Some properties of planetary Rossby waves and zonal flow acceleration by them on a β-plane are investigated analytically by using the two-scale method. The zonal flow (u) is assumed to be westerly channel flow and is allowed to have both lateral and (small) vertical shear. We also assume u=0 at two zonal walls. It is shown that the lateral structure of planetary waves has the following properties: The lateral scale of planetary waves is larger than that of the mean zonal flow. When the zonal flow is weak, the maximum of the wave amplitude appears at a latitude different from that of the maximum zonal wind and, as the zonal wind speed increases, the lateral profile of the wave amplitude becomes close to that of the mean flow. In general, the phase lags in latitudes where the zonal flow is fast in a positive vertical shear flow and it leads there in a dissipative medium. In an asymmetric (with respect to the center of the flow channel) flow, the phase maximum of dissipative waves shifts toward the jet side for a weak zonal flow and toward the opposite side of the jet for a strong mean flow. It is also found that, the stronger is the mean zonal flow, the smaller is the phase inclination with latitude. The zonal flow acceleration by dissipative waves in a symmetric jet flow has the following nature: When the zonal flow is intense and the jet is sharp, the easterly acceleration is largest near the jet latitude. Except in such cases, the easterly acceleration is largest near boundaries. In an asymmetric jet flow, the jet shifts toward a lateral boundary for a weak zonal flow and toward the center for a strong zonal flow. Thus, planetary waves and the associated zonal flow acceleration show the distinct differences in their properties depending on the magnitude of the zonal wind speed. Moreover, the inclination of the latitudinal phase of planetary waves and the lateral profile of the zonal flow acceleration are sensitive to the ratio of the radiative damping rate to the mechanical one.
Non-linear interaction between mean zonal flow and a baroclinic wave is investigated numerically by using a two-layer quasi-geostrophic β-channel model with inclusion of friction and diabatic heating. In a series of experiments, meridional gradient of the heating is varied to elucidate the seasonal variation of the characteristics of non-linear baroclinic waves. Results obtained by these experiments are summarized as follows: (1) As a result of non-linear interaction, there exists an energy variation with a period of 2-3 weeks as well as 3-4 days. (2) For small meridional gradient of the diabatic heating, energy variation of 2-3 week period is maintained by the fluctuation of horizontal eddy momentum flux. Namely, the dominant energy process of this frequency range is the barotropic conversion. (3) The baroclinic energy transfer becomes prominent with increasing the meridional gradient of the heating. The energy cycle is mainly accompanied by the fluctuation of eddy heat flux. It is suggested that the zonal flow-braoclinic wave interaction is one possible mechanism to explain the quasi-periodic variation in the real atmosphere with time scales of two to three weeks, which is known as the "index cycle" or "tropospheric vacillation" (Webster and Keller, 1975; McGuirk and Reiter, 1976).
The generation of the mean zonal winds in the lower thermosphere is discussed, on the basis of momentum transport by dissipating solar diurnal tidal waves. The most important factor to control the amplitude of tidal waves and the magnitude of the induced mean winds in the lower thermosphere is the dissipative effect due to small scale motions in the mesosphere and the lower thermosphere which is parameterized in the form of eddy diffusion or the form of Rayleigh friction. In both cases of parameterizations, the behavior of the tidal wave agrees well with observations. The induced mean zonal winds in case of eddy diffusion-type parameterization are found to be three times larger than those of the case of Rayleigh friction-type parameterization. The weaker zonal flow is interpreted to result from the removal of net momentum. As the observed mean zonal winds distribution is not definitive, we cannot decide which parameterization is suitable for the present problem. However, the present results confirm that the dissipating solar diurnal tidal wave contributes greatly to the configulation of the mean zonal winds in the lower thermosphere.
The winter mean circulation over and around the North American continent, including the Rocky Mountains, was investigated by using twice-daily wind, temperature and geopotential height data at eight standard pressure levels for the period of 1 December 1978 through 28 February 1979. Surface pressures, temperatures, and winds were estimated over a 2.5° latitude by 2.5° longitude resolution smoothed topography, as determined by Berkofsky and Bertoni (1955). Winter mean surface winds near the California coast tend to split into two major streams which flow around the high American Rocky Mountains. However, a significant part of these low-level winds also flow over the highest mountains and surrounding lower topographies. Boundary layer frictional effects, which result in significantly reduced wind speeds, extend upward through the 700mb level over a limited area of the highest American Rockies. At 300mb, a strong jet stream south of the American Rockies at approximately 28°N is characterized by pronounced eastward acceleration, which is primarily associated with winter mean, nongeostrophic southerly winds. Conversely, momentum flux convergence due to transient disturbances is the major factor in maintaining a less pronounced 300mb polar jet stream near the Alaskan coast, which is associated with northerly winds and slight eastward acceleration. A pronounced thermally direct (indirect) vertical circulation occurs south (north) of 30°N along the west coast of the U.S. Topographic enhancement of the descending branch of the direct Hadley cell is evident over the southeastern corner of the American Rockies (35°N, 105°W). Off the east coast of the U.S. at around 60°W, indirect (direct) vertical circulations are found to the north (south) of the jet stream axis (38°N), but are only weakly defined as compared to the vigorous overturnings along the U.S. west coast. At 700mb, winter mean temperatures are colder over the American Rockies than over the surrounding areas to the east and west. From the surface through 500mb, significant northward sensible heat fluxes due to transient eddies are observed over the following three regions: (1) from the Gulf of Alaska to northern Alaska; (2) from the warm northeast Pacific, over the American Rockies, into the central northern U.S. and Canada; and (3) from the Gulf of Mexico into the northeastern U.S.
Through the analysis of the geopotential and wind fluctuation during the summer monsoon season over and around India, the predominant periodicity of about 40 days was confirmed especially in the lower and upper troposphere as a major active-break cycle of the monsoon activity. As well as the cloudiness fluctuation of the same period (Yasunari, 1979; Yasunari, 1980), these elements except the geopotential height in the upper level showed a marked northward propagation from the equator toward the Himalayan region. The geopotential height at 200 mb showed, in contrast, a standing oscillation over India. Cross-spectral analyses revealed that the vertical structure of the atmosphere is gradually modified during the northward phase shift of the anomaly cloudiness with the 40-day period. This modification is most apparent in the temperature field. The modification of the vertical structure from the south to the north over India seems to be attributed to the gradual enhancement of cumulus convection from the south to the north. It is also suggested that this cycle is caused by the periodical cold air outbreak over the middle and upper troposphere of the equatorial zone which may be associated with the index cycle of the westerly wave movements in the Southern Hemisphere. Finally, a multicell structure of the anomaly Hadley circulation regime over India through the Indian Ocean was proposed, which gives reasonable interpretations on various aspects of the active-break cycle of monsoon activity with this mode.
The height and temperature fields at the mandatory levels during a two-month period(December 1977-January 1978) are used to evaluate the conversion between available potentialenergy (A) and kinetic energy (K), C(A, K). The results reveal: 1. The energy conversion due to the mean meridional circulation, C(Az, Kz)=-0.18Wm-2, and due to the eddy motions, C(AE, KE)=2.6Wm-2. 2. C(Az, KZ) is attributed to the standing (2-month mean) mode, while C(AE, KE) is due tothe transient eddies. 3. The contributions to C(AE, KE) from various wave number regimes, long waves (n=1-4), and cyclone and short waves (n=5-15), are: a. Transient cyclone and short waves are dominant in the mid-latitudes and the middlelayer of atmosphere. b. Transient long waves are significant in the middle layer of the atmosphere at mid-and high latitudes. c. Standing long waves are not negligible in the mid-latitudes and the middle layer ofatmosphere.
A new mathematical model of the two-dimensional atmospheric boundary layer over undulating terrain is presented. Neither the hydrostatic assumption nor the Bousinesque as sumption need to be introduced in this model. The system of equation is described with orthogonal curvilinear coordinates, and one of the axes (ξ) coincides with the undulating ground surface. Then, the system of equations are expanded in the Fourier series of ξ and the time, following the spectral method. In this way, the equations can be reduced to a system of second order simultaneous ordinary differential equations. The advantages of the model are as follows: (1) easy application to an arbitrarily un dulating ground surface, (2) the possibility of a precise discussion about a phenomenon with an appreciable vertical acceleration like a sea breeze front and (3) the elimination of com putational instability in the solutions by wave number truncation. An example of the calcu lated result for land and sea breeze circulation with our model suggests that the model could be used in a study of the other orographic environment.
Stably stratified airflows over a hill or mountain are studied by a wind tunnel and also by a theoretical model with special forcus on the upstream stagnant zone. The wind tunnel experiment shows that a stagnant zone is formed upstream of an obstacle when the Froude number is less than some critical value. The critical Froude number is found to vary with the obstacle height. In the stagnant zone, the airflow is negligible or reverse and the thickness of the zone decreases gradually with the distance from the obstacle.
A heavy rainfall from very shallow convective clouds is studied. We pay attention to the causes of large condensation rate and of high precipitation efficiency which seem to be necessary for the occurrence of heavy rain from very shallow clouds. Synoptic features are as follows: 1) A weak tropical depression was nearly stationary over the sea to the southwest of the heavy rain areas. 2) Warm and moist air was observed below inversion layers in the eastern part of the depression. 3) Stratification in the lower troposphere was latently unstable. Distributions of rainfall amount seem to be strongly afected by mountain ranges. A narrow and straight echo band which might be composed of crowded cumuli repeatedly appeared over the area on the windward side of a mountain range. Precipitation efficiency for a heavy rain area was very high, if we assume from the results of analyses that the airflow below 900mb was blocked by the mountain range and ascended penetratively up to 650mb. Crowded maritime cumuli and very moist air observed around the heavy rain area might be favorable for the high precipitation efficiency.
In order to find the cause of positive electric-fields measured in blowing-snow and negative fields measured in blowing-dust, a new apparatus was constructed, and some experimental analyses were carried out. From the analyses, we found an interesting regularity which controls the sign of electriccharge on particles and simultaneously generated ions: the sign of small particles suspended in the space of the apparatus and predominantly generated ions agree with that of chargecarrier of particle materials. This regularity may be supposed as one of effective integrated mechanism of many kinds of strong electric-field generation such as thunder-cloud, the volcanic eruption, the sand-storm and many other explosion phenomena which have occurred at every kind of plants using powder particles.
Selenium content and its chemical form in rain water and aerosol in Tokyo was studied during the period from June 1975 through the end of 1977. Analysis of selenium was carried out by fluorometric method. The content of total selenium in rain water ranged from 5ng 1-1 to 118ng 1-1 with an average value of 69ng 1-1. Most of selenium in rain water was in tetravalent state which occupied 0.5 to 0.9 in the total. And the rest of selenium in rain water was present in particulate forms. On the other hand, the content of selenium in aerosol in Tokyo ranged from 1.7ng m-3 to 4.2ng m-3 with an average of 3.0ng m-3. It was found that the chemical form in a water soluble part of selenium in aerosol is tetravalent ion, and its ratio to total is 0.5 to 0.6.
Solar spectra in the wavelength region 427-451nm were observed by a spectrophotometer on board a balloon flown at Sanriku Balloon Center (39.2°N, 141.8°E) from noon to sunset on May 29, 1978. The NO2 slant column density along the solar ray path was calculated by a statistical analysis to find the very weak absorption structure of NO2 in the solar spectra, referring to that obtained at a solar zenith angle of 35° and at a balloon altitude of 24km. A vertical distribution of NO2 in the 14-35km altitude region was obtained from the apparent variation of the slant column density with solar zenith angle. The NO2 profile obtained in this study is close to those obtained with the visible absorption method in Canada. The peak density was around 5×109 molecules•cm-3 at 22-25km, and the vertical column density, 7×1015 molecules•cm-2.
An electron-probe X-ray microanalysis of the reaction rings of atmospheric particles on the thin film of barium chloride was carried out to detect the distribution of sulfur and barium. The purpose of the experiment was to establish the validity of the vapor-deposited thin film method of barium chloride for the detection of soluble sulfate in individual atmospheric particles. The results indicate that the reaction rings on the thin film of barium chloride are composed of barium sulfate and hence validate the value of the method for atmospheric samples.