Electrification of minor showerclouds which frequently appear in the Kyoto basin during the winter season (Shigure) has been investigated. Three models are presented in this paper, that is, the Gauss type developing model, the dissipating charge model, and the dissipating current model, assuming the two (main and subsidiary) current sources. The variation patterns of the ground electric fields calculated using these models are compared with the observed patterns, and it is found that the Gauss type developing model best fits the observed results, and that the subsidiary source current of 0.004A in the lower portion of the cloud coexists with the main source current of 0.02A in the upper portion of the cloud: two different charge generating mechanisms function in the minor showerclouds. The atmospheric temperature levels of these current sources are nearly same as the case of general thunderstorms, that is, the main current source works at -10°C level and the subsidiary current source does in the region near -5°C level. The associated typical charge distribution is estimated, that is, the positive charge of 3.3 Coul is located at 3.0km height, the negative charge of 4.5 Coul at 2.5km, and the positive charge of 1.0 Coul at 1.0km.
The electrical and precipitation-physical structures of snow clouds were observed by means of "Altielectrographs", "Snow Crystal Sondes", electric charge sondes and the usual radiosondes on the Ishikari Coast, Hokkaido in the winter seasons of 1969 and 1970, simultaneously with ground-based observation. The following results were obtained. 1. A thick layer of positive space charge was found generally distributed in the middle layer of the snow clouds. The charge was carried by small snow' crystals. A thin layer of negative space charge was found below the layer of positive space charge. This charge was carried by large snow crystals. 2. Local positive space charges carried by positively charged graupel pellets frequently existed in the active regions in the lower portion or below the cloud base. This probably caused the electrical structure of snow clouds to be complicated. 3. Good correspondences between the patterns of electrical structures observed in clouds and on the ground showed that the structure aloft was transported by the descent of graupel pellets and snow crystals to the ground without any remarkable modifications. 4. The positive electrification of graupel pellets were presumably caused by the collision with neighboring unrimed snow crystals in the warm temperature region between -5°C and -10°C levels.
Velocities of lightning leader and return strokes were measured with the optical detectors in two ground flashes (flash G-20 and flash G-22) initiated by upward streamers from a tall chimney. Dart-type leaders are confirmed both on the light signals and on the electric field changes. The leader propagating downward with a speed of 9×106m/s is noted in the flash G-20. 17 impulsive light signals are found to precede a return stroke signal in the development of upward streamers. On the three negative return strokes following downward dart-type leaders in G-2U and G-22, the direction of the propagation is found to be upward and the speed is found to range from 1.2×108m/s to 2.3×108m/s.
Simultaneous observations of aerosols, gases, and precipitation chemistry were carried out at the cloud base level and the surface during the fall of 1979, the winter of 1979-1980 and the summer of 1980. With due regard to the effects of the evaporation of precipitation particles and the absorption of gases, the relative importance of in-cloud scavenging and below-cloud scavenging, and the collection efficiency for water soluble particles were estimated on the basis of data obtained during the observation periods. For the mass of sulfate particles, the percentage of below-cloud scavenging to total precipitation scavenging was about 20% in the case of rain drops and 40% in the case of snow particles. As for the mass of all the water-soluble particles, it was about 30% in the case of rain drops and 50% in the case of snow particles, respectively. The collection efficiency, which is defined to be the ratio of the actual collection cross section to the geometric cross section, of rain drops was slightly greater than that of snow particles. However, from the viewpoint of the mass of aerosol particles collected by unit mass of precipitation, snow scavenging was several times as efficient as rain scavenging, inversely. The collection efficiencies for sulfate, nitrate, and sea salt particles increased in that order. This was accounted for by the size difference of aerosol particles which contained each chemical constituent.
In order to obtain the knowledge of the dependence of the volume fraction of water soluble material (ε) in atmospheric aerosols on their size, an experimental study was carried out for aerosols with radii between 0.02 and 0.lμm. By means of a differential mobility separator, nearly monodisperse aerosols were extracted from the atmospheric aerosols in dry condition, and then they were humidified to grow to larger particles under some relative humidity conditions. The particle sizes before and after the humidification were measured by a second order differential mobility analyzer. From these experimental data, the value of ε was estimated as a function of particle radius on the assumption that water soluble material in particles was ammonium sulfate. The measurements were made in December 1981 and in February 1982. It was found that the value of ε was in the range of 0.2-1, and had a tendency to increase with increasing particle radius from 0.02 to 0.lμm.
The role of particle-growing processes such as coagulation and condensation in the decay phase of the stratospheric aerosol layer enhanced by the volcanic eruption was discussed by using a one-dimensional and time-dependent numerical model which includes eddy diffusion, coagulation, condensation and sedimentation. Result of calculation suggests that the characteristic time of the decay of the stratospheric aerosol layer is about 1.5-3.0 years for the volcanic eruption which injects a large amount of SO2gas into the stratosphere.
The effect of cloud condensation nuclei (CCN) on the production of large cloud droplets in a shallow cumulus cloud was studied by numerical modeling. Dynamical processes were treated in an Eulerian framework in an axially symmetric model. Microphysical processes in the layer near cloud base were treated in a Lagrangian framework using air-parcels which ascend successively, in order to avoid the influence of artificial broadening of droplet size distribution on the formation of large cloud droplets. Following conclusions were reached. When the concentration of nuclei in the range of Aitken size (radius_??_0.lμm) is low, large droplets are produced mainly by coalescence which occurs between droplets formed on nuclei smaller than 1μm in radius (large nuclei). In this case droplets formed on giant nuclei (radius>1μm) do not contribute to the concentration of large cloud droplets. When the concentration of nuclei in the range of Aitken size is high, droplets formed on giant nuclei contribute largely to the concentration of large droplets and most of large droplets are produced by coalescence between droplets formed on giant nuclei.
Observations of snow crystals in the lower atmosphere of Arctic Canada were made by means of snow crystal sondes. The number and shapes of crystals, the size distribution of hexagonal plates and columnar crystals at each observation height and the growth mode of columns were studied in the air temperature of -21 to -31°C. The results show that snow crystals of peculiar shapes were involved constantly amounting to about 2.5% of total number in the height from surface to 150m. Although the predominant shapes of snow crystals were columns, single bullets, crossed plates and combination of bullets, hexagonal plates were also observed in considerable percentage. The growth mode of columns was similar to that of columnar crystals observed by Sato et al. (1981) at South Pole Station. The mean sizes of hexagonal plates and columnar crystals were gradually increased with the decrease of observation height. This may be due to the existence of enough amount of water vapor for growth of those crystals in the atmosphere near surface to several hundred meters in height, locally around the observation site. The mass growth rate of columns was 2.5×10-9g•sec-1 at the air temperature of -31°C, and was larger than that obtained in field observation at -35°C by Kikuchi and Hogan (1979) and that obtained in cold chamber experiment at -26°C by Yamashita (1974). It seems that this discrepancy of mass growth rate at cold temperature regions is caused by the difference of size or mass of crystals.
The transfer of solar radiation in an optically anisotropic, homogeneous cloud layer for which the single-scattering properties vary with the incident angle of light beam of interest has been solved by means of the doubling method. The method was applied to model ice clouds with a hypothetical anisotropy with respect to volume extinction coefficient, asymmetry factor for phase function, and single-scattering albedo to provide the cloud radiative characteristics of reflectance and absorptance for solar radiation. The sensitivity of the cloud radiative characteristics to the anisotropic single-scattering properties were evaluated. The reflectance and absorptance are most sensitive to anisotropy in the asymmetry factor and single-scattering albedo, respectively. The impact of the anisotropic single-scattering properties is most noticeable for clouds of optical thickness of the order of unity. Importance of the anisotropy effects for the radiative transfer in natural ice clouds composed of horizontally oriented ice crystals is also discussed.
Vertical diffusion from elevated line sources were estimated using the structure model of the atmospheric boundary layer proposed by Yokoyama et al. (1977a, b, c). The twodimensional differential equation of diffusion was computed numerically for stationary and horizontally homogeneous conditions. Eddy diffusivity for elevated sources was assumed to be proportional to the travel time of diffusing particles in the early stage of diffusion, and in the long range, proportional to the eddy diffusivity of momentum. From this model the Lagrangian time scale of eddies in the vertical direction is estimated and compared with experiments. The estimated vertical spread normalized by characteristic parameters of turbulence at the source height can be approximated by the relation derived from Taylor's statistical theory with an exponential Lagrangian velocity correlation function. The results were compared with experiments and a simplified relation between σz/σEs (σEs: standard deviation of elevation angle at the source height) and downwind distance was proposed for practical application.
Energetics characteristics over Siberia, Northeastern Asia, China and Japan Sea are studied with two winter's upper air data. The Siberia region, which is frequently occupied by a surface high pressure and an upper anticyclonic flow, shows destruction by cross-isobaric flow and negative dissipation of kinetic energy in the winter mean balance of kinetic energy. The Northeastern Asia and Japan Sea areas, which are frequently occupied by a surface low and an upper cyclonic flow, show generations and dissipations of kinetic energy. From the comparison of the regional balances of kinetic energy, the upper atmosphere over the China and Japan Sea regions together with the adjacent oceanic areas may be considered as the most energetically active area over the northern hemisphere in winter. The studies of kinetic energy budgets for various flow patterns show that with the exception of Siberia, the kinetic energy generation, outflow and dissipation are associated with the cyclonic type flows. Even though the flow patterns over the China and Japan Sea regions are predominantly cyclonic, their kinetic energy budgets show extremely intense transformation in comparison with that of an average cyclonic flow over other regions in this study or over North America.
The history data of winter simulation by the GLAS climate model and the NCAR community climate model are used to examine the generation of atmospheric kinetic energy. The contrast between the geographic distributions of the generation of kinetic energy and divergence of kinetic energy flux shows that kinetic enemy is generated in the upstream side of jets, transported to the downstream side and destroyed there. The contributions from the time-mean and transient modes to the counterbalance between generation of kinetic energy and divergence of kinetic energy flux are also investigated. It is observed that the kinetic energy generated by the time-mean mode is essentially redistributed by the time-mean flow, while that generated by the transient flow is mainly responsible for the maintenance of the kinetic energy of the entire atmospheric flow.
Atmospheric diabatic heating rate in the lower troposphere in January of nine years is estimated as the residual in the thermodynamic equation from the data of observed temperature and geopotential height. The heating rate shows marked year-to-year variation. Particularly, they heat source over the North Atlantic has two preferred locations and exhibits some seesaw feature.
Synoptic analyses were conducted of the major active-break cycle of the summer monsoon and its interaction with the circulation in Eurasia and the western Pacific (10-70°N, 20-180°E) in a MONEX year (1979) and are compared to the recent years (1964-1974). The series of 5-day mean 500mb height and sea level pressure data were used for above regions to monitor the change in the monsoon and adjacent circulations. The weekly rainfall data for the meteorological sub-divisions in India for 1964-1974, 1979 were used to monitor the major active-break cycle of the summer monsoon rainfall in Central India. Evidence has been shown that development of the major break monsoon in Central India during the high summer period (50 days from 15 July to 2 September) are deeply associated with the circulation in the middle latitudes of Eurasia and western North Pacific near Kyushu Island. The major break monsoon during the high summer are preceded by the development of a 500mb ridge near the Caspian Sea (50°N, 50°E). If a sharp drop in the sea level pressure at Naze 28°23'N, 129°30'E) to a value below 5-day mean of 1004mb (often associated with the major typhoons moving north near 30°N, 120-130°E) are observed, the major break monsoon in Central India were shown to begin within one week of this event.
Preliminary measurement of the stratospheric aerosol layer using multiwavelength laser radar (λ=0.6943μm and 0.3471μm) are presented. This result suggested that there was noticeable change on the vertical distribution of size distribution and/or chemical composition of the aerosol particles. The contribution of Mie scattering component at λ=0.3471μm to the total scattered light becomes apparently smaller than that at λ=0.6943μm owing to the so-called "dependence of λ-4 in Rayleigh scattering", and this enables us to search out easily the fitting point which is used to distinguish the Mie scattering component from the measured total scattering power intensity.
Stratospheric ozone in the altitude region of 15-25 km has been measured by a balloonborne sun-photometer. Concentrations of ozone deduced from the absorption of sunlight in the Chappuis band are generally in good agreement with those obtained by ozonesondes on board the same balloons. Possible causes of differences between the profiles obtained by the two different methods are discussed and the accuracy of the present method is estimated.