1.
Cirrus cloud
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Cirrus is a genus of atmospheric cloud generally characterized by thin, wispy strands, giving the type its name from the Latin word cirrus, meaning a ringlet or curling lock of hair. This cloud can form anywhere between 16,500 and 45,000 feet in the sky, the strands of cloud sometimes appear in tufts of a distinctive form referred to by the common name of mares tails. On planet Earth, cirrus generally appears white or light gray in color and it forms when water vapor undergoes deposition at altitudes above 5,500 m in temperate regions and above 6,400 m in tropical regions. It also forms from the outflow of tropical cyclones or the anvils of cumulonimbus cloud, since cirrus clouds arrive in advance of the frontal system or tropical cyclone, it indicates that weather conditions may soon deteriorate. While it indicates the arrival of precipitation, cirrus clouds only produce fall streaks, jet stream-powered cirrus can grow long enough to stretch across continents while remaining only a few kilometers deep. When visible light interacts with the ice crystals in cirrus cloud, it produces optical phenomena such as sun dogs, Cirrus is known to raise the temperature of the air beneath the main cloud layer by an average of 10 °C. When the individual filaments become so extensive that they are virtually indistinguishable from one another, convection at high altitudes can produce another high-based genus called cirrocumulus, a pattern of small cloud tufts that contain droplets of supercooled water. Cirrus clouds form on planets, including Mars, Jupiter, Saturn, Uranus. They have even seen on Titan, one of Saturns moons. Some of these extraterrestrial cirrus clouds are composed of ammonia or methane ice rather than water ice, the term cirrus is also used for certain interstellar clouds composed of sub-micrometer-sized dust grains. Cirrus cloud ranges in thickness from 100 m to 8,000 m, with an average thickness of 1,500 m. There are, on average,30 ice crystals per liter, but this ranges from one ice crystal per 10,000 liters to 10,000 ice crystals per liter, a difference of eight orders of magnitude. The length of each of these ice crystals is usually 0.25 millimeters long, the ice crystals in contrails are much smaller than those in naturally occurring cirrus cloud, as they are around 0.001 millimeters to 0.1 millimeters in length. Cirrus can vary in temperature from −20 °C to −30 °C, the ice crystals in cirrus clouds have different shapes in addition to different sizes. Some shapes include solid columns, hollow columns, plates, rosettes, the shape of the ice crystals is determined by the air temperature, atmospheric pressure, and ice supersaturation. Cirrus in temperate regions typically have the shapes segregated by type, in the northern Arctic region, cirrus tend to be composed of only the columns, plates, and conglomerations, and these crystals tend to be at least four times larger than the minimum size. In Antarctica, cirrus are usually composed of only the columns, scientists have studied the characteristics of cirrus using several different methods. One, Light Detection and Ranging, gives highly accurate information on the altitude, length
2.
Wind gradient
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It is the rate of increase of wind strength with unit increase in height above ground level. In metric units, it is measured in units of meters per second of speed, per kilometer of height. This layer, where friction slows the wind and changes the wind direction, is known as the planetary boundary layer. Daytime solar heating due to insolation thickens the boundary layer as winds at the surface become increasingly mixed with winds aloft. Radiative cooling overnight decouples the winds at the surface from the winds above the layer, increasing vertical wind shear near the surface. Typically, due to drag, there is a wind gradient in the wind flow just a few hundred meters above the Earths surface—the surface layer of the planetary boundary layer. Wind speed increases with increasing height above the ground, starting from zero due to the no-slip condition, flow near the surface encounters obstacles that reduce the wind speed, and introduce random vertical and horizontal velocity components at right angles to the main direction of flow. The reduction in velocity near the surface is a function of surface roughness, rough, irregular ground, and man-made obstructions on the ground, retard movement of the air near the surface, reducing wind velocity. Because of low surface roughness on the smooth water surface. Over a city or rough terrain, the wind gradient effect could cause a reduction of 40% to 50% of the wind speed aloft, while over open water or ice. For example, typical values for the predicted gradient height are 457 m for large cities,366 m for suburbs,274 m for open terrain, although the power law exponent approximation is convenient, it has no theoretical basis. The shearing of the wind is usually three-dimensional, that is and this is related to the Ekman spiral effect. After sundown the wind gradient near the surface increases, with the increasing stability, atmospheric stability occurring at night with radiative cooling tends to contain turbulent eddies vertically, increasing the wind gradient. In the convective layer, strong mixing diminishes vertical wind gradient. The design of buildings must account for wind loads, and these are affected by wind gradient, the respective gradient levels, usually assumed in the Building Codes, are 500 meters for cities,400 meters for suburbs, and 300 m for flat open terrain. Vertical wind-speed profiles result in different wind speeds at the blades nearest to the ground compared to those at the top of blade travel. The wind gradient can create a bending moment in the shaft of a two bladed turbine when the blades are vertical. The reduced wind gradient over water means shorter and less expensive wind turbine towers can be used in shallow seas and it would be preferable for wind turbines to be tested in a wind tunnel simulating the wind gradient that they will eventually see, but this is rarely done
3.
Wind
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Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the movement of air. Winds are commonly classified by their scale, their speed, the types of forces that cause them, the regions in which they occur. The strongest observed winds on a planet in the Solar System occur on Neptune, Winds have various aspects, an important one being its velocity, another the density of the gas involved, another its energy content or wind energy. In meteorology, winds are referred to according to their strength. Short bursts of high speed wind are termed gusts, strong winds of intermediate duration are termed squalls. Long-duration winds have various names associated with their strength, such as breeze, gale, storm. The two main causes of large-scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet, within the tropics, thermal low circulations over terrain and high plateaus can drive monsoon circulations. In coastal areas the sea breeze/land breeze cycle can define local winds, in areas that have variable terrain, mountain, Wind powers the voyages of sailing ships across Earths oceans. Hot air balloons use the wind to take trips, and powered flight uses it to increase lift. Areas of wind caused by various weather phenomena can lead to dangerous situations for aircraft. When winds become strong, trees and man-made structures are damaged or destroyed, Winds can shape landforms, via a variety of aeolian processes such as the formation of fertile soils, such as loess, and by erosion. Wind also affects the spread of wildfires, Winds can disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect populations. When combined with temperatures, wind has a negative impact on livestock. Wind affects animals food stores, as well as their hunting, Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the pressure area. On a rotating planet, air will also be deflected by the Coriolis effect, globally, the two major driving factors of large-scale wind patterns are the differential heating between the equator and the poles and the rotation of the planet. Outside the tropics and aloft from frictional effects of the surface, near the Earths surface, friction causes the wind to be slower than it would be otherwise
4.
Wind speed
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Wind speed, or wind flow velocity, is a fundamental atmospheric quantity. Wind speed is caused by air moving from high pressure to low pressure, Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications. Wind speed is now commonly measured with an anemometer but can also be classified using the older Beaufort scale which is based on observation of specifically defined wind effects. Wind speed is affected by a number of factors and situations and these include the pressure gradient, Rossby waves and jet streams, and local weather conditions. There are also links to be found between wind speed and wind direction, notably with the gradient and terrain conditions. Pressure gradient is a term to describe the difference in air pressure between two points in the atmosphere or on the surface of the Earth and it is vital to wind speed, because the greater the difference in pressure, the faster the wind flows to balance out the variation. The pressure gradient, when combined with the Coriolis effect and friction, Rossby waves are strong winds in the upper troposphere. These operate on a scale and move from West to East. The Rossby waves are themselves a different wind speed from what we experience in the lower troposphere, the wind gust was evaluated by the WMO Evaluation Panel who found that the anemometer was mechanically sound and the gust was within statistical probability and ratified the measurement in 2010. The anemometer was mounted 10 m above ground level, the pattern and scales of the gusts suggest that a mesovortex was embedded in the already strong eyewall of the cyclone. The now second highest surface wind speed ever recorded is 372 km/h at the Mount Washington Observatory,6,288 ft above sea level in the US on 12 April 1934. The anemometer, specifically designed for use on Mount Washington was later tested by the US National Weather Bureau, Wind speeds within certain atmospheric phenomena may greatly exceed these values but have never been accurately measured. Directly measuring these tornadic winds is rarely done as the violent wind would destroy the instruments, another method of estimating is to use Doppler on Wheels to sense the wind speeds remotely. The figure of 486 km/h during the 1999 Bridge Creek–Moore tornado in Oklahoma on 3 May 1999 is often quoted as the surface wind speed. However, another figure of 512 kilometres per hour has also quoted for the same tornado. Yet another number used by the Center for Severe Weather Research for that measurement is 486 ±32 km/h, however, speeds measured by Doppler radar are not considered official records. Wind speed is a factor in the design of structures. It is often the governing factor in the required strength of a structures design
5.
Wind direction
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Wind direction is reported by the direction from which it originates. For example, a wind blows from the north to the south. Wind direction is reported in cardinal directions or in azimuth degrees. Wind direction is measured in degrees clockwise from due north and so a wind coming from the south has a direction of 180 degrees. A variety of instruments can be used to wind direction, such as the windsock. Both of these work by moving to minimize air resistance. The way a weather vane is pointed by prevailing winds indicates the direction from which the wind is blowing. The larger opening of a windsock faces the direction that the wind is blowing from, its tail, with the smaller opening, modern instruments used to measure wind speed and direction are called anemometers and wind vanes, respectively. These types of instruments are used by the energy industry. In situations where modern instruments are not available, a finger can be used to test the direction of wind. This is accomplished by wetting the finger and pointing it upwards, the side of the finger that feels cool is the direction from which the wind is blowing. The same principle is used to measure the dew point using a sling psychrometer, another primitive technique for measuring wind direction is to take a pinch of grass and drop it, the direction that the grass falls is the direction the wind is blowing. This last technique is used by golfers because it allows them to gauge the strength of the wind as well. Yamartino method for calculating the standard deviation of wind direction Apparent wind Weather vane Wind power Air masses
6.
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
7.
Synoptic scale meteorology
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The synoptic scale in meteorology is a horizontal length scale of the order of 1000 kilometres or more. This corresponds to a horizontal scale typical of mid-latitude depressions, most high and low-pressure areas seen on weather maps such as surface weather analyses are synoptic-scale systems, driven by the location of Rossby waves in their respective hemisphere. Low-pressure areas and their related frontal zones occur on the edge of a trough within the Rossby wave pattern. Most precipitation areas occur near frontal zones, the word synoptic is derived from the Greek word συνοπτικός, meaning seen together. The Navier–Stokes equations applied to atmospheric motion can be simplified by scale analysis in the synoptic scale and it can be shown that the main terms in horizontal equations are Coriolis force and pressure gradient terms, therefore, one can use geostrophic approximation. In vertical coordinates, the equation simplifies to the hydrostatic equilibrium equation. The first weather maps in the 19th century were drawn well after the fact to help devise a theory on storm systems, use of surface analyses began first in the United States, spreading worldwide during the 1870s. Use of the Norwegian cyclone model for frontal analysis began in the late 1910s across Europe, surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation, or other important information. For example, an H represents high pressure, implying good, an L represents low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, areas of precipitation help determine the frontal type and location. Mesoscale systems and boundaries such as cyclones, outflow boundaries. Isobars are commonly used to place surface boundaries from the horse latitudes poleward, the descriptor extratropical refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet. These are the phenomena which along with anti-cyclones, drive the weather over much of the Earth. An extratropical cyclone can transform into a storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection. High-pressure systems are associated with light winds at the surface and subsidence through the lower portion of the troposphere. Subsidence will generally dry out an air mass by adiabatic, or compressional, thus, high pressure typically brings clear skies. During the day, since no clouds are present to reflect sunlight, there is more incoming solar radiation. At night, the absence of means that outgoing longwave radiation is not absorbed
8.
Microburst
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A microburst is a small downdraft that moves in a way opposite to a tornado. Microbursts are found in strong thunderstorms, there are two types of microbursts within a thunderstorm, wet microbursts and dry microbursts. They go through three stages in their cycle, the downburst, outburst, and cushion stages, a microburst can be particularly dangerous to aircraft, especially during landing, due to the wind shear caused by its gust front. A microburst often has high winds that can knock over fully grown trees and they usually last from a couple of seconds to several minutes. Fujita also coined the term macroburst for downbursts larger than 4 km, a distinction can be made between a wet microburst which consists of precipitation and a dry microburst which typically consists of virga. Microbursts are recognized as capable of generating wind speeds higher than 75 m/s, Microbursts have also been called air bombs. When rain falls below the base or is mixed with dry air, it begins to evaporate. The cool air descends and accelerates as it approaches the ground, when the cool air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst. High winds spread out in type of pattern showing little or no curvature are known as straight-line winds. Wet microbursts are downbursts accompanied by significant precipitation at the surface which are warmer than their environment and these downbursts rely more on the drag of precipitation for downward acceleration of parcels than negative buoyancy which tend to drive dry microbursts. As a result, higher mixing ratios are necessary for these downbursts to form, melting of ice, particularly hail, appears to play an important role in downburst formation, especially in the lowest 1 km above ground level. These factors, among others, make forecasting wet microbursts a difficult task, the evolution of downbursts is broken down into three stages, the contact stage, the outburst stage, and the cushion stage. The virtual temperature correction usually is small and to a good approximation. In some storms this term has an effect on updrafts but there is not much reason to believe it has much of an impact on downdrafts. The second term is the effect of buoyancy on vertical motion, clearly, in the case of microbursts, one expects to find that B is negative meaning the parcel is cooler than its environment. This cooling typically takes place as a result of phase changes, precipitation particles that are small, but are in great quantity, promote a maximum contribution to cooling and, hence, to creation of negative buoyancy. The major contribution to this process is from evaporation, the last term is the effect of water loading. Whereas evaporation is promoted by large numbers of small droplets, it requires a few large drops to contribute substantially to the downward acceleration of air parcels
9.
Downburst
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A downburst is a strong ground-level wind system that emanates from a point source above and blows radially, that is, in a straight line in all directions, from the point of contact at ground level. Downbursts are created by an area of significantly rain-cooled air that, after reaching ground level, dry downbursts are associated with thunderstorms with very little rain, while wet downbursts are created by thunderstorms with high amounts of rainfall. Microbursts and macrobursts are downbursts at very small and larger scales respectively, another variety, the heat burst, is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking. Heat bursts generate significantly higher temperatures due to the lack of rain-cooled air in their formation, Downbursts create vertical wind shear or microbursts, which is dangerous to aviation. This is because the properties of a downburst are completely different from those of a tornado. To differentiate between tornado damage and damage from a downburst, the term straight-line winds is applied to damage from microbursts, Downbursts are particularly strong downdrafts from thunderstorms. Downbursts in air that is free or contains virga are known as dry downbursts. Most downbursts are less than 4 km in extent, these are called microbursts, Downbursts larger than 4 km in extent are sometimes called macrobursts. Downbursts can occur over large areas, straight-line winds are very strong winds that can produce damage, demonstrating a lack of a rotational damage pattern. Such rotational damage patterns are associated with cyclonic storms including tornadoes, straight-line winds are common with the gust front of a thunderstorm or originate with a downburst from a thunderstorm. These events can cause damage, even in the absence of a tornado. The winds can reach 130 km/h and can last for periods of twenty minutes, such straight-line wind events are most common during the spring when instability is highest and weather fronts routinely cross the country. Straight-line wind events in the form of derechos can take place in areas outside of the traditional tornado alley, straight-line winds may be damaging to marine interests. Small ships, cutters and sailboats are at risk from this meteorological phenomenon, the formation of a downburst starts with hail or large raindrops falling through drier air. Hailstones melt and raindrops evaporate, pulling latent heat from surrounding air, cooler air has a higher density than the warmer air around it, so it sinks to the ground. As the cold air hits the ground it out and a mesoscale front can be observed as a gust front. Areas under and immediately adjacent to the downburst are the areas which receive the highest winds and rainfall, also, because the rain-cooled air is descending from the middle troposphere, a significant drop in temperatures is noticed. Due to interaction with the ground, the downburst quickly loses strength as it fans out, Downbursts usually last only a few minutes and then dissipate, except in the case of squall lines and derecho events
10.
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
11.
Mountain
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A mountain is a large landform that stretches above the surrounding land in a limited area, usually in the form of a peak. A mountain is steeper than a hill. Mountains are formed through tectonic forces or volcanism and these forces can locally raise the surface of the earth. Mountains erode slowly through the action of rivers, weather conditions, a few mountains are isolated summits, but most occur in huge mountain ranges. High elevations on mountains produce colder climates than at sea level and these colder climates strongly affect the ecosystems of mountains, different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, the highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m, there is no universally accepted definition of a mountain. Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain, whether a landform is called a mountain may depend on local usage. The highest point in San Francisco, California, is called Mount Davidson, notwithstanding its height of 300 m, similarly, Mount Scott outside Lawton, Oklahoma is only 251 m from its base to its highest point. Whittows Dictionary of Physical Geography states Some authorities regard eminences above 600 metres as mountains, in addition, some definitions also include a topographical prominence requirement, typically 100 or 500 feet. For a while, the US defined a mountain as being 1,000 feet or taller, any similar landform lower than this height was considered a hill. However, today, the United States Geological Survey concludes that these terms do not have technical definitions in the US, using these definitions, mountains cover 33% of Eurasia, 19% of South America, 24% of North America, and 14% of Africa. As a whole, 24% of the Earths land mass is mountainous, there are three main types of mountains, volcanic, fold, and block. All three types are formed from plate tectonics, when portions of the Earths crust move, crumple, compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features. The height of the feature makes it either a hill or, if higher and steeper, major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity. Volcanoes are formed when a plate is pushed below another plate, at a depth of around 100 km, melting occurs in rock above the slab, and forms magma that reaches the surface. When the magma reaches the surface, it builds a volcanic mountain. Examples of volcanoes include Mount Fuji in Japan and Mount Pinatubo in the Philippines, the magma does not have to reach the surface in order to create a mountain, magma that solidifies below ground can still form dome mountains, such as Navajo Mountain in the US
12.
Troposphere
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The troposphere is the lowest portion of Earths atmosphere, and is also where nearly all weather takes place. It contains approximately 75% of the mass and 99% of the total mass of water vapor. The average depths of the troposphere are 20 km in the tropics,17 km in the mid latitudes, the lowest part of the troposphere, where friction with the Earths surface influences air flow, is the planetary boundary layer. This layer is typically a few hundred meters to 2 km deep depending on the landform, atop the troposphere is the tropopause, which is the border between the troposphere and stratosphere. The tropopause is a layer, where the air temperature ceases to decrease with height. Most of the phenomena we associate with day-to-day weather occur in the troposphere, by volume, dry air contains 78. 09% nitrogen,20. 95% oxygen,0. 93% argon,0. 04% carbon dioxide, and small amounts of other gases. Air also contains an amount of water vapor. The chemical composition of the troposphere is essentially uniform, with the exception of water vapor. The source of vapor is at the surface through the processes of evaporation. Thus the proportion of water vapor is normally greatest near the surface, the pressure of the atmosphere is maximum at sea level and decreases with altitude. This is because the atmosphere is nearly in hydrostatic equilibrium. The temperature of the troposphere generally decreases as altitude increases, the rate at which the temperature decreases, − d T / d z, is called the environmental lapse rate. The ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The reason for this difference is that the ground absorbs most of the suns energy. Meanwhile, the radiation of heat at the top of the results in the cooling of that part of the atmosphere. The ELR assumes the atmosphere is still, but as air is heated it becomes buoyant, when a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air expands, it pushes the surrounding air outward. As energy transfer to a parcel of air by way of heat is very slow, such a process is called an adiabatic process
13.
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
14.
Severe weather
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Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, regional and seasonal severe weather phenomena include blizzards, snowstorms, ice storms, and duststorms. Meteorologists generally define severe weather as any aspect of the weather that poses risks to life, a narrower definition of severe weather is any weather phenomena relating to severe thunderstorms. According to the World Meteorological Organization, severe weather can be categorized into two groups, general severe weather and localized severe weather, noreasters, European wind storms, and the phenomena that accompany them form over wide geographic areas. These occurrences are classified as severe weather. Downbursts and tornadoes are more localized and therefore have a limited geographic effect. These forms of weather are classified as localized severe weather, the term severe weather is technically not the same phenomenon as extreme weather. Extreme weather describes unusual weather events that are at the extremes of the distribution for a given area. Organized severe weather occurs from the conditions that generate ordinary thunderstorms, atmospheric moisture, lift. A wide variety of conditions cause severe weather, several factors can convert thunderstorms into severe weather. For example, a pool of air aloft may aid in the development of large hail from an otherwise innocuous appearing thunderstorm. However, the most severe hail and tornadoes are produced by thunderstorms. Both of these types of storms tend to form in environments high in wind shear, floods, hurricanes, tornadoes, and thunderstorms are considered to be the most destructive weather-related natural disasters. Although these weather phenomena are all related to clouds, they form and develop under different conditions. The relationship between these events and their formation requirements are used to develop models to predict the most frequent. This information is used to notify affected areas and save lives, severe thunderstorms can be assessed in three different categories. These are approaching severe, severe, and significantly severe, approaching severe is defined as hail between 1⁄2 to 1 inch diameter or winds between 50 and 58 M. P. H. In the United States, such storms will usually warrant a Significant Weather Alert, severe is defined as hail 1 inch diameter or larger, winds 58 M. P. H. or stronger, or a tornado
15.
Thermal wind
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The Thermal wind is wind that varies with height due to a balance between the Coriolis and pressure-gradient forces in the atmosphere. It is the physical mechanism for the jet stream and plays an important role in other large-scale atmospheric phenomena. Mathematically, the thermal wind relation defines a vertical wind shear--a variation in speed or direction with height. The wind shear in this case is a function of a temperature gradient. Also called baroclinic flow, the wind varies with height in proportion to the horizontal temperature gradient. The thermal wind relation results from hydrostatic balance and geostrophic balance in the presence of a gradient along constant pressure surfaces. The term thermal wind is considered a misnomer, since it really describes the change in wind with height. However, one can view the thermal wind as a wind that varies with height. In this way, the thermal wind relation acts to define the wind itself, many authors retain the thermal wind moniker, even though it describes a wind gradient, sometimes offering a clarification to that effect. The thermal wind is the change in the amplitude or sign of the wind due to a horizontal temperature gradient. The geostrophic wind is a wind that results from a balance of forces along a horizontal dimension. Whenever the Earths rotation plays a dominant role in dynamics, as in the mid-latitudes. Intuitively, a difference in pressure pushes air across that difference in a similar way that the horizontal difference in the height of a hill causes objects to roll downhill. However, the Coriolis force intervenes and nudges the air towards the right and this is illustrated in panel of the figure below. The balance that develops between two forces results in a flow that parallels the horizontal pressure difference, or pressure gradient. In addition, when acting in the vertical dimension are dominated by the vertical pressure-gradient force. In a barotropic atmosphere, where density is a function only of pressure, however, if a horizontal temperature gradient exists along isobars, the isobars will be thicker. This causes the slope of the isobars to increase with height and this is illustrated in panel of the figure to the left
16.
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
17.
Virga
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In meteorology, virga is an observable streak or shaft of precipitation that falls from a cloud but evaporates or sublimates before reaching the ground. A shaft of precipitation which does not evaporate before reaching the ground is a precipitation shaft and it is very common in the desert and in temperate climates. In North America, it is seen in the Western United States. It is also common in the Middle East, Australia. Virga can cause varying effects, because as rain is changed from liquid to vapor form. Precipitation falling into these cooling down drafts may eventually reach the ground, in some instances, these pockets of colder air can descend rapidly, creating a wet or dry microburst which can be extremely hazardous to aviation. Conversely, precipitation evaporating at high altitude can compressionally heat as it falls and this fairly rare phenomenon, a heat burst, also tends to be of exceedingly dry air. The word is derived from Latin virga meaning twig or branch, sulfuric acid rain in the atmosphere of Venus evaporates before reaching the ground due to the high heat near the surface. Similarly, virga happens on gas giant planets such as Jupiter, in September 2008 NASAs Phoenix lander discovered a snow variety of virga falling from Martian clouds. Aviation safety Cavum Precipitation shaft Sun pillar National Science Digital Library - Virga Viewing the Vagaries and Verities of Virga Alistair B, fraser and Craig F. Bohren, Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania,2 November 1992 and 25 January 1993
18.
Twilight
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Twilight is the illumination of the Earths lower atmosphere when the Sun itself is not directly visible because it is below the horizon. Twilight is produced by scattering in the upper atmosphere, illuminating the lower atmosphere so that the surface of the Earth is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs, the further the Sun is below the horizon, the dimmer the twilight. When the Sun reaches 18 degrees below the horizon, the brightness is nearly zero. When the Sun again reaches 18 degrees below the horizon, nighttime becomes morning twilight, Twilight should not be confused with auroras, which can have a similar appearance in the night sky at high latitudes. By analogy with evening twilight, the word twilight is also used metaphorically, to imply that something is losing strength. For example, very old people may be said to be in the twilight of their lives, the collateral adjective for twilight is crepuscular which is sometimes applied to insects, fish, and mammals that are most active during that time. Twilight is defined according to the elevation angle θs, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight. Morning civil twilight begins when the center of the sun is 6° below the horizon. Evening civil twilight begins at sunset or when the center of the sun is 0°50′ below the horizon. In the United States military, the initialisms BMCT and EECT are used to refer to these periods, morning nautical twilight begins and evening nautical twilight ends when the geometric center of the sun reaches 12° below the horizon. Morning astronomical twilight begins and Evening astronomical twilight ends when the center of the Sun reaches 18° below the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight, under clear weather conditions, civil twilight approximates the limit at which solar illumination suffices for the human eye to clearly distinguish terrestrial objects. Enough sunlight renders artificial sources unnecessary for most outdoor activities, at civil dawn, the beginning of morning civil twilight, and at civil dusk, the end of evening civil twilight, sunlight clearly defines the horizon while the brightest stars and planets can appear. As observed from the Earth, sky-gazers know Venus, the brightest planet, law-makers have enshrined the concept of civil twilight. Such statutes typically use a period after sunset or before sunrise. The period may affect when pilots require a rating to fly aircraft
19.
Aurora
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An aurora, sometimes referred to as a polar lights or northern lights, is a natural light display in the sky, predominantly seen in the high latitude regions. The resulting ionization and excitation of atmospheric constituents emits light of varying colour, the form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere, proton auroras are usually observed at lower latitudes. A region that currently displays an aurora is called the auroral oval, early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis, and later Hermann Fritz and S. Tromholt in more detail, day-to-day positions of the auroral ovals are posted on the internet. In northern latitudes, the effect is known as the Aurora Borealis or the Northern Lights, the former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind. The Aurora Australis is visible from southern latitudes in Antarctica, Chile, Argentina, New Zealand. A geomagnetic storm causes the auroral ovals to expand, and bring the aurora to lower latitudes and it was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The aurora can be seen best at this time, which is called magnetic midnight, Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be sub-visual. Auroras are occasionally seen in latitudes below the zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the sunspot cycle or during the three years after the peak. An aurora may appear overhead as a corona of rays, radiating from a distant and apparent central location, an electron spirals about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the “pitch angle” of the particle, the distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the travels to a region of greater field strength nearer to the atmosphere. Thus it is possible for particles to return, or mirror. Other particles that do not mirror enter the atmosphere and contribute to the display over a range of altitudes. Other types of auroras have been observed from space, e. g. poleward arcs stretching sunward across the cap, the related theta aurora. These are relatively infrequent and poorly understood, there are other interesting effects such as flickering aurora, black aurora and sub-visual red arcs
20.
Mojave Desert
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The Mojave Desert is an arid rain-shadow desert and the driest desert in North America. It is located in the southwestern United States, primarily within southeastern California and southern Nevada, very small areas also extend into Utah and Arizona. The central part of the desert is sparsely populated, while its peripheries support large communities such as Las Vegas, Lancaster, Palmdale, Victorville, the Mojave Desert is bordered by the Great Basin Desert to its north and the Sonoran Desert to its south and east. Topographical boundaries include the Tehachapi Mountains to the west, and the San Gabriel Mountains, the mountain boundaries are distinct because they are outlined by the two largest faults in California – the San Andreas and Garlock faults. The Mojave Desert displays typical basin and range topography and it occupies less than 50,000 sq mi, making it the smallest of the North American deserts. The Mojave Desert is often referred to as the desert, in contrast to the low desert. However, the Mojave Desert is generally lower than the Great Basin Desert to the north, the spelling Mojave originates from the Spanish language while the spelling Mohave comes from modern English. The Mojave Desert receives less than 13 in of rain a year and is generally between 2,000 and 5,000 feet in elevation, zion National Park in Utah lies at the junction of the Mojave, the Great Basin Desert, and the Colorado Plateau. Despite its aridity, the Mojave has long been a center of production, fed by irrigation coming from groundwater. The Mojave is a desert of temperature extremes and two distinct seasons, winter months bring comfortable daytime temperatures, which dip precipitously to around 20 °F on valley floors, and below 0 °F at higher elevations. Storms moving from the Pacific Northwest can bring rain and in places even snow. More often, the shadow created by the Sierra Nevada as well as mountain ranges within the desert such as the Spring Mountains, bring only clouds. By early June, it is rare for another Pacific storm to have a significant impact on the regions weather, summer weather is dominated by heat. Temperatures on valley floors can soar above 120 °F and above 130 °F at the lowest elevations, low humidity, high temperatures, and low pressure, draw in moisture from the Gulf of Mexico creating thunderstorms across the desert southwest known as the North American monsoon. Autumn is generally pleasant, with one to two Pacific storm systems creating regional rain events, october is one of the driest and sunniest months in the Mojave, and temperatures usually remain between 70 °F and 90 °F on the valley floors. After temperature, wind is the most significant weather phenomenon in the Mojave, during the June Gloom, cooler air can be pushed out into the desert from Southern California. In Santa Ana wind events, hot air from the desert blows out into the Los Angeles basin, wind farms in these areas generate power from these winds. The other major factor in the region is elevation
21.
Knot (unit)
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The knot is a unit of speed equal to one nautical mile per hour, approximately 1.151 mph. The ISO Standard symbol for the knot is kn, the same symbol is preferred by the IEEE, kt is also common. The knot is a unit that is accepted for use with the SI. Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a log in a specific time. 1 international knot =1 nautical mile per hour,1.852 kilometres per hour,0.514 metres per second,1.151 miles per hour,20.254 inches per second,1852 m is the length of the internationally agreed nautical mile. The US adopted the definition in 1954, having previously used the US nautical mile. The UK adopted the international nautical mile definition in 1970, having used the UK Admiralty nautical mile. The speeds of vessels relative to the fluids in which they travel are measured in knots, for consistency, the speeds of navigational fluids are also measured in knots. Thus, speed over the ground and rate of progress towards a distant point are given in knots. Until the mid-19th century, vessel speed at sea was measured using a chip log, the chip log was cast over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 8 fathoms -47 feet 3 inches from each other, passed through a sailors fingers, the knot count would be reported and used in the sailing masters dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, the difference from the modern definition is less than 0. 02%. On a chart of the North Atlantic, the scale varies by a factor of two from Florida to Greenland, a single graphic scale, of the sort on many maps, would therefore be useless on such a chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier, speed is sometimes incorrectly expressed as knots per hour, which is in fact a measure of acceleration. Prior to 1969, airworthiness standards for aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles. In 1969, these standards were amended to specify that distances were to be in nautical miles. At 11000 m, an airspeed of 300 kn may correspond to a true airspeed of 500 kn in standard conditions. Beaufort scale Hull speed, which deals with theoretical estimates of maximum speed of displacement hulls Knot count Knotted cord Metre per second Orders of magnitude Rope Kemp
22.
Turbulence
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Turbulence or turbulent flow is a flow regime in fluid dynamics characterized by chaotic changes in pressure and flow velocity. It is in contrast to a flow regime, which occurs when a fluid flows in parallel layers. Turbulence is caused by kinetic energy in parts of a fluid flow. For this reason turbulence is easier to create in low viscosity fluids, in general terms, in turbulent flow, unsteady vortices appear of many sizes which interact with each other, consequently drag due to friction effects increases. This would increase the energy needed to pump fluid through a pipe, however this effect can also be exploited by such as aerodynamic spoilers on aircraft, which deliberately spoil the laminar flow to increase drag and reduce lift. The onset of turbulence can be predicted by a constant called the Reynolds number. However, turbulence has long resisted detailed physical analysis, and the interactions within turbulence creates a complex situation. Richard Feynman has described turbulence as the most important unsolved problem of classical physics, smoke rising from a cigarette is mostly turbulent flow. However, for the first few centimeters the flow is laminar, the smoke plume becomes turbulent as its Reynolds number increases, due to its flow velocity and characteristic length increasing. If the golf ball were smooth, the boundary layer flow over the front of the sphere would be laminar at typical conditions. However, the layer would separate early, as the pressure gradient switched from favorable to unfavorable. To prevent this happening, the surface is dimpled to perturb the boundary layer. This results in higher skin friction, but moves the point of boundary layer separation further along, resulting in form drag. The flow conditions in industrial equipment and machines. The external flow over all kind of such as cars, airplanes, ships. The motions of matter in stellar atmospheres, a jet exhausting from a nozzle into a quiescent fluid. As the flow emerges into this external fluid, shear layers originating at the lips of the nozzle are created and these layers separate the fast moving jet from the external fluid, and at a certain critical Reynolds number they become unstable and break down to turbulence. Biologically generated turbulence resulting from swimming animals affects ocean mixing, snow fences work by inducing turbulence in the wind, forcing it to drop much of its snow load near the fence
23.
Weather front
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A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena outside the tropics. In surface weather analyses, fronts are depicted using various colored triangles and half-circles, the air masses separated by a front usually differ in temperature and humidity. Cold fronts may feature narrow bands of thunderstorms and severe weather, Warm fronts are usually preceded by stratiform precipitation and fog. The weather usually clears quickly after a fronts passage, some fronts produce no precipitation and little cloudiness, although there is invariably a wind shift. Cold fronts and occluded fronts generally move from west to east, because of the greater density of air in their wake, cold fronts and cold occlusions move faster than warm fronts and warm occlusions. Mountains and warm bodies of water can slow the movement of fronts and this is most common over the open ocean. The Bergeron classification is the most widely accepted form of air mass classification, air mass classification involves three letters. The first letter describes its moisture properties, with c used for air masses. The second letter describes the characteristic of its source region, T for tropical, P for polar, A for arctic or Antarctic, M for monsoon, E for equatorial. The third letter is used to designate the stability of the atmosphere, if the air mass is colder than the ground below it, it is labeled k. If the air mass is warmer than the ground below it, it is labeled w. Fronts separate air masses of different types or origins, Surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying fair weather, an L on the other hand may represent low pressure, which frequently accompanies precipitation. Low pressure also creates surface winds deriving from high pressure zones, various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on the weather map. In addition, areas of precipitation help determine the frontal type, there are two different meanings used within meteorology to describe weather around a frontal zone. The term anafront describes boundaries which show instability, meaning air rises rapidly along, a katafront is weaker, bringing smaller changes in temperature and moisture, as well as limited rainfall. Cold fronts often bring heavy thunderstorms, rain and hail, Cold front can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary. Cold fronts come in association with a low-pressure area, the concept of colder, dense air wedging under the less dense warmer air is often used to depict how air is lifted along a frontal boundary. The cold air wedging underneath warmer air creates the strongest winds just above the ground surface and this lift would then form a narrow line of showers and thunderstorms if enough moisture were present
24.
Tropopause
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The tropopause is the boundary in the Earths atmosphere between the troposphere and the stratosphere. Going upward from the surface, it is the point where air ceases to cool with height, more formally, the tropopause is the region of the atmosphere where the environmental lapse rate changes from positive, as it behaves in the troposphere, to the stratospheric negative one. The troposphere is one of the lowest layers of the Earths atmosphere, it is located right above the boundary layer. The troposphere extends upwards from right above the layer, and ranges in height from an average of 9 km at the poles. In the absence of inversions and not considering moisture, the lapse rate for this layer is 6.5 °C per kilometer, on average. The tropopause location coincides with the lowest point at which the lapse rate falls below a prescribed threshold. Since the tropopause responds to the temperature of the entire layer that lies underneath it, it is at its peak levels over the Equator. On account of this, the coolest layer in the lies at about 17 km over the equator. Due to the variation in starting height, the extremes are referred to as the equatorial tropopause. It is formed with the aid of potential vorticity, which is defined as the product of the isentropic density, instead of using the vertical temperature gradient as the defining variable, the dynamic tropopause surface is expressed in potential vorticity units. Nevertheless, the tropopause is useless at equatorial latitudes because the isentropes are almost vertical. For the extratropical tropopause in the Northern Hemisphere the WMO established a value of 1.5 PVU and it is also possible to define the tropopause in terms of chemical composition. For example, the stratosphere has much higher ozone concentrations than the upper troposphere. The tropopause is not a hard boundary, vigorous thunderstorms, for example, particularly those of tropical origin, will overshoot into the lower stratosphere and undergo a brief low-frequency vertical oscillation. Such oscillation sets up an atmospheric gravity wave capable of affecting both atmospheric and oceanic currents in the region. Most commercial aircraft are flown in the stratosphere, just above the tropopause. Jet stream Maximum parcel level Andrews, D. G. Holton, J. R. Leovy, C. B. R. Dmowska, Holton, a First Course in Atmospheric Thermodynamics
25.
Clear air turbulence
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Clear-air turbulence is the turbulent movement of air masses in the absence of any visual clues such as clouds, and is caused when bodies of air moving at widely different speeds meet. The atmospheric region most susceptible to CAT is the troposphere at altitudes of around 7. Here CAT is most frequently encountered in the regions of jet streams, at lower altitudes it may also occur near mountain ranges. Thin cirrus clouds can also indicate high probability of CAT, CAT can be hazardous to the comfort, and rarely the safety, of air travelers. However, it can be detected with instruments that can measure turbulence with optical techniques, such as scintillometers, Doppler LIDARs. Although the altitudes near the tropopause are usually cloudless, thin cirrus cloud can form there are abrupt changes of air velocity. Detecting and predicting CAT is hard for meteorologists because it is at such heights that even when caused by factors that can be measured, intensity, however, because this turbulence affects long range aircraft that fly near the tropopause, CAT has been intensely studied. Several factors affect the likelihood of CAT, often more than one factor is present. 64% of the non-light turbulences are observed less than 150 nautical miles away from the core of a jet stream, rossby waves caused by this jet stream shear and the Coriolis force cause it to meander. A temperature gradient is the change of temperature over a distance in some given direction, where the temperature of a gas changes, so does its density and where the density changes CAT can appear. From the ground upwards through the temperature decreases with height. Such variations are examples of temperature gradients, a horizontal temperature gradient may occur, and hence air density variations, where air velocity changes. An example, the speed of the jet stream is not constant along its length, additionally air temperature, Wind shear is a difference in relative speed between two adjacent air masses. An excessive wind shear produces vortices, and when the shear is of sufficient degree. As is explained elsewhere in this article, temperature decreases and wind velocity increase with height in the troposphere, and these differences cause changes in air density, and hence viscosity. The viscosity of the air thus presents both inertias and accelerations which cannot be determined in advance, vertical wind shear above the jet stream is sharper when it is moving upwards, because wind speed decreases with height in the stratosphere. This is the reason CAT can be generated above the tropopause, on the other hand, vertical wind shear moving downwards within the stratosphere is more moderate and CAT is never produced in the stratosphere. Similar considerations apply to the troposphere but in reverse, when strong wind deviates, the change of wind direction implies a change in the wind speed
26.
Windward and leeward
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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
27.
Eddy (fluid dynamics)
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In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the side of the object. This phenomenon is naturally observed behind large emergent rocks in swift-flowing rivers, the propensity of a fluid to swirl is used to promote good fuel/air mixing in internal combustion engines. In fluid mechanics and transport phenomena, an eddy is not a property of the fluid, turbulent flow is defined as the flow in which the systems inertial forces are dominant over the viscous forces. This phenomena is described by Reynolds number, a number used to determine when turbulent flow will occur. Conceptually, the Reynolds number is the ratio between inertial forces and viscous forces, blood flow in straight sections of the arterial tree are typically laminar, but branches and curvatures in the system cause turbulent flow. Lift and drag properties of golf balls are customized by the manipulation of dimples along the surface of the ball, oceanic and atmospheric currents transfer particles, debris, and organisms all across the globe. Eddy formations circulate trash and other pollutants into concentrated areas which researchers are tracking to improve clean-up, mesoscale ocean eddies play crucial rolls in transferring heat poleward, as well as maintaining heat gradients at different depths. Eddies are common in the ocean, and range in diameter from centimeters to hundreds of kilometers, the smallest scale eddies may last for a matter of seconds, while the larger features may persist for months to years. Eddies which are between about 10 and 500 km in diameter and persist for periods of days to months are known in oceanography as mesoscale eddies. Mesoscale eddies can be split into two categories, static eddies, caused by flow around an obstacle, and transient eddies, when the ocean contains a sea surface height gradient this creates a jet or current, such as the Antarctic Circumpolar Current. This current as part of an unstable system meanders and creates eddies. Mesoscale ocean eddies are characterized by currents which flow in a circular motion around the center of the eddy. The sense of rotation of these currents may either be cyclonic or anticyclonic, oceanic eddies are also usually made of water masses that are different from those outside of the eddy. That is, the water within an eddy usually has different temperature, there is a direct link between the water mass properties of an eddy and its rotation. Warm eddies rotate anti-cyclonically, while cold eddies rotate cyclonically, because eddies may have a vigorous circulation associated with them, they are of concern to naval and commercial operations at sea. Further, because eddies transport anomalously warm or cold water as they move, they have an important influence on heat transport in certain parts of the ocean
28.
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
29.
Inversion (meteorology)
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In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion, i. e. an increase in temperature with height. An inversion can lead to such as smog being trapped close to the ground. An inversion can also suppress convection by acting as a cap, if this cap is broken for any of several reasons, convection of any moisture present can then erupt into violent thunderstorms. Temperature inversion can notoriously result in freezing rain in cold climates. g, given the right conditions, the normal vertical temperature gradient is inverted such that the air is colder near the surface of the Earth. This can occur when, for example, a warmer, less-dense air mass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warm fronts, with sufficient humidity in the cooler layer, fog is typically present below the inversion cap. This effect is virtually confined to regions as the ocean retains heat far longer. In the polar regions during winter, inversions are nearly always present over land, a warmer air mass moving over a cooler one can shut off any convection which may be present in the cooler air mass. This is known as a capping inversion, such capping inversions typically precede the development of tornadoes in the Midwestern United States. In this instance, the layer is actually quite warm. An inversion can develop aloft as a result of air gradually sinking over an area and being warmed by adiabatic compression. A stable marine layer may develop over the ocean as a result. The accumulated smog and dust under the inversion quickly taints the sky reddish and this can become a problem in cities where many pollutants exist. During a severe inversion, trapped air pollutants form a haze that can cause respiratory problems. The Great Smog of 1952 in London, England, is one of the most serious examples of such an inversion and it was blamed for an estimated 11,000 to 12,000 deaths. Sometimes the inversion layer is at a high altitude that cumulus clouds can condense. This decreases the amount of sunlight reaching the ground and prevents new thermals from forming, as the clouds disperse, sunny weather replaces cloudiness in a cycle that can occur more than once a day
30.
Friction
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Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
31.
Outflow boundary
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Outflow boundaries can persist for 24 hours or more after the thunderstorms that generated them dissipate, and can travel hundreds of kilometers from their area of origin. New thunderstorms often develop along outflow boundaries, especially near the point of intersection with another boundary, Outflow boundaries can be seen either as fine lines on weather radar imagery or else as arcs of low clouds on weather satellite imagery. From the ground, outflow boundaries can be co-located with the appearance of roll clouds, Outflow boundaries create low-level wind shear which can be hazardous during aircraft takeoffs and landings. If a thunderstorm runs into a boundary, the low-level wind shear from the boundary can cause thunderstorms to exhibit rotation at the base of the storm. Strong versions of these features known as downbursts can be generated in environments of vertical wind shear, microbursts have a diameter of influence less than 4 kilometres, while macrobursts occur over a diameter greater than 4 kilometres. Wet microbursts occur in atmospheres where the low levels are saturated, an outflow boundary, also known as a gust front or arc cloud, is the leading edge of gusty, cooler surface winds from thunderstorm downdrafts, sometimes associated with a shelf cloud or roll cloud. A pressure jump is associated with its passage, Outflow boundaries can persist for over 24 hours and travel hundreds of kilometers from their area of origin. A wrapping gust front is a front that wraps around the mesocyclone, cutting off the inflow of warm moist air and this is sometimes the case during the event of a collapsing storm, in which the wind literally rips it apart. The term was defined as affecting an area 4 kilometres in diameter or less, distinguishing them as a type of downburst and they are normally associated with individual thunderstorms. Microburst soundings show the presence of dry air, which enhances evaporative cooling. Organized areas of thunderstorm activity reinforce pre-existing frontal zones, and 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 and this feature is commonly depicted in the warm season across the United States on surface analyses, as they lie within sharp surface troughs. A macroburst, normally associated with lines, is a strong downburst larger than 4 kilometres. A wet microburst consists of precipitation and an atmosphere saturated in the low-levels, a dry microburst emanates from high-based thunderstorms with virga falling from their base. All types are formed by precipitation-cooled air rushing to the surface, downbursts can occur over large areas. At ground level, shelf clouds and roll clouds can be seen at the edge of outflow boundaries. Through satellite imagery, an arc cloud is visible as an arc of low clouds spreading out from a thunderstorm, if the skies are cloudy behind the arc, or if the arc is moving quickly indicate that high wind gusts are likely behind the gust front
32.
Density
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The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
33.
Temperature
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A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, geology, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale. Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, nevertheless, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials
34.
Humidity
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Humidity is the amount of water vapor present in the air. Water vapor is the state of water and is invisible. Humidity indicates the likelihood of precipitation, dew, or fog, higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in an index table or humidex. The amount of vapor that is needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of water becomes lower it will not reach the point of saturation without adding or losing water mass. The differences in the amount of vapor in a parcel of air can be quite large. For example, a parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, there are three main measurements of humidity, absolute, relative and specific. Absolute humidity is the content of air expressed in gram per cubic meter. Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum for that temperature, specific humidity is the ratio of the mass of water vapor to the total mass of the moist air parcel. Absolute humidity is the mass of water vapor present in a given volume of air. It does not take temperature into consideration, absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C. Absolute humidity is the mass of the vapor, divided by the volume of the air and water vapor mixture. The absolute humidity changes as air temperature or pressure changes and this makes it unsuitable for chemical engineering calculations, e. g. for clothes dryers, where temperature can vary considerably. Mass of water per unit volume as in the equation above is defined as volumetric humidity. Because of the confusion, British Standard BS1339 suggests avoiding the term absolute humidity. Units should always be carefully checked, many humidity charts are given in g/kg or kg/kg, but any mass units may be used. The field concerned with the study of physical and thermodynamic properties of mixtures is named psychrometrics
35.
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
36.
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
37.
Stationary front
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A stationary front is a pair of air masses, neither of which is strong enough to replace the other. On a weather map, this is shown by a series of blue spikes pointing one direction. They tend to remain essentially in the area for extended periods of time. A wide variety of weather can be found along a front, but usually clouds, prolonged precipitation. When there is a lot of water vapor in the air mass. Stationary fronts will either dissipate after several days or devolve into shear lines, additionally, if one air mass enters the other, then it will change into a cold or warm front, and the stationary front will be classified as moving. For instance, if an air mass enters a cold air mass, since the advancing air mass is warm. When a warm or cold front stops moving, it becomes a stationary front
38.
Surface weather analysis
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Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations. The first weather maps in the 19th century were drawn well after the fact to help devise a theory on storm systems, use of surface analyses began first in the United States, spreading worldwide during the 1870s. Use of the Norwegian cyclone model for frontal analysis began in the late 1910s across Europe, surface weather analyses have special symbols that show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying clear skies, an L, on the other hand, may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, areas of precipitation help determine the frontal type and location. The use of charts in a modern sense began in the middle portion of the 19th century in order to devise a theory on storm systems. The development of a network by 1845 made it possible to gather weather information from multiple distant locations quickly enough to preserve its value for real-time applications. The Smithsonian Institution developed its network of observers over much of the central, the U. S. Army Signal Corps inherited this network between 1870 and 1874 by an act of Congress, and expanded it to the west coast soon afterwards. The weather data was at first less useful as a result of the different times at which weather observations were made, the first attempts at time standardization took hold in Great Britain by 1855. The entire United States did not finally come under the influence of time zones until 1905, other countries followed the lead of the United States in taking simultaneous weather observations, starting in 1873. Other countries then began preparing surface analyses, the use of frontal zones on weather maps did not appear until the introduction of the Norwegian cyclone model in the late 1910s, despite Loomis earlier attempt at a similar notion in 1841. Since the leading edge of air mass changes bore resemblance to the fronts of World War I. The effort to automate map plotting began in the United States in 1969, hong Kong completed their process of automated surface plotting by 1987. In the United States, this development was achieved when Intergraph workstations were replaced by n-AWIPS workstations, recent advances in both the fields of meteorology and geographic information systems have made it possible to devise finely tailored weather maps. Weather information can quickly be matched to relevant geographical detail, for instance, icing conditions can be mapped onto the road network. This will likely continue to lead to changes in the way surface analyses are created and displayed over the several years. The pressureNET project is an attempt to gather surface pressure data using smartphones. When analyzing a weather map, a model is plotted at each point of observation
39.
Tropics
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The tropics are a region of the Earth surrounding the equator. The tropics are also referred to as the zone and the torrid zone. The tropics include all the areas on the Earth where the Sun is at a point directly overhead at least once during the solar year. The tropics are distinguished from the climatic and biomatic regions of Earth, which are the middle latitudes. Tropical is sometimes used in a sense for a tropical climate to mean warm to hot and moist year-round. Many tropical areas have a dry and wet season, the wet season, rainy season or green season, is the time of year, ranging from one or more months, when most of the average annual rainfall in a region falls. Areas with wet seasons are disseminated across portions of the tropics and subtropics, under the Köppen climate classification, for tropical climates, a wet season month is defined as a month where average precipitation is 60 millimetres or more. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is distributed through the year. When the wet season occurs during the season, or summer, precipitation falls mainly during the late afternoon. The wet season is a time when air quality improves, freshwater quality improves and vegetation grows significantly, floods cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients diminish and erosion increases, the incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for the wetter regime, unfortunately, the previous dry season leads to food shortages into the wet season, as the crops have yet to mature. Regions within the tropics may well not have a tropical climate, there are alpine tundra and snow-capped peaks, including Mauna Kea, Mount Kilimanjaro, and the Andes as far south as the northernmost parts of Chile and Argentina. Under the Köppen climate classification, much of the area within the tropics is classed not as tropical but as dry including the Sahara Desert. Tropical plants and animals are those native to the tropics. Tropical ecosystems may consist of rainforests, dry forests, spiny forests, desert. There are often significant areas of biodiversity, and species present, particularly in rainforests. In biogeography, the tropics are divided into Paleotropics and Neotropics, together, they are sometimes referred to as the Pantropic
40.
Tropical wave
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All tropical waves form in the easterly flow along the equatorward side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone. Tropical waves are carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of cyclones in the north Atlantic. Tropical wave study is aided by Hovmöller diagrams, a graph of meteorological data, a tropical wave normally follows an area of sinking, intensely dry air, blowing from the northeast. After the passage of the line, the wind veers southeast, the humidity abruptly rises. This yields widespread showers and thunderstorms, sometimes severe, as the wave moves westward, the showers gradually diminish. An exception to this rain is in the Atlantic, sometimes, a surge of dry air called the Saharan Air Layer follows a tropical wave, leaving cloudless skies, as convection is capped by the dry layer inversion. Also, any dust in the SAL reflects sunlight, cooling the air below it, Tropical waves in the Atlantic basin develop from disturbances which develop as far east as Sudan in east Africa and drift over the continent into the Atlantic ocean. These are generated or enhanced by the African Easterly Jet, approximately 60% of Atlantic tropical cyclones originate from tropical waves, while approximately 85% of intense Atlantic hurricanes develop from tropical waves. Tropical cyclones can sometimes degenerate back into a tropical wave and this normally occurs if upper-level wind shear is too strong. The storm can redevelop if the upper level shear abates, if a tropical wave is moving quickly, it can have strong winds of over tropical storm force, but is not considered a tropical storm unless it has a closed circulation. An example of this was Hurricane Claudette in 2003, where the wave had winds of 45 mph before developing a circulation. It has been suggested that some eastern Pacific Ocean tropical cyclones are formed out of tropical waves that originate in North Africa as well. A screaming eagle is a wave whose convective pattern loosely resembles the head of an eagle. This phenomenon is caused by shearing from either westerly winds aloft or strong winds at the surface. These systems are located within 25 degrees latitude of the equator. Rain showers and surface winds gusting to 29 mph are associated with these waves and they move across the ocean at a rate of 15 mph. Strong thunderstorm activity can be associated with the features when located east of an upper tropospheric trough
41.
Atlantic Ocean
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The Atlantic Ocean is the second largest of the worlds oceans with a total area of about 106,460,000 square kilometres. It covers approximately 20 percent of the Earths surface and about 29 percent of its surface area. It separates the Old World from the New World, the Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Eurasia and Africa to the east, and the Americas to the west. The Equatorial Counter Current subdivides it into the North Atlantic Ocean, in contrast, the term Atlantic originally referred specifically to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast. The Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of years ago. The term Aethiopian Ocean, derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century, many Irish or British people refer to the United States and Canada as across the pond, and vice versa. The Black Atlantic refers to the role of ocean in shaping black peoples history. Irish migration to the US is meant when the term The Green Atlantic is used, the term Red Atlantic has been used in reference to the Marxian concept of an Atlantic working class, as well as to the Atlantic experience of indigenous Americans. Correspondingly, the extent and number of oceans and seas varies, the Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea, to the east, the boundaries of the ocean proper are Europe, the Strait of Gibraltar and Africa. In the southeast, the Atlantic merges into the Indian Ocean, the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. In the 1953 definition it extends south to Antarctica, while in later maps it is bounded at the 60° parallel by the Southern Ocean, the Atlantic has irregular coasts indented by numerous bays, gulfs, and seas. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23. 5% of the ocean and has a volume of 310,410,900 km3 or 23. 3%. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3, the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S, the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2000 m along most of its length, the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other
42.
Pacific Ocean
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The Pacific Ocean is the largest and deepest of the Earths oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west, the Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 metres. Both the center of the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean, the oceans current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favourable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means peaceful sea, important human migrations occurred in the Pacific in prehistoric times. Long-distance trade developed all along the coast from Mozambique to Japan, trade, and therefore knowledge, extended to the Indonesian islands but apparently not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality, from 1404 to 1433 Zheng He led expeditions into the Indian Ocean. The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and he named it Mar del Sur because the ocean was to the south of the coast of the isthmus where he first observed the Pacific. Later, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Castilian expedition of world circumnavigation starting in 1519, Magellan called the ocean Pacífico because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters. The ocean was often called the Sea of Magellan in his honor until the eighteenth century, sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands, the Aru Islands, and Papua New Guinea. In 1542–43 the Portuguese also reached Japan, in 1564, five Spanish ships consisting of 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi and sailed to the Philippines and Mariana Islands. The Manila galleons operated for two and a half centuries linking Manila and Acapulco, in one of the longest trade routes in history, Spanish expeditions also discovered Tuvalu, the Marquesas, the Cook Islands, the Solomon Islands, and the Admiralty Islands in the South Pacific. In the 16th and 17th century Spain considered the Pacific Ocean a Mare clausum—a sea closed to other naval powers, as the only known entrance from the Atlantic the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western end of the Pacific Ocean the Dutch threatened the Spanish Philippines, Spain also sent expeditions to the Pacific Northwest reaching Vancouver Island in southern Canada, and Alaska. The French explored and settled Polynesia, and the British made three voyages with James Cook to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest, one of the earliest voyages of scientific exploration was organized by Spain in the Malaspina Expedition of 1789–1794. It sailed vast areas of the Pacific, from Cape Horn to Alaska, Guam and the Philippines, New Zealand, Australia, and the South Pacific. Growing imperialism during the 19th century resulted in the occupation of much of Oceania by other European powers, and later, Japan, in Oceania, France got a leading position as imperial power after making Tahiti and New Caledonia protectorates in 1842 and 1853 respectively. After navy visits to Easter Island in 1875 and 1887, Chilean navy officer Policarpo Toro managed to negotiate an incorporation of the island into Chile with native Rapanui in 1888, by occupying Easter Island, Chile joined the imperial nations
43.
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
