The stability of non-divergent horizontal shear flows in a homogeneous rotating fluid is investigated by means of a weakly non-linear theory. Velocity profiles of the shear flows considered in this paper are given by U(y)=tanh y and U(y)=sech2 y, where y is the coordinate in the cross-stream direction. The effect of variation of the Coriolis parameter _??_(beta effect) and that of the Ekman friction at the bottom surfaces are included. The coefficients of the generalized Landau equation, which describes temporal and spatial modulation of the amplitude of periodic waves, are calculated for various values of β=df/dy. It is found that the barotropic instability of the shear flows belongs to so-called supercritical type for all values of β used in this study. Therefore, we can expect a steady-state configuration betweenn a finite-amplitude wave and the distorted flow for a supercritical Reynolds number. The stability of the finite-amplitude steady wave with respect to so-called side-band modes is also examined. It is found that, for a given supercritical Reynolds number, the finiteamplitude wave is stable if the wavenumber k0 satisfies the inequality S(κ1-κc)<κ0-κc<S(κ2-κc), where κ1 and κ2(κ1<κ2) are the wavenumbers of the neutral waves for the Reynolds number, kc is the wavenumber of the neutral wave at the critical Reynolds number and S is a constant. For U(y)=tanh y, S is 1/√3 when β=0. S becomes small as the absolute value of β is increased. Thus, the wavenumber range in which the finite-amplitude wave is stable decreases with increasing β. For U(y)=sech2 y, S is equal to zero when the absolute value of β is small (in terms of non-dimensional beta, β=-1.9-0.5), so that the finite-amplitude wave is unstable. When β is outside of this range, S becomes large as the absolute value of β is increased. The value of S, however, is always smaller than 1√3.
The stability analysis of a finite-amplitude wave solution of the generalized Landau equation due to Stuart and DiPrima (1978) is extended. For a given supercritical stability parameter, a finite-amplitude wave of wavenumber ko is stable if ko satisfies -S(k1-kc)<k0-kc<S(k2-kc), where k1 and k2 are the wavenumbers of the neutral waves, kc the wavenumber of the neutral wave at the marginally stable state. It is shown that S is a function of only two real quantities, the amplitude dispersion factor d and the wavenumber dispersion factor l, which, in turn, are functions of the coefficients of the generalized Landau equation. The functional form of S(d, l) is completely determined, so that the value of S is calculated for all possible values of the coefficients of the generalized Landau equation.
Viscous dissipation and Newtonian cooling suppress the breaking of internal gravity waves particularly in the vicinity of the critical levels. Stabilization criteria for suppressing wave breakdown are obtained incorporating the effects of viscous dissipation and Newtonian cooling separately when the basic Richardson number is large. The stabilization criterion associated with viscous dissipation derived here is more consistent than that obtained by Fritts and Geller (1976). Newtonian cooling, which is less important for the short horizontal wavelength, predominates over viscosity as the horizontal wavelength increases. Both effects become comparable when the horizontal wavelength is about 250 km in the stratosphere and is much longer in the mesosphere. Characteristics of internal gravity waves at 20km altitude such as wave amplitude and momentum flux are estimated on the basis of the thickness of the turbulence layer observed in the lower stratosphere.
The splitting analysis method can be used to study the relation of the low-level jet (LLJ) and heavy rainfall. The vertical circulation in the entrance and exit region associated with the jet results from the adjustment process in response to the imbalance caused by advection along the jet. Under the conditionally unstable and nearly saturated atmosphere, if the equivalent horizontal scale R<L0, where L0 is the characteristic scale of the adjustment process, then the adjustment process can lead to an instability of the gravity-inertia wave, whose mechanism is the positive feedback between the nonthermal wind and the vertical circulation. The coupling of upper tropospheric jet and LLJ and its relation to heavy rains have been discussed. The triggering effect of LLJ and the fact that the ageostropheric wind often occurs in LLJ over the heavy rain area and some other synoptic analysis results have also been explained. The available potential energy for the unstable gravity inertia wave is generated by the condensation heating in the relatively warm area, which can increase the horizontal temperature gradient and make the gravity-inertia wave developing in the adjustment process. Its energy source is quite different from that of a several local storm which results from the energy of the static stability.
A two-dimensional model for ozone changes by the planetary wave in the stratosphere is formulated. It is found that the temperature wave may reduce the zonal mean value for the photochemical loss rate of ozone through the temperature effect. This reduction in the photochemical loss owes substantially to the strong negative correlation between the ozone concentration and temperature, and results in an enhancement of the zonal mean ozone concentration. Such an effect has not been presented in the previous models. This effect is evaluated to find that a 50% enhancement of the zonal mean ozone concentration can be produced by the temperature wave of 15°K amplitude when the zonal mean temperature is 240°K.
Eliassen-Palm (E-P) flux whose direction is interpreted as that of planetary wave propagation in the meridional plane, is used for diagnosing planetary waves for the 1973 sudden stratospheric warming. E-P flux by zonal wavenumber 1 component was focused into the polar stratosphere prior to the circulation reversal. By the focusing there occurred the intense convergence of E-P flux which embodies the forcing of waves on mean flow. The convergence brought about the intense deceleration of mean zonal wind and the poleward residual mean meridional flow in the stratosphere. A discussion is made of the "refractive index" Q defined as mean quasi-geostrophic potential vorticity gradient divided by mean zonal wind. It is the maximum of Q which was situated in the polar stratosphere prior to the warming that is interpreted as a main factor which determines the switching of E-P flux from equatorward to poleward. After the easterly winds appeared in the polar stratosphere the convergence of E-P flux concentrated around the zero wind line, suggesting that the mechanism of critical layer absorption was driven.
In Kanto area, Japan, the towering cumuli and cumulonimbi are often observed in a clear day of summer over Boso and Izu peninsulas, while over Miura peninsula such cumuli are never observed. In this study it was tried to investigate numerically the effects of peninsular width and thermal condition on the sea-breeze over a peninsula, using a two-dimensional model in the vertical plane. Some interesting results are summarized as follows: (1) The strong ascending flow appears at the center of a peninsula in the evening, and is weakened rapidly corresponding with the increase of the peninsular width. (2) There is the peninsular width of about 30-50 km where the most preferable vertical velocity is observed, and the velocity reaches three times greater than that for the so-called sea-breeze. This width is equivalent to those of Boso and Izu peninsulas. (3) In the case of the large width crossing over 150km, the strong vertical motion such as stated in (1) disappears excepting that for the sea-breeze circulation which develops in daytime.
Characteristic features of mountain and valley winds are investigated by two-dimensional numerical model. It is found that the mountain and valley winds on the series of plain, slope and plateau with scale of 50-100km consist of two systems. One is a circulation caused by differential heating between the air above the plain and that on the plateau, and the other is a slope wind. In the daytime, the dominant flow is a plain-to-plateau flow. Its front penetrates about 100km into the plateau. The intensity of the flow is well correlated to the temperature difference between the air above the plain and that on the plateau. If the horizontal scale of a slope is smaller than, or equal to that of the plain and of the plateau, the up-slope wind modifies the plain-to-plateau flow in two ways: A slight increase of the maximum wind velocity in the case of high plateau, and a slower penetration of the flow onto the plateau in the case of low plateau. In the night time, the down-slope wind is strong and confined to the thin layer on the slope. The cooling over the plateau results in a weaker plateau-to-plain flow. The intensity of this flow is also related to the temperature difference between the air above they plain and that on the plateau. The intensity of the down-slope wind is well explained by the linear theory by Prandtl (1942) (see Sutton (1953)).
Observations on three dimensional distribution of air temperature were carried out at the Moshri Basin, Hokkaido in midwinter. It was found that the cooling of air on the slope of the basin started a few hours earlier than on the bottom in the small land basin. Analyzing the observational result by the use of potential temperature of air, it was considered that a down-slope wind occurred directly toward the bottom only for several hours, and after this cooling stage the wind was replaced by small eddy currents along the slope except the foot of the basin. A cold air lake of about 40m depth was formed at the bottom mainly by the cooling of surface air due to the heat exchange with the extremely cooled surface of snow cover. The extremely low temperature of surface air in the basin was attributed to the lack of the down-valley wind which would play a role in prevention of extreme cooling of air near the surface.
Turbulence measurements of wind and temperature were made by sonic anemometerthermometers in the first thirty meters of the atmosphere. Turbulent statistics obtained by direct measurements were analyzed, using the Monin-Obukhov similarity theory. The behaviors of the terms in the turbulent energy budget were examined, together with the relation of turbulent statistics to the measured parameters such as mean wind speed, stability and height. A model of the turbulent energy budget was derived from the results. Under near neutral conditions, mechanical production and viscous dissipation are dominant and essentially in balance, while turbulent transport and buoyant production are not important. In unstable conditions, each term in the budget is important. Buoyant production is a gain and turbulent transport is a loss. In stable conditions, all terms except turbulent transport are significant. Mechanical production and the imbalance are the sources of turbulent energy and the others energy sinks. For both stable and unstable conditions, the imbalance increases with the magnitude of stability.
In order to detect the fluctuations of the global circulation patterns and their relation to the Asian summer monsoon, an empirical orthogonal function (EOF) analysis was applied to the July monthly mean smoothed surface pressure data for 106 years (1871-1976) covering most of the globe. The 1st component (31% of the total variance) shows a contrasting spatial pattern between the Southern Hemisphere through the equatorial zone and the Northern Hemisphere mid-latitudes. This mode may represent the major re-distribution of the global-scale pressure patterns from the "Little Ice Age" to the recent warmer period. The 2nd component (19% of the total variance) reflects a pressure seesaw between the subtropical oceans and the Afro-Eurasian continents, which seems to be largely responsible for the strength of the Asian monsoon. These two dominant modes seem to correspond well with the long-term global-scale SST change. The 3rd component (14% of the total variance) represents a north-south (or east-west) shift of the main centers of action, and is also closely connected with the monsoon circulation. The EOF analysis of the original year-to-year data has revealed that the mode of the Southern Oscillation is also dominant as a fluctuation with periods less than 10 years, which is well correlated with the shorterperiod fluctuations of the monsoon.
Surface meteorological and satellite observations during the winter MONEX observational period over the Indonesian Maritime Continent have been analyzed. The results of the analysis show the existence of large scale disturbances in the pressure field. These disturbances, which affect the entire region, have periods of approximately 20 days and amplitudes of about 1 to 2 millibars. They appear to have no appreciable movement. There is no significant correlation between the pressure disturbances and the cloudiness distribution.
The possibility of estimating liquid water amount in the atmosphere from satellite microwave data was studied numerically by making use of a cloud model in which the size distribution of water drops and other factors were varied, and integrated liquid water amount in an extended cloud over the AMTEX area was estimated by using Nimbus-5 microwave data at 19.35 GHz (ESMR). Numerical calculations show that integrated liquid water amount can be estimated from satellite microwave data with the error less than 10% even in consideration of the effect of different size distribution of water drops on estimated value, if it is less than 0.30 g/cm2. In the atmosphere over the AMTEX area integrated liquid water amount was smaller than 0.12 g/cm2 during the period of cold-air outbreak from the Asian Continent (Feb. 25 to 27 in 1974). It was smaller than 0.03 g/cm2 in the system composed of only low-level clouds and it was between 0.05 and 0.12 g/cm2 in the two-layers cloud system composed of low-level clouds and middle-level clouds. The rate of conversion of cloud water into rainwater in an extended cloud was discussed on the basis of integrated liquid water amount derived from satellite microwave data and rainfall intensity measured on the ground.
Through the analysis of calibration data of Multi Spectral Scanner onboard Landsat, the followings characteristics in the responsivity of the detectors are found. (1) Both long and short term variations are found. (2) Silicon photodiode detectors for the spectral band of Band 7 (0.8-1.1μm) are more stable than photomultiplier tubes used for Bands 4, 5 and 6 (0.5-0.6, 0.6-0.7 and 0.7-0.8μm).(3)The hysterisis is found in photomultiplier tube with a larger gain just after the observation of bright scene. (4) It seems a positive correlation exists between ambient temperature and photomultiplier tube detector output.
In the model of spherical atmosphere in some planets the intensity of tertiary scattering becomes very predominant, then we must further execute the calculation to a great height of order.The author has devised a new method of evaluation of the phase function of higher order's scattering which is different from the method in the case of tertiary. This can be easily converted to the computer program.
Two typical examples of the mirror image relation between the electric field and precipitation charge in winter thunderclouds were analyzed, by making an approximation of the vertical distributions of electric field, precipitation charge density and non-precipitation charge density with sinus curves. As a result it was theoretically found that a good mirror image relation is obtained immediately after the gravitational charge separation (downward shift of precipitation charge from non-precipitation charge) but the electric field resulting from the separation is very small, and that as the separation proceeds the relation becomes deformed and finally reaches a positive relation, although the magnitude of electric field itself increases.
To find out a direct evidence of the long range transport of volatile and non-volatile elements derived from Mt. St. Helens' eruption on May 18, 1980, the concentrations of Zn, Sb, Se, Fe, Cl, Cu and 210Pb were determined in the surface air at Tsukuba. A pronounced peak of Zn, Sb, Se and Cl concentration was observed on June 4, 1980. Especially in case of Zn concentration, it increased as high as 7.1μgm-3 which was 50times higher than usual. The ratios of Zn/Se and Zn/Sb in airborne particles at Tsukuba were in good agreement with those in volcanic plume of Mt. St. Helens in June, 1980 over the United States. The period of the higher concentration of Zn in the surface air coincided with that of the increment of the stratospheric aerosol particles observed by Lidar system. Then it is concluded that these abrupt increase of Zn, Sb, Se and Cl in the surface air observed at Tsukuba in Japan may be due to the effect of the fallout derived from the volcanic debris from Mt. St. Helens which circled the world.