The Comprehensive Flowmeters Resource

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absolute humidity: the ratio of the mass of water vapor to the volume of air in which it is present.(g/m^3)

acid rain: rain that has become acidic after contact with certain atmospheric gases (primarily sulfur dioxide, carbondioxide, and nitrogen oxides)

afforestation: process of establishing a forest.

air mass: a large body of air all of similar temperature and humidity.

air pressure: barometric pressure; weight of the atmosphere at a particular point of interest. Some Meteorologists use hPa – hectopascal for atmospheric air pressure. The hectopascal is equivalent to the mbar (millibar)

Anemometer: Wind Meter . A gage for recording the speed and direction of wind, see Anemometer

anomaly 1: unusual temperature or precipitation for a given region over a specified period. Also see anomaly 2 (Orbital Mechanics section).

anticyclone: high pressure area with counterclockwise winds in the Southern Hemisphere and clockwise winds in the Northern Hemisphere.

Atmospheric Infrared Sounder: advanced sounding instrument designed to retrieve vertical temperature and moisture profiles in the troposphere and stratosphere achieving a temperature retrieval accuracy of 1 degree C with a 1 km vertical resolution. It has been selected to be onboard the EOS-PM1 a remote sensing satellite to take orbit in the year 2000.

atmospheric pressure: force exerted on a surface area, created by the weight of air above it.


barometer: tool for measuring atmospheric pressure.

blizzard: severe weather in which there is low temperatures, strong winds and heavy amounts of snow falling or blowing.


climate: average meteorological conditions in a certain area over a certain period.

clouds: a suspended mass of water vapor in the atmosphere. Clouds can be categorized into two general groups: cumulus clouds (tall, cotton ball) and stratus clouds (layered); these can be divided even further to 4 sub-groups describing altitude: 20,000 ft and above are the cirrus or cirro clouds (cirrocumulus, cirrostratus), composed of mostly ice crystals; from 6,500 to 20,000ft are the alto clouds (altostratus, altocumulus); Low clouds develop up to 6,500ft (stratocumulus, nimbostratus) ,can contact the ground and when they do so, are called fog; existing at many heights, extending far from their bases are the Vertical clouds, such as the cumulus (Cumulonimbus clouds, can have their base near the ground yet reach heights of 75,000ft.)

convection:the process in which cool air delves down, while warmer air rises to the top. The warm air usually cools in the cooler, higher sections of the atmosphere and again begins to return back down. Local breezes, wind and even thunderstorms are a result of convection.

cryosphere: a component of the Earth's system that is frozen water; the forms include: snow, permafrost, floating ice, and glaciers. The cryosphere component is directly related to ocean sea-level, therefore is indirectly related to changes in the atmosphere and biosphere.


dew: condensed moisture (water vapor), appearing as small drops on a cool surface; usually occurs after or during a very warm day.

dew point: the certain temperature at which dew begins to form and water vapor chages to liquid form.

doldrums: area near equator that experiences low pressures and light shifting winds.

Doppler radar: weather radar system that employs the apparent shift in frequency of radio waves to perceive air motion and consequently predict tornadoes and precipitation sooner than previous radars, as well as measure the speed and direction of rain and ice.


eclipse: solar=partial to total darkening of sun due to moon coming between Earth and sun, lunar=partial to total darkening due to Earth casting its shadow on a full moon.

El Ni–o: warming of surface waters in the eastern equatorial Pacific that brings about strange anomolous weather patterns to the coastal regions. Certain economical and ecological disasters can be linked to this phenomena.

evaporation: the process by which an element changes phase from a liquid to a gas; the opposite of condensation.

exosphere: the outer-most layer of the Earth's atmosphere (500 to 1000km above surface); the only part of the atmosphere where an appreciable amount of atmospheric gases escape the Earth.


Fahrenheit: temperature scale in which water boils at 212 ?F and freezes at 32 ?F under standard atmospheric pressure; named after the designer of the scale, the German scientist Gabriel Fahrenheit.

front: boundary that defines two separate air masses; where two different air masses collide, sometimes resulting in severe weather changes.

frost: water that has condensed at a temperature below the freezing point, thus has turned to


glacier: a large mass of ice (at least .1km^2) set in motion by the Earth's gravity, which is a result of accumulated snowfall with little snow melt.

green house effect:process in which green house gases, like carbon dioxide in the Earth's atmosphere, cause thermal radiation emitted by the Earth's surface to be reflected back down, therefore causing the climate to warm. This natural process is enhanced by man's added pollutants and can reach proportions at which a number of animal and plant species can be threatened with extinction, not to mention cause drastic changes in the Earth's natural weather patterns.

gulf stream: ocean current flowing along the coast of the Eastern United States to Ireland, Great Britain, and the Scandivanian countries, making the latter three warmer than they otherwise would be.


hail: precipitation composed of chunks of ice that form atop cumulonimbus clouds and fall as soon as they become too heavy for the cloud updrafts to hold.

haze: a concentration near the surface of the Earth, of fine particles (wet or dry dust, salt, etc.,) .

Haze Meter: An instrument that measures visibility or light transmission. Also known as a Transmissometer

humidity: is the quantity of water vapor in the air. Relative humidity is the ration between the actual quantity of watervapor and the amount of watervapor that the air can hold at a given temperature.

hurricanes: tropical storms with winds exceeding 74 mph originating over the North Atlantic and North Pacific oceans near high humidity and light winds. One well known characteristic of a hurricane is it's eye, which is generally about 5 to 25 miles in diameter and in which are present calm conditions, with clear skies and light winds. Hurricanes can move rather quickly losing intensity as soon as land is encountered, but not without having created very high tides and possibly massive destruction.

hydrosphere: all the components of water present on the Earth, including bodies of water, water vapor, ice, etc.

Hygrometer – Hygrometers are instruments designed to measure relative humidity (RH)


jet stream: high speed air flow in the atmosphere forming air rivers several hundred miles across that generally move west to east and mark the boundary that separates two global air masses with significant differences in temperature.


low (low pressure system): area with lower atmospheric pressure than its surrounding areas; this makes air from surrounding areas to flow into the low, the end result of which is probably cloudiness and precipitation.


mesopause:the uppermost boundary of the mesosphere with the lowest temperature in the atmosphere.

mesosphere: atmospheric layer above the stratosphere (50-85 km altitude).

Meter - See

Metric Conversion Online See

monsoon: season of wind originating from the Indian Ocean and southern Asia, these winds are usually accompanied by heavy rains.


ozone: gaseous form of oxygen that constitutes less than one part per million of the gases in the atmosphere, yet absorbs most of the ultraviolet radiation which has been proven to be harmful to humans as well as other life forms on Earth.


precipitation: rain, drizzle and other forms of moisture falling from clouds. Raindrops form around particles of dust or salt, join other water droplets or ice droplets and fall when sufficently heavy in the from of liquid or ice, depending on the quantity of collected ice crystals.


sea breeze: wind blowing from the ocean to land at the coast, due to the cool air replacing the warmer air that has moved up on the coastline.

sea level: the imaginary line from which sea depth and land elevation are measured.

stratosphere: region between the troposphere and mesosphere, extending from 10 to 30 miles above the Earth's surface.


temperature: measure of the quantity of thermal energy in a substance. High temperature indicates more heat energy than low temperature.


Weather Station: Weather Stations gather , record and send out meteorological data . Some may also analyze meteorological data and patterns. Typical weather stations use several types of measuring instruments which might included thermometers, barometers, hygrometers, anemometers, wind vanes, rain gauges . Weather stations supporting airports usually have instruments for measuring rain drop size distribution or Disdrometers , transmissmeters for measuring cloud visibility and ceiling projectors for cloud ceiling