Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Volume 56 , Issue 5
Showing 1-17 articles out of 17 articles from the selected issue
  • Hajime Nakamura
    1978 Volume 56 Issue 5 Pages 317-340
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Reexamination of schemes for the vertical finite-difference and for the pressure gradient force in the σ-coordinate system is made following the discussions of Arakawa (1972), Corby et al. (1972) and Phillips (1974) in order to find a scheme suitable for incorporating steep mountains in general circulation models and numerical forecasting models. It is possible to classify the schemes proposed so far by using integral constraints such as the conservation of the total energy, the conservation of the potential temperature (θ) and its square and the surface torque condition. Furthermore, a new scheme is obtained from the classification.
    Truncation errors of the hydrostatic relation, the pressure gradient force and the advection terms are compared among the schemes obtained by the classification for the case of the atmosphere at rest. By revising schemes errors are reduced to be considerably small over a steep mountain. For example, the errors of the pressure gradient force and the advection terms of the momentum equation are about 1m/s in geostrophic wind over a slope with 4km/300km inclination if the grid size is 300km.
    We also examined truncation errors in a more realistic case. A steep mountain like the Tibetan Plateau is placed in the westerly flow. It is assumed that the atmosphere has a stable stratification in the vertical and that the westerly flow is forced so as to be restored to a barotropic equilibrium wind. Computational domain is a half-hemisphere.
    The results obtained by the runs having different grid resolutions and different schemes are compared with that of a high resolution run which has 12 layers and the 2.5° horizontal grid size. The result of the low horizontal resolution run with the 5° grid size is a little different from that of the high resolution run. The difference in wind is about 10m/s over the mountain but is negligibly small in the other region. Therefore, it seems that the errors in the low horizontal resolution run are tolerable for the numerical simulation of the largescale flow of the atmosphere generated by the steep mountain. Difference between the 6-layer run and the 12-layer run is negligibly small, probably because in this situation (baro-tropic equilibrium state) the effect of vertical resolution is not so important as that of horizontal resolution. Difference among the various schemes is also very small compared with that due to horizontal grid resolution. As a whole truncation errors over a steep mountain are considerably smaller than that has been expected so far by some workers.
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  • Hajime Nakamura
    1978 Volume 56 Issue 5 Pages 341-352
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    To examine dynamical effects of mountains on a westerly jet numerical experiments are made using the model developed in Part I. The jet is forced directly in such a way that it is restored to a prescribed equilibrium state, in which it has no vertical shear. The temperature of the atmosphere has a constant lapse rate in the equilibrium state. Three types of mountains are considered. Their scales are of the order of that of the Tibetan Plateau. The first mountain has the smoothest slope at the side boundaries with the average inclination of 4km/20° and the second one has the sides with the slopes of the 4km/5°inclination. The last one has the vertical walls at the sides.
    We examine two effects of mountains, that is, the blocking effect on the flow and the streching and shrinking effect of vortex tube over the mountain slopes. The latter effect produces stationary planetary waves coupled with the β-effect. The appearance of these effects depends on the steepness of mountains. The blocking effect is the weakest for the mountain with the smoothest side boundaries and is the strongest for the one with the vertical
    walls. On the contrary, the stationary trough in the downstream of the mountain is the weakest for the mountain with the vertical walls and is the strongest for the one with the smoothest side boundaries. The Taylor column effect is important for the blocking of the westerly by the mountains.
    Splitting of a westerly jet by the Tibetan Plateau is examined by the model simulation.
    When the jet axis is located at the center or at the southern boundary of the mountain, the jet splits into northern and southern branches around the mountain. However, when it is located at the northern boundary, splitting is very weak. The result agrees well qualitatively with the observation of the seasonal change of the westerly jet over the Plateau.
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  • Hajime Nakamura
    1978 Volume 56 Issue 5 Pages 353-367
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    In order to investigate dynamical effects of mountains on the general circulation of the baroclinic atmosphere, the model developed in Part I is integrated for about 150 days. A simplified diabatic heating function and the Newtonian cooling evaluated from observational data are adopted for the thermal process in the model. The 6.5°K/km convective adjustment is used to parametarize the vertical convective mixing of heat. The nonlinear viscosity
    and the vertical momentum diffusion are also included.
    Time integrations are performed with and without an idealized steep mountain like the Tibetan Plateau. The model without the mountain simulates' successfully the gross features of the general circulation similar to the real atmosphere. That is, the westerly wind in the middle latitudes, the easterly wind in the tropics and the meridional three cell circulation are well simulated. Baroclinic unstable waves are well developed, though a little less active than the real ones. However, there are some defficiency in the model atmosphere. For example, the subtropical jet is too strong and its position is too south compared with the real atmosphere due to the large latitudinal gradient of the diabatic heating near 20°latitude. The active region of baroclinic waves is limited to relatively higher latitudes.
    Incorporating the mountain does not change these features largely. The most remarkable change is the northward shift of the subtropical high. It is located at 30° latitude in the model without the mountain while it is at 45° latitude in the model with the mountain. The region of the downward motion in the subtropics also expands northward. This is due to the geostrophic adjustment of the pressure field to the westerly wind weakened by the blocking effect of the mountain. This phenomenon may be one of the causes of the northward shift of the dry area in the Eurasian continent. We may also speculate that this process contributes to the formation of the Siberian high to some extent.
    The mountain does not excite stationary planetary waves so much as expected from the observation and other studies, because of the weak westerly wind over the mountain.
    In addition, a zonally symmetric circulation is obtained. Though there is a large difference between it and the real atmosphere, it is considerably similar to the real atmosphere compared with the results of Hunt (1973) who also investigated a zonally symmetric circulation. It is supposed that one of the causes of the difference between the two results is the difference of the scheme used for the nonlinear horizontal viscosity in the two models.
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  • Yasumasa Ookouchi, Michiya Uryu, Ryukichi Sawada
    1978 Volume 56 Issue 5 Pages 368-386
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Thermal and dynamical effects of mountain on the land and sea breezes are studied numerically, by paying special attention to the growth and decay of the circulations and the extent of them.
    A two dimensional model in a vertical plane perpendicular to a seacoast line and a mountain chain is used. The horizontal extent and the depth of the computational region are assumed to be 130km and 3km, respectively. The mountain is assumed to have a simple trapezoidal form with 8km in width and 450m in height, and is located at 18km from the coastal line.
    In order to estimate the thermal and dynamical effects of the mountain, numerical experiments are conducted for the following three cases:
    case (a) no mountain
    case (b) mountain with thermally insulated boundary condition (insulated mountain)
    case (c) mountain with the diurnal change of its surface potential temperature (heating mountain)
    Main conclusions are summarized as follows:
    (1) The sea breeze can not invade inland beyond the heating mountain, while the breeze invades inland beyond the insulated mountain faster and deeper than expected in case of no mountain.
    (2) The land breeze develops strong in case of the heating mountain. This is due to the down-slope winds. In case of the insulated mountain, this down-slope winds do not develop and the land breeze remains weaker than that of no mountain case.
    (3) The phase difference between the time of the maximum land-and-sea surface temperature contrast and that of the strongest induced circulation is much reduced, compared to the case of no mountain, regardless of the thermal boundary condition of the mountain surface.
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  • Masanori Yoshizaki
    1978 Volume 56 Issue 5 Pages 387-404
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    A numerical model including dynamical and cloud physical processes is formulated to simulate the observational evidences, concerning the severe storms frequently observed in the North American Continent. Our concerns are restricted to five points; (1) generation of a cold dome and a convergence line at the surface, (2) upshear tilting of an updraft, (3) a long-lasting nature, (4) a right-moving convective cloud and (5) generation of vertical vdrticity. To examine roles of vertical wind profiles on the above-mentioned features, we make numerical calculation for four cases with different wind profiles.
    It is shown that the point (1) can be explained by cooling due to evaporation of raindrops falling in the subcloud layer. In the case for which the direction of the basic wind shear turns with height, a long-lasting nature of the convective cloud, upshear tilting of an updraft and the small deviation of the rain region movement from the environmental wind direction are obtained. The jet type wind plays an important role in (3), because it transports raindrops not to cut off the supply of fresh air from the subcloud layer into the updraft region. Vertical vorticity is created mainly by the tilting term at the developing stage and then the vertical advection and the divergence term as well as the tilting term are principal terms. A pair of strong anticyclonic and weak cyclonic vortices are found in the rain region.
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  • Yukio Gocho
    1978 Volume 56 Issue 5 Pages 405-423
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Our study of the rainfall around the Suzuka mountains during the past ten years has shown that the heavy rainfalls with a maximum daily precipitation of 200mm or more usually occur in connection with typhoons. The heavy rainfall areas lie on the lee side along the mountains and near the ridge. During those storms, strong south-easterly winds prevailed across the mountains in the lower troposphere, the middle and lower troposphere were almost saturated, and the stability was convectively unstable or nearly neutral. In some cases, the stability was nearly neutral, the time change of the rainfall rate was relatively small, and the convective rainband was not found by radar observation. Assuming these cases are due to a stratiform cloud, numerical experiments are carried out in order to make a model of such orographic heavy rainfall.
    In the first model, steady airflow over simplified mountains with the scale similar to that of the Suzuka mountains is computed, based on a two-dimensional and linearized equation, assuming that the atmosphere is saturated and has a pseudo-adiabatic lapse rate in which the undisturbed basic flow across the mountains has its maximum speed in the lower troposphere. The generation of precipitation is assumed to be due to the process of warm rain. A portion of the condensed liquid water in the ascending current is converted into cloud droplets with a certain size distribution, and another portion is spent to grow drops. In this cloud, drops grow by the collision and coalescence process, and evaporation occurs in the descending current. Some drops fall to the ground as rain. The steady state of these processes is computed. The computed rainfall rate with the model is very small having a maximum of only about 1mm/hr around the ridge, and the distribution is different from that observed around the Suzuka mountains.
    In the second model, in addition to the first, uniform light rain with the function of seeding falls from the upper cloud. The results using the second model are similar to that observed. It is found that the function of the rain from the upper cloud with the rainfall rate of a few millimeters per hour is important for such orographic heavy rainfall. In fact, the smaller the rate of decrease of the wind speed above the low level strong wind crossing
    the mountains, the more the heavy rainfall area shifts leeward with the rainfall over the lee side of the mountains becoming heavy. A similar relationship is obtained in this experiment.
    Furthermore, it is found from the experiment that the precipitation distribution around the ridge changes considerably due to the size distribution of drops of uniform rain falling from the upper cloud and the number density of cloud drops. The smaller the drops of rain falling from the upper cloud, the larger the rainfall rate around the ridge. On the other hand, the larger the generated cloud droplets or the smaller the number density of cloud drops, the larger the rainfall rate. The rainfall rate around the ridge decreases considerably if the number density of cloud drops exceeds about 100/cm3.
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  • Part I: Development of a Convectively Mixed Layer
    Tomio Asa, Kozo Nakamura
    1978 Volume 56 Issue 5 Pages 424-434
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Development processes of a convectively mixed layer is investigated numerically with a two dimensional model dealing with convection roll parallel to the general wind. Evolution of individual small-scale connections is explicitly followed by integrating the convection equations, and the structure and its temporal variation of the convective layer averaged in the horizontal direction perpendicular to the general wind are discussed. The moist convectively mixed layer accompanying convective clouds forms the multiple-layer structure, i.e., (1) a super-adiabatic surface layer in the lowest, (2) a subcloud layer above the surface layer with a uniform potential temperature and a slightly decreasing specific humidity with height, (3) a lower half of a cloud layer in which both the rates of increase in potential temperature and decrease in specific humidity with height are rather small and the heating due to condensation of water vapor is dominant, (4) an upper half of the cloud layer in which both the rates of variation of potential temperature and specific humidity with height are very large and the cooling due to evaporation of cloud water predominates over the heating due to convergence of convective heat flux, and (5) a stable uppermost layer eroded from below. It is indicated that convective clouds play an effective role in deepening a convectively mixed layer.
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  • Kanzaburo Gambo
    1978 Volume 56 Issue 5 Pages 435-442
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    By making use of data at the 500-mb level during the winter season, the spectral densities of ultra-long waves in the frequency domain are examined. The result shows that the spectral densities for zonal wavenumbers k=1∼3 are approximately proportional to the minus second power of the frequency. From this result the day to day variations of the amplitude of ultra-long waves are examined as a stationary random process. In order to clarify the different characteristic features between ultra-long waves and baroclinic waves, the spectral density for zonal wavenumber of k=6 is also examined. In the case of the baroclinic wave (k=6), the maximum value of spectral density is obtained at the period of about a few days.
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  • Nobushige Mori
    1978 Volume 56 Issue 5 Pages 443-456
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Recent trends for changes of the temperature field in the northern hemisphere are described by using the annual-mean data for 25 years (1950-1974) in the lower layer (1, 000-500mb) and for 20 years (1956-1975) in the upper layer (500-100mb). We expressed a given time series in terms of Tchevychef's orthogonal polynomial, and it was decided by using a statistical test for goodness of fit how many terms should be chosen in the polynomial. The usual type transformed from the above polynomial was used as a trend or a measure for the change of a given time series.
    As for long-term-mean temperature fields at first, a characteristic aspect in the upper layer is shown in comparison with that in the lower layer. The zonal-mean temperature in 80°N was a linearly upward change in the lower layer but a linearly downward change in the upper layer. In the lower layer, it has become warmer in the west-hemispherical side of 8°N, where a cold-air source was located, and colder in the east-hemispherical side of 80°N where it was a warmer region. It was assumed that the area between 80°N and 30°N could be classified into three latitudinal zones on trend types and those correspondence between the lower and upper layers. The first is 80°N, the second 70°N and 60°N and the third south of 50°N, and features in each of the zones are mentioned. The trend of areal-mean temperature was expressed by a quadratic formula in the lower layer and by the third-order formula in the upper layer. The changes of the meridional and zonal gradients of temperature both have generally a descending trend in the lower layer and an ascending trend in the upper layer. Namely, the temperature field has changed as becoming flatter in the lower layer and steeper in the upper layer, and it is suggested energetically that the lower layer has lost zonal and eddy available potential energies both and the upper layer has acquired those.
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  • Vernon E. Kousky, Pao Shin Chug
    1978 Volume 56 Issue 5 Pages 457-465
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Fluctuations in annual rainfall totals for 229 stations in Northeast Brazil are analyzed by various statistical methods. Smoothed spectral density estimates are calculated for more than 140 stations using the Parzen lag window. Spectral peaks are observed to occur within the period ranges of 2-3 years, 3-5 years and 10-20 years. The regional distribution of the shorter period peaks is discussed. An analysis of trend is performed using the Mann-Kendall rank statistic and time series which are smoothed using a low pass Gaussian filter. Areal analyses of the percent of the 30-year normal rainfall (1931-1960) are used to illustrate the regional distribution and variability of precipitation.
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  • Kanzaburo Gambo
    1978 Volume 56 Issue 5 Pages 466-480
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    A turbulence closure model for atmospheric boundary layers is examined, under the assumption that the turbulent flow is steady in its ensemble average and the advection and diffusion terms in the turbulent Reynolds stress and heat flux equations are neglected. The constants which are introduced in order to obtain a closure system are determined referring the experimental results obtained in the wind tunnel. The validity of the closure model thus obtained is checked referring the observational results obtained in the constant-flux layer. In order to apply our model to the planetary boundary layer, simple forms for the eddy transport coefficients of momentum and heat are formulated. In this case the parametarization of the scale-length l=l(z) (z: heihgt) which is introduced in estimating the dissipation rate of turbulent kinetic energy with height is discussed in order to satisfy the observational result.
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  • Toshio Harimaya, Choji Magono, Syunzo Adachi, Kunihiko Hozumi
    1978 Volume 56 Issue 5 Pages 481-488
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Cloud observations were carried out both from the ground by the stereophotogrammetric method and from a commercial passenger airplane during AMTEX'75. The vertical velocity in an active cloud area is estimated by the stereophotographic observation on the ground, and the fractional area covered by the active parts of the clouds is estimated from both aerial photographs of clouds and satellite cloud pictures. The cloud mass flux is directly estimated from these values.
    The results show that the upward mass flux exists in the cloud area in spite of the mean downward motion over the large-scale triangle area (4.6×104km2) on 20 February during AMTEX'75.
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  • Hisashi Shio
    1978 Volume 56 Issue 5 Pages 489-500
    Published: 1978
    Released: October 19, 2007
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    The effect of the crystallographic characteristics of the surface of a specimen with special regards to the frictional charging phenomenon was investigated. Single crystal ice plates cut from samples from the Mendenhall Glacier ice of Alaska were used and the frictional electrification was measured at ambient temperatures from - 2 to -21°C in a cold room.
    As a result, the following new facts, which can not be completely explained by Latham et al's and Jaccard's theories, were revealed.
    In the case of an asymmetrical rubbing between pairs of faces differently orientated with respect to crystal axes, the rubbed face of the prism plane was invariably positively electrified against that of the basal plane, regardless of the temperature difference between the pairs of the rubbed faces. However, at about -6°C the electric potential of the prism plane against the basal plane was greatly reduced and became so little as to be neglected.
    Moreover, as regards the asymmetrical rubbing between pairs of faces identically orientated with respect to crystal axes, the electric potential of the rubbed face with a cold spot against that of a hot spot was reversed from positive to negative at -6°C or thereabouts as the ambient temperature rose. The above tendency is taken to be the same as that found for the artificial ice formed with polycrystallization of which the size of grains is about 5 mm in diameter on an average as described in the previous paper (Magono and Shio: 1966).
    The absolute magnitude of the potential was about 3 volts, which was two orders higher than the results calculated by theories over a wide temperature range except in the vicinity of -6°C.
    It was concluded that the sign of charge did not depend upon the temperature difference, but upon the difference in hardness between the two rubbed faces of the specimens on the basis of the recrystallization effect of the rubbed face.
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  • Kikuo Okada, Yutaka Ishizaka, Toshiyuk Masuzawa, Kenji Isono
    1978 Volume 56 Issue 5 Pages 501-507
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    The gaseous chlorine in the atmosphere and the water-soluble material of the aerosols collected at Owase in October 1975 were analyzed. The concentration of gaseous chlorine was found to be 3.1μg/m3. It is found that the C1/Na ratios inn the aerosols were always lower than that of seawater. Their mean value was 0.67. On the basis of this value, it was estimated that the amount of C1 deficiency in the aerosols was 2.1μg/m3 which is 61% of the theoretical C1 content of sea-salt particles. The amount of C1 deficiency cor-responded to the concentration of {2(SO4)ex.+NO3-NH4} in the aerosols. Thus, it is sug-gested that the C1 deficiency is mainly due to the chemical reaction between the sea-salt particles and H2SO4 and HNO3 originated from the gaseous materials such as SO2 and NO2, in the atmosphere. According to the relationship between the amount of C1 deficiency in the aerosols and the concentration of gaseous chlorine in the atmosphere, it was considered that a considerable amount of the gaseous chlorine in the coastal atmosphere at Owase was released from sea-salt particles.
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  • Tadao Aoki
    1978 Volume 56 Issue 5 Pages 508-515
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Using the technique of the semi-direct random model recently developed by this author, the functional form of the average transmittance has been derived for the absorption band in which lines obey to the exponential-tailed S-1 intensity distribution. The accuracies of this model and the other semi-direct random models previously developed by this author have been examined by calculating the transmission functions of H2O rotation band and CO2 15μ band. It has been shown that the accuracies depend on the vaule of the interval, to which the average transmittances are calculated. The highest accuracy is chieved by the semi-direct quasi-rondom model with relatively small values of the interval. The semi-direct random models, especially for the exponential intensity distribution, can also give good accuracies in view of the present uncertainty in the theoretical values of the line intensities or line half-widths.
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  • Masayasu Hayashi, Osayuki Yokoyama, Yasuhiro Kobori
    1978 Volume 56 Issue 5 Pages 516-522
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    An acoustic sounding system with a Doppler analyser is developed. The Doppler shift of the return sound echo is measured by counting a time duration for a certain number of sound waves. The outputs of the system, echo intensity and the vertical velocity, are visualized by a computer controlled dot-printer which gives more minute information than the facsimile record. The output of the Doppler shift analyser is calibrated by the echo from a balloon descending or ascending near the sounder. The case study for thermal plumes shows a reasonable vertical velocity field.
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  • R. L. Pitter
    1978 Volume 56 Issue 5 Pages 523-526
    Published: 1978
    Released: October 19, 2007
    JOURNALS FREE ACCESS
    Numerical investigations of riming by thin ice plates were conductde, includnig the effects of coulombic forces on collision efficiency. A superposition method was used to determine the trajectories of the ice crystal and aerosol particle. The results indicate that electrostatic forces may be important in the evolution of cloud microstructure because they reduce the critical size to which an ice crystal must grow before it can begin to rime.
    In an environment of -10°C, 700mb, the smallest uncharged ice plate capable of riming lies between 147 and 160μm half-width. At -18°C, 400mb, the critical size of the ice plate is reduced to between 103 and 133μm for the uncharged case, and to less than 103μ when moderate attractive electric charges are present on the ice plate and water droplet.
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