Atmosphere Flashcards
- 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.
Sun’s angle in the sky decreases towards the poles due to the curvature of the Earth, which spreads heat energy over a larger surface area. (1 mark) Sun’s rays are concentrated on tropical latitudes as the intensity of insolation is greatest where rays strike vertically. (1 mark) Sun’s rays have less atmosphere to pass through at the tropics, so less energy is lost through absorption and reflection by clouds, gas and dust. (1 mark) Albedo rates differ from the darker forest surfaces at the tropics absorbing radiation, in contrast to the ice-/snow-covered polar areas reflecting radiation. (1 mark) Tilt of the axis results in the Sun being higher in the sky between the tropics throughout the year, focusing energy. (1 mark) No solar insolation at the winter solstices at the poles producing 24-hour darkness, whereas the tropics receive insolation throughout the year. (1 mark)
- Analyse the impact of the ITCZ on the rainfall pattern in West Africa.
The movement of the ITCZ is connected to the arrival of seasonal rains in West Africa. A surplus of energy leads to the warming of air near the equator. This air becomes less dense and rises. At the ITCZ, warm air rises and condenses, forming tall clouds with associated rainfall. Maximum monthly rainfall is associated with the ITCZ being overhead. The ITCZ moves north during the summer months bringing rain with it. As a result, places to the south of the ITCZ come under the influence of the tropical maritime air mass. This brings hot and humid conditions for longer periods of the year. In the southern part of West Africa, total annual rainfall is higher due to the presence of this air mass. Two peaks of rainfall are common nearer the coast of West Africa due to the movement north of the ITCZ in the summer and the return of the ITCZ en route to the equator in the winter. In the northern part of the region, total annual rainfall is significantly lower. Here a long dry season dominates because of the tropical continental air mass, which brings hot and dry conditions.
- Explain how atmospheric circulation cells and the associated surface winds assist in redistributing energy around the world.
Warm air rises at the Equator and travels in the upper atmosphere to around 300 N and S, cools and sinks (1 mark). Air moves from the tropical high to the low pressure area at the equator creating the Hadley cell/Trade Winds (1 mark) Cold air sinking at the poles moves to 60oN/S to form the Polar Cell/Polar Easterlies (1 mark). The cold air from the poles meets warmer air from the tropics, causing air to rise creating the Ferrel Cell low pressure. (1 mark) Air is moved from the tropical HP, towards LP at the polar front, forming the westerlies (1 mark) This convergence causes the air to rise, with some of this flowing in the upper atmosphere to the Poles where it sinks, forming the Polar cell. Easterly winds blow away from the high pressure at the Pole. (1 mark). Warm air from the Equator is distributed to higher and cooler latitudes and cold air from the Poles distributed to lower and warmer latitudes (1 mark). Due to the Coriolis effect winds are deflected to the right in the northern hemisphere (1 mark).
