Empirical orthogonal function analysis was applied to 3.5-5.5 day filtered wind, temperature, and geopotential height data for the 1978-79 winter (1 December 1978 to 28 February 1979) at seven levels (the surface, 850, 700, 500, 300; 200 and 100mb) over the Tibetan Plateau region (20° to 50°N and 57.5 ° to 117.5 °E). The resulting eigenvector series were then truncated at eigenmode 12 to remove unwanted, small-scale noise which is of questionable accuracy. This was followed by the compositing of each meteorological variable at every level and grid point, with reference to changes in the first eigenvector coefficients for 3.5-5.5 day filtered meridional wind data at 200mb. Composite charts of 3.5-5.5 day filtered winds and geopotential heights at 200mb reveal that northeast-southwest oriented trough and ridge systems systematically propagate eastward with nearly the same phase speed (-12m•s-1) throughout the entire Tibetan Plateau region. However, the amplitudes of these systems decrease as they pass over the Tibetan Plateau. Thus, this area of high mountains appears to exert some measure of control on the activity of 3.5-5.5 day wave perturbations even at the 200mb level. At 500mb, wind changes associated with the eastward passage of major trough and ridge systems are much less pronounced over the Tibetan Plateau than those to the north. These weak wind variations over the Plateau are probably a result of the 500mb level being located within the planetary boundary layer above this highly elevated area. Similarly, midlatitude systems do not appear to extend across the Tibetan Plateau into the subtropical troposphere below 500mb due to the frictional (or mechanical blocking) effects of these high mountains. This is demonstrated by the rapid weakening of cyclonic (anticyclonic) cells as they propagate northeastward over northern India toward the southern border of the Himalaya Mountains. Interestingly, 700mb composite charts suggest that small-scale low (high) pressure cells develop near the northeastern periphery of the Tibetan Plateau. These orographically induced, small-scale disturbances then move southward along the eastern border of the Tibetan Plateau, and become most intense over the Red Basin before dissipating near the southeastern corner of the Plateau. Over central China, 700mb northerlies (cold monsoonal surges) are strongest when an orographically induced anticyclonic cell in the lee of the Tibetan Plateau approaches the Red Basin and a major trough is over northeastern China. However, these northerly surges do not appear to penetrate into the South China Sea region. In contrast, 700mb northerly surges with periods of 6-9 days may extend as far south as 20°N, and possibly beyond.may extend as far south as 20°N, and possibly beyond.
Empirical orthogonal function analysis was applied to 12-20 day filtered wind, temperature and geopotential height data for the 1978-79 winter (1 December 1978 to 28 February 1979) at seven levels (the surface, 850, 700, 500, 300, 200 and 100mb) over the Tibetan Plateau region (20° to 50°N and 57.5° to 117.5°E). The resulting eigenvector series were then truncated at eigenmode 6 to remove unwanted, small-scale noise which is of questionable accuracy. This was followed by the compositing of each meteorological variable at every level and grid point, with reference to changes in the first eigenvector coefficients for 12-20 day filtered meridional wind data at 200mb. Composite charts of 12-20 day filtered vorticity perturbations at 200mb exhibit prominent standing oscillations anchored in the vicinity of northeastern India and Burma. Nonlinear interaction between the winter mean absolute vorticity field and 12-20 day disturbances is primarily responsible for the development of 200mb vorticity perturbations over this region. These standing vorticity perturbations are superimposed upon weak eastward propagating modes, which move slowly (-4 m•s-1) in the subtropical westerlies (-45 m•s-1) south of the Tibetan Plateau. Velocity potential fields at 200mb are greatly enhanced by local topographic effects and tend to reduce the eastward advection effect of the strong westerly flow. Over Indochina and the northern South China Sea along about 100° to 110°E, northsouth oriented, divergent vertical overturning (departure from winter mean) is thermally indirect (direct) when an upper level trough (ridge) system intensifies over the northeastern India-Burma region. Substantial temperature changes (±1.5°) in the lower troposphere below about 700mb over southern China are associated with these intraseasonal variations in local vertical overturnings.
The Midlatitude standing waves forced by topography and stationary heat sources are investigated by means of a quasi-geostrophic, linear, steady-state, 34-level model with eddy viscosity and Newtonian cooling effect included. The results show that increased vertical resolution contributes significantly to the solution of the finite difference equations of motion and the thermodynamic equation, i.e., our 34-level model with increased vertical resolution in both the troposphere and stratosphere, gives better results when compared to simpler models such as the "two-levels" model. The computed vertical and zonal distributions of amplitude and phase for winter are in good agreement with observed standing geopotential and temperature waves. Similarly, computed and observed summer standing wave positions are also fiarly consistent. However, the computed trough over the central Pacific Ocean in summer appears to be too weak. The eddy viscosity, and the meridional wavelength of the topography and diabatic heating seem to have a strong influence on the response of a model atmosphere to forcing by topography and diabatic heating.
This study composites the horizontal structure of mixed layer elements penetrating into the overlying inversion layer, as observed by aircraft during AMTEX '75. For the particular day examined, the westerly momentum increases significantly upward across the inversion layer. The composite analysis suggests that the penetrating mixed layer elements are accelerated horizontally by entrainment and perturbation pressure gradients associated with flow of faster free flow air around the penetrating mixed layer air. As a result of this acceleration, the downdraft occurs downstream from the updraft. The interface between the mixed layer air and the free flow air is thicker on the downstream side of the penetrated mixed layer elements suggesting significant mixing and the possibility of a downstream turbulent wake.
In this paper the air layer between the ground and the 850mb surfaces are taken as the atmospheric boundary layer. First, the longwave radiation balance of the atmospheric boundary layer at every 2100JST in the whole year of 1975 are theoretically computed from radiosonde data at four stations in Japan. Then the theoretically computed results are parameterized in terms of air temperature and water vapor pressure at screen level and cloudiness.
The downward radiation from the pollutants is extremely small compared with those from the water vapor and the carbon dioxide, and so it is quite difficult to estimate the effect of the pollutants on the downward long-wave radiation from the value of downward radiation in a city measured by the ordinary radiometer. However, since within the range of the wave length where the emissivity of the radiation of the water vapor is small, the additional radiation from the pollutants becomes relatively large to the radiation from the water vapor, the detection of the additional radiation can be expected to be relatively easy. On this understanding, we have measured the downward radiation from the direction of zenith above the central part of Tokyo at a cloudless night, using a cylindrical radiometer which can sense the radiation of the wavelength between 8-17μm. As a result, we have observed a conspicuous increase in radiation which can be considered to have been caused by the pollutants, and we have also determined the relationship between the ratio of increase in the radiation from the zenith and the visibility. Furthermore, we have calculated and determined the relationship between the increase rate of the flux of the long-wave radiation from all the directions and the visibility, based on the result of the aforementioned observation. According to the result of this calculation, when the visibility is more than 32km, the effect of the radiation by the pollutants has not been recognized, but the flux of the downward radiation has increased as the visibility has fallen, and the ratios of increase, for example, have been 1.3%, 2.8% and 6.0% when the visibilities have been 20km, 10km and 2km respectively.
The concentration and size of Aitken particles were measured by use of an automatic Pollak counter equipped with a diffusion pipe for the two years from February 1977 to January 1979 at Syowa Station (69°00'S, 39°35'E), Antarctica. On the basis of these data, events of sudden increase in the concentration of Aitken particles are investigated. In the investigation are also taken into account the results of other aerosol observations simultaneously carried out, such as measurements of Mie particles (dia.>0.3μm), electronmicroscopic examination of particles, and furnace experiments for volatility measurement of Aitken particles. It is found that there are two types of sudden increase in the concentration of Aitken particles. Type-1 is characterized by a preferential increase of fine particles less than 0.01*m in diameter, the highly volatile nature of increased particles, and a preferential occurrence in the summer months. Type-2, which always accompanies stormy weather, is characterized by an increase of particles in a wide size range, the non-volatile nature of increased particles and a minimum occurrence in the summer months. Both types of the events reported here correspond closely to the events which have been observed only on the Antarctic Ice Cap so far. The event of Type-1, together with the results of electron-microscopic examination of particles, leads us to the tentative conclusion that Antarctica is covered with clouds of Aitken particles composed of photo-chemically produced sulphuric acid during the summer months. A ladder along which the acid particles descend to the ground may be provided by a cold frontal surface. The event of type-2 gives evidence that a cyclone system plays an important role in the transportation of maritime aerosols into the inland of the Antarctic continent. The present results suggest that there are two main components of aerosols over Antarctica and their relative importance varies with the seasons. In the winter season, aerosols of maritime origin transported by cyclone systems are predominant, whereas in the summer season aerosols produced by nucleation of trace gases are predominant.