2.2 The Global Energy Bugdet

• The atmosphere is an open energy system recieving energy from both the sun and the earth
• INcoming SOLar radiATION = INSOLATION

• In January highest temperatures over land are found in Australia and Southern Africa.
• The lowest temperatures are found over parts of Siberia, Greenland and the Canadian Arctic.
• There is a decline in temperatures northwards from the Tropic of Capricorn
• However there are important anomalies such as the effect of the Andes in South America and the effect of the cold ocean currents off the coast of Namibia.
• In July, Maximum temperatures are found over the Sahara.
• Near East, Northern India and parts of southern USA and Mexico
• Areas in the Southern Hemisphere are cooler.
• These patterns reflect the general decrease of insolation from the equator to the poles.

• On maps pressure is adjusted to mean sea level (MSL) which is 1013mb.
• Low pressure systems result in air rising and unstable conditions.
• High pressure systems result in cold dense air sinking, causing stable conditions.

Pressure Belts

• In the Northern Hemisphere there are greater seasonal contrasts, due to the unequal distribution of land and sea.
• One of the more permanent features is the Sub-tropical High Pressure (STHP) belt which is found at 30 degrees Lattitude.

Wind Belts

• Winds between the tropics converge on a line known as the Intertropical convergence Zone (ITCZ)

Lattitude

• This is the most important factor determining temperature.
• Two factors affect the temperature:
  • The angle of the overhead sun
  • The thickness of the atmosphere
• At the equator the sun is overhead and therefore the insolation recieved is of a greater intensity.
• At the poles the sun is low in the sky, the amount of insolation recieved is low and the thickness of the atmosphere is greater, resulting in more reflection.

• The amount of heat needed to raise the temperature of a body by 1 degree.
• water heats slower because:
  • It's clear, the sun's rays penetrate to great depth
  • Tides and currentd cause the heat to be further distributed
• It takes five times as much heat to raise temperature of water by 2 degrees as it does to raise land temperatures.

• Surface ocean currents are caused by the infuence of prevailing winds.
• the dominant pattern of surface ocean currents is roughly circular flow.
• Clockwise in the northern hemisphere, anticlockwise in the southern hemisphere.
• The main exception is the circumpolar current that flows around Antarctica from west to east.

Pressure and Wind

• Vertical air motion is important on local scale wehreas horizontal motion is important at many scales, from small-scale eddies to global wind systems.

Pressure Gradient

• The driving force is the pressure gradient (Difference in pressure between any two points)
• Ait blows from a high pressure to a low pressure - High pressure over land in winter and sea in summer. 
• The coriolis effect is the deflection of moving objects caused by the easterly rotation of the Earth.
• The coriolis force is at right angles to wind direction.
• The balance of forces between the pressure gradient force and the coriolis force is known as the Geostrophic balance and the resulting wind in known as the geostrophic wind.
• The centrifugal force is the outward force when you drive around a corner.

• Warm air is transferred polewards and is replaced by cold air moving towards the equator.
• Air that rises is associated with low pressure, whereas air that sinks is associated with high pressure.
• Low pressure produces rain, high pressure produces dry conditions.
• At the ITCZ, convectional storms lift air into the atmosphere, which increase air pressure near the troposhpere, causing winds to diverge at high altitude.
• They move out of the equatorial regions towards the poles, gradually losing heat by radiation.
• As they contract, more air moves in and the wieght of the air increases the pressure at the subtropial high pressure zone. 
• The denser air sinks, causing subsidence (stability)
• The north/south component of the Hadley cell is known as meriodnal flow.

• Jet streams are strong, regular winds which blow in the upper atmosphere about 10km above the surface, they blow between the poles and the tropics (100-300 km/h)
• There are two jet streams in each hemisphere - one between 30 degrees and 50 degrees, the other between 20 degrees and 30 degrees.
• In the northern hemisphere the polar jet flows eastwards and the subtropical jet flows westwards.
• Rossby waves are "Meandering rivers of air" formed by westerly winds. There are three to six waves in each hemisphere. They are formed by major relief barriers such as the Rockies and the Andes, by thermal differences and uneven land-sea interfaces.
• The jet streams result from differences in equatorial and sub-tropical air, and between polar and subtropical air.
• The greater the temperature difference, the stronger the jet stream.