What is usually measured by rain gauges?

Rain gauges are specifically designed to measure the amount of precipitation that falls within a given period. They collect rainwater and allow meteorologists and researchers to quantify how much rain has fallen, which is crucial for various weather-related analyses and forecasts. This measurement helps in understanding weather patterns, monitoring drought conditions, and managing water resources.

The other options refer to different meteorological variables: humidity levels are measured by hygrometers, wind speed is assessed using anemometers, and temperature variations are gauged with thermometers. Each instrument serves its own unique purpose in the field of meteorology, highlighting the importance of specialized equipment for accurate data collection.