Further statistics on the exchange of kinetic energy between harmonic components of the atmospheric flow

The transfers of kinetic energy between harmonic components of the 500 mb geostrophic flow over the Northern Hemisphere have been measured for an ensemble of daily maps covering a nine-year period, based on a truncation at zonal wave number, n = 15. The results show (1) that, in the mean, all waves (n = 1–15) transfer their energy to the zonally-averaged motion (n = 0) and, of more physical significance, the aggregate of all waves in the group n = 2–15 transfer energy to support the asymmetric polar vortex comprised of wave numbers zero and one, and (2) that, among the waves themselves, waves of n = 2 and 5–10 are sources of kinetic energy and all the rest are sinks. The energy source at n = 2 seems to be a significant new result indicating a strong forced conversion of energy on the scale of the major continents and oceans. Seasonal variations are discussed.