The induction and transmission of mean motion by quasi-geostrophic disturbances are discussed. Two types of momentum transport process, i.e., that by a propagating internal wave packet and that by vortex tube stretching, are discussed by the use of a simple inviscid Boussinesq fluid channel model. The disturbance is excited by transient motion of the corrugated bottom, and the evolution of mean zonal flow is examined. From a preliminary theoretical consideration, it is shown that the change of mean zonal momentum is caused by the divergence of wave momentum flux. Thus, the concept of ″momentum radiation born by a wave packet″ is useful in the problem of internal Rossby wave-mean zonal flow interaction. By applying the conservation law of wave action to the approximated zonal mean potential vorticity equation, a simple formula for the induced mean zonal flow is obtained. The utility of the formula is confirmed by the numerical computations and also by the application to the actual atmospheric situation. Numerical time-integrations are conducted for three cases; (1) the Rossby parafeter β is zero, (2) β≠0 and the bottom moves westward and (3)β≠0 and the bottom moves eastward. In the first case, the induced mean zonal motion cannot be transmitted vertically deep into the fluid layer due to the stratification just as seen in the spin-up (or down) process of a stratified viscous fluid. In the second case, the mean zonal flow (easterly) is induced by a propagating internal Rossby wave packet and transmitted vertically upward accompanied with the wave packet. In the third case, the westerly induction by vortex tube stretching process and the easterly acceleration by propagating internal waves counteract each other. Easterly flows are induced at upper levels and westerlies at lower levels. As the applications of the present results, the effect of planetary waves on the earth's upper atmospheric mean circulation is discussed, and further some conjectures are made upon the solar atmospheric equatorial acceleration.
In order to obtain a basis for better understanding of the properties of atmospheric moist convection, numerical experiments are performed using a simplified model in which the pseudoadiabatic assumption is adopted. Therefore, the model does not include evaporation and drag force of liquid water and cloud microphysical processes. Furthermore, it is assumed that motions are always moist adiabatic in ascending area. The present study is made as an extension of a previous study (Yamasaki, 1972) in which Kuo (1961, 1965)'s perturbation theory for moist convection was re-examined with a complete set of boundary conditions. The objective of this paper is to study how the results obtained from the perturbation theory are modified by finite-amplitude effects. In particular, it is attempted to clarify the effects of finite-amplitude on the horizontal scale of ascending motion and on the interaction among convective cells. The present study is restricted to such situations that neither ambient wind nor large-scale convergence exist. It is shown that finite-amplitude effects act to make the size of ascending area larger than that expected from the perturbation theory, particularly in the lower part of convection. However, it is rather emphasized that the characteristic size of ascending area is not significantly modified by finite-amplitude effects. This means that the characteristic size in finite-amplitude convection can be approximately predicted from the perturbation theory. When the initial size of ascending area is small or large compared to the size expected from the perturbation theory, the characteristic size tends to approach the theoretical value during the growing stage. Therefore, the size of ascending area at the mature stage does not depend much on the initial size. Although these results are not necessarily true for actual atmospheric convection because of some assumptions used, it may be expected that the results obtained in this paper will provide us with a useful basis for further studies of moist convection. The results as to the size of ascending area are also discussed in comparison with those obtained by Asai (1967).
The characteristic features of disturbances during the period of January, February and March in 1968 over the China continent and the East China Sea are studied in connection with the Air Mass Transformation Experiment (AMTEX) which is planned as one of the GARP subprogram. In January, wave disturbances with 6-7-day period which correspond to long waves in middle latitudes are found over the China continent and the East China Sea. In middle January, short waves of 2-3-day period with upper troughs exist and the time-spectra of the mixing ratio of water vapour show large power density in this short period range. In March, the activity of wave disturbances is weak but the East China Sea area is affected by the passage of long waves whose center is located at higher latitudes.