The Eulerian- and the Lagrangian-mean flows induced by steady, dissipating equatorial waves are discussed. The waves are assumed to be excited by the bottom corrugation and to be dissipated by Newtonian cooling and Rayleigh friction with an equal relaxation time. Four wave modes considered are Kelvin waves, mixed Rossby-gravity waves, Rossby waves with n=1 (n is the meridional mode number, see Matsuno (1966)) and westward propagating inertio-gravity waves with n=1. For all equatorial normal modes, both of the Eulerian- and the Lagrangian-mean meridional circulations do not get across the equator. This result follows from the symmetry properties of equatorial waves, and can hold even if the feed-back effects of the wave-induced mean zonal flow are taken into account. In other words, in order for air parcels to go across the equator, an asymmetric configuration of the mean zonal flow is necessary. In case of Kelvin waves, it is shown that the Lagrangian-mean meridional circulations are identical with the Eulerian-mean counterparts, and have downward flows above the equator. It is also shown that, in the Boussinesq limit, both the Eulerian- and the Lagrangian-mean meridional circulations cannot be caused by Kelvin waves. The present results show that throughout all the cases of modes, the Lagrangian-mean meridional circulations have simpler structures than the Eulerian-mean counterparts. For example, in case of mixed Rossby-gravity wave, the Eulerian-mean meridional circulation has two cells opposite to each other in one hemisphere, while the Lagrangian-mean one has only one cell in the same hemisphere. In addition, it is emphasized that, in the case of mixed Rossby-gravity waves, the deviation from the geostrop.hic balance between the Eulerian-mean zonal flow and pressure gradient is remarkably large as in the case of westward propagating inertio-gravity wave with n=1.
The movement of the cyclonic vortex is examined by some numerical experiments of barotropic models. It is confirmed that the northward acceleration of axially symmetric non-divergent vortex on a β-plane is proportional to the scale and the strength of the vortex, which was predicted by Rossby (1948). It is found that the accelerative motion is accompanied by the motion with a nearly constant northward speed. The speed is approximately represented by the relation Cy=0.52β0.6L01.2U00.4 in the range of BL02/U0<0.01, where β, L0 and U0 are the northward gradient of the Coriolis parameter, the characteristic size and intensity of the vortex, respectively. The oscillatory motion on the vortex path is also found in our experiments. The period is in the range from 10 to 30 hours. However the dependence of the period on the size and intensity of the vortex is not necessarily in agreement with the theoretical result by Yeh (1950) and Kuo (1950).
Radiative effects of clouds on 8-day northern hemispheric prediction are investigated in the real data prediction experiment using several versions of a 4-level northern hemispheric primitive equation model. They are C0-model (0% cloud cover at all levels), C1-model (100% cloud cover at all levels) and CP-model (cloud cover at each level is determined from the predicted relative humidity). Main differences of 8-day northern hemispheric predictions between C0 and C1 are found in the vertical profile of average temperature over the whole horizontal area both in summer and in winter, and in the latitudinal gradient of both temperature at lower troposphere and 500mb height in winter. The differences can be interpreted to stem from the following three effects of clouds through radiation; greenhouse effect through infrared radiation, albedo effect through solar radiation and ground effect through sensible and latent heat flux at the ground surface. The greenhouse effect works to warm the air under the cloud and to cool the air above the cloud, compared with C0-model. The albedo effect works to cool the air under the cloud and to warm the air above the cloud, compared with C0-model. Since the upward sensible and latent heat flux at the ground surface are produced by warming of the ground surface due to absorption of solar radiation, the ground effect works to cool the air under the cloud compared with C0-model. For cloudy cases the greenhouse effect tends to make the troposphere unstable, while the albedo and the ground effect tend to make the troposphere stable, compared with clear cases. The albedo effect is limited in the daytime, and the ground effect is limited in the daytime and over the land area. Therefore, the greenhouse effect of clouds is the most dominant effect in interpreting the differences of the 8-day northern hemispheric predictions by C0-and C1-model.
Synoptic analyses were conducted of interannual variations of the tropical winter monsoon circulation during the 20-year period from 1961 to 1980. The 150mb easterly wind at Singapore was used as an indicater of the strength of the tropical winter monsoon over the WMONEX area (South China Sea-Indonesia-northern Australia). Evidence has been shown that interannual fluctuations of the winter monsoon are deeply associated with the corresponding changes in the Walker circulation. The monsoon was found to be strong when the sea level pressure was high near Tahiti and low near the Cocas Islands. The monsoon was weak when the opposite conditions were observed. The 1978-79 MONEX winter was one with a weak monsoon. There is a strong tendency for the formation of two ITCZs when the monsoon is strong. In comparison, only one ITCZ near New Guinea is observed during weak monsoon years.
It has been reported occasionally that meso-scale vortex-like echo patterns are detected by radar observation. Three meso-scale vortex-like disturbances aligned along the coast of Wakasa Bay observed on 9 February 1968 are investigated. Structures of the disturbances, their temporal variation and the general field in which the disturbances are imbedded are analyzed using all the available data of PPI radar observation at Fukui and surface weather observation in Hokuriku and Kinki districts. The disturbances have the horizontal scale of -100km in a lower half of the troposphere. These disturbances are characterized by the cyclonic rotation with the vertical component of vorticity of 10-3-10-4s-1 and the horizontal convergence of -10-4s-1 and by the lower pressure of -1mb at the center of the disturbance than the environment at the surface. The precipitation amount of several millimeter per hour is accompanied by passage of the disturbances. The air colder as much as 1°C is found around the center of the depression in the early stage and then replaced later by warmer air at the surface. A series of the three disturbances are imbedded in a remarkable cyclonic horizontal shear zone located in the surface pressure trough in the general field.
Three-dimensional distributions of precipitation water in a maritime cumulus cloud are investigated in detail through the life time by analyzing digital data of radar echo which were obtained at Miyako Island in the East China Sea during AMTEX'75. A preliminary consideration on the budget of precipitation water in the early period of the mature stage is also presented under a hypothetical assumption of vertical velocity. The macroscopic feature of the radar echo observed is that the maximum radar reflectivity is 42dB, the maximum height 4.9km and the life time 44min or so. The main results obtained in this study are as follows. (1) Although the cloud has a fairly long "nursing stage", the evolution is very rapid as soon as it begins to develop. The maximum ascent rate of the top of the radar echo is about 9m/s. (2) The larger value of radar reflectivity is analyzed around the central portion of the radar echo, which is located at 3 to 4km level during the mature stage. This suggests the existence of the localized accumulation zone of higher precipitation water. (3) In the early period of the mature stage, the radar echo shows little inclination together with little change of horizontal dimension in the vertical in spite of the existence of noticeable vertical wind shear. (4) The averaged horizontal size of the major portion of the radar echo is about 4 times in the early period of the mature stage and the most extensive region through the life time, which appears at a fairly low level (1.5 to 2km) in the decaying stage, is about 7.5 times as large as that just before development. (5) The movement of the radar echo is governed by the wind at extremely low level (about 1km) during the mature stage and it moves to the left of the wind in the middle layer. (6) According to a preliminary consideration on the budget of precipitation water, the generation of precipitation water is prominent in the middle layer of the cloud to result in its net increase against the loss due to mixing with the environmental air together with vertical advection. On the other hand, the increase due to vertical advection in the upper layer is almost canceled by evaporation, relative sedimentation and turbulent mixing, while in the layer around the cloud base evaporation is noticeable. We compared our results with some of the works by other researchers.
Clear-air echoes were observed in Nagoya with two radars of 3.2cm in wavelength. Most of echoes were dot echoes. The target of dot echoes are inferred to be insects on the basis of their backscattering cross sections and the time variation of received signals of each echo. Diurnal variations of the number of dot echoes were carefully studied. And it was suggested that the number and spatial distribution of dot echoes have close relation to growth and break down of the mixing layer. Horizontal speeds of dot echoes were also examined, and they were not always indicating wind speeds in light wind condition. There also appeared another type of clear-air echoes which seemed to be attributed to refractive index fluctuations in the atmosphere. They were observed as wavelike echoes associated with internal gravity waves. The value of Cn2 estimated on the basis of the intensity of the echoes would be as high as 10-12cm-2/3. This value implies the possibility of the existence of intense turbulence in stable stratification which can be detected even by the radar of 3.2cm in wavelength.
The diffusely reflected radiation in the daytime and diffusely transmitted radiation at night from an inhomogeneous, plane parallel planetary atmosphere bounded by the ocean surface was calculated at the 3.7μm infrared window region. In the daytime the effect of the solar radiation from top was taken into account. This spectral region corresponds to the channel 3of the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA-6 satellite. Thus the deviation from the sea surface temperature (SST) was evaluated in the mid-latitude region in summer, where it is defined by the difference between the given surface temperature and the calculated brightness temperature obtained at the top of the atmosphere. The present study has dealt with the problem of no cloud contamination in data. In the atmosphere, water vapor, molecular nitrogen, nitrous oxide, carbon dioxide and methane as absorbent constituents and aerosols as the scattering constituent were taken into account. The ocean surface as a lower boundary was simulated by many facets whose slopes are according to the isotropic Gaussian distribution (Cox and Munk, 1955). The slope of the facet depends upon the ocean surface wind. The refractive index of the ocean surface as well as the aerosols in the atmosphere is assumed to be that of water by Hale and Querry (1973). Computational results show that it is suitable for deriving the optical thickness in the direction of about 15° away from the specular direction. Hence the ocean surface temperature can be evaluated with the aid of the optical thickness thus derived, whereas the influence of the atmosphere to SST can not directly be estimated by the use of single channel of 11μm window region. On applying this result to the NOAA-AVHRR data (30°N, 147°E) on Aug. 2, 1979 together with the wind speed reported by ship, the very clear atmosphere simulates SST within the accuracy of 1-2°K at the center of the sunglint and within the accuracy of 0.5°K in the rest of the region. This atmospheric condition agreed with the ship data of visibility. To discuss the accuracy further, comparison of the radiometric measurements of SST by ships with temperature measured by satellite is essential.
The numerical model calculation was conducted of pH of cloud water on the assumption that the cloud droplets formed on H2SO4 and other sulfate and nitrate nuclei dissolve acidic and alkaline gases to achieve gas-liquid equilibrium in a very short time. With the initial concentration of gases and particulate components as found in the real atmosphere the pH of the cloud water is calculated to be three. The calculation inetrprets pH, and the concentrations of SO42-, NO3- and other species in cloud water observed on a mountain fairly well.