The previous simple baroclinic model (Tokioka, 1970, 1971) is extended to include Convective effects, i.e., convective heating and momentum exchange, and an attention is focused on the most unstable mode. In the wavenumber range studied, convective heating is more effective to the wave than momentum exchange due to convective motions. The preferred scale shifts to smaller scales and the growth rate increases owing to convective effects. The preferred scale in the meridional direction decreases abruptly with the decrease in wthe Richardson number (Ri) for relatively small Ri. In accordance with this change, the structure of the wave tends to have several characteristic differences from ordinary Eady's type baroclinic waves.
Wave disturbances appeared in the China continent and the Eastern China Sea in February 1968 are studied by the spectral method and the dynamical computations of the vertical velocityand the diabatic heating. Two types of disturbances are obtained. The one is the wave with 4-to 5-day period and the other is the wave with 1.5-to 2-day period. The disturbances with 4-to 5-day period exist in the regions to the south of 32*N where the southern jet currents flow. These disturbances propagate from west to east with the wavelength about 4, 000-5, 000km and their amplitude becomes large in the Eastern China Sea. The vartical structure of the disturbance is similar to that of a baroclinic unstable wave. Some disturbances of these waves develop suddenly as going over the Eastern China Sea. The diaba tic heating and the coupling between the lower tropospheric disturbances and the troughs in the upper troposphere may play an important role in the extreme development of the disturbances. Short-period disturbances with 1.5- to 2-day period exist in the lower troposphere below 600mb in the southern part of the Eastern China Sea especially during the period from 1 to 10 February. These disturbances have the wavelength about 2, 000km and their vertical structure is also similar to that of the baroclinic wave, i.e., the trough axes tilts slightly westward with height, warm air covers the region on and the east of the trough and upward motion occurs to the east of the trough. These medium-scale disturbances can be seen in the synoptic patterns. The Richardson number of the mean field is order of unity and these medium-scale disturbances are the baroclinic waves developing in the atmosphere of low Richardson number as suggested theoretically by Gambo (1970, a, b) and Tokioka (1970).
An investigation is made of the stability of the Ekman boundary layer flow with a thermally unstable stratification based on perturbation analysis. Three different types of the instability associated with the flow may be found, preference of which depends on Reynolds number, and Richardson number. The thermal instability, which is of gravitational origin modified by the shear flow, is dominant for Ri_??_10-3, while the other two, which are of inertial origin modified by the thermal stratification, are found for Ri_??_10-3 where the Richardson number Ri is taken to be positive for unstable stratification. One of the inertial instabilities may occur for low Reynolds number ranging 55_??_Re_??_150 and the other predominates for Re_??_ 150. Stability properties of the three different types and characteristics of the associated unstable perturbations are examined in detail by means of numerical solution of the perturbation equations. It is noticed that both the types of the inertial instability are slightly influenced by thermally unstable stratification in the range of Ri_??_10-3.
The horizontal movement of cumulus humilis clouds near Sapporo was measured by the stereophotogrammetric method in the summer seasons of the years 1969 to 1971 in Sapporo. The direction and speed of individual cloud movements were presented on charts. The environmental meteorological conditions were obtained from the Sapporo rawinsonde soundings. By comparing the analytical results of clouds with the environmental meteorological conditions, the following results were obtained. The direction of horiz ontal movement of the higher cumulus humilis clouds was nearly the same as that of prevailing wind direction at the cloud level (exactly speaking, near cloud base level), however, the direction of the lower clouds was not in agreement with the wind direction. The critical ground height for the agreement of cloud motion direction with wind direction was found to be about 700 meters. The speed of horizontal movement of cumulus humilis clouds was generally less than prevailing wind speed at the level of cloud base. It was also found that the speed of larger clouds was slower than that of the smaller clouds when their heights were the same. The general tendency was that the lower the clouds, the lower the motion speeds, and the greater the vertical wind shear, the lower the cloud speed. The slowness of cloud speed was qualitatively explained by considering the upward transportation of low horizontal momentum in thermal convections under a condition of the positive vertical wind shear.
An experimental study on the ice nucleating properties of oxides of some rare earth elements has been carried out by the use of differential interference microscope. The humidity around the nuclei was controlled by a wall of ice. It has been found that the ice nucleating properties of lanthanum oxide, praseodymium oxide are most prominent among the oxides examined.
Using a simple drop-freezing technique as in earlier studies, the ice nucleation activities of certain iodide and iodate systems, with and without soluble salts, have been investigated. It has been found that, of the systems tested, the iodide systems commonly used in the conventional cloud seeding, which are AgI.NaI and AgI.KI, are the least active. Also, the iodate system used in the pyrotechnic seeding, which is AgIO3+KIO3, is not the most active. Better nucleating systems have been named for possible use in both the types of seeding. The comparative activities noticed of the systems tested have been explained on certain qualitative considerations.