An Observational Study of Kinetic Energy Conversions in the Atmosphere

The total kinetic energy in the atmosphere has been subdivided into four energy reservoirs. The partition of the kinetic energy is accomplished by dividing the total flow into the vertical mean flow (the barotropic corrponent) and the vertical shear flow (the baroclinic component). Each of these components is subdivided into the zonal components and the eddy components. The complete energy exchange diagram is derived by dividing a given energy conversion into the contribution from the quasi-non-divergent flow and the contribution from the divergent flow. Such a subdivision of the energy conversion is advantageous because the calculations are based on geopotential data. Calculations have been carried out for five months (January, April, July, October 1962 and January 1963) based on five isobaric surfaces (20, 30, 50, 70, and 85 cb.). The complete energy diagrams are presented for each month together with an averaged diagram representing the annual mean. The results obtained for the four months in 1962 are in good agreement with each other showing not only the same directions of the energy conversions but also a marked annual variation for the major, non-divergent conversions generally with a minimum during the summer season. The annual mean diagram is compared with the mean diagram obtained in a numerical simulation of the atmospheric general circulation. The results in the observational study which depend entirely on the mean meridional circulation suffer from the fact that the present data can not give a true picture of the Hadley circulation in the low latitudes. The energy conversion which depends entirely on the eddies is larger in the observational study than in the experimental study. The reason for this discrepancy is ascribed to the lower intensity of the eddies in the experimental study and, in particular, to the lack of energy on the planetary scale in the general circulation experiment. Good agreement is found in most energy conversions with two major exceptions.