Aconvection cell is best described as

Convection cell in the sun's rays are the ones that carry energy to travel within its surface and outside.

There are three types of heat transfer or heat propagation; conduction, convection and radiation. Heat transfer is the process by which heat projects externally however, depending on the temperature and pressure. Also called the movement of heat from a low temperatured state which increases as heat progresses.
Conduction is the heat transfer by contact, immediate contact.
Convection is the transfer of heat through air and water.
Radiation is the transfer of heat regardless of the presence of atoms or particles. 

The answer is telescope.

Spherical shaped cell might increase the surface area and decrease the volume.