100 100 127 127 137 137 VIII. Horizontal Heat Transport:
1. Variation in Receipt of Heat Energy:
i. The receipt of heat energy is very unequal geographically, and that, this must lead to great lateral transfers of energy across the surface of the earth.
ii. Near the equator, about 50% of the entering insolation reaches the ground, whereas near the pole less than 20% is absorbed by the surface. This difference is due to the low angle of attack of the sun's rays to pass through a much greater thickness of atmosphere than at the pole and thus to experience proportionately greater losses by reflection and absorption. Also, the surface albedo is much greater in high latitudes, so that a much greater proportion of short-wave energy is reflected from snow-covered surfaces of Arctic and polar regions than in low latitudes.
iii. There is a large region of surplus radiation from about 40oN to 30oS, and two high-latitude regions of deficit. On the diagram, the areas labeled "deficit" are together equal to the area labeled "surplus", as the radiation balance requires.
iv. It is obvious from above picture that the earth's energy balance can be maintained only if heat is transported from the low-latitude belt of surplus to the two high-latitude regions of deficit. This poleward movement of heat is described as meridional transport, for example, moving north (or south) along the meridians of longitude. The rate of meridional heat transport is greatest in middle latitudes, and this fact is shown by the figure in the table below.
2. The Horizontal Transport of Heat:
The meridional flow of heat is carried out by circulation of the atmosphere and oceans.
a. The Effect of Atmospheric Circulation:
i. The horizontal transport occurs in the form of both latent heat and sensible heat. It varies in intensity according to the latitude and the season.