The construction of zonally symmetric geostrophic eigensolutions to Laplace's tidal equations which have properties consistent with those of the nonzonal eigensolutions is discussed. We have derived a differential equation which defines geostrophic eigensolutions for zonal wave number zero in the limit as the zonal wave number tends to zero in Laplace's tidal equation for geopotential. These eigensolutions are similar to the counterparts for non-zero zonal wave number. In special cases of Lamb's parameter ε=0 and ε=∞, the properties of the associated eigensolutions closely correspond to those of Haurwitz waves and equatorial waves, respectively, for non-zero wave number. It is shown that the set of eigensolutions for positive ε (including ε=0) forms a complete set for zonally symmetric geopotential and the associated geostrophic wind.
The stationary planetary waves responding to forcing by topography and stationary heat sources in summer are investigated by means of a steady-state, linear, quasi-geostrophic, 34-level model, with Rayleigh friction, the effect of Newtonian cooling and the horizontal kinematic thermal diffusivity included in a spherical coordinate system. The results show that the main stationary planetary waves responding to forcing by both topography and heat sources in summer are confined to the troposphere over the subtropics. A secondary peak of the maximum amplitude is also found in the upper troposphere at high latitudes for zonal wave numbers κ=1 and κ=2. The amplitude of stationaryplanetary waves responding to forcing by heat sources is larger than that responding to forcing by topography. In this computation, the role of refractive index square of stationary planetary waves in summer is also discussed in order to make clear the differences of response of a model atmosphere to forcing in cases of winter and summer.
A Lagrangian-type description of transport mechanisms of tracers in the stratosphere and troposphere is presented on the basis of trajectory analysis of a large number of marked air parcels using a hemispheric GCM. It is demonstrated that the transport of the lower stratospheric air is due both to slow advective general circulation and to large-scale quasihorizontal eddy diffusion, while the transports within the troposphere are highly diffusive both in the horizontal and vertical directions. The present simulation shows that the tropospheric air parcels are well mixed within one month throughout the troposphere by quasihorizontal mixing due to cyclones and vertical mixing due to small-scale convection. It is also shown that the stratospheric air can be supplied mainly from the tropical tropopause. Only the bottom layer (below∼100mb) of the extratropical stratosphere may be intruded by tropospheric air parcels through the subtropical tropopause gap. However, such intrusion can hardly affect the levels above the bottom layer. In this paper, the age of the stratospheric air is analyzed; the age of an air parcel is defined as the length of time elapsed since it entered the stratosphere. The results show that the tropical stratosphere consists of 'new' air parcels, which is thought to retain properties of the tropospheric air, while the polar stratosphere involves relatively 'old' air parcels which have long-term residence in the stratosphere. This interpretation may be useful to understand major features of distributions of tracers originating either the surface or the stratosphere.
A 10-layer dry numerical model which includes convective adjustment, surface friction, and vertical momentum diffusion is used to identify the mechanical effects of a- mountain on transient eddies during winter. Thermal effect is simplified to the form of Newtonian cooling. Observed winter zonal mean temperature is prescribed as an equilibrium state. The mountain has a simple elliptic shape. The numerical integration was performed for 72 days, but a detailed analysis was done only for the 16-day period from day 21 to day 36. The 16-day mean fields show that the westerly jet tends to flow around, rather than over the mountain and splits into two branches in the lower troposphere. At 500 mb, winds are weakest over the mountain with a distinct splitting of the jet north and south of the mountain. Above 300 mb, the jet flows south of the mountain. These features agree well with those of the 1978-79 winter mean fields (Murakami, 1981a). At 850 mb, significant temperature perturbations originate at the northwest periphery of the mountain and extend clockwise around the mountain until reaching the southern part of the mountain. These low-level disturbances, which are trapped below 700 mb along the periphery of the mountain, are referred to as “edge” disturbances in this paper. These edge disturbances receive their eddy available potential energy via nonlinear interaction with 16- day mean temperature fields. Their eddy available potential energy is not converted into eddy kinetic energy; namely, the baroclinic conversion process contributes little to the development of edge disturbances. They acquire their kinetic energy through flux convergence of geopotential energy due to the nongeostrophic components of winds. At 500 mb, the kinetic energy of the disturbances is weakest, and baroclinic conversion is directed from eddy kinetic to the available potential energy, over the mountain. Here, the major contributing process in the generation of eddy kinetic energy is the horizontal flux convergence of eddy geopotential energy. The disturbances supply (extract) energy to (from) 16-day mean winds outside (over) the mountain. At 200 mb, a belt of large eddy kinetic energy lies south of the mountain, where the strong upper tropospheric jet stream prevails. The barotropic conversion process feeds energy to the 16-day mean westerly flows there. Again, the major generation factor for eddy kinetic energy is the flux convergence of eddy geopotential energy, while other terms, such as, baroclinic conversion are negligible.
A numerical experiment using a 10-layer hemispheric dry model produced prominent low-level cold surges and subsequent lee-cyclogenesis on the east and southeast sides of a hypothetical facsimile of the Tibetan Plateau. These phenomena were preceded by a sequence of events that occurred along the western, northern, and eastern periphery of the prescribed mountain. (1) When a major anticyclone approaches the western end of the mountain, cold air advected from the north accumulates in the lower troposphere due to the barrier effect of the east-west elongated mountain. (2) The cold air pool is then advected rapidly eastward along the northern periphery of the mountain by the prevailing low-level westerly jet. Associated with this cold air pool is the development of a small-scale edge anticyclone trapped below 700 mb near the northeastern side of the mountain. (3) The clockwise (southward) movement of the edge anticyclone is substantially reduced east of the mountain. However, it is still faster than the movement of the edge cyclone which has already passed the eastern periphery, and became nearly stagnant at the southeast corner of the mountain. The phase speed difference between the edge anticyclone to the north and the edge cyclone to the south, results in a sudden increase in the pressure gradient with prominent subgeostrophic northerlies east of the mountain. These subgeostrophic northerlies are responsible for the strong advection of cold air from the north. Here, the advected cold air pool takes a form similar to a gravity-type shock (cold) front. (4) The edge cyclone begins to shift eastward by the prevailing southwesterlies near the southeast corner of the mountain. The subsequent phase is the amalgamation of the edge cyclone with a major trough which has travelled north of the mountain along about 50°N. Also occurring during this merging phase is the eastward extension of cold front from the southeastern corner of the mountain to as far downstream as eastern China. The merged lee-cyclone intensifies into a major mid-latitude system due to the active baroclinic conversion process occurring around the extended cold front. To the rear of this intensified lee-cyclone are widespread northerly cold surges, which penetrate southward to the South China Sea.
In order to investigate the mechanism for the amplification of planetary waves, various analyses (structure of waves, energetics, relationships with the zonal mean flow and so on) are made for large-amplitude waves of wavenumbers 1 through 3 based on geopotential height and temperature data for 10 winter seasons. The results are as follows: The wave disturbances of wavenumber 3 amplify after baroclinic waves develop in longitudes where the nonlinear term due to the baroclinic waves has in phase relation with the zonal wind component of wavenumber 3 in the mean zonal wind with weak lateral shear in 50°-55°N (the latitude band where the large-amplitude wave of wavenumber 3 is formed). It is also found that the wave disturbances of wavenumber 3 again amplify after baroclinic waves of wavenumber 6 grow at the decay stage of wavenumber 3. Thus, the large-amplitude wave of wavenumber 3 appears several times in one winter. The development of wavenumber 2 occurs in many cases when a westward-moving barotropic mode with a long period approaches a stationary mode. For such a situation, the northward wind component of wavenumber 2 becomes in-phase with the temperature wave of wavenumber 2. Hence the zonal available potential energy is converted into the eddy available potential energy of wavenumber 2. The mechanism for the amplification of wavenumber 1 seems to be similar to that of wavenumber 3 from view of energetics, but possibilities of other mechanisms are also suggested. Discussions are also made for comparison between our observational results and theoretical studies.
Spatial and temporal variations of the heat source over the eastern Tibetan Plateau are analyzed based on the FGGE Level II-b upper-air observation data during the Summer MONEX in 1979. The budget results of mass, heat and moisture obtained over the four divided subareas show that the upward mass circulation, large-scale apparent heat source and moisture sink predominate in the eastern Plateau as a whole, but there exist considerable spatial and temporal variations. Over the Plateau region higher than 3000m surface elevation, the maximum heating of about 4°C d-1 exists around 400mb and both the effects by the heat supply from the elevated surface and the latent heat release contribute nearly equally to the net total heating. It is suggested from the moisture budget analysis that the water vapor lost by the condensation over the Plateau is generally balanced by the surface evaporation and that the effect of moisture convergence by large-scale motions is rather small. On the contrary, the low-level southwesterly monsoon flow brings a lot of water vapor and heavy precipitation occurs over the southern part of the Plateau including the Assam region. Large amounts of the condensation heating are liberated in the whole troposphere with the maximum near 400mb. Small amounts of heating and relatively large amounts of heating are observed over the northern and eastern slopes of the Plateau, respectively. It is found that there exist large diurnal variations of the upward motion and the heat source over the eastern Tibetan Plateau except in its northern part. Larger upward motion and heat source are found at 1200GMT (-1800LT) than at 0000GMT (-0600LT). Amplitudes of the diurnal variations are 1mb h-1-2mb h-1 for the vertical p-velocity and 1°C d-1-2°C d-1 for the heat source, respectively. These diurnal variations over the Plateau might be generated by the intense convective activity enhanced by the solar heating absorbed on the elevated Plateau surface during the daytime. Total heating, precipitation and relative vorticity in the upper troposphere averaged over the eastern Plateau have long-period fluctuations with the periods of 10-15 days and -30 days. Large heating corresponds to large amounts of precipitation and strong upperlevel anticyclonic circulation. Time variations of the heat source and precipitation over the eastern Plateau show general out of phase relationships with the precipitation over the central India. The long-period fluctuations of the heat source over the Tibetan Plateau appear to be a part of the oscillation of the whole summer monsoon activity.
The largeand meso-scale features of a subtropical rainband which caused thunderstorms over western Japan (-33N/130E) in 25-7 July 1981 are studied. This case aroused our interest because the convective activities persisted for about three days in the west side of a slowmoving ridge. Radar observations showed a persistent convective echo band of -800km length extending in NNW-SSE direction. This echo band was not accompanied with front-like strong thermal gradient. Satellite IR imageries showed that the rainband was a part of a long subtropical cloud zone formed along the northern periphery of the extremely moist tropical maritime airmass in the lower troposphere. The enhancement of cloud zone and the formation of the rainband was owing to the incessant feeding of moisture accompanied with the northward intrusion of the moist tropical maritime air along the western hem of the slow- moving ridge. Real data forecast experiments on the cloud zone and rainband were made using a coarseand a fine-mesh primitive equation model. While only the large-scale zone of weak precipitation relevant to the observed cloud zone was produced in the coarse-mesh (380kmmesh) model, the narrow rainband with low-level convergence was simulated in the finemesh (77km-mesh) model. The "dry experiment" (a experiment without condensation) did not produce any low-level convergence zone. This indicated influence of condensation process on the formation of this subtropical rainband.
A relationship between cumulus convective activity and large-scale meteorological parameters was studied by aerial cloud observations during AMTEX '74 and AMTEX '75. The cloud volume per 1km2 was adopted as a measure of cumulus convective activity and large-scale meteorological parameters were represented by the mean values over the analyzed area enclosed by four aerological stations. It was found that some strong cumulus convective activity of more than 2km3 in the cloud volume per 1km2 was associated with some large upward motion and water-vapor flux convergence. On the other hand, when the cumulus convective activity was as weak as less than 1km3 in the cloud volume per 1km2, meteorological parameters showed even suppressed conditions such as downward motion and divergence of water-vapor flux. Systematic relations were not found in this analysis between the cloud volume per 1km2 and both relative humidity and v-component of winds.
A numerical simulation study on the evolution of raindrops in a maritime warm cumulus is presented by taking interaction of dynamical and micropohysical processes into consideration. The model is two-dimensional with axisymmetric feature of deep moist convection. Microphysical processes considered in the model are condensation of water vapour on condensation nuclei, diffusional growth of droplets, stochastic coalescence, evaporation, sedimentation, and drop breakup. In Part I, the effect of the way of treatment of water drops on the aspect of precipitation as well as on the overall behavior of a model precipitating convective cloud with detailed microphysical processes is investigated. Characteristic features of the parameterized microphysics model used Berry's and Kessler's parameterizations are also examined with emphasis on the comparison with the detailed microphysics model. The result shows that the way of treatment of water drops has a significant effect on the evolutional process of raindrops as well as on the dynamical aspect of the cloud. A smaller number of size-groups of water drops considerably distorts physically meaningful features of various aspects of clouds, leading to an exceedingly earlier onset of rainfall and a spuriously high rainfall efficiency through the life time. This is due to a numerical spreading of the droplet spectrum. The parameterized microphysics model in combination with the Marshall-Palmer distribution for raindrop sizes also fairly distorts the result and gives an exceedingly high rainfall efficiency as welll as a spuriously earlier onset of precipitation. The effect is caused by overestimation of mean terminal velocities of raindrops, particularly in the developing stage of the cloud. The present results are compared with those by other researchers.
The electric charge of precipitation particles was measured both at the ground and in the clouds at Ponape, Micronesia. Results were analysed as a function of drop size, surface potential gradient and cloud top height in order to identify the charge separation processes. It was found that the electric structure of a cloud differs greatly with cloud top height, suggesting that charge separation processes in the cloud are primarily determined by microphysical processes. Different charging processes have been proposed to explain the differences between warm and cool cloud electrification. Thunderstorm electrification was explained as an extension of the cool cloud electrification mechanism.
Concentrations of metallic elements, including Fe, Mn, Cu and Zn in the air over the western North Pacific were determined in the periods from April to May, 1980 and March, 1981. Sampling of airborne particles was done on board by use of a high volume air sampler. During the southward traverse, at the west side of a cold front, the high concentration of iron reaching as high as 2550ng m-3 was observed in the air over the ocean and then it decreased rapidly to the background level. The GMS imageries and meteorological conditions suggest that the high concentrations of iron and manganese in the air over the ocean during the spring season are caused by the transport of the continental dust (load up to 64μg m-3) originating from the east Asian deserts.
The technique for high quality measurements of the atmospheric CO2 concentration has been developed by improving many facets of the commercial nondispersive infrared CO2 analyzers. The precision of better than ±0.05ppm was attained for both continuous and flask-sample analyses. The standard gases of CO2-in-air mixture have been prepared by the gravimetric method using an extremely precise balance; the absolute accuracy of the CO2 concentrations were estimated to be better than ±0.3ppm. The problems of great importance in the flask sampling technique, i.e., possible deterioration risk of air samples stored in the flasks and effect of water vapor condensed in the sample flask on measured values of the CO2 concentration, have been examined.
The effect of the passage of solar sector boundaries (SSB) on the variation of zonal mean fields below the 100mb level is investigated for the period from November 1963 to March 1978. From a key-date analysis it is found that the polar temperature in the troposphere reaches a minimum on the passage date of SSBs during winter in the period from December 1964 to February 1972. At the 500mb level of the North Pole, the filtered temperature on the passage date deviates -2.59K from the mean. Such a large deviation as -2.59K was not obtained in the random sampling of key dates. This response appears in each of 8 winters from 1965 to 1972 and each of 3 months in winter.