Chapter 1: Weather Variables Key Terms

Weather: A Concise Introduction Second Edition (pgs. 1 - 18) GENED 1158 at Harvard College

temperature

a measure of the heat content of air, therefore related to the kinetic energy of air molecules

wind

girl please

precipitation

liquid or solid water particles falling faster than the updrafts in which they are embedded

pressure

a quantity characterizing the frequency and intensity of average molecular collision, defined as the net force per unit area

weather variables

temperature, pressure, wind, and precipitation

heat

amount of energy that moves between bodies due to temperature contrasts. On average, heat transfers energy from warm to cold objects

kinetic energy

energy associated with motion that forms the basis for defining temperature as a measure of the average kinetic energy of a large number of air molecules

conduction

transfer of heat by contact, as kinetic energy is transferred between particles of matter through collision

thermometer

a measure of the heat content of air, therefore related to the kinetic energy of air molecules

radiosonde

instrument that measures variables of the atmosphere as it ascends with a helium-filled balloon, and radios the measurements back to a receiving station

tropopause

boundary between the troposphere and the stratosphere

troposphere

first layer of the atmosphere extending from the surface to the altitude where temperature stops decreasing with height (the tropopause). Essentially all weather occurs in this layer

ideal gas law

equation of state describing the relationship between the pressure, volume, mass (or density), and temperature of an “ideal” gas (where molecular collisions are perfectly elastic), typically expressed as pV = nR T, or p = ρRT, where p is the pressure, V is the volume, n is the number of molecules in volume V, T is the temperature, ρ is the density, R is a universal constant that applies to any gas, and R is a gas constant specific to the atmosphere

F = p * A

resulting force = pressure applied * surface area

atmospheric pressure

pressure exerted on a horizontal surface by a column of air extending above that surface, due to the effect of gravity on that air column. Atmospheric pressure is typically expressed in hectopascal, millibars, millimeters of mercury, inches of mercury, kilograms per square centimeter, or pounds per square inch

barometer

instrument used to measure atmospheric pressure

mercury barometer

instrument used to measure atmospheric pressure, made of an inverted glass tube containing mercury up to the level where the weight of the column of mercury is balanced by the atmospheric pressure applied to the surface of the mercury in the reservoir

wind measurements

speed & direction

anemometer

instrument used to measure wind speed and direction, commonly used in weather stations

Beaufort wind scale

a wind scale used in marine meteorology, originally based on observations of the effects of the wind on the sails of a ship, and later extended to include observations of the sea state and land-based effects

wind gusts

a local, sudden, and brief increase in wind speed due to the transport of higher momentum air from a different altitude by turbulent eddies

sustained wind

speed of the wind averaged over a standard time period, such as one minute

instantaneous wind

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rain gauge

instrument that measures the amount and, for certain designs, the rate of liquid precipitation (ex

weather station

assemblage of various weather instruments at conventional heights or, more generally, the location where these meteorological observations are made

air parcel

imaginary volume of air with uniform characteristics that does not exchange heat or mass with its surroundings, and always has the same pressure as the surrounding air; used especially in comparisons with the surrounding environment when determining the stability of the atmosphere

Law of Conservation of Energy

a law of nature stating that energy cannot be created or destroyed in a system

Law of Conservation of Momentum

a law of nature stating that the total momentum of a system, where momentum is defined as the product of the mass (or density) and velocity of the bodies constituting the system, remains unchanged unless acted upon by a force, as implied by Newton’s laws of motion

turbulent eddies

swirls of air that mix air up and down on a variety of scales, causing the formation of wind gusts

trace

precipitation of less than 0.2 mm (0.01 inches)