Help with Geography Midterm

PHYSICAL GEOGRAPHY

LECTURE 3: ATMOSPHERE

Geographers are interested in how the atmosphere works, how it functions, and its evolution. The

processes which are most significant to understand are: (definitions below in section D).

* photosynthesis

* ozone creation

* carbon storage

These processes are central to understanding how the atmosphere maintains health (producing

oxygen and ozone creation), as well as reducing the harmful impact of pollution (plants absorb

CO2).

A. FUNCTIONS OF THE ATMOSPHERE: Together these processes allow a stable composition of the atmosphere, and enable the

atmosphere to balance global temperatures and filter incoming SR.

The functions of the atmosphere which are most significant are:

1. Balance incoming (shortwave) and outgoing (longwave) SR

2. Protect life (ozone absorption of UV rays and carbon storage)

3. Balance global temperatures through atmospheric movement (wind)

On a daily basis we can see the importance of atmospheric stability. Examine page 92-93 in

great detail. This graph shows how the atmosphere balances SW and LW Solar radiation. Recall

that the atmosphere reacts to SR in three ways.

1. ABSORBS SR: elements which absorb SR are shown on page 92-93 as clouds (or water

vapor), gases and dust, and ozone. As more particulate matter and clouds accumulate in the

atmosphere, less SW reaches the surface. As you see on page 92, only 45% of all incoming SW

is absorbed by the earth's surface. At night, the presence of such materials may limit LW

escape.

2. SCATTER SR: particles such as dust, pollution, and other elements (chlorine) may scatter

solar radiation, heating the atmosphere. Again, SW may not reach the surface. Scattering does

create the color of our atmosphere (sky), the wavelength of radiant energy most scattered by the

particles in the atmosphere lie in the frequency of blue, visible light. As the declination of the

sun changes with sunset, more of the light in the orange and red frequencies are affected,

creating pretty sunset coloration. The greater amount of particulate matter, we see greater

coloration at sunset (more material to scatter wavelengths). Perhaps smog has one benefit.

3. REFLECT SR: particles in the atmosphere can also reflect solar radiation back to space.

Some surfaces (such as snow) may reflect up to 90 % of incoming SW. See pages 88, 92-93.

Compared to asphalt which may reflect as little as 5% of incoming SR. The term for reflection

by a surface is albedo.

Overall there is a balance between incoming (SW) and outgoing (LW) SR. If too much SW

radiation enters the atmosphere, then we can experience global warming. If we have changed

the Earth by creating the urban heat island, paving the surface with asphalt and pumping the

atmosphere full of pollutants (mostly CO 2), we can the balance between SW and LW. Asphalt

may increase SW absorbed by the surface, as smog limits LW escape. Unlike a greenhouse,

which is a natural imbalance caused by cloud cover (retaining LW), an urban heat island does

not change temperatures temporarily. This imbalance may cause the earth to attempt to

redistribute this heat to the poles creating melting of the polar ice caps, submerging land up to

200 feet in elevation.

B. COMPOSITION OF THE ATMOSPHERE:

The most important elements to understand of the atmosphere's composition are the following:

1. oxygen - 21%

2. nitrogen - 78%

3. carbon dioxide (CO2) - 0.036 % *(for greater details see page 92)

I am not concerned that you understand the homosphere and heterosphere, if you do, that is

great! But, please do not worry about the elevation, depth and all the details listed in the text. I

want you to understand the processes which create this composition (photosynthesis, and carbon

storage), and how this composition is related to the ozone layer (ozone creation).

C. STRUCTURE OF THE ATMOSPHERE:

1. spheres - please examine figure 3-3, page 64. Here you will see a graph of the

atmosphere. I want you to focus upon the temperature structure of the atmosphere,

recognizing the following regions, starting at the earth's surface;

a. troposphere- dominated by the normal lapse rate

b. stratosphere - housing the ozone

c. mesosphere-

d. thermosphere -

The importance of these regions is how they warm and cool the earth. Look at the temperature

characteristics of each region. In the troposphere, the airs cools as it rises in altitude, (this is

called the normal lapse rate) causing clouds and weather phenomena. In the stratosphere, the

temperature rises with increasing altitude (as the ozone absorbs UV rays). In the mesosphere,

the temperature falls with altitude (causing clouds), and again, in the thermosphere, the

temperature rises with increasing altitude (due to the absorption of SR as the solar constant

enters the top of the atmosphere).

The most important spheres to understand are the troposphere and the stratosphere. The

normal lapse rate in the troposphere allows the earth to cool LW radiation released at night.

This allows us to balance SW and LW radiation on a daily basis. Simply remember the ratio: the

troposphere cools by 3.5 degrees Fahrenheit for every 1000 feet in altitude. You have

experienced this yourself, as you drive up into the Sierras. As you reach increasing elevation,

the temperature cools (our way to escape the heat-- a global example is shown on page 114).

On nights when the troposphere is dominated by clouds, the normal lapse rate may become

inverted. A temperature inversion is the name for this situation. What this means is that

instead of cooling with increasing altitude, the atmosphere may warm. Please see page 75.

In Figure 3.8, the top graph shows the normal lapse rate. On the bottom graph it shows a

temperature inversion. During an inversion, heat rises from the surface and begins cooling, yet,

when atmospheric particles (smog, dust) or clouds are present the LW radiation is absorbed and

warms the upper atmosphere. Above such an inversion, there is cool air which often traps the

warmer air below (since cool air sinks), limiting any LW escape.

Two examples of temperature inversions are the greenhouse effect and the urban heat

island.

1. The Greenhouse Effect is the term used to discuss how clouds trap LW radiation, warming

the lower atmosphere. This creates an imbalance of energy (LW>SW). Yet, this phenomenon is

only temporary, within a few days, the clouds dissipate or precipitate, allowing LW radiation to

escape and restoring the balance between SW and LW radiation.

2. The Urban Heat Island is the term used to discuss how clouds trap LW radiation. Also

warming the lower atmosphere, and sometimes changing wind and temperature patterns around

large cities. The key to understanding this phenomenon is to recognize that in urban areas we

have increased the amount of pollution (from autos and industry) and altered the surface to

asphalt and concrete (changing albedo). The pollution limits LW escape, and the asphalt

increases SW absorption. The problem with this inversion is that it may be permanent. Unlike

clouds, smog may not dissipate over time, creating a permanent temperature inversion. This may

lead to global warming on a longterm basis.

D. HOW THE ATMOSPHERE DEVELOPED:

Scholars have estimated the evolution of the atmosphere from ice cores, ocean cores, and other

dating techniques. What is important to understand are the changes that the atmosphere

experienced. Each change (stage) is associated with a process.

1. Primordial Atmosphere - during this stage, the earth had no atmosphere, the surface was

too hot for life, and there was no water collected on the surface (no ability to cool). In

this stage, there was too much CO2, similar to the Greenhouse Effect we see on Venus.

2. Evolutionary Atmosphere - this stage is marked by the process of chemosynthesis.

During this stage, water vapor is released through volcanic eruption (outgassing),

allowing bodies of water to collect. Chemosynthesis is the production of oxygen

through rock decay. As rocks decayed, the composition of the atmosphere began to

change, oxygen was increasing.

3. Living Atmosphere -as the name suggests this is the stage, when the processes which

enable life to exist on the planet are stimulated. In this stage, plant life exists in the

oceans where it is shielded from harmful UV rays. The process of photosynthesis begins

to alter the atmosphere's composition and structure. Photosynthesis is the term used to

address plant respiration and transpiration. Plants take in carbon dioxide (CO2) and

water (H2O), and release oxygen (O2) and water vapor (H2O) --for visuals, see page 9.

Plants then store the carbon as energy (which we eat). Photosynthesis stimulates two key

processes; first it creates an abundance of oxygen in the atmosphere, and secondly, it

initiates carbon storage.

Ozone creation occurs high in the stratosphere as oxygen (O2) molecules and water

vapor (H20) are increasingly present. Incoming SW radiation causes the hydrogen to

split with the oxygen in the water vapor molecule. The hydrogen (H2) escapes to space,

and the extra 0's begin to combine with the O2 molecules (O2 + O = O3), forming ozone.

O3 is the chemical composition of ozone, as you will note on the image on page 66.

Carbon Storage is also a bi-product of photosynthesis. The vast amount of CO2 found in

the primordial and evolutionary atmospheres is reduced through photosynthesis (absorbed

by plants), which then becomes stored in the rock layer as plants decay and sediments

along the ocean floor become lithified (turned into rock). These pockets of decayed

vegetation are known as hydroflurocarbons, which we call petroleum. As they

metamorphisized they become coal, and eventually diamonds.

a. Modern Atmosphere - as the ozone begins to absorb UV rays, and photosynthesis

and carbon storage continue to occur, the composition of the atmosphere becomes

stable. Our current composition (listed above) is the result of these processes. In the

Modern Atmosphere, the atmosphere works as it should; it balances SW and LW

radiation, the ozone protects life, and the atmosphere redistributes energy across the

planet through wind, ocean currents and weather phenomena.

b. Anthropogenic Atmosphere- Take a second to break down the title of this stage; anthro-

means man and genic means made. Therefore, the anthropogenic atmosphere is looking

at the "man-made" atmosphere, or human impact upon the atmosphere. The key is to

evaluate the impact we have had upon the composition, structure and processes of the

atmosphere.

The knowledge that we have regarding the function, composition and structure of the atmosphere

derive from studies of current problems and their effects upon global temperatures (see lecture

3.5). For example, looking at the hole in the ozone (Focus Study 3.1, p.68-69) we can see the

relationship between depletion and increased crop loss, cataracts, skin cancer, and some

immunity diseases in regions with greater amounts of incoming UV rays. The greater amount of

UV rays allowed into the atmosphere may lead to global warming, an imbalance between

shortwave (SW) and longwave (LW) radiation causing the urban heat island, or global

greenhouse effect. Some scholars believe

the earth is balancing these temperatures by moving more deficit energy to the tropics and more

surplus energy to the poles, causing more severe storm patterns through the midlatitudes. This

would explain El Nino, La Nina and the intensity of tornadoes, hurricanes and other snow storms

experienced across North America in the last few years.