Meteorology Chapter 6 - Air Pressure

Air Pressure

Force that is exerted on every surface due to collisions of gas

Barometer

Measures pressure in inches

Sea Level Pressure

14.7 lbs./in²

Pressure Gradient

• Difference of pressure across some region

• Created by heating differences

• Caused the air to move from high pressure to low pressure

PGF

Due to heating differences air flowing is directed from high pressure to low pressure

Coriolis

Due to Earth’s rotation

• NH - apparent deflection to the right

• SH - apparent deflection to the left

• Acts at a right angle to the wind

• Affects wind direction

• Wind speed - faster winds mean greater deflection

• Latitude - strongest at poles weakest at equator

Centrifugal Force

Outward pull in a curved flow that is a function of wind speed

Friction

• Acts opposite of the wind

• Slows down wind speed and affects wind direction

• Acts at the surface; no friction occurs in upper levels of the atmosphere

Gravity

• Downward directed toward the center of the Earth

Geostrophic Wind

• Balance between PGF and Coriolis → air flows parallel to straight line isobars

Gradient Winds

All upper-level winds are parallel to isobars

High vs Low Pressure Winds

• High: clockwise & outward

• Low: Counter-clockwise & inward

Flow Summary

SH Upper Level

• H: CCW & parallel

• L: CW & parallel

SH Surface

• H: CCW & outward

• L: CW & outward

NH Upper levels

• H: CW & parallel

• L: CCW & parallel

NH Surface

• H: CW & outward

• L: CCW & outward

Anticyclone

• Area of high pressure

• Flows anticyclonically

• Pressure increases

• Temperature increases

• RH decreases

• Air is stable, sinks and flows outward at the surface

Cyclone

• Area of low pressure

• Flows cyclonically

• Pressure decreases

• Temperature decreases

• RH increases

• Air is unstable

Wind Vane

• Points into the wind and measures wind direction

Cup Anemometer

• Measures wind speed