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Nov9_atmospheric_physics1.pptx

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The Atmosphere a blanket of a gases surrounding a planet.

Two aspects

Physics

Basic variables that define the

atmosphere. What are they?

2. Weather

How do these basic variables change?

Goal of next three classes

1. Lay out basic structure and processes of the Earth’s atmosphere

2. Why does it rain? (or snow)

3. Why does the temperature change?

4. Related to the above- what controls wind speed

Structure of the Atmosphere

What do people notice when they climb a tall mountain?

Two effects of increasing altitude

1) Air gets colder- snow capped peaks

2) Air gets thinner (fewer air molecules, less pressure)- hard to breathe; Everest climbers carry oxygen tanks

Two fundamental properties of the air:

1. temperature- measure of energy of each molecule

2. pressure– number of air molecules pressing against you. Weight of the air/unit area.

Two views of atmospheric Pressure

Pressure comes from weight of molecules above you pressing down

If fewer molecules  pressure goes down

If more molecules  pressure goes up

What happens above Mt. Everest?

Picture from a high altitude balloon

Does air keep getting thinner?

Does air keep getting colder?

Yes to the first, but no to the 2nd question

The air warms up again in the stratosphere (but its very thin!)

The reason:

you’re in the ozone layer and ozone is a special

form of oxygen which absorbs the suns UV rays and heats up

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Earth’s atmosphere has distinct layers defined by changes in temperature.

Most of Earth’s weather happens in the troposphere but is influenced by winds in the stratosphere.

Commercial air travel occurs in the upper troposphere.

We live in the lower troposphere

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So where does the atmosphere officially end?

It depends on what you’re interested in.

Do you need to breathe? You run out of enough molecules by the time

you reach airline altitudes. About 35,000 feet. Climbers on Mt. Everest

(29,000 feet) can spend a few hours without an oxygen tank but

its called the “death zone”. Can’t spend the night above 26,000 feet.

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So where does the atmosphere officially end?

It depends on what you’re interested in.

Do you like blue skies? You run out of enough molecules by

to make the ski blue around 55,000 feet. But this is the stratosphere- the

Ozone layer. You can still ride in a balloon (this picture is from a

Stratospheric balloon). Can still fly military aircraft.

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So where does the atmosphere officially end?

What if you’re a little meteor- like a pebble?

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Further up- the mesosphere. Are we in space yet?

Nope: there are enough air molecules to cause small

meteors to burn up. A “shooting star” is occurring

in the mesosphere.

Also occasional thin clouds because the mesosphere is cold

Clouds at the edge of space!

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Eventually you run out of enough molecules to support any kind

of winged aircraft- need a rocket.

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Official “space” starts

About 62 miles (100 km)

up in altitude. NASA

awards you astronaut wings

if you ride a vehicle to this

altitude

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Continue with atmospheric variables

We have defined the vertical structure using temperature and pressure

Two more:

3. Composition: What gases make up the molecules.

Related to this is: humidity. How many of these molecules are water vapor?

4. How does air move from one place to another.

Weather is caused by how air moves.

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Another property of an atmosphere

Chemical Composition

What is the dry air made of?

Nitrogen (about 78 %, and which does very little)

Oxygen (about 21%, which we breathe)

The other 1%

Argon (an inert gas- doesn’t do much)

Carbon dioxide (plants breathe, absorbs heat and is

increasing due to pollution

Ozone (a form of high altitude oxygen that protects us from sun’s UV)

And obviously, water vapor which is so variable, its usually not

counted in the percentages given above

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