1. Conduction – the transfer of heat by the physical contact of molecules having different kinetic energy (temperature). Heat flow from warmer to colder regions.
2. Convection – the transfer of heat by the physical displacement or mixing of matter that has differing kinetic energy (temperature).Mostly occurs through thermals at the surface (vertical) and affection of air (horizontal).
3. Radiation – the transfer of heat between bodies by means of electromagnetic waves. Any substance with a temperature than a 0°K emits radiant energy.
I would have to say Radiation in the upper troposphere. That is why the Ozone layer is in that part of the atmosphere. The lower part underneath this layer would trap in most of the heat from radiation.
