How Barometric Pressure Works

Barometric pressure, also known as atmospheric pressure, is a term used for the measurement of the weight of the mass of air above a particular spot. The air in the atmosphere presses down upon the earth at different rates, in different situations. These changes can be measured with a device called a barometer. The highest levels of barometric pressure typically occur in areas at or below sea level, since these areas have the greatest amount of air above them, pressing down. Areas with a higher elevation have lower barometric pressure, since they have a smaller amount of atmosphere above them. Barometers are standardized by setting them to measure the pressure that would occur in an area if it were at sea level.

Air masses are constantly moving through the atmosphere, and interacting with one another. Cold, dry air masses typically originate at the north and south poles, and are less dense, resulting in lower barometric pressure. Warm and wet air masses originate at the equator. Due to their water content, warm air masses are heavier, and result in higher barometric pressure readings.

When a cold air mass meets with a warm air mass, the warm air mass rises up to go above the cold air mass. The space left behind where the warm air mass used to be is now vacant, which causes the barometric pressure on the surface of the earth in that area to drop, and the cold air mass to move forward to fill the gap. As the cold air moves forward, causing the barometric pressure to increase, more of the warm air mass rises. The cold air mass rushes in once more, which begins a cycle that leads to a storm. The rapid rise and fall of barometric pressure that signals a storm is in reaction to this warm and cold air mass exchange.

References

• Weather Basics
• Atmospheric Pressure