What are some of the measurement devices we use to describe the weather?

1 Answer
Sep 18, 2017


Barometer, Thermometer, Anemometer, Hygrometer and Rain gauge. To name a few.


A Barometer measures atmospheric pressure. An aneroid barometer is one of the most common types of Barometer along with a Torricellian Barometer. An Aneroid Barometer uses a sealed can of air to detect changes in atmospheric pressure. As the atmospheric pressure goes up, it pushes in on the can, and a series of levers move the dial accordingly to the air pressure. Air Pressure is generally measured in Pascals.

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A Thermometer measures Temperature. Temperature in simple terms is the amount of energy an object has. Typically Thermometers use a glass tube filled with a metal called Mercury as the temperature rises the volume of the liquid expands, and the liquid contracts when it cools down, representing a decrease in temperature. Modern Thermometers use special sensors that directly measure the air using infrared sensors, but mercury thermometers measure temperature indirectly. This makes modern thermometers substantially more accurate.

A Hygrometer measures relative humidity. Relative humidity is the amount of water vapor in the air, expressed as a percentage of the maximum amount of water vapour the air can hold at a given temperature. Predominantly we use a type of Hygrometer called a Psychrometer, which measures the relative humidity using two Thermometers called a dry bulb and a wet bulb . In the case of a sling psychrometer the two thermometers are places in a sling. The dry bulb is exposed to the air and measures the temperature of the air. The second, the wet bulb , is dipped into water and then spun around and as it is spun around water evaporates cooling the bulb. Afterwards the temperatures of the Thermometers are compared. If the air is dry more water evaporates cooling the wet bulb further. The opposite applies, if the air is humid.

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This is the interior of a Stevenson Screen showing a thermometer and a hygrometer, in this case a wet bulb thermometer. The electric wire goes to an electric psychrometer. Both are used to verify accuracy.

An Anemometer measures windspeed . There are two main types of Anemometers: cup and windmill anemometers. The wind pushes the cups and causes the arms to rotate at a rate proportional to the wind speed. A windmill anemometer is a common instrument used at weather stations to obtain the wind speed. The concept is similar to how your speedometer in your car works. Most Anemometers also measure wind direction the instrument that measures wind direction is called a Wind Vane.

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A rain gauge is an instrument used to measure the amount of liquid precipitation over a certain length of time. In the most simplest of terms it is a "can that collects water". The depth of the rain can be measured with a ruler - usually in millimetres or inches. We then discern the rate of precipitation by dividing the precipitation by the Rain gauges are placed in open areas where there are no obstructions such as fields. Rain gauges do have limitations though such as in hurricanes and when the temperature is below or at zero.

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