Answer:
Explanation:
The troposphere undergoes circulation because of convection. Convection is a mode of heat transfer wherin the heat moves with the material. Warm air, becuase it is less dense than cooler air, rises and cold air sinks back toward the surface. Convection in the atmosphere is mainly the result of the fact that more of the Sun's heat energy is received by parts of the Earth near the Equator than at the poles.
Thus air at the equator is heated reducing its the density. Lower density causes the air to rise. At the top of the troposphere this air spreads toward the poles.
