Weather

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Diurnal Range Noun

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[dy-ur-nl reynj]

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Diurnal Range

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The difference between the maximum and minimum temperature recorded within a single 24-hour period at a specific location.

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Example: This map shows diurnal temperature variation across the U.S. Dry inland areas (red) have a large range, while areas near water (purple) have a small range.

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Six's Thermometer Noun

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[siks-iz ther-mom-i-ter]

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Six's Thermometer

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A specific type of thermometer used to measure the maximum and minimum temperatures reached over a period of time.

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Example: This diagram shows a Six's thermometer, which uses mercury and alcohol to push two steel indexes, recording the highest and lowest temperatures over a period.

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Anemometer Noun

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[an-uh-mom-i-ter]

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Anemometer

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A meteorological instrument specifically designed for measuring the speed or velocity of the wind at a particular location.

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Example: This diagram shows a simple cup anemometer model; wind catches the cups, causing the central axle to spin, which allows for measuring wind speed.

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Wind Vane Noun

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[wind veyn]

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Wind Vane

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An instrument that pivots to show the direction from which the wind is blowing, often shaped like an arrow.

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Example: A wind vane has a pointer, like the red arrow, that freely rotates on a pivot to align with the wind's direction, indicating which way the wind is coming from.

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Barometer Noun

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[buh-rom-i-ter]

Back

Barometer

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A scientific instrument used in meteorology to measure the weight of the atmosphere, also known as atmospheric pressure.

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Example: This diagram shows how a mercury barometer works. Atmospheric pressure pushes down on the mercury in the dish, supporting a column of mercury in the tube.

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Millibars (mb) Noun

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[mil-i-barz]

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Millibars (mb)

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A standard unit of measurement for atmospheric pressure, commonly used on weather maps to depict pressure systems.

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Example: This weather map uses lines called isobars to connect areas with the same air pressure, which is measured in units called millibars (mb).

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Relative Humidity Noun

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[rel-uh-tiv hyoo-mid-i-tee]

Back

Relative Humidity

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The ratio of water vapor in the air to the maximum amount the air can hold at that temperature.

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Example: This image shows that relative humidity is like a glass being filled with water; it's the percentage of water vapor the air currently holds compared to the maximum it could hold.

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Hygrometer Noun

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[hy-grom-i-ter]

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Hygrometer

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An instrument, often a wet and dry bulb thermometer, used for measuring the amount of water vapor (humidity).

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Example: This image shows a hygrometer, a weather instrument used to measure humidity, which is the amount of water vapor in the air.

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Oktas Noun

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[ok-tuhz]

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Oktas

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A unit of measurement used in meteorology to describe the amount of cloud cover, measured in eighths of the sky.

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Example: This chart shows the Okta scale, where each number from 0 (clear sky) to 8 (overcast) represents how many eighths of the sky are covered by clouds.

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Campbell-Stokes recorder Noun

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[kam-buhl stohks ri-kawr-der]

Back

Campbell-Stokes recorder

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An instrument that records the duration of bright sunshine by focusing sunlight onto a card, scorching a line.

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Example: These are recording cards from a Campbell-Stokes recorder. Focused sunlight burns a track on the card, showing the hours of bright sunshine in a day.