LECTURE                              AIR CYCLE
The temperature of air changes in a zig-zag fashion in various layers. 
For global circulation and "weather" only the troposphere is important.

CIRCULATION OF AIR - hot air rises

- thermals are rising columns of air
- heated air cools as it hits higher elevations of the atmosphere
- Warm air is less dense than cold air and therefore warm air rises and cool air sinks.

- When air rises it creates a vacuum or an area of low pressure
- this sucks in new, cooler air at ground level to take its place.
- OTOH, when cold  air sinks it allows new, hotter air to flows in at a higher level.
- these two patterns form a complete convection path, rising, flowing at high level, sinking, and returning at low level.

– This can take place within a room or over a large portion of the earth.

– The earth is warmed most by the sun at the equator and cooled, by radiation into space, at the poles.  This causes the air to rise at the equator and sink at the poles.

–  If the earth were not rotating, there would be a flow of air from the poles to the equator at ground level and from the equator to the poles at high altitudes. The air is less dense and this creates a vacuum. The air at ground level moves in. 

Hot rising columns of air is always seen at the equator.  Here is an example of hot rising air in Wisconsin or Michigan.  The rising hot air sets up the condition where the cooler air over water moves inland. 

Hot air rises over land, sheer cliffs and bluffs.  These "thermals" are used by gliding birds, gliding type airplanes and hang gliders. 


CIRCULATION OF AIR -  the rotation of the Earth causes winds

– The earth is warmed by the sun at highest intensity at the equator and cooled, by radiation into space, most at the poles.  This causes the air to rise at the equator and sink at the poles.

–  If the earth were not rotating, there would be a flow of air from the poles to the equator at ground level and from the equator to the poles at high altitudes. The air is less dense and this creates a vacuum. The air at ground level moves in. 

Go HERE, read and answer the 3 questions



- Objects that are not attached to the Earth, like the molecules of air, do not move at the same speed as the rest of the Earth. 
- Because air is also rising or falling, it deflects or twists right or left. 
- This deflection is felt as winds 
- This also causes the single large thermal cell to break into smaller cells of rising and falling air
- This is the Coriolis effect

Objects at the equator move faster than those at the pole.
EQUATOR: 1000 mph
next    800 mph
next 600
poles... 0

Because of the Coriolis force:
-- air flowing toward the equator curves toward the west producing an easterly wind (west toward east) while air flowing toward the poles curves toward the east producing a westerly wind (east toward west).
-- this causes the flow pattern to break into cells.
–  Instead of flowing all the way between the equator and the poles, the air sinks at latitude 30^0 and rises at latitude 60^0 producing three cells in each hemisphere.
–in the northern hemisphere this produces
northeasterly winds (the northeast trade winds) between the equator and 30^0 north latitude.
–  northwesterly winds between 30^0 and 60^0 north latitude,
– northeasterly winds between 60^0 north latitude and the poles.
– the same is true in the south, except reversed
"Low pressure systems are generally very warm due to the fact the warm air rises making the system it is on having low pressure. This is generally the reason for storms and Tropical cyclones."
"High pressure systems occur often when there is an uneven heating of the ground, causing the hot air to rise and spread out. This rising air creates an air 'void', or a low-pressure system in the area above the ground. However, when the air cools and sinks back down to the ground, a high-pressure system is created. High pressure systems are associated with clear, cool weather."
- Where the air is mainly rising or falling, near the equator, 0o, 30o, 60o, and the poles, the winds are light and variable.
– sailing ships the region near the equator, 0o, was called the doldrums and the regions near 30o north and south latitude were called the horse latitudes.
- sailing ships must take wind direction and still air areas into account
-- story.  standing dead trees at 30o, 60o
- The belt of rising air near the equator is a region of heavy rainfall and the land is heavily forested. The picture at right shows rain forest. 

- The belts of sinking air near 30o north and 30o south latitudes produce the belts of desert that are found on either side of the rain forests.  Picture at right shows deserts. 

- local climate is strongly affected by local continental features.
- where winds "go east" like in the US,  high mountains force moist air up where it cools and drops rain so the coastal area is wet
- dry air coming back down the eastern slopes of produce the deserts and dry plains
– the  eastern US is affected by air flowing up from the Gulf of Mexico and south from northern Canada.

"Warm, humid air flows from over the Pacific Ocean east across the mountains of the western USA.  As the wind pushes the air over the mountains, it cools and much of the humidity in it condenses to form clouds, rain and snow that fall on the western slopes of the mountains.
The cooled, and now much drier, air continues its journey across the mountains to flow down the eastern slopes, when conditions are right.
As the air flows down the mountains, it warms at the rate of about 5.5 degrees Fahrenheit per 1,000 feet of descent. By the time the air reaches the western Plains, it has warmed up significantly, and is also very dry.
The warm, dry winds blowing down the mountains often quickly evaporate snow on the ground, which is why local forecasters refer to down slope winds off the Rockies as "Chinook" winds, which literally means snow eater." http://www.usatoday.com/weather/wdnslope.htm

Oxygen is extremely abundant, but because it is so reactive in wanting electrons it is not usually found "free".  Most oxygen is bound in mineral combinations or with hydrogen to make water. 

Earth did not have much free oxygen until the evolution of cyanobacteria resulted in photosynthesis with the release of oxygen. Free oxygen also made the ozone layer (O3) possible which blocks UV and is protecting of life.  All living things need oxygen except some archea bacteria and those like nitrogen fixing bacteria and those are poisoned by oxygen. 

The main role of free oxygen in biologic systems is in respiration where it combines with hydrogen to make water.  And water is split during photosynthesis to release free oxygen. Oxygen is found in all nearly all organic molecules. 

CO2 was the most abundant molecule in the air when Earth began. It is still the most abundant on Mars and Venus.  But the removal and sequestration of CO2 by biological systems in buried organic material is strong proof of the GAIA theory. 

When organic matter is completely broken down in the presence of oxygen the result is CO2 and H2O.  But during the course of the evolution of the Earth much of the organic matter was NOT completely broken down and instead became buried by rock sediments and encased.  Organic material in oceans became oil, organic material buried on land became coal.  The bottom of any pond and many swamps similarly do not have enough oxygen and organic matter is still being buried. "In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column." 

In addition to burying CO2 as organic material marine and fresh water creatures combine the carbonate with calcium to make limestone.  There are inorganic ways that CO2 was turned into limestone as well.  Acid rain, however, releases CO2 from limestone. 

Nitrogen is chemically very inert and unreactive.  It is an essential element of DNA, RNA and proteins.  Nitrogen is the key element in fertilizers.  Although it is highly abundant in the air it is in its elemental form which cannot be used until it has been converted into an ionic form by, for example, nitrogen fixing bacteria or lightning.  Nitrogen fixing bacteria are poisoned by oxygen so some plants have evolved "nodules" where these bacteria can live without oxygen, where they are "fed" and produce fixed nitrogen. 

A lot of energy is used to produce ammonia type fertilizers from nitrogen deposits.  "The Haber Bosch Process (or Haber Process) is probably the most important chemical reaction in the world today. Approximately 1% of all of the energy used in the world today goes into making this one reaction happen!
The reaction occurring in the Haber Bosch process is in fact a very simple one: hydrogen gas (H2) and nitrogen gas (N2) are combined to form ammonia (NH3):
3H2 + N2 ---> 2NH3
This is typically done a high temperature and under very high pressures. "

Genetically engineering nitrogen fixation into crop plants that dont have them, like corn, is undoubtedly in the works. 

Review questions:

Draw a picture and discuss the  circulation of the atmosphere for a single cell at the equator.  How does this circulation affect climate and rainfall in the adjacent areas?  What drives this circulation?
What is the coriolis force, what causes the coriolis force, how does it change the single cell model of air circulation?
Discuss the winds and climate at the equator.
What happens to air flow at the  Doldrums and Horse latitudes?
What causes high pressure systems?  What causes low pressure systems?
What causes belts of desert that surround the earth at certain latitudes?
Discuss how local continental features affect weather/climate using the west and east side of the Rocky Mountains as an example.