Air Pressure and Wind Notes
Air Pressure is the weight of the gases in the atmosphere pushing
on the surface of the Earth.
- At sea level, standard air pressure is 14.7 lb/in2 or 1013.2 mb
or 29.92 in Hg.
How does air pressure change with altitude?
The pressure of the atmosphere decreases
as altitude increases.
- The greatest change in air pressure occurs in the
lower atmosphere (troposphere).
Air pressure is measured with a Barometer.
Aneroid
Mercury
Why Does Air Pressure Change?
Air pressure can be analyzed on a weather map using
Isobars- lines that connect points of equal air pressure.
- Each line differs in pressure by 4 millibars.
- Isobars on a map are used to determine the
location of pressure system and act as a way to
forecast weather.
So far we know the air pressure decreases with altitude because there are less air molecules
pushing down from above.
- It also changes with temperature & humidity.
Characteristics of High and Low Pressure Systems (Draw in arrows & pressures)
High Pressure
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Low Pressure
Cool temperatures
Rising barometer
Fair weather
Air moves out from center - clockwise
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Warm temperatures
Falling barometer
Poor weather
Air moves toward centercounterclockwise
A Pressure Gradient is change in pressure between two places. This creates a force that
makes wind move from areas of high pressure to areas of low pressure.
What causes Wind & Pressure Differences?
Differences in the heating of land and water creates different pressure systems.
- Land heats up and cools faster than water.
- On a local level, this difference in heating creates Breezes.
Sea Breeze
Land Breeze