Download Air Pressure

Air Pressure
Air Movement
Pressure Systems/Cyclones
Local Winds
Air Pressure Basics
• Air pressure = weight of
atmosphere pressing down
• Most of Earth’s air mass is in the
lower atmosphere.
–Moving from space to Earth’s
surface, air pressure increases.
• Change in atmospheric pressure =
change in weather.
Mapping Air Pressure
• Meteorologists use isobars to identify high
pressure and low pressure air systems.
– Isobars  lines that connect areas of equal
air pressure
Low Pressure Systems = Cyclones
• The center of the isobar rings
Bird’s Eye View
with lowest pressure
• Marked with “L”
• Air moves:
– UP
– INTO
Profile View
– COUNTERCLOCKWISE
• Rising air cools, condenses, &
precipitates = cloudy & stormy
weather
High Pressure Systems = Anticyclones
• The center of isobar rings has
highest pressure
Bird’s Eye View
• Marked with “H”
• Air moves:
– DOWN
– OUT
– CLOCKWISE
Profile View
• Sinking air warms and retains
(keeps) its moisture = clear, dry
weather
Low vs. High Pressure
Winds
• Wind is air in motion.
• The way air moves depends on 3 things:
–Air pressure
–Coriolis Effect
–Shape of the land (topography)
1. Air Pressure
• Air ALWAYS flows from high
to low pressure.
• Closer isobars =
faster changes in
pressure = faster air
movement = stronger
wind!!!
1. Air Pressure:
Global Winds
• Caused by temperature/pressure differences
– Poles—cold—dense air sinks—pushes out air
– Equator—hot—less dense air rises—leaves space
2. Coriolis Effect
• Rotation of Earth causes
winds to deflect/spin
– Northern Hemisphere =
deflected to the right
(clockwise)
– Southern Hemisphere =
deflected to the left
(counterclockwise)
3a. Shape of the Land:
Land and Sea Breezes
Warmer
Land
Land Breeze
(Night time)
Cool sea breeze
Cooler
Ocean
Caused by low
pressure over land
Cool land breeze
Cooler
Land
Warm air rises
Warm air rises
Sea Breeze
(Day time)
Warmer
Caused by low Ocean
pressure over water
3b. Shape of the Land:
Local Winds—Mountain and
Valley Breezes
Valley Breeze
(Day time)
Mountain Breeze
(Night time)