By making use of height data at the 500-mb level during a winter season (December 1974, January 1975, February 1975), the spectral densities of vorticities for ultra-long waves in the frequency domain are examined. The result shows that the spectral densities for zonal wavenumber k=1-3 are approximately proportional to the minus second power of the frequency in middle latitudes. The spectral densities for each term in the vorticity equation of ultra-long waves, such as the advection term and so-called β term, are also examined. And it is shown that the nonlinear interaction of baroclinic waves due to the advection term in the vorticity equation plays an important role in determining the rate of change of vorticity for ultra-long waves. In the last part of this paper, the statistical forecast of the height for ultra-long waves at the 500-mb level is discussed under the assumption that the height is regarded as a stationary random process. And it is noted that the mean square of forecast error tends to the climate variance in a few days.
Empirical Orthogonal Function analysis was applied to 4-6 day filtered wind and temperature data over eastern China, the East China Sea, southern Japan, the South China Sea, and the tropical western Pacific during the period 16 November 1970 through 15 March 1971. Eigen vector patterns for the first two modes indicate anomalous low-level northerly surges which tend to move progressively eastward across the China-East China Sea-Japan region. The combination of anomalous northerlies, below normal temperature, and abnormally strong descending motions results in a northward sensible heat flux and local kinetic energy generation below 700mb over this region. The outstanding features of the third eigen vector occur over the South China Sea where strong low-level northerly surges are contrasted with pronounced upper-level southerlies and much higher than normal temperature above 300mb. This region is also characterized by abnormal ascending motions and strong diabatic heating in the deep atmospheric layer from 850 to 200mb, perhaps reflecting pronounced convective activity. Flow patterns of the third eigen vector indicate the existence of a local Hadley cell with updrafts over the South China Sea and downdrafts near Japan.
A subtropical frontal depression brought heavy rainfalls over western Japan on June 27, 1972. In the present study, we intend to describe the mesoscale features of precipitation over the depression with relation to air-mass stratification and circulation. The echo band along the trailing portion of front brought intense convective rainfalls. The area of unstable air (saturated, -∂θe/∂p--12°K/400mb) was localized around the echo band. There was 1-3 hours time lag between the generation of strong instability and onset of heavy rainfalls. The area of maximum rainfalls shifted northward -30km from the area of maximum instability. Radar observation indicated the suppression of weak echoes around strong echoes. The stability change associated with the release of instability is evaluated by cumulus parameterization scheme and heat energy budget calculation.
A turbulence model is proposed for the prediction of the asymptotic behavior of turbulence statistics in neutral surface layer. Following equations are analytically investi-gated: ones for the second-order moments of turbulence, and one for its length scale. A few empirical assumptions are made for the turbulent transport terms in the equations of second-order moments. With the present model, are deductively obtained the well-known semiempirical results: the turbulent length scale proportional to the mixing length, and the logarithmic vertical distributions for the mean wind velocity and the mean potential temperature. The asymptotic solutions of kinematic and thermal second-order moments of turbulence are also obtained.
The turbulent structure under stable conditions in the atmospheric boundary layer (ABL) has been investigated by tower measurements, of the turbulent fluctuations and vertical mean profiles of wind velocity and air temperature. The results are summarized as follows: (1) For the parameter of thickness of the turbulent ABL under stable conditions, the height hq at which turbulent heat flux disappears is a more reasonable choice than the height hθ derived from the potential temperature profile, and hq has linear relation to the Monin-Obukhov stability length. (2) Unlike the constant flux layer near the ground, the absolute values of vertical heat flux (q) and momentum flux (u*) decrease with height in the stable ABL. According to these results, the ABL model proposed by Yokoyama et al. (1977, 1979) is applied to the turbulent ABL under stable conditions. We conclude that the vertical profiles of q and u* are approximated by the power function ζm andζn, respectively (where, ζ=1-z/hq, z: height, hq: thickness of the layer, m _??_3/2, n _??_1/2) and the same relations which described the turbulence quantities, temperature and wind velocity gradients in the constant flux layer are valid for whole stable ABL by replacing surface values of q and u* by their local values.
It is studied how the size distribution of the so-called giant aerosols is changed by the diffusion-sedimentation and washout in the atmospheric boundary layer. An instantaneous and a continuous sources of infinite horizontal extent are assumed for ejection of aerosols into the atmosphere. The size distribution are calculated numerically as a function of time and height above ground for various combinations cf the eddy diffusivity profile and the rainfall intensity. The computational results are as follows. (1) The size distribution changes with time or height in such a way that the concentration of particles decreases with increase of particle size. (2) The effect of the diffusion-sedimentation simply reflects on the deforma-tion of the size distribution of larger particles. (3) The degree of deformation of the size distribution by the washout increases with increase of particle size in the case of instantaneous source, and it is most pronounced for intermediate particle size range when the time duration of particle emission is sufficiently long.
Multistation observation of the electric field-changes due to lightning discharges have been made around Unoke near Kanazawa during the winters of 1976-1977 and 1977-1978. The following characteristics of the cloud discharge have been found from these observa-tions by using the data of 221 cloud discharges in seven storms. (1) The occurrence frequency of the cloud discharge is 77% of all lightning discharges. The average duration of the cloud discharge is 330ms. (2) The cloud discharges are preferentially initiated by ascending negative streamers in contrast with those in summer storms, which are initiated by descending positive streamers. (3) The winter thunderstorms can be classified into three types in accordance with the direction of the streamer development in cloud discharge and with the polarity of ground discharges. (4) In the storm on Dec. 2, 1977 the heights of positive and negative charges were estimated; they were about 6 km and 3 km, which corresponded to the temperature heights of -30°C and -10°C respectively in the storm cloud.
Assuming the initial streamer development of the cloud discharge be represented by the movement of a point charge with constant velocity, the parameters of the initial streamer, such as height of starting point, charge amount, direction and velocity of propagation, were determined by using the data of electric field-change measured simul-taneously at three to seven stations. The following characteristics of the initial streamer of the cloud discharge were deduced from the analyses of thirteen discharges in the winter thunderstorms at the Hokuriku coast: (1) Cloud discharges originate in the region of the temperature from -6°to -10°, which is the same temperature range as that in the summer thunderclouds. (2) The electric charge carried by an initial streamer is about 30 to 130C, and the average value is 63C. (3) The direction of streamer progress is upward, and the zenith angle of the progress is less than 30°. (4) The streamer velocity is of the order of 104m/s, and depends on the altitude of its starting point.
Freely falling water droplets 20-100μm in diameter were frozen by collision with ice crystals at temperatures between -10 and -20°C. Crystalline nature of frozen droplets depended on the nature of the crystal faces to which they accreted. Frozen droplets on the prism face were single-crystalline with the same crystal orientation as the ice crystal. Frozen droplets on the basal face were also single-crystalline with the same orientation as the ice crystal at temperatures above -13°C, and were poly-crystalline at temperatures below -19°C. Two types of the growth of frozen droplets were observed. In most cases of single-crystalline frozen droplets, circular crystal faces appeared and the droplets grew to snow crystals with well-known crystal habit as shown by Nakaya's diagram. In the case of poly-crystalline frozen droplets and several single-crystalline droplets frozen at temperatures below about -17°C, steps parallel to the basal faces were formed or the spherical surface of the droplets became rugged in shape. Some of the steps or a part of the rugged surface grew into plate-like crystals. Such plate-like growth occurred even at temperatures below -24°C and seems to be related to the formation of snow crystals of a combination of columns and plates.
One of the most significant advances in numerical forecasting has been the introduction of the semi-implicit time differencing technique, which allows a computational saving of factors up to three over conventional explicit methods. The method does, however, involve casting the primitive equations in a more elaborate form and solution procedures of greater sophistication are required. Along with this increased complexity have come several difficulties of formulation, including the derivation of the Laplacian operator for the Helmholtz equations; and the selection of an appropriate computational grid on which to solve these equations. In the past, semi-implicit schemes have encountered trouble from the above-mentioned sources and were only able to be successfully implemented after careful reworking of the methods (McGregor and Leslie (1977), McGregor et al. (1978)). Because of the important economic value of the semi-implicit approach, it is timely to emphasize again what has been learned about the vagaries of the semi-implicit method, particularly when a scheme proposed recently by Kudoh (1978) appears to have overlooked the problems.
The cumulus mass flux obtained by the diagnostic analysis is verified by using digital SMS-1 IR brightness data and precipitation calculated from radar measurements. The time variations of the cloud mass flux due to deep clouds correlate quite well with those of IR brightness and precipitation. The precipitation calculated from the model is comparable to that observed. Relationships of the cloud mass flux, IR brightness and precipitation to the African wave disturbance are also discussed.
This study examines 16 recurving tropical storms and typhoons that occurred in the western North Pacific Ocean in 1971, to determine the characteristics of the storms after they became extratropical. Many of the extratropical storms that evolved from tropical cyclones maintained destructive seas and winds as long as 5 days after the point of recurvature. Six of the 16 extratropical storms crossed the North Pacific and affected the Aleutians or western North America.