1. To learn about the composition of the atmosphere and the significance of the gases in the atmosphere.

2. To learn about the causes and patterns of air movement in the atmosphere.

3. To understand the Coriolis effect and its influence on the movement of both air and water parcels.

4. To understand how the atmosphere and ocean interact with each other. Some examples include the sea breeze, monsoons, hurricanes, and El Nino.

Important concepts

1. The solid earth is blanketed by two fluid bodies, the atmosphere surrounding the globe and the oceans covering most of its surface.

- Both the atmosphere and the oceans behave like fluids and are constantly in motion as the result of gravity acting on air and water masses having different densities.

- Incoming short wavelength solar radiation penetrates the atmosphere easily to warm the earth's surface, which in turn warms the atmosphere.

- Excess heat gained by the earth in equatorial regions is transferred to higher latitudes by winds and ocean currents to moderate the climate.

2. Density differences in the atmosphere lead to pressure differences at the surface.

- Atmospheric pressure is a measure of the force pressing down on the earth's surface by the overlying air.

- Low air density results in rising air and low surface pressure.

- High air density results in descending air and high surface pressure.

3. The rotation of the earth coupled with negligible friction between the atmosphere and the earth results in an apparent deflection in the path of moving parcels of air when they are viewed from the surface of the globe (Coriolis effect).

- Points on the surface of the earth rotate eastward at a speed that depends on latitude. This speed is roughly 1700 km/hr at the equator, 1450 km/hr at 30=F8N and S, 850 km/hr at 60=F8N and S, and zero at the poles.

- An air mass that appears stationary at one latitude will be moving eastward with the rotating earth at a velocity equal to the rotational velocity of the earth's surface at that latitude.

- If the air mass then moves closer to the equator, it will move over points on the surface that have a higher eastward velocity than it does. Consequently, to an observer on the surface, the air mass will appear to lag behind the eastward rotation of the planet, or it will appear to be moving westward.

- The Coriolis effect reaches a maximum at the poles and decreases to zero at the equator when the direction of the apparent deflection reverses itself from one hemisphere to the other.

4. With the earth's rotation and subsequent action of the Coriolis effect, atmospheric circulation consists of three convection cells.

- The three circulation cells in each hemisphere occur between bands of latitude 30=F8 wide from 0 - 30, 30 - 60, and 60 - 90 degrees N and S.

- At the equator and 60=F8N and S latitude rising air creates belts of low pressure with cloud cover and frequent precipitation.

- At 30=F8 and 90=F8N and S latitude descending air creates belts of high pressure with generally clear skies and little precipitation.

- From 30=F8 to 60=F8N and S surface winds move towards the poles to produce the westerlies.

- From 60=F8 to 90=F8N and S the surface winds blow away from the poles to create the polar easterlies.

- From the equator to 30oN and S winds move from the east and toward the equator. These are the trade winds.

5. To approximate the real earth even more closely, we need to consider the effects of seasonal changes in the earth's surface temperature and the presence of large landmasses interrupting a water-covered planet.

- Middle latitudes experience large seasonal changes in surface temperature, particularly over land which has a relatively low heat capacity and will gain or lose heat rapidly.

- Water's high heat capacity and its great mobility combine to minimize the variation of temperature in the oceans.

- In the northern hemisphere there is a nearly equal area of land and water on the surface. This produces distinct patterns of high and low atmospheric pressure that change with the seasons.

- Atmospheric circulation in the northern hemisphere is clockwise around high-pressure cells and counterclockwise around low pressure low pressure cells. In the southern hemisphere this is reversed.

- Hurricanes can form over the ocean when disturbances in the tropical easterly winds lead to intensification of low-pressure systems.

6. Large seasonal temperature variations over land can produce major climatic changes in coastal regions. One example of this is the monsoon effect.

- During summer months a large low-pressure system forms over India and Southeast Asia in response to the heating of the land. Counterclockwise air flow around this system carries warm, moist air from the Indian Ocean over the continent where the moisture condenses as the air rises and cools. This results in a steady, heavy rain over the land that is referred to as the wet or summer monsoon.

- During winter months the loss of heat from the land will cool the overlying air, producing a high-pressure system over the continent. Clockwise circulation around this system carries cool, dry air from the interior of the continent over the coastal regions. This is the dry, or winter, monsoon.

7. Daily temperature variations over land can produce small-scale weather changes in coastal regions.

- The land will heat up faster during the day than the adjacent water. This will cause rising air over the land that will be replaced by air blowing onshore from the ocean. This is the onshore or sea breeze. It is usually strongest in the afternoon when the temperature difference between the land and the water is greatest.

- At night the land will cool off more rapidly and air will sink over the land and blow offshore out to sea. This is the offshore or land breeze. It is usually strongest in the late night and early morning hours.

8. The prevailing southeast trade winds that create the nearly permanent zone of divergence and upwelling along the west coast of South America occasionally fail and the upwelling ceases. This situation is called the El Nino and is characterized by abnormally high sea surface temperatures in the eastern Pacific. The El Nino is often followed by abnormally cold periods call La Nina which can also affect atmospheric circulation strongly.

- Along the western coast of South America off Ecuador and Peru, the southeast trade winds drive water away from the land creating a nearly constant region of divergence with upwelling water rich in nutrients. These cold waters are extremely productive with dense populations of plankton that support a large and valuable food chain.

- Periodically, the trade winds break down and the divergence stops.

- The increase in surface temperature of the water along the coasts of Ecuador and Peru can be as great as 7=F8C and may last for a period of months, or in extreme cases, for over a year.

- The El Nino typically appears near Christmas and lessens by mid-summer.