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.Cosmic 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.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.MICMeteorologist 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
flaresPhotochemical SmogAir pollution containing ozone and other reactive chemical compounds formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight.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.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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