Since warmer air is less dense, it tends to rise, and regions of upwelling air form. Another way to force upward motion is when a horizontal wind encounters a mountain. The blowing air gets redirected up the mountain side. The cooler air is denser, and tends to stay near the ground, while the warmer, lighter air rides up and over the cooler mass. Energy Sunlight is the energy source driving Earth's weather and climate.
Clouds alter the Earth's energy balance by altering both the incoming and outgoing energy.
Stability Updrafts are a response to instability. When warmer, less dense air is underneath cooler, denser air, the atmosphere is unstable. The warm air tends to rise until it is stable. This is convection, and it also explains why a pot, heated from below, boils. When warm air is on top of colder air, the atmosphere is stable, and convection is inhibited.