The generalized Lagrangian-mean (GLM) description formulated by Andrews and McIntyre is extended to the general coordinate system. Four-dimensional Lagrangian coordinates are introduced to obtain a general relationship between the Lagrangian coordinate mean (LCM) and the GLM. It is shown that the choice of an initial hypersurface in space-time is essential in the determination of the relationship. The Eulerian mean and the GLM tensors are defined referring to a given coordinate system, so that mean quantities are dependent on the choice of the coordinate system. Symmetries in the Lagrangian density for fluids and related conservation laws are discussed for energy-momentum, pseudoenergy-pseudomomentum and wave-action. The extended GLM description provides a wider applicability in practice, owing to the less stringent assumptions for the initial conditions.
Infrasonic waves generated by the explosions of the volcano Sakurajima are observed frequently at Kariya, located about 700km to the east-north-east of the volcano (Tahira, 1982). The waves recorded at Kariya usually have the form of wave trains lasting for a minute or so. However, in the summer season when long-distance sound propagation toward the east is possible only through the thermospheric duct, signals made up of a few peaks and dips of very low frequencies (about 0.08Hz) are sometimes recorded. Such low frequency signals recorded in the summer months of 1984 and 1985 are examined in detail in this paper. As a result, it has been shown that many of such signals are classified by their waveform into three types, and that in all such signals the period is 5-6 times that of the explosion shocks (2.5sec) observed 5km from the crater. Geometric ray tracing has been performed with an atmospheric model for the summer season including the contribution of the solar atmospheric tidal components. Comparing the travel times computed from the ray analysis with the observed ones, it has been shown that the separation into different types of waveform is due to the number of times the ray has been reflected from thermospheric height. The majority of the recorded signals are inferred to have propagated to Kariya along the ray paths reflected twice in the thermosphere. These results suggest that the stretching of the waves is caused by nonlinear effects at thermospheric heights and that the π/2 phase shift at the caustics at or near the turning point plays an important role in determining the waveform of the infrasonic signals at long distances.
Waveform deformation of volcanic infrasonic waves propagating long distances through thermospheric ducts is discussed. Ray tracing using a realistic atmospheric model including the vertical variation of temperature and mean wind has been performed. Burgers' equation, modified to include the effects of spreading of the sound wave, density stratification, and mean wind, is solved numerically along the computed ray paths to obtain the waveform deformation of the infrasonic waves propagating through the thermospheric duct. The effect of the caustic at or near the turning point is also taken into account. This procedure has been applied to the infrasonic waves generated by the explosions of the volcano Sakurajima, and the waveforms expected to be observed at Kariya, 710km from the volcano have been computed. As a result, the characteristics of the waveform, amplitudes and frequencies computed for the rays reflected twice at the thermospheric level are in good agreement with the characteristics of the waves frequently observed at Kariya in summer season classified as type I in Tahira (1988). Those computed for the rays reflected three times explain well the observed nature of the waves of type III.
The main purpose of this paper is to study numerically how the low level water vapor supply modifies the circulation of conditional symmetric baroclinic instability (CSBI), and how the convective clouds are induced and controlled by CSBI circulation. The numerical model is basically the same as that used in Part I by the same authors, whereas the water vapor is supplied from the surface. Three cases of numerical experiment are considered: no water vapor supply, a small water vapor supply, and a large water vapor supply. Developments of clouds, rainfall and stratification are the main features inspected in the three cases. When the water vapor supply is moderate, a slantwise cloud is also developed due to the CSBI circulation, as in the case of no water vapor supply. However, nodal convective cells appear embedded in the slantwise cloud. A number of narrow, strong precipitation areas are embedded in the weak and wide-spread precipitation area and are associated with these nodal cells. Convective cells above the slantwise cloud (generating cells) are also developed in the mid-troposphere. When the water vapor supply increases, strong convective clouds rapidly grow at the convergence zone of CSBI circulation and at the slantwise convective unstable layer. The horizontal extension of the rainfall area becomes narrow but the rainfall intensity is greatly enhanced. One of the most important features of the CSBI circulation in rainband formation is to induce the slantwise convective unstable layer, which is appreciably enhanced as the rate of water vapor supply increases. At the same time, an increase of water vapor supply tends to activate cumulus clouds through the combined effect of low level convective unstable layer due to water vapor supply and flow convergence due to CSBI circulation.
This paper describes the results obtained from numerical experiments of winter land and sea breezes on the Sagami Plain in Japan. Three kinds of experiments were conducted in order to investigate the relations between the local circulation and topography. The no-mountain model results showed that a bay or a peninsula near a straight coast line has little effect on the local circulation. However, the topography model showed that mountains play an important role in these local circulations. The numerical simulations of winter breezes in the Sagami Plain seems reasonable when compared with observations, although there remained some differences between the observed and simulated wind regimes.
The influence of a change in soil characteristics due to a deforestation of the tropical rain forest on climate is studied by the use of an atmospheric general circulation model (MRI⋅GCM-I). Four experiments are run for four months, beginning on May 1 00Z and time averages for June through August are analyzed. The control run (C) has a spatially uniform soil moisture capacity and a seasonally varying surface albedo compiled by Matthews. The second is a soil moisture experiment (W) where the soil moisture capacity is reduced between 0° and 12°N over Africa (the anomaly region). The third is an albedo experiment (A) where the surface albedo is increased to 0.30 corresponding to a desert condition instead of the realistic one in the anomaly region. The final experiment (AW) changes both the soil moisture capacity and the surface albedo in the anomaly region. The experiments show that the changes in soil moisture and surface albedo have very different effects on the local climate. In W, the decrease of evapotranspiration does not always result in a decrease of precipitation since there is an accompanying increase in the horizontal moisture flux convergence. This is accomplished by an increased surface temperature, greater diabatic heating in the lower troposphere by the increased sensible heat flux resulting in an increased convergence in the moisture flux. In A, the decrease of precipitation is greater than that of evapotranspiration, so the updraft is much suppressed and the net moisture flux divergence occurs. Since the surface heat energy nearly balances between the reduced absorption of solar radiation due to the increased surface albedo and the resulting reduced evapotranspiration, the decrease of surface air temperature is slight. Local responses obtained by AW are almost equal to the sum of those obtained in W and A. The local Hadley circulation is weakened in AW. Heating anomalies over the anomaly region are negative in the upper and middle troposphere due to the reduced precipitation, and positive in the lower troposphere due to the increase in the sensible heat flux. The reverse is the case in the Sahel region where precipitation increased. The differences in the zonal wind over West Africa between AW and C resemble those observed during the wet and dry periods in the Sahel region. The east-west circulation in AW, consisting of the lower tropospheric westerlies (African monsoon flow) and updrafts, is strengthened by the increased heating associated with a greater sensible heat flux convergence. Clear changes occur in the east-west circulation between the African continent and the Indian Ocean, suggesting a westward displacement of the Indian monsoon precipitation maximum. The zonally symmetric circulation anomalies are also found. Anticyclonic circulations in the upper troposphere subtropics of both hemispheres are strengthened in AW. Superposed on these circulations are three well-defined quasi-stationary wave trains which are accompanied by precipitation and temperature anomalies.
Climatological large-scale features of the cloud distribution and their seasonal variation are investigated using cloudiness data derived from GMS-IR cloud images for the area between 90°E-170°W and 50°S-50°N. The large-scale distribution of clouds with tops determined to be above the 700mb level and the seasonal change in this distribution are described quantitatively for the three years from June 1983 to June 1986 except June 1984. The distribution and seasonal variation in cloud-top-height and cloud type (tall convective clouds and stratiform clouds) are investigated by computing a ratio between the amount of high-cloudiness (tops higher than 400mb level) and the amount of high- and middle-cloudiness (tops higher than 700mb level) and by examining the standard deviation of cloud-top-height in 1°×1° areas covered with cloud. Results of this study show that the maximum cloudiness (-4/10) is observed in the tropics except east of 150°E with a secondary maximum (3/10-4/10) in the mid-latitudes along the cyclone tracks, and the minimum cloudiness (1/10-2/10) is observed around the subtropical highs. The annual mean cloud-top-height is higher in the tropics than in the mid-latitudes. In the mid-latitudes, a significant difference in cloud-top-height between cyclone tracks is observed in both hemispheres; the mean cloud-top-height along the lowest-latitude cyclone tracks is much higher than along the other cyclone tracks. Large annual variations in cloudiness (2/10-4/10) are observed in tropical monsoon areas. In addition, cloud-top-height decreases significantly during the winter over continents and their vicinity (within about 1000km) for the tropical monsoon areas, which suggests deep convection is strongly suppressed there and active deep convection, which may be enhanced with a cold surge, is restricted to the regions away from the continents during the winter. The decrease of cloud-top-height during the winter is also observed for the region from the southern part of China to Japan, which corresponds to a subtropical monsoon area. Over the southern part of China and the East China Sea, this large seasonal variation of cloud-top-height is accompanied by a significant seasonal change in cloud type; tall convective clouds in the warm season to stratiform middle-clouds in the cold season. In addition to-the tropical and subtropical monsoon areas, tall convective clouds also increase over the Asian Continent even in the higher-latitude to 50°N during the summer and high-cloudiness increases to ti 2/10. This is significantly different from the fact that high-cloudiness over the Australian Continent is small (-0.5/10) throughout the year except for the tropical monsoon area.
Spatial and temporal variations of the sea surface temperature (SST) over the Indian Ocean are examined by using empirical orthogonal function (EOF) analysis. The first EOF mode explains 20.54% of the total variance indicating positive values which reveal coherent interannual variations over the study area. Time coefficients of the first EOF mode show a strong relationship with the Pacific SST anomalies. Therefore, the El Nino/Southern Oscillation (ENSO) events are observed in the time coefficients of the first EOF mode almost simultaneously. Power spectrum analysis reveals a dominant peak ranging from 18 to 48 months which covers the quasi-biennial oscillation (QBO) and the dominant cycle in the Southern Oscillation phenomenon (30 to 40 months). The second and third EOF modes explain relatively less contributions, 5.6% and 5.1% of the total variance. A weak positive correlation coefficient is observed between the time coefficients of the first EOF mode of SST anomalies and the time coefficients of the first EOF mode of the rainfall over Sri Lanka when all months are considered, but strong relationships are noticed for the months of October, November and December which coincide with the mature and decay stages of ENSO events. The positive relationships between SST anomalies of the Pacific and Indian Oceans and rainfall anomalies of the above mentioned months first appear in March and April, and then gradually build up towards the significant level in the concurrent months. In the case of the summer monsoon season, Arabian Sea SSTs, where strong seasonal and regional variations are found, strongly influence the rainfall of Sri Lanka, particularly striking in the southwestern quadrant of the island. Rainfall of this season has a significant positive correlation with the SST over the Arabian Sea during the concurrent period, but significant negative correlation with the previous months, before six months. The changes in the sign of the correlation coefficients occur in the months of November-December of the year before the summer monsoon, thus it may be useful to foreshadow the excess and deficit rainfall over Sri Lanka few months in advance.
The observational study by using station data has been conducted to investigate the edge disturbances around the Tibetan Plateau which are found in numerical simulations. Two types of effects of the mountain are found; one is the effect on synoptic disturbances, which corresponds to the main cold surge events, and the other is the excitation of the edge disturbances whose horizontal scale is consistent with the radius of deformation. This corresponds to the disturbance simulated in the numerical model. It is also found that the edge disturbance is not always excited. A relationship between the intensity of a trough ahead of the Tibetan Plateau and the excitation of edge disturbances is suggested by this study. The existence of two different types of influence by the Tibetan Plateau is consistent with the different paths of cold air outbreak over Mainland China.
Generally speaking, it is well known that the annual mean rainfall and the times of heavy rainfall in Hokkaido Island, Japan are smaller than those of Honshu Island, Japan. In the Orofure mountain range in Iburi sub-prefecture in Hokkaido, however, they have a relatively large annual mean rainl'all and several periods of heavy rainfall per year. Further, based on the previous researches by Konno and Kikuchi (1981), the distribution pattern of the rainfall of the southeastern slope of Orofure mountain range was classified into five patterns; that is to say, Orographic rainfalls, Seaside rainfalls, Plain-centered rainfalls, Northwest slope rainfalls and other type rainfalls, according to the locations where the maximum peak of rainfall was located. To investigate these patterns further we set up our special mesoscale raingauge stations mainly in the southeastern slope of the mountain range and carried out the observations from June through to October, 1980 and 1981, respectively. In the case of orographic rainfall, the maximum peaks of rainfall were very frequently located on the Orofure Pass (930m a.s.l.) and the Shiraoi Waterfall (380m a.s.l.). The fact that the maximum rainfall amount was on the Shiraoi Waterfall in spite of the relatively low altitude was studied from the viewpoint of topography of the southeastern slope of Orofure mountainous regions. As a result, it was considered that when the warm and wet air from the southeast over the Pacific Ocean flowed toward the mountain range, comparatively weak rainfall occurred on the seaside and plain regions owing to the gentle slope, and the heavy rainfall occurred on the mountainous regions owing to the steep slope. Thus, it was expected that the horizontal convergence would increase the rainfall amount on the mountainous regions because the valley became narrower from the seaside to the mountain side. Numerical experiments were carried out to simulate the above prediction. The results of the calculated rainfall taking into account only the forced updraft owing to the mountain slope were smaller than the observed rain in the regions where horizontal convergence appeared to be present.
The structure of the upper part of mixed layer and the exchange mechanism between mixed layer and upper stable layer are investigated using the humidity (Q) and potential temperature (θ) data observed on an airplane. It was found that Q was nearly constant with height in the mixed layer and decreased sharply at some upper height. This height is coincident in almost all the cases with the mixed layer height determined from the vertical profile of θ. During the developing process of the mixed layer, the humid air-mass is brought to the upper layer by thermal convections, and these convections penetrate into the upper stable layer as humid and cold plumes. At the top of the mixed layer, a wave-like surface is formed due to the influence of the wave-motion in the upper stable layer and intake-flows are induced in the vicinity of the upper boundary of the mixed layer. The dry and warm air in the upper layer is taken into the mixed layer by these intake-flows. During the decay of the thermal convections, the thickness of the mixed layer decreases with time due to these descending flows. The boundary surface between the mixed and upper stable layers has periodic undulations and their wavelength is about 2000-3000m and the amplitude is 100-200m.
To study the nature and formation process of atmospheric nitrate particles, aerosol particles collected in summer at Nagoya were investigated with an analytical electron microscope. The individual nitrate-containing particles were identified with a vapor deposited nitron thin film method. Then, the elemental and chemical compositions of individual nitrate-containing particles were determined with an electron probe X-ray microanalysis (EPMA) and other reagent thin film methods. The results indicated that while N03-rarely existed in the fine particles, it existed in the coarse particles at all of the sampling times. Nitrate did not exist as a pure nitrate salt, but was internally mixed with sulfate in the fine particles. In the coarse particles, it was found that, in addition to sea-salt particles, soil particles (or flyash) were also important carriers of nitrate in the urban atmosphere. It is indicated that the neutralized sulfate particles can serve as an active center for the nitrate formation in the fine particle under humid conditions.
Based on accurate solutions of the transfer of solar radiation for realistic models of the turbid atmosphere, the photometric and colorimetric properties of the solar aureole were studied for various conditions of atmospheric turbidity. The radiation flux density in the vicinity of the sun becomes more predominant for turbid conditions especially at shorter visible wavelengths. In spite of this general feature, the percentage error of the Angstrom's turbidity parameter due to the aureole flux density involved in the sunphotometry becomes more serious for clear conditions than for turbid conditions. This is because even a small aureole flux density added to the direct solar radiation diminishes the aerosol optical thickness significantly for clear conditions. The colorimetric property of the solar aureole varies noticeably place by place for the atmosphere containing larger particles, although the most reddish (the lowest color temperature) point does not change its position of about 1.6° from the sun for different turbidity conditions. Comparing with non-absorbing aerosols, absorbing aerosols make the aureole region more bluish for clear conditions, and more reddish for turbid conditions.