Weather Definitions Ipsum

Word Lists: Weather Definitions

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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. absorption: the process in which incident radiant energy is retained by a substance. the absorbed radiation is then transformed into molecular energy. barotropy: the state of a fluid in which surfaces of constant density or temperature are coincident with surfaces of constant pressure. it is considered zero baroclinity. cold high: a high pressure system that has its coldest temperatures at or near the center of circulation, and horizontally, is thermally barotropic. it is shallow in nature, as circulation decreases with height. associated with cold arctic air, it is usually stationary. also known as a cold core high. contrast with a warm high. cold wave: a rapid fall in temperature within twenty-four hours to temperatures requiring substantially increased protection to agriculture, industry, commerce, and social activities. national weather service criteria includes the rate of temperature fall and the minimum to which it falls, depending on the region of the country and time of the in year. the weather channel uses the following criteria for a cold wave: a cold spell of two days or more with below normal temperatures in at least fifteen states, with at least five of them more than fifteen degrees below normal. continental air mass: an air mass with continental characteristics. it is a secondary characteristic of an air mass classification, signified by the small "c" before the primary characteristic, which is based on source region. for example, cp is an air mass that is continental polar in nature. contrail: acronym for condensation trail. a cloud-like streamer or trail often seen behind aircraft flying in clear, cold, humid air. a vapor trail is created when the water vapor from the engine exhaust gases are added to the atmosphere. dawn: the first appearance of light in the eastern sky before sunrise. it marks the beginning of morning twilight. the visual display is created by the scattering of light reaching the upper atmosphere prior to the sun's rise to the observer's horizon. deepening: used in describing the history of a low pressure system or an area of cyclonic circulation, it means a decrease in the central pressure of the system. although it usually describes the action of a pressure system on a constant pressure chart, it also means a surface low is increasing in cyclonic circulation and acquiring more energy. the opposite of filling. diffluence: a rate at which wind flow spreads apart along an axis oriented normal to the flow in question. the opposite of confluence. level of free convection (lfc): the level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely. this occurs most readily in a conditionally unstable atmosphere. low latitudes: the latitude belt between 30 and 0 degrees north and south of the equator. also referred to as the tropical or torrid region. meridional flow: atmospheric circulation in which the north and south, or meridional, component of motion is unusually pronounced. this weakens the zonal flow. positive vorticity advection: the advection of higher values of vorticity into an area. it is also known as cyclonic vorticity. pressure change: the net difference between the barometric pressure at the beginning and ending of a specified interval of time, usually the three hour period preceding an observation. rocketsonde: a type of radiosonde that is shot into the atmosphere by a rocket, allowing it to collect data during its parachute descent from a higher position in the atmosphere than a balloon could reach. shower: precipitation from a convective cloud that is characterized by its sudden beginning and ending, changes in intensity, and rapid changes in the appearance of the sky. it occurs in the form of rain (shra), snow (shsn), or ice (shpe). it is reported as "sh" in an observation and on the metar. straight-line winds: any surface wind that is not associated with rotation. an example is the first gust from a thunderstorm, as opposed to tornadic winds. stratosphere: the layer of the atmosphere located between the troposphere and the mesosphere, characterized by a slight temperature increase and absence of clouds. it extends between 11 and 31 miles (17 to 50 kilometers) above the earth's surface. it is the location of the earth's ozone layer. thermocline: a vertical negative temperature gradient in some layer of a body of water which is appreciably greater than the gradients above and below it. in the ocean, this may be seasonal, due to the heating of the surface water in the summer, or permanent. tropic of capricorn: the most southern point on the earth where the sun is directly overhead, located at approximately 23.5 degrees south latitude. veering: a clockwise shift in the wind direction in the northern hemisphere at a certain location. in the southern hemisphere, it is counterclockwise. this can either happen horizontally or vertically (with height). for example, the wind shifts from the north to the northeast to the east. it is the opposite of backing. vorticity: the measurement of the rotation of a small air parcel. it has vorticity when the parcel spins as it moves along its path. although the axis of the rotation can extend in any direction, meteorologists are primarily concerned with the rotational motion about an axis that is perpendicular to the earth's surface. if it does not spin, it is said to have zero vorticity. in the northern hemisphere, the vorticity is positive when the parcel has a counterclockwise, or cyclonic, rotation. it is negative when the parcel has clockwise, or anticyclonic, rotation. windward: the direction from which the wind is blowing. also the upwind side of an object. the opposite of the downwind or leeward side. zulu time: one of several names for the twenty-four hour time which is used throughout the scientific and military communities..

Ball lightning: a relatively rare form of lightning consisting of a luminous ball, often reddish in color, which moves rapidly along solid objects or remains floating in mid-air. boyle's law: states that when the temperature is held constant, the volume of a gas is inversely proportional to its pressure. therefore, if the pressure increases, the volume decreases and visa versa. for example, if the volume if halved, then the pressure is doubled. if the temperature is held constant, it becomes an isothermal process. discovered by robert boyle (1627-1691), an irish physicist and chemist and co-founder of the royal society. convection: motions in a fluid that transport and mix the properties of the fluid. these properties could be heat and/or moisture. when used to imply only upward vertical motion, it is then the opposite of subsidence. disturbance: this has several applications. it can apply to a low or cyclone that is small in size and influence. it can also apply to an area that is exhibiting signs of cyclonic development. it may also apply to a stage of tropical cyclone development and is known as a tropical disturbance to distinguish it from other synoptic features. frontogenesis: the birth or creation of a front. this occurs when two adjacent air masses exhibiting different densities and temperatures are brought together by prevailing winds, creating a front. it could happen when either air mass, or both, move over a surface which strengthens their original properties. however, it occurs most often along the eastern coasts of north america and asia, when the air mass moving out over the ocean has a weak or no distinct boundary. the opposite of frontolysis. heat balance: the equilibrium which exists on the average between the radiation received by the earth and atmosphere from the sun and that emitted by the earth and atmosphere. the balance between heat loss (long wave radiation from the earth back into the atmosphere) and heat gain (incoming solar radiation). inversion: a departure from the usual increase or decrease of an atmospheric property with altitude. it usually refers to an increase in temperature with increasing altitude, which is a departure from the usual decrease of temperature with height. mesohigh: a small, concentrated area of high pressure that may be created by the cold outflow and rain-cooled air from thunderstorms. it often forms a pseudo cold front or squall line on its leading edges. minimum: the least value attained by a function, for example, temperature, pressure, or wind speed. the opposite of maximum. moist adiabat: the line on a skew t-log p chart that depicts the change in temperature of saturated air as it rises and undergoes cooling due to adiabatic expansion. as saturated air rises, the temperature changes at a rate of 0.55°c per 100 meters (2-3°f per 1,000 feet). pressure: the force per unit area exerted by the weight of the atmosphere above a point on or above the earth's surface. 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. sargasso sea: an area of the north atlantic ocean between bermuda and the azores. it is in the middle of the north atlantic oceanic gyre, with converging surface waters. consequently, it has less biological features than any other region of the ocean because the lack of mixing with more nutrient-rich waters. severe weather: generally, any destructive weather event, but usually applies to localized storms, such as blizzards, intense thunderstorms, or tornadoes. snow level: the elevation in mountainous terrain where the precipitation changes from rain to snow, depending on the temperature structure of the associated air mass. snowpack: the amount of annual accumulation of snow at higher elevations. swell: ocean waves that have traveled out of their generating area. swell characteristically exhibits a more regular and longer period and has flatter wave crests than waves within their fetch. teleconnections: information used by forecasters to determine what the weather might be elsewhere when compared with past weather conditions at the same degree of longitude. troposphere: the lowest layer of the atmosphere located between the earth's surface to approximately 11 miles (17 kilometers) into the atmosphere. characterized by clouds and weather, temperature generally decreases with increasing altitude..

Barometric pressure: the pressure exerted by the atmosphere at a given point. its measurement can be expressed in several ways. one is in millibars. another is in inches or millimeters of mercury (hg). bwer: acronym for bounded weak echo region. refers to radar echo signatures with low reflectivity in the center, surrounded by higher reflectivity. it is associated with strong updrafts and is found in the inflow region of a thunderstorm. cloudburst: a sudden, heavy rainfall of a showery nature. continent: a large land mass rising abruptly from the deep ocean floor, including marginal regions that are shallowly submerged. continents constitute about one-third of the earth's surface. crepuscular rays: contrasting, alternating bright and dark rays in the sky. sunlight is scattered by molecules and particles rendering these bright rays visible. contrast is enhanced by haze, dust, or mist. these rays are more likely to be seen in the late afternoon, as clouds come between the sun and the observer. a similar effect occurs when the sun shines though a break in a layer of clouds. 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. gustnado: a weak, and usually short-lived, tornado that forms along the gust front of a thunderstorm, appearing as a temporary dust whirl or debris cloud. infrared: the long wave, electromagnetic radiation of radiant heat emitted by all hot objects. on the electromagnetic spectrum, it can be found between microwave radiation and visible light. water vapor, ozone, and carbon dioxide are capable of absorbing or transmitting infrared radiation. may be referred to as ir. isodrosotherm: the line drawn on a weather map connecting points of equal dew point. neap tide: a tide of decreased range, which occurs about every two weeks when the moon is at one quarter or three-quarters full. 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. sea mile: a unit of length distinguished from a nautical mile. one sea mile is equivalent to 1,000 fathoms (6,000 feet). 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. tropical cyclone: a warm core low pressure system which develops over tropical, and sometimes subtropical, waters, and has an organized circulation. depending on sustained surface winds, the system is classified as a tropical disturbance, a tropical depression, a tropical storm, or a hurricane or typhoon. wasatch winds: strong winds blowing easterly out of the wasatch mountains in utah, sometimes reaching speeds greater than 75 miles per hour. 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. 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..
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