Geography-Atmosphere-General

51% absorbed by Earth

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• 16%absorbed by dust,water vapour and other gases
• 3% absorbed by clouds
• 6% scattered by gas
• 20% reflected by clouds
• 4% reflected by earth's surface
• Then:
• 6% emmitted as long wave radiation
• The remaining 94% is absorbed by water vapour and carbon dioxide in the atmosphere and re-radiated.

The amount of energy actually absorbed by the surface depends on the Albedo effect (eg: the proportion of radiation which is reflected by different surfaces).

• sun’s rays concentrated on tropical latitudes as the intensity of insolation is greatest where the sun’s rays strike vertically
• • sun’s rays have less atmosphere to pass through at the Tropics so less energy is lost through absorption and reflection
• • sun’s angle in the sky decreases towards the Poles and due to the earth’s curvature the heat energy is spread over a much larger area
• • albedos differ between the Tropics and the Poles – darker forest surfaces absorb radiation, whereas ice covered surfaces reflect radiation
• • between the Tropics the rays from the noon day sun are high in the sky throughout the year thereby focussing energy
• • zero solar insolation at the winter solstice at the Poles – the sun shines at equatorial latitudes all through the year.

• The hadley cell operates between 0 and 30N/S of the equator.
• Maximum solar heating at the equator causes air to rise forming the equilateral low pressure zone.
• Air spreads out at high altitude to 30N/S where it sinks forming the sub-tropical high pressure.
• Some air continues back towards the equator as the NE traid winds and some air is transferred to the ferrel cell

• The Ferrel cell operates between 30N/S and 60N/S of the equator.
• Air from the Hadley cell moves north/south as surface winds(south westerlies/North westerlies)
• At 60N/S the air rises forming the sub-polar low pressure
• Some air moves back towards the sub-tropical HP at high altitude
• Some air is transferred to the polar cell where it continues polewards

• The Polar cell operates from 60N/S to each pole
• Air moves towards the poles at high altitude in the polar cell and sinks at the poles, forming the Polar High Pressure.
• Air then moves back towards the sub-polar low pressure as surface winds (polar easterlies)

• currents follow loops or gyres – clockwise in the North Atlantic. In the Northern Hemisphere the clockwise loop or gyre is formed with warm water from the Gulf of Mexico (Gulf Stream/North Atlantic Drift) travelling northwards and colder water moving southwards eg the Canaries Current.
• • currents from the Poles to the Equator are cold currents whilst those from the Equator to the Poles are warm currents. Cold water moves southwards from Polar latitudes – the Labrador Current. This movement of warm and cold water thus helps to maintain the energy balance.
• • ocean currents are greatly influenced by the prevailing winds, with energy being transferred by friction to the ocean currents and then affected by the Coriolis effect, and the configuration of land masses which deflect the ocean currents. Due to differential heating, density differences occur in water masses, resulting in chilled polar water sinking, spreading