In order to theoretically interpret the Eliassen-Palm diagnostics of wave-mean flow interactions, necessary and sufficient conditions are derived for the Eliassen-Palm flux divergence to approximate the zonal acceleration in the absence of mean damping. It is shown by a simple analytical model that a violation of these conditions due to the effect of the lower boundary condition may explain why some observational diagnostic studies indicate that transient eddies accelerate westerlies in the mid-latitude upper troposphere in the absence of mean damping, although the transient E-P flux divergence is easterly there. It is also suggested on the basis of simple diagnostic relations that the steady state upper tropospheric westerlies can be either enhanced or reduced by transient eddies depending on mean damping and radiative heating.
In order to theoretically interpret the Eliassen-Palm diagnostics of wave-mean flow interaction, necessary and sufficient conditions are derived for the Eliassen-Palm flux divergence to balance the steady state residual circulations induced by eddies in the presence of mean damping. It is shown by a simple analytical model that this balance holds for strato spheric planetary waves when the mean Rayleigh friction coefficient is one order smaller than the mean Newtonian cooling coefficient, although the tall mean flow condition (Andrews and McIntyre, 1976) is not violated. In this case, the Eliassen-Palm flux divergence can be interpreted as approximating the steady state residual circulations (_??_Lagrangian mean circulations) induced by eddies as well as the net mean acceleration in the absence of mean damping. This balance is consistent with the stratospheric circultions of a dynamical model (Holton and Wehrbein, 1980a, b) and the GFDL "SKHI" general circulation model (Andrews et al. 1983).
Using a two-scale method, the mean wind induced by a slowly varying internal gravity wave packet on the spherical earth is treated. An analysis shows that the induced mean winds have a net mean zonal momentum only in the latitudes where the wave packet exists. The net mean zonal momentum is transferred to the mean field in the presence of dissipation. Results of numerical calculations show that, if the selective transmission of internal gravity waves occurs, internal gravity wave packets play an important role in the momentum budget in the upper mesosphere as presented by Lindzen (1981) and Matsuno (1982).
A quasi-geostrophic, barotropic, low-order model with bottom topography is constructed to investigate the bifurcation properties of steady solutions and time-dependent solutions in a numerical model of geophysical fluid system. The low-order model with six dependent variables is a direct extension of that in the pioneering work by Charney and DeVore (1979). This is the most simplified system in which spectral components consist of two symmetry groups. Compared with the three-variables model in Charney and DeVore (1979) and some other studies, new bifurcation properties are obtained such as (1) bifurcation of steady solutions with symmetry breaking, (2) appearance of periodic solutions due to Hopf bifurcation, (3) symmetric saddle-node bifurcation, period doubling bifurcation and intermittent chaos. As for the multiplicity of stable solutions, there exist stable periodic solutions in addition to stable steady solutions for some given external parameters.
Detailed structure of the edge front associated with the cold surge discussed by Nakamura and Murakami (1983) and Murakami and Nakamura (1983) was investigated using a higher resolution model with 1°×1°horizontal grid interval and 16 vertical levels. (Here edge' is applied to the disturbances attached to the mountain boundary.) The increase of the resolution made the edge front more intensified. A strong cold front was formed at the northeast corner of the model elliptic shaped mountain. Temperature gradient became about 15°K/100km. The ageostrophic northerly wind with magnitude of 20-25m/s appeared across the cold front. This edge front was trapped along the mountain boundary and propagate clockwise with the speed of 20-25m/s. One day later it moved to the south of the mountain and then reached west of the mountain where it dissipated. This behavior indicates the feature of gravity waves, being similar to the coastal Kelvin waves. During the propagation, the wind and pressure fields behind the edge front hold well geostrophic balance. Cross isobaric wind is found only at the head of the edge front. Wind velocity behind the front was about 20m/s, while the propagating speed of the edge front was about 25m/s. Nonlinear advection was dominant in the propagation of the edge front. We also demonstrated the generation of the Kelvin waves by a shallow water equation model. It indicated that the generation of the Kelvin waves is one of major factors for the initiation of the edge front. However, there is a possibility that the shelf waves (topographic Rossby waves) may work in geostrophic adjustment during the propagating stage of the edge front and in determining its lateral scale.
Atmospheric response to the observed;sea surface temperature anomaly (SSTA) over the Pacific and Atlantic Oceans is studied with the use of the MRI (Meteorological Research Institute)⋅GCM for the period from May to June of 1983. El Nub event was still active during the period. The model is the tropospheric five layer grid model of which horizontal resolution is 5°in longitude and 4°in latitude. Two groups of run are performed, one with the observed SST in 1983 (abbreviated as "R"), and the other with the climatological SST (abbreviated as "N"). Each group consists of five runs among which the initial time varies from 00Z 1 May to 00Z 3 May with a half day interval. Atmospheric response to the SSTA is studied by comparing the results of and "N". The monthly mean differences between "R" and "N" are statistically significant and the basic feature of the response is similar to that of previous studies. The "Walker circula tion" is diminished in "R". The reduction of precipitation occurs over the Indian Ocean. Anomalous anti-cyclonic pair straddles the equator in the upper troposphere and subtropical jets are intensified. In middle-latitudes, larger responses are obtained in the southern hemisphere. In the northern hemisphere a PNA-like pattern appears, shifted eastward from the location in winter. Initial development of atmospheric anomalies is also studied. Westward traveling Rossby and eastward traveling Kelvin wave responses are dominated in the tropics. The Rossby wave train emanating from the eastern equatorial Pacific is clearly detected in the middlelatitudes.
Detailed observational study and numerical prediction experiment are made on the extremely strong dry wind event over the northeastern Japan in 27 April 1983, which causedbig forest fires of -9000ha. This extremely strong dry wind took place under the synoptic situation of strong pressure gradient between an extratropical cyclone over the Japan Sea and an anticyclone over the Pacific. The observational study reveals that the abrupt increase of SW-WSW wind with the decrease of relative humidity and temperature rise took place around noon over the lee-side of mountains. The distinct low-level inversion layer observed at 09LST 27 over Sendai (the Pacific coast of the northeastern Japan) was not observed at 21LST 27. The thick dry neutral layer observed at 21LST indicates that the inversion layer was destroyed by convective motions generated over the ground heated by insolation. At the peak period (15LST) of the strong wind, the wind speed at the surface reached to that at 900mb. These observed features suggest that the convective mixing of the momentum is one of the important factors to cause the strong surface wind in 27 April 1983. The prediction experiment of this strong wind event was made by using a 16-layer 64 km-mesh primitive equation model which includes parameterization schemes of various boundary layer physical processes. While a model including both diurnal variation of insolation and mountains (S-M model) simulates the strong dry wind event fairly accurately, a model including only the diurnal variation of insolation (S model) does not simulate. The analysis of the predicted result indicates that the orographically induced downward motion in the S-M model suppresses the formation of cloud against the thermally generated convection and maintains the strong radiative heating and concomitant convective mixing throughout the afternoon. This prediction experiment demonstrates that even the localized strong wind event can be predicted by the high resolution primitive equation model.
The upper tropospheric disturbances propagating westward with a period of about 4 days and a wavelength of 2000km-3000km are detected over the equatorial Arabian Sea by the stationary polygon ship observations during the period from 18 May to 30 May 1979. The disturbances are concentrated in the shallow layer between 300mb and 150mb with the strongest meridional wind fluctuations (-5ms-1 amplitude) and relative vorticities (-2×10-5s-1) near 200mb. Convergence occurs on and ahead of the cyclonic circulation center and divergence behind the center. Temperature anomalies due to the disturbances are quite small. Analyses of 200-mb wind fields using the ECMWF FGGE level III-b data show that these disturbances are present in the equatorial Arabian Sea region (50°E-80°E) during the limited short period (middle May-middle June). Wind maps for individual disturbances reveal that these disturbances are initiated by the deepening of the extended troughs from middle latitudes which are located temporarily over the central Arabian Sea during the premonsoon period. There is some indication that the upper tropospheric disturbances have links with the lower tropospheric disturbances.
With a premise that the patterns of the general circulation undergo continuous variations at various time scales, experiments with a multiple regression scheme are conducted in the long-range forecasting of temperature and precipitation using upper air parameters and sea surface temperature for the period 1963-1983. The scheme uses five predictors; it also effectively eliminates the problem of multi-collinearity. The scheme gives a lead time of predictors two to eleven months preceding predictands. The forecast scheme performs the complete regression analysis as an annual updating procedure for the teleconnection of the large-scale flow patterns. In forecast experiments, the data from the forecast year are excluded from the data base of the entire study period in the regression analysis. This also ensures that the forecast experiments are completely independent of the data of the forecast year. The experiments indicate that the predictands properly selected over various sizes of large areas of the United States, Canada and the USSR show considerable forecast skill.
Surface heat balance of the Western Pacific including the ocean mixed layer is analyzed for May 1979, when MONEX observations were practiced. Each flux elements at the sea surface is derived from the marine meteorological reports with application of an aerodynamical bulk method for the turbulent heat fluxes and empirical formulae for the radiation heat fluxes. The rate of heat storage in the ocean is estimated by using the surface heating rate and the depth of the ocean mixed layer. The flux divergence of oceanic heat transport is estimated as a residual. The features of the surface heat balance are almost decided by the latent heat flux and the solar radiation flux. In the ocean, heat flux diverges for the most part south of 30°N and converges north of that latitude, that is, the tropical region south of 30°N is source of the northward heat transport. The poleward heat flux across 30°N (120 to 180°E) in the ocean is estimated at 5.9×1014Wm-2. In the present study several errors in flux estimation caused by careless analysis are reduced. On average for May 1979 in the tropical region between 0°N and 20°N, if one defines the insolation at the top of the atmosphere as 100%, 52% is absorbed in the ocean; thereafter the ocean loses 10% by infrared radiation, 2% by sensible heat and 23% by latent heat. The residue is 17%, of which 7% is transported away by the oceanic motion and 10% raises the water temperature in the mixed layer.
The atmospheric budgets of heat and moisture are analysed for the Baiu season of the western part of Japan on July 5-12, 1970. The eastward and northward wind increase with height which in both cases the maximum value is found at about 250mb. Mixing ratio of the water vapor falls uniformly with height but relative humidity has a maximum value at about 900mb. The convergence exists in the lower layer and divergence in the upper layer. Largescale upward motion dominates in the whole layer and the maximum is found in the middle layer. Net heat source and moisture sink are found in the whole layer. The calculated precipitations from large-scale apparent moisture sink and the observed precipitations for the analysis period show a good agreement.
An application of the Arakawa-Schubert (1974) cumulus cloud parameterization model to the estimation of precipitation during the period of Baiu season is presented over the western part of Japan on July 5-12, 1970. The cloud sub-ensemble thermodynamic properties are determined from the conservation of mass, moist static energy and total water (vapor, suspended liquid water and precipitation). The cloud work function for each cloud type which is defined in the Arakawa-Schubert model is calculated from the observed data sets. Calculations of the large-scale forcing and the mass flux kernel in the discrete model are performed. The unknown cloud base mass flux is determined by the integral equation. Precipitations due to cumulus cloud in the parameterization model and large-scale condensation are calculated. Results show that the cloud work function is large in the middle layer and small in the lower layer. It is emphasized that the choice of a particular value for M"B(j')Δt' of mass flux kernel is important to treat the precipitation of cumulus in middle latitudes such as that in Baiu season. In this paper, the particular constant value of M"B(j')Δt'=85kg m-2 is chosen as a reasonable one. Amounts of precipitation of cumulus cloud are variable when the constant of mass flux kernel changes. It is also shown that period of July 5-12, 1970 can be divided into two periods, i. e., the period when the precipitation of large-scale condensation is predominant and the period when the precipitation of cumulus cloud is predominant.
Considering the growth of hydrometeors along with electrical state and interaction among all categories of particles in thunderclouds, the effect of screening charge transport on electric field, precipitation intensity, charge, size and fall velocity of hydrometeors, has been studied. The study reveals that screening charge transport increases the growth rates of electric fields and decreases the precipitation intensities. The calculations show that thunderclouds containing low precipitation intensities, can also generate high electric fields within appropriate time intervals.