Download Winds and fronts

Winds & Fronts
A. How wind develops:
Caused by a difference in air pressure due to
unequal heating of the atmosphere.
1.
Two types of winds:
local
 global

B. Winds are created by….
1. Heating the air, decreases pressure (warm
air rises creating low pressure)
2. Cool air rushes into replace the warm air
(cooler dense air, produces high pressure)
3. As air goes from high to low pressure,
winds form.
C. Local Winds
1.
Sea breeze- warm air expands & rises over
land, & cool sea/lake air moves toward the
land.
Local winds cont.
2. Land breeze- warm air over water rises, cool
land air moves toward the water.
Remember! Air rises over warm areas
and sinks over cold areas
Air rises in warm regions
where pressure is low
(convection)
ex the tropics
Air descends in cold areas
where pressure is high
(subsidence)
ex the poles
D. Global Winds
1. Don’t travel North and South because of the
Earth rotating on its axis.
a. 4 Types of Global Winds
– Doldrums: calm, warm winds at equator
– Trade Winds: equator-30° N&S of equator,
gentle/sinking air
– Prevailing Westerlies: 30-60° Strong (big temp. diff.),
impacts U.S. weather
– Polar Easterlies: 60-90° cold, weak winds from
poles
D. Global c.Winds
Polar Easterlies
b.
Cool air descend
d.
Prevailing Westerlies
e.
Trade winds
f.
Doldrums
a.
e.
Trade winds
d.
Prevailing Westerlies
c.
Polar Easterlies
Warm air rises
E. Coriolis Effect
1. Winds do not blow directly from high to
low pressure …. they get deflected by the
Coriolis force (rotation of the Earth)
F. North American Air Masses
Temperature
1. Air masses from N 50º latitude
POLAR (P)
2. Air masses from the tropics
TROPICAL (T)
North American Air Masses
Humidity
1. Air masses from over oceans
MARITIME (m)
2. Air masses from over land
CONTINENTAL (c)
Local Air Masses
2.
1.
cP
4.
mP
mP
3.
6.
5.
mT
cP
cT
7.
mT
G. Front
1. The Boundary between two different air
masses.
a. Water vapor drives storm systems
D. Types of Fronts
Name: Cold Front
What’s happening: cold air moves into warm air
Result: Lot’s of rain, cool temps, thunderstorms
Name: Warm front
What’s happening: warm air moves into cold air
Result: little rain/clouds, warmer temps.
Name: Stationary front
What’s happening: neither masses move the
other
Result: clouds & precipitation
Name: Occluded front
What’s happening: warm air mass caught
between cold air masses
Result: warm air cut off, cloudy & rain