3 zones of Upward motion:

ITCZ

polar fronts

and windward sideof a mountain

air rises, cools, and may condense

4 zones of Downward motion:

poles

30ºN and S

and leeward sideof a mountain

warms, so lower RH and dry conditions

Winds blow because of differences in

atmospheric pressure.

Wind DIRECTION depends on:

PRESSURE GRADIENT FORCE

andCORIOLIS EFFECT

force derived from the difference in the pressure

winds “want” to blow from high pressure to low pressurethe steeper the pressure gradient, the stronger the wind

isobars (lines of equal barometric pressure) close together

acts to deflect the wind

greatest at the polesstronger wind, greater effect

Winds are named by where they are

FROMFROM.. A NORTH wind in Jacksonville is likely to be a COLD

wind.

A SOUTH wind is likely to be a WARM wind.

Coriolis Effect deflects winds to the right in thenorthern hemisphere

High Low

N

Low

Low

Low

NW

SW

NE

SE

Coriolis Effect deflects winds to the left in thesouthern hemisphere

High Low

N

Low

Low

Low NW

SW

NE

SE

Wind speed depends on:

pressure gradient force

greater the difference in pressure, the stronger the wind

friction

friction occurs from interference with the earth’s surface

friction acts to slow down the wind

GEOSTROPHIC WINDS

high altitude winds

have little effect from friction

geostrophic winds blow parallel to the isobars

H

L

JET STREAMcenter of fast moving winds in the upper tropospherecenter of the geostrophic winds

Northern Hemisphere

Southern Hemisphere

surface

winds

geostrophic

winds

H

cw, out

L

ccw, in

H

cw

L

ccw

coriolis deflects to the right

coriolis deflects to the left

H

ccw, out

L

cw, in

H

ccw

L

cw

HIGH PRESSURE

anti-cyclone

LOW PRESSURE

cyclone

other winds

foehn or chinook--those warm, dry winds that blow down the leeward sides of mountains

katabatic winds--cold winds that sink down off of a mountain because the cold air is very dense and heavy

MONSOONS

seasonal shift in the prevailing wind directions

noted for bringing seasonal precipitation

January

H

July

L

Valley Breeze

warms warms

during the day, the valley air warms, becomes less dense, and rises

Mountain Breeze

cools

at night, the top of the mountain cools faster because of the thinner air, and the colder, denser air sinks down

the mountain

along a coastline

water landHOTCOLD

SEA BREEZE

H L

During the day, the land heats faster than the water, the warm air rises, and low pressure develops. The air over the water becomes cold and heavy, sinking, creating high pressure. Air moves from highs toward lows, so a SEA BREEZE develops coming from the water.

water landHOT COLD

HL

LAND BREEZE

At night, the land cools faster than the water, the cold air sinks, and high pressure develops. The air over the water becomes warm and light, rising, creating low pressure. Air moves from highs toward lows, so a LAND BREEZE develops coming from the land.