Abstract
We introduce a new energetics concept and apply it to the NCAR Community Climate Model. The new features of our approach are that the energy is split into balanced and transient parts and that the balanced energy consists of rotational energy and balanced gravitational energy. The time evolution and distribution of the balanced and transient parts of the gravity waves among vertical modes and zonal waves am analyzed.
Both balanced gravitational energy and transient energy concentrate and oscillate rapidly with time at vertical modes 7–8 and zonal wavenumbers 1–5. This explains why the iteration scheme used in nonlinear normal mode initialization would not converge, in general, for high vertical modes and long zonal waves. All the gravity waves associated with vertical modes 0–2 and any zonal wavenumber can be freely adjusted in the initialization to suppress the high-frequency oscillations.
The lower vertical modes, 2–6, contain more balanced gravitational energy than transient energy, but for the higher baroclinic modes, 7–8, both energies are of almost the same magnitude. In general, longer zonal waves contribute more energy to the balanced gravitational energy. Zonal wavenumber 1 contributes the most to both transient energy and balanced gravitational energy. To examine whether the energy of gravity waves is balanced or not during the initialization, it is inappropriate to express the energy in terms of zonal wavenumbers only. The vertical resolution, discretization scheme, and physical parameterization may distort the gravitational energy in the high vertical modes.
