Experimental results on the thermal structure of baroclinic waves observed in a rotating fluid annulus, subjected to a horizontal temperature difference, are reported. The main maximum of the amplitude of the wave is observed in the uppermost layer and the secondary maximum is observed in the lowest layer. Because its axis inclines forward (direction of the basic rotation) with height, the latter maximum seems to be associated with a different kind of wave from that of the Eady type which predominates in the uppermost layer. While the wave number is unchanged, the amplitude increases with increasing rotation rate below the level of the main maximum. The phase difference between upper and lower levels decreases with the rotation rate. With a fixed rotation rate and a horizontal temperature difference, different wave numbers may be observed with different temperature distributions such that the distribution for a larger wave number is more or less similar to that for a smaller wave number at a lower rotation rate. The zonal mean temperature distribution in the wave regime is of constant gradients both in the vertical and in the radial directions in the almost entire meridional plane. The zonal mean temperature gradient does not change with the rotation rate and wave number except in the uppermost outer region and in the lowest inner region.
Stratospheric wave disturbances over the tropical western Pacific during Dec. 1968-Apr. 1969 are analysed for about 10 day period. It is found that two types of disturbances which propagate in the opposite direction are dominant in this period range. One is the Kelvin wave which is prevailing below 40 mb. The other is the westward propagating disturbance observed above 40 mb, which exhibits both zonal and meridional wind fluctuations. It may be identified with the n=1 Rossby wave. The vertical structure of these two types of waves is compared with the calculation based upon the wave theory (Lindzen, 1971, 1972). It has been noted by earlier studies that there exists a difference between the vertical structure of waves above and below the westerly shear zone when Kelvin waves are dominant. The present study suggests that the difference would most probably be due to the mixture of Rossby waves with Kelvin waves.
The characteristic features of the wind profile, the momentum and kinetic energy budget in the mixed layer of the polar air-mass transformed over the Kuroshio region are analyzed for the three periods of polar outbreak in AMTEX '74 and '75. While there is a strong geostrophic wind shear in the mixed layer, the wind distribu-tion in the mixed layer is characterized by the almost vertically uniform northerly winds. In the lower part of the mixed layer, the strong ageostrophic winds are directed toward the low pressure, while in the upper part of the mixed layer, the strong ageostrophic winds are directed toward the high pressure. These characteristic features indicate vertical (convective) mixing of momentum. The momentum budget calculations show that the magnitude of the frictional force in the lowest 50 mb is about 6×10-4m/sec2. The kinetic energy budget calculations show that the generation of K and the frictional loss of K approximately balance in the lower part of the mixed layer. In the upper part of the mixed layer, however, the balance is primarily between the “negative generation term” (i.e., ageostrophic winds are directed toward the high pressure) and the substantial decrease of K. The results of calculation also indicate that both the generation and the frictional loss of K are very large (∼5 watt/m2) in the anticyclonic branch of the polar outbreak (i.e., over the western AMTEX region) and relatively small (∼2 watt/m2) in the cyclonic branch of the outbreak (i.e., over the eastern AMTEX region).
For the period February 14 to 28th, 1975, the second phase of the Airmass Transformation Experiments (AMTEX) over Southwest Islands of Japan, heat and moisture budgets have been estimated. Three different case studies (average for the whole period, average for the undisturbed period, and average for the disturbed period) have been carried-out over a square area. For the period as a whole, on the average there is an inversion layer around 800mb and the downward motion (ω-positive) is maximum near that level. The apparent moisture source is also maximum near that level. Through there is no apparent heat sink, heat source of the large-scale motion system is minimum near that level. In the disturbed case, when the area was under the influence of warm southerlies, there is a depression to the north of the area, and there is no inversion. There is no significant apparent moisture source, but there is a significant apparent moisture sink around 750mb. The apparent heat source is also near 750mb with a maximum upward motion (ω-negative). The undisturbed period is characterized by the cold northerly winds. Just like in general case, in this case also there is an apparent moisture source near 800mb, the lower inversion level. For a similar study of AMTEX '74, Nitta (1976) used a low-pass filter to remove short period fluctuations less than a day. For determining the height (Pt), at which the transportation of heat flux due to convective clouds vanishes, he used the vertical thermal structure of individual observations and computed the cloud tops. From that he evaluated the area averaged Pt. In the present study, no filter has been used. Further, the total heat transports by eddies are assumed to be confined below the inversion base and so Pt has been taken as the base of the inversion layer. In the case of no-inversion, the layer of minimum lapse-rate is assumed to limit the vertical heat transport. The average total heat supply from the sea surface (873ly day-1) is in general agreement with that estimated by the bulk aerodynamic method independently. While it is only 140ly per day in the case of disturbed situation, it is as high as 1200ly per day during the period of cold air out-break, similar to that estimated by Ninomiya (1968). For the general as well as the other two cases, sensible heat and Bowen's ratio have also been computed.
Transfers of heat and momentum in winter for the East China Sea and adjacent seas were estimated by means of an aerodynamic bulk method under diabatic conditions. It is found that at the Kuroshio region the sensible and latent heat losses (H+lE) are primarily compensated for by the heat convergence caused by the oceanic eddy and/or current transport. The secondary contribution to the heat balance is due to the net flux radiation and the oceanic heat storage. On the basis of heat balance consideration, the thermal diffusivity of the ocean of K= 1.0×108cm2 s-1 is obtained for a period of about one month. There is also suggested that in the Yellow Sea there occurs a counterclockwise circulation of water. The average value of H+lE over the AMTEX area for the entire period of AMTEX '74 is by about 10 to 20% smaller than the climatological normal value for he corresponding period. The value of H+lE estimated by the present aerodynamic method agrees in general with those obtained by the atmosph ric budget computations by Nitta (1976) and Murty (1976) for both the period of AMTEX '74 and AMTEX '75. During an intense cold-air outbreak the very large amount of latent heat of about 500 to 800W m-2 is supplied to the atmosphere over the Kuroshio, while only a small amount is supplied to the atmosphere over the shallow seas of the continental shelf. The Bowen ratio (H/lE) is about 0.7 to 0.8 over the Yellow Sea, whereas it is 0.3 to 0.4 over the AMTEX region, and 0.1 to 0.2 over the sub-tropical ocean.
Behaviors of two long-lasting cellular echoes, which were found out among several tens of cellular echoes near Owase Meteorological Station on the 14th of September in 1972, are analysed in detail using photographs of PPI radar echoes taken every 3 minutes. Both echoes landed at the nearly same point with the speed of travelling which became slower and slower with approaching the land. It is found out that long-lasting echo formed in a cluster of cellular echoes which had appeared over the sea about 100km east-south-eastward from Owase. Though new echoes had a tendency to form in the back region of old echoes in initial stage of the cluster, they appeared in the fore region of echoes existing previously after the formation of the longlasting echo. On the basis of the results of analyses the mechanism of formation of organized precipitating convective clouds will be discussed.
The problem of convective clouds at Owase in the cases of heavy rain is studied by a quasi steady-state one-dimensional jet model of cumulus convection which includes dynamic entrainment and simple cloud physical processes with no glaciation process. In this study the author assumes hypothetically that one of the characteristic mechanisms at Owase in the cases of heavy rain lies in the horizontal convergence at subcloud layer and updraft velocity at cloud base reflects the convergence. The height of cloud and the profiles of many variables obtained from our cloud model depend upon the updraft velocity at cloud base. This property is different from that of modified parcel method or bubble model of cumulus convection. First, to test whether this cloud model correctly predicts the heights reached by clouds the author compares observational results with those obtained from this numerical model on the case in Aug. 30th 1971. By this comparison it is indicated that the coincidence is pretty well. Then, as examples of heavy rain, 51 cases for these ten years are adopted and the numerical computations are repeated. The main characteristics obtained are as follows. (1) The height of most convective clouds is less than 5 km above the ground surface and the ratio which it exceeds 6 km is only 5 to 18 percent of all the convective clouds whose heights exceed 1 km under the assumption with less than 2m/s of updraft velocity and no excess temperature at cloud base. (2) The frequency distribution of the height of cloud top is rather concentrated in the ranges of 1 to 2km and 3 to 4km except very shallow clouds. From these results it is inferred that small scale or shallow convective clouds whose heights are less than 5km are generated with considerable frequencies around the Owase area in the cases of heavy rain.
A model experiment of the developing stage of a cumulus cloud was performed by the use of NH3 gas and HCl gas which release heat of reaction by mixing. The white smoke of NH4Cl (thermal) grew upwards because of the buoyancy created by heat of reaction. The thermal had a strong tendency to grow upwards at the vigorous reacting stage and the half-broadening angle was inversely proportional to the height of the top of the thermal. Such properties were also observed in a large natural cumulus cloud. The entrainment coefficient of this thermal was 0.24. This value is in fairly good agreement with that of McCarthy's observation (0.3). The Froude number of thermal in the experiment was estimated as 4.0. This value was larger than that of a thermal with a constant total buoyancy.
During the winters from 1972/73 to 75/76, we have observed winter thunderstorms in Hokuriku Area, Japan and we have found from the observations that most of return strokes neutralized positive charge in the thunderclouds contrary to the strokes in summer which neutralized negative charge in the clouds. Though only one, we have observed a cloud-to-ground discharge initiated by a upward streamer from a structure lower than 15m. The study of such upward streamer in winter seems to be very important for protection of transmission lines against damage by lightnings.
Lightning channels in thunderclouds are investigated with the thunder technique, and the relationship between the channel direction and the storm characteristics is discussed. It is confirmed that the channels of ground flashes horizontally extend in clouds and the channel directions tilt to the downstream of the wind in the upper atmosphere. It is found that the distribution on a horizontal plane, of the directions of horizontal channel projections inside the clouds relates with the speed of storm motion, and channel directions tend to tilt to the downstream with increasing speed of storm motion. The distribution of the channel inclinations in clouds seems to relate with the flash frequency of the storm, which is controlled by the updraft in the clouds.
The crystalline nature of water drops 45-465μm in diameter, frozen and deformed in free fall, was observed. The deformation of the frozen drop is closely related to its crystalline nature. For example, shattering is inferred to occur mostly when a water drop freezes single-crystalline, and a shattered fragment is mostly an almost hemispherical single-crystal-line particle with c-axis perpendicular to its fractured face. A spike, a relatively long protrusion, is formed mostly when a water drop freezes poly-crystalline and protrudes from the crystal boundary.