Download - Air Pressure & Wind
Air Pressure & Wind
What is Air Pressure?
Air pressure is the weight of the atmosphere as it pushes down on the Earth’s surface.
How do we measure air pressure?
Instrument used is called a barometer.
mercury barometer aneroid barometer
What units are used?
INCHES - average (at sea-level) is 30 inches.
MILLIMETERS - average (at sea-level) is 760mm.
MILLIBARS - used by meteorologists
average (at sea-level) 1013 mb.
Factors that Affect Air Pressure
Change in Elevation - the higher the altitude, the lower the air pressure.
Factors that Affect Air Pressure Temperature - as temperature increases
the air pressure decreases (at sea-level).
Why? Air molecules spread out as they heat up.
Factors that Affect Air Pressure
Humidity - The more water vapor the lighter the air.
Why? Water molecules have less mass than nitrogen and oxygen (NO) and pushes the nitrogen and oxygen out of the way.
Dry Air
99% nitrogen & oxygen
Warm Air
97% nitrogen & oxygen
Changes in Air Pressure
Air Pressure changes can be used in forecasting weather (not always accurate).
As air pressure decreases often signals warmer, more humid, along with rain or snow.
As air pressure increase it signals cooler, drier air, and fair weather.
Air Pressure & Wind
Changes in air pressure causes the wind to blow.
What Causes Wind to Blow?
Wind is caused by uneven heating of the Earth’s surface, thus causing changes in air pressure.
Wind moves from an area of high pressure to areas of low pressure.
Winds are named for the direction from which they come.
Analyzing Air Pressure Isobars - points on
a map having the same air pressure.
Close together = fast wind speed.
Far apart = calm wind
High Pressure - Happy
Anti-Cyclone - air moving clockwise away from the pressure center.
Cold air - weighs more Dry air Sunny No precipitation
Symbol indicated on a weather is:
H
Low Pressure - Lousy
Cyclones - air moving counter clockwise toward the pressure center
Warm air Humid/moist air Cloudy Precipitation
Symbol indicated on a weather is:
L
Wind blows from Hi to Lo pressure regions