A three-level linear-balance model for studies of the general circulation using the spectral method is presented with some preliminary results of time integration of the model for a specified terrestrial atmospheric condition. The model is, firstly, integrated for 180 model days under a specified condition to obtain a quasi-steady state without eddies, starting from a calm atmosphere. The zonally symmetric state thus obtained is unstable for the disturbance with zonal wavenumber 5 or 6, according to the linear theory of baroclinic instability. Secondly, after adding disturbances with small amplitudes to the above results of zonally symmetric model, the model integration is continued for another 180 model days to obtain a quasi-steady state with including eddies. The baroclinic instability appears to be released around the day 40, and thereafter the near-equilibrium state is obtained. The results are illustrated mainly for the zonal mean field averaged during either the period of the last 100 days or that of release of baroclinic instability (the day 30-50), and for the time evolutions of energy components and energy conversion terms. The results are not necessarily realistic, because somewhat large values are used tentatively for a part of several parameters, such as the vertical eddy mixing coefficient. Nevertheless, reasonable results are obtained and they are consistent under the model assumption. In order to study extensive problems concerning the general circulation and the climate of the planetary atmospheres, such a numerical model as is simple, economical and easy to handle is useful and worth-while to construct. So far as the preliminary results are concerned, we may say that the present model is one of powerful tools for further studies on the above subjects.
As a continuation of a previous study (Yamasaki, 1975), several numerical experiments are performed to investigate the properties of a CISK mode which is not essentially affected by surface friction. A set of equations used for time integrations includes equations for cloud water and rainwater with parameterized cloud physical processes such as autoconversion, collection and so on. The horizontal grid size is taken to be 200m in the convective area so that individual cumulus clouds may be properly described. For the save of computational time we adopt an initial condition such that formations of cumulus clouds are limited in a small area with a scale of only several tens of kilometers. The depth of the conditionally unstable layer is taken to be shallow so that the vorticity of the disturbance, which develops through its interaction with cumulus clouds, does not become large enough to cause appreciable frictional convergence. Numerical experiments indicate that the advection of momentum as well as the pressure gradient force are important terms in the equation of horizontal motion. The convective transport of momentum acts to suppress rapid intensification of the meridional circulation which is caused by the temperature gradient due to collective effects of convective heating. The Coriolis force has only modifying effects on the growth and structure of the disturbance. Rainfalls in the convective area do not occur randomly but systematically to some extent. In particular, outward propagations of rainfall area are notably found. It is unlikely that cumulus clouds are successively formed when the autoconversion from cloud water to rainwater is not taken into account. It seems that the evaporation and drag force of rainwater play an essential role in the CISK mode under consideration. The statistical effects of cumulus clouds on the large-scale heat and water vapor budgets as well as the behaviors of individual cumulus clouds are also discussed.
Some of the characteristic features of monsoonal surges during the northern winter were investigated using wind and temperature data over China, the East and South China Seas, and the extratropical and tropical Western North Pacific during the period 16 November 1970 through 15 March 1971. Low-level monsoonal surges are most pronounced over the East China Sea, with dominant spectral peaks around 4.3-4.6 days for meridional winds, temperature, vertical velocity, and heating rate below about 700mb. For 4.3-4.6 day oscillations in the lower troposphere, the cospectrum between temperature and meridional winds is positive (northward sensible heat transport), while temperature is negatively correlated with vertical p-velocity (local kinetic energy generation). In comparison, the South China Sea is characterized by dominant spectral peaks at 6.0-6.7 days, with secondary maxima occurring around 4.3-4.6 days. The coherence between the East and South China Seas is generally higher than 0.5 in the lower troposphere. Strong monsoonal surges over the South China Sea coincide with above normal ascending motions and consequent condensation heating throughout the troposphere. Another feature of interest in computed spectra is the existence of marked peaks around 20-30 days, which are clearly separated from short-period (4-6 day) oscillations associated with monsoonal surges. Composite 200mb maps for 20-30 day filtered geopotential data depict eastward phase propagation (-4-10m s-1) in tropical latitudes, which is most distinctly defined over the Bay of Bengal-Malaysia-South China Sea region. This is opposed to near zero phase speed (standing) at higher latitudes around 50°-60°N. It appears that wet (dry) spells near Malaysia occur in association with the passage of eastward propagating ridge (trough) systems. During wet (dry) spells, the atmospheric temperature becomes warmer (colder) than usual with above (below) normal ascending motions, as confirmed from a large negative cospectrum for 20-30 day oscillations between these two quantities. Phase changes between wet and dry spells over the South China Sea region are closely related to longperiod monsoonal fluctuations over the East China Sea and its vicinity. The coherence for T and v between these two regions is substantially large (>0.5) for 20-30 day period oscillations, with the South China Sea lagging behind the East China Sea by about 1-2 days.
A simple but practical model for the growth of a connective mixing layer is derived by integrating the entrainment rate equation proposed by Deardorff et al. (1969). The development of the mixing layer height is determined by three parameters which are the potential temperature gradient in the stable layer capping the mixing layer, integrated surface heat flux and initial value of the mixing depth. Also a model for the time-height variation of the turbulence structure in the mixing layer is proposed based on the above growth theory and turbulence structure model of the mixing layer presented by Yokoyama et al. (1977a). In this paper, the surface heat flux is assumed to be proportional to the insolation disregarding absorption by the atmosphere. The model is applied to data obtained by airplane over flat terrain in the vicinity of Tokyo, in March 1972, summarized by Gamo et al. (1976a). Estimation of the diurnal variation of the mixing layer structure including potential temperature, energy dissipation rate, rms of vertical wind fluctuations and turbulent eddy diffusivity seems to agree favorably with observations.
Snow crystals extended in the direction of the b-axis were observed in a temperature range from -8°C to -10°C at the summit of Mt. Teine. They had almost the skeleton structure and possessed double plates. Observing this type of snow crystals in different stages, it was considered that when a prism face develops abnormally in the direction of the b-axis, neighbouring two frames curve and approach to each other, and then are combined to a new frame extending in the direction. The occurrence frequency of this type of crystals was about 2% in all snow crystals observed throughout 10 hours. This type of snow crystals was morphologically the same as Schaefer's flare crystals and Yamashita's trigonal dendrites except for a strange behaviour of frames. It is considered that the abnormal growth towards the b-axis occurs when a prism face develops at a rate of more than twice of those of neighbouring prism faces. Snow crystals with the repeated growth of the b-axis were also observed. It is considered that the repeated growth of the b-axis was due to the bunching of growth layers.
The properties of diamond dust type ice crystals were studied from replicas obtained during the 1975 austral summer at South Pole Station, Antarctica. The time variation of the number concentration and shapes of crystals, and the length of the c-axis, the axial ratio (c/a) and the growth mode of columnar type crystal were examined at an air temperature of -35°C. Columnar type crystals prevailed, but occasionally more than half the number of ice crystals were plate types, including hexagonal, scalene hexagonal, pentagonal, rhombic, trapezoidal and triangular plates. A time variation of two hour periodicity was found in the number concentration of columnar and plate type crystals. When the number concentration of columnar type crystals decreased, the length of the c-axis of columnar type crystals also decreased. When the number concentration of columnar type crystals increased, the length of the c-axis of the crystals also increased. There was sufficient water vapor to grow these ice crystals in a supersaturation layer several tens to several hundred meters above the surface. The growth mode of columnar type crystals was different from that of warm and cold region columns reported by Ono (1969). The mass growth rate was 6.0×10-10gr•sec-1, and was similar to that obtained in cold room experiments by Mason (1953), but less than that found in field experiments by Isono, et al. (1956). The plate type crystals prevailed occasionally at an air temperature of -35°C, at which the sheath, hollow and solid prism (column) usually prevail. An important question arises with respect to the crystal habit with air temperature lower than -22°C in the Ta-Δρ diagram consolidated by Kobayashi (1961).
Synchronous meteorological satellite data for the tornado producing squall line of March 20, 1976 were examined. Both the Infrared and Visible observations were found to be more than adequate to define one of these meso-convective systems on the scale of the cloud. Covariance and cross-covariance functions were modeled from the data and subsequently used to infer a sampling lattice in xyt sufficient to explain at least 85% of the signal variance.