 At equilibrium, the rate of net energy production in the system must equal the rate of energy loss due to frictional dissipation at the surface, i.e.The rate of energy loss per unit surface area from surface friction, formula_19, is given by

where formula_21 is the density of near-surface air ([kg/m3]) and formula_22 is the near surface wind speed ([m/s]).The rate of energy production per unit surface area, formula_23 is given by

where formula_25 is the heat engine efficiency and formula_26 is the total rate of heat input into the system per unit surface area.