Another example of buoyancy, much closer to the driving force of thunderstorms, are hot air balloons. Hot air balloons are filled with – hot air. The hotter the air (or any gas), the more it expands and the lower its density. As the hot air (Tb) contained in the balloon is less dense than the cooler (Ts) surrounding air, it is positively buoyant and forced to rise – taking the balloon and passengers with it*.
A hot air balloon uses gas burners to heat the air. In nature, daytime warming of the air near the ground causes the warm air buoyantly rise.
* – minor nit pick: while any air parcel with temperature higher than the surrounding air buoyantly rises, it the example with the balloon the warm air needs to be sufficiently warmer than the surrounding air for the buoyancy to overcome the weight of the balloon.