The growth rates of solid precipitation particles in a supercooled cloud were studied by numerical computations for the case when sublimation and the capture of cloud droplets take place simultaneously. The principal conclusions obtained from the computations are as follows. (1) The necessary condition for the predominance of the capture-process in the growth of solid precipitation particles (in other words, the condition for the formation of graupel) is that the particle is initially a “frozen drop” with radius larger than a critical value, which is dependent mainly upon the initial height of the particle. (2) The relationship between the radii of graupel particles at cloud base and the height of the cloud top which was obtained from computations is in satisfactory agreement with that obtained from observations. (3) The computationally obtained probability that “frozen drops” of the critical size are formed due to the nucleation of supercooled water drops by their collision with ice crystals associated with atmospheric ice nuclei is about 10% of that expected from observations.
Cirrus uncinus clouds were observed by stereophotographs, and were analysed by means of the trigonometric method. It was confirmed, as a result, that the trail of the cloud had a spatial structure, and that the velocity of the movement of the cap of the cirrus uncinus cloud and the end of its trail coincided with the wind velocity at the respective level. From this fact it was explained that the cloud extended and rotated on a horizontal plane. Namely, the cloud showed the tendency for the trail of the cloud to approach in direction parallel to the prevailing vertical wind shear.
The cirrus uncinus cloud is considered to be a trail of ice crystals released from the mothercloud. In the present paper a theoretical and observational study was made to determine the influencing factors related to the characteristic shape of the clouds. The shape of the clouds was numerically computed under reasonable conditions of temperature, humidity and wind velocity based, on observational data. As a result of the computation, it was found that the shape of cirrus uncinus clouds depended on the mass of cirrus uncinus cloud particles and on the vertical wind shear at the cloud level, however it was found that the shape of the clouds did not generally depend on the type of cirrus uncinus cloud particles except in the case of needle type particles with large axial ratios.
The distribution of atmospheric motion with height following a change in terrain roughness is studied by numerically integrating the equations of motion. Instead of employing the boundary layer approximation method discussed by Elliott and by Panofsky and Townsend, we specify a functional form for the coefficient of eddy viscosity. For a shallow atmospheric layer, where we may neglect the Coriolis force and assume the eddy viscosity to vary linearly with height, there is a remarkable accordance between our numerical calculations and the results of other theoretical and experimental studies.
A method of evaluating the atmospheric turbidity coefficient from direct solar radiation measurements without using filters and from simultaneous radio sonde observations is formulated, and the relation between the turbidity coefficient and Linke's turbidity factor is discussed. By application of the present method to the IGY data, the distribution of the turbidity coeffcient in the northern hemisphere and its seasonal variation are estimated. The effect of water vapor in the atmosphere and of rain or snow on the turbidity coefficient are discussed.
The cumulus model proposed by Asai (1967) is applied to cellular cumulus convection in a moist atmospheric layer uniformly heated below and cooled above. The governing system of equations derived has a steady state solution of cumulus convection independent of initial input disturbances. A preferred mode of steady cumulus convection can be expressed in terms of an amount of heat supply, employing the selection principle that a preferred mode is one for which the lapse rate of temperature is the lowest. An examination of the results shows a coincidence with the feature of cumulus clouds in colder air over warmer water. However, tall vigorous cumulus convection is hardly expected to develop by uniform heating even with a large amount of heat supply.
The power spectra of the meridional component of the wind from the ground to the 30-kmlevel at 17 stations in the tropical and sub-tropical Pacific are studied based on special upper wind observations taken during the period April through July 1962. In equatorial latitudes, the power spectra show a peak at a period close to 4 days corresponding to the passage of "equatorial waves" in the lower tropospheric easterlies. A very large spectral density is found at the periods 4 to 5 days throughout the upper troposphere and the lower stratosphere where the mean wind is from the west. The peak spectral density reaches a maximum at about the 17-km level near the tropopause. The spectral density gradually decreases with height in the stratosphere where the mean wind is from the east. In sub-tropical latitudes, large disturbance energy is associated with the upper tropospheric westerlies and a large portion of the spectral density is contained in the wave period longer than 5days. A sharp suppression of the spectral density takes place at the lower boundary of the stratospheric easterlies. From the computation of the coherence and the phase difference of the meridional component of the wind, the vertical and horizontal structure of the disturbances is studied. The large horizontal extent and the westward inclination of phase lines of the disturbances in the upper troposphere and in the lower stratosphere are revealed. The horizontal coherence of the lower tropospheric disturbances in the east-west direction is very low. The phase lines of the lower tropospheric disturbances are inclined eastward with height. The average wavelength of the disturbances at various levels is estimated from the relation between the phase difference and the longitudinal difference of the stations.