Contributions to the growth and decay of large‐scale eddy available potential energy

ABSTRACT To study the growth and decay of eddy available potential energy associated with the large‐scale atmospheric waves, we have computed composite averages of the terms in the available potential energy equation in the wave‐number domain. We found that the eddy available potential energies of the ultra‐long waves of wave numbers 1 and 3 grow essentially by receiving energy through the resultant meridional and vertical eddy heat transport process; whereas during the period of decay, the energy loss is essentially through the non‐linear heat transport process. We also found that the eddy available potential energies of the synoptic‐scale waves of wave numbers 4 to 8 increase by receiving energy and decay by losing energy through both the non‐linear and the resultant meridional and vertical eddy heat transport processes. However, the main source of eddy available potential energy for wave number 2 is the contribution of diabatic processes, although diabatic processes contribute to the maintenance of the seasonal mean but not to the growth and decay of the eddy available potential energy of wave number 2. Its time change is also determined by the eddy heat transport processes. It is also found that the amplitude oscillations of eddy available potential energy are generally in‐phase with those of eddy kinetic energy in the same wave number. However, the growth of the former usually occurs slightly behind that of the latter. The growth of eddy available potential energy may be interpreted as an indirect consequence of the growth of the eddy kinetic energy of the wave, which enhances the eddy heat transport, thereby increasing the available potential energy of the wave; whereas the growth of the eddy kinetic energy is a result of the receipt of kinetic energy from other waves through barotropic non‐linear exchange processes as described by Tsay and Kao (1978).