It is shown that a model characterised by the quasi-geostrophic momentum and thermodynamic equations incorporating the full effects of the earth's sphericity is governed by an extended form of the potential vorticity equation for a single unknown, the geopotential. That equation contains several additional terms that represent the vortex stretching due to the horizontal divergence of the quasigeostrophic flow and the advection of planetary vorticity by the nongeostrophic component of the flow. They are shown to have significant quantitative impacts in the context of two simple nontrivial dynamical problems. First, the analytical and numerical investigations of the fundamental modes of oscillation verify that both the frequency and structure of the normal modes in this system closely approximate those of the corresponding Hough modes. The counterpart frequency obtained with the additional approximations as in a traditional quasi-geostrophic model overestimates by about 25 %. The relative error is larger for the longer waves. Second, the difference between Matsuno's eq. for planetary wave propagation and the linearised form of the governing eq. derived in this study is identified. The wave propagation governed by the two equations is structurally quite similar and Matsuno's eq. yields a somewhat stronger response under the same parameter condition. The sample calculations reveal that the forced wave field governed by the corresponding conventional Q-G eq. is structurally more distorted than that obtained with Matsuno's equation, although the maximum amplitude is closer to that obtained with the equation derived in this study. The corresponding conventional Q-G equation has an intrinsic deficiency in that the wave propagation has a spurious dependence upon the constant of integration in the expression for the basic geopotential field associated with a given geostrophic basic flow.
Successive measurements of atmospheric ozone up to an altitude of 3km through 24 hours have been made using a differential absorption lidar (DIAL). The wavelengths 277nm and 313nm were chosen for the DIAL taking into account the solar-blind effect due to to the stratospheric ozone. The performances of the compact ozone lidar developed are evaluated in the actual lidar observations, and it is demonstrated that the lower tropospheric ozone can be measured in daytime without deterioration in the SN ratio if the solar-blind effect is considered. The errors in the ozone concentration due to aerosols, NO2 and 502 are discussed and the data are corrected for the aerosols. It is expected that the altitude range can be extended from the ground to 10km, making upward and downward observations from an airplane at altitudes of 3km and 6km. In three sets of successive measurements, the lidar was used to observe the ozone around the boundary between the free atmosphere and the Ekman layer. In the absence of a surface inversion layer, the nighttime ozone density in the mixed layer decreased considerably.
Interactions between breaking internal gravity waves with phase speeds of 0, ±10, ±20, ±30ms-1, and the diurnal tide in the mesosphere and lower thermosphere (70-120km) are investigated using a time dependent numerical model of the tide. The gravity wave breaking and stress are calculated using a modified Lindzen's parameterization making allowance for interactions with a diurnally varying zonal wind superimposed on a zonal mean wind field. In order to avoid difficulties with the WKB approximation used in the parameterization, the interactions are only considered in the extratropics. However, the gravity wave stress is shown to suppress the amplitude of the diurnal tide at all latitudes in the upper mesosphere and lower thermosphere. It is also shown that gravity wave stresses modified by the diurnal tide induce significant semidiurnal and terdiurnal tides in the mesosphere and thermosphere.
Probable precipitation is estimated from a complete-duration data set of the AMeDAS data, which has a dense station coverage over Japan, instead of annual maximum precipitation data sets used in previous studies. Thus, we can obtain probable precipitation with a relatively small estimation error due to the large size of the data set. The probable precipitation is estimated by applying the gamma distribution to the AMeDAS data. The results are summarized as follows: 1) The geographical distribution of probable daily precipitation is closely related to topography, and that of probable hourly precipitation shows large latitudinal difference. In Kyushu, the high-ranked stations in probable hourly precipitation are distributed in the western part, and those in probable daily precipitation are found along the backbone range. Also, in eastern Shikoku, the probable hourly precipitation and probable daily precipitation are greater in coastal regions and mountainous regions, respectively. These differences indicate that the duration and intensity of heavy rain differ with geographical factors, such as topographical conditions and latitude, its cause having peculiar regional characteristics. 2) The relationship between probable precipitation R(t) and time t can be expressed by the equation R(t)=ctn. A station with a large value of n has long duration of heavy rains. The value of n at each station changes slightly with the length of a return period, and the regional difference in the value becomes increasingly large with an increase in the length.
As an extension of the 'aqua planet' experiments by Hayashi and Sumi (1986, HS86), GCM experiments with various SST distributions and cumulus parameterizations are performed in order to examine the structure of cumulus activity and its parameter dependence. In part I, the results of the analyses concentrating on the super clusters are described. The super clusters, which were named by HS86, are expressed in the model as continuously moving precipitating areas of the grid scale. The associated circulation structure can be explained in terms of the wave-CISK dynamics of Kelvin waves. The super clusters become more active when a warmer SST is used. On the other hand, the 30 day oscillation, that is an eastward-moving planetary scale structure, is more distinct when a colder SST is used. The behavior of cumulus activity is highly sensitive to the choice of cumulus parameterization. When the moist convective adjustment scheme is used instead of Kuo's (1974) scheme, the eastward-moving structure of the grid scale is no longer observed at the equator. However, the planetary scale structure still clearly appears in the experiment with the moist convective adjustment scheme.
The results of 'aqua planet' GCM experiments are analyzed, concentrating on the planetary scale structure and the structure of precipitating areas around the ITCZ region. The 30 day oscillations, that is, eastward-moving structures on the planetary scale, appear in a similar way regardless of the cumulus parameterization utilized. These structures are considered to be maintained by the dependence of evaporation on wind speed, i, e., the evaporation-wind feedback mechanism. For the maintenance of the disturbances on the synoptic scale, this mechanism is considered to be less effective and other mechanisms such as wave-CISK are more important. It is suggested that the coexistence of two different maintenance mechanism of disturbances is relevant to the existence of hierarchical structure of cumulus activity in the model. At the double ITCZ latitudes in the experiments with Kuo's cumulus parameterization, there are areas of high cumulus activity on the grid scale, which are moving eastward continuously. In the experiment with moist convective adjustment, on the other hand, westward-moving areas of high cumulus activity associated with vorticity, which correspond well to the easterly wave disturbances in the real tropics, are observed. It is revealed that a process which can be called 'evaporation-wind feedback for the zonal mean field' exists and contributes to the separation of the ITCZ into double bands in the experiments with Kuo's parameterization.
A model for nonlinear resonant Rossby waves is utilized to obtain analytical solutions. "Identical twin" approach is adopted, in which one specific solution is chosen as the control which serves as pseudo-observation. Then initial condition is varied and thus specified various solutions are compared with the control. The cost function is computed and plot vs. the initial condition. Multiple minima are revealed in the cost function. In the context of variational adjustment approach to four-dimensional data assimilation, which is usually conducted with some minimization scheme based on the gradient information, this multiple-minimum phenomenon in cost function implies nonuniqueness, i. e., the final convergent solution depends upon the first guess for the initial condition. Such nonuniqueness problem becomes more serious due to the increasing complexity of the cost function as the assimilation period gets longer. The relation to nonlinear energy exchange is discussed.
A peculiar downward water vapor flux was observed over the Gobi desert in the daytime on the fine days of test observations of HEIFE in 1988 and 1991. However, further analysis of the characteristics of the turbulence structure over the Gobi desert has revealed that they are in good agreement with surface layer similarity theory and also with other observations in the past.