Physical GeographyLecture 4.5

EARTH’S ATMOSPHERE

Ready for a quick review?

1. What’s the difference between shortwave and longwave electromagnetic radiation? Which of these does Earth predominantly radiate?

2. What are the two important principles of EMR emissions?

3. What is the solar constant? Why do we care?

4. The amount of insolation received by an area on Earth’s surface depends on what?

5.How are the Tropics of Cancer and Capricorn related to Earth’s axial tilt?

6.How are the Arctic and Antarctic Circles related to Earth’s axial tilt?

7.What are aphelion and perihelion? On about what date do they occur?

8.True or false? Earth’s axial tilt shifts over time. By 2015, it will be 25°.

9.What causes Earth’s seasons?

10. What is the subsolar point? How is it related to the solstices and equinoxes?

How is insolation “processed” by Earth’s atmosphere?

First, we need to ask:What is the make-up of Earth’s

atmosphere?

Air is...where?

Air has weight, it has mass

Air is attracted by Earth’s gravity

Composition of the Atmosphere

The atmosphere is composed of two types of gases:

1. Those which generally do not change their concentrations from place to place

2. Those which do

Proportional Volume of Atmospheric Gases

Particulates in the Atmosphere

The Importance of Particulates

Absorb and reflect sunlight This reduces the amount of sunlight that

reaches Earth’s surface Scatter sunlight

Mostly in the blue range of the spectrum, giving the sky its blue color

At sunrise and sunset, most of the blue has been scattered in the upper atmosphere, leaving red and yellow

The Importance of Particulates

They also act as condensation nuclei...

Condensation Nuclei Condensation nuclei are

necessary elements for the formation of cloud droplets

Without them, conditions may be perfect for the formation of clouds or fog, yet condensation does not occur

Excess condensation nucleii also may cause condensation before the saturation point has been reached

Some particles are hygroscopic—they attract and absorb water (salt)

Vertical Structure of the Atmosphere

Thermal Structure of the Atmosphere Troposphere

Temp. decreases with increasing altitude (surface warmed by the sun is its heat source)

Conduction Conduction is the

passing of heat from molecule to molecule by touch

Conduction Temperature is an

expression of molecular motion

As one molecule bangs into another, it makes the next one vibrate, as well—thus passing on its molecular motion and increasing the temperature of the molecule it just “sped up”

Thus the heat passes up the metal bar until it reaches the hand holding it…

Conduction in the Troposphere

The sun’s radiation is absorbed at Earth’s surface and reradiated upward as heat

But air is a poor conductor of heat (the molecules are too far apart and move around too much)

So heat is not transferred upward very far

This is why the Troposphere is warmest at the surface and gets colder as you rise upward

ELR The rate at which air temperature

drops as you rise through the Troposphere can be roughly estimated:

6.5ºC/1000 m or 3.5ºF/1000 ft

This rate is called the Environmental Temperature Lapse Rate, or ELR

Thermal Structure of the Atmosphere Troposphere

Temp. decreases with increasing altitude (surface warmed by the sun is its heat source)

Stratosphere Temp. increases as ozone

absorbs UV light

A Little Bit About the Importance of Ozone…

The Ozone Hole

Thermal Structure of the Atmosphere Troposphere

Temp. decreases with increasing altitude (surface warmed by the sun is its heat source)

Stratosphere Temp. increases as ozone

absorbs UV light Mesosphere

Temp. decreases (no heat source)

Thermosphere Temp. increases as

stratified layers of gases absorb high-intensity ultraviolet radiation and are split apart

Exosphere Merging into space So few molecules of gas in

this layer that “temperature” really doesn’t apply

Vertical Structure of the Atmosphere Ionosphere—begins in the

Mesosphere blocks extremely harmful

short wave radiation (UV-B and UV-C), some cosmic rays, and high energy particles from the sun

reflects radio waves back to the surface, aiding long-distance communications

source of the arorae (borealis and australis), a.k.a. the Northern and Southern Lights

Homosphere Mixed gases in roughly equal

concentrations Heterosphere

Gases so far from Earth’s surface that the effect of gravity is minimized—gases are stratified (layered) by molecular weight

A little more review:1.Why are most of Earth’s atmospheric

gases found near the surface?2.Name 3 important variable-amount gases

found in Earth’s atmosphere. Why is each one important?

3.Why are atmospheric particulates important?

4.What would happen if there were no condensation nuclei in the atmosphere? What happens when there is an abundance of nuclei?

5.What is ozone? In which thermal layer of the atmosphere is it found? How does it affect temperatures within that layer?

6.What generally happens to the surrounding air temperature as you rise through the troposphere?

7.What happens in the -pauses?

8.What is conduction? Is air a good conductor of heat?

9.What is the ELR? What is the rate of change of the ELR? To which thermallayer of the atmosphere does it apply?

10.What is the homosphere? What is the heterosphere? What does the ionosphere do?

Practice drawing the vertical structure of the atmosphere diagram in a notebookWatch a Khan Academy video (see the post on Oct. 5 for links, about mid-way down the post)

Finish reading Chapter 3. Take notes. Write questions in the margins.

Review the class slidesStudy the chapter review questions

To Work On: