Firstly conduction is the transfer of heat through matter by molecular activity. The energy of molecules is transferred through collisions from one molecule to another, with the heat flowing from the higher temperature to the lower temperature.
Secondly, convection is flow of heat through currents within a fluid. It is a movement of liquid or gaseous volumes. In convection, energy is carried around by atoms or molecules.
Thirdly, radiation is the transfer of heat by electromagnetic waves. It does not need a propagating medium. The heat radiated by the sun can be exchanged between the solar surface and the earth’s surface without heating the transitional space.
The heat transfer of the earth-atmosphere works on a single basic principle-heat moves from warmer to colder areas. The difference in the distribution of heat energy from the sun over the earth’s surface and the net radiation balance has led to the heat transfer.
There is a heat budget of the earth, the heat transfer takes place to maintain the heat budget balance. From the resource sheets, there is a net surplus radiation for earth-atmosphere system between 35。S and 40。N and a net deficit to the pole ward side of those latitudes. There is positive heat balance within the tropics and a negative heat balance both at high latitudes and low altitudes, so major heat transfers take place to prevent tropical areas from overheating. Without heat transfer mechanisms, the equator will be more than 50。C and polar region will be much colder.
There are two major heat tranfers, vertical and horizontal heat transfer. According to the normal environmental lapse rate, there is a general decrease of temperate with altitude. This produces a temperature gradient between the atmosphere and the earth’s surface which leads to the vertical heat transfer.
For the horizontal transfer, because of the angle of sun, altitude, geographic position and other factors, the distribution of heat energy from the sun over the earth’s surface is different, deficit region and energy surplus region. As the topics do not progressively hotter or the high latitude colder, a redistribution of world heat energy from tropics to the poles must constantly occur.
Pole ward heat transport takes place within the atmosphere and ocean and it is estimated that the former accounts for about 2/3 of the required total. The intensity of the pole ward horizontal energy flow is closely related to the meridonal temperature gradient. In winter, this temperature gradient is at a maximum and in consequence the hemispheric air circulation is most intense and so do energy flow.
