Seasonal variation of stratospheric aerosol content is discussed on the basis of laser radar measurements at Nagoya (35°N, 137°E) Japan. Analytical results suggest that there were noticeable winter maximum of aerosol content, and this was in good agreement with other investigators' measurements (Hofmann et al., 1975; Bigg, 1975; Hofmann and Rosen, 1977; Reiter et al., 1979). In summer season 1977, and possibly 1976, second maximum of aerosol content was suggested in laser radar measurements at Nagoya. Maximum of stratospheric aerosol content in summer season can be found, though it is small, in the analytical results by Gras and Laby (1979) who suggested the second maximum of aerosol ocntent in summer (southern hemisphere) 1975, and by Reiter et al. (1979) whose results contained small maxi-mum of loading in summer 1977, and 1978. Summarizing various measurements, the winter maximum of aerosol content is always observed on the global scale, and summer second maximum of loading can be sometimes observed. Present analytical results suggest that the flux of sulfur compounds of 5×107 (S) atoms/cm2/sec from troposphere to stratosphere is necessary to compensate the sedimentational loss of particulate matter if it is assumed that the stratospheric aerosol is composed of sulfuric acid of 75% in weight.
The decay of stratospheric aerosol content after the volcanic eruption of Mt. Fuego (Oct. 1974) is discussed on the basis of laser radar measurements at Nagoya (35°N, 137°E). The results show that the decay time constant of stratospheric aerosol content is about 2 years, and this value is a little longer than the previous measurements (Hofmann and Rosen, 1977; Russell and Hake, 1977). This discrepancy is due to mainly the difference of observational periods between present and previous analysis, and observational periods were too short to make clear the decay time scale in previous investigations. More recently, Reiter et al. have summarized the results measured at many different laser radar sites (1980). It can be easily found out in their results, though they didn't present the value of decay time scale, that the decay time scale was about 2 years. This value is comparable one with present result.
In order to make clear how much extent urban aerosol particles are inactivated as con-densation nuclei, possibly by the effect of organic materials, an experimental study was made using a vertical thermal diffusion chamber and an impactor. Inactive particles, which grew slowly or not at all under the supersaturation less than about 1%, were collected separated from active particles, and the concentration of inactive particles was compared with that of atmospheric aerosol particles by means of a transmission electron microscope. It was found that inactive particles scarcely existed. This result indicates that most of the atmospheric aerosol particles are not greatly inactivated as condensation nuclei even in the possible pres-ence of organic materials in the urban area.
Routine surface meteorological data at three weather stations in Japan, i.e., Wajima (sea shore), Matsumoto (inland), and Nikko (inland), were analyzed in order to obtain the relation-ship between the occurrence of the types of precipitation of snow, sleet, and rain on the ground and surface meteorological elements. The results indicate that the types of precipi-tation were dependent on surface relative humidity as well as surface air temperature. Even at the same air temperature, the precipitation types varied depending on humidity, and that critically. Two critical humidities were recognized at a given air temperature and the precipi-tation types were characterized by these critical humidities. Below a lower critical humidity, precipitations were all snow. Within some range above the critical humidity, they could be snow, sleet, or rain. Above a higher critical humidity on the top of the range, only rains were observed. These facts suggest that melting of snowflakes proceeds rapidly at higher relative humidity. From statistical analyses, two critical humidities for snow and rain (%) were obtained as a function of surface air temperature (°C). The obtained relations at each station were as follows: RHcri(snow)=-7.5T+93, RHcri(rain)=46√6.2-T, Wajima RHcri(snow)=-7.3T+96, RHcri(rain)=39√7.2-T, Matsumoto RHcri(snow)=-6.2T+91, RHcri(rain)=43√6.8-T, Nikko where RHcri (snow) is a lower critical humidity and RHcri (rain) a higher critical one. The relations for snow are hardly different among the observation stations, but those for rain are different. The difference of the relations for rain suggests that the size and density of snowflakes are different from station to station and that the difference affects the speed of the generation of raindrops due to melting. The non-difference of the relations for snow, on the other hand, suggests that the, difference in physical properties of snowflakes does not exert any influence on the relations for snow. Sleet was obtained in the transition region surrounded by two relations for snow and rain and its occurrence was associated with high precipitation rate together with air tempera-ture and humidity. These analytical results are explained well using the calculated results previously obtained by Matsuo and Sasyo (1981,a).
Continuous observation of the infrasonic wave has been recently started at Aichi Uni-versity of Education in Kariya City. Major interest is in the infrasounds frequently radiated into the atmosphere by the summit explosion of the volcano Sakura-jima. In detection of the infrasonic signal in the turbulent boundary layer, it is often indis-pensable to reduce the irregular noise caused by the turbulent fluctuation of the wind. In the present study, a new type of wind noise reducer has been designed. It is a multi-pipe line microphone, having a number of branches of pipes of equal diameter. The function of it is to take the equally-weighted spatial average of the pressure field along a straight line, and is essentially the same as the Daniels' line microphone (1959). However, the manufacturing of the multi-pipe line microphone is practically easier than the Daniels' type. Another merit of the new device is in that it is as easy to take the two-dimensional average if necessary. From several field tests, it has been shown that the wind noise is remarkably attenuated by the use of multi-pipe line microphone, although the measured noise attenuation has been smaller than the theoretical estimation based on the turbulence model given by Priestley(1965) by about 5dB in average.
Spectral characteristics of wind velocity fluctuations in the marine atmospheric surface layer were investigated using data collected in field observations mostly at a tower in the sea, with paying special attention to possible effects due to wave motions of the water surface. The data of wind fluctuations and waves measured simultaneously in the cases when both winds and waves traveled toward almost the same directions were selected and analyzed. Two-dimensional wind fields in the plane parallel to the mean horizontal wind direction (u-component) and to the vertical direction (w-component) were discussed. The wind velocity spectra of u- and w-components in the lower frequency region, ob-served over sea, deviate upward from those model spectra proposed by Kaimal et al. (1972) and by Busch (1973) on the basis of Monin-Obukhov's similarity theory. From the coherence function analyses, it was found that the wind velocity fluctuations over sea contain a fairly good amount of 'wave coherent perturbations' in addition to the regular turbulences in the atmospheric surface layer. A spectrum excluding the spectral con-tribution of the wave coherent perturbations shows almost to agree with the model spectrum. The perturbation seems to give little contribution to a cospectrum between u and w, and may, therefore, not yield any significant amount of vertical momentum flux. The results of the frequency response function analyses suggest that the pattern of motion of the perturbation may be an ellipse with a horizontal axis a little longer than a vertical one. The results also suggest that the perturbation may be induced effectively by the wave components whose phase speeds are faster than the measured wind speed, and that an attenuation of the perturbation amplitude with height is small in the observed range of height (50-400cm above the mean sea level). From the above mentioned experimental results, the wave coherent perturbations were recognized as an origin to increase the spectral densities in the lower frequency region. The wave effects on spectral characteristics of winds in the marine atmospheric surface layer may have been first described in this study on the basis of the similarity theory.
The Eulerian- and the Lagrangian-mean flows induced by stationary, dissipating pianetary waves are discussed by using a simple channel model on a beta-plane. The wave is assumed to be excited by the bottom undulation and to be dissipated by Newtonian cooling with relaxa-tion time α and by Rayleigh friction with, λα(λ being constant). Three cases with, λ=1 are mainly discussed; (1) the basic zonal wind U0 and the dissipation rate a are both constant, (2) U0 varies with height, while α is constant and (3) U0 and α vary with height. In Case (1), it is shown how the Eulerian- and the Lagrangian-mean fields depend on the difference be-tween the dissipation scale-height and the density scale-height (cf. Dunkerton, 1979; Uryu, 1980). In Case (2) and Case (3), it is shown how the results for Case (1) are modified under slightly more realistic situations. The assumption, often used in the study of vertical propagation of planetary waves (cf. Dickinson, 1969a), that planetary waves are dissipated by Newtonian cooling only (λ=0) is re-examined. In Case (1), it is shown that unless λ«|(UR-U0)/U0|(where UR is the speed of two dimensional Rossby wave), the Rayleigh friction term cannot be neglected in the poten-tial vorticity equation. In addition, if this assumption is incorporated with the assumption that the Eulerian-mean zonal flow is damped by Rayleigh friction (cf. Dickinson, 1969b; Uryu, 1980), the resulting Lagrangian-mean flows become quite different from those obtained when the wave-dissipation mechanism includes Rayleigh friction, except for the case where the basic zonal wind is very small; for example, the Lagrangian-mean meridional circuation is of 3-cell structure in the meridional direction when U0=30m/sec and α=1/7 day-1. It is noted that the Eulerian-mean flows do not show any qualitative difference. This suggests that the plausibility of assumptions used should be examined also by the Lagrangian-mean dynamics.
The large-scale budget of vorticity over the Marshall Islands area is re-examined based on wind data during the period April-July 1956. Efforts are made to obtain accurate estimates of the horizontal advection and twisting terms in the vorticity equation. The mean vertical profile of the budget residual for disturbed conditions shows a large apparent source of positive vorticity in the upper troposphere and a sink near the surface. However, this mean profile is more complicated than those previously obtained for this area. The mean vorticity budget for undisturbed cases is characterized by a large local time change which is nearly com-pensated by the horizontal advection of absolute vorticity.
Real data response of Arakawa-Scubert cumulus parameterization (CU) is studied for the case of heavy rainfalls occurred over Kyushu (western part of Japan) on June 27, 1972. We study the influence of large-scale forcing on heavy rainfalls through time-integration of a simple one-dimensional model including CU, large-scale condensation (LSC) and middlelevel convective adjustment (ML) with observed rate of large-scale heating and moistening. Model simulates observed features well. Results indicate that ML plays an important role inwarm sector of depression, while LSC and CU play around the trailing portion of front where heavy rainfalls occur. During the earlier period of heavy rainfalls, LSC plays an important role and during the latter half period CU plays an important role. CU and ML work to stabilize the stratification cancelling the stability change caused by large-scale forcing.
GMS (Geostationary Meteorological Satellite) observations reveal a long-lived mediumscale Cb cluster which migrates along -32N latitude circle over the Asian subtropical humid region in 12-16 July 1979. In the present synoptic and subsynoptic-scale study based on upper, surface, radar and GMS infrared data, we describe the features and structure of the Cb cluster and its developing process in relation to the large-scale situations. The Cb cluster is associated with a medium-scale upper westerly trough and migrates with speed of -1, 000km/day. Although the convective activity in the cluster indicates time variations with meso-scale period, the medium-scale cluster as a whole lasts for several days. TBB (equivalent black body temperature measured by GMS infrared observation, which is almost equal to the cloud top temperature) of -75--60°C is observed for several days. Intense rainfalls of 50-100mm/hour and radar echoes of 12-15km height are found under the high cloud shield where TBB is less than -70°C. Considering the features of cloud system and medium-scale circulation, we subdivide the life history of the Cb cluster into "Cb cluster stage (12 GMT 12-12 GMT 14)" and "medium- scale depression stage (12 GMT 14-00 GMT 16)". During passage over the China continent where baroclinicity in the lower troposphere is extremely weak, the Cb cluster remains as an isolated oval-shaped Cb cluster and the depression in the lower level is not formed (Cb cluster stage). When the Cb cluster moves into the baroclinic zone in the Pacific area, the isolated cloud system changes into elongated cloud system and the depression is formed in the lower layer (medium-scale depression stage).
Principal time and space variations of snowfall (precipitation) over the Japan Sea coastal region are described in terms of empirical orthogonal function (EOF). Daily precipitation data at -40 stations in 15 winters (30 months) are used. The first two functions account for -65% of the total variance of precipitation. The spatical functions (B1 and B2) are related to the topography of the analyzed area. Basing on the magnitude of time variation functions (A1 and A2), we classify precipitation pattern of each day into three types; "mountain-", "normal-" and "plain-snowfall type". Inspecting time series of time variation functions for 30 months, we find that a certain snowfall type appears frequently in a particular winter. Especially P-type is dominant in the extraordinarily heavy snowfall winter. In the latter part of this paper, we focus our attention on the heavy snowfall days (areaaveraged precipitation_??_20mm/day). The heavy snowfalls continue generally for a few days as a "heavy snowfall period", and a certain snowfall type tends to continue through a heavy snowfall period. It is inferred that the heavy snowfalls of a certain type occur under a certain large-scale situation. This will be studied in Part II of this paper.
In Part I of the present study, spatial distributions of daily snowfall (precipitation) over Niigata Prefecture (the Japan Sea coastal side of Japan) are classified into three types (Mountain-, Normal- and Plain-type) in terms of EOF. In Part 2, we examine the large-scale situations in the heavy snowfall period (three days) of these three types, basing on composite analysis. One of the important features found commonly for heavy snowfalls of the three types is that the air in the upper trough is much colder than in moderate/light snowfall cases. The intrusion of very cold upper trough to south over the warm Japan Sea results in formation of thick layer of transformed airmass (mixed layer). M-type heavy snowfalls (heavy snowfalls concentrated in high mountain [-1, 000m] area) occur when a wedge-shaped deep upper trough propagates fast over the Japan Islands, accompanied with a rapidly developing surface depression. For this type of snowfalls, the formation of the thick mixed layer and its orographic lifting (low-level wind is perpendicular to the mountain range) will be essential. P-type snowfalls occur when a cold vortex slowly propagates to east after protruding southward over the Japan Sea. In this case the surface depressiondoes not rapidly develop. The mixed layer is very deep and active cumulus convection develop there. The orographic lifting is not primarily important because the wind is not perpendicular to the mountain ranges.
When it is fine and surface pressure gradient is weak, a small-scale Cyclonic vortex is often formed under the mountain breeze regime in the planetary boundary layer of the Kanto plains. This wind system is quite different from what will be deduced from the theory of land-sea breeze. The horizontal dimension of the vortex is about 100km and it extends to 1km in height. Vorticity of the vortex is as large as 3•10-4 sec-1. Convergence in the lowest layer and divergence above it bring an upward flow in the vortex. The circulation in the vertical cross section may well be regarded as a secondary circulation which pumps the air in the Ekman layer up into the free atmosphere.