Derive the value of the flow of energy from Earth's surface to the atmosphere as a result of evapotranspiration. Express your answer in units of watts/m2. Hint: you will need to know, or derive, how much precipitation falls each year on a typical square meter of Earth's surface and you will need to look up in the Appendix to COW a value for the heat of vaporization of water.
US precip = 5.6 x 10^12 m^3/yr
US evapotranspiration = 3.95 x 10^12 m^3/yr
latent heat of vaporization:
at 100C = 2.258 x 10^6J/kg
at 17C = 2.459 x 10^6 J/kg
at 0C = 2.499 x 10^6 J/kg
b. In answering part a., you probably ignored the energy required to lift water vapor to the atmosphere. Estimate the magnitude of that contribution to the total flow of energy powering the hydrocycle -- is it significant compared to the energy needed to evaporate the water? [Hint: the work against gravity on Earth to lift a mass, m, to a height, h, is mgh, where g is the acceleration of gravity at Earth's surface: g = 9.8 m/sec2.