially during times when the atmosphere is cooler such as during the spring or fall. On calm summer afternoons with little prevailing wind, sea breezes from both coasts may collide in the middle, creating severe storms down the center of the state
12.
Extratropical cyclone
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Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale low pressure systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, the term cyclone applies to numerous types of low pressure areas, one of which is the extratropical cyclone. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics and they are termed mid-latitude cyclones if they form within those latitudes, or post-tropical cyclones if a tropical cyclone has intruded into the mid latitudes. Weather forecasters and the public often describe them simply as depressions or lows. Terms like frontal cyclone, frontal depression, frontal low, extratropical low, non-tropical low, Extratropical cyclones are classified mainly as baroclinic, because they form along zones of temperature and dewpoint gradient known as frontal zones. They can become barotropic late in their cycle, when the distribution of heat around the cyclone becomes fairly uniform with its radius. Extratropical cyclones form anywhere within the regions of the Earth. A study of extratropical cyclones in the Southern Hemisphere shows that between the 30th and 70th parallels, there are an average of 37 cyclones in existence during any 6-hour period, a separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter. Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, initially, cyclogenesis, or low pressure formation, occurs along frontal zones near a favorable quadrant of a maximum in the upper level jetstream known as a jet streak. The favorable quadrants are usually at the rear and left front quadrants. The divergence causes air to rush out from the top of the air column and this in turn forces convergence in the low-level wind field and increased upward motion within the column. The increased upward motion causes atmospheric pressure at ground level to lower and this is because the upward air motion counteracts gravity, lessening the weight of the atmosphere in that location. The lowered pressure strengthens the cyclone, as the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as the air ahead of the system is denser. Later, the cyclones occlude as the portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal. Eventually, the cyclone will become cold and begin to weaken. Atmospheric pressure can fall very rapidly when there are upper level forces on the system
13.
Rain
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Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for power plants. The major cause of production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus which can organize into narrow rainbands. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass, the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes. The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities, global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. The globally averaged annual precipitation over land is 715 mm, climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges, rainfall amounts can be estimated by weather radar. Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water. Air contains water vapor, and the amount of water in a mass of dry air. The amount of moisture in air is commonly reported as relative humidity. How much water vapor a parcel of air can contain before it becomes saturated, warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it, the dew point is the temperature to which a parcel must be cooled in order to become saturated. There are four mechanisms for cooling the air to its dew point, adiabatic cooling, conductive cooling, radiational cooling. Adiabatic cooling occurs when air rises and expands, the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a surface, usually by being blown from one surface to another. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath, evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation
14.
Snow
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Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime. As snow accumulates into a snowpack, it may blow into drifts, over time, accumulated snow metamorphoses, by sintering, sublimation and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form, otherwise, snow typically melts seasonally, causing runoff into streams and rivers and recharging groundwater. Major snow-prone areas include the regions, the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture. In the Southern Hemisphere, snow is confined primarily to mountainous areas, Snow affects ecosystems, as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold. Snow develops in clouds that themselves are part of a weather system. The physics of snow crystal development in clouds results from a set of variables that include moisture content. The resulting shapes of the falling and fallen crystals can be classified into a number of shapes and combinations. Occasionally, some plate-like, dendritic and stellar-shaped snowflakes can form under clear sky with a cold temperature inversion present. Two additional and locally productive sources of snow are lake-effect storms and elevation effects, miid-latitude cyclones are low pressure areas which are capable of producing anything from cloudiness and mild snow storms to heavy blizzards. During a hemispheres fall, winter, and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall, in the Northern Hemisphere, the northern side of the low pressure area produces the most snow. For the southern mid-latitudes, the side of a cyclone that produces the most snow is the southern side, a cold front, the leading edge of a cooler mass of air, can produce frontal snowsqualls—an intense frontal convective line, when temperature is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow. This type of snowsquall generally lasts less than 30 minutes at any point along its path, in cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed thundersnow. A warm front can produce snow for a period, as warm, moist air overrides below-freezing air, often, snow transitions to rain in the warm sector behind the front. The same effect occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the air mass is uplifted by the orographic influence of higher elevations on the downwind shores
15.
Great Lakes
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Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth, containing 21% of the worlds surface fresh water by volume. The total surface is 94,250 square miles, and the volume is 5,439 cubic miles. Due to their sea-like characteristics the five Great Lakes have also long been referred to as inland seas, Lake Superior is the second largest lake in the world by area, and Lake Michigan is the largest lake that is entirely within one country. The southern half of the Great Lakes is bordered by the Great Lakes Megalopolis, the lakes have been a major highway for transportation, migration and trade, and they are home to a large number of aquatic species. Many invasive species have been introduced due to trade, and some threaten the regions biodiversity, though the five lakes reside in separate basins, they form a single, naturally interconnected body of fresh water, within the Great Lakes Basin. The lakes form a chain connecting the interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, the lakes drain a large watershed via many rivers, and are studded with approximately 35,000 islands. There are also several smaller lakes, often called inland lakes. The surface area of the five primary lakes combined is roughly equal to the size of the United Kingdom, while the area of the entire basin is about the size of the UK. Lake Michigan is the one of the Great Lakes that is located entirely within the United States. The lakes are divided among the jurisdictions of the Canadian province of Ontario and the U. S. states of Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania, and New York. Both Ontario and Michigan include in their boundaries portions of four of the lakes, Ontario does not border Lake Michigan, New York and Wisconsins jurisdictions extend into two lakes, and the remaining states into one of the lakes. This designation, however, is not universal and those living on the shore of Lake Superior often refer to all the other lakes as the lower lakes, because they are farther south. This corresponds to thinking of Lakes Erie and Ontario as down south, vessels sailing north on Lake Michigan are considered upbound even though they are sailing toward its effluent current. The Chicago River and Calumet River systems connect the Great Lakes Basin to the Mississippi River System through man-made alterations, the St. Marys River, including the Soo Locks, connects Lake Superior to Lake Huron. The Straits of Mackinac connect Lake Michigan to Lake Huron, the St. Clair River connects Lake Huron to Lake St. Clair. The Detroit River connects Lake St. Clair to Lake Erie, the Niagara River, including Niagara Falls, connects Lake Erie to Lake Ontario. The Welland Canal, bypassing the Falls, connects Lake Erie to Lake Ontario, the Saint Lawrence River connects Lake Ontario to the Gulf of St. Lawrence, which connects to the Atlantic Ocean
16.
Lake-effect snow
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The same effect also occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, the areas affected by lake-effect snow are called snowbelts. A lake-effect blizzard is the blizzard-like conditions resulting from lake-effect snow, if the air temperature is low enough to keep the precipitation frozen, it falls as lake-effect snow. For lake-effect rain or snow to form, the air moving across the lake must be significantly cooler than the surface air. Specifically, the air temperature at an altitude where the air pressure is 850 millibars should be 13 °C lower than the temperature of the air at the surface. Lake-effect occurring when the air at 850 millibars is much colder than the surface can produce thundersnow, snow showers accompanied by lightning. A temperature difference of 13 °C between the temperature and the height in the atmosphere provides for absolute instability and allows vigorous heat. The distance that an air mass travels over a body of water is called fetch, because most lakes are irregular in shape, different angular degrees of travel will yield different distances, typically a fetch of at least 100 km is required to produce lake effect precipitation. Generally, the larger the fetch the more precipitation that will be produced, larger fetches provide the boundary layer with more time to become saturated with water vapor and for heat energy to move from the water to the air. If directional shear between the surface and the height in the atmosphere at which the pressure measures 700 mb is greater than 60 degrees. If the directional shear between the body of water and the height at which the pressure measures 700 mb is between 30 and 60 degrees, weak lake-effect bands are possible. In environments where the shear is less than 30 degrees, strong, speed shear is less critical, but should be relatively uniform. However, assuming the surface to 700 mb winds are uniform, an overall velocity will work to transport moisture quicker from the water. A lower upstream relative humidity will make it difficult and time consuming for lake effect condensation, clouds. The opposite is true if the moisture has a high relative humidity, allowing lake effect condensation, cloud and precipitation to form more readily. Any large body of water upwind will impact lake-effect precipitation to the lee of a lake by adding moisture or pre-existing lake-effect bands. Upwind lakes do not always lead to an increase of precipitation downwind, vorticity advection aloft and large upscale ascent help increase mixing and the convective depth, while cold air advection lowers the temperature and increases instability
17.
Occluded front
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An occluded front is formed during the process of cyclogenesis when a cold front overtakes a warm front. When this occurs, the air is separated from the cyclone center at the Earths surface. The point where the front and the occluded front meet is called the triple point. The trowal is the projection on the Earths surface of the trough of warm air aloft formed during the process of the depression. Occluded fronts usually form around mature low pressure areas, there are two types of occlusion, warm and cold, In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front, and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is not as cool as the air ahead of the warm front. The occluded front symbol should thus be plotted at the position where the air is intersecting the surface. It thus varies between warm and a cold occlusions, the trowal on the other hand, being the projection of the warm air trough aloft, is at the same position in both cases. The position of the front is often misplaced with the associated weather on a weather map. A cold front would be seen as spikes and a front as semi-circles in a traditional weather map. An occluded front, is a combination of two signs. On the other hand, trowal are indicated by junction of blue and red lines like the junction of cold, a wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Additionally, cold core funnel clouds are possible if shear is significant along the cold front, small isolated occluded fronts often remain for a time after a low pressure system has decayed and these create cloudy conditions with patchy rain or showers. However, the clouds and precipitation are not really where the projection on the Earths surface of the front is. A film clip AIR MASSES AND FRONTS - THE OCCLUDED FRONT is available at the Internet Archive Occluded Front
18.
Warm front
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A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. This also forces temperature differences across warm fronts to be broader in scale, clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage, clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, on weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel. Air masses are bodies of air with similar properties of temperature. The warm air mass behind a front is not only warmer. Because of a warm air mass’s higher temperature and thus lesser density, being light, the warm air mass is unable to displace the cooler air mass and instead is forced upward along the upper boundary of the colder air in a process known as overrunning. The boundary between the two air masses has a slope of 1,200 and lifting is slow but persistent. As the air rises into regions of lower pressure, it expands. As it cools, any water vapor that is present will condense, the first clouds that indicate an approaching warm front tend to be mostly high cirrus at first, changing to cirrostratus as the front approaches. However, if cirrocumulus also appears, there is greater airmass instability approaching ahead of the front, when these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 8 hours away. Once the clouds have thickened to 2,500 metres from the earth’s surface, if unstable altocumulus castellanus accompanies or takes the place of the main altostratus layer, cumulus congestus or cumulonimbus producing showers or thunderstorms may follow. Low stratus and stratocumulus commonly form underneath the main precipitating clouds, a warm front is also defined as the transition zone where a warmer air mass is replacing a cooler air mass. Warm fronts generally move from southwest to northeast, if the warmer air originates over the ocean, it is not only warmer but also more moist than the air ahead of it. If the air mass is relatively stable, rainfall will increase until the front reaches the location, once the front passes, the location experiences some warming and clearing. If the air mass is unstable, thunderstorms may precede and follow the front, in the northern hemisphere, a warm front causes a shift of wind blowing from southeast to southwest, and in the southern hemisphere a shift from winds blowing from northeast to northwest. Common characteristics associated with warm fronts include, The warm sector is the area of air behind a warm front. Temperatures are often warmer than they are before the front or after the cold front
19.
Wind shear
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Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as vertical or horizontal wind shear. Vertical wind shear is a change in speed or direction with change in altitude. Horizontal wind shear is a change in speed with change in lateral position for a given altitude. Wind shear has a significant effect during take-off and landing of aircraft due to its effects on control of the aircraft and this phenomenon is a concern for architects. Sound movement through the atmosphere is affected by shear, which can bend the wave front, causing sounds to be heard where they normally would not. The thermal wind concept explains how differences in speed at different heights are dependent on horizontal temperature differences. Wind shear refers to the variation of wind over either horizontal or vertical distances, airplane pilots generally regard significant wind shear to be a horizontal change in airspeed of 30 knots for light aircraft, and near 45 knots for airliners at flight altitude. Vertical speed changes greater than 4.9 knots also qualify as significant wind shear for aircraft, Low level wind shear can affect aircraft airspeed during take off and landing in disastrous ways, and airliner pilots are trained to avoid all microburst wind shear. Wind shear is also a key factor in the creation of severe thunderstorms, the additional hazard of turbulence is often associated with wind shear. Weather situations where shear is observed include, Weather fronts, significant shear is observed when the temperature difference across the front is 5 °C or more, and the front moves at 30 knots or faster. Because fronts are three-dimensional phenomena, frontal shear can be observed at any altitude between surface and tropopause, and therefore be seen both horizontally and vertically, vertical wind shear above warm fronts is more of an aviation concern than near and behind cold fronts due to their greater duration. Associated with upper level jet streams is a known as clear air turbulence. The CAT is strongest on the anticyclonic shear side of the jet, when a nocturnal low-level jet forms overnight above the Earths surface ahead of a cold front, significant low level vertical wind shear can develop near the lower portion of the low level jet. This is also known as wind shear since it is not due to nearby thunderstorms. When winds blow over a mountain, vertical shear is observed on the lee side, if the flow is strong enough, turbulent eddies known as rotors associated with lee waves may form, which are dangerous to ascending and descending aircraft. When on a clear and calm night, an inversion is formed near the ground. The change in wind can be 90 degrees in direction and 40 kt in speed, even a nocturnal low level jet can sometimes be observed
20.
Cyclone
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In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. A cyclone differs from a hurricane or typhoon only on the basis of location, a hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure, the largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within the smaller mesoscale, Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the Tropical Upper Tropospheric Trough during the summer months in the Northern Hemisphere. Cyclones have also seen on extraterrestrial planets, such as Mars. Cyclogenesis describes the process of formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones and these zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their cycle, extratropical cyclones occlude as cold air masses undercut the warmer air. A cyclones track is guided over the course of its 2 to 6 day life cycle by the flow of the subtropical jet stream. Weather fronts mark the boundary between two masses of air of different temperature, humidity, and densities, and are associated with the most prominent meteorological phenomena. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, such fronts form west of the circulation center and generally move from west to east, warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. Warm fronts move poleward ahead of the cyclone path, occluded fronts form late in the cyclone life cycle near the center of the cyclone and often wrap around the storm center. Tropical cyclogenesis describes the process of development of tropical cyclones, Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core. Cyclones can transition between extratropical, subtropical, and tropical phases, mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability, henry Piddington published almost 40 papers dealing with tropical storms from Calcutta between 1835 and 1855 in The Journal of the Asiatic Society. He also coined the term cyclone, meaning the coil of a snake, in 1842, he published his landmark thesis, Laws of the Storms. There are a number of characteristics common to all cyclones
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Mesoscale meteorology
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Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers, examples of mesoscale weather systems are sea breezes, squall lines, and mesoscale convective complexes. As in synoptic frontal analysis, mesoscale analysis uses cold, warm, on weather maps mesoscale fronts are depicted as smaller and with twice as many bumps or spikes as the synoptic variety. Microscale meteorology Misoscale meteorology POLYGON experiment Storm scale Surface weather analysis Synoptic scale meteorology http, //meted. ucar. edu/mesoprim/mesodefn/print. htm
22.
Hurricane Isidore
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Hurricane Isidore was the ninth named storm and the second hurricane in the 2002 Atlantic hurricane season. Isidore was the fifth of eight named storms to occur in September, the tropical cyclone peaked as a Category 3 hurricane, causing damage as well as four fatalities in Jamaica, Cuba, Mexico, and the United States. Its primary impact was the heavy rainfall fell across southeast Mexico. On September 9, a tropical wave moved off the coast of Africa, despite moving through a dry environment, its convection became organized as an anticyclone developed over the wave. On September 14, convection was well-organized enough around a closed wind circulation to classify the system as Tropical Depression Ten near Trinidad. Land interaction from Venezuela later weakened the depression back to a tropical wave, the wave continued west-northwestward through the Caribbean, and redeveloped into a tropical depression on September 17 while 140 miles south of Jamaica. Embedded within a weak steering current, it drifted to the northwest, after grazing the island, it quickly intensified to a hurricane late on September 19 while south of Cuba. Isidores maximum sustained winds reached 100 miles per hour near the Isle of Youth, the hurricane crossed the island, then slowed as it moved westward across the Gulf of Mexico. Favorable conditions aloft with warm water temperatures allowed Isidore to quickly intensify to a peak of 125 miles per hour winds on September 21 and it is the lowest minimum pressure ever observed for an Atlantic hurricane which did not exceed Category 3 intensity. With nearly ideal conditions for development, Isidore was forecast to reach winds of 150 miles per hour over the northern Gulf of Mexico, high pressures to its north forced it southward, and Isidore made landfall at Telchac Puerto in Yucatán as a major hurricane on September 22. It weakened rapidly as it stalled over Yucatán, and was only a minimal tropical storm after being inland for 30 hours. The inner core of convection collapsed while over southeast Mexico, and upon moving northward and reaching the Gulf of Mexico again, it was a large, conditions favored significant strengthening, but Isidore did not redevelop central convection until reaching the northern Gulf of Mexico. The strengthening system hit Grand Isle, Louisiana on September 26 as a 65 miles per hour tropical storm, the system raced to the northeast, and became an extratropical cyclone on September 27 before becoming absorbed in a frontal zone over Pennsylvania that night. Before Isidore became a hurricane, there were fears that the storm would end up being a significant threat, the upper level environment ahead of the storm was very favorable, and the oceanic heat content was very high. Just ten months after the destructive Hurricane Michelle, Hurricane Isidore threatened to cause effects in Cuba. In preparation for the storm, about 292,000 people, Hurricane Warnings were posted about 48 hours before landfall, leaving ample time to prepare for the storm. Once in the Gulf of Mexico, Hurricane Isidore became a major Category 3 storm with winds of 125 miles per hour, initially expected to remain north of the peninsula, hurricane warnings were issued just over a day prior to landfall, with no watch preceding Isidores passage. More than 70,000 people were evacuated, and ports on the Gulf coast of Yucatán were closed, Mexican authorities declared a state of emergency prior to the arrival of the storm
23.
Dvorak technique
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The Dvorak technique is a widely used system to estimate tropical cyclone intensity based solely on visible and infrared satellite images. Within the Dvorak satellite strength estimate for tropical cyclones, there are visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The primary patterns used are curved band pattern, shear pattern, central dense overcast pattern, central cold cover pattern, banding eye pattern, both the central dense overcast and embedded eye pattern use the size of the CDO. The CDO pattern intensities start at T2.5, equivalent to minimal tropical storm intensity, the shape of the central dense overcast is also considered. The eye pattern utilizes the coldness of the cloud tops within the mass of thunderstorms. The larger the difference is, the stronger the tropical cyclone. Once a pattern is identified, the features are further analyzed to arrive at a particular T-number. The CCC pattern indicates little development is occurring, despite the cold cloud tops associated with the quickly evolving feature, the initial development of this technique occurred in 1969 by Vernon Dvorak, using satellite pictures of tropical cyclones within the northwest Pacific ocean. The system as it was initially conceived involved pattern matching of cloud features with a development, constraints on short term intensity change are used less frequently than they were back in the 1970s and 1980s. The central pressures assigned to tropical cyclones have required modification, as the estimates were 5-10 hPa too low in the Atlantic. This led to the development of a separate wind-pressure relationship for the northwest Pacific, devised by Atkinson and Holliday in 1975, since tropical cyclone satellite patterns can fluctuate over time, automated techniques use a six-hour averaging period to lead to more reliable intensity estimates. Development of the objective Dvorak technique began in 1998, which performed best with tropical cyclones that had eyes and it still required a manual center placement, keeping some subjectivity within the process. By 2004, an advanced objective Dvorak technique was developed which utilized banding features for systems below hurricane intensity, the structure and organization of the tropical cyclone are tracked over 24 hours to determine if the storm has weakened, maintained its intensity, or strengthened. Various central cloud and banding features are compared with templates that show typical storm patterns, in each case a T-number and a Current Intensity value are assigned to the storm. These measurements range between 1 and 8, the T-number and CI value are the same except for weakening storms, in which case the CI is higher. For weakening systems, the CI is held as the tropical cyclone intensity for 12 hours, the table at right shows the approximate surface wind speed and sea level pressure that corresponds to a given T-number. The amount a tropical cyclone can change in strength per 24‑hour period is limited to 2.5 T-numbers per day. Within the Dvorak satellite strength estimate for tropical cyclones, there are visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity
24.
Low-pressure area
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A low-pressure area, low, or depression is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in the levels of the troposphere. The formation process of an area is known as cyclogenesis. Within the field of meteorology, atmospheric divergence aloft occurs in two areas, the first area is on the east side of upper troughs, which form half of a Rossby wave within the Westerlies. A second area of wind divergence aloft occurs ahead of embedded shortwave troughs, diverging winds aloft ahead of these troughs cause atmospheric lift within the troposphere below, which lowers surface pressures as upward motion partially counteracts the force of gravity. Thermal lows form due to localized heating caused by greater sunshine over deserts, since localized areas of warm air are less dense than their surroundings, this warmer air rises, which lowers atmospheric pressure near that portion of the Earths surface. Large-scale thermal lows over continents help drive monsoon circulations, low-pressure areas can also form due to organized thunderstorm activity over warm water. When this occurs over the tropics in concert with the Intertropical Convergence Zone, Monsoon troughs reach their northerly extent in August and their southerly extent in February. When a convective low acquires a well-hot circulation in the tropics it is termed a tropical cyclone, Tropical cyclones can form during any month of the year globally, but can occur in either the northern or southern hemisphere during November. Since clouds reflect sunlight, incoming solar radiation decreases, which causes lower temperatures during the day. At night the effect of clouds on outgoing longwave radiation, such as heat energy from the surface. The stronger the area of low pressure, the stronger the winds experienced in its vicinity, globally, low-pressure systems are most frequently located over the Tibetan Plateau and in the lee of the Rocky mountains. In Europe, recurring low-pressure weather systems are known as depressions. Cyclogenesis is the development and strengthening of cyclonic circulations, or low-pressure areas, cyclogenesis is the opposite of cyclolysis, and has an anticyclonic equivalent which deals with the formation of high-pressure areas—anticyclogenesis. Cyclogenesis is a term for several different processes, all of which result in the development of some sort of cyclone. Meteorologists use the term cyclone where circular pressure systems flow in the direction of the Earths rotation, the largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Subtropical cyclones are of intermediate size, cyclogenesis can occur at various scales, from the microscale to the synoptic scale
25.
Squall
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A squall is a sudden, sharp increase in wind speed that is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to an increase in the winds over a short time interval. There are different versions of the origins, By one version, the word appears to be Nordic in origin. It probably has its roots in the word skvala an Old Norse word meaning literally, by another version, it is an alteration of squeal influenced by bawl. The term squall is used to refer to a sudden wind-speed increase, in Australia, a squall is defined to last for several minutes before the wind returns to the long term mean value. In either case, a squall is defined to last about half as long as the definition of sustained wind in its respective country, usually, this sudden violent wind is associated with briefly heavy precipitation. Known locally as pamperos, these are characterized as strong downsloped winds that move across the pampas, offshore Central America, a gully squall is characterized by strong increases of the wind forced through sharp mountain valleys on the Pacific Ocean side of the isthmus. A bayamo is a squall emanating from tropical thunderstorms near the Bight of Bayamo, such a strong outflow occurring in fjords and inlets is referred to by mariners as a squamish. Bulls Eye Squall is a term used offshore South Africa for a squall forming in fair weather and it is named for the appearance of the small isolated cloud marking the top of the squall. In most parts of the country, squalls are called subasko and are characterized by heavy rains driven by blustery winds, local fishermen at sea are often on the lookout for signs of impending squalls on the open water and rush to shore at its early signs. Barat is a term for a northwest squall in Manado Bay in Sulawesi, Sumatra squall is a term used in Singapore and Peninsular Malaysia for squall lines that form over the island of Sumatra and move east across the Straits of Malacca. Gusts can reach up to 28 m/s, a squall line is an organized line of thunderstorms. It is classified as a cluster, meaning a thunderstorm complex comprising many individual updrafts. They are also called multi-cell lines, squalls are sometimes associated with hurricanes or other cyclones, but they can also occur independently. Squall lines require significant low-level warmth and humidity, a frontal zone. Significant squall lines with multiple bow echoes are known as derechos, pressure perturbations within an extent of a thunderstorm are noteworthy. With buoyancy rapid within the lower and mid-levels of a mature thunderstorm, however, this is not the case. With downdrafts ushering colder air from mid-levels, hitting ground and propagating away in all directions, high pressure is to be found widely at surface levels, wind shear is an important aspect to measuring the potential of squall line severity and duration
26.
Eye (cyclone)
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The eye is a region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a circular area, typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather occurs, the cyclones lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm. In strong tropical cyclones, the eye is characterized by light winds and clear skies, surrounded on all sides by a towering, symmetric eyewall. In weaker tropical cyclones, the eye is well defined and can be covered by the central dense overcast. Weaker or disorganized storms may also feature an eyewall that does not completely encircle the eye or have an eye that features heavy rain. In all storms, however, the eye is the location of the minimum barometric pressure - where the atmospheric pressure at sea level is the lowest. A typical tropical cyclone will have an eye of approximately 30–65 km across, the eye may be clear or have spotty low clouds, it may be filled with low- and mid-level clouds, or it may be obscured by the central dense overcast. There is, however, very little wind and rain, especially near the center and this is in stark contrast to conditions in the eyewall, which contains the storms strongest winds. Due to the mechanics of a cyclone, the eye. While normally quite symmetric, eyes can be oblong and irregular, a large ragged eye is a non-circular eye which appears fragmented, and is an indicator of a weak or weakening tropical cyclone. An open eye is an eye which can be circular, but the eyewall does not completely encircle the eye, also indicating a weakening, both of these observations are used to estimate the intensity of tropical cyclones via Dvorak analysis. Eyewalls are typically circular, however, distinctly polygonal shapes ranging from triangles to hexagons occasionally occur. While typical mature storms have eyes that are a few miles across, rapidly intensifying storms can develop an extremely small, clear. Storms with pinhole eyes are prone to fluctuations in intensity. Small/minuscule eyes—those less than 10 nmi across—often trigger eyewall replacement cycles and this can take place anywhere from fifteen to hundreds of kilometers outside the inner eye. The storm then develops two concentric eyewalls, or an eye within an eye, in most cases, the outer eyewall begins to contract soon after its formation, which chokes off the inner eye and leaves a much larger but more stable eye. While the replacement cycle tends to weaken storms as it occurs and this may trigger another re-strengthen cycle of eyewall replacement
27.
Tropical cyclone basins
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Traditionally, areas of tropical cyclone formation are divided into seven basins. The western Pacific is the most active and the north Indian the least active, an average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones. This region includes the North Atlantic Ocean, the Caribbean Sea, tropical cyclone formation here varies widely from year to year, ranging from one to over twenty-five per year. Most Atlantic tropical storms and hurricanes form between June 1 and November 30, on average,11 named storms occur each season, with an average of 6 becoming hurricanes and 2 becoming major hurricanes. The climatological peak of activity is around September 10 each season, the United States Atlantic coast and Gulf Coast, Mexico, Central America, the Caribbean Islands, and Bermuda are frequently affected by storms in this basin. Venezuela, the 4 provinces of Atlantic Canada, and Atlantic Macaronesian islands also are occasionally affected, many of the more intense Atlantic storms are Cape Verde-type hurricanes, which form off the west coast of Africa near the Cape Verde islands. Hurricane Vince, which made landfall on the southwestern coast of Spain as a depression in October 2005, is the only known system to impact mainland Europe as a tropical cyclone. The Northeastern Pacific is the second most active basin and has the highest number of storms per unit area, the hurricane season runs between May 15 and November 30 each year, and encompasses the vast majority of tropical cyclone activity in the region. In the 1971–2005 period, there were an average of 15–16 tropical storms,9 hurricanes, storms that form here often affect western Mexico, and less commonly the Continental United States, or northern Central America. Tropical storms in 1939,1976 and 1997 brought gale-force winds to California, the CPHC previously tasked with monitoring tropical activity in the basin was originally known as the Joint Hurricane Warning Center, today it is called the Joint Typhoon Warning Center. Central Pacific hurricanes are rare and on average 4 to 5 storms form or move in this area annually, the Northwest Pacific Ocean is the most active basin on the planet, accounting for one-third of all tropical cyclone activity. Annually, an average of 25.7 tropical cyclones in the basin acquire tropical storm strength or greater, also, the basin occupies all the territory north of the equator and west of the International Date Line, including the South China Sea. The basin sees activity year-round, however, tropical activity is at its minimum in February, sometimes, tropical storms in this region affect Cambodia, Laos, Malaysia, Thailand and even Singapore. The coast of China sees the most landfalling tropical cyclones worldwide, the Philippines archipelago receives an average of 6–7 tropical cyclone landfalls per year. This basin is divided into two areas, the Bay of Bengal and the Arabian Sea, with the Bay of Bengal dominating, still, this basin is the most inactive worldwide, with only 4 to 6 storms per year. This basins season has a peak, one in April and May, before the onset of the monsoon. Although it is a basin, the deadliest tropical cyclones in the world have formed here, including the 1970 Bhola cyclone. Nations affected include India, Bangladesh, Sri Lanka, Thailand, Myanmar, rarely do tropical cyclones that form in this basin affect the Arabian Peninsula or Somalia, however, Cyclone Gonu caused heavy damage in Oman on the peninsula in 2007
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Maximum sustained wind
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The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Surface winds are variable due to friction between the atmosphere and the Earths surface, as well as near hills and mountains over land. Over the ocean, satellite imagery determines the value of the sustained winds within a tropical cyclone. Land, ship, aircraft reconnaissance observations, and radar imagery can also estimate this quantity and this value helps determine damage expected from a tropical cyclone, through use of such scales as the Saffir-Simpson scale. However, the United States National Weather Service defines sustained winds within tropical cyclones by averaging winds over a period of one minute, measured at the same 10 metres height. This is an important distinction, as the value of the highest one-minute sustained wind is about 14% greater than a sustained wind over the same period. In most tropical cyclone basins, use of the satellite-based Dvorak technique is the method used to determine a tropical cyclones maximum sustained winds. The extent of banding and difference in temperature between the eye and eyewall is used within the technique to assign a maximum sustained wind. Central pressure values for their centers of low pressure are approximate, the intensity of example hurricanes is derived from both the time of landfall and the maximum intensity. The tracking of individual clouds on minutely satellite imagery could be used in the future in estimating surface winds speeds for tropical cyclones, ship and land observations are also used, when available. Doppler weather radar can be used in the manner to determine surface winds with tropical cyclones near land. Friction between the atmosphere and the Earths surface causes a 20% reduction in the wind at the surface of the Earth, surface roughness also leads to significant variation of wind speeds. Over land, winds maximize at hill or mountain crests, while sheltering leads to wind speeds in valleys. Compared to over water, maximum sustained winds over land average 8% lower, in most basins, maximum sustained winds are used to define their category. In the Atlantic and northeast Pacific oceans, the Saffir-Simpson scale is used and this scale can be used to determine possible storm surge and damage impact on land. In most basins, the category of the cyclone is determined from the cyclones maximum sustained wind. Only in Australia is this quantity not used to define the tropical category, in their basin
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Atmospheric pressure
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Atmospheric pressure, sometimes also called barometric pressure, is the pressure exerted by the weight of air in the atmosphere of Earth. In most circumstances atmospheric pressure is approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimetre in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilograms and that force is a pressure of 10.1 N/cm2 or 101 kN/m2. A column 1 square inch in cross-section would have a weight of about 14.7 lb or about 65.4 N and it is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The standard atmosphere is a unit of pressure defined as 101325 Pa, the mean sea level pressure is the average atmospheric pressure at sea level. This is the pressure normally given in weather reports on radio, television. When barometers in the home are set to match the weather reports, they measure pressure adjusted to sea level. The altimeter setting in aviation, is an atmospheric pressure adjustment, average sea-level pressure is 1013.25 mbar. In aviation weather reports, QNH is transmitted around the world in millibars or hectopascals, except in the United States, Canada, however, in Canadas public weather reports, sea level pressure is instead reported in kilopascals. The highest sea-level pressure on Earth occurs in Siberia, where the Siberian High often attains a sea-level pressure above 1050 mbar, the lowest measurable sea-level pressure is found at the centers of tropical cyclones and tornadoes, with a record low of 870 mbar. Pressure varies smoothly from the Earths surface to the top of the mesosphere, although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases, one can calculate the atmospheric pressure at a given altitude. Temperature and humidity affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph at right was developed for a temperature of 15 °C, at low altitudes above the sea level, the pressure decreases by about 1.2 kPa for every 100 meters. See pressure system for the effects of air pressure variations on weather, Atmospheric pressure shows a diurnal or semidiurnal cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few millibars and these variations have two superimposed cycles, a circadian cycle and semi-circadian cycle. The highest adjusted-to-sea level barometric pressure recorded on Earth was 1085.7 hPa measured in Tosontsengel
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Windward
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Windward is the direction upwind from the point of reference. Leeward is the direction downwind from the point of reference, the side of a ship that is towards the leeward is its lee side. If the vessel is heeling under the pressure of the wind, during the age of sail, the term weather was used as a synonym for windward in some contexts, as in the weather gage. Windward and leeward directions are important factors to consider when sailing a sailing ship, other terms with broadly the same meaning are widely used, particularly upwind and downwind. The windward vessel is normally the more maneuverable vessel, for this reason, rule 12 of the International Regulations for Preventing Collisions at Sea stipulates that the windward vessel gives way to the leeward vessel. The opposing warship to leeward could often do little but comply without exposing itself unduly and this was particularly important once artillery was introduced to naval warfare. The ships heeled away from the wind so that the vessel was exposing part of her bottom to shot. Leeward and windward refer respectively to what a game stalker would call downwind and upwind, the terms are used by seamen in relation to their ships but also in reference to islands in an archipelago and to the different sides of a single island. In the latter case, the side is that side of an island subject to the prevailing wind. The leeward side is the side protected by the elevation of the island from the prevailing wind, thus, leeward or windward siting is an important weather and climate factor on oceanic islands. In the case of an archipelago, windward islands are upwind and leeward islands are the downwind ones
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Lee wave
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In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves and these were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above the Krkonoše. They can also be caused by the wind blowing over an escarpment or plateau. The vertical motion forces periodic changes in speed and direction of the air within this air current and they always occur in groups on the lee side of the terrain that triggers them. Usually a turbulent vortex, with its axis of rotation parallel to the range, is generated around the first trough. The strongest lee waves are produced when the lapse rate shows a layer above the obstruction, with an unstable layer above. Lee waves are a form of gravity waves produced when stably stratified flow is forced over an obstacle. This disturbance elevates air parcels above their level of neutral buoyancy, oscillations tilted off the vertical axis at an angle of ϕ will occur at a lower frequency of N cos ϕ. These air parcel oscillations occur in concert, parallel to the wave fronts and these wave fronts represent extrema in the perturbed pressure field, while the areas between wave fronts represent extrema in the perturbed buoyancy field. Energy is transmitted along the fronts, which is the direction of the wave group velocity. In contrast, the propagation of the waves points perpendicular to energy transmission. Waves may also form in dry air without cloud markers, Wave clouds do not move downwind as clouds usually do, but remain fixed in position relative to the obstruction that forms them. Around the crest of the wave, adiabatic expansion cooling can form a cloud in shape of a lens, multiple lenticular clouds can be stacked on top of each other if there are alternating layers of relatively dry and moist air aloft. The rotor may generate cumulus or cumulus fractus in its upwelling portion, the rotor cloud looks like a line of cumulus. It forms on the lee side and parallel to the ridge line and its base is near the height of the mountain peak, though the top can extend well above the peak and can merge with the lenticular clouds above. Rotor clouds have ragged edges and are dangerously turbulent. A foehn wall cloud may exist at the lee side of the mountains, a pileus or cap cloud, similar to a lenticular cloud, may form above the mountain or cumulus cloud generating the wave. Adiabatic compression heating in the trough of each wave oscillation may also evaporate cumulus or stratus clouds in the airmass, lee waves provide a possibility for gliders to gain altitude or fly long distances when soaring
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Thunderstorm
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Thunderstorms occur in association with a type of cloud known as a cumulonimbus. They are usually accompanied by winds, heavy rain, and sometimes snow, sleet, hail, or, in contrast. Thunderstorms may line up in a series or become a rainband, strong or severe thunderstorms, known as supercells, rotate as do cyclones. Thunderstorms result from the upward movement of warm, moist air. As the warm, moist air moves upward, it cools, condenses, as the rising air reaches its dew point temperature, water vapor condenses into water droplets or ice, reducing pressure locally within the thunderstorm cell. Any precipitation falls the long distance through the clouds towards the Earths surface, as the droplets fall, they collide with other droplets and become larger. Thunderstorms can form and develop in any location but most frequently within the mid-latitude. Thunderstorms are responsible for the development and formation of many weather phenomena. Thunderstorms, and the phenomena that occur along them, pose great hazards. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, stronger thunderstorm cells are capable of producing tornadoes and waterspouts. There are four types of thunderstorms, single-cell, multi-cell cluster, multi-cell lines, supercell thunderstorms are the strongest and the most associated with severe weather phenomena. Mesoscale convective systems formed by vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes. Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires from the heat generated from the lightning that accompanies them. Several means are used to study thunderstorms, weather radar, weather stations, past civilizations held various myths concerning thunderstorms and their development as late as the 18th century. Beyond the Earths atmosphere, thunderstorms have also observed on the planets of Jupiter, Saturn, Neptune. Warm air has a lower density than air, so warmer air rises upwards. Clouds form as relatively warmer air, carrying moisture, rises within cooler air, the moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning, Meteorological indices such as convective available potential energy and the lifted index can be used to assist in determining potential upward vertical development of clouds
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Ocean current
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Depth contours, shoreline configurations, and interactions with other currents influence a currents direction and strength. Therefore ocean currents are primarily horizontal water movements, Ocean currents flow for great distances, and together, create the global conveyor belt which plays a dominant role in determining the climate of many of the Earth’s regions. More specifically, ocean currents influence the temperature of the regions through which they travel, for example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any region at the same latitude. Another example is Lima, Peru where the climate is cooler than the tropical latitudes in which the area is located, in these wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. In addition, the areas of ocean currents move somewhat with the seasons. Deep ocean basins generally have a surface current, in that the eastern equatorward-flowing branch is broad. These western boundary currents are a consequence of the rotation of the Earth, Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation is known as the oceans conveyor belt. These currents, called submarine rivers, flow under the surface of the ocean and are hidden from immediate detection, where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling. Deep ocean currents are currently being researched using a fleet of robots called Argo. The South Equatorial Currents of the Atlantic and Pacific straddle the equator, though the Coriolis effect is weak near the equator, water moving in the currents on either side of the equator is deflected slightly poleward and replaced by deeper water. Thus, equatorial upwelling occurs in these westward flowing equatorial surface currents, upwelling is an important process because this water from within and below the pycnocline is often rich in nutrients and greatly benefits the growth of marine organisms. By contrast, generally poor conditions for growth prevail in most of the tropical ocean because strong layering isolates deep. Ocean currents are measured in sverdrup, where 1 sv is equivalent to a flow rate of 1,000,000 m3 per second. Surface currents are found on the surface of an ocean, and are driven by large scale wind currents and they are directly affected by the wind—the Coriolis effect plays a role in their behaviors. Horizontal and vertical currents also exist below the pycnocline in the deeper waters. The movement of water due to differences in density as a function of water temperature, ripple marks in sediments, scour lines, and the erosion of rocky outcrops on deep-ocean floors are evidence that relatively strong, localized bottom currents exist
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California
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California is the most populous state in the United States and the third most extensive by area. Located on the western coast of the U. S, California is bordered by the other U. S. states of Oregon, Nevada, and Arizona and shares an international border with the Mexican state of Baja California. Los Angeles is Californias most populous city, and the second largest after New York City. The Los Angeles Area and the San Francisco Bay Area are the nations second- and fifth-most populous urban regions, California also has the nations most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The Central Valley, an agricultural area, dominates the states center. What is now California was first settled by various Native American tribes before being explored by a number of European expeditions during the 16th and 17th centuries, the Spanish Empire then claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its war for independence. The western portion of Alta California then was organized as the State of California, the California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom. If it were a country, California would be the 6th largest economy in the world, fifty-eight percent of the states economy is centered on finance, government, real estate services, technology, and professional, scientific and technical business services. Although it accounts for only 1.5 percent of the states economy, the story of Calafia is recorded in a 1510 work The Adventures of Esplandián, written as a sequel to Amadis de Gaula by Spanish adventure writer Garci Rodríguez de Montalvo. The kingdom of Queen Calafia, according to Montalvo, was said to be a land inhabited by griffins and other strange beasts. This conventional wisdom that California was an island, with maps drawn to reflect this belief, shortened forms of the states name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, various estimates of the native population range from 100,000 to 300,000. The Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups also were diverse in their organization with bands, tribes, villages. Trade, intermarriage and military alliances fostered many social and economic relationships among the diverse groups, the first European effort to explore the coast as far north as the Russian River was a Spanish sailing expedition, led by Portuguese captain Juan Rodríguez Cabrillo, in 1542. Some 37 years later English explorer Francis Drake also explored and claimed a portion of the California coast in 1579. Spanish traders made unintended visits with the Manila galleons on their trips from the Philippines beginning in 1565
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Wayback Machine
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The Internet Archive launched the Wayback Machine in October 2001. It was set up by Brewster Kahle and Bruce Gilliat, and is maintained with content from Alexa Internet, the service enables users to see archived versions of web pages across time, which the archive calls a three dimensional index. Since 1996, the Wayback Machine has been archiving cached pages of websites onto its large cluster of Linux nodes and it revisits sites every few weeks or months and archives a new version. Sites can also be captured on the fly by visitors who enter the sites URL into a search box, the intent is to capture and archive content that otherwise would be lost whenever a site is changed or closed down. The overall vision of the machines creators is to archive the entire Internet, the name Wayback Machine was chosen as a reference to the WABAC machine, a time-traveling device used by the characters Mr. Peabody and Sherman in The Rocky and Bullwinkle Show, an animated cartoon. These crawlers also respect the robots exclusion standard for websites whose owners opt for them not to appear in search results or be cached, to overcome inconsistencies in partially cached websites, Archive-It. Information had been kept on digital tape for five years, with Kahle occasionally allowing researchers, when the archive reached its fifth anniversary, it was unveiled and opened to the public in a ceremony at the University of California, Berkeley. Snapshots usually become more than six months after they are archived or, in some cases, even later. The frequency of snapshots is variable, so not all tracked website updates are recorded, Sometimes there are intervals of several weeks or years between snapshots. After August 2008 sites had to be listed on the Open Directory in order to be included. As of 2009, the Wayback Machine contained approximately three petabytes of data and was growing at a rate of 100 terabytes each month, the growth rate reported in 2003 was 12 terabytes/month, the data is stored on PetaBox rack systems manufactured by Capricorn Technologies. In 2009, the Internet Archive migrated its customized storage architecture to Sun Open Storage, in 2011 a new, improved version of the Wayback Machine, with an updated interface and fresher index of archived content, was made available for public testing. The index driving the classic Wayback Machine only has a bit of material past 2008. In January 2013, the company announced a ground-breaking milestone of 240 billion URLs, in October 2013, the company announced the Save a Page feature which allows any Internet user to archive the contents of a URL. This became a threat of abuse by the service for hosting malicious binaries, as of December 2014, the Wayback Machine contained almost nine petabytes of data and was growing at a rate of about 20 terabytes each week. Between October 2013 and March 2015 the websites global Alexa rank changed from 162 to 208, in a 2009 case, Netbula, LLC v. Chordiant Software Inc. defendant Chordiant filed a motion to compel Netbula to disable the robots. Netbula objected to the motion on the ground that defendants were asking to alter Netbulas website, in an October 2004 case, Telewizja Polska USA, Inc. v. Echostar Satellite, No.02 C3293,65 Fed. 673, a litigant attempted to use the Wayback Machine archives as a source of admissible evidence, Telewizja Polska is the provider of TVP Polonia and EchoStar operates the Dish Network
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University of Wyoming
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It is known as UW to people close to the university. The university was founded in March 1886, four years before the territory was admitted as the 44th state, the University of Wyoming is unusual in that its location within the state is written into the states constitution. The university also offers education in communities throughout Wyoming and online. The University of Wyoming consists of seven colleges, agriculture and natural resources, arts and sciences, business, education, engineering and applied sciences, health sciences, the university offers over 190 undergraduate, graduate and certificate programs including Doctor of Pharmacy and Juris Doctor. The University of Wyoming was featured in the 2011 Princeton Review Best 373 Colleges, in addition to on-campus classes in Laramie, the university’s Outreach School offers more than 41 degree, certificate and endorsement programs to distance learners across the state and beyond. These programs are delivered through the use of technology, such as online, the Outreach School has nine regional centers across the state, with several on community college campuses, to give Wyoming residents access to a university education without relocating to Laramie. On September 27,1886, the cornerstone of Old Main was laid marking the beginning of the University of Wyoming, the stone is inscribed Domi Habuit Unde Disceret, which is often translated, He need not go away from home for instruction. The following year, the first class of 42 men and women began their college education, for the next decade the building housed classrooms, a library and administration offices. The style of Old Main set a precedent for all future University buildings, the main stone used is rough-cut sandstone from a quarry east of Laramie and the trim stone is smooth Potsdam Sandstone from a quarry near Rawlins. Old Main was designed to be a structure and was designed to be a symmetrical building with a prominent central spire as the focal point. The building was designed to reflect the character of Wyoming. The design of Old Main had an effect on university structures. In 1916, the spire was removed due to structural concerns. In 1949, the building was thoroughly remodeled—the auditorium and exterior stairs were completely removed and it also became officially known as Old Main and the name was carved above the east entrance. Currently, Old Main houses university administration including the Presidents Office, Prexys Pasture is a large grassy area located within a ring of classroom and administrative buildings and serves as the center mall of the campus. The name is attributed to a rule that the university president. During the administration of Arthur G. Crane the name, Prexys Pasture, was formally declared, Prexys, as it is often called today, is also known for the unique pattern formed by concrete pathways that students and faculty use to cross the pasture. When the University of Wyoming first opened its doors in 1887, the football team played their games on the pasture until 1922, when Corbett Field opened at the southeast corner of campus
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National Weather Service
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It is a part of the National Oceanic and Atmospheric Administration branch of the Department of Commerce, and is headquartered in Silver Spring, Maryland. The agency was known as the United States Weather Bureau from 1890 until it adopted its current name in 1970, the NWS performs its primary task through a collection of national and regional centers, and 122 local weather forecast offices. As the NWS is a government agency, most of its products are in the public domain, the agency was placed under the Secretary of War as Congress felt military discipline would probably secure the greatest promptness, regularity, and accuracy in the required observations. Within the Department of War, it was assigned to the U. S. Army Signal Service under Brigadier General Albert J. Myer, General Myer gave the National Weather Service its first name, The Division of Telegrams and Reports for the Benefit of Commerce. The agency first became an enterprise in 1890, when it became part of the Department of Agriculture. The first Weather Bureau radiosonde was launched in Massachusetts in 1937, the Bureau would later be moved to the Department of Commerce in 1940. On July 12,1950, bureau chief Francis W, the Weather Bureau became part of the Environmental Science Services Administration when that agency was formed in August 1966. The Environmental Science Services Administration was renamed the National Oceanic and Atmospheric Administration on October 1,1970, at this time, the Weather Bureau became the National Weather Service. NEXRAD, a system of Doppler radars deployed to improve the detection and warning time of local storms, replaced the WSR-57. Bob Glahn has written a history of the first hundred years of the National Weather Service. The NWS, through a variety of sub-organizations, issues different forecast products to users, although, throughout history, text forecasts have been the means of product dissemination, the NWS has been using more forecast products of a digital, gridded, image or other modern format. Each of the 122 Weather Forecast Offices send their graphical forecasts to a server to be compiled in the National Digital Forecast Database. The NDFD is a collection of weather observations used by organizations and the public, including precipitation amount, temperature. Specific points in the database can be accessed using an XML SOAP service. The National Weather Service issues many products relating to wildfires daily, for example, a Fire Weather Forecast, which have a forecast period covering up to seven days, is issued by local Weather Forecast Offices daily, with updates as needed. The forecasts contain weather information relevant to fire control and smoke management for the next 12 to 48 hours, such as direction and speed. The appropriate crews use this information to plan for staffing and equipment levels, the ability to conduct scheduled controlled burns, and assess the daily fire danger. Once per day, NWS meteorologists issue a coded fire weather forecast for specific United States Forest Service observation sites that are input into the National Fire Danger Rating System
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National Oceanic and Atmospheric Administration
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The National Oceanic and Atmospheric Administration is an American scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. NOAA warns of dangerous weather, charts seas, guides the use and protection of ocean and coastal resources, and conducts research to improve understanding and stewardship of the environment. In addition to its employees, over 11,000 as of 2015, NOAA research. NOAA plays several roles in society, the benefits of which extend beyond the U. S. economy and into the larger global community. NOAA supplies information to its customers and partners pertaining to the state of the oceans and this is clearly manifest in the production of weather warnings and forecasts through the National Weather Service, but NOAAs information products extend to climate, ecosystems, and commerce as well. A Provider of Environmental Stewardship Services, NOAA is also the steward of U. S. coastal and marine environments. A Leader in Applied Scientific Research, the five fundamental activities are, Monitoring and observing Earth systems with instruments and data collection networks. Understanding and describing Earth systems through research and analysis of that data, assessing and predicting the changes of these systems over time. Engaging, advising, and informing the public and partner organizations with important information, managing resources for the betterment of society, economy and environment. NOAA formed a conglomeration of several existing agencies that were among the oldest in the federal government, NOAA was established within the Department of Commerce via the Reorganization Plan No.4 of 1970. In 2007 NOAA celebrated 200 years of service with its ties to the United States Coast, the NOAA Commissioned Officer Corps is a uniformed service of men and women who operate NOAA ships and aircraft, and serve in scientific and administrative posts. And in addition more than a dozen staff offices, including the Office of the Federal Coordinator for Meteorology, the NOAA Central Library and this is done through a collection of national and regional centers,13 river forecast centers, and more than 120 local weather forecast offices. They are charged with issuing weather and river forecasts, advisories, watches and they issue more than 734,000 weather and 850,000 river forecasts, and more than 45,000 severe weather warnings annually. NOAA data is relevant to the issues of global warming. The NWS operates NEXRAD, a network of Doppler weather radars which can detect precipitation. Many of their products are broadcast on NOAA Weather Radio, a network of transmitters that broadcasts weather forecasts, severe weather statements, watches. The National Ocean Service focuses on ensuring that ocean and coastal areas are safe, healthy, in 1960 TIROS-1, NOAAs first owned and operated geostationary satellite was launched. Since 1966 NESDIS has managed polar orbiting satellites and since 1974 it has operated geosynchronous satellites, in 1979 NOAAs first polar-orbiting environmental satellite was launched
