Glossary of Terms

ANEMOMETER – An anemometer is an instrument which measures wind speed.

BAROMETER – A barometer is an instrument used to measure atmospheric pressure. Two examples are the aneroid barometer and the mercurial barometer.

BAROMETRIC PRESSURE – Barometric pressure is the pressure exerted by the atmosphere at a given point. Using a barometer, it’s measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg). Also known as atmospheric pressure.

HUMIDITY – Humidity is the amount of water vapor in the air. It is often confused with relative humidity or dew point. Types of humidity include absolute humidity, relative humidity, and specific humidity.

HYGROMETER – A hygrometer is an instrument that measures the water vapor content of the atmosphere.

INCHES OF MERCURY (Hg) – The name comes from the use of mercurial barometers which equate the height of a column of mercury with air pressure. One inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. (See barometric pressure.) First devised in 1644 by Evangelista Torricelli (1608-1647), an Italian physicist and mathematician, to explain the fundamental principles of hydromechanics.

KNOT – A knot is a nautical unit of speed equal to the velocity at which one nautical mile is traveled in one hour. Used primarily by marine interests and in weather observations. A knot is equivalent to 1.151 miles per hour or 1.852 kilometers per hour.

MERCURIAL BAROMETER – A mercurial barometer is an instrument used for measuring the change in atmospheric pressure. It uses a long glass tube, open at one end and closed at the other. After first filling the open end with mercury, it is then temporarily sealed and placed into a cistern of mercury. A nearly perfect vacuum is established at the closed end after the mercury descends. The height of the column of mercury in the tube is a measurement of air pressure. As atmospheric pressure increases, the mercury is forced from the cistern up the tube; when the atmospheric pressure decreases, the mercury flows back into the cistern. Measurement is taken in inches of mercury. Although mercurial barometers are very accurate, practicality has led observers to use aneroid barometers. First used by Evangelista Torricelli (1608-1647), an Italian physicist and mathematician, to explain the fundamental principles of hydromechanics.

METEOROLOGY/METEOROLOGIST – Meteorology is the science and study of the atmosphere and atmospheric phenomena. Various areas of meteorology include agricultural, applied, astrometerology, aviation, dynamic, hydrometeorology, operational, and synoptic, to name a few. A scientist who studies the atmosphere and atmospheric phenomena is known as a Meteorologist.

MOISTURE – Moisture refers to the water vapor content in the atmosphere, or the total water, liquid, solid or vapor, in a given volume of air.

NOR’EASTER – A Nor’Easter is a cyclonic storm occurring off the east coast of North America. These winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A Nor’easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.

PRECIPITATION – Precipitation is any and all forms of water, liquid or solid, that falls from clouds and reaches the ground. This includes drizzle, freezing drizzle, freezing rain, hail, ice crystals, ice pellets, rain, snow, snow pellets, and snow grains. The amount of fall is usually expressed in inches of liquid water depth of the substance that has fallen at a given point over a specified time period.

RAIN – Rain is precipitation in the form of liquid water droplets greater than 0.5 mm. If widely scattered, the drop size may be smaller. It is reported as “R” in an observation and on the METAR. The intensity of rain is based on rate of fall. “Very light” (R–) means that the scattered drops do not completely wet a surface. “Light” (R-) means it is greater than a trace and up to 0.10 inch per hour. “Moderate” (R) means the rate of fall is between 0.11 to 0.30 inch per hour. “Heavy” (R+) means over 0.30 inch per hour.

RAIN GAUGE – A rain gauge is a device for collecting and measuring the amount of rain which falls.

RELATIVE HUMIDITY – A type of humidity that considers the ratio of the actual vapor pressure of the air to the saturation vapor pressure.

TEMPERATURE – Temperature is the measure of molecular motion or the degree of heat of a substance. It is measured on an arbitrary scale from absolute zero, where the molecules theoretically stop moving. It is also the degree of hotness or coldness. In surface observations, it refers primarily to the free air or ambient temperature close to the surface of the earth.

THERMOMETER – A thermometer is an instrument used for measuring temperature. The different scales used in meteorology are Celsius, Fahrenheit, and Kelvin or Absolute.

TIDE – The tide is the periodic rising and falling of the earth’s oceans and atmosphere. It is the result of the tide-producing forces of the moon and the sun acting on the rotating earth. This propagates a wave through the atmosphere and along the surface of the earth’s waters.

TIDE CLOCK – A tide clock is a specially designed clock that keeps track of the Moon’s apparent motion around the Earth. Along many coastlines, the Moon contributes the major part (67%) of the combined lunar and solar tides. The exact interval between tides is influenced by the position of the Moon and Sun relative to the Earth, as well as the specific location on Earth where the tide is being measured.

WEATHER STATION – A weather station is a device that collects data related to the weather and environment using many different sensors. Weather stations are also called weather centers, personal weather stations, professional weather stations, home weather stations, weather forecasters and forecasters. Weather stations sensors may include a thermometer to take temperature readings, a barometer to measure the pressure in the atmosphere,  wind instruments, as well as other sensors to measure rain, wind, humidity and more. Weather stations range from simple analog technology to digital technology. Some even connect to your computer or the internet, so the data collected can be analyzed using weather station software.

WIND SPEEDWind speed is the rate of the motion of the air on a unit of time. It can be measured in a number of ways including, mph (Mile per Hour), m/s (Meters per Second), ft/m (Feet per Minute), km/h (Kilometers per Hour), kt (Knots) and B (Beaufort Force).

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