Energy transfers and insolation
Energy transfers and insolation
Energy transfers occur within the atmosphere in order to maintain a balance between the amount of energy received at the poles and the equator.
As the diagram beneath shows, there is an excess of radiation in all places on earth apart from the poles, and this imbalance needs to be addressed.
If there were no transfers of energy throughout the atmosphere, the Poles would continue to decrease in temperature, whilst the equator would continue to increase in temperature.
Negative heat balance: Exists at the poles - a loss of energy to the atmosphere.
Positive heat balance: Exists within the tropics, a surplus of energy.
Horizontal and vertical heat transfers take place to balance the situation.
Horizontal heat transfers
The transfer of heat from the equator to the poles occurs via winds - 80% (large scale to small scale) and ocean currents (20%).
Vertical heat transfers
Exist to stop the atmosphere from cooling and the Earth's surface from overheating. They occur via conduction, convection, latent heat transfers and radiation.
The main heat transfers in the atmosphere are shown in the diagram below:
These are factors which influence the amount of radiation reaching the Earth that remain relatively constant over time.
Height of the Sun:
Lower latitudes (equatorial regions) have higher temperatures than higher latitudes (Poles) this is as a result of the amount of heating that each area receives. Places near the equator receive direct heat on a small surface area, and experience little energy loss via absorption, scattering and reflection, as there is a relatively small amount of atmosphere to pass through. Towards the Poles, the surface area to be heated increases, as does the amount of atmosphere to pass through, increasing losses via, absorption, scattering, and reflection.
Height above sea level:
It is important to remember that the atmosphere is heated from ground level upwards via long-wave radiation. The higher up a mountain you go, the smaller the surface area available to heat the atmosphere above. This, in combination with a decrease in the ability of the air to retain heat results in lower temperatures.
Distance from land and sea:
Land and sea have vastly different specific heat capacities (the amount of energy needed to raise 1kg of a substance by 1 degree). They have different abilities to absorb, transfer and radiate heat energy. Generally, land surfaces respond to heating on a daily basis (diurnal) meaning that differences between day and night temperatures can be into double figures, but sea surfaces respond over a period of months and retain heat for longer. The sea heats up and cools down more slowly than the land, acting to moderate temperatures for coastal locations.
The temperature of a wind and the subsequent effect it has on an area is dependent on:
- Where it originated.
- The surfaces it has blown over.
Winds coming from the land in winter can be exceptionally cold, whilst winds coming from the sea in winter will be mild in comparison.
Red line = warm current (coastal temperatures raised).
Blue line = cold current (coastal temperatures lowered).
As shown on the diagram above, ocean currents can be either warm or cold and they act to either raise or lower temperatures of the coastal areas they flow towards. The North Atlantic drift is the major current acting on the UK and subsequently raises temperatures above what they should be for places along the same latitude.
The position of the sun changes as outlined below:
21st March and 22nd September sun overhead at the equator (spring and autumn equinoxes).
21st June sun overhead at the tropic of Cancer (northern hemisphere) summer solstice.
22nd December sun overhead at the tropic of Capricorn (southern hemisphere) winter solstice.
The result is the northern hemisphere receives greater amounts of insolation between March and September, resulting in higher temperatures in spring and summer. At the same time, the southern hemisphere experiences its winter.
Day and night:
As insolation is only received in daylight hours, longer days allow for greater amounts of insolation. Equatorial areas receive equal lengths of day and night due to the Sun being directly overhead. At the other extreme, Polar areas experience periods of continuous daylight in their summer and continuous darkness in their winter.
Amount of cloud cover:
Little cloud in the day reduces the amount of absorption, reflection and scattering that occurs, allowing for more insolation to reach the Earth. At night, the same situation allows more heat to escape into the atmosphere - lowering temperatures. At night, cloud acts to trap heat in the lower atmosphere - moderating temperatures.
As shown on the diagram, the way a slope faces can have a large impact on the amount of insolation received. This becomes important when planting crops in valleys, as one slope will be cooler than the other, leading to a shorter growing season.