How do people with
arthritis know when it’s
going to rain?
Aim: How does air pressure affect
the weather?
Topic: Unit 6 Meteorology
 Main Idea: Barometric pressure

1) What is a barometer?

It is an
instrument that
measures air
pressure.
2) What causes air pressure?

The weight of the
air molecules in
the atmosphere
above us.
3) On a standard day, what is the
atmospheric pressure at sea level?

It is 1013.2 mb
(millibars) or
29.92 inches of
mercury (“Hg)
or 14.7 psi.
Temperature
•
•
Higher temperature =lower pressure
Molecules spread out so there is less
pressure
Moisture
More moisture = less pressure
• Water molecules are lighter than air
molecules (they replace air molecules)
• Falling barometer = more moisture
•
Altitude
As altitude increases, air pressure
decreases
• The air molecules are farther apart at
high altitudes
•
5) Low Pressure
Low (Oh, No!!)
 Storm conditions
 Warm, lots of moisture

5) High Pressure
High rhymes with Dry
 Cool, clear day
 Very little clouds

How can we predict a change by
looking at a barometer?
Falling barometer= storm approaching
 Rising barometer= cool, clear weather

6) Convert these pressures:
A) 30.15 inches
 B) 978 mb
 C) 29.73 inches
 D) 1019 mb

1021 mb
 28.88 inches
 1007 mb
 30.09 inches

Do Now





1. What is the most abundant element in the earth's atmosphere?
A) Argon.
B) Carbon dioxide.
C) Nitrogen.
D) Oxygen
2. Which layer of the atmosphere has the highest density of gas molecules?
A) Mesosphere.
B) Stratosphere.
C) Thermosphere.
D) Troposphere
3. Which layer of the atmosphere contains the ozone layer?
A) Mesosphere.
B) Stratosphere.
C) Thermosphere.
D) Troposphere.
4. What frequencies of electromagnetic radiation are absorbed by the earth's ozone
layer?
A) Infrared light.
B) Microwaves.
C) Ultraviolet light.
D)Visible light.
5. In which layer do virtually all weather phenomena take place?
A) Mesosphere.
B) Stratosphere.
C) Thermosphere.
D) Troposphere.