On conversion between potential and kinetic energy in the atmosphere

Abstract

The mechanism of conversion between potential and kinetic energy in different parts of the Northern Hemisphere is discussed. In low latitudes, between the Equator and 30° N, a large part of the total energy conversion occurs in connection with a mean meridional circulation, the «Hadley circulation». In this the rate of conversion amounts to about 35×1010 kilojoules per second during the winter season. In higher latitudes, however, mean meridional circulations are of minor importance. Here the energy conversion, necessary to maintain the kinetic energy against the frictional dissipation, essentially occurs in connection with atmospheric disturbances. Examples of the energy conversion in such disturbances are presented. It is shown that the rate of conversion between potential and kinetic energy in developing cyclones can reach values of 10–20×1010 kilojoules per second over relatively limited regions. The influence of diabatic processes, especially the turbulent heat transfer from the earth's surface and the liberation of latent heat due to condensation, is further on discussed. An attempt is also made to estimate the total rate of conversion in the Northern Hemisphere. For the winter season the rate of conversion should, according to the estimate, amount to at least 80–100×1010 kilowatts. With the assumption that the rate of energy conversion has about the same magnitude in the Southern Hemisphere the efficiency of the whole atmosphere as a thermodynamic engine is estimated at about 2 per cent.