Abstract
It is shown that the tropical divergent circulation in the nine-level Geophysical Fluid Dynamics Laboratory (GFDL) spectra model is dominated by the lowest frequency gravity modes for vertical mode 4. The importance of diabatic heating during normal mode initialization is studied and results indicate that a considerable amount of divergent circulation can be generated during initialization if the true heating rates are known; in the absence of a knowledge of the heating rates it is preferable to leave the lowest-frequency gravity modes uninitialized. Model integrations with and without various physical parameterizations show that processes connected with convection exert the greatest influence on the evolution of the velocity potential field.
