Meteorology 1010
Vocabulary July 23, 2014
Note to students: The definitions below are more or less informal, based on class discussion. More
formal or official definitions are found in the textbook. This vocabulary, as described below, is more
likely to appear in exams than other definitions found in the class textbook. For convenience, some
definitions are provided for you. Others you should create yourself by comparing class discussion with
the textbook and other sources.
----------------------------------------------------------------------------------------------------------------------------------------Absolute humidity – the actual volume or weight of water vapor in the air. The water that would drip
out of a sponge that was squeezed perfectly well to remove all water. See Relative Humidity.
Adiabatic – the change in measured temperature when air is either compressed or decompressed.
Energy is either concentrated or de-concentrated by changing air pressure, with resulting change in
temperature that does not result in gain or loss of energy. Compare adiabatic to ‘lapse rate’.
Advection – mostly horizontal movement of air that may produce fog as moist air cools to condensation
so that invisible vapor becomes visible liquid water.
Albedo – the reflectivity of a surface. High albedo surfaces absorb little energy. Shiny and/or white
surfaces such as ice and snow tend to exhibit high albedo, with greater than 90% of energy being
reflected rather than absorbed. Liquid water tends to have an albedo of less than 10%.
Circumference – the distance all the way around a sphere or circle at its widest location. Compare to
diameter.
CFC – chloro-fluoro-carbons. Synthetic molecules that form the basis for thousands of useful products.
CFC molecules sometimes escape into the atmosphere where they destroy atmospheric ozone. CFC
production has been banned for many years, and many more years will be needed before the earth’s
“ozone layer” will recover because CFC molecules persist for decades, and each CFC molecule can
destroy thousands of ozone molecules.
Chinook wind – see also Katabatic wind
Climate zones (A-E and H) Climograph – provides two major categories of weather and climate information: annual temperature
range and rainfall, both by monthly totals, averages, and extremes.
Clouds – when vapor condenses back to liquid and becomes visible. Clouds are liquid water suspended
in the air. Major types include: stratus (layered) alto (mid-level), cirrus (higher altitude) and cumulus.
High-altitude clouds are ice particles. Some cumulus clouds are classed “vertical development” because
humidity and heat produce unstable conditions, wherein rising air condenses out moisture and heat,
provoking further rising air. Clouds of vertical development can produce violent weather as rapidly
rising air provokes high-speed surface winds and strong turbulence aloft, and likelihood of lightning, hail
and possibly tornadoes.
Cloud Seeding –
Condensation – compare to evaporation and latent heat. Condensation is the release of invisible water
vapor and latent heat back to liquid water and sensible heat (heat you can feel and measure as
temperature). So, evaporation is the process of ‘hiding’ heat when energy is used to evaporate liquid
into vapor, and condensation is the reverse process where vapor returns to liquid.
So, if evaporation is a cooling process, then condensation is a warming process. That is why cumulonimbus clouds may continue to rise: latent heat is released when clouds form.
Conduction – transfer of sensible heat (as temperature) between substances by direct contact or touch.
Transfer of energy does not include the objects themselves moving, but only that energy is transmitted
through the objects.
Convection – transfer of sensible heat or energy by flow or movement of fluids (air or liquid) across
space. Energy transfer is by movement of the substance that is holding the energy.
Convergence – where masses of air are moving toward each other. The ITCZ represents masses of air
moving toward the Equator from either side before lifting.
Cooling Degree Day (CDD) – the difference between a daily average temperature and a base
temperature of 65 degrees F. CDD represents the amount of building cooling needed in order to reach a
standard indoor daily temperature average of 65 degrees F. Each degree of daily average temperature
above 65 degrees F amounts to one cooling degree day (CDD). The cooling load needed for a building
across an entire year is found by adding up all of the daily average temperatures that are above 65
degrees F. See Degree Days and Heating Degree Days.
Degree Days – The difference between outside air temperature and the ideal or standard indoor
temperature of 65°F. Each daily average deviation from that standard adds to either the need for indoor
heating (furnace) or indoor cooling (air conditioning). The total deviation per day is called either
“Heating Degree Days” or “Cooling Degree Days” CDD. Severe climates exhibit high heating degree
days (HDD) and/or high cooling degree days (CDD).
Dew point –
Diameter – the distance across the center of a sphere or circle, usually at the widest place.
Divergence – a high-pressure air flow where parcels or air are moving away from each other. Compare
to convergence.
El Niño – A seasonal reversal or slow-down of the west-moving trade winds. The result is that warmer
water does not concentrate in the far western Pacific (for storms), but remains more in the eastern or
American side of the Pacific Ocean, resulting in more precipitation in areas that tend to be dry. See La
Niña.
(Students: Take time to study the “El Niño phenomenon that starts on page 210 in the textbook. More
discussion later.)
Equinox – when world-wide days and nights are the same length, 12 hours each. Vernal (Spring)
equinox is on or about March 20 and Autumnal (Fall) equinox is on or about September 20.
Fog – clouds of visible, liquid water suspended in air: orographic (upslope or mountain), advection,
radiation and steam fog.
Frontal or wedge – storms. Convective storms that are especially vigorous or violent because the nearby
presence of cooler, drier air induces more vigorous updrafts of warmer, more humid air. Violent
thunderstorms, including hail, lightning and damaging winds are associated with “frontal” weather
where cooler air “wedges” underneath more buoyant air.
Greenhouse gas –
Hadley Cell – World-wide air circulation based on rising air in the tropics moving north and south and
then subsiding. Similar north-south cells of rising and falling air exist in latitude bands further north and
south.
Hail – even on a hot day, a thunderstorm high in the troposphere typically includes ice crystals that
serve as condensation nuclei. Such nuclei help coax precipitation to occur by providing a surface on
which vapor can convert back to liquid. In other words, dirty surfaces that can hold or absorb water
help precipitation to occur. A hailstone begins with vapor condensing to liquid by attaching to a bit of
dirt or ice.
A hailstone represents ice that is blown back up into icy clouds to receive additional coatings of ice until
the ‘stone’ is heavy enough to fall to earth. Hailstones often contain many layers, after being blown
back into the sky many times by updrafts that occur in low-pressure, rising air events like
thunderstorms, tornadoes and hurricanes.
Heating Degree Day (HDD)– the difference in daily average outdoor temperature below a standard base
of 65 degrees F. If a daily average temperature reaches 64 degrees F, then the heating requirement to
maintain the base of 65 degrees would be one degree. The total annual HDD, or heating load required
to maintain 65 degrees F, is the total annual number of degrees by which average daily outdoor air
temperature is lower than 65 degrees F. See Cooling Degree Day (CDD).
Humidity - relative versus absolute.
Hurricane –
Hydrocarbons – organic compounds composed mainly of hydrogen and oxygen bonds. Most fuels,
foods, and living things are hydrocarbons. Hydrocarbons store vast amounts of solar energy in the form
of organic compounds that are living, or once were alive.
Intertropical Convergence Zone (ITCZ) – where converging tropical air masses meet, generally near the
equator, but tending to follow the sun’s center of illumination north and south with the seasons. The
ITCZ is associated with rainy, warm weather. The ITCZ is the equatorial edge of Hadley cells where air
masses are buoyant due to being warm and humid. The far edges of Hadley cells typically display the
return flow of air, descending drier, cooler air that warms by adiabatic compression as it nears the
surface of the earth. Desert or dry conditions prevail at roughly 30°N and 30°S of the ITCZ. Utah and
Arizona are not far from the dry end of Hadley cell activity, with the opposite end being rainy and
tropical wherever the ITCZ is located.
In June, the ITCZ is mostly in the northern hemisphere, bringing a “rainy season” to those areas, with the
reverse being true in December.
Inversion – normal daily air temperature rising in the morning as solar air is absorbed and becomes
thermal or heat. When that normal pattern is blocked, air becomes layered rather than mixed.
Isoline – a line connecting points of equal value. Isohyet is a line that connects locations that experience
the same amount of rainfall. Isotherms connect locations with the same temperature. Isobars connect
points that have the same air pressure. Isobar is a line of equal air pressure; isohyet is a line of equal
precipitation, etc.
Jet Streams –
Katabatic wind – see also “Chinook”
Kinetic energy – motion of substances due to absorption of sufficient energy. Molecules vibrate more
vigorously, pushing away from each other, with a tendency to create less density. Substances that are
less dense tend to rise above heavier or denser substances.
La Niña – see El Niño
Lapse rate – The general tendency for air temperature to decline with increasing altitude. On Earth,
most energy-absorbing substance are near the surface of the earth, so daily warming occurs near the
surface as well. For class discussion, humid air is presumed to be cooler by 3°F for each 1,000 feet of
higher altitude. Dry air will tend to be cooler by 5°F for each gain in altitude of 1,000 feet. Compare
lapse rate to Adiabatic.
Latent heat – thermal energy that you can’t normally detect or feel, or even measure as temperature.
Latent or ‘hidden’ heat is bound up in vapors, such as water vapor. If enough kinetic energy (heat) is
applied to cause molecules in liquid to lose cohesion bonds, gases form and that energy becomes latent,
or hidden in the vapor. That latent heat returns to being sensible or measurable by thermometer when
water vapor condenses back to liquid. With lower kinetic motion, vapor returns to liquid and latent heat
becomes sensible, or measurable by thermometer. We can see the liquid and we can feel the heat.
Macro, Meso and Micro-scale winds Meridional Flow – jet stream flow that undulates north and south as it moves from west to east.
Meridional flow tends to provide more opportunity for air masses of differing humidity and temperature
to mix and produce storms.
Microburst – a strong downdraft of air that often occurs at the conclusion of a thunderstorm. Cooling
air can descend rapidly, sometimes brought down even faster by the weight of falling rain. Evaporation
of falling rain (virga) can further accelerate downdrafts as evaporative cooling occurs. Damaging winds
can spread out at the surface.
Monsoon – seasonal reversal of winds. When monsoon winds occur over coastlines, then on-shore
breezes will bring rain to land areas. The reverse brings wind from land to the ocean, preventing
moisture from reaching land from the ocean. The Indian sub-continent is a classic example: as the ITCZ
moves northward in June, moisture from the ocean is drawn over land areas. During winter, the ITCZ is
far southward, resulting in dryness in India as high-pressure conditions prevail. The Utah/Arizona
monsoon is based on prevailing high pressure that rotates clockwise, drawing moisture from the Gulf of
Mexico that can result in brief thunderstorms and rain as daily rising ‘thermals’ lift that moisture to
condensation level (dew point).
Nimbus – associated with rain or precipitation.
Orographic – precipitation associated with mountains. Air is compelled to rise due to an obstacle. The
result is cooling by decompression. If dew point is reached, then precipitation may occur. See also
Convective and Frontal or wedge storms.
Ozone –
Ozone layer Pi – π –
Radiation – long wave vs short wave. Radiation is the only means by which solar energy reaches the
earth. Radiation is not heat or kinetic motion until it has been absorbed by substances. Most solar
energy is relatively short wave length, whereas most out-going radiation is in the longer wavelengths.
Radiation can also occur as a means of transferring energy between substances, in addition to incoming
and outgoing radiation. Solar radiation that is not absorbed and converted to kinetic energy (motion,
heat), is due to being reflected back into outer space.
Reflection – solar rays or other electromagnetic energy that “bounces” off a reflective surface at the
same angle it arrived. Reflected energy is not absorbed, does not convert to kinetic or thermal energy
and is generally not part of the earth’s greenhouse effect.
Relative humidity – compare to absolute humidity. Relative humidity is a ratio, or comparison between
how much actual (absolute) water is present in a parcel of air, and how much could be present in that
same parcel. Relative humidity is a ratio of actual compared to capacity. Absolute humidity is simply
the mass of vapor in the air, which relative humidity compares that vapor to the potential vapor that
might be present if saturation occurred.
Ridge – a line of higher-pressure air. Areas of higher air pressure tend to produce descending air, with
dry or mild conditions. Compare to Trough.
Sensible heat – thermal energy or heat that you can sense or feel, measured as temperature. Sensible
heat is kinetic energy, the energy of molecular movement or vibration. Compare to latent heat.
Solstice –
Stratosphere – the ‘layered’ part of the atmosphere, such as the ozone layer.
Super Cell – see also Meso-Scale convective complex
Theory – a well-tested hypothesis that is widely useful and consistently reliable. An extremely useful
theory may someday be regarded as a ‘paradigm’. Even the best paradigms seldom meet the test of full
proof. We live and die by theories and paradigms.
“Tornado Alley” –
Trade Winds
Tropic:
-
Of Cancer
Of Capricorn
Equatorial climate
Troposphere – the lower atmosphere where mixing and turbulence occur. Gases are mixed and much
water vapor and aerosols are present. Compare to the stratosphere where atmospheric gases are
layered and general stagnant.
Trough – a line of lower-pressure air. A trough of low-pressure indicates rising air. Lower or falling air
pressure tends to produce clouds and storminess. Compare to Ridge.
Ultraviolet - Uv
Urban “heat island” effect – large cities tend to include vast amounts of dark, hard surfaces rather than
natural cover, such as earth, water and green vegetation. The result is summer concentration of
excessive daily heat over large urban areas, with concentration of air pollution resulting from rising air
that draws pollution toward the center.
Vapor – a state of being evaporated, or vaporized. Adding enough energy to a substance to result in
going from solid or liquid state to a vapor state, the most energetic state of atoms and molecules.
Virga – rainfall that evaporates before it reaches the ground. Evaporative cooling by virga can lead to
rapid downdrafts of air, or even a damaging “micro burst”.
Zonal Flow – westerly jet stream flow that tends to be straight-line from west to east, rather than
undulating north or south along its path to the east. See Meridional flow.