Cirrus clouds were observed by stereophotogrammetric methods at Sapporo, Hokkaido, from August to October in 1964 and 1965. From the analytical results of the environmental situation near the cirrus cloud level, the following significant facts were found. The cirrus clouds were observed in a layer with the dry adiabatic lapse rate and vertical wind shear. In the case of the cirrus uncinus clouds, remarkably stable layers existed above and below the cloud and the trail of the cloud was in the stable layer below. In the case of cirrus fiblatus cloud and cirrus spissatus cloud, the layer above was stable but the layer below was not quite stable and had a nearly dry adiabatic lapse rate. It was noted that the static stability in the lower part of cirrus clouds was important to explain the characteristic shape of the cirrus clouds. From the resutls, a useful information was obtained to decide the height of a cirrus cloudeven if it is one point observation.
Studies have been made of the freezing of supercooled drops of radii ranging from 0.106 cm to 0.134 cm suspended from insulating supports in an environment whose temperature could be varied from 0°C to -45°C. It was found that the probability of a drop freezing within a fixed interval of time was appreciably greater over the temperature range 0 to -22°C if the surface of the drop was disrupted by either electrical or mechanical forces to produce a filament of liquid emanating from the localised area of rupture. For example, for a five-minute test-interval the fraction of drops studied that froze at temperatures -5°C, -10°C, -15°C and -20°C were 0.44, 0, 62, 0.75 and 0.88 respectively if the drop wasl disrupted by means of an electric field, 0.25, 0.44, 0.50 and 0.58 respectively if the surface was penetrated by an insulating fibre or conducting wire at the same temperature as the drop, but only 0, 0.02, 0.07 and 0.18 respectively if the drop surface was not disrupted during this interval, but remained undisturbed, was situated in a strong electric field just below the disintegration threshold, or shaken violently on its support. These observations are totally inconsistent with the criterion for the occurrence of electrofreezing deduced by Pruppacher (1963 a, b), namely that the phenomenon is always associated with the movement of a triple-phase boundary. However, the observations are in agreement with the suggestion of Loeb (1963) that the most essential condition for the occurrence of electrofreezing is that a portion of the drop be drawn out into a thin filament; Loeb et al. (1938) had previously shown that such a filament may contain molecular aggregates which act as excellent freezing nuclei. These conclusions were reinforced by high-speed photographs demonstrating that freezing originated from the area of disruption. The influence upon the freezing probability of air-bubbles released into the liquid during the disruption process was shown to be secondary. A review of observations that have been made on natural clouds indicates that although no definitive evidence exists for the occurrence of electrofreezing, a considerable body of indirect information suggests strongly that electrofreezing was responsible for the observed existence of ice particles at extremely high temperatures within supercooled clouds. The characteristics of the observed frozen particles are consistent with those which would be expected from electrofreezing.
The mesoscale disturbances are characterized by the gravity wave which accompanies the field of convergence of the order of 10-4sec-1. This amount of convergence strongly controls the convective activity and has a significant influence upon the wind field through the momentum exchange process. Numerical experiments are made by means of the simplified two layer version of sheared flow incorporated with convective momentum transfer which is parameterized empirically. It is shown that the downward momentum transfer in the lower-level coinvergence area has an effect of increasing the lower-level wind velocity and decreasing the upper-level wind velocity and thus results in the self-intensification of lower-level convergence and increasing the velocity of propagation downstream. The redistribution in the wind profile, however, contributes to the strengthening of frictional dissipation, which is partly compensated by the energy conversion from convective kinetic energy.
Three methods of continuous particle sampling are presented and their merits and defects are discussed one another. One is the replication method. This method had an advantage because it was possible to record ice crystals and water droplets simultaneously, however several precautions were required for the practical operation. Another is the water-blue method. This method was employed without difficulty, and the traces of water droplets were obtained very clearly. For the observation of clouds which had no hydrometeors this was better than the replication method. The other is the photomicrograph method. The use of this method was difficult in flight observations. Continuous airborn samplers were designed for these three methods. From the practical point of view it is advisable to employ those two methods at the sametime.
A method of objective analysis of the temperature and moisture fields of the atmosphere taking into account of the energy supply from the underlying sea surface and the cumulus cloud distribution is discussed in a most simplified formulation. The thermal and moisture fields in the subcloud and cloud layers, are obtained objectively by using a set of linear equation derived from the thermodynamic equation and the continuity equation of water vapor in which certain empirical relations concerning the connective transfer of the heat energy and assumptions of steady and geostrophic conditions are introduced.
A numerical experiment has been performed on a tropical disturbance embedded in easterlies to test the dependency of the vertical coupling on the value of Richardson number in tropics. By a 2-layer primitive equation model in sigma system of coordinates integrations have been performed for a period of 24hours with two different sets of initial conditions in which the three dimensional structure of the initial easterly pattern is specified through pre-specified wind shear and different values of the Richardson number. The order of magnitude of vertical velocities, the time rate of change of kinetic energy and the phase speed of the disturbances is discussed for both the cases. The preliminary results indicate that, even the tropical motions have appreciable degree of vertical coupling and baroclinic nature in the cases of low Richardson number. The results seem to be of special interest in context of the fact that even the mean monthly values of static stability during summer are found to be very small and even negative in the middle and lower troposphere in the tropics.
The author's previous study on an objective analysis method (1958) is extended, by introducing terms of time variation and the dynamical equations which describe the time variation, for the purposes : 1) to filter and suppress unnecessary meteorological high frequency noises contained in the initial data and forecast fields and 2) to obtain the dynamically sound initial values for the areas or layers of lacking observation. The fundamental concept of the method is explained using the most simple examples of dynamical constraints; linear advection and linear diffusion.