energy transfer

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. There is a net surplus radiation for earth-atmosphere system between 35S and 40N and a net deficit to the poleward side of those latitudes. There is positive heat balance within the tropics and a negative heat balance both at high latitudes and low latitudes, so major heat transfers take place to prevent tropical areas from overheating. Without heat transfer mechanisms, the equator will be more than 50C and polar region will be much colder.

Ther are two major heat transfers, vertical and horizontal heat transfer. According to the normal environmental lapse rate, there is a general decrease of the 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 heat 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, then a horizontal temperature gradient is formed between energy deficit region and energy surplus region. As the tropics do not progressively hotter or the high latitude colder, a redistribution of world heat energy from tropics to the poles must constantly occur.

Poleward 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 poleward horizontal energy flow is closely related to the meridional 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.