Chapter 6 - Air Pressure & Winds

Atmospheric pressure

Force per unit area of a column of air above you

Air pressure in the atmosphere

Decreases with height

High pressure flows towards

Low pressure

Warm air aloft

Creates high pressure

Cold air aloft

Creates low pressure

When air converges and goes up

There is low pressure at the surface

When air diverges and goes down

The surface high

Barometer

Measures bars (force over a given area)

Aneroid barometers

Most common home barometer

Why inches of Mercury

Only responded to atmospheric pressure

Caused by rising air above the surface low

Clouds and storms (low pressure centers)

Caused by sinking air above the surface high

Fair weather (high pressure centers)

Station pressure

Pressure measured at any location

Isobars

Lines connected points of equal pressure

Midlatitude cyclone

Low pressure center (counter-clockwise)

Anticyclone

High pressure center (clockwise)

Horizontal pressure variations create

Low heights = low pressure = cold temperature
High heights = high pressure = warm temperature

Air rises

Above a surface low pressure

Cold air aloft means

Low pressure, trough region

Warm air aloft means

High pressure, ridge regions

What warm air is associated with at upper levels

High heights / pressure

What cold air is associated with at upper levels

Low heights / pressure

Pressure Gradient Force (PGF)

Air flowing from high to low pressure force

Stronger gradient = stronger wind

Closer isobars means

Stronger pressure gradient force (and wind) will be

Coriolis force

Apparent force due to rotation
Turns moving objects / parcels to the right in northern hemisphere, left in the southern

Faster motion means

Stronger Coriolis force

Coriolis force only affects

Direction

Geostrophic Wind

Wind parallel to lines of pressure with no other forces

PGF and Coriolis force being in balance

Centrifugal force

Outward rotating force

Faster speeds and tighter curves indicate

Greater centrifugal force

Gradient wind

Involves PGF, Coriolis, Centrifugal forces, flow is parallel to curved isobars

Low pressure northern hemisphere

Counterclockwise motion

Low pressure southern hemisphere

Clockwise motion

Friction

Wind is slowed by drag from ground, trees, buildings

How friction lessens Coriolis

Friction slows down wind and Coriolis is dependent on wind speed

Cyclostrophic wind

Balance is between PGF and centrifugal forces in really small but strong pressure gradients (tornadoes)

Coriolis increases with

Latitude

Friction always moves

Opposite of wind direction

Wind

Characterized by direction, speed, & gustiness

Onshore wind

Wind from the sea

Offshore wind

Moving out to sea

Upslope wind

Moving from upwards

Downslope wind

Moving from downward

Prevailing wind

Wind direction most often observed during a given time period and can greatly affect climate