This process is called convection . As the equatorial air rises, air at low latitudes and from higher latitudes in both hemispheres moves toward the equator to take its place. This flow is balanced by a flow way from the equator at higher altitudes. While flowing poleward, the upper air cools by radiation to space. Convection is the process by which heat is carried upwards by a moving mass of air or liquids.
Convection is the main process responsible for upward movement of air in the troposphere.
There are many familiar examples of convection. A radiator heats cool air. The air expands, becomes less dense and rises, displacing cooler air which sinks and enters the radiator at its base to complete the convection cycle. A pot of water placed on a stove is heated from below. Warm water tends to expand and rise over the hottest part of the pot bottom, displacing cooler water that sinks near the edge of the pot.