Answer:
Solar constant - Heat flux density.
Step-by-step explanation:
The solar constant (GSC) is a flux density measuring mean solar electromagnetic radiation (solar irradiance) per unit area. It is also defined as the rate at which solar radiation is received on a unit surface that is perpendicular to the direction of incident radiation just outside Earth's atmosphere at Earth's mean distance from the Sun; equal to 2 cal/cm^2.min.