Atmosphere Flashcards
describe how the sun effects tropical latitudes
opical Latitudes
• Due to the curve of the Earth the sun’s rays are concentrated on a much smaller surface area over the tropical latitudes, resulting in more energy.
• The intensity of insolation is greatest on the equator because the angle of the sun is higher, at close to 900.
• The Sun’s rays are more concentrated, as the midday Sun is high in the sky throughout the year.
• Rays have less atmosphere to pass through at the Tropics so less energy is lost through absorption and reflection.
• The darker forested areas and dense vegetation in the Tropics absorb radiation so albedo is lower
describe how the sun effects polar latitudes
Due to the curve of the earth, the sun’s angle of insolation is lower at the poles so the rays of energy are spread out over a much larger area and are therefore less intense.
• The sunlight travels at an angle and so through more distance of atmosphere, which means less energy reaches the surface of polar regions.
• Lighter snow/ice covered areas at the poles reflect more radiation and so polar regions have a higher albedo.
• Due to the tilt of the Earth there is no insolation at the poles during the winter solstices/tropical areas receive insolation all year round.
describe the redistribution of energy
• Energy is transferred from lower latitude energy surplus areas to higher latitude energy deficit areas by atmospheric circulation.
• Warm air rises at the Equator to a height of 18 kilometres and travels in the upper atmosphere to around 300 N and S towards the poles, forming the westerlies.
• The air gradually cools and sinks to the surface, flowing back to the equator.
• Air moves from the tropical high to the low pressure area at the equator creating the Hadley Cell/Trade Winds.
• Some of the rising air from the Equator travels in the upper atmosphere to the Poles where it sinks, forming the Polar cell.
• Cold air sinking in the polar region moves to 600N/S to form the Polar Cell/Polar Easterlies.
• The cold air from the poles meets warmer air from the tropics, causing air to rise creating the Ferrel Cell.
• The Ferrel Cells, which unlike the other cells, are not driven by temperature and they flow in the opposite direction to Hadley and Polar cells.
• Overall, warm air from the Equator is distributed to higher and cooler latitudes and cold air from the Poles distributed to lower and warmer latitudes.
• If there was no atmospheric circulation, lower latitudes would get hotter and hotter and higher latitudes colder and colder.
describe the oceanic circulation
Energy is moved from areas of surplus to those of deficit.
• Warm currents transport warm water in the direction of the poles and cold currents transport colder water to lower latitudes.
• Overall, ocean currents transfer about 25 per cent of the Earth’s global heat budget.
• The pattern of current flow is clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere.
• Currents follow loops or gyres, clockwise in the Northern Atlantic.
• Ocean currents flowing away from the equator are warm currents, for example the Gulf Stream and the North Atlantic Drift.
• Cold currents return cool water from the poles, for example the Labrador.
Ocean currents are influenced by the prevailing winds with energy being transferred by friction to the ocean currents.
The Coriolis effect caused by the earth’s rotation deflects currents to the right in the Northern Hemisphere which means that ocean currents do not flow due north or due south.
Large land masses like North America divert ocean currents.
• Due to differential heating and/or salinity, density differences occur in water. This means that chilled polar water sinks and spreads towards the Equator, displacing warm water which moves towards the poles.
describe the ITCZ
• The Intertropical Convergence Zone, or ITCZ, is a band of low pressure around the Earth which generally lies near to the equator.
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• The trade winds of the northern and southern hemispheres come together at the ITCZ.
• The intense sun and warm water of the equator heats the air in the ITCZ, raising its humidity and making it buoyant. Aided by the convergence of the trade winds, the buoyant air is forced upward.
• As the air rises it expands and cools, resulting in a band of thunderstorms and heavy rain around the globe.
• The air that is forced to rise along the ITCZ moves towards the poles and slowly descends leading to large areas of high pressure in the sub-tropics.
• As the ocean heats up more slowly than land, the ITCZ tends to move further north and south over land than over water.
• The ITCZ shifts north and south seasonally according to the movement of the Sun.
• In July and August, the ITCZ lies well to the north of the equator over Africa, Asia and Central America before moving south into South America, central Africa and Australia by January and February.
• The ITCZ causes erratic weather patterns with stagnant calms (doldrums) and violent thunderstorms.
• Seasonal shifts in the location of the ITCZ drastically affects 台 rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes.
• Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas.
