What is the primary tool used to measure relative humidity?

The primary tool used to measure relative humidity is a psychrometer. This device typically consists of two thermometers: a dry bulb thermometer that measures air temperature and a wet bulb thermometer, which has a wetted wick that cools as water evaporates from it. The difference in readings between the two thermometers is used to calculate relative humidity. When air has a high amount of moisture, the wet bulb temperature is closer to the dry bulb temperature, while in drier conditions, the wet bulb temperature will be significantly lower.

This measurement is crucial in meteorology as relative humidity plays a vital role in weather forecasting, climate studies, and understanding atmospheric processes. The psychrometer's ability to provide accurate measurements across various conditions makes it an essential instrument for meteorologists.