The wind field in the lower layer in a moving typhoon of circular concentric isobar pattern is discussed. Effect of storm movement results in higher wind in the right semicircle than in the left, and the effect of surface friction adds front-rear asymmetry to that due to storm movement. Numerical estimation of the wind field in the friction layer of the moving typhoon depicts characteristics of actually observed asymmetry.
Experiments on artificial stimulation of clouds using warm cloud seeding technique have been conducted, on randomized basis, from ground for 4 monsoon periods at Jaipur, 6 monsoon periods at Agra and 9 monsoon periods at Delhi, in North India. The seedings were also conducted from aircraft, during one monsoon period at Delhi. Orographic clouds have been seeded for two summer seasons at Munnar in South India. Results have been evaluated on the basis of rainfall amounts obtainedd from raingauges in the respective target and control sectors in each region. Evaluation has also been done on the basis of data obtained by high power microwave radar in the case of a few series of trials conducted at Delhi. A net increase in precipitation was suggested in each area as a result of seeing. The percentage increase in rainfall as a result of ground-based seeding varied from 18.6 to 58.5 according to the area. Statistical evaluation indicated that the results obtained could be significant.
Estimation of evaporation from Lake Nojiri, which has an average depth of 21m, was made by means of the aerodynamic method as well as the heat budget method. Nearly same results were obtained independently by the two methods. Evaporation is found to be greater in August-September and less in February-April. A comparison was made between the seasonal change in evaporation from Lake Nojiri and that from Lake Towada which is deeper than the former lake. The conclusion reached is that when the lake is deeper, maximum or minimum evaporation occurs later due to the delaying effect of the heat energy stored in the lake.
Based upon arguments by Syono and Yamasaki (1966), numerical experiments for simulating the developmental process of tropical cyclones are carried out with the use of primitive equations. Thermal effects of deep cumulus clouds are incorporated in the same manner as proposed by Ooyama (1964), and Charney and Eliassen (1964). The numerical experiments are performed using a four-layer model. The effect of surface friction is included through the equations of motion applied to the lowest level. Latent heat released by cumulus clouds is distributed to two tropospheric layers, and the heat partition ratio is assumed to be timeindependent. In a case in which 57 per cents of released latent heat is given to the upper troposphere and 43 per cents to the lower one, a given weak vortex develops to the mature stage in about 8 days. The structure of the computed tropical cyclone is similar to that of observed tropical cyclones. The deviation from the gradient wind balance is notable in the upper level near the center. The ratio of kinetic energy production to released latent heat increases with time and it attains 3 per cents at the mature stage. In order to investigate the relation between the gr iwth rate (and structure) of computed tropical cyclones and various physical parameters (such as mixing ratio of water vapor of surface air q, heat partition ratio to the lower troposphere 1, static stability S, the Coriolis parameter f and the drag coefficient CD), several numerical experiments are carried out. The horizontal scale of computed tropical cyclones is decreased with decrease of the Coriolis parameter. The experiments further reveal that the growth rate of cyclones is very sensitive to the static stability of the lower layer. In a case in which 70% of released latent heat is given to the upper layer, a given vortex does not develop. The growth rate of computed tropical cyclones is increased with increase of q, l and CD.
As a continuation of the previous study (Yamasaki, 1968), several numerical experiments for the development of tropical cyclones are performed with a time-dependent vertical partition of released latent heat. This partition ratio is expressed in terms of the large scale temperature field and, the pseudo-wet-bulb potential temperature (θsw) of cumulus clouds. First experiment is made with the constant θsw. The result shows that the warm core formation begins in the upper layer. When the stratification becomes less unstable in the upper layer, the heat partition ratio to the lower layer is increased and thereby a rapid development occurs. At the mature stage the stratification becomes moist neutral near the center. The results of other experiments reveal that the growth rate of computed tropical cyclones is sensitive to the initial static stability. It is also found that the radial profile of the tangential velocity assumed at the initial time is an important factor not only to the growth rate but also to the formation of eye. Finally, a case is discussed in which surface air temperature is kept to be a constant value and surface air is always saturated with water vapor. In this case the deepening of the surface pressure induces the increase of θsw and in turn the increase of θsw induces further deepening of the surface pressure. It is, however, shown that there exist an upper limiting value of θsw and a lower limiting one of the surface pressure. The limiting values are dependent on surface air temperature.
Large scale wave disturbances in equatorial regions, and, in particular, those described by Maruyama (1967), are discussed in terms of forced oscillations. In doing this we are able to explain the importance of the waves' tilts, the role of the beta effect, and the waves' contributions to the mean zonal momentum, Consideration of the last items leads us to conjecture on the nature of those disturbances in the equatorial stratosphere which were not isolated in the analysis of Maruyama.
A line echo on the radar scope is sometimes observed across the Bay of Toyama under the winter monsoon situation. It seems to be related to the orography of the Noto Peninsula to the west and to cause a considerable amount of snowfall to the east. It is found that its appearance has a period of 2-3 hours which characterizes mesoscale disturbances and that a remarkable line echo develops when the mesoscale convergence field comes to influence. The orientation of the row is approximately in the direction of thermal wind. The “convective warming” along the coastal area results in a remarkable temperature gradient within the cloud layer which amounts to as much as 5°C/100km. The fact that this row of cumulus convection takes place in a particular locality strongly suggests the influence of orography.
A theoretical study of the dynamics of long and ultra-long waves in a baroclinic tonal current is made by the use of quasi-geostrophic equations. The stability of the tonal current and the characteristics of wave perturbations are iinvestigated numerically with the finite difference approximation of the linearized perturbation equations applied to a multi-layer model. It is found that the wave solutions are classified into three types : (i) a pair of amplifying and decaying waves, (ii) neutral waves without steering levels in the basic current and (iii) neutral waves with a steering level. They are divided into various regimes in accordance with their vertical structure. The examination of the vertical structure of wave disturbances, as well as of the phase velocity, is made in terms of the wavelength and the vertical shear of the zonal current. Some remarks on the validity of the finite difference approximation by a simple 2-layer model are added in relation to the results obtained by the multi-layer model. The energy conversion processes are discussed by making a comparison between the unstable waves of the first mode and the higher mode. It is found that the maintenance of the unstable wave of the higher mode is only due to the increase of the eddy available potential energy caused by northward heat transport. Finally a comparison between the characteristics of ultra-long waves obtained by the present study and those of the observation is made.