Major Climate Controls
Atmospheric heat budget
Heat Budget: Balance between incoming solar radiation and outgoing terrestrial radiation
Amount of Incoming solar radiation (Short wave) is determined by:
1. The solar constant: Varies slightly and effects long term climate not short term weather variation.
2. Distance from the sun: Eccentric orbit of the Earth can cause up to 6% variation.
3. Length of day and night: 23.5 degrees tilt of the sun means some regions near the Poles receive no insolation at certain times of the year.
4. Altitude of the sun in the sky: The equator receives more energy as solar radiation strikes the Earth head on, whereas at 60 N or 60 S the angle creates twice the area to cover and increases the amount of atmosphere to go through.
Amount of Incoming solar radiation (Short wave) is determined by:
1. The solar constant: Varies slightly and effects long term climate not short term weather variation.
2. Distance from the sun: Eccentric orbit of the Earth can cause up to 6% variation.
3. Length of day and night: 23.5 degrees tilt of the sun means some regions near the Poles receive no insolation at certain times of the year.
4. Altitude of the sun in the sky: The equator receives more energy as solar radiation strikes the Earth head on, whereas at 60 N or 60 S the angle creates twice the area to cover and increases the amount of atmosphere to go through.
Horizontal Heat Transfers
Advection: Transfer of surplus energy through wind. The surplus energy heats the wind and this process helps to redistribute 80% of the Earth's energy.
Vertical Heat Transfers
Conduction: Contact between molecules of air results in a transfer of energy.
Convection: Movement of a pocket of air that is at a different temperature to it's surroundings. Warmer air is less dense and thus will rise transferring energy from the earth's surface.
Radiation: Release of long wave radiation from the Earth's surface into the atmosphere and out into space.
Latent Heat transfer: Energy used for the evaporation of water (liquid => water vapour). To evaporate 1g of water it takes approx. 590 calories. Water vapour is then transferred vertically by convection before condensation occurs. As the water vapour condenses the latent heat is no longer required so it continues as rises up into space.
Convection: Movement of a pocket of air that is at a different temperature to it's surroundings. Warmer air is less dense and thus will rise transferring energy from the earth's surface.
Radiation: Release of long wave radiation from the Earth's surface into the atmosphere and out into space.
Latent Heat transfer: Energy used for the evaporation of water (liquid => water vapour). To evaporate 1g of water it takes approx. 590 calories. Water vapour is then transferred vertically by convection before condensation occurs. As the water vapour condenses the latent heat is no longer required so it continues as rises up into space.
Atmospheric Circulation
Wind
Pressure Gradients: Change in air pressure over an area caused by winds flowing from high to low pressure. High temperatures creates low pressure due to the rising heat. Pressure decreases with altitude causing the rising heat to slowly fall.
Coriolis Force: Winds deflected due to the rotation of the Earth.
Northern Hemisphere :- clockwise wind movement
Southern Hemisphere :- anti-clockwise movement
Rossby waves: 4-6 in each hemisphere stretching from the Polar to Tropical latitudes often flowing irregularly.
Jet streams: Are the product of a large temperature gradient between two air masses.
Coriolis Force: Winds deflected due to the rotation of the Earth.
Northern Hemisphere :- clockwise wind movement
Southern Hemisphere :- anti-clockwise movement
Rossby waves: 4-6 in each hemisphere stretching from the Polar to Tropical latitudes often flowing irregularly.
Jet streams: Are the product of a large temperature gradient between two air masses.
3 cell model
Hadley Cell
Ferrel Cell
Polar Cell
- The Intertropical Convergence Zone draws in surface air from the subtropics. When this subtropical air reaches the equator, it rises into the upper atmosphere because of convergence and convection.
- High solar radiation, with hot air moving polewards due to pressure gradient.
- 30 degrees North the air meets colder air, forcing the air to sink and head back to the equator and also into the Ferrel cell.
Ferrel Cell
- Higher latitudes 30- 60 degrees N and S.
- Air is pulled towards the poles forming the warm southwesterlies in the northern hemisphere and northwesterlies in the southern hemisphere.
- Moisture is picked up from the ocean.
- The warmer less dense air meets colder Polar air around 60 N and S. This difference in density causes the air to rise over the Polar air.
- This uplift causes low pressure at the surface resulting in unstable mid latitude depressions.
Polar Cell
- On the surface at the north and south poles, descending air from the Polar Cell results in high pressure. This causes air to move towards the mid latitude low pressure belt.
Ocean circulation
Thermohaline Circulation: Ocean circulation driven by density differences. Density depends on temperature and salinity of the water.
- Cold dense polar water sinks, then spreads towards the equator where it pushes up the less dense warmer water which moves off towards the polar areas.