Simple Answer:
Warm air rises during convection. Perhaps better said, natural convection of air is the rising of less-dense warm air relative to the more-dense cold air.
This is a simple matter of buoyancy. Gravity pulls everything downward, but the pull is proportional to mass and items immersed in a fluid that have lower mass per unit volume than the fluid will tend to float, i.e. experience a buoyant force up as gravity pulls harder downward on the surrounding fluid.
Causes and Explanation:
Everyone says "Warm air rises" and that is an example of natural convection. Convection requires a fluid, heat source and gravity. The heat source causes a temperature gradient in the fluid so that buoyancy of the warmer fluid causes it to rise.
Buoyancy is the reasons bubbles rise and hot air balloons float and anything light, like a piece of wood, raises to the surface. The gravitational force experienced by a volume of material is just its weight, i.e. mass times gravity. Mass is the density of the material times its volume. So, if the object (like wood) has a lower density than water, the force of gravity on the object is less than the equivalent volume of water. The buoyant (upward) force is the difference in the wight of the object and the weight of the same volume of liquid.
Light objects experience the upward buoyant force and if the fluid (air or water or any fluid) is heated and expands, then it has a larger volume and less density and it also experiences the upward force.
The natural buoyancy of warmer fluids causes the force that moves the fluid and that movement is what we call natural convection.
Other Aspects:
Conduction
The transfer of heat (therms) through fluid (including air) motion.
convection occurs in fluids such as water and air
Convection takes place because cool air is less dense than warm air.
Convection currents
Convection
Convection happens due to the transfer of heat by the motion of a heated fluid such as air or water.
... is called "convection"
due to forced convection and molecular motion
The transfer of heat (therms) through fluid (including air) motion.
Not conduction, but convection currents, are what drive winds and many ocean currents.
convection current
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
Convection refers to the transfer of heat energy by the motion of a fluid such as air or water caused by differences in temperature within the fluid. Therefore convection happens wherever there is a fluid with a temperature gradient. This means that convection is happening continuously in the air around us and in bodies of water. A car heater and a convection oven are also considered to transfer heat by convection, but this is using the term liberally since the movement of the fluid (air) in these two cases is caused by a fan, not temperature gradient. So, while not perhaps being absolutely accurate examples of convection, still the heat is transferred through fluid motion.
Convection is transferred by the larger-scale motion of currents in the fluid.
what produces convection currents in earth's atmosphere
move in circular motion.
in fact all:) since convection is a kind of conduction, which means heat is transferred via motion of the air surround us, we loose heat by conduction with our clothes, convection from our uncovered skin areas and radiation the same