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(1) the ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air (2) mass of water contained in a unit volume of moist air.

growth of a cloud or precipitation particle by the collision and union of a frozen particle (ice crystal or snowflake) with a super-cooled liquid droplet which freezes on impact.

the extent to which the readings of an instrument approach the true value of the calculated or measured quantities, supposing that all possible corrections are applied.

rain or snow containing acidic substances, resulting from the atmospheric pollution mainly with sulfur and nitrogen; acid precipitation has a lower pH than unpolluted rain.

the horizontal transfer of air mass properties by the velocity field of the atmosphere.

fog which forms in the lower part of a warm moist air mass moving over a colder surface (land or water).

non-gaseous substances, divided into solid particles or liquid droplets, held in suspension in the atmosphere.

an extensive body of the atmosphere in which physical properties, particularly temperature and humidity, exhibit only small and continuous differences in the horizontal plane; it may extend over an area of several million square kilometers and over a height of several kilometers.

the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 to two meters above ground; also called surface temperature.

a non-dimensional, unitless quantity that measures how well a surface reflects solar energy; ranges from 0 - 1; a value of 0 means the surface is a “perfect absorber,” where all incoming energy is absorbed, a value of 1 means the surface is a “perfect reflector,” where all incoming energy is reflected and none is absorbed.

a low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada.

the low pressure center located near the Aleutian Islands on mean charts of sea level pressure during the winter; it represents one of the main centers of action in the atmospheric circulation of the northern hemisphere.

a principal middle level cloud type (cloud genus), white or gray, or both white and gray, which occurs as a layer or patch with a wave aspect, the elements of which appear as laminae, rounded masses, rolls, etc; these elements usually are sharply outlined, but they may become partly fibrous or diffuse; they may or may not be merged, and they generally have shadowed parts; most of the regularly arranged altocumulus elements have an apparent width of 1 - 5 degrees.

a principal middle level cloud type (cloud genus) in the form of a grayish (gray) or bluish cloud sheet or layer of striated, fibrous, or uniform appearance, totally or partly covering the sky; the layer has parts thin enough to reveal the position of the sun; halo phenomena do not usually occur.

any wind blowing up a steep incline or mountain; the opposite of katabatic wind.

in synoptic meteorology, a detailed study of the state of the atmosphere over a particular region based on the actual observations.

an instrument which measures wind speed or wind speed and direction; a cup anemometer measures the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis; a byram anemometer is a variety of the cup anemometer; a counting anemometer has cups or a fan whose rotation is transmitted to a technical counter which integrates directly the air movement speed; a hand anemometer is small portable anemometer held at arm's length by an observer making a wind speed measurement; a pressure tube anemometer (dines anemometer) is an instrument which derives wind speed from measurements of the dynamic wind pressures - wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static, this pressure difference is proportional to the square of the wind speed.

a Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed.

a Russian anemometer combined with a vane to determine the wind direction.

an instrument for measuring atmospheric pressure; it is constructed on the following principles: an aneroid capsule (vidie capsule, which is a thin, disk-shaped box or capsule, usually metallic) is partially evacuated of gas, and is restrained from collapsing by an external or internal spring; the deflection of the spring will be nearly proportional to the difference between the internal and external pressures; magnification of the spring deflection is obtained both by connecting capsules in series and by mechanical linkages.

deviation of a meteorological quantity value in a given region from the normal (mean) value for the same period.

the line of latitude 66° 34′ S (often taken as 66.5° S); along this line the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice.

also known as the antarctic convergence; the southern front of the antarctic circumpolar current that separates the antarctic zone in the south from the polar frontal zone in the north; taken by many to delineate the actual northern boundary of the antarctic zone; characterized by sea surface temperatures near 5°–6° C and a salinity minimum of 33.8–34.0 psu produced by high rainfall.

the region between the antarctic circle (66° 34′ S) and the South Pole; climatically, the limit of the zone may be set at about 60° S, poleward of which the prevailing westerly winds give place to easterly or variable winds; over most of this region the average temperature does not rise above 0°C (32°F) even in summer.

the prevention of ice accumulation of aircraft, ships and other objects; the most common measures are heating or applying a dressing by brush or spray to weaken adhesion and facilitate removal.

area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; it is outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; this term is used interchangeably with high.

area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; used interchangeably with high..

system of air movements (atmospheric circulation) associated with an anticyclone, which is clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere.

(from Greek arktikos which means northern) northern polar region of the earth which includes almost the whole area of the Arctic Ocean and adjacent areas of Eurasian and North American continents.

mass of very cold air in the arctic regions which invades lower latitudes at irregular intervals.

the line of latitude 66 degrees 34 minutes N (often taken as 66.5 degrees N); along this line, the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice.

(1) the semi-permanent, semi-continuous front between the deep, cold arctic air and the shallower, basically less cold polar air of northern latitudes (2) south boundary of the arctic air mass.

haze in arctic regions which reduces horizontal and slant visibility and which may extend to a height of about 10 km; it appears blue-grey when viewed away from the sun, and reddish-brown toward it.

a weak high which appears over the arctic basin during late spring, summer and early autumn; one of the centers of action in the atmosphere.

a mist of ice crystals; a very light ice fog.

an atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes (about 45 degrees N) on time scales ranging from weeks to decades; the oscillation extends through the depth of the troposphere, and from January to March, it extends upward into the stratosphere where it modulates in the strength of the westerly vortex that encircles the arctic polar cap region; the north atlantic oscillation and arctic oscillation are different ways of describing the same phenomenon.

evaporation (steam) fog produced above a surface of open water within arctic ice when the air is stable and relatively cold.

the northern limit of tree growth; the sinuous boundary between tundra and boreal forest; taken by many to delineate the actual southern boundary of the arctic zone.

(1) geographically, the area north of the arctic circle (66° 34′ N) (2) (same as tundra) biogeographically, the area extending northward from the arctic tree line; also used for the level above the timber line in mountains.

the envelope of air surrounding the earth and bound to it more or less permanently by virtue of the earth's gravitational attraction; the system whose chemical properties, dynamic motions, and physical processes constitute the subject matter of meteorology.

the large-scale movement of air, and the means by which heat is distributed on the surface of the Earth; may vary from year to year.

as commonly used in weather observing practice, an observable occurrence of particular physical significance within the atmosphere; from the viewpoint of weather observations, the atmospheric phenomena include all hydrometeors (precipitation types and fogs), blowing snow, thunderstorms, tornadoes, waterspouts, and others.

pressure (force per unit area) exerted by the atmosphere on any surface by virtue of its weight; it is equivalent to the weight of a vertical column of air extending above a surface of unit area to the outer limit of the atmosphere.

longwave (infrared) radiation emitted by or being propagated through the atmosphere.

luminous phenomena, in the form of arcs, bands, draperies, or curtains in the high atmosphere over high latitudes; auroras are related to magnetic storms and the influx of charged particles from the sun, the phenomena are called aurora borealis in the northern hemisphere and aurora australis in the southern hemisphere.

arithmetic mean (m) of a number (n) of values (x1, x2, ... xn), defined by the equation: m = sxi/n; annual average value is calculated from 12 monthly means; daily average (or mean) value is calculated from 24 hourly readings of a meteorological element, or often from the average of the daily maximum and minimum values (for example, of temperature); monthly average is usually calculated as the average of the daily average values.

the semipermanent subtropical high over the North Atlantic Ocean, especially when it is located over the eastern part of the ocean; the same high over the western part of the Atlantic is called the Bermuda high; on mean charts of sea level pressure, this high is one of the primary centers of action in northern latitudes.

a barometer that records barometric pressure over time (days or weeks).

an instrument for measuring atmospheric pressure; two types of barometers are commonly used in meteorology: the mercury barometer and the aneroid barometer.

the semipermanent subtropical high over the North Atlantic Ocean, especially when it is located over the western part of the ocean; the same high over the eastern part of the Atlantic is called the Azores high; on mean charts of sea level pressure, this high is one of the primary centers of action in northern latitudes.

a cold wind blowing down an incline; a kind of katabatic wind.

a buoy, either fixed or floating, which carries instruments for sensing various meteorological elements and for transmitting the data by radio.

A reservoir of carbon dioxide that is increasing in size.

a warm wind blowing down an incline; a kind of katabatic wind.

the large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar region; also called polar vortex.

a principal high-level cloud type (cloud genus), appearing as a thin, white patch or layer of cloud without shading, composed of very small elements in the form of grains, ripples, etc., merged or separated, and more or less regularly arranged; most of the elements have an apparent width of less than 1 degree.

a principal high-level cloud type (cloud genus), appearing as a transparent, whitish cloud veil of fibrous (hair-like) or smooth appearance, totally or partially covering the sky, and often producing halo phenomena, either partial or complete.

a principal high-level cloud type (cloud genus), appearing as detached clouds in the form of white, delicate filaments or white or mostly white patches or narrow bands; these clouds have a fibrous (hair-like) appearance, or a silky sheen, or both; because cirrus elements are too narrow, they do not produce a complete circular halo.

sky with a total cloud cover of less than one okta (or one-tenth in the united states).

synthesis of weather conditions in a given area, characterized by long-term statistics (mean values, variances, probabilities of extreme values, etc.) of the meteorological elements in that area; polar climate (arctic climate) is generally the climate of a geographical polar region, most commonly taken to be a climate which is too cold to support the growth of trees.

a study dealing with variations in climate on many different time scales from decades to millions of years, and the possible causes of such variations; (1) in the most general sense, the term climate change encompasses all forms of climatic inconstancy (that is, any differences between long-term statistics of the meteorological elements calculated for different periods but relating to the same area) regardless of their statistical nature or physical causes; climate change may result from such factors as changes in solar activity, long-period changes in the earth's orbital elements (eccentricity, obliquity of the ecliptic, precession of equinoxes), natural internal processes of the climate system, or anthropogenic forcing (for example, increasing atmospheric concentrations of carbon dioxide and other greenhouse gases) (2) the term climate change is often used in a more restricted sense, to denote a significant change (such as a change having important economic, environmental and social effects) in the mean values of a meteorological element (in particular temperature or amount of precipitation) in the course of a certain period of time, where the means are taken over periods of the order of a decade or longer.

representation of the climate system based on the mathematical equations governing the behavior of the various components of the system and including treatment of key physical processes and interactions, cast in a form suitable for numerical approximation with computers.

(1) in the most general sense, the term climate variability denotes the inherent characteristic of climate which manifests itself in changes with time; the degree of climate variability can be described by the differences between long-term statistics of meteorological elements calculated for different periods, (in this sense, the measure of climate variability is the same as the measure of climate change) (2) the term climate variability is often used to denote deviations of climate statistics over a given period of time (such as a specific month, season or year) from the long-term climate statistics relating to the corresponding calendar period; (in this sense, climate variability is measured by those deviations, which are usually termed anomalies).

atlas composed mainly of climatological charts; it represents especially the monthly and annual distributions of the principal climatic elements of a specific region for a relatively long period.

the scientific study of climate; the aspect of meteorology which studies processes of climate formation, distribution of climates over the globe, analysis of the causes of differences of climate (physical climatology), and the application of climatic data to the solution of specific design or operational problems (applied climatology); climatology may be further subdivided according to purpose or point of view: agricultural climatology, air-mass climatology, aviation climatology, bioclimatology, dynamic climatology, medical climatology, macroclimatology, mesoclimatology, microclimatology, paleoclimatology, synoptic climatology, etc..

a hydrometeor consisting of a visible aggregate of minute particles of liquid water or ice, or both, suspended in the free air and usually not touching the earth's surface; it may also include larger particles of liquid water or ice (precipitation particles) and non-aqueous liquid or solid particles such as those present in fumes, smoke and dust (aerosols); cloudiness is the same as cloud cover; but usually it is used in a very general sense.

that portion of the sky cover which is attributed to clouds; the unit of measurement is the okta or tenths (meaning one-eighth or one-tenth) of the sky dome as seen by the observer.

any non-occluded front that moves in such a way so that colder air replaces warmer air; the leading edge of a relatively cold air mass.

at a given level in the atmosphere, any low that is generally characterized by colder air near its center than around its periphery; the opposite of a warm low.

the location that has the lowest annual mean temperature in its hemisphere.

the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation; in meteorological usage, this term is applied only to transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed sublimation, as is the reverse process.

the transport of energy entirely resulting from the random motions of individual molecules, and not from any concerted group movement; occurs in response to temperature gradients; contrasts with convection, in which energy is transported by molecules moving together in coherent groups.

the transport of energy resulting from the concerted movement of molecules in coherent groups; contrasts with conduction in which energy is transported by the random motions of molecules; atmospheric convection is nearly always turbulent and results in the vertical transport and mixing of atmospheric properties.

cumuliform cloud which forms in the atmosphere as a result of convection; such clouds are also called clouds of vertical development, a cloud that has its base in the low height range but extends upward into the middle or high altitudes.

apparent force, due to the rotation of the earth, which acts normal to, and to the right of the velocity of a moving particle in the northern hemisphere, the movement of the particle being considered relative to that of the earth.

one of the earth's spheres of irregular form existing in the zone of interaction of the atmosphere, hydrosphere and lithosphere, distinguished by negative or zero temperature and the presence of water in the solid or super-cooled state; the term refers collectively to the portions of the earth where water is in solid form, including snow cover, floating ice, glaciers, ice caps, ice sheets, seasonally frozen ground and perennially frozen ground (permafrost).

like cumulus; generally descriptive of all clouds; vertical development in the form of rising mounds, domes or towers; driven by thermal convection and have vertical velocities greater than 1 meter (3.3 feet) per second.

a principal cloud type (cloud genus) of vertical development, exceptionally dense and vertically developed clouds, occurring either as isolated clouds or as a line or wall of clouds with separated upper portions; these clouds appear as mountains or huge towers, at least a part of the upper portions of which are usually smooth, fibrous, or striated, and almost flattened; this part often spreads out in the form of an anvil (incus) or vast plume; under the base of cumulonimbus, which is very dark, there frequently exist virga, precipitation, and low, ragged clouds, either merged with it or not; its precipitation is often heavy and always of a showery nature.

a principal low-level cloud type (cloud genus) in the form of individual, detached elements which are generally dense and possess sharp non-fibrous outlines; these elements develop vertically, appearing as rising mounds, domes, or towers, the upper parts of which often resembles a cauliflower; the sunlit parts of these clouds are mostly brilliant white; their bases are relatively dark and nearly horizontal; near the horizon the vertical development of cumulus often causes the individual clouds to appear merged; if precipitation occurs, it is usually of a showery nature.

process of initiation or intensification of a cyclonic circulation in the atmosphere; the opposite to cyclolysis.

process of weakening or terminating of a cyclonic circulation in the atmosphere; the opposite of cyclogenesis.

area in the atmosphere in which the pressures are lower than those of the surrounding region at the same level; it is represented on a synoptic chart by a system of isobars at a specified altitude level (or a system of contours at a specified pressure level) which enclose relatively low values of pressure (or altitude); a cyclone begins when a wave (young) cyclone forms and moves along a front; a mature cyclone has well-developed warm sectors and both cold and warm fronts; an occluded cyclone is that within which there has developed an occluded front.

atmospheric circulation associated with a cyclone (depression, low pressure area); it is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.

the spatial displacement of a center of low pressure caused by the local redistribution of mass in the atmosphere; the trajectory of the center is often altered by heating or cooling on the air column, which can result from thermal fluxes at the surface or latent heat transformations associated with cloud formation and precipitation; these processes change the temperature distribution in the air column, resulting in density changes which modify the surface pressures.

the removal of ice accumulation on aircraft, ships and other objects by mechanical, thermal or chemical devices.

in meteorology, an area of low pressure (i.e. a low); usually applies to a particular stage in the development of a cyclone.

vertical interval between the top surface of a snow layer and the ground beneath; the layer is assumed to be evenly spread over the ground which it covers.

the temperature to which a given parcel of air must be cooled at constant pressure and constant water-vapor content in order for saturation to occur; when this temperature is below 0 degrees Celsius, it is called the frost point.

a type of precipitation composed of slowly falling, very small, unbranched crystals of ice which often seem to float in the air; it may fall from a high cloud or from a cloudless sky, it usually occurs under frosty weather conditions (under very low air temperatures).

either of the two points on the earth's surface at which magnetic meridians converge; the horizontal component of the magnetic field of the earth becomes zero at this point; also called the magnetic pole.

floating (or drifting on ice) ocean buoy equipped with meteorological and/or oceanographic sensing instruments linked to transmitting equipment for sending the observed data to collecting centers.

snow raised from the surface of the earth by the wind to a height of less than 1.5 to 2.0 meters (5 to 6.6 feet) above the surface; it dose not restrict horizontal visibility at 2 meters (6.6 feet) or more above the surface.

the total infrared radiation emitted from the earth's surface; to be carefully distinguished from effective terrestrial radiation, atmospheric radiation, and insolation.

the difference between the outgoing infrared (longwave) terrestrial radiation of the earth's surface and the downward infrared counter-radiation from the atmosphere.

an oscillation of the electric or magnetic field associated with the propagation of energy; characterized by their wavelengths and amplitude; propagate at the speed of light.

the amount of electromagnetic energy (primarily at wavelengths longer than 1.0 micrometer) that an object emits; for example, the earth emits longwave radiation primarily in the infrared part of the electromagnetic spectrum, but also in longer microwave wavelengths; the emissivity of an object varies as the fourth power of its absolute temperature.

either of the two points of intersection of the sun's apparent annual path and the plane of the earth's equator; in the northern hemisphere the spring (vernal) equinox falls on or about 21 March, and the autumnal equinox on or about 22 September.

the difference between a measured value of a quantity and its true value; different types of errors are inherent to observations.

the physical process by which a liquid or solid substance is transformed to the gaseous state; the opposite of condensation; in meteorology, evaporation usually is restricted in use to the change of water from liquid to gas, while sublimation is used to the change from solid to gas as well as from gas to solid.

fog formed as a result of evaporation of water that is warmer than the air.

a cold wind blowing down an incline; a kind of katabatic wind.

a region of space at each point of which a given physical or mathematical quantity has some definite value; for example, a gravitational field, magnetic field, or electric field; and, in meteorology, a pressure field, temperature field, etc; if the quantity specified at each point is a vector quantity, the field is said to be a vector field.

a warm wind blowing down an incline; a kind of katabatic wind.

a hydrometeor consisting of a visible aggregate of minute water droplets (or ice crystals), suspended in the atmosphere near the earth's surface; according to international definition, fog reduces visibility below one kilometer, fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface; when composed of ice crystals, it is termed ice fog.

a measure of how cold it has been and how long it has been cold; the cumulative fdd is usually calculated as a sum of average daily degrees below freezing for a specified time period (10 days, month, season, etc.).

drizzle, the drops of which freeze on impact with the ground or with objects on the earth's surface or with aircraft in flight.

rain, the drops of which freeze on impact with the ground or with objects on the earth's surface or with aircraft in flight.

in meteorology, generally, the interface or transition zone between two air masses of different density; since the temperature distribution is the most important regulator of the atmosphere density, a front almost invariably separates air masses of different temperature; when warmer air replaces the colder, it is a warm front, and vice-versa.

the condition which exists when the temperature near the earth's surface and earth-bound objects falls below freezing (0 degrees Celsius or 32 degrees Fahrenheit).

the highest temperature at which atmospheric moisture will sublimate in the form of hoarfrost on a cooled surface; it is analogous to the dew point.

fog-like clouds, due to the contact of cold air with relatively warm water, which appear over newly-formed leads, or leeward of the ice edge, and which may persist while new ice is forming.

the phase transition of a substance passing from the solid to the liquid state, melting; in meteorology, fusion is understood to refer to the melting of ice, which, if the ice is pure and subjected to one standard atmosphere of pressure, takes place at the ice point of 0 degrees Celsius (32 degrees Fahrenheit).

in meteorology, general term for any device that measures strength of wind, pressure, and other parameters; the most widespread gauges on meteorology are balance snow gauge, barometer gauge, density-of-snow gauge, dew gauge, distance gauge, rain-and snow gauge, rain-intensity gauge, standard gauge, wind gauge, etc..

of the atmosphere; complete statistical description of atmospheric motions over the earth.

numerical representation of the atmosphere and its phenomena over the entire earth, using the equations of motion and including radiation, photochemistry, and the transfer of heat, water vapor, and momentum.

the point of intersection of the Earth's surface with the axis of a simple magnetic dipole that best approximates the Earth's actual, more complex magnetic field; if the Earth's magnetic field were a perfect dipole then the field lines would be vertical at the geomagnetic poles, and they would therefore coincide with the magnetic poles: however, the dipole approximation is in fact far from perfect, so in reality the magnetic and geomagnetic poles lie some distance apart.

theoretical wind which results from the equilibrium between horizontal components of the pressure gradient force and the coriolis force (deviating force) above the friction layer; only these two forces (no frictional force) are supposed to act on the moving air; it blows parallel to straight isobars or contours.

a coating of ice, generally clear and smooth but usually containing some air pockets, formed on exposed objects by freezing of a film of super-cooled water deposited by rain, drizzle, fog, or possibly condensed from super-cooled water vapor; glaze is denser, harder and more transparent, than either rime or hoarfrost.

global network of observational stations which is the coordinated system of methods, techniques and facilities for making observations on a world-wide scale in the framework of the World Weather Watch, a World Meteorological Organization program.

the coordinated global system of telecommunication facilities and arrangements for the rapid collection, exchange and distribution of observational data in the framework of the World Weather Watch, a World Meteorological Organization program.

the same as geostrophic wind, but blowing parallel to curved isobars or contours; the curved airflow pattern around a pressure center results from a balance among pressure-gradient force, coriolis force, and centrifugal force.

a wave disturbance in which buoyancy (or reduced gravity) acts as a restoring force on parcels displaced from hydrostatic equilibrium; there is a direct oscillatory conversion between potential and kinetic energy in the wave motion.

a cold wind blowing down an incline; a kind of katabatic wind.

the anticyclone that appears to overlie Greenland; analogous to the antarctic anticyclone.

a finite collection of points to which the meteorological variables used in a numerical model, or interpolated from observations, apply; a field of such regular values (points) is termed gridded field.

precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 millimeters (0.2 to 2.0 inches), or sometimes bigger, falling either separately or agglomerated into irregular lumps; when the diameter is less than about 5 millimeters (0.2 inch), the balls are called ice pellets.

group of optical phenomena, in the form of rings, arcs, pillars or bright spots around the sun or moon, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere (cirrus clouds, diamond dust, etc.).

fine dust or salt particles dispersed through a portion of the atmosphere; the particles are so small that they cannot be felt or individually seen with the naked eye, but they diminish horizontal visibility and give the atmosphere a characteristic opalescent appearance that subdues all colors; a type of lithometeor.

equilibrium between the gain and loss of heat at a specific place or for a specific system.

the equilibrium that exists between the radiation received by the earth and atmosphere from the sun and that emitted by the earth and atmosphere.

relation between fluxes of heat into and out of a given region or body and the heat stored by the system; in general, this budget includes advective, evaporative, and other terms as well as a radiation term.

the amount of heat transferred across a surface of unit area in a unit time.

process, or region, in which energy is removed from the atmosphere in the form of heat.

process, or region, in which energy is added to the atmosphere in the form of heat.

area of high pressure in the atmosphere; used interchangeably with anticyclone.

typically thin, white clouds above 6,000 meters (20,000 feet); at these altitudes, temperatures are so cold that clouds are composed primarily of ice crystals; includes cirrus, cirrocumulus and cirrostratus clouds.

a deposit of interlocking ice crystals (hoar crystals) formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc.; the surfaces of these objects are sufficiently cooled, mostly by nocturnal radiation, to cause the direct sublimation of the water vapor contained in the ambient air.

(1) water vapor content of the air. (2) some measure of the water-content of air; see also absolute humidity, relative humidity, specific humidity, dew point.

any product of condensation or sublimation of atmospheric vapor, whether formed in free atmosphere or at the earth's surface; also any water particles blown by the wind from the earth's surface.

an instrument which measures the water vapor content in the atmosphere; there are several different means of transduction used in measuring this quantity and hence various types of hygrometers; these are: a) the psychrometer, which utilizes the thermodynamic method; b) the class of instruments which depends upon a change of physical dimension due to absorption of moisture (hair hygrometer, for example); c) those which depend upon condensation of moisture (dew point hygrometer); d) the class of instruments which depend upon the change of chemical or electrical properties due to absorption of moisture, and some others.

white glare on the underside of low clouds indicating presence of ice which may be beyond the range of vision.

a suspension of numerous minute ice crystals in the air, reducing visibility at the earth's surface; the crystals often glitter in the sunshine; ice fog produces optical phenomena such as luminous pillars and small haloes.

a research ship which performs ice surveys in polar regions.

precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 millimeters (0.2 to 2.0 inches), or sometimes more, falling either separately or agglomerated into irregular lumps; when the diameter is less that about 5 millimeters (0.2 inch), the balls are called ice pellets.

a fall of unbranched ice crystals, in the form of needles, columns, or plates, often so tiny that they seem to be suspended in the air; these are visible mainly when they glitter in the sunshine (diamond dust); they may then produce a luminous pillar or other halo phenomena; this hydrometeor, which is frequent in polar regions, occurs at very low temperatures and in stable air masses.

the low pressure center near Iceland (mainly between Iceland and southern Greenland); on mean charts of sea-level pressure, it is a principal center of action in the atmosphere circulation of the northern hemisphere.

hanging spike of clear ice formed by the freezing of dripping water.

electromagnetic radiation of wavelengths between approximately 0.75 and 1000 millimeters; see also atmospheric radiation, terrestrial radiation, longwave radiation.

(1) exposure of an object to the sun (2) intensity of incoming solar radiation incident on a unit horizontal surface at a specific level.

structure to protect certain instruments from insolation and weather while at the same time ensuring sufficient ventilation.

in meteorology, a departure from the usual (normal) decrease or increase with altitude of the value of an atmospheric property; also, the layer through which this departure occurs (the inversion layer); this term almost always refers to a temperature inversion.

a line of equal or constant pressure; it most often refers to a line drawn through all points of equal atmospheric pressure.

a line drawn through geographical points recording equal amounts of precipitation during a specific period.

a line of equal or constant temperature.

relatively strong winds concentrated within a narrow stream in the atmosphere; generally refers to a quasi-horizontal jet stream of maximum winds embedded in the midlatitude westerlies, and concentrated in the high troposphere.

any wind blowing down an incline; if the wind is warm, it is called a foehn or chinook; if cold, it may be a fall wind (bora), or a gravity wind (mountain wind); the opposite of anabatic wind.

thin plate, sheet or layer; laminae (plural).

the relatively dark appearance of the underside of a cloud layer when it is over land that is not snow covered; this term is used largely in polar regions with reference to the sky map; land sky is brighter than water sky, but is much darker than ice blink or snow blink.

the rate of change of any meteorological element with height.

atmospheric processes with a representative scale (large-scale) of 10,000 kilometers (6,200 miles); in meteorology, it is a scale in which the curve of the earth is not negligible; the large-scale atmospheric flows are essentially nearly hydrostatic, nearly geostrophic and wave-like in appearance; they exist mainly in response to the latitudinal differences in radiative heating, to the particular value of the coriolis force and to the spatial distribution of the oceans and continents.

the downwind side.

general term for dry atmospheric suspensoids, including dust, haze, smoke and sand.

heat radiation with wavelengths greater than 4 millimeters.

area of low pressure in the atmosphere.

clouds in the lower region of the atmosphere, from ground level to 6500 feet (2000 meters); includes stratus, stratocumulus, the bases of cumulus and cumulonimbus, and sometimes nimbostratus clouds.

white or sometimes reddish vertical streaks of light extending from above and below the sun; they are caused by light reflected off the mirror-like surfaces of ice; most commonly seen at sunrise and sunset.

either of the two points on the earth's surface at which magnetic meridians converge; the horizontal component of the magnetic field of the earth becomes zero at this point; also called the dip pole.

a climate dominated by the ocean; because of the moderating effect of water, sites having this climate are considered relatively mild.

a mercury-filled glass tube in which the height of the mercury column is a measure of air pressure.

an atmospheric circulation in a vertical plane oriented along a meridian; it consists of the vertical and the meridional (north or south) components of motion only.

top of the mesosphere, situated at about 80-85 kilometers (50-53 miles).

the region of the atmosphere between about 50 kilometers (31 miles) and 80-85 kilometers (50-53 miles), extending from the top of the stratosphere to the upper temperature minimum; it is characterized by a broad temperature maximum (near 0 degrees Celsius) at its base, from which the temperature decreases to a minimum (about -90 degrees Celsius) at the mesopause level.

any one of the properties or conditions of the atmosphere which together specify the weather at a given place for any particular time (for example, air temperature, pressure, wind, humidity, thunderstorm and fog).

study of the atmosphere and its phenomena, including its structure, properties, and physical processes.

in terms of wavelength, microwaves range from 1 millimeter to 1 meter, and are much longer than the shorter visible (0.38-0.78 micrometer) wavelengths; these longer wavelengths allow microwave energy to penetrate through clouds; because these sensors measure microwave energy, they do not rely on sunlight for illumination so they can acquire images regardless of time of day; can be either passive or active; passive sensors detect and record naturally upwelling microwave energy emitted from objects; active sensors generate their own beam of energy, generally with an antenna, which then detects the returned energy patterns (backscatter) that indicate the presence of features and their position relative to the sensor; radar (radio detection and ranging) was an original active microwave sensor that became widely operational with the onset of World War II.

clouds composed of ice crystals and water droplets in the middle region of the atmosphere, from 2,000 - 6,000 meters (6,500 to 23,000 feet); includes altocumulus, altostratus, nimbostratus, and portions of cumulus and cumulonimbus clouds.

precipitation consisting of a mixture of rain and wet snow; it usually occurs when the temperature of the air layer near the ground is slightly above freezing; the British term for this mixture is sleet (which has a different meaning in the United States).

a cold wind blowing down an incline; a kind of katabatic wind.

the difference between accumulation and ablation; usually expressed in terms of volumes of water equivalent per unit area.

difference between the downward and upward terrestrial radiation fluxes; net flux of terrestrial radiation.

a principal cloud type (cloud genus); gray and often dark; rendered diffuse by more or less continuously falling rain, snow, sleet, etc. of the ordinary varieties and not accompanied by lightning, thunder, or hail; precipitation in most cases reaches the ground; may or may not merge with low, ragged clouds that frequently occur below.

the relatively weak general area of high pressure which, as shown on mean charts of sea-level pressure, covers most of North America during winter; this pressure system is not nearly as well-defined as the analogous Siberian high.

an oscillation in the strength of the Icelandic Low and Azores High, the two dominant surface pressure features in the North Atlantic. When both are unusually strong, the North Atlantic Oscillation (NAO) is in its positive phase; when both are unusually weak, it is in its negative phase. The NAO has climate impacts not just in the Arctic, but in North America and Europe. The NAO, identified by Sir Gilbert Walker in the 1920s, is similar to the Arctic Oscillation.

a weather or meteorological observation is an evaluation of one or more meteorological elements that describes the state of the atmosphere either at the earth's surface or aloft.

a group of stations (surface meteorological, upper-air, or other) spread over a given area for making regular observations.

a nearly colorless (but faintly blue) gaseous form of oxygen, with a characteristic odor like chlorine; has a formula of O3 and a molecular weight of 48; found in trace quantities in the earth's atmosphere at all times, primarily in the stratosphere between heights of about 10 to 50 kilometers (6 to 31 miles; the ozonosphere or ozone shield) where its production results from photochemical processes involving ultraviolet radiation; its maximum concentration occurs between 20 to 25 kilometers (12 to 16 miles); in the lower atmosphere, ozone is commonly formed as a product of electrical discharges through the air.

stratospheric ozone layer, giving protection to the earth's surface due to intense absorption of harmful solar ultraviolet radiation by the gas.

stratospheric ozone layer, giving protection to the earth's surface due to intense absorption of harmful solar ultraviolet radiation by the gas.

(1) a term used loosely by many meteorologists for almost any meteorological quantity or element (2) an arbitrary constant or variable appearing in a mathematical expression; changing it can give various outcomes for the phenomena represented.

in a mixture of gases, each gas has a partial pressure, which is the pressure the gas would have if it occupied that volume alone.

predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour or six hours), specified in the international synop code.

layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C for at least several years; it exists where summer heating fails to reach the base of the layer of frozen ground.

power of hydrogen; a measure of the activity of hydrogen ions in solution, and therefore, its acidity or alkalinity.

in polar regions, the portion of the year when the sun is continuously in the sky; its length changes from twenty hours at the arctic/antarctic circle (latitude 66 degrees, 33 minutes N or S) to 186 days at the north and south poles.

a person working for a long time at one of the polar observing stations; Russian word is polyarnik.

small, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass; its motion is approximately the same as the air stream in which it is embedded.

in polar regions, the portion of the year when the sun does not rise above the horizon; its length changes from twenty hours at the arctic/antarctic circle (latitude 66 degrees, 33 minutes N or S) to 179 days at the North and South Poles.

regions around the North and South Poles, north of the Arctic, or south of the Antarctic Circles, respectively; characterized by polar climate, very cold temperatures, heavy glaciation, and dramatic variations in daylight hours (24 hrs darkness in winter, 24 hrs daylight in summer).

large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions; it is often called circumpolar vortex.

Russian word for a person working for a long time at one of the polar observing stations.

(1) any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground; includes: rain, drizzle, snow, snow grains, snow pellets, diamond dust, hail, and ice pellets; see also acid precipitation (2) accumulated depth of rain, drizzle and the melted water content of frozen forms of precipitation.

the degree of agreement between independent measurements of a single quantity obtained by applying a specific measurement procedure several times under prescribed conditions.

weather at a station at the time of observation.

a type of stress characterized by uniformity in all directions; in dynamics, it is that part of the stress tensor that is independent of viscosity and depends only upon the molecular motion appropriate to the local temperature and density; it is the negative of the mean of the three normal stresses, and is, therefore, a scalar quantity expressed in units of force per unit area; in meteorology, commonly used for atmospheric pressure.

the character and amount of atmospheric pressure change for a three-hour or other specified period ending at the time of observation.

an instrument used for measuring the water vapor content of the atmosphere; a type of hygrometer; it consists of two thermometers, one of which (the dry bulb) is an ordinary glass thermometer, while the other (wet bulb) has its bulb covered with a jacket of clean muslin which is saturated with distilled water prior to an observation; when the bulbs are suitably ventilated, they indicate the thermodynamic wet- and dry-bulb temperatures of the atmosphere; one variety is the assman psychrometer (a special form of aspiration psychrometer for which the ventilation is provided by a suction fan).

tables prepared from psychrometric data and used to obtain vapor pressure, relative humidity, and dew point from wet- and dry-bulb temperatures.

RAdio Detection And Ranging was an original active microwave sensor that became widely operational with the onset of World War II.

(1) emission or transfer of energy in the form of electromagnetic waves (2) the process by which electromagnetic radiation is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space; this concept is to be distinguished from conduction and convection.

instrument intended to be carried by a balloon up through the atmosphere, equipped with sensors to measure one or several meteorological variables (pressure, temperature, humidity, etc.), and provided with a radio transmitter for sending this information to the observing station.

radiosonde which is tracked by radar or radio-theodolite to measure the wind aloft.

the (dimensionless) ratio of the actual vapor pressure of the air to the saturation vapor pressure; usually expressed as a percent, and can be computed from psychrometric data.

in meteorology, an elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow.

a white or milky and opaque granular deposit of ice formed by the rapid freezing of super-cooled water drops as they impinge upon an exposed object; it is denser and harder than hoarfrost, but lighter, softer, and less transparent than glaze.

the condition in which the partial pressure of any fluid constituent (water in the atmospheric air) is equal to its maximum possible partial pressure under the existing environmental conditions, such that any increase in the amount of that constituent will initiate within it a change to a more condensed state; evaporation ceases under such conditions.

the maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water; this is the maximum water vapor the air can hold for any given combination of temperature and pressure.

(1) a series of marks at regular intervals for the purpose of measuring (scale of an instrument, for example, a thermometer) (2) system of units for measuring ( 3) proportion between the size of something and the map, diagram, etc. which represents it (4) order of magnitude of a phenomenon or of a meteorological parameter.

evaporation fog formed when water vapor is added to air which is much colder than the vapor's source; most commonly, when very cold air drifts across relatively warm water; also called steam fog.

temperature of the water film at the sea surface.

the atmospheric pressure at mean sea level, either directly measured or, most commonly, empirically determined from the observed station pressure.

high pressure area largely predominate during a major portion of the year where an anticyclone appears on the mean monthly pressure charts.

slowly moving or motionless cyclone.

same as enthalpy; the heat absorbed or transmitted by a substance during a change of temperature which is not accompanied by a change of state; used in meteorology in contrast to latent heat.

a screen to shield a rain-gauge from the influence of the wind, or to shield a thermometer against insolation.

in meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0.4 to 4.0 microns in wavelength) from longwave (terrestrial) radiation.

an area of high pressure which forms over Siberia in winter, and which is particularly apparent on mean charts of sea-level pressure.

(1) (United States) frozen raindrops that bind on impact with the ground (2) (elsewhere) a mix of rain and snow, a mix of rain and hail, or melting snow.

currently used as a synonym for general air pollution; it was originally created by combining the words smoke and fog.

a bright white glare on the underside of clouds, produced by the reflection of light from a snow-covered surface; snowblink is lighter than ice blink, and much lighter than land sky or water sky.

the total electromagnetic radiation emitted by the sun.

the point in time when the vertical rays of the sun are striking either the Tropic of Cancer (23 degrees, 30 minutes N, the summer solstice in the northern hemisphere) or the Tropic of Capricorn (23 degrees, 30 minutes S, the winter solstice in the northern hemisphere); represents the longest or shortest day of the year; in the northern hemisphere, the summer solstice falls on or about 21 June, and the winter solstice on or about 22 December.

the mass of water vapor per unit mass of air, including the water vapor (usually expressed as grams of water vapor per kilogram of air).

either of the two points of intersection of the sun's apparent annual path and the plane of the earth's equator; in the northern hemisphere, the spring (vernal) equinox falls on or about 21 March, and the autumnal equinox on or about 22 September.

air mass having static stability in its lower layers; it is free from convection, has a low degree of turbulence and may have stratiform clouds or fog, or no clouds.

atmospheric pressure observed at a station.

evaporation fog formed when water vapor is added to air which is much colder than the vapor's source; most commonly, when very cold air drifts across relatively warm water; also called sea smoke.

in meteorology, a basic fluid flow which exerts a strong influence upon the direction of movement of disturbances embedded in it; in the atmosphere, it is usually an air flow in the middle or upper troposphere which govern directions of the disturbances at low levels.

a principal low-level cloud type (cloud genus), predominantly stratiform, in the form of relatively low gray and/or whitish layer, sheet or patch; its elements are often arranged in bands or rolls that lie across the wind; light rain, snow, or sleet may fall from stratocumulus.

the boundary layer between the stratosphere and the mesosphere at about 50 to 55 kilometers (31 to 34 miles).

a layer of the Earth’s atmosphere, between the troposphere and mesosphere, that is stratified in temperature such that cooler layers are closer to the Earth’s surface, and warmer layers are higher up (opposite the pattern of the troposphere near the Earth’s surface); situated between about 10 to 50 kilometers (6 to 31 miles) in altitude above the surface of the moderate latitudes; at the poles, it starts at about 8 km in altitude; composition is basically the same as that of the lower atmosphere, with the addition of ozone.

a principal low-level cloud type (cloud genus) in the form of a low-altitude, light to dark gray cloud layer with a rather uniform base; generally diffuse and dull; this cloud formation has little structure and looks like fog, except that it is above the ground, stratus does not usually produce precipitation, but when it does occur, it is in the form of minute particles, such as drizzle, ice crystals, or fine snow grains.

a meteorological observation made on the earth's surface, in contrast with an upper-air observation.

the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 - 2.0 meters (5.0 - 6.6 feet) above ground; also called air temperature.

wind blowing near the earth's surface; it is measured, by convention, at a height of 10 meters (33 feet) above ground in an area where the distance between the anemometer and any obstruction is at least 10 times the height of the obstruction.

a substance dispersed throughout another substance; also called suspended phase.

the study of the synoptic observation data plotted on synoptic charts aimed at analysis of the atmospheric disturbances (for example, fronts, cyclones, and anticyclones).

a weather chart reflecting the state of the atmosphere over a large area at a given moment.

a code approved by the World Meteorological Organization, by which meteorological elements observed at the earth's surface at synoptic times are encoded in groups of five figures and transmitted internationally through the GTS (Global Telecommunications System).

hour (UTC - Coordinated Universal Time) determined by international agreement at which meteorological observations are made simultaneously throughout the world; the primary synoptic hours are every six hours, commencing at 00:00 UTC.

the study and analysis of synoptic weather information (synoptic charts, synoptic weather observations); thus, it is a study of macro-scale atmospheric processes, as well as weather prediction based on results of synoptic studies.

an observation made at periodic times (usually at 3-hour and 6-hour intervals specified by the World Meteorological Organization) of sky cover, state of the sky, cloud height, atmospheric pressure at sea level, temperature, dew point, wind speed and direction, amount of precipitation, hydrometeors and lithometeors, and special phenomena that prevail at the time of the observation or observed since the previous specified observation.

the scale of the high- and low-pressure systems of the lower atmosphere; dimensions typically range from 1000 to 2500 kilometers (620 to 1550 miles; synoptic-scale circulation).

a physical quantity characterizing the mean random motion of molecules in a physical body; in other words, it is a measure of the degree of hotness or coldness of a substance.

longwave radiation emitted by the earth, including its atmosphere.

an optical instrument used to visually track a radiosonde balloon and determine its bearing and elevation while in flight.

an instrument continuously recording temperature.

an instrument for measuring temperature; in meteorology, generally used to measure the temperature of the air or the soil.

(1) in mountainous regions, the line above which climatic conditions do not allow the upright growth of trees (2) the poleward limit of tree growth, also known as the tree line.

the northern parallel of maximum solar declination, approximately 23° 27′ N latitude; the farthest northern latitude at which the sun can appear directly overhead, which occurs on the day of the summer solstice.

the southern parallel of maximum solar declination, approximately 23° 27′ S latitude; the farthest southern latitude at which the sun can appear directly overhead, which occurs on the day of the summer solstice.

the boundary layer between the troposphere and stratosphere, where an abrupt change in temperature lapse rate usually occurs; it is defined as the lowest level at which the lapse rate decreases to 2 degrees Celsius per kilometer or less, provided that the average lapse rate between this level and all higher levels within 2 kilometers does not exceed 2 degrees Celsius per kilometer; occasionally, a second tropopause may be found if the lapse rate above the first tropopause exceeds 3 degrees Celsius per kilometer.

lower part of the atmosphere, extending from the surface up to a height varying from about 7 to 9 kilometers (4.3 to 5.6 miles) at polar regions to approximately 17 kilometers (10.6 miles) in tropics; characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor content, and weather.

in meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.

electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays; roughly, radiation in the wavelength interval from 10 to 4000 angstroms.

air in which static instability prevails; this condition is determined by the vertical gradients of air temperature and humidity.

an observation made in the free atmosphere either directly or indirectly.

the general term applied to the atmosphere above the mesopause.

instrument used to measure wind direction; also called wind vane.

the pressure exerted by water vapor molecules in a given volume of air.

precipitation that evaporates before reaching the ground.

a measure of a fluid’s resistance to flow; can be thought of as a measure of fluid friction.

the greatest distance that prominent objects can be seen and identified by unaided, normal eyes.

the forward edge of an advancing warm air mass that is displacing cooler air in its path.

at a given level in the atmosphere, any low that is generally characterized by warmer air near its center than around its periphery; the opposite of a cold low.

the dark appearance of the underside of a cloud layer when it is over a surface of open water; it is darker than land sky, and much darker than ice blink or snow blink.

water substance in vapor (gaseous) form; one of the most important of all constituents of the atmosphere.

the state of the atmosphere, mainly with respect to its effects upon life and human activities; distinguished from climate by focusing on short-term (minutes to about 15 days) variations of the atmosphere state.

the dominant west-to-east motion of the atmosphere, centered over the middle latitudes (35 to 65 degrees latitude) of both hemispheres.

created by the World Meteorological Convention and recognized as a special agency of the United Nations in 1951; the WMO consists of more than 185 member countries; and facilitates international cooperation in all aspects of meteorology.

any scientific project (field experiment, inter-comparison, etc.) internationally performed under the aegis of the World Meteorological Organization.

the world-wide, coordinated system of meteorological facilities and services provided by World Meteorological Organization members for the purpose of ensuring that all members obtain the meteorological information required both for operational work and for research; the essential elements of the WWW are: the global observing system, the global data-processing system, and the global telecommunication system.

References:

American Meteorological Society. "Glossary of Meteorology." http://amsglossary.allenpress.com/glossary [Accessed August 16, 2006].

Beltz, Ellin. "Glossary of Glacier Terms." http://ebeltz.net/glacier/glacglos.html [Accessed August 16, 2006].

CO2 Science. "Global Change Dictionary." http://www.co2science.org/scripts/CO2ScienceB2C/education/dictionary/define.jsp [Accessed December 19, 2006].

Ferguson, Sue A., 1992. Glaciers of North America: A field guide. Golden, CO: Fulcrum Publishing.

Huschke, Ralph E., ed. 1959. Glossary of Meteorology. Boston: American Meteorological Society.

Khromov, S. P. and L. A. Mamontova, 1974. Glossary of Meteorology. Lenningrad: Gidrometeoizdat.

Van Everdingen, ed. 1994. Multilanguage Glossary of Permafrost and Related Ground-Ice Terms. Alberta: Arctic Institute of North America.

"Wikipedia." http://en.wikipedia.org/wiki/Main_Page [Accessed August 16, 2006].

1992. International Meteorological Vocabulary. Geneva, Switzerland: World Meteorological Organization.

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