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Baroclinity: the state of stratification in a fluid in which surfaces of constant pressure intersect surfaces of constant density. also known as baroclinicity. an example is the tight temperature gradient along the east coast of the united states during the winter that gives rise to intense cyclogenesis. beaufort wind scale: a system of estimating and reporting wind speeds. it is based on the beaufort force or number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. the scale was devised by sir francis beaufort (1777-1857), hydrographer to the british royal navy. chromosphere: a thin layer of relatively transparent gases above the photosphere of the sun. it is observed best during a total eclipse of the sun. corposant: a luminous, sporadic, and often audible, electric discharge. it occurs from objects, especially pointed ones, when the electrical field strength near their surfaces attains a value near 1000 volts per centimeter. it often occurs during stormy weather and might be seen on a ship's mast or yardarm, aircraft, lightning rods, and steeples. earthquake: a sudden, transient motion or trembling of the earth's crust, resulting from the waves in the earth caused by faulting of the rocks or by volcanic activity. friction layer: the thin layer of atmosphere adjacent to the earth's surface. surface friction is effective in slowing down wind up to approximately 1,500 to 3,000 feet above the ground. above this level, air tends to flow parallel to the isobars. wind distribution within this layer is determined by vertical temperature gradient and the physical contours of the underlying surface features. nexrad: acronym for next generation weather radar. a network of advanced doppler radars implemented in the united states between 1992 and 1996, it detects the location and intensity of precipitation out to a range of 143 miles from the radar site. nexrad doppler radar is highly sensitive and can detect precipitation from very light rain and snow up to the strongest thunderstorms with accuracy and detail. however, sometimes the radar's extreme sensitivity will cause ground clutter and other non-precipitation echoes to be displayed in the vicinity of the radar site. skew t-log p diagram: a thermodynamic diagram, using the temperature and the logarithm of pressure as coordinates. it is used to evaluate and forecast air parcel properties. some values that can be determined are the convective condensation level (ccl), the lifting condensation level (lcl), and the level of free convection (lfc). standing wave: an atmospheric wave that is stationary with respect to the medium in which it is embedded. translucent: not transparent, but clear enough to allow light to pass through. world meteorological organization (wmo): from weather prediction to air pollution research, climate change related activities, ozone layer depletion studies and tropical storm forecasting, the world meteorological organization coordinates global scientific activity to allow increasingly prompt and accurate weather information and other services for public, private and commercial use, including international airline and shipping industries. established by the united nations in 1951, it is composed of 184 members. : for more information, contact the woe, located in geneva, switzerland. : :.

Aleutian low: a semi-permanent, subpolar area of low pressure located in the gulf of alaska near the aleutian islands. it is a generating area for storms and migratory lows often reach maximum intensity in this area. it is most active during the late fall to late spring. during the summer, it is weaker, retreating towards the north pole and becoming almost nonexistent. during this time, the north pacific high pressure system dominates. altocumulus castellanus: a middle cloud with vertical development that forms from altocumulus clouds. it is composed primarily of ice crystals in its higher portions and characterized by its turrets, protuberances, or crenelated tops. its formation indicates instability and turbulence at the altitudes of occurrence. awips: acronym for advanced weather interactive processing system. it is the computerized system that processes nexrad and asos data received at national weather service forecast offices. blowing spray: salt spray that is raised by the wind to heights of six feet or greater. it is reported as "blpy" in an observation and on the metar. downdraft: a sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower. dropsonde: a radiosonde dropped with a parachute from an aircraft rather than lifted by a balloon to measure the atmosphere below. dynamics: a branch of mechanics that deals with forces and their relations to patterns of motion. in metorology, this relates especially to wind and water patterns. flanking line: a line of attached cumulus or towering cumulus clouds of descending height, appearing as stair steps (usually on the southwest side) of the most active part of a supercell. haze: a suspension of fine dust and/or smoke particles in the air. invisible to the naked eye, the particles reduce visibility by being sufficiently numerous to give the air an opalescent appearance. it is reported as "hz" in an observation and on the metar. hurricane watch: a formal advisory issued by forecasters at the national hurricane center when they have determined that hurricane conditions are a potential threat to a coastal area or group of islands within a 24 to 36 hour period. a watch is used to inform the public and marine interests of the storm's location, intensity, and movement. inches of mercury (hg): the name comes from the use of mercurial barometers which equate the height of a column of mercury with air pressure. one inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. first devised in 1644 by evangelista torricelli (1608-1647), an italian physicist and mathematician, to explain the fundamental principles of hydromechanics. lithosphere: the solid, outer portion of the earth's crust coupled to the rigid upper mantle. part of the geosphere. monsoon: the seasonal shift of winds created by the great annual temperature variation that occurs over large land areas in contrast with associated ocean surfaces. the monsoon is associated primarily with the moisture and copious rains that arrive with the southwest flow across southern india. the name is derived from the word mausim, arabic for season. this pattern is most evident on the southern and eastern sides of asia, although it does occur elsewhere, such as in the southwestern united states. multiple vortex tornado: a tornado which has two or more condensation funnels or debris clouds, often rotating around a common center. noctilucent clouds: rarely seen clouds of tiny ice particles that form approximately 75 to 90 kilometers above the earth's surface. they have been seen only during twilight (dusk and dawn) during the summer months in the higher latitudes. they may appear bright against a dark night sky, with a blue-silver color or orange-red. poles/polar: the poles are the geographic point at 90 degrees latitude north and south on the earth's surface. they are equal distance from the equator. the polar region is considered to be that area between 60° and 90° latitude, both north and south. refraction: the bending of light or radar beam as it passes through a zone of contrasting properties, such as atmospheric density, water vapor, or temperature. scattering: the process by which small particles suspended in the air diffuse a portion of the incident radiation in all directions. this is a primary reason for colors, such as blue skies, rainbows, and orange sunsets. when working with radars, this often refers to the more or less random changes in direction of radio energy. slush: snow or ice on the ground that has been reduced to a softy watery mixture by rain and/or warm temperatures. snow blindness: temporary blindness or impaired vision that results from bright sunlight reflected off the snow surface. the medical term is niphablepsia. snow garland: snow appearing as a beautiful long thick rope draped on trees, fences and other objects. formed by the surface tension of thin films of water bonding individual snow crystals. standing wave: an atmospheric wave that is stationary with respect to the medium in which it is embedded. upslope fog: fog that forms when warm, moist surface air is forced up a slope by the wind. it is adiabatically cooled to below its initial dew point, which means the air cools by expansion as it rises. it forms best where there is a gradual slope, and it can become quite deep, requiring considerable time to dissipate. visibility: a measure of the opacity of the atmosphere, and therefore, the greatest distance one can see prominent objects with normal eyesight. the national weather service has various terms for visibility. surface visibility is the prevailing visibility determined from the usual point of observation. prevailing visibility is considered representative of visibility conditions at the station. sector visibility is the visibility in a specified direction that represents at least a 45 degree arc of the horizon circle. tower visibility is the prevailing visibility determined from the airport traffic control tower (atct) at stations that also report surface visibility. zonal flow: the flow of air along a latitudinal component of existing flow, normally from west to east..

Convergence: wind movement that results in a horizontal net inflow of air into a particular region. convergent winds at lower levels are associated with upward motion. contrast with divergence. cut-off high: a warm high which has become displaced and is on the polarward side of the jet stream. it occurs mostly during the spring and is most frequent over northeastern siberia, alaska, and greenland. it is an example of a blocking high. diablo winds: dry winds in the diablo mountain range in central california that can exceed 60 miles per hour. similar to the santa ana winds, they develop as the wind flows from high pressure over nevada to lower pressure along the central california coast. dust bowl: the term given to the area of the great plains including texas, oklahoma, kansas, colorado, and new mexico that was most greatly affected during the great drought of the 1930's. d-value: the deviation of actual altitude along a constant pressure surface from the standard atmosphere altitude of that surface. gravitation: the mutual attraction between two masses of matter. the rotation of the earth and the atmosphere modifies this attraction to produce the field of gravity. gulf stream: the warm, well-defined, swift, relatively narrow ocean current which exists off the east coast of the united states, beginning near cape hatteras. the term also applies to the oceanic system of currents that dominate the western and northern atlantic ocean: the florida current, which flows through the florida straits between the florida keys and cuba and northwards; the gulf stream, which begins around cape hatteras and flows northeasterly off the continental slope into the north atlantic; and the north atlantic current, which begins around the grand banks off newfoundland and continues east-northeastwards towards the british isles. mean temperature: the average of temperature readings taken over a specified amount of time. often the average of the maximum and minimum temperatures. mesolow: a small scale low pressure center, ranging from the size of an individual thunderstorm to many tens of miles. nexrad: acronym for next generation weather radar. a network of advanced doppler radars implemented in the united states between 1992 and 1996, it detects the location and intensity of precipitation out to a range of 143 miles from the radar site. nexrad doppler radar is highly sensitive and can detect precipitation from very light rain and snow up to the strongest thunderstorms with accuracy and detail. however, sometimes the radar's extreme sensitivity will cause ground clutter and other non-precipitation echoes to be displayed in the vicinity of the radar site. opaque: a condition where a material, such as a cloud, blocks the passage of radiant energy, especially light. opaque sky cover refers to the amount of sky cover that completely hides all that might be above it. peak gust: the highest instantaneous wind speed observed or recorded. pollutant: particles, gases, or liquid aerosols in the atmosphere which have an undesirable effect on humans or their surroundings. something unfavorable to health and life that has been added to the environment. pre-frontal squall line: a line of thunderstorms that precedes an advancing cold front. pressure: the force per unit area exerted by the weight of the atmosphere above a point on or above the earth's surface. prevailing visibility: it is considered representative of visibility conditions at the observation station. it is the greatest distance that can be seen throughout at least half the horizon circle, but not necessarily continuous. psychrometer: an instrument used to measure water vapor content of the atmosphere. it consists of two thermometers, a wet bulb and dry bulb. may also be referred to as a sling psychrometer. sea ice: ice that is formed by the freezing of sea water. it forms first as small crystals, thickens into sludge, and coagulates into sheet ice, pancake ice, or ice floes of various shapes and sizes. sea spray: sometimes called salt spray, it is the drops of sea water (salt water) blown from the top of a wave. siberian high: the semi-permanent high pressure area that forms over siberia during the winter. the average central pressure exceeds 1030 millibars from late november to early march. it is characterized by clear, dry weather. over southern asia, the predominate surface wind is northeasterly, just the opposite of the predominate summer winds which bring the monsoon. small craft advisory: an advisory issued for marine interests, especially for operators of small boats or other vessels. conditions include wind speeds between 20 knots (23 mph) and 34 knots (39 mph). smoke: small particles produced by combustion that are suspended in the air. a transition to haze may occur when the smoke particles have traveled great distance (25 to 100 miles or more), and when the larger particles have settled out. the remaining particles become widely scattered through the atmosphere. it is reported as "fu" in an observation and on the metar. theodolite: an optical instrument used to track the motion of a pilot balloon, or pibal, by measuring the elevation and azimuth angles. tilt: the inclination to the vertical of a significant feature of the pressure pattern or of the field of moisture or temperature. for example, midlatitide troughs tend to display a westward tilt with altitude through the troposphere. trough: an elongated area of low atmospheric pressure that is associated with an area of minimum cyclonic circulation. the opposite of a ridge. virga: streaks or wisps of precipitation, such as water or ice particles, that fall from clouds but evaporate before reaching the ground. from a distance, the event sometimes may be mistaken for a funnel cloud or tornado. typically, it may fall from altocumulus, altostratus, or high based cumuonimbus. wall cloud: an abrupt lowering of a cloud from its parent cloud base, a cumulonimbus or supercell, with no visible precipitation underneath. forming in the area of a thunderstorm updraft, or inflow area, it exhibits rapid upward movement and cyclonic rotation. it often develops before strong or violent tornadoes. weather vane: originally used as a wind vane, it is an instrument that indicates the wind direction. the name developed based on observations on what kind of weather occurred with certain wind directions. creative designs often adorn the tops of barns and houses..

Adiabatic process: a thermodynamic change of state in a system in which there is no transfer of heat or mass across the boundaries of the system. in this process, compression will result in warming and expansion will result in cooling. blue norther: refers to a swift-moving cold frontal passage in the southern great plains, marked by a dark, blue-black sky with strong wintery winds from the northwest or north and temperatures that may drop 20°f to 30°f in a few minutes. centripetal force: the force required to keep an object moving in a curved or circular path. it is directed inwards toward the center of the curved path. cheyenne fog: an upslope fog formed by the westward flow of air from the missouri river valley, producing fog on the eastern slopes of the rockies. dynamics: a branch of mechanics that deals with forces and their relations to patterns of motion. in metorology, this relates especially to wind and water patterns. high clouds: a term used to signify cirriform clouds that are composed of ice crystals and generally have bases above 20,000 feet. the main types of high clouds are cirrus,cirrocumulus, and cirrostratus. this altitude applies to the temperate zone. in the polar regions, these clouds may be found at lower altitudes. in the tropics, the defining altitudes for cloud types are generally higher. isotherm: the line of equal or constant air temperature. if something is isothermal, it is of equal or constant temperature with respect to either time or space. : : mountain wave: a wave in the atmosphere caused by a barrier, such as a mountain. sometimes it is marked by lenticular clouds to the lee side of mountain barriers. may be called a standing wave or a lee wave. pollutant: particles, gases, or liquid aerosols in the atmosphere which have an undesirable effect on humans or their surroundings. something unfavorable to health and life that has been added to the environment. pressure characteristic: the pattern of the pressure change during the specified period of time, usually the three hour period preceding an observation. this is recorded in three categories: falling, rising, or steady. shear: it is the rate of change over a short duration. in wind shear, it can refer to the frequent change in wind speed within a short distance. it can occur vertically or horizontally. directional shear is a frequent change in direction within a short distance, which can also occur vertically or horizontally. when used in reference to doppler radar, it describes the change in radial velocity over short distances horizontally. short wave: a progressive wave of smaller amplitude, wave length, and duration than a long wave. it moves in the same direction as the basic current in which it is embedded and may induce upward vertical motion ahead of it. they are more numerous than long waves and often disappear with height in the atmosphere. stratopause: the boundary zone or transition layer between the stratosphere and the mesosphere. characterized by a decrease in temperature with increasing altitude. sun pillar: horizontal ice crystals in the form of plates, which occur in clouds and ice fog near the earth's surface, reflect sunlight into vertical sun pillars for a spectacular display. syzygy: the points in the moon's orbit about the earth at which the moon is new or full. : : tropical depression: a tropical cyclone in which the maximum sustained surface winds are 38 miles per hour (33 knots) or less. characteristically having one or more closed isobars, it may form slowly from a tropical disturbance or an easterly wave which has continued to organize. upslope effect: the cooling of an air flow as it ascends a hill or mountain slope. if there is enough moisture and the air is stable, stratiform clouds and precipitation may form. if the air is unstable, there might be an increased chance of thunderstorm development. wind shear: the rate of wind speed or direction change with distance. vertical wind shear is the rate of change of the wind with respect to altitude. horizontal wind shear is the rate of change on a horizontal plane..

Absolute instability: when the lapse rate of a column of air is greater than the dry adiabatic lapse rate. the term absolute is used because this applies whether or not the air is dry or saturated. barometer: an instrument used to measure atmospheric pressure. two examples are the aneroid barometer and the mercurial barometer. circulation cells: large areas of air movement created by the rotation of the earth and the transfer of heat from the equator toward the poles. circulation is confined to a specific region, such as the tropics, temperate, or polar, that influences the type of weather prevailing there. el niño: the cyclical warming of east pacific ocean sea water temperatures off the western coast of south america that can result in significant changes in weather patterns in the united states and elsewhere. this occurs when warm equatorial waters move in and displace the colder waters of the humbolt current, cutting off the upwelling process. ground clutter: a pattern of radar echoes reflecting off fixed ground targets such as buildings or hills near the radar. this may hide or confuse the proper return echo signifying actual precipitation. hypothermia: this situation occurs when the core temperature of one's body falls below normal. it is the failure of the body to maintain adequate production of heat under conditions of extreme cold. : mesosphere: the layer of the atmosphere located between the stratosphere and the ionosphere, where temperatures drop rapidly with increasing height. it extends between 31 and 50 miles (17 to 80 kilometers) above the earth's surface. middle clouds: a term used to signify clouds with bases between 6,000 and 18,000 feet. at the higher altitudes, they may also have some ice crystals, but they are composed mainly of water droplets. altocumulus, altostratus, and nimbostratus are the main types of middle clouds. this altitude applies to the temperate zone. in the polar regions, these clouds may be found at lower altitudes. in the tropics, the defining altitudes for cloud types are generally higher. mist: a collection of microscopic water droplets suspended in the atmosphere. it does not reduce visibility as much as fog and is often confused with drizzle. outflow: also referred to as an outflow boundary, it is the outward flow of air from a system, such as a thunderstorm. it is the result of cold downdrafts and its passage includes a wind shift and temperature drop. pascal's law: when an external pressure is applied to any confined fluid at rest, the pressure is increased at every point in the fluid by the amount of external pressure applied. it means that the pressure of the atmosphere is exerted not only downward on the surface of an object, but also in all directions against a surface which is exposed to the atmosphere. formulated by blaise pascal (1623-1662), a french mathematician, theologian, and physicist. polar front: a semi-continuous, semi-permanent boundary between polar air masses and tropical air masses. an integral part of an early meteorological theory known as the polar front theory. polar-orbiting satellite: a satellite whose orbit passes over both of the earth's between poles. small craft advisory: an advisory issued for marine interests, especially for operators of small boats or other vessels. conditions include wind speeds between 20 knots (23 mph) and 34 knots (39 mph). smoke: small particles produced by combustion that are suspended in the air. a transition to haze may occur when the smoke particles have traveled great distance (25 to 100 miles or more), and when the larger particles have settled out. the remaining particles become widely scattered through the atmosphere. it is reported as "fu" in an observation and on the metar. subtropical air: an air mass that forms over the subtropical region. the air is typically warm with a high moisture content due to the low evaporative process. tropical air mass: an air mass that forms in the tropics or subtropics over the low latitudes. maritime tropical air is produced over oceans and is warm and humid, while continental tropical air is formed over arid regions and is very hot and dry. warm high: a high pressure system that has its warmest temperatures at or near the center of circulation. contrast with a cold high. wave length: the least distance between particles moving in the same phase of oscillation of a wave. in oceanography, it is the horizontal distance between the highest parts of two successive wave crests above the still water level, separated by a trough that is below the still water level, and it is measured in meters. zodiac: the position of the sun during the course of the year as it appears to move though successive constellations. also, the band where the ecliptic runs centrally through the celestial sphere and contains the sun, the moon, and all the planets except venus and pluto..