HIGHER GEOGRAPHY PHYSICAL CORE ATMOSPHERE GMTs describe and

HIGHER GEOGRAPHY PHYSICAL CORE ATMOSPHERE

GMTs Ø describe and interpret climate maps, diagrams and graphs Ø construct and analyse climate graphs Ø describe and explain climate graphs Ø comment on the accuracy of statements which describe climate patterns shown on maps etc.

By the end of this topic you should be able to: Ø explain with the aid of an annotated diagram, why Tropical latitudes receive more of the sun’s energy than Polar regions Ø explain why there is a net gain of solar region in the Tropical latitudes and a net loss towards the poles Ø describe the role of atmospheric circulation in the redistribution of energy over the globe Ø describe and explain the earth’s energy exchanges shown on a diagram Ø describe the factors which affect the amount of sunlight reflected from the earth’s surface Ø describe and account for the generalised pattern of atmospheric circulation and global winds, or ocean currents shown on a world map Ø describe the variations in world temperature for the last 100 years (shown eg. on a graph) and suggest both physical and human reasons for these variations Ø describe and explain the origin, nature and weather characteristics of Tropical Maritime (m. T) and Tropical Continental (c. T) air masses which affect West Africa Ø with reference to the Inter-Tropical Convergence Zone and the movement of air masses, describe and account for the variations in West African rainfall.

SINGLE CELL MODEL At the Equator the atmosphere is heated Air becomes less dense and rises. Rising air creates low pressure at the equator. Air cools as it rises because of the lapse rate. Air spreads. As air mass cools it increases in density and descends. Descending air creates high pressure at the Poles. Surface winds blow from HP to LP. 0º Equator LP 90º Pole HP

warm air is less dense therefore lighter air rises in the Tropics this creates a zone of LOW PRESSURE air spreads N and S of the Equator air cools and sinks over the Poles this is a zone of HIGH PRESSURE air returns as surface WINDS to the Tropics

SINGLE CELL MODEL The single cell model of atmospheric circulation was developed to explain the transfer of energy from the Tropics to the Poles. This was later improved and a three cell model was developed. Today the three cell model is also considered to be an oversimplification of reality.

HADLEY CELL ITCZ = Inter-tropical convergence Zone (Low Pressure) STH = Sub-tropical High (High Pressure)

THREE CELL MODEL Hadley Cell 0º Equator LP Polar Cell Ferrel Cell 30º HP 60º LP 90º Pole HP

ENERGY TRANSFER Warm air rises at the Equator Inter-Tropical Convergence Zone (ITCZ). Equatorial air flows to ~30º N then sinks to the surface and returns as a surface flow to the tropics. This is the Hadley cell. Cold air sinks at the North Pole. It flows S at the surface and is warmed by contact with land/ocean, by ~60º N it rises into the atmosphere. This the Polar cell. Between 60º N and 30º N there is another circulation cell. This is the Ferrel cell. The Hadley cell and the Polar cell are thermally direct cells. The Ferrel cell is a thermally indirect cell.

ENERGY TRANSFER Hadley Cell Ferrel Cell Polar Cell Heat energy is transferred from the Hadley Cell to the Ferrel Cell and from the Ferrel Cell to the Polar Cell. In this way heat is transferred from the Equator where there is an energy surplus to the Poles where there is an energy deficit.

convergence divergence 0º Equator LP divergence convergence WINDS 30º HP 60º LP 90º Pole HP winds blow from high pressure zones to low pressure zones

CONVERGENCE and …………DIVERGENCE