6.1 Introduction to the Atmosphere

composition of the atmosphere

nitrogen - 78%
oxygen - 21%
argon - 0.9%
carbon dioxide - 0.04%
water vapour ~0-2%

carbon dioxide necessity

• photosynthesis - plants need CO2 to make oxygen in order to survive

• greenhouse effect - traps heat within the atmosphere, warming earth

oxygen necessity

• respiration - in order for all living organisms to live

• combustion - without oxygen, combustion and burning would not be able to take place

nitrogen necessity

• rapid burning - prevents rapid burning at the earths surface through diluting oxygen

• nutrients - provides living organisms with nutrients in order to grow and survive

atmospheric stratification

the formation of distinct layers in the atmosphere based on temperature, density, and composition changes at different altitudes

atmospheric layers

• troposphere - lowest layer, weather (clouds, precipitation, and gas mixing) occur here

• stratosphere - 10 to 50km, contains the ozone layer which absorbs and blocks most UV radiation from the sun

• mesosphere - 50 to 80km, coldest layer, highest clouds appear here.

• thermosphere - 80 to 700km, hot due to direct solar radiation, low gas density

• exosphere - 700 to 1,000km, outermost boundary, air thins out.

importance of the inner layers (troposphere and stratosphere)

• regulates climate and supports life on earth

• in the troposphere, chemical reactions occur that impact air quality and climate

• in the stratosphere, chemical reactions involving ozone maintain the ozone layer and protect living organisms from UV

differential heating

the uneven absorption of solar radiation across the Earth's surface, primarily caused by the planet's curved, spherical shape.

earths energy budget

the balance between the energy Earth receives from the Sun and the energy it radiates back into space. most energy comes from solar radiation and some of that is reflected from earths surface (albedo), the rest is absorbed and turned into heat. earth also releases the absorbed energy back into space.

differential heating explanation

The equator receives more direct sunlight because the sun's rays hit it at a high angle, concentrating the energy in a small area.

The poles are curved surfaces, so the sun's rays hit the same amount of energy spread over a larger area

tri-cellular model

Earth redistributes heat from the equator to the poles using three distinct thermal and dynamic circulation cells in each hemisphere: the Hadley, Ferrel, and Polar cells which are all pressure cells. In these pressure cells, hot air rises and cooler air sinks through the process of convection

Hadley cells - Warm air rises at the equator to form a low-pressure belt with heavy rain. Air cools and sinks at 30° latitude to create high-pressure zones and dry deserts.

Ferrel cells - Surface air moves poleward from 30° high pressure to 60° low pressure, deflected by the Coriolis effect into westerlies. Warm and cold air masses clash here, creating unstable weather.

Polar cells - Cold, dense air sinks at the poles to create high pressure. Surface air flows toward 60° latitude, warming and rising at the polar low-pressure belt. Upper-level air returns to the pole and sinks.

wind formation

Air always moves from areas of higher pressure to lower pressure and this movement of air generates wind. This pressure difference is because the Sun heats the Earth's surface unevenly

pressure cell distribution

• as the sun heats the earths surface, air expands and begins to rise, and surface pressure lowers

• the air risen increases atmospheric pressure, making it denser

• because its denser, it sinks, lowering the atmospheric pressure

• once it sinks the surface pressure rises again

• this process repeats over and over again

influence on terrestrial biomes

Near the equator, rising warm air leads to high rainfall and high temperatures

• This creates tropical rainforests and savannas (within the Hadley cell)

Mid-latitudes experience varying weather because of warm and cold air, resulting in temperate climates with moderate precipitation

• This creates temperate forests and grasslands

High latitudes, influenced by descending cold air, have low temperatures and limited precipitation

• This creates polar deserts and tundra