# Why Are Hygrometers Important In the Field of Meteorology?

Why Are Hygrometers Important In the Field of Meteorology?

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1. Introduction

For thousands of years, scientists have been predicting weather patterns with varying degrees of accuracy.  The knowledge of when or if it will rain was and still is crucially important to civilizations dependent on farming.  Measuring certain atmospheric parameters is also critical to warn the public of impending dangerous weather.

Humidity in the Atmosphere

One important atmospheric condition is the measure of humidity in the air.  Humidity is the measure of water vapor in the air at a specific time, temperature and pressure.  Relative humidity is actually the ratio of the weight (mass) of water vapor in the air to the weight (mass) of dry air (water vapor amount relative to dry air amount).  At different temperatures, dry air can hold specific amounts of water vapor.  Warmer air can hold more water vapor than cooler air.

Psychrometry and the Weather

Psychrometry is the study of the properties of water vapor in the air.  There are equations that can be used to calculate relative humidity as well as other important factors meteorologists (those who study and predict the weather) use in their forecasts.  When air at a certain temperature cannot hold anymore water vapor, it is said to be saturated with water.  If the temperature increases, the air can hold more water vapor.  If the temperature decreases, condensation takes place and the water vapor creates clouds and/or rain.

Hygrometers and Humidity Measurement

A hygrometer is a psychrometric instrument that measures the relative humidity.  The device contains two thermometers that indicate the amount of water vapor in air at a given atmospheric temperature.  The two thermometers measure the minimum and maximum amounts of water vapor in the air at certain temperatures and compare that with the actual conditions.  Relative humidity can also be determined by using a psychrometric chart which shows intersections of water vapor amounts at certain temperatures.

Effect of Hydrometers on Meteorology

As relative humidity in the atmosphere increases, the chance of rain increases. Using hydrometers, meteorologists observe warm air absorbing moisture and then rising higher into the atmosphere.  As warm, moist air rises, it begins to cool.  If the warm air has a high relative humidity as it cools, the water will condense (form droplets) and form clouds.  As this continues, these clouds become saturated with water vapor until the weight of the water is too great and it falls out of the sky as rain.

Other Important Uses for Hydrometers

Not only are hydrometers an important prediction of the chance of rain, but they are also used in other applications.  Greenhouses are effective for raising plants because they are a controlled environment with a mixture of light, temperature and moisture in the air.  Hydrometers assist with the measurement of moisture in the air.  When moisture in the air is not desirable, such as in museums and humidors, hydrometers are used to monitor water vapor.