why is there surplus heat in the tropics

• • Due to the earth’s curvature, the angle of incidence of the sun’s rays decreases with increasing latitudes
  • The angle of incidence affects the degree of beam spreading and atmospheric beam depletion 
  • At the tropics, the insolation reaches the surface at high angles of incidence. At the equator, this is almost 90. This means that the beam is concentrated in a small area, resulting in a greater intensity of radiation, and thus higher surface temperatures. 
  • In contrast, the sun’s rays hit the earth’s surface at lower angles, distributing the energy over a greater area
• • In addition, at the tropics, because of higher angles of incidence, the layer of atmosphere that the solar radiation, must penetrate before reaching the surface is thinner compared to areas of higher latitudes 
  • This reduces the amount of radiation lost to absorption and backscattering by the atmosphere. This contributes to higher insolation receipts at the surface at lower latitudes