Abstract:Problems of instability of rotating atmospheric motions are investigated by using nonlinear governing equations and the variational principle. The method suggested in this palter is universal for obtaining criteria of instability in all models with all possible basic flows. For example, the model can be barotropic or baroelinic,layer or continuous, quasi-geostrophic or primitive equations, the basic flow can be zonal or nonzonal, steady or unsteady. Although the basic flows possess a great deal of variety,they all are the stationary points in the functional space determined by an appropriate invariant functional. The basic flow is an unsteady one if the conservation of angular momentum is included in the associated functional. The second variation, linear or nonlinear, gives the criteria of instability. Especially, the general criteria of instability for unsteady basic flow, orographically disturbed flow as well as nongeostrophic flow are first obtained by the method described in this paper. It is also shown that the difference between the criteria of instability obtained by the linear theory and our variational principle clearly indicates the importance of using nonlinear governing equations. In the appendix the theory is extended to cases such as in a 13-plane where the fluid does not possess finite total energy,hence the variational principle can not be directly applied. However, a generalized Liapounoff norm can still be obtained on the basis of variational consideration.

Abstract:Through analytical solution to microwave scattering by an ellipsoid, a quantitative relationship is established of radar reflectivity and extinction coefficient to size spectrum, precipitation rate and incideat wavelength with the aid of computed curves. The results are compared with those based on the spherical scattering theory.

Abstract:In this paper, by using the method provided in modern physics, the time series data of ENSO evidence are expanded in phase space. The data include: (1) SSTA at 2.5°S, 120°W in the equatorial East pacific during the 1958—1972 period and (2) SOI during the 1949—1983 period. The correlation of the attractors is calculated and the dimension determined, being d_E=3.1 and d_s=3.2 respectively, so that the ENSO events possess strange attractors. As a result, they should be described by at least employing 4 order ordinary differential equations for holding the strange sttractor.

Abstract:Three typical large-scale autumn rainfall fields are obtained by use of empirical orthogonal expansion and causes of the large-scale autumn rainfall anomaly are analyzed. It is pointed out that there is a close relation between the anomalies of the autumn large-scale precipitation in China and the Southern Oscillation/El niño. The Southern Oscillation is used as the predictor and the autumn rainfall data from 1951 through 1984 are reconstructed by the statistical methodResults show that the average absolute error is only 0.70 of the mean square error. Trial forecasting made for 1985 and 1988 is quite satisfactory.

Abstract:Based on the simulations of the topographic parameters (mean orientation, slope and terrain screen angle) in a hilly area, discussion is made term by term of the way of modelling for the components in the surface radiation balance over a rugged terrain, presenting a computer model for each component. In terms of the experimental data, calculation is performed of the components for each of the mesh grids of 100×100m over 3.0×3.5km² in the hilly area of Zhaogongling, southern Dabieshan Mountains and a map is prepared showing the distribution of the components for January and July. Results indicate that the hilly-land surface radiation field well matches the terrain element field, which reveals the decisive function of the latter, with orientation dominant in winter and terrain screen most significant in summer. The simulation technique presented in this paper is in principle applicable to the calculation for the radiation field in any topography, thus providing a means for further exploration of the hilly-land climatic resources.

Abstract:Dry-wet spells and weather cycle probability models are presented for the daily rainfall series at five representative stations in eastern China based on Markov chain theory. Some valuable statistical parameters, such as the mean length and variance of the dry-wet spell, the mean length and variance of the dry-wet cycle and the limit distribution probability of the dry-wet day evolution, are calculated. The results reflect the characteristics of the monsoon climate in eastern China and provide the climatic basis not only for agricultural production and water resource utilization but also for daily weather forecasting.

Abstract:In this paper a brief discussion is carried out on the quantity order of turbulent energy flux divergence within and above vegetation, and a universal model of mixing length in the surface layer based on the turbulent energy budget equation is developed (see Eq.22), that is, Karman’s model (1)is extended to the stratified atmosphere having turbulent energy flux divergence and dissipation. Thus, the model is more suitable to the study of the surface-layer turbulence structure than ziiitinkevich-Laikhtman’s model (3). This study is expected to make some contribution to the current canopy turbulence measurement and research.

Abstract:The influence of alfalfa canopy spectral reflectance caused by wind are analyzed in detail, the spectral reflectance averaging 1.5Hz. Obser. tion indicates that generally the spectral reflectance is much smaller under windy conditions than under calm conditions. Deviations of the reflectance vary with wavelengths. Probabilities of relative deviations greater than 3% are. 80% in TMA and TMB bands, 100% in TMC band and 60% in TMD band. The effects of wind on spectral reflectance of flexible canopy are so complicated that the errors caused by wind cannot be eliminated by using simple methods for determining the mean or medium values. Some vegetation indexes, such as brightness, greenness, redness and yellowness, are sensitive to wind and are not suitable when used under windy conditions. So the standard deviation vegetation indexes are recommended for windy areas.

Abstract:Mainly using the observational data and the 1.5×1.5 latitude-longitude grid data obtained by Gaussian weighted interpolation, this paper analyzes the monsoon stream tube during the seven occurrences of extensive torrential rainfall over the Jiang-Huai Area in June-July of the years from 1983 to 1986. Based on the analysis, the planetary scale and mesoscale systems in the monsoon stream tube are separated by the smooth filtering method and calculation is made of the vortieity, divergence and vertical velocity fields and their evolution.Results show that the monsoon stream tube is an east-west continuous monsoon vertical circulation system. The filtering method contributes to farther understanding the features of multi-scale systems and their interactions. It is pointed out that the mesoscale system in the monsoon stream tube is very active and has a direct influence on the tube itself as well as the location and intensity of the corresponding heavy rain and rain belt. This study helps to reveal the mechanisms of the monsoon heavy rain and rain belt and is expected to improve the weather forecasting.

Abstract:Based on the compilation and analysis of the 1954—1983 total Meiyu rainfall and relevant data from some 500 stations in eight provinces and one municipality over the basin, the demarcation and coverage of the Meiyu climates are presented. A preliminary analysis is done of the annual variations in rainfall in the Meiyu-climate regions and climatic oscillations. From the annual samples a scheme is proposed of three categories and six types of the characteristic rainfall distribution along with their respective climatic departure charts, revealing clearly the features of the rainless and rainy Meiyu periods as well as the rainbelt distribution. The main difference among the types is displayed by use of the corresponding mean circulation and isentropic charts for the season. The scheme delineates objectively the climatic distribution of the Meiyu rainfall over the basin for the last 30 years, providing a useful climatic background for weather prediction and a reference for the colleague researchers in their work.

Abstract:In this study, Walsh coefficients of the precipitation fields are used as predictands and mixed Chebyshev-Fourier polynomial coefficients of the height fields as predictors based on Reference. The precipitation fields can thus predicted by Walsh inverse transform upon the prediction of the Walsh coefficients by stepwise regression. The result is found to be quite desirable.

Abstract:Usiug the tetroon data at the 300-meter height in the Dachang district of Nanjing, calculations and preliminary analyses are made of the turbulence intensity, autocorrelation coefficient, integration sclae and spectrum. Some structural characteristics of the turbulence field in the boundary layer are described, which will contribute to a better understanding of the mechanism of the turbulence activities.

Abstract:The interface circuit presented in this paper is designed for the real-time echo processing system in Model-713 radar. The circuit is composed waveform and amplitude trans forming circuit of triggering pulse and antenna 0° of azimuth-elevation,amplitude amplification of echo video signals from the receiver and translating circuit at the base level,through which suitable signals are supplied for the successor circuits.