Atmosphere Flashcards
describe the changing rainfall pattern as you move inland from Abidjan to Nioro and
suggest reasons for these differences. (8)
The north is very dry with a much wetter south - Nioro with only 305mm, Abidjan with 1390mm (1 (i) mark) This is because Abidjan on the coast is influenced by mT air for most of the year (1 (ii) mark) Nioro, on the other hand, is under the influence of cT air for most of the year brining very low precipitation (1 (ii) mark). Ouagadougou has a clear wet season/dry season regime whereas Abidjan has year round rainfall (1 (i) mark). This is due to the movement of the ITCZ - the ITCZ is an area of low pressure where the trade winds meet (1 (ii) mark). A band of rainfall is created where the two air masses meet pushing the maritime air up, cooling and condensing to form clouds (1 (ii) mark) – meaning very heavy rain under this area. Abidjan has two peaks – June and October- whereas all the other areas have one (1 (i) mark). The twin precipitation peaks can be attributed to the ITCZ moving northwards in the early part of the year and then southwards later in the year (1 (ii) mark) in line with the thermal equator (1 (ii) mark). This also helps explain why Abidjans peak rainfall is in June at 350mm whereas this is later as you move north – August in Nioro (1 (i) mark) – ITCZ is over Tropic of Cancer in about July.
Compare the rainfall patterns across West Africa;
Suggest reasons for variations (10).
Agadez has 200mm rainfall compared, Lagos with 1600mm (1). Agadez has a peak in August, whereas at Lagos there is a higher peak June (1) Agadez has a distinct dry season from October to May whereas Lagos has year round rainfall (1). Lagos has two peaks (June and October) whereas Agadez and Bobo-Dioulasso only have one (1). These variations are due to the tropical airmasses – tropical continental and maritime and the ITCZ -the ITCZ is an area of low pressure where the trade
winds meet (1) A band of rainfall is created where the two air masses meet pushing the maritime air up, cooling and condensing to form clouds (1). It gets drier as you move north due to Lagos on the coast being influenced by mT air for most of the year (1) Agadez, on the other hand, is under the influence of cT air for most of the year brining very low precipitation (1). The twin precipitation peaks in Lagos can be attributed to the ITCZ moving northwards in the early part of the year and then southwards later in the year (1) in line with the thermal equator (1).. Agadez has peak in August as the ITCZ sits along the Tropic of Cancer at this time which is just above Agadez at 22.5 degrees North – Agadez is about 18 degrees north (1)
“Describe and account for the pattern of ocean currents in either the Atlantic Ocean or the Pacific Ocean”
Ocean currents are surface movements of water
In the North Atlantic, they follow circular, clockwise routes.
In the South Atlantic, they follow circular, anti-clockwise routes.
This is because atmospheric circulation cells produce prevailing winds which blow over the surface of the ocean.
As a result, the ocean currents are dragged in the same direction as the prevailing winds i.e. clockwise in North hemisphere, anti-clockwise in the Southern hemisphere.
“Describe and explain the origin, nature and characteristics of the Tropical Maritime and Tropical Continental air masses”
Tropical maritime Originates over Atlantic Ocean in tropical latitudes.
As a result, air is warm, moist and unstable.
Associated weather is hot-very hot and humid.
Tropical continental Originates over Sahara Desert, a large land mass in tropical latitudes.
As a result, air is warm, dry and stable.
Associated weather is very warm, dry weather in winter and extremely hot, dry weather in summer.
Explain why only around 50% of the solar energy reaching the edge of the atmosphere reaches the surface of the Earth (8).
When solar energy reaches the atmosphere – roughly 48% of it is lost. Clouds have a high albedo effect and cause 17% of solar energy to be reflected back upwards (1).
Thick clouds such as cumulonimbius clouds reflect the most (about 90% of insolation reflected) (1).
8% of solar energy reaching atmosphere is scattered as it hits off atmospheric gases and dust (1).
Largest amount lost in atmosphere is absorbed (4% by clouds and 19% by water vapour, gases and dust) (1).
This causes 54% to continue the journey on to Earth. However, 6% is reflected back when it hits the Earth due to albedo effect (1).
Amount absorbed varies throughout the Earth (1).
At the equator, dark forest dominates which is less reflective and causes large amount of absorption (1).
At the poles, the white surfaces of the ice caps are reflective and have a much higher albedo effect (1).
Explain how atmospheric cells and associated surface winds assist in redistributing energy around the world
(8-10 marks)
The equator receives more insolation from the sun because the Earth is fatter and closer to the sun here.
The equator has an energy surplus, while the poles have energy deficit. Atmospheric circulation works to fix this and takes energy polewards.
Hadley
Air is heated at the equator and rises with low pressure, this air then spreads out high in the atmosphere.
When the air reaches the tropics (33ON) it sinks (as it has cooled down) at the high pressure zone.
Surface winds then return the air back to the equator but are deflected to the left because of the Earth’s spinning (coriolis effect)
Polar
At the North Pole (90ON) dense cold air sinks and starts the Polar cell
Surface air is (again) defected due to Earth’s rotation but always travels from areas of high to low pressure
When air reaches 66ON it hits low pressure and rises up into the atmosphere, here it spreads and loops round into the Polar cell.
Ferrel
The Ferrel cell takes energy between Hadely and the Polar cell but is thermally indirect (not affected by differences in heat) and only works to complete the cycle.
These cell movements are mirrored in the southern hemisphere.
Explain why there is a surplus of solar energy in the tropical latitudes and a deficit of solar energy towards the Poles. You may wish to use an annotated diagram or diagrams (8).
The curvature of the earth means that insolation has different size areas to insolate due to sphere shape (1).
Band of insolation near North Pole has to heat a larger area so spread out, while band at equator heats a smaller area so energy is more concentrated (1).
The thickness of atmosphere has an effect, the further away from the equator the more atmosphere the radiation has to penetrate (due to spherical shape of earth) (1) – therefore more lost due to scattering, absorption and reflection in polar regions (1).
Poles have a high albedo due to ice caps being light in colour which means heat is lost as reflected back (1).
Equatorial regions have low albedo due to dark colours of forests which absorb heat (1).
When Earth tilts, angle of the sun’s rays changes throughout the year – at Winter Solstice (21st December), the North Pole is tilted away from sun (no insolation), overhead sun is at Tropic of Capricorn (maximum insolation) (1).
In summer solstice, maximum overhead sun now at Tropic of Cancer – Northern Hemisphere get maximum insolation.
South pole is receiving none at all due to curve of Earth (1).
Tropical areas always receive insolation no matter what time of year as they lie in middle of Earth between Tropic of Cancer and Capricorn (1).
