Download Air Pressure

Air Pressure
What is Air Pressure anyway?
• It is caused by the weight of all the air in the
atmosphere pushing down on Earth.
• Air pressure changes with the height and also
when the air warms and cools.
• Changes in air pressure cause changes in
weather.
Low Pressure
• When air rises, it leaves behind an
area of lower pressure, the upward
moving air is not pressing down so
hard on the surface.
High Pressure
• Areas of high pressure are formed where air is
sinking back down, and also pushing down
harder.
The highs and lows
• There are many areas of high and low
pressure above the Earth’s surface due to
uneven surface heating.
• Air moves from high pressure to low pressure
forming winds.
• The greater the difference between the high
and low pressure areas is, the higher the wind
speed is.
Pressure around the World
• Pressure is different all
over the world.
• Lows are areas of low
pressure with the
lowest pressure in the
center.
• Lows usually bring wet,
cloudy weather.
• Highs are areas of high pressure with the
highest pressure at the center.
• Highs bring sunnier, dry weather.
• The way these move from day to day causes
the changes in the weather.
How do we measure pressure?
• Air pressure is measured in millibars (mb) on a
barometer.
• The simplest kind of barometer is a mercury
barometer and pressure is measured in mm (in)
of mercury.
• An aneriod barometer can measure more
conveniently.
• A barograph is a special kind of barometer which
records continuous changes in air pressure.