How do people with How do people with arthritis know when arthritis know when it’s going to rain?it’s going to rain?

Aim: How does air pressure Aim: How does air pressure affect the weather?affect the weather? Topic: Unit 6 MeteorologyTopic: Unit 6 Meteorology Main Idea: Barometric pressureMain Idea: Barometric pressure

1) What is a barometer?1) What is a barometer? It is an It is an

instrument instrument that measures that measures air pressure.air pressure.

2) What causes air 2) What causes air pressure?pressure?

The weight of The weight of the air the air molecules in molecules in the the atmosphere atmosphere above us.above us.

3) 3) On a standard day, what is On a standard day, what is the atmospheric pressure at sea the atmospheric pressure at sea level?level?

It is 1013.2 It is 1013.2 mb mb (millibars) or (millibars) or 29.92 inches 29.92 inches of mercury of mercury (“Hg) or 14.7 (“Hg) or 14.7 psi.psi.

TemperatureTemperature• Higher temperature =lower Higher temperature =lower

pressurepressure• Molecules spread out so there is Molecules spread out so there is

less pressureless pressure

MoistureMoisture• More moisture = less pressureMore moisture = less pressure• Water molecules are lighter than Water molecules are lighter than

air molecules (they replace air air molecules (they replace air molecules)molecules)

• Falling barometer = more Falling barometer = more moisturemoisture

AltitudeAltitude• As altitude increases, air pressure As altitude increases, air pressure

decreasesdecreases• The air molecules are farther apart The air molecules are farther apart

at high altitudesat high altitudes

5) Low Pressure5) Low Pressure Low (Oh, No!!)Low (Oh, No!!) Storm conditionsStorm conditions Warm, lots of moistureWarm, lots of moisture

5) High Pressure5) High Pressure High rhymes with Dry High rhymes with Dry Cool, clear dayCool, clear day Very little cloudsVery little clouds

How can we predict a change by How can we predict a change by looking at a barometer?looking at a barometer? Falling barometer= storm approachingFalling barometer= storm approaching Rising barometer= cool, clear weatherRising barometer= cool, clear weather

6) Convert these 6) Convert these pressures:pressures:

A) 30.15 inchesA) 30.15 inches B) 978 mbB) 978 mb C) 29.73 inchesC) 29.73 inches D) 1019 mbD) 1019 mb

1021 mb1021 mb 28.88 inches28.88 inches 1007 mb1007 mb 30.09 inches30.09 inches

Do NowDo Now 1. What is the most abundant element in the earth's atmosphere?1. What is the most abundant element in the earth's atmosphere?

A) Argon.A) Argon.B) Carbon dioxide.B) Carbon dioxide.C) Nitrogen.C) Nitrogen.D) OxygenD) Oxygen

2. Which layer of the atmosphere has the highest density of gas molecules?2. Which layer of the atmosphere has the highest density of gas molecules?A) Mesosphere.A) Mesosphere.B) Stratosphere.B) Stratosphere.C) Thermosphere.C) Thermosphere.D) TroposphereD) Troposphere

3. Which layer of the atmosphere contains the ozone layer?3. Which layer of the atmosphere contains the ozone layer?A) Mesosphere.A) Mesosphere.B) Stratosphere.B) Stratosphere.C) Thermosphere.C) Thermosphere.D) Troposphere.D) Troposphere.

4. What frequencies of electromagnetic radiation are absorbed by the earth's 4. What frequencies of electromagnetic radiation are absorbed by the earth's ozone layer?ozone layer?A) Infrared light.A) Infrared light.B) Microwaves.B) Microwaves.C) Ultraviolet light.C) Ultraviolet light.D)Visible light.D)Visible light.

5. In which layer do virtually all weather phenomena take place?5. In which layer do virtually all weather phenomena take place?A) Mesosphere.A) Mesosphere.B) Stratosphere.B) Stratosphere.C) Thermosphere.C) Thermosphere.D) Troposphere.D) Troposphere.