From an analysis of dense pibal data in terms of time and space, it is shown that a nocturnal low-level jet exists on summer days over the Kanto plains, Japan. This will be the first presentation of an analytical study on the nocturnal low-level jet flowing over Japan.
   The low-level jet studied in this report is quite similar to that over the Great Plains of the United States, though it is smaller in horizontal scale. Southwest jet maxima, about 20 m s^-1, occur around midnight at an altitude of 200 to 700 m. Observed wind maxima seem to be supergeostrophic in terms of large-scale pressure field. An interesting result is that as the jet flow passes over land, the amplitude of diurnal wind variations of wind speeds becomes greater with decreasing average wind speeds, the height of the maximum amplitude becomes lower, and the momentum of the jet concentrates in the relatively lower layer. A discussion referring to momentum concentration in the lower layer with time is made between the low-level jet and the nocturnal cyclonic vortex both found in the Kanto Plains.

View full abstract

   The vertical turbulent diffusivity K_z in the atmospheric boundary layer was calculated from the trajectory data of the South Kanto Plain Project, the Akita Bay Area Experiment, and the Eastern Tennessee Trajectory Experiment, on the basis of the statistical theory of turbulence. And the seasonal and topographical effects affecting the diurnal variation and profile of K_z were investigated.
   In consequence, it was found as expected that K_z has a diurnal variation like a sine curve without regard to season or topography. It can be conjectured that the phase of diurnal variation is affected by the possible duration of sunshine, and the amplitude by topography and stability of the atmospheric boundary layer.
   The maximum vertical turbulent diffusivity K_max was observed within the region of 0.15≤z/z_i<0.50 on the K_z profiles throughout the whole data. And z_m at which K_max was observed differed with season and topography.

View full abstract

   To study the atmospheric turbulent diffusion and transport of air pollutants, the air tracer technique is an effective means, and several kinds of air tracer material such as sulfur hexafluoride and fluorescent particles have been developed up to now. However, it is difficult to see how much is contributed by the emissions of the respective pollutants to the receptors, and to know the complex transport processes of the tagged air parcels, by simultaneously using these air tracers. Such being the case, a multiple air tracer system has been demanded.
   Therefore, we applied the activable multiple air tracer method (AMAT system) to the investigation of the land and sea breeze. The AMAT system is that the particulate rare-earth elements are released into the atmosphere with pressurized air through the atomizer as air tracers and collected on filter paper; the samples collected are analyzed quantitatively by the neutron activation technique.
   The AMAT system is based on the principle that the field experiment with multiple air tracers can be conducted easily by selecting the elements with the suitable characteristics. As the elements, Eu, Dy, Ho and Lu are appropriate.
   In a comparison experiment between the AMAT and SF₆, we could find that there was no discernible difference in the concentration between the AMAT and SF₆, with small exceptions. Furthermore, we could get a good agreement between the predicted and the observed concentration of the AMAT in the Niihama Experiment.

View full abstract

   The ocean surface is simulated by many facets whose slopes are according to the isotropic and anisotropic Gaussian distribution with respect to surface wind. The slope of the facets depends upon the ocean surface wind (Cox and Munk, 1955). The reflection characteristics of the surface are expressed by the incident and emergent directions of radiation. The discussions are applied to the investigations of the ocean surface characteristics as well as to the atmospheric aerosols by the use of the AVHRR data on board the NOAA-6 satellites (visible, 3.7μm and 11μm window regions).
   The reflectance (or emissivity) of the model surface in the case of the isotropic Gaussian distribution of slopes are tabulated as a function of surface wind.

View full abstract

   Volcano Aso had frequent eruptions from 1979 through 1980, and a large amount of volcanic smoke and ash was emitted from its crater. The area spread over by the volcanic smoke and the area covered by the volcanic ash of this period were investigated by the optical analysis method of the Landsat MSS image.
   Volcanic smoke and ash-fall area were clearly detected from the Landsat MSS image. Their detectable area was seen to change with the transition of volcanic activity, and the maximum extension of volcanic smoke was about 70 km from the crater, and that of volcanic ash-fall area was about 10 km around the crater.
   By observation from the Landsat, it is possible to get information on the wide horizontal distribution of volcanic smoke or ash-fall, and the data from the Landsat are very useful for volcano observation.

View full abstract

   A method of inference of the vertical temperature profiles of the lower atmosphere with the ground-based spectrometer is proposed. The measurements were carried out under clear and overcast sky conditions. Under these conditions the inferred profiles by this method agree with those observed by radio sondes. For cases of partly cloudy sky reliable spectral measurements of radiation are difficult to obtain. In such cases, numerical simulations were carried out and the results were found satisfactory except for warm and humid weather conditions.

View full abstract

   The plutonium content of the water sampled from ten main rivers in Japan was determined. The average content of total plutonium is 0.37 fCi 1^-1 in which 0.09 fCi 1^-1 is associated with suspended matter. Considering that 27% of the total plutonium is derived directly from rain drops on the river surface, the amount of leaching from drainage is estimated to be only 0.03% of the accumulated plutonium on land (1.2 mCi km^-2). This suggests that plutonium is adsorbed on the soil surface firmly and it is difficult to be leached out to river water.

View full abstract

   X-ray fluorescence spectrometry was applied to the metal determination of daily aerosol samples. It was found that a series of used filter can serve as calibration standards for environmental monitoring. An aliquot of the same air filter used for X-ray fluorescence spectrometry was digested with mineral acids and the content of metals was determined by atomic absorption spectrometry. Some of the results on the concentration of iron, manganese, copper and zinc in the surface air at Tsukuba from June 1980 to June 1981 were given as an example.

View full abstract

   A simple method is described for the preconcentration and determination of some of the atmospheric chlorofluorocarbons by using the GC-QMS method. The halogenated hydrocarbons in 100 ml of air sample were preconcentrated into 1.7 ml of cold trap by using helium stream and were injected into a GC column. The determination of F-11 and F-12 was done by electron impact mode of the GC-QMS method. Recovery of this method is 100% and the results of replicate determinations are in good agreement with each other within the analytical error.

View full abstract

   Results of study on the concentration of uranium and the activity ratio of ²³⁴U/²³⁸U in surface air in Tokyo and Tsukuba Science City indicate that the average concentrations of uranium are 24±15 pg m^-3 and 14±10 pg m^-3 respectively, and the average activity ratio is about 1.0. The high ratio up to 1.7 observed in three spring seasons. The causes of these high isotopic ratios of ²³⁴U/²³⁸U may be due to the effect of ablated debris deriving from the atmospheric burn-up of Cosmos-954 on 24 Jan. 1978 over northern Canada.

View full abstract

   Fundamental experiments on turbulent diffusion in thermally stratified turbulent boundary layers in the wind tunnel were carried out in order to make clear the mechanism of turbulent diffusion.
   The wind velocity for this study was 1.6 m/sec and turbulent boundary layer was made by setting an L-shaped metallic bar, whose side length was 19 mm, at the leading edge of a flat plate (Fig. 1). In this boundary layer, temperature profiles were made in nearly straight lines in temperature gradient (1.5K/cm in the case of stable condition and -1.8K/cm in the case of unstable condition on the average; see Fig. 2).
   Pure propane gas was emitted from a point source at several heights (h_s=0.1∼9 cm) which was set at x=100 cm, and the concentration distributions were measured three-dimentionally.
   Statistic quantities of turbulence were measured by temperature-compensated hot-wire anemometers (single hot-wire, V-meter and X-meter, Pt-plated tungsten wire of 2 mm in length and 5 μm in diameter) and cold wire (same material as the anemometer, 2 mm and 5 μm) (Figs. 2, 5, 6, 7, 9).
   Turbulent diffusion is obviously affected by the thermally stratified layers (Figs. 10 and 12).
   It is clear that the concentration distribution in lateral direction is normal distribution (Fig. 11), then, the concentration of the case of a line source for each source height can be calculated from eq. (4). The distributions of the synthetic concentration are shown in Figs. 13(a)∼(d). by the series of symbol Ο. The two-dimentional diffusion equation in stationary state is u (∂C_L/∂x) = ∂/∂z (K_z (∂C_L/∂z)), where K_z is the vertical diffusion coefficient and C_L the concentration from a line source. Integrating the equation with z, the vertical diffusion coefficient K_z can be calculated from the concentration distribution for the line source and wind velocity (eq. (6)).
   The profiles of K_z for each condition are shown in Figs. 14(a)∼(c). It is evident that K_z is proportional to height z; K_z=k·z, where k is a proportional constant. The values of constant k for each source height and each condition are shown in Table 3.
   On the other hand, Sakagami (1954) solved the diffusion equation in which K_z was assumed to be proportional to height z (K_z=k_s·z). Sakagami's solution for the line source is given in eq. (8). The concentration distributions for each source height are obtained by choosing suitable parameter B and shown by solid lines in Figs. 13(a)∼(d).
   The values of k_s (proportional constant for the vertical diffusion coefficient in Sakagami's solution) are calculated from eq. (10) and shown in Table 4(b). The mean values of k_s in the region of x=120∼150 cm agree well with the experimental ones except the case of the source height h_s=0.1 cm (Table 3 and Table 4(b)).

View full abstract