Download Atmospheric Pressure and Winds

Atmospheric Pressure and
Winds
Chapter 19
Air Pressure
• The weight of the atmosphere per unit
area.
– 1kg per cm² at sea level
– 14.7 lbs/in² at sea level
• Directed equally in all directions
• Barometer
– 76cm / 30in at sea level
– given in metric unit of millibars (mb)
Barometer
• Instrument that
measures air pressure
• Mercury Barometer
– Requires a tall column
of mercury
• Aneroid Barometer
– Uses no liquid
Mercury Barometer
Air Pressure Records
Why Air Pressure Changes
• Temperature Changes
– warm air is lighter than cold air
• Changing Humidity
– the more water vapor, the lighter the air
– water vapor pushes out heavier O2 and N2 of
the dry air
What Makes Wind Blow
• Pressure Gradient Force
– the difference in air pressures that cause
winds
• Local Winds
– Sea Breeze: daytime wind from sea, land
heats faster than water and causes air to rise
– Land Breeze: nighttime wind from land to
sea, water is warmer than land
Local Winds: Sea Breeze
Local Winds: Land Breeze
Earth’s Rotation and Weather
Systems
• Coriolis Effect
– Turns wind to the right
• Clockwise
– Out of HIGH pressure
• Counterclockwise
– Into LOW pressure
High Pressure Center
Low Pressure Center
Global Air Currents
Air Masses and Fronts
Chapter 20
Air Masses
• Huge section of air that
has the same weather
throughout
• Take on the
characteristics of the area
they originated over
• maritime tropical – mT
• continental tropical – cT
• maritime polar – mP
• continental polar - cP
Air Mass Source Regions
Fronts
• Boundary between 2
air masses
• Causes warm air to
rise
– Where temperatures
and humidity change
Warm Front: Map View
• Slow moving
• Long lasting rain
• Cirrus to stratus
clouds, then
nimbostratus
Warm Front: Side View
Warm Front: Side View
Cold Front: Map View
• Fast moving
• Unstable air
• Cumulus –
cumulonimbus clouds
• Thunderstorms
• Clears quickly and
leaves clear skies
Cold Front
Cold Front
Occluded Front: Map View
• When a cold front
overtakes a warm
front
• Form low pressure
systems
Occluded Front: Side View
Warm Air
Cold Air
Cold Air