ratio of energy transferred by convection to that by conduction
Heat transfer The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system.
Earth's energy budget The geothermal heat flux from the Earth's interior is estimated to be 47 terawatts.[10] This comes to 0.087Â watt/square metre, which represents only 0.027% of Earth's total energy budget at the surface, which is dominated by 173,000 terawatts of incoming solar radiation.[11]