Simulations using a three-dimensional shallow cloud model with detailed microphysics showed that even in maritime clouds, an ice-phase enhanced precipitation particle production compared to that occurring solely from warm rain processes. Rain fell earlier, was heavier, and lasted longer from maritime ice clouds than from warm clouds. The most remarkable result was a strong interaction between precipitation and wind shear as ice grew in the cloud. Rain fell in such a way that the low-level convergence was intensified. Modelled ice clouds with wind shear lasted much longer and produced much heavier rainfall than did similar clouds without ice, or clouds with ice but no wind shear.
An experiment was made to study turbulent transport processes and turbulence characteristics of scalar quantities such as sensible heat, water vapor and carbon dioxide within and above rice plant canopies. Two sets of sonic anemometer-thermometers and infrared carbon dioxide-humidity fluctuation meters were used to measure the turbulent fluxes of scalar quantities or momentum and related turbulence statistics within and above a paddy field. The direction and magnitude of each turbulent flux varied depending on the strength of its source and sink within plant canopies. In general, turbulent fluxes above plant canopies were much larger than those within plant canopies. Comparison of turbulence statistics of humidity and carbon dioxide within and above plant canopies showed that the magnitude or signs of turbulence statistics of each quantity were different in the daytime and nighttime and that they also depended on irrigation conditions. Fluctuations of CO2 with very large values were observed within plant canopies when the irrigation water was covering the soil surface. These were produced by CO2 in high concentrations being pushed out from the soil by the irrigation water.
The characteristics of the subtropical high around Kyushu as the water transport system toward the Baiu front was examined. Two periods in early July of 1988 were selected in this study (the period (I) : 6 to 10 July and (II) : 11 to 15 July) when the special rawinsonde upper-air observation was made there. In period (I) the northward transport of moisture across the ridge line of the subtropical high was very weak. The air was very dry, especially above the 900 mb level. In period (II) the enhancement of the northward transport of moisture was accompanied by a strong low-level southerly wind. It is noted that the specific humidity above the 900 mb level (∼above the planetary boundary layer) also increased then, which results in a large amount of precipitable water in the subtropical high area in period (II). In period (I) the amount of low-level clouds is very small in the subtropical high area, while it attains 20 to 60% due to the activation of shallow cumulus convection there in period (II). Furthermore, the maximum phases of diurnal variations of the amount of low-level clouds, specific humidity and relative humidity were in coincidence with each other over the sea. The moisture content did not decrease along the low-level southerly wind in the subtropical high area in period (II). Although the present study does not examine the moisture budget there, the shallow cumulus convection might play an important role in sustaining the large moisture content, especially above the planetary boundary layer, in the subtropical high area to the south of the Baiu front.
The simultaneous relationship between sea-surface temperature (SST), tropical convection. and weather over Japan is statistically examined for winter, using monthly-mean SST, outgoing longwave radiation (OLR), and the temperature over Japan. In a previous study (Miyazaki, 1989), it was clarified that the winter temperature over Japan is negatively correlated to convective activity around the Philippines. In this study, it is found that winter convective activity around the Philippines is positively correlated to SST in the warm-water pool over the western tropical Pacific and negatively to SST in the central and eastern equatorial Pacific. These results indicate that winter SST in the tropics can influence the atmospheric circulation in the xtratropical Northern Hemisphere through the fluctuation of tropical convection. An examination is made of the direct correspondence between the January temperature over Japan and sea-water temperature in the western tropical Pacific observed along 137°E. In most cases, lower sea-water temperature corresponds to higher temperature over Japan. On the other hand, higher seawater temperature corresponds in many cases to lower temperature and in several cases (1972, 1989) to higher temperature. In Januaries 1972 and 1989, EU (Europe+) and PNA (Pacific+) patterns appeared at 500 mb. In January 1989, tropical convection shifted westward to the Indian Ocean.
Unsteady and quasi-steady state solutions of shallow water flow having a lee hydraulic jump over a mountain range in a channel of variable width are calculated by expanding Houghton and Kasahara's (1968) theoretical model. In an unsteady flow regime in which a lee jump moves downstream, both the decrease of the channel width and the increase of the mountain height contribute to the increase in the moving speed of the lee jump. This result confirms Arakawa's (1969) suggestion which indicated that a steady state flow is deformed by the channel width in the same way as by the mountain height. On the other hand, in the quasi-steady flow regime in which a lee jump stays in the lee of the mountain, the jump develops at the more leeward side when the channel width decreases, while it tends to develop at the more windward side when the mountain height increases. Namely, Arakawa's (1969) suggestion does not hold for the location of the stationary jump. This response of the lee jump in a quasi-steady regime to the magnitude of the channel width is analogous to the behavior of an internal hydraulic jump in a non-linear flow over a mountain range with a col. The velocity of the fluid just before the hydraulic jump increased with the decrease of the channel width. This result corresponds to the fact that strong downslope winds tend to occur in the lee of a col of a mountain range.
For the analysis of the tropical wind fields, Heta (1990, 1991) applied the two-dimensional MASCON model, which adjusts and smoothes the interpolated wind data to satisfy the continuity equation at the lower (850 hPa) level. However, the upper level (200 hPa) was evaluated only by interpolation. In the present paper, the analysis scheme of the three-dimensional MASCON model is developed, that provides us with the three-dimensional wind fields (μ, ν, ω) over the whole troposphere in the tropical regions using the variational calculus technique as the extension of the previous two-dimensional model. The spatially sparse wind data set of satellite cloud and rawinsonde wind data is adjusted to satisfy continuity equation at all levels consistently. By the use of this new scheme, the tropical wind fields surrounding the same tropical disturbances as the previous papers are reanalyzed and the previous results are certified to be correct.
A large zonally symmetric diurnal variation is found in temperature and wind fields in a model general circulation of the middle atmosphere. This variation has a vertical wavelength of about 25 km and shows similar structures to those of the basic mode of zonally symmetric diurnal tides. The zonal component of diabatic heating projected to the horizontal structure function of this mode shows a prominent diurnal change with large amplitudes near the surface. The simulated zonally symmetric diurnal variation therefore is the basic mode of the upward propagating tides thermally excited in the lower troposphere, the amplitude of which mode becomes appreciably large in the middle atmosphere due to the density effect.