Advanced Search

1994 Vol. 11, No. 4

Display Method:
Simplified Dynamic Models of Grass Field Ecosystem
Zeng Qingcun, Zeng Xiaodong, Lu Peisheng
1994, 11(4): 385-390. doi: 10.1007/BF02658157
Some simplified dynamic models of grass field ecosystem are developed and investigated. The maximum simpli-fied one consists of two variables, living grass biomass and soil wetness. The analyses of such models show that there exists only desert regime without grasses if the precipitation p is less than a critical value pc; the grass biomass continuously depends on p if the interaction between grass biomass and the soil wetness is weak, but the strong interaction results in the bifurcation of grass biomass in the vicinity of pc; the grass biomass is rich as p > pc, but it becomes desertification as p < pc. Periodic solutions also exist in the model, if the seasonal cycle of model’s parameters is introduced. An improved model consists of three variables, i.e. the living grass biomass x, the nonliving grass biomass accumulated on the ground surface y and the soil wetness z. The behaviours of such three variables model are more complicated. The initial values of y and z play a very important role.
Study of Effects of Beta Term and Nonlinear Advection on the Structure of Tropical Cyclones
Luo Zhexian
1994, 11(4): 391-398. doi: 10.1007/BF02658158
The effects of the Beta term on the typhoon structure are examined within the linear framework in terms of an analytical method of 2-D Fourier representation and numerical experiments by a Beta-plane quasi-geostrophic barotropic model. Results show that the joint effects of the difference of Rossby phase velocities and the dispersion of typhoon energy keep the maximum wind velocity reasonably evolving rather than irrestrictively increasing. On the one hand, the nonlinear advection accelerates typhoon vortex damping, and on the other, the high pressure system formed downstream due to energy dispersion makes it easy to maintain.
Numerical Modellings of Properties of the Summer Quasi-Stationary Circulation Systems and Their Monthly Variations
Qian Yongfu, Qian Yun, Wang Qianqian
1994, 11(4): 399-407. doi: 10.1007/BF02658159
An ocean-atmosphere and land-air coupled numerical model system is used to study the basic properties and the monthly time variations of the summer quasi-stationary circulation systems. It is found that either at the upper or at the lower levels of the atmosphere, the circulation patterns have a two-wave structure in the zonal direction at the mid and high latitudes of the Northern Hemisphere. Such a structure of circulation is totally matchable to that of the land-sea distribution there. It is proved, hence, that the land-sea distributive pattern is the fundamental cause for the summer quasi-stationary circulation pattern. The topography in the globe is the secondary factor for circulation sys-tems. The circulation centres of the quasi-stationary systems are always located in certain areas due to the thermodynamic contrast between land and sea.From the time evolutions of the circulation systems it is seen that the change is larger at the beginning period of the time integration, it is because of using the zonally averaged mean fields as the initial values of the model. As long as the basic simulated pattern of circulations reaches the state similar to that of the real climatic fields resulting from the coefficients of the land-sea distribution and the topography, the circulation systems modelled will change slowly and tend to a quasi-stationary state. Therefore, the time integration does not need to last for a very long time, if the pur-pose of numerical modellings is to test sensitivities of some factors influencing the climate. 20 model days may be enough for sensitive experiments.
The Theoretical Model of Atmospheric Turbulence Spectrum in Surface Layer
Liu Shida, Liu Shikuo, Xin Guojun, Liang Fuming
1994, 11(4): 408-414. doi: 10.1007/BF02658160
It is shown that the slope of energy spectrum obtained from the velocity solution of Kdv-Burgers equation lies between -5/3 and -2 in the dilogarithmic coordinates paper. The spectrum is very close to one of Kolmogorov’s isotropic turbulence and Frisch’s intermittent turbulence in inertial region. In this paper, the Kdv-Burgers equation to describe atmospheric boundary layer turbulence is obtained. In the equation, the 1 / Re, corresponds to dissipative coefficient v, to dispersive coefficient β, then (v/ 2β)2 corresponds to .We prove that the wave number corresponding to maximum energy spectrum decreases with the decrease of stability (i.e., the increase of in eddy-containing region. And the spectrim amplitude decreases with the increase of (i.e., the decrease of stability). These results are consistent with actual turbulence spectrum of atmospheric surface layer from turbulence data.
Statistical Regression Analysis of Response of Northern Mid and Upper Tropospheric Circulation to Winter Eurasian Snow Cover Effects
Xu Jianjun
1994, 11(4): 415-420. doi: 10.1007/BF02658161
Response for anomalous circulation in relation to snow coverage is derived by use of regression coefficients in dealing with the Eurasian snow cover time series and northern mid and upper tropospheric height data, Results show that not only does the regression response pattern represent the correlation between snow coverage and circulation change but reflects the amplitude strength in correlation cores as well, with a greater amplitude or the circulation response in the mid troposphere and remarkable equivalent barotropy in the mid to upper levels, and that the response of winter-summer circulations to winter snow cover displays noticeable stationary planetary-scale wavetrain, leading to NEUP and NPNA patterns in winter, slightly changed forms in spring months and LEU and EANA in summer time. Also, the study demonstrates that the response-produced wavetrain is marked by branch and propagates ener-gy in a wave-front manner with the energy trapped at subtropical latitudes.
Temperature and Water Vapor Weighting Functions from Radiative Transfer Equation with Surface Emissivity and Solar Reflectivity
Li Jun
1994, 11(4): 421-426. doi: 10.1007/BF02658162
Linearization of Radiative Transfer Equation (RTE) is the key step in physical retrieval of atmospheric tempera-ture and moisture profiles from InfRared (IR) sounder observations, In this paper, the successive forms of tempera-ture and water vapor mixing ratio component weighting functions are derived by applying one term variation method to RTE with surface emissivity and solar reflectivity contained. Retrivals of temperature and water vapor mixing ra-tio profiles from simulated Atmospheric Infrared Sounder (AIRS) observations with surface emissivity and solar reflectivity arc presented.
Seasonal Variation of Stationary and Low-Frequency Rossby Wave Rays
Lu Keli, Zhu Yongchun
1994, 11(4): 427-435. doi: 10.1007/BF02658163
The wave rays and their seasonal variation of stationary and low-frequency Rossby waves are studied by using the Runge-Kutta scheme. The results show that for stationary waves the rays can reach lower latitudes in winter, and are limited in higher latitudes in summer. The main differences between the stationary and low-frequency wave rays are that low-frequency waves can propagate across the equator and the easterlies will not be an obstacle on their propagation. It explained to some extent the interaction of disturbances between the Northern and Southern Hemi-spheres. The lower wave frequencies and the stronger easterly flow are, the more difficult low-frequency waves will be to propagate across the equator. The waves with 20-day period are easier to propagate across the equator than that with 50-day period. The winter is the most favorable season for low-frequency waves to propagate into another hem-isphere.
Efficient Anomalous Forcings for Linear Problems
Li Zhijin, Ji Liren
1994, 11(4): 436-446. doi: 10.1007/BF02658164
For linear forcing problems, a method is developed to provide a set of forcing modes which form a complete orthonormal basis for the finite-time response to steady forcing in the energy inner product space. The forcing modes are found by calculating eigenvectors of a positive definite and symmetric matrix determined from given equations of motion. The amplitude of responses to forcing modes is given in terms of the associated eigenvalues. This method is used in a nondivergent barotropic model linearized about the 300 hPa zonally-varying climatological flow both for northern summertime and wintertime. The results show that the amplitude of response varies considerably with dif-ferent forcing modes. Only a few of forcing modes associated with the leading eigenvalues, called efficient forcing mode, can excite significant response. The efficient forcing modes possess highly localized spatial structure with wavetrain appearance. Most of the efficient forcings are located to the south of regions of the jet cores. The forcings located over polar regions are also efficient. In addition, the response is larger in wintertime than in summertime for a given forcing.
A Data-Adaptive Filter of the Tahiti-Darwin Southern Oscillation Index and the Associate Scheme of Filling Data Gaps
Zhang Banglin
1994, 11(4): 447-458. doi: 10.1007/BF02658165
The Tahiti-Darwin Southern Oscillation index provided by Climate Analysis Center of USA has been used in numerous studies. But, it has some deficiency. It contains noise mainly due to high month-to-month variability. In order to reduce the level of noise in the SO index, this, paper introduces a fully data-adaptive filter based on singular spectrum analysis. Another interesting aspect of the filter is that it can be used to fill data gaps of the SO index by an iterative process. Eventually, a noiseless long-period data series without any gaps is obtained.
The Fractal Dimension Distribution of the Short-Term Climate System in China and It’s Connection with the Monsoon Climate
Zhang Fuqing, Lin Zhenshan, Jiang Quanrong
1994, 11(4): 459-462. doi: 10.1007/BF02658166
By analyzing the Fractal Dimension (FD) distribution of the Short-range Climate system (SCS) in China, it is found that the FD varies in different region and this just agrees with the regionality of the monsoon climate in China. The FD of the SCS Lays between 2.0 and 5.0. In the vast eastern area of China, the FD almost grows gradually with the latitude. Line 4.0 is along the mountain chains from the Nanlin Mountain to the Wuyi Mountain. North of the line the FD varies only slightly and all are above 4.0. Only in coastal islands the FD is smaller than 3.0.
Seasonal Variation Features of Western North Pacific Tropical Cyclone Tracks with Their Predictability
Peng Yongqing, Yan Shaojin
1994, 11(4): 463-469. doi: 10.1007/BF02658167
Analysis is done or monthly and seasonal variations as climatic features of the tracks from 1196 tropical cyclones originating in the western North Pacific over the period 1949 to 1980, followed by the investigation of 301 onland cy?clone tracks over China mainland in terms of methodology for nonlinear system, Obtained by computing the accumu?lated distance distribution function of the tracks is the characteristic chaos quantity for the related dynamic systems and then the fractual dimensionality d = 4.86 and Kolmogorov entropy approximation K2 = 0.0164, thereby leading to the predictability time scale = 2.54 days. It is found that the reference path among the onland typhoon No.23 of 1971, or Bess in the international nomenclature. Our results could be of operational use as a kind of reference.
Microwave Simulations of Precipitation Distribution with Two Radiative Transfer Models
Liu Jinli, Lin Longfu
1994, 11(4): 470-478. doi: 10.1007/BF02658168
Two microwave radiative transfer models of precipitating cloud are used to simulate the microwave upwelling radiances emerging from precipitating clouds. Comparison of the simulation results shows that significant difference of microwave upwelling radiances exists between these two radiative transfer models. Analysis of these differences in different cloud and precipitation conditions shows that it is complicated but has certain trend for different microwave frequencies. The results may be useful to quantitative rainfall rate retrieval of real precipitating clouds.
A Two-Step Shape-Preserving Advection Scheme
Yu Rucong
1994, 11(4): 479-490. doi: 10.1007/BF02658169
This paper proposes a new two-step non-oscillatory shape-preserving positive definite finite difference advection transport scheme, which merges the advantages of small dispersion error in the simple first-order upstream scheme and small dissipation error in the simple second-order Lax-Wendroff scheme and is completely different from most of present positive definite advection schemes which are based on revising the upstream scheme results. The proposed scheme is much less time consuming than present shape-preserving or non-oscillatory advection transport schemes and produces results which are comparable to the results obtained from the present more complicated schemes. Elementary tests are also presented to examine the behavior of the scheme.
Power and Cross-Spectra for the Turbulent Atmospheric Motion and Transports in the Domain of Wave Number Frequency Space: Theoretical Aspects
M. Y. Totagi
1994, 11(4): 491-498. doi: 10.1007/BF02658170
The study of large-scale atmospheric turbulence and transport processes is of vital importance in the general cir-culation of the atmosphere. The governing equations of the power and cross-spectra for the atmospheric motion and transports in the domain of wave number frequency space have been derived. The contributions of the nonlinear interactions of the atmospheric waves in velocity and temperature fields to the conversion of kinetic and potential en-ergies and to the meridional transports of angular momentum and sensible heat in the atmosphere have been discussed.
A Modeling Study of Climate Change and Its Implication for Agriculture in China Part II: The Implication of Climate Change for Agriculture in China
Dai Xiaosu, Ding Yihui
1994, 11(4): 499-506. doi: 10.1007/BF02658171
The potential CO2-induced impacts on the geographical shifts of wheat growth zones in China were studied from seven GCMs outputs. The wheat growth regions may move northward and westward under the condition of a doub-ling CO2 climate. The wheat cultivation features and variety types may also assume significant changes. Climatic warming would have a positive influence in Northeast China, but high temperature stress may be produced in some regions of central and southern China. Higher mean air temperatures during wheat growth, particularly during the reproductive stages, may increase the need for earlier-maturing and more heat-tolerant cultivars.