Ocean currents
-At the equator, water moves towards the west
- this is because of the coriolis force. This is the force that causes deflection in the winds and the Renault ant global winds which pushes water to the west by frictional drag
- this is aided by the fact that this area has the most intense heating and so the convection currents are set up within the water
- examples in the Atlantic Ocean are the north and south equation along currents
- when these currents reach land such as North America, they are deflected to the north and south
- thus transferring warmer water from the equator towards the poles.
-eg of these currents could be the Gulf Stream
- at around 30 degrees N+S of the equator, the currents are pulled eastwards again
As they are caught up in the next bands of global winds eg North Atlantic drift
- they are then deflected of the land again and some of the water is deflected back towards the water again
- thus completing a large circulation cell or gyre
- these circulate clockwise in the northern hemisphere and anticlockwise in the south
They bring warmer water to cooler areas and vies versa, thus helping balance the surplus and deficit due to global isolation
The colder currents are denser and so move out at lower levels. Warmer currents are nearer the surface
- What is atmospheric circulation
Ferrell 3 cell model
Whats the ICTZ movement and impact on Western Africa
The ITCZ and its associated winds (TMand TC) move north and south with the overhead sun
The ictz is furthest south in December and migrates ro its most northerly position in June.
The tc and Tm air masses move with it in Dec/ Jan and the area its overhead will experience rainfall
As the ictz moves north, the tm winds are pulled further south, bringing wet weather to places which are south of the ictz
Places to the north of the ictz are still under the influence of the TC so are hot and dry
This means that towns recieve rain for a spell of the summer, known as seasonal rainfall- the rainy seasons get shorter the further north you go
Sometimes places will have 2 peaks of rainfall, this could be when the ICTZ moves over on its way north and south again
Whats the ITCZ
Inter tropical convergence zone
Describe the ITCZ
The thermal equator
Rainy water as air rises where 2 wind bands reach
tropical continental
It’s very hot and dry
Not as high levels of insolatiom
Dry as comes over land eg Sahara
Low humidity- 10-17%
Tropical marine
Warm and wet
War as area of greater insoaltion
-unstable air mass- changeable weather
define ferrels 3 cell model -
atmospheric circulation
what is atmospheric circualtion
-warm air rises at the equator. as it rises it cools and splits to the north and south and an area of low pressure is created at the surface
- as the air moves away from the equator it cools further and sinks back to the earth at 30 degrees north and south, creating an area of high pressure at the surface. thus completing the hadley cell
at 60 degrees north and south, warm air coming from the direction of the quator meets the cooler air coming from the poles
this warm air is forces up creating an area of low pressure at the surface. again, this air rises and splits. some heads back towards the equator, completing the ferrel cell
this is when air heads towards the poles and cools further and sinks back to eart, creating high pressure at the surface. this air then flows from high to low at the surface, thus completing the polar cell. this assists in the redistriubution of solar energy
this sets up t pattern of global surface winds as air flows from high to low pressure areas. because of the earths rotation, these winds are deflected to the right in the north hemisphere and to the left in the southern. this is known as the corrolis force. also known as trade winds
Global insolation
It is warmer in the tropics and colder in the poles because the sun has more atmosphere to travel through to reach the poles. This means there is more chance of deflection because of dust, gasses etc. so less reaches the poles
- the angle of incidence is greater at the poles 120 Degrees compared to the equator 90 degrees
- because of earth, the suns energy is more concentrated at the equator. The same amount of energy is spread over a wider area at the poles
- at the equator we have more green vegetation which absorbs the suns energy, making it warmer. At the poles white ice and snow reflect energy through the albedo effect so its cooler
- due to the earths orbit around the sun, north the north and south hemisphere spend parts of the year tilted away from the sun so recieve less energy. The sun is always overhead in the tropics so they recieve energy all year round making it warmer.
Global heat budget
Earth absorbs 50% of the solar energy is because 20% is reflected back from the albedo effect which is when surfaces reflect sunlight , and they get reflected back into the atmosphere by white clouds
Another 20% is absorbed by the atmosphere by having 3% absorbed by dark colours and a further 17% by atmospheric dust and vapours. 5% of solar energy is reflected back into the atmosphere by light surfaces on earth such as snow and ice
The earth then recieved 50% which is primarily absorbed by dark surfaces such as rainforests and deep oceans
