The two-layer quasi-geostrophic spectral model with friction and diabatic heating, which was used by Lorenz (1963) for the study of the mechanics of vacillation, is extended to a less severe truncated model with m lateral modes on a β-plane, in order to investigate the dynamical properties of non-linear baroclinic waves in a rotating fluid with differential heating. Two experiments are performed by using this extended model: One is 4-mode experiment aiming to depict the barotropic process more sufficiently than Lorenz's model through higher modes, and the other is β-plane experiment to clarify the effect of sphericity on finite amplitude baroclinic waves. In the 4-mode experiment the flow regimes qualitatively similar to the result of laboratory experiments are obtained with the aid of analytical and numerical procedures. Zonal mean flow, eddy fluxes and energy budget are also calculated to elucidate the feature of vacillation. It is found that vacillations are primarily caused by the alternating dominance of baroclinic and barotropic processes. Results of the β-plane experiment indicate that the regimes of flow do not change so drastically by the β-effect but the cycle of vacillation is elongated due to the change of the phase velocity of disturbances.
Several numerical experiments of axially symmetric tropical cyclones are performed by use of Arakawa-Schubert (1974)'s parameterization of cumulus convection. The main purpose of the study is to examine whether or not the development and structure of tropical cyclones can be simulated by their parameterization. The model includes five layers, four of which correspond to the free atmosphere and one to the mixed layer. According to the height of cloud top level, clouds are classified into three types; the tallest type (H-type), the middle type (M-type) and the lowest type (L-type). Their top heights are assumed to be 13km, 9km and 5km, respectively. The results of the numerical experiments indicate that the development of tropical cyclones can be simulated realistically by using their parameterization. Many features of the structure as well as evolution of a parameterized cumulus ensemble, are also well simulated. An eye and an eyewall are formed in the rapid developing stage when the tangential velocity near the center becomes strong. The eyewall is located around the radius of the maximum tangential velocity. Clouds in the eyewall are occupied by the H-type clouds in the later stage, although the M- and L-type clouds coexist with the H-type clouds in the early stage. In contrast to eyewall clouds, clouds in the outer region tend to have propagating nature. The effect of the surface friction is also investigated. The following results, which were obtained by Yamasaki (1977b) with a non-parameterized model, are confirmed with the present model: (1) Surface friction is indispensable to the formation of an eyewall and an eye. (2) Surface friction does not play an essential role to the development of a vortex at the stage when the vorticity is weak. The tropical cyclone simulated in this study is similar to that of Yamasaki (1977a) in many respects. Numerical experiments are also performed by changing the initial condition and the value of hM (moist static energy in the mixed layer). It is found that the initiation of rapid development sensitively depends on the magnitude of the cloud work function for the H-type.
Thermal and dynamical structures of the Convective motions in a rotating fluid annulus, heated internally by passing an a.c, current through the fluid, are studied experimentally. The effects of internal heating are seen in the following results. 1) The measurements of the rate of radial heat transport to the inner wall and the drift angular velocity of the vortex disturbances show that they depend on the rotation rate Ωin a similar way, with the minimum at a certain rotation rate Ωm. 2) The distributions of the zonal mean temperature show that, when Ω>Ωm, the region nearby the mean radius of the fluid layer becomes warmer than the inner and outer regions at the same height. 3) The mean zonal flow of the wave motion for Ω>Ωm, as well as the axisymmetric zonal flows, has the distribution of the vertical component of vorticity with negative values over a wide region at the top-surface. 4) The amplitudes of the temperature and pressure deviations increase with Ω and, near Ωm, the inclination of the axes of the temperature deviation from the vertical direction becomes least and the most active outward heat transport due to the vortex disturbances takes place. The analysis shows that the fundamental structures of the vortex disturbances developing in the internally heated system are the same as those of the baroclinic waves analyzed by Matsuwo et al. (1976, 1977) in the wall-heated system. Therefore, the indication by Hide and Mason (1970), namely, that the principal characteristics of the flow (in the rotating fluid annulus) are fairly insensitive to the radial dependence of heating and cooling, is supported from the view-point of structure analysis.
Cell patterns of the finite-amplitude Bénard-type convection in a shear flow with a curved vertical temperature profile are investigated near the critical state by means of the Landau amplitude equations. The steady solutions are obtained and their stability is discussed in relation to three parameters which represent the deviation of temperature from the linear profile, the magnitude of the shear of the basic flow and the deviation of the Rayleigh number from the critical value for the curved vertical temperature profile, (ΔR)*. The following results are obtained: (1) The roll solution is unstable only in a narrow range of positive (ΔR)* when the magnitude of the shear is lesss than a critical value. When its magnitude exceeds the critical value, the solution becomes stable for all positive values of (ΔR)*. (2) The solution which is reduced to a hexagonal one in the absence of the shear is modified to give a longitudinal one as the magnitude of the shear is increased. The solution becomes unstable when the magnitude of the shear exceeds a critical value.
The effects of the mixing layer which will develop over the land in the daytime on the sea breeze circulation are investigated by the two-dimensional numerical model using Yamamoto's empirical eddy diffusion formula in the transition layer. The results show when the mixing layer well develops the sea breeze is stronger and the penetration speed of the sea breeze front is faster than in the hypothetical cases in which the mixing layer is not well developed. Diffusion processes of pollutants associated with the land-sea breeze are also investigated by the both Lagrangian and Eulerian methods. It is found when the sources of pollutants exist only near the coast, no high concentration of the pollutants occurs in the mixing layer, because as the sea breeze is entering inland, the sources of the pollutants are left out of the mixing layer and the ascending flow at the sea breeze front prevents the pollutants from entering the mixing layer.
A method of numerical time integration is proposed on the basis of a moving variable grid system which efficiently approximates the solution. The grid movement is continuously performed on the Lagrangian concept. A barotropic, free surface model is numerically integrated to examine the accuracy and computational stability of numerical integration with the moving variable grid. Results of the proposed method appear nearly the same as the control run with a fine uniform grid.
Thermal stratification in medium-scale (wave length of -1, 000km and period of -20 hour) disturbances in the Asian subtropical humid region is studied based on dense upper observation data. Attention is focussed on thermodynamic process associating with variation of instability in the lower troposphere (600-900mb). Generation of instability in the southeast quadrant of the disturbances was mainly due to the rise of equivalent potential temperature, which was primarily attributed to advection of high θe with southerly wind in the lower layer (-900mb). While the release of the generated instability is mainly due to differential heating in the narrow (-(200km)2) area of active convections in the disturbances. Cumulus mass flux, associated stability change and the height of cloud top in the unstable area of the disturbances are estimated by applying the cumulus parameterization scheme to the observed soundings. Soundings in the Asian subtropical humid region are compared with those in tropical squall lines in VIMHEX and GATE areas.
A method for the detection of individual submicron nitrate particles has been developed. It is based on the reaction of the nitrate ion with a nitron thin film. A nitron thin film is prepared by a vacuum deposition of nitron and, from the measurements of infrared spectra, it is found that a nitron thin film is not modified in the process of a vacuum deposition. The reaction of nitrate in individual particles with a nitron thin film proceeds . under the octanol saturated atmosphere. Under this reaction condition, the presence of nitrate in individual particles is indicated by the appearance of a bundle of needle-like crystals and the reaction is reproducible. It is also found that under this reaction condition the sulfate and chloride ions contained in atmospheric aerosols do not interfer, The method is specific for nitrate and particles containing nitrate of more than 10-14gr can be detected. An example of the application of the method to atmospheric aerosols is shown.