Which instrument is primarily used to measure atmospheric pressure?

The instrument used to measure atmospheric pressure is a barometer. Barometers operate on the principle that changes in atmospheric pressure result in changes to the height of a liquid column in a sealed tube or affect the pressure on a sensing element. There are various types of barometers, such as mercury and aneroid barometers, each utilizing different methods to gauge pressure.

In meteorology, understanding atmospheric pressure is essential as it helps in weather forecasting and is a critical factor in determining weather patterns. A decrease in atmospheric pressure typically indicates that stormy weather may be approaching, while increases often suggest calmer conditions.

The other instruments listed serve different purposes. An anemometer measures wind speed, which is important for understanding wind dynamics but does not provide information about atmospheric pressure. A hydrograph is used to measure the quantity of water flow in rivers or streams over time, primarily for hydrological studies rather than atmospheric measurements. A pyranometer measures solar radiation, which is valuable for solar energy assessments and climate studies but does not relate to pressure measurement.