Atmosphere

Atmosphere

A blanket of gases surrounding Earth, held in place by the force of gravity

What are the three functions of the atmosphere?

• Provides the correct balance of gases to allow us to breathe

• Acts as a filter to remove harmful amounts of solar radiation

• Helps the Earth retain heat to support life and move head around to reduce extreme temperatures at different latitudes

Global heat budget input

Incoming solar radiation (insolation)

Global heat budget output

Terrestrial radiation

Incoming solar radiation (insolation)

Energy from the sun is called insolation or short-wave energy

Terrestrial radiation

Energy emitted from the Earth is long-wave radiation

Global heat budget

The balance between incoming solar radiation and outgoing terrestrial radiation

What three conditions cause reflection in the global heat budget and what is the percentage?

• Clouds: 20%

• Dust and gas particles: 5%

• Albedo effect: 5%

What two conditions cause absorption in the global heat budget and what is the percentage?

• Clouds: 3%

• Dust and gas particles: 17%

What percentage of the global heat budget is absorbed by the Earth’s surface?

50%

What are the two conditions in the atmosphere that contribute to the global heat budget?

Clouds and dust and gas particles

What is the condition on the Earth’s surface that contributes to the global heat budget?

The albedo effect

Differences in insolation

There is a net gain of energy in the tropics and a net loss of energy at the poles

What four things contribute to a net gain of energy at the tropics and a net loss at the poles?

• Albedo effect

• Curvature of the Earth

• Seasonal variation

• Thickness of the atmosphere

Albedo effect

At polar regions, large amounts of snow and ice increase the albedo effect, more insolation is reflected at the poles than from the denser vegetation and oceans at the tropics

Curvature of the Earth

Heat energy is spread over a larger area at the poles, weakening the energy whereas at the tropics the sun’s energy is more concentrated, so the intensity of insolation is greater

Seasonal variation

The tilt of the Earth also changes at different times of the year, so insolation levels vary

Thickness of the atmosphere

The sun’s rays pass through less atmosphere at the equator, therefore less energy is lost through absorption and reflection

Seasonal variation in June

The northern hemisphere tilts towards the sun, meaning more solar energy is released, this creates summer conditions

What are the two ways that energy moves from the equators to the poles?

Atmospheric circulation and ocean currents

Atmospheric circulation

This is the transfer of energy from tropical latitudes where there is a net gain, to polar latitudes where there is a net loss

Air pressure

The weight of the gases in the atmosphere as they press down on the Earth’s surface

Low air pressure

When air is heated, it rises away from the surface which reduces the weight of air pressing down

High air pressure

When air is cold, it sinks towards the surface which increases the weight of the air pressing down

Which areas do air pressures blow from?

Winds always blow from areas of high pressure to low pressure on the Earth’s surface

What are the three weather cells that control the movement of heat?

• Polar cell

• Ferrel cell

• Hadley cell

Characteristics of the hadley cell

• Heat from the sun is concentrated at the equator

• Warm air rises at the equator due to intense heating from the sun, creating low pressure

• As the warm air rises, it cools and sinks over the tropics, creating high pressure

Characteristics of the ferrel cell

• Warm air from the hadley cell feeds into the ferrel cell

• This warmer air then feeds into the polar cell

• This transfers heat from the equator to the poles

Characteristics of the polar cell

• Cold air sinks at the poles, creating high pressure

• Cold polar air is transferred from lower latitudes by surface winds

• Contact with the Earth’s surface causes it to warm and rise

Formation of the ferrel cell

This cell forms as a result of temperature differences between the hadley and polar cells

What are the three parts of atmospheric circulation?

• Part one: air pressure

• Part two: weather cells

• Part three: surface wind patterns

What are the seven latitudes included in the surface wind patterns?

• North pole

• Arctic circle

• Tropic of Cancer

• Equator

• Tropic of Capricorn

• Antarctic circle

• South pole

What are the three surface wind patterns?

• Polar easterlies

• Westerlies

• Trade winds

Polar easterlies

Winds that travel from the poles to 60 degrees north and south

Westerlies

Winds that travel from 30 degrees north and south

Trade winds

Winds that travel from 30 degrees north (northeast trade winds) and south (southeast trade winds) of the equator

Convergence

The point where different winds meet or descend on a low pressure zone

Divergence

The point where different winds move away from the high pressure zones

What are the three points of convergence?

• Arctic circle

• Equator

• Antarctic circle

What are the four points of divergence?

• North pole

• Tropic of Cancer

• Tropic of Capricorn

• South pole

Rossby waves (jet streams)

Wave-like patterns found in the westerlies that form as a result of temperature and pressure differences that can assist in energy transfer

Landmass deflection

The shape and height of the land can disrupt winds

How do rossby waves assist in energy transfer?

As they loop southwards, cold air is transferred to lower latitudes, and as they loop northwards, warm air is transferred to higher latitudes

Surface wind patterns

Ocean currents

This is the permanent or continuous movement of oceanwater from one place to another

How do ocean currents transfer energy?

They can flow for thousands of km and can result in warm water being transferred to high latitudes (the poles) to cool water being transferred to low latitudes (the equator and tropics)

What is the purpose of ocean currents?

To warm up the poles and cool down the equator and tropics

What are the two types of ocean currents?

Cold currents and warm currents

Characteristics of cold currents

• Flow from the poles towards the equator

• Carry cold water (relative to the surrounding water)

• They act to lower the temperatures of coastal areas

Characteristics of warm currents

• Flow from the equator to the poles

• Carry warm water (relative to the surrounding water)

• They raise the temperatures of coastal areas making them warmer than would be expected for their latitude

Named example: cold currents

Labrador current

Named example: warm currents

North Atlantic drift

Pattern of ocean currents

What are the five things that affect the movement of ocean currents?

• Prevailing winds

• Coriolis effect

• Water density

• Gyres

• Thermohaline circulation

Prevailing winds

Ocean currents are greatly influenced by the prevailing winds, energy is transferred by friction

Coriolis effect

This deflects currents to the right in northern latitudes and to the left in southern latitudes

Water density

Cold water is denser than warm water, so the cold water sinks away from the poles towards warmer regions

Gyres

The currents are obstructed by continental land masses, forming gyres as the currents loop

Thermohaline circulation

Colder water and that with a higher salt content is much denser than warmer waters with a lower salt content

Case study: ocean currents

The North Atlantic

What are the six currents in the North Atlantic?

• North Equatorial Current

• Warm current- Gulf Stream

• North Atlantic Drift

• Warm current- North Atlantic Drift

• Cold current- Labrador Current

• Cold current- Canaries Current

Inter-tropical convergence zone

This is where the tropical continental and tropical maritime airmasses converge, bringing rising air from the tropics to the equator which results in low pressure

What kind of weather does low pressure bring?

Cloudy and windy weather with possible rain and/or storms

What kind of weather does high pressure bring?

Light winds and settled weather

Air mass

This is a large volume of rising air with the same humidity and temperature, bringing clouds, frequent thunderstorms, and heavy rainfall due to the low pressure

Air mass: polar and tropical

Polar refers to polar latitudes and tropical refers to tropical latitudes

Air mass: continental and maritime

Continental refers to air from across land and maritime refers to air from across the sea

What are the two air masses that influence the weather in Africa?

Tropical continental and tropical maritime

What kind of weather does tropical continental bring?

Brings extremely warm temperatures, dry stable air with no clouds or rainfall from the Sahara desert

What kind of weather does tropical maritime bring?

Brings humid, unstable air causing rainfall and thunderstorms from the Gulf of Guinea

Migrating ITCZ

As the Earth’s tilt changes throughout the year so does the thermal equator along Africa

Migrating ITCZ in June

In July, the sun is directly over the Tropic of Cancer, causing the ITCZ to migrate northwards, which brings the wet season from the tropical maritime air mass

Migrating ITCZ in January

In January, the sun is directly over the Tropic of Capricorn, causing the ITCZ to migrate southwards, which brings the dry season from the tropical continental air mass

Climate graphs

This displays the levels of precipitation and temperature in a country during the dry and wet seasons