Air Pressure Air Masses Air Pressure Air pressure

Air Pressure & Air Masses

Air Pressure ✶Air pressure is the force of air over a specific location. ✶Air is matter, it has mass & volume. ✶The weight of the atmosphere on the Earth is constant.

Amount of Air Pressure ✶More air molecules, closer together = More pressure ✶Depends on the density, temperature, altitude, & the amount of moisture in the air. ✶Density depends on the mixture of gases, dust/pollution, & water vapor.

Altitude ✶Gravity is the force that keeps the atmosphere from drifting into space. ✶Gravity is strongest near the surface of the earth. ✶Air pressure decreases with height because there are fewer gas molecules to press down.

Air exerts pressure Less dense Air Pressure Most dense Earth

Cold Front ✶Low pressure- cloudy & damp ✶Warm air is less dense & is forced upward by cool dense air. ✶Air cools as it rises, increasing the relative humidity. ✶Then, water vapor condenses into clouds creating precipitation.

Warm Front ✶High pressure- “nice” weather ✶Cool dense air sinks toward the earth’s surface & becomes warmer. ✶Air warms, decreasing the relative humidity. ✶Droplets of water in the clouds evaporate causing fair weather.

Low Pressure ✶Air is less dense; less molecules in the same amount of space. – Warm air (more energy = more movement = more space). – Moisture-laden air (water vapor has less mass than dry air). – Air at higher elevations (gravity is less with more distance).

High Pressure ✶Air is more dense; more molecules in the same space. – Cold air (less energy = less movement = closer together). – Dry air (more mass=more density). – Low elevations or sea level ( greater force of gravity pulls molecules down more = closer together).

Barometer ✶Tool used to measure air pressure in (atm), standard is 29. 92 atm. ✶The farther pressure drops from 29. 92 atm, the greater the chance of a storm. ✶The farther the pressure raises above 29. 92 atm, the greater the chance of fair weather.

Air Masses & Fronts

Air Masses ✶Large bodies of air that form over land or water, can be as large as several states. ✶Formed when air stays in the same place, allowing it to cool or warm as it tries to match the temperature & humidity of the surface below it.

Air Masses ✶Weather is caused by the development & movement of large air masses. ✶Equalize the global temperatures. ✶Usually form in the tropical & polar regions because the air in the middle latitudes moves too much.

✶If it forms over land: Dry ✶If it forms over water: Wet ✶If it forms near Equator: Warm ✶If it forms near the poles: Cold