Understanding Meteorological Instruments: Barometers, Hygrometers, Thermometers & More!

Knowing how to read meteorological instruments is key to understanding the weather forecast. Most people already know what the readings on a thermometer mean, but may be unfamiliar with how to read a barometer, anemometer, or hygrometer. All of these meteorological instruments work together to give the weather services a complete picture of the day's weather patterns. Here is a quick guide to understanding the basic types of meteorological instruments.

Understanding meteorological instruments: Thermometer

Of course, everyone is familiar with the basic thermometer, which reports the air temperature. The mercury in a traditional thermometer expands as it heats up, making it rise up through the thermometer's chamber. The markings on the thermometer are designed to match up with the expected expansion of the mercury based on each temperature. The official meteorological thermometers are set up five feet above the ground to minimize the effect of the land on the reported temperature. In certain areas, the official weather service thermometers must be placed inside a protective shelter to reduce the impact of the wind or precipitation in the area.

Understanding meteorological instruments: Hygrometer

The humidity in the air is measured by a hygrometer. The older style of this meteorological instrument is called a psychrometer. It is made up of two thermometers, one of them which is kept dry and the other one is kept wet. The moisture on the wet bulb evaporates, dropping the temperature of that thermometer. The relative humidity in the air is calculated by measuring the difference between the two thermometers' temperatures. The hygrometer is one of the more difficult meteorological instruments to calibrate and read.

Understanding meteorological instruments: Barometer

A barometer is the meteorological instrument used to measure the pressure in the atmosphere. This measurement can be obtained by using air, mercury, or a water-based barometer. The barometer is often used to predict trends in the weather or approaching storms. If the barometer is dropping, this usually is a sign that a storm is on the way. A rising barometer generally means that the storm is going away and the weather will be getting warmer.

Understanding meteorological instruments: Anemometer

An anemometer is used by meteorologists to measure the velocity of the wind by registering the strength of the air blowing past the detector. To get an official wind speed reading, the anemometer must be mounted 33 feet above the ground. These meteorological instruments are usually installed on a tall building or at the airport. The most common type of anemometer are the cup anemometers, which have a series of cups that spin around a pole. The wind velocity is determined by measuring the number of spins the cups make per minute.