The parameterization devised by Lindzen (1981) for the dissipation induced by the breaking of internal gravity waves in the mesosphere has been incorporated into a general circulation model which extends from the surface to 100km. The principal changes produced were a considerable reduction in the strength of the previous over-intense winter mesospheric jet, the establishment of easterlies above that jet, and the replacement of the previous multi-celled mean meridional circulation in the mesosphere by a virtual pole-to-pole circulation. The wave dissipation was found to be much stronger in the winter as compared to the summer mesosphere, but at a given latitude exhibited considerable temporal variability. Although a general improvement with observation was achieved it appears that, because of other model problems, the role of gravity waves is overestimated in the current model. The inclusion of the diurnal variability in the model, and the subsequent excitation of tides, had a profound effect on the synoptic activity above about 75km. Much improved agreement with observation was obtained, and the dominant control of the synoptic processes in the middle atmosphere by the tides was clearly illustrated. For the first time an indication can be obtained from the model of the overall synoptic environment in which individual point observations have traditionally been made.
The intraseasonal behaviors of outgoing long wave radiation (OLR) obtained from polar orbiting satellites are investigated for the period from January through November 1979. The power spectrum of the OLR data for the whole period has revealed the existence of 30-60 day and 15-25 day periodicities. The intense power for the 30-60 day period range appears over southern Indonesia to northern Australia during the Southern Hemisphere summer, and over South Asia during the Northern Hemisphere summer. The relationship between the intraseasonal variations and tropical cyclone activities was analyzed. In most cases during both hemisphere summers, the generation and growth of tropical cyclones occur during the active phase of the intraseasonal variations. The relationship between the intraseasonal variations and short-period (3-10 days) fluctuations was also investigated. The 3-10 day fluctuations show clear amplitude modulation with 30-60 day period which is the same periodicity as the intraseasonal variations. The amplitude of short-period fluctuations becomes large (small) during the active (break) phase of the intraseasonal variations. Eastward moving wavenumber 1 component is prominent for the amplitude modulation of the 3-10 day fluctuations with 30-60 day period.
Energy transformations of cyclonic development in the Asian winter monsoon from the Asian continent to the western Pacific are studied for the FGGE year. Computational analysis is done with a moving area defined for each observation encompassing the primary storm system. Energy budgets are grouped according to the evolving stages of the storm system to derive a composite view of storm development. Five individual cases are also selected and examined. A very significant portion of kinetic energy generation, 86%, is from local baroclinic conversion by eddies. This consistent with the fact that the cyclone growth takes place over the ocean. However, there is an additional energy source within the storm system. The amount of eddy conversion also depends on the storm path, with the largest conversion in cases of rapidly developing storms over a large area of the warm ocean. The intensity and balance of kinetic energy change drastically from its incipient stage to the late mature and actively occluded stages. In the incipient stage generation and export of kinetic energy are the largest, while dissipation is the smallest. As generation and export decrease, dissipation increases sharply to the later stages of development. In these later stages, the system also imports a large amount of kinetic energy.
The low level jet and the associated low level south-west vortex are the main mesoscale systems which bring heavy rains over East Asia. In order to examine the influence of Qinghai-Tibet Plateau (QTP) on these circulation systems, a control and two experiments were performed with the ECMWF grid point limited area model for a typical heavy rainfall case during the presummer rainy (Mei-yu) season. The control experiment, in which the orography represents the mean value over a grid box, reproduces the variation of the low level jet, the formation of the south-west vortex and the heavy rainfall area. When the height of QTP is halved, the south-west monsoon south of the Plateau interacts with the middle latitude westerlies. A baroclinic disturbance then develops instead of the meso-scale systems, and the heavy rainfall zone is shifted to the east. Increasing the QTP height causes the meso-scale systems to be enhanced and restricted to the vicinity of the Plateau, and the rainfall zone is shifted to the west. The results show that the forcing effect of the QTP on the three low level branches of the flow (the northerlies from middle latitude, the south-west monsoon from the Bay of Bengal and the easterlies from the West Pacific) develops and maintains the meso-scale rain-bearing systems.
The evolution of radiation fog has been investigated by numerical simulations. A onedimensional boundary layer model was adopted for the atmosphere. No moisture transport in the soil layer was assumed; the dew and falling droplets are assumed to be stored at the ground surface. The P3-approximation method was employed to incorporate the effect of radiative transfer into the boundary layer model. With the development of radiation fog, the radiative cooling rate increases greatly and temperature decreases rapidly just below the fog top. This effect accelerates the condensation of water vapor near the fog top and, consequently, increases the height and liquid water content of the fog. The sudden increase of downward radiative flux from the fog layer enhances the rise of surface temperature, and the temperature profile in the fog layer turns from stable into unstable. With the increase of instability of temperature stratification in the fog layer, eddy diffusivities also increase rapidly. This effect enhances the transport of water vapor from the surface to the fog layer, and the development of the fog is again accelerated. In contrast to that within the fog layer, the temperature profile above the fog layer remains stable; consequently a sharp temperature inversion appears near the fog top. The height of this inversion rises gradually as the height of the fog top increases. When the moisture stored on the ground surface is exhausted and the transport of water vapor from the surface to the fog layer vanishes, the surface temperature rises suddenly and fog begins to disappear from the lowest layer near the ground.
In order to estimate the volume and mass of yellow sand dust, a number size distribution model of these particles was established by combining two zeroth-order logarithmic distributions. This model was based on the mass size spectra measured by Andersen air samplers at three points in Japan, and has a siginficant mode in a range between 0.5 and 1.0μm radius. The optical properties of a dusty atmosphere containing yellow sand dust were distinguished theoretically by the use of this size distribution model. As a result, the volume of yellow sand dust in the air depends strongly on Angstrom's turbidity coefficient and only weakly on his wavelength exponent. The relationship between Angstrom's turbidity coefficient and Yamamoto's turbidity coefficient was also examined under the same turbid conditions. This examination was required for the purpose of applying the direct solar radiation data obtained at 12 stations of the Japan Meteorological Agency, because the measurements were made without using filters. A fairly simple relationship was found between them so that the volume of yellow sand dust over Japan was estimated for the three Kosa events from 1981 to 1983. The volume concentrations in the vertical air column in these Kosa events were in the range 150 to 4001/km2 (0.4-1.0×10-4g/cm2) at the stations which actually observed the duststorm. This result also suggests that a considerable amount of dust is supplied at times when a Kosa is not recognized, because the meteorological stations having the values less than 1501/km2 did not report the duststorm. The mass flux of yellow sand dust over Japan in the latitudes of 30-41°N was estimated as 3.5-4.5×106 tons in a spring season, and 4.1-5.3×106 tons per year.
A superimposed sinusoidal model is proposed to investigate the effects of cloud dimension and geometrical fine structure on the light scattering of cumulus clouds in the visible region. For various cloud shapes, cloud dimension, and solar zenith angle, efficiency of shadowing and conversion from directional light to diffused light, albedo, upwelling reflectance, the horizontal pattern of scattering, and upwelling radiance are calculated by using the Monte Carlo method. Finite small perturbation on the upper cloud surface is found to be an important factor which governs the mean and the variance of radiative properties of clouds. The mean albedo of cumuliform cloud field is lower than that of the conventional cuboidal model due to the asymmetry of cloud shape. Therefore, neither the right parallelpiped cloud model nor simple sinusoidal one is a representative of the radiative properties of cloud group with various shapes. The variance of cumulus radiative properties are so large that the relation between cloud dimension and radiance is valid only for a statistical number of clouds in estimating liquid water content.
The fine structure of layer clouds at upper and middle-levels was observed by a laser radar and a vertically pointing radar of 8.6mm wavelength. Firstly we examined the possibility of identifying whether cloud-composing particles are water droplets or ice particles by measuring the depolarization ratio using the laser radar. Secondly we studied the growth processes of falling ice particles in middle-level clouds. A case study was made for layer clouds situated near a warm front and it was revealed that the layer of supercooled water droplets existed at middle-levels and ice particles generated in upper-level cells were falling through this layer. Ice particles in some streaks grew rapidly in the layer of supercooled water droplets. There was a difference in the growth rate of ice particles in the layer and the growth rate was dependent upon the amount of supercooled water droplets. The growth processes of ice particles were discussed.
The aim of this study is to find a linkage of atmospheric responses to the solar sector boundary (SSB) passages (Wilcox et al., 1974; Misumi, 1981; 1983). Variations of both zonal mean fields and planetary waves around the SSB passages are investigated using the transformed Eulerian mean (TEM) equations system including the refractive index. Deviations from the time mean field in 8 winters from 1964 to 1972 are mainly discussed. It is found that the Eliassen-Palm (EP) flux for zonal wavenumber 2 and 3 in the troposphere begins to decrease about 5 days prior to SSB passages. Such decrease leads to the divergence of the EP flux near the tropopause in high latitudes. This is responsible for the temperature decrease in the polar troposphere, and consequently for the decrease of the vorticity area index in the upper troposphere. The decreases of the EP flux for both wavenumber 2 originating from the troposphere and wavenumber 1 being at the 150mb level on 4 days before the SSB passages seem to create the minimum of the polar temperature in the middle stratosphere. Among above mentioned processes, only the decrease of the EP flux is not diagnosed by the TEM equations system. The decrease of the EP flux in the troposphere is statistically significant and is seen only in the same period that other atmospheric responses occur. This type response would be due to the external modulation.
Variations of the solar surface and the interplanetary space that are responsible for the reported response in the lower atmosphere to the solar sector boundary (SSB) passages are discussed. Special attention is paid to elucidate the facts that the atmospheric response occurs 5 days before the SSB passages and is found only in the 8 winters from 1964 to 1972. The geomagnetic index Kp and the intensity of the galactic cosmic ray are used as the monitor of the corpusqular radiation and the 10.7cm solar radio flux intensity is used as the monitor of X-ray and EUV range intensity. The variation of the visible range is considered to be negligibly small. Although the corpusqular radiation is closely related to the SSB passage, the starting day and the solar cycle dependence of its variation do not accord with those of the reported atmospheric response. The 10.7cm flux does not have the physically controlled variation around the SSB passages. However, the 10.7cm flux intensity had been accidentally and significantly weak during 8 days before the SSB passages in the 8 winters in the period from 1964 to 1972. The period and the starting day of this variation is perfectly in accord with those of the reported atmospheric response.