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Active ProminenceIn solar-terrestrial terms, a prominence displaying material motion and changes
in appearance over a few minutes of time.Active Prominence Region (APR)In solar-terrestrial terms, a portion of the solar limb displaying active prominences.Astronomical DawnThe time at which the sun is 18 degrees below the horizon in the morning. Astronomical dawn is that point in time at which the sun starts lightening the sky. Prior to this time during the morning, the sky is completely dark.Astronomical DuskThis is the time at which the sun is 18 degrees below the horizon in the evening. At this time the sun no longer illuminates the sky.Astronomical Unit(abbrev. AU)- The mean earth-sun distance, equal to 1.496x1013 cm, or 214.94 solar radii.Chemistry ModelA computer model used in air pollution investigations that simulates chemical and photochemical reactions of the pollutants during their transport and diffusion.Cold Air Damming (CAD)The phenomenon in which a low-level cold air mass is trapped topographically. Often, this cold air is entrenched on the east side of mountainous terrain. Cold Air Damming often implies that the trapped cold air mass is influencing the dynamics of the overlying air mass, e.g. in an overrunning scenario.
Effects on the weather may include cold temperatures, freezing precipitation, and extensive cloud coverCosmic RayAn extremely energetic (relativistic) charged particle.Dry MicroburstA microburst with little or no precipitation reaching the ground; most common in semi-arid regions. They may or may not produce lightning. Dry microbursts may develop in an otherwise fair-weather pattern; visible signs may include a cumulus cloud or small Cb with a high base and high-level virga, or perhaps only an orphan anvil from a dying rain shower. At the ground, the only visible sign might be a dust plume or a ring of blowing dust beneath a local area of virga.Dynamic IceIn hydrologic terms, pressure due to a moving ice cover or drifting ice. Pressure occuring at movement of first contact termed Ice Impact PressureDynamic LiftingThe forced uplifting of air from various atmospheric processes, such as weather fronts, and
cyclones.Dynamic Wave Routing Model (DWOPER)A computerized hydraulic routing program whose algorithms incorporate the complete one-dimensional equations of unsteady flowDynamicsGenerally, any forces that produce motion or effect change. In operational meteorology, dynamics usually refer specifically to those forces that produce vertical motion in the atmosphere.EmissivityThe ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area.Eruptive Prominence on Limb (EPL)In solar-terrestrial terms, a solar prominence that becomes activa-
ted and is seen to ascend from the sun.Evaporation-mixing FogFog that forms when the evaporation of water raises the dew point of the adjacent air.First Law of ThermodynamicsThe law of physics that states that the heat absorbed by a system either raises the internal energy of the system or does work on the environment.fMinIn solar-terrestrial terms, the lowest radiowave frequency that can be reflected from the
ionosphere.FumigationA pattern of plume dispersion produced when a convective boundary layer grows upward into a plume trapped in a stable layer. The elevated plume is suddenly brought downward to the ground, producing high surface concentrations.Global WarmingAn overall increase in world temperatures which may be caused by additional heat being trapped by greenhouse gases. Hail ContaminationA limitation in NEXRAD rainfall estimates whereby abnormally high reflectivities associated with hail are converted to rainfall rates and rainfall accumulations. These high reflectivity values are mistaken by the radar for extremely heavy rain, thus "contaminating" (inflating) its estimation of how much rain has fallen over the affected area.HumidityGenerally, a measure of the water vapor content of the air. Popularly, it is used synonymously with relative humidity.Humidity RecoveryThe change in relative humidity over a given period of time; generally between late evening and sunrise. The moisture change in the fine fuels during this period is directly related to the amount of humidity recovery.HypothermiaA rapid, progressive mental and physical collapse that accompanies the lowering of body temperature.Intermittent StreamIn hydrological terms, a stream that flows periodicallyLaminarSmooth, non-turbulent. Often used to describe cloud formations which appear to be shaped by a smooth flow of air traveling in parallel layers or sheets.Laminar FlowStreamline flow in which successive flow particles follow similar path lines and head loss varies with velocity to the first power.Loop Prominence System(abbrev. LPS) In solar-terrestrial terms, a system of loop prominences associated with
major flares.MI1) Mile
2) MichiganMICMeteorologist In ChargeMicrobarographA instrument designed to continuously record a barometer's reading of very small changes in atmospheric pressure. MicroburstA convective downdraft with an affected outflow area of less than 2½ miles wide and peak winds lasting less than 5 minutes. Microbursts may induce dangerous horizontal/vertical wind shears, which can adversely affect aircraft performance and cause property damage.MicroclimateThe climate of a small area such as a cave, house, city or valley that may be different from that in the general region.MicronUnit of length equal to one thousandth (1/1000) of a millimeter; one millionth (1/1000000) of a meter (1x10-6 m).MicroscalePertaining to meteorological phenomena, such as wind circulations or cloud patterns, that are less than 2 km in horizontal extent.MicrowaveA type of electromagnetic radiation with wavelengths between those of infrared radiation and radio waves.Microwave BurstIn solar-terrestrial terms, a radiowave signal associated with optical and/or X-ray
flaresMIDMiddleMid-Flame WindWind measured at the midpoint of the flames, considered to be most representative of the speed of the wind that is affecting fire behavior.Mid-Latitude AreasAreas between 30o and 60o north and south of the Equator.Mid-level CoolingLocal cooling of the air in middle levels of the atmosphere (roughly 8 to 25 thousand feet), which can lead to destabilization of the entire atmosphere if all other factors are equal.Middle Clouds(or Mid-Level Clouds) - A term used to signify clouds with bases between 6,500 and 23,000 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. Middle Latitudes1) The latitude belt roughly between 35 and 65 degrees North and South. Also referred to as the temperate region.
or
2) With specific reference to zones of geomagnetic activity, "middle latitudes" refers to 20º to 50º geomagneticMie ScatteringAny scattering produced by spherical particles whose diameters are greater than
1/10 the wavelength of the scattered radiation. This type of scattering causes the clouds to
appear white in the sky. Often, hail exhibits in this type of scattering.MillibarA unit of atmospheric pressure equal to 1/1000 bar, or 1000 dynes per square centimeter.MINMinimum (or) MinuteMinimum Discernible SignalIn a receiver, it is the smallest input signal that will a produce a detectable signal at the output. In radar terms, it is the minimal amount of back scattered energy that is required to produce a target on the radar screen. In other words, MDS is a measure of the radar's sensitivity. Minimum TemperatureThis is the lowest temperature recorded during a specified period of time. The time period can be 6, 12 or 24 hours. The most common reference is to the daily minimum temperature, or "low."Minor FloodingA general term indicating minimal or no property damage but possibly some public inconvenience.Minor Tidal OverflowMinor flooding caused by high tides that results in little if any damage. MINTminimum temperatureMISCMiscellaneousMISGMissingMisoscaleThe scale of meteorological phenomena that ranges in size from 40 meters to about 4 kilometers. It includes rotation within a thunderstorm.MistA visible aggregate of minute water particles suspended in the atmosphere that reduces visibility to less than 7 statute miles, but greater than or equal to 5/8 statute miles. It does not reduce visibility as much as fog and is often confused with drizzle.Mixed LayerAn atmospheric layer, usually the layer immediately above the ground, in which pollutants are well mixed by convective or shear-produced turbulence.Mixed PrecipitationAny of the following combinations of freezing and frozen precipitation: snow and sleet, snow and freezing rain, or sleet alone. Rain may also be present.Mixing DepthVertical distance between the ground and the altitude to which pollutants are mixed by turbulence caused by convective currents or vertical shear in the horizontal wind.Mixing HeightsThe height to which a parcel of air, or a column of smoke, will rise, mix or disperse. A column of smoke will remain trapped below this height.Mixing RatioThe ratio of the weight of water vapor in a specified volume (such as an air parcel) to the weight of dry air in that same volume.Nautical MileA unit of distance used in marine navigation and marine forecasts. It is equal to 1.15 statue miles or 1852 meters. It is also the length of 1 minute of latitude.Photochemical SmogAir pollution containing ozone and other reactive chemical compounds formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight.Plume-dominated FireA fire whose behavior is governed primarily by the local wind circulation produced in response to the strong convection above the fire rather than by the general wind.Predominant WindThe wind that prevails and generates the local component of the significant sea conditions across the forecast area. This is the wind included in all marine forecast products and is defined as a 10-meter wind, except over the nearshore marine zones where it is defined to be the wind at a 3-meter height.Preliminary ReportNow known as the "Tropical Cyclone Report". A report summarizing the life history
and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of
the cyclone life cycle and pertinent meteorological data, including the post-analysis
best track (six-hourly positions and intensities) and other meteorological statistics. It
also contains a description of damage and casualties the system produced, as well
as information on forecasts and warnings associated with the cyclone. NHC writes
a report on every tropical cyclone in its area of responsibility.Prominence A term identifying cloud-like features in the solar atmosphere.
The features appear as bright structures in the CORONA above the
solar LIMB and as dark FILAMENTs when seen projected against the
solar DISKQuiescent Prominence (Filament) Long, sheet-like prominences nearly vertical
to the solar surfaceRadio EmissionEmissions of the sun in radio wavelengths from centimeters
to dekameters, under both quiet and disturbed conditions.
Type I. A noise storm composed of many short, narrow-band bursts
in the metric range (300 - 50 MHz).
Type II. Narrow-band emission that begins in the meter range
(300 MHz) and sweeps slowly (tens of minutes) toward deka-
meter wavelengths (10 MHz). Type II emissions occur in
loose association with major FLAREs and are indicative of
a shock wave moving through the solar atmosphere.
Type III. Narrow-band bursts that sweep rapidly (seconds) from
decimeter to dekameter wavelengths (500 - 0.5 MHz). They
often occur in groups and are an occasional feature of complex
solar ACTIVE REGIONs.
Type IV. A smooth continuum of broad-band bursts primarily in the
meter range (300 - 30 MHz). These bursts are associated with
some major flare events beginning 10 to 20 minutes after the
flare maximum, and can last for hoursRadiofacsimileAlso known as HF FAX, radiofax or weatherfax, is a means of broadcasting graphic weather maps and other graphic images via HF radio. HF radiofax is also known as WEFAX, although this term is generally used to refer to the reception of weather charts and imagery via satellite. Maps are received using a dedicated radiofax receiver or a single sideband shortwave receiver connected to an external facsimile recorder or PC equipped with a radiofax interface and application software. Relative HumidityA dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point.Snow Data Assimilation System (SNODAS)A physically based, mass conserving snow water equivalent (SWE) model.Solar MinimumIn solar-terrestrial terms, the month(s) during the solar cycle when the 12-month mean of monthly average sunspot numbers reaches a minimum.Specific HumidityIn a system of moist air, the ratio of the mass of water vapor to the total mass of the system.Terminal Aerodrome ForecastThis NWS aviation product is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each country is allowed to make modifications or exceptions to the code for use in each particular country. TAFs use the same weather code found in METAR weather reports.ThermistorA resistor whose resistance changes with temperature. Because of the known dependence of resistance on temperature, the resistor can be used as a temperature sensor.Thermodynamic ChartA chart containing contours of pressure, temperature, moisture, and potential temperature, all drawn relative to each other such that basic thermodynamic laws are satisfied. Such a chart typically is used to plot atmospheric soundings, and to estimate potential changes in temperature, moisture, etc. if air were displaced vertically from a given level. A thermodynamic chart thus is a useful tool in diagnosing atmospheric instability.Thermodynamic DiagramUsed interchangably with Thermodynamic Chart; a chart containing contours of pressure, temperature, moisture, and potential temperature, all drawn relative to each other such that basic thermodynamic laws are satisfied. Such a chart typically is used to plot atmospheric soundings, and to estimate potential changes in temperature, moisture, etc. if air were displaced vertically from a given level. A thermodynamic chart thus is a useful tool in diagnosing atmospheric instability.ThermodynamicsIn general, the relationships between heat and other properties (such as temperature, pressure, density, etc.) In forecast discussions, thermodynamics usually refers to the distribution of temperature and moisture (both vertical and horizontal) as related to the diagnosis of atmospheric instability.Tornado FamilyA series of tornadoes produced by a single supercell, resulting in damage path segments
along the same general line.TransmitterThe radar equipment used for generating and amplifying a radio frequency (RF) carrier signal, modulating the carrier signal with intelligence, and feeding the modulated carrier to an antenna for radiation into space as electromagnetic waves. Weather radar transmitters are usually magnetrons or klystrons.TsunamiA series of long-period waves (on the order of tens of minutes) that are usually generated by an impulsive disturbance that displaces massive amounts of water, such as an earthquake occurring on or near the sea floor. Underwater volcanic eruptions and landslides can also cause tsunami. The resultant waves much the same as waves propagating in a calm pond after a rock is tossed. While traveling in the deep oceans, tsunami have extremely long wavelengths, often exceeding 50 nm, with small amplitudes (a few tens of centimeters) and negligible wave steepness, which in the open ocean would cause nothing more than a gentle rise and fall for most vessels, and possibly go unnoticed. Tsunami travel at very high speeds, sometimes in excess of 400 knots. Across the open oceans, these high-speed waves lose very little energy. As tsunami reach the shallow waters near the coast, they begin to slow down while gradually growing steeper, due to the decreasing water depth. The building walls of destruction can become extremely large in height, reaching tens of meters 30 feet or more as they reach the shoreline. The effects can be further amplified where a bay, harbor, or lagoon funnels the waves as they move inland. Large tsunami have been known to rise to over 100 feet! The amount of water and energy contained in tsunami can have devastating effects on coastal areas. Tsunami AdvisoryFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto Rico, Virgin Is.), Indian Ocean): The third highest level of tsunami alert. Advisories are issued to coastal populations within areas not currently in either warning or watch status when a tsunami warning has been issued for another region of the same ocean. An Advisory indicates that an area is either outside the current warning and watch regions or that the tsunami poses no danger to that area. The Center will continue to monitor the event, issuing updates at least hourly. As conditions warrant, the Advisory will either be continued, upgraded to a watch or warning, or ended.
For products of the West Coast/Alaska Tsunami Warning Center (WC/ATWC - Alaska, British Columbia and Western States, Canada, Eastern and Gulf States, Puerto Rico, U.S Virgin Islands): A tsunami advisory is issued due to the threat of a potential tsunami which may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories are normally updated to continue the advisory, expand/contract affected areas, upgrade to a warning, or cancel the advisory.Tsunami Information StatementA tsunami information statement is issued to inform emergency management officials and the public that an earthquake has occurred, or that a tsunami warning, watch or advisory has been issued for another section of the ocean. In most cases, information statements are issued to indicate there is no threat of a destructive tsunami and to prevent unnecessary evacuations as the earthquake may have been felt in coastal areas. An information statement may, in appropriate situations, caution about the possibility of destructive local tsunamis. Information statements may be re-issued with additional information, though normally these messages are not updated. However, a watch, advisory or warning may be issued for the area, if necessary, after analysis and/or updated information becomes available. Tsunami WarningFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto Rico, Virgin Is.), Indian Ocean): The highest level of tsunami alert. Warnings are issued due to the imminent threat of a tsunami from a large undersea earthquake or following confirmation that a potentially destructive tsunami is underway. They may initially be based only on seismic information as a means of providing the earliest possible alert. Warnings advise that appropriate actions be taken in response to the tsunami threat. Such actions could include the evacuation of low-lying coastal areas and the movement of boats and ships out of harbors to deep water. Warnings are updated at least hourly or as conditions warrant to continue, expand, restrict, or end the warning.
For products of the West Coast/Alaska Tsunami Warning Center (WC/ATWC - Alaska, British Columbia and Western States, Canada, Eastern and Gulf States, Puerto Rico, U.S Virgin Islands): A tsunami warning is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave. Warnings also alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled. To provide the earliest possible alert, initial warnings are normally based only on seismic information.Tsunami WatchFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto Rico, Virgin Is.), Indian Ocean): The second highest level of tsunami alert. Watches are issued based on seismic information without confirmation that a destructive tsunami is underway. It is issued as a means of providing an advance alert to areas that could be impacted by destructive tsunami waves. Watches are updated at least hourly to continue them, expand their coverage, upgrade them to a Warning, or end the alert. A Watch for a particular area may be included in the text of the message that disseminates a Warning for another area.
For products of the West Coast/Alaska Tsunami Warning Center (WC/ATWC - Alaska, British Columbia and Western States, Canada, Eastern and Gulf States, Puerto Rico, U.S Virgin Islands): A tsunami watch is issued to alert emergency management officials and the public of an event which may later impact the watch area. The watch area may be upgraded to a warning or advisory - or canceled - based on updated information and analysis. Therefore, emergency management officials and the public should prepare to take action. Watches are normally issued based on seismic information without confirmation that a destructive tsunami is underway. Wet MicroburstA microburst accompanied by heavy precipitation at the surface. A rain foot may be a visible sign of a wet microburst.
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