The term 'Rising Current of Warm Air' is a reference to a THERMAL, which is a type of atmospheric phenomenon that occurs when warm air rises due to convection. This rising current of warm air is caused by the sun heating the ground, which in turn warms the air above it. As the air rises, it creates an updraft that carries the warm air upwards. This rising current of warm air can cause clouds to form and can also lead to thunderstorms and other weather events.