Analytical studies of day-to-day behaviour of the travelling and quasi-stationary ultra-long waves in the 1967/68 winter stratosphere are made by means of the time-filter method [Iwashima and Yamamoto (1971)]. A brief description of the method of analysis and a criterion of numerical reliability for treating erroneous data are provided in the first place. Daily variations of zonal mean temperature and zonal mean wind which characterize the sudden warming are firstly depicted. Secondly from the analysis of the total ultra-long waves with wavenumbers one, two and three, such a few characteristic features as amplitude-decay of the wavenumber one and simultaneous amplification of the wavenumber two at the sudden warming, which has been suggested by Teweles (1963), etc., are confirmed again. Thirdly, in order to show the process of applying the time-filter method, the wavenumber two is analyzed somewhat in detail, because of its predominance during the period of sudden warming. It is found out that the amplification of several fluctuating components of the quasi-stationary part is accompanied with the sudden warming. The travelling part is classified into the westsward and eastwardmoving modes. Finally, the travelling and quasi-stationary parts of the ultra-long waves with the wavenumbers one, two and three are described in meridional- and verticaltime sections. The travelling part of wavenumber one predominates during the warming stage and rapidly decays at the mature stage of the warming. The former stage may correspond to the "third stage of the sudden warming" by Miyakoda (1963) or the "migratory-stage" termed by Hirota (1967). While the quasi-stationary parts of wavenumber one and both parts of wavenumber two amplify with the warming and decay afterward. Taking account of the results of the former observational and theoretical studies [Hirota (1968), Matsuno (1971), etc.], we may infer the following close relations: i) the non-linear interaction between the travelling part of wavenumber one and that of wavenumber two, and ii) the interaction between the quasi-stationary part and the travelling one of the respective wavenumber, as Murakami (1960) showed the energetical relation between the stationary disturbance and the transient eddy.
The movement of zonal harmonic waves with wavenumbers n=1-6 and with different periods is studied at the 500-mb level and 60°N in 20 winters since 1947/48. The deviations from various running means and the 24-hour tendency field are utilized, and on the basis of time-longitude harmonic analysis, which is essentially equivalent to quadrature spectrum analysis, the movement of travelling waves is investigated in the wavenumber-period space. It is shown that the planetary waves with n=1 and 2 and with periods from 10 to 50 or 60 days move generally westward, and that the wave n=2 with a period of 3 days, the wave n=3 with periods smaller than 10 days and waves n≥4 with periods smaller than 30 days, move mostly eastward. For n=3 retrogressive and progressive waves are observed in the range of periods from 10 to 30 days. Thus for periods larger than about 10 days the wave n=3 separates the travelling waves into retrogressive and progressive waves. The travelling wave n=6 with longer periods are considered to be non-existent because the amplitude of the wave is very small. For the remaining periods the existence of travelling waves is not known mainly owing to the lack of sufficient data. Accordingly the wavenumber-period space is composed of five domains and a schematic model of the travelling planetary-scale waves is presented. In general the amplitude of planetary waves increases with increasing period and decreasing wavenumber but it is almost independent of the period for the higher wavenumbers. As regards the amplitude the wavenumber-period space is divided into two domains, and the amplitude is nearly proportional to period and wavenumber in the first and second domains respectively.
The role of higher mode component oscillations in the atmospheric lunar tides is discussed to show that higher mode component oscillations can modify significantly the vertical and latitudinal distributions of the tides. For example, a distinct phase inversion with height of the northerly-wind oscillation is shown to form around 120km for an atmospheric model.
The response of the tropical atmosphere for the large-scale (wavenumber 4) initial forcing is examined in terms of the vertical scale using a 10-layer primitive model. In case of the initial forcing over the equator, the induced distrurbance broadly spreads to the middle latitude when the forcing has a large vertical scale. As the vertical scale becomes small, the response is strongly confined to the equatorial region and the disturbance resembles the mixed Rossbygravity wave. The response is also examined for the initial forcing given at the middle latitude boundary. When the vertical scale of the forcing is large, the tropical atmosphere is affected intensely, but the influence does not propagate far into the equatorial region in case of the small vertical scale. It is also shown that the horizontal shear between the equatorial easterly and the mdilatitudinal westerly tends to prevent the above interaction. Under the shear of 10 m⋅s-1/10°, the influence of the mid-latitudinal initial forcing of wavenumber 4 does not penetrate into the tropics even for the large vertical scale. Some interpretation of recent works of tropical data assimilation is also mentined based on the results of this study.
Measurements of falling velocity of individual ice crystals produced by dry ice seeding were made in a cold room. The falling velocity was measured by stroboscopic photographs of falling ice crystals and each crystal was replicated to observe the shape and size. The relationship between the falling velocity and the dimension of crystals was obtained for the plane and the columnar type of crystals. Moreover, the measured falling velocity was generally explained by the computation method which use the drag coefficient obtained from the model experiment.
A stereoscopic treatment of successive radar pictures was devised for the analysis of movement of PPI radar echoes. The stereoscopic method was applied to the analysis of mesoscale wind structure in snow clouds in the winter monsoon season in Hokkaido. The results of the analysis showed that the method was highly useful for analyzing such mesoscale structures, and it was discovered that mesoscale convergence and divergence zones were alternatively distributed and that they were vertical to the prevailing wind direction at the echo level. The wave length of the alternative distribution of the zones was, about 20km, and it was considered that the distribution was originated from an internal gravitational wave disturbance. Considering the wave length, the disturbance analyzed, was of intermediate scale between cumulonimbus clouds and mesoscale disturbance of about 100km size previously found by Matsumoto, Ninomiya and Akiyama (1967) in snowy weather.