Download AIR PRESSURE

AIR PRESSURE
What is Air Pressure ?
 The weight of the atmosphere above a
location per unit of area
 Measured in atmospheres, millimeters of
Mercury or Millibars
 Standard Atmospheric Pressure (at Sea
BAROMETER
Level) = 1 atmosphere= 14.7 psi

760 mm or 29.92 inches

1013.25 mb
Factors that Affect Air Pressure
1. TEMPERATURE- as temperature increases, air
pressure decreases ( warm air rises and expands)
2. Amount of WATER VAPOR- moist air weighs less
than dry air- water weighs less than Nitrogen or
Oxygen molecules
3. ALTITUDE- as you increase elevation, air pressure
decreases, there are fewer molecules as you go up
Air Pressure Changes
 WARM AIR weighs less than Cold Air
warm air rises and expands, less dense
 HUMID AIR weighs less than Dry Air
water weighs less than Nitrogen or Oxygen
gas
Weather Changes with A.P. Changes
 FALLING BAROMETER –
changeable weather (rain/snow/clouds)
warmer, more humid air
 RISING BAROMETER
good (fair ) weather
cooler, drier air
Drawing ISOBARS
Differences in Air Pressure