weather theory part i (group c)

Weather TheoryPart I. The Atmosphere

Group C: Second Year

Essential Questions

• What is the atmosphere and what is its lowest level?

• How does atmospheric circulation work? What factors manipulate this circulation?

• What is the Coriolis Effect?• What is atmospheric pressure? What factors

effect it?• What are standard atmosphere conditions?• How does altitude relate to aircraft

performance? The human body?

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Important Terms

• Density – mass of something per volume• Pressure – force of something per volume• Coriolis Effect – the modification of air

circulation patterns due to Earth’s rotation

Section I. Atmosphere• Body of air that surrounds the Earth• Always striving to achieve equilibrium – always

in motion due to unequal heating of Earth’s surface

• High/low pressure• Supports all forms of life on Earth

Composition of the Atmosphere

• 78% nitrogen, 21% oxygen, 1% other• Water demo• Troposphere– Surface to 20,000 feet MSL– Possesses most weather activity– -2°C per 1,000 feet of altitude– -1 inch of Hg per 1,000 feet of altitude

• Tropopause traps most weather inside troposphere

Atmospheric Circulation

• Warm air is thin (less dense) and has lower pressure, therefore it rises

• Cool air is thick (more dense) and has higher pressure, therefore it sinks

• Water/oil demo• Unequal heating is due to Earth’s curved

surface and that it rotates on a tilted axis• Air is heated at equator, rises to pole, cools,

and sinks back to equator – process repeats itself

Balloon Activity 1• Step 1. Put the balloon into the top of the

bottle without dropping it. Seal the top of the bottle with the lip of the balloon.

• Step 2. Cover the hole and try to inflate the balloon.

• Step 3. Uncover the hole and try to inflate the balloon.

• What’s the difference? What happened during each trial?

Atmospheric Pressure• The force exerted by the weight of air molecules• Atmospheric circulation also affects atmospheric

pressure• A column of air would weigh more at sea level than

at 18,000 feet• Pressure can be affected by altitude, temperature,

and density• Pressure conditions affect aircraft performance, such

as takeoffs, rates of climb, and landings• Generally, most high pressure exists over polar

regions and most low pressure exists over equatorial regions because of difference in temperature

Balloon Activity 2

• Step 1. Blow up your balloon.• Based on the previous slide, what can you

conclude about the differences in air pressure?

Section II. Coriolis Effect• Pattern of air circulation is modified by rotation

of Earth, called coriolis effect• Northern Hemisphere:– Air deflected to right– Air rotates clockwise around high pressure areas– Air rotates counterclockwise around low pressure

areas• Southern Hemisphere:– Air deflected to left– Air rotates counterclockwise around high pressure

areas– Air rotates clockwise around low pressure areas

Section II. Coriolis Effect

• Coriolis deflects more closer to the equator and less closer to the poles

Section III. Measurement of Atmosphere Pressure

• Measured in inches of mercury (Hg) by a barometer

• Atmospheric pressure also called barometric pressure

• Pressure of atmosphere pushes on a column of Hg that is advanced up a glass tube on a scale

• ISA – International Standard Atmosphere– Standard pressure = 29.92’’ Hg (at sea level)– Standard temperature = 15°C (59°F)

Section III. Measurement of Atmosphere Pressure

Mercurial Barometer

Section IV. Altitude and Atmospheric Pressure

• Atmospheric pressure decreases as altitude increases

• Pressure decreases by 1’’ Hg per every 1,000 feet

• Pressure decrease = density decrease• Air density is changed by temperature which

changes pressure

Section V. Altitude and Flight

• Takeoff/landing distances and climb rates increase at higher altitudes due to decreased atmospheric pressure

• More speed is required to takeoff if air is thinner (less of it exists in the same area)

• Propellers are also less efficient at higher altitudes – reduced rates of climb

Section VI. Altitude and the Human Body

• Hypoxia• Less oxygen exists at higher altitudes, even

though concentration stays constant• Hypoxia generally begins around 10,000 feet

but can begin as low as 5,000 feet• Cabin oxygen systems allow some planes to fly

at very high altitudes

Water Activity

Box A Box B

N O

N12

67%

O6

33%N O

N6

67%

O3

33%

:Gas::Quantity:

:Concentration:

Quantity vs. Concentration

Quiz Time!!!

• How does a barometer work?

Atmospheric pressure exerts force on mercury which advances up a glass tube.

Quiz Time!!!

• Explain the difference between quantity and concentration.

Quantity is the actual total amount of something within a given area, whereas concentration is the amount of that something in relation to the whole.

Quiz Time!!!

• How much does pressure decrease as altitude increases?

1’’ Hg per 1,000 feet of altitude

Quiz Time!!!

• What are standard atmosphere conditions?

29.92’’ Hg15°C (59°F)

Quiz Time!!!

• Why is the atmosphere always in constant motion?

It strives to achieve equilibrium by replacing low pressure with high pressure until the pressures are equal.

Quiz Time!!!

• What happens to warm air? What happens to cool air?

Warm air: less dense/thinner, risesCool air: more dense/thicker, sinks

Quiz Time!!!

• What is the composition of the atmosphere?

78% nitrogen21% oxygen1% other

Essential Questions

• What is the atmosphere and what is the bottom-most level?

• How does atmospheric circulation work? What factors manipulate this circulation?

• What is the Coriolis Effect?• What is atmospheric pressure? What factors

change it?• What are standard atmosphere conditions?• How does altitude relate to aircraft

performance? The human body?

? ?

Questions?

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