Atmosphere Flashcards
Global heat budget
Insolation is solar radiation received in the earths atmosphere or at its surface. Energy emitted from the sun is short wave radiation.
From 100% of the energy from the sun, around 20% is absorbed by the atmosphere which 17% absorbed by atmospheric dust, gas and water vapour while the other 3% is absorbed by dark clouds. Another 5% of energy from the sun is scattered by dust and dust.
Another 20% of the suns energy is reflected back up by white clouds. Reflection is known as the albedo effect which is the ability for surfaces to reflect sunlight. Reflected heat is long wave radiation which gets trapped in our atmosphere, keeping it warm. This is known as the natural greenhouse effect.
55% of the suns energy makes it down to earth. 5% is reflected back up by shiny white surfaces such as snow and ice at the poles and the remaining 50% is absorbed by dark surfaces such as tropical rainforests or deep oceans.
Global insolation
There is an energy surplus at the equator making it warmer, and an energy deficit at the poles, making it colder.
One reason for this is that the suns energy has more atmosphere to travel through to reach the poles. This means there is more chance of reflection and absorption by dust, gases and clouds so less heat reaches the surfaces at the poles.
Because of the earth curvature, the suns energy is more concentrated at the equator but the same amount of energy is spread over a wider surface area at the poles so it is cooler.
The angle of incidence which is the angle sunlight hits the earths surface, is greater at the poles (120°) than the equator (90°) so the energy is more spread out.
Due to the earths orbit around the sun, both north and south poles spend part of the year tilted away from the sun and so receive less overall making it cooler. The sun is always overhead and high in the sky between the tropics so this region receives the suns energy all year round making it hotter.
At the equator, there is lots of green vegetation at rainforests which absorbs energy due to low albedo. There is a high albedo at the poles due to lots of snow an ice which means more energy is reflected back making it cooler.
How does the earths atmosphere redistribute its energy
Atmospheric circulation
Ocean currents
Explain Ferrels 3 cell model of atmospheric circulation
Warm air rises at the equator creating an area of low pressure at the surface. As it rises it cools and splits to the north and south. As the air moves away from the equator, it further cools and sinks back to the earth at 30° north and south creating an area of high pressure at the surface completing the Hadley cell.
At 60° north and south, warmer air coming from the equator is forced up over cooler air coming from the direction of the poles. This again creates an area of low pressure at the surface. As the air rises and cools it splits. Air heading back towards the equator completes the Ferrell cell.
The air which travels towards the poles cools further and sinks at 90° north and south creating an area of high pressure at the surface. Air then flows from high pressure at 90° to low pressure at 60°, thus completing the polar cell.
This sets up a pattern of global surface winds as air always flows from high pressure to low pressure areas. Because of the earth rotation (The Coriolis Force), these are always deflected to the right in the northern hemisphere and to the left in the southern hemisphere. These are known as trade winds.
Describe the pattern of ocean currents
Ocean currents move to the west at the equator
They circulate in loops known as gyres
They go clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere
They take warm water to cooler areas and cool water to warm areas for example the Gulf Stream
Cooler water is denser than warmer water
The saltier the water is the denser it is
Explain ocean circulation
At the equator, water moves to the west. This is because of the Coriolis force which causes deflection, and the resultant global winds which push water to the west by frictional drag. This is aided by the fact that this area has the most intense heating and so convection currents are sun up within the water.
For example the north equatorial current in the Atlantic Ocean.
When these currents reach land they are deflected to the north and south, thus transferring warmer water from the equator towards the poles. For example the Gulf Stream.
At around 30° north and south of the equator, the currents are pulled eastwards again as they are caught in the next band of global winds such as the North Atlantic drift.
These are then deflected off the land again. Some of the water is deflected back towards the equator again for example the canary current, thus completing a large circulation cell known as a gyre.
These circulate clockwise in the northern hemisphere and anti-clockwise in the south. They bring warmer water to cooler areas and cooler water to warmer areas which helps to balance out the surplus and deficit of energy due to global insolation. The colder currents are dense so move at lower levels and the warmer currents are nearer the surface.
Characteristics of tropical maritime (TM) and tropical continental (TC)
The TM and TC air masses meet at a band called the ITCZ (inter tropical convergence zone).
They bring weather from their source area. The TC and TM are both hot because they are both areas of greatest insolation. The TC is also dry because it travels over land so doesn’t pick up any moisture but the TM travels over water so does pick up moisture (rain).
The TM originates in the Atlantic Ocean and is an unstable and humid air mass. The TC originates in the Sahara desert and is a stable air mass. It also creates the harmattan winds.
Along the ITCZ it is rainy as the air rises up when the two air masses meet and creates a band of low pressure (equatorial low).
The ITCZ moves with the overhead sun.
Impacts of the ITCZ on Western Africa on places that receive rainfall
- Provides water for agriculture. Provides people with food as well as farmers with money if they sell crops
- rivers may flood allowing alluvium to be deposited on food plains. Improves soil fertility and crop growth
- water can be stored for farming and drinking which can be used through dry seasons
- in rural areas and shanty towns, open sewers can flood increasing the risk of diseases eg cholera
- tracks can become muddy making them impassable making things like communication and trade more difficult
- heavy rain on dry soils can lead to soil erosion or top soil being washed away which is important crop growth so can impact food supply
- heavy rain can also leach nutrients out of soils which can also impact crop growth
- rain allows plants and bushes to flourish which can provide feed for animals as well as fruit etc for locals to eat
Impacts of the ITCZ on Western Africa in places that don’t receive any rainfall (ITZC doesn’t reach north enough)
- farming systems cannot operate properly as nothing will grow without rain so no crops for food, farmers income or trade
- famine starvation and lack of water can weaken people and also make them more susceptible to other diseases
- these in turn may encourage rural to urban migration putting pressure on these areas
- also any desertification impact
The seasonal movement of the ITCZ and its impact on rainfall in Western Africa
The ITCZ and its associated air masses (TM and TC) move north and south with the overhead sun. The ITCZ is furthest south in December and January and migrates to its most northerly point in June or July, moving the air masses with it.
In December and January, the ITCZ is north of town A brining rainfall. Town A is under the influence of the TM winds all year round so it is always a warm and wet climate (hence it has rainforests).
As the ITCZ and TM air masses move north, this brings wet weather with it to towns directly below or south of the ITCZ as it goes. Towns to the north of the ITCZ will experience the TC air mass so will be hot and dry.
By the time we get to June or July, only town D will be dry as it is never under u Dee the influence of the TM air mass, as the ITCZ doesn’t reach that far north so it is a hot desert area.
The ITCZ then heads south again after December or January and the rainy season ends for each town. The further north a town is, the shorter the rainy season as it spends less time under the influence of the TM air mass.
