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1992 Vol. 9, No. 2

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A Further Study on an Extended Nonlinear Ocean-Atmosphere Coupled Hydrodynamic Characteristic System and the Abrupt Feature of ENSO Events
Zhong Qing, Ji Liren
1992, 9(2): 131-146. doi: 10.1007/BF02657504
An extended ocean-atmosphere coupled characteristic system including thermodynamic physical processes in ocean mixed layer is formulated in order to describe SST explicitly and remove possible limitation of ocean-atmos-phere coupling assumption in hydrodynamic ENSO models. It is revealed that there is a kind of abrupt nonlinear characteristic behaviour, which relates to rapid onset and intermittency of El Nino events, on the second order slow time scale due to the nonlinear interaction between a linear unstable low-frequency primary eigen component of ocean-atmosphere coupled Kelvin wave and its higher order harmonic components under a strong ocean-atmos-phere coupling background. And, on the other hand, there is a kind of finite amplitude nonlinear characteristic behaviour on the second order slow time scale due to the nonlinear interaction between the linear unstable primary eigen component and its higher order harmonic components under a weak ocean-atmosphere coupling background in this model system.
Effects of Turbulent Dispersion of Atmospheric Balance Motions of Planetary Boundary Layer
Liu Shikuo, Huang Wei, Rong Pingping
1992, 9(2): 147-156. doi: 10.1007/BF02657505
New Reynolds' mean momentum equations including both turbulent viscosity and dispersion are used to analyze atmospheric balance motions of the planetary boundary layer. It is pointed out that turbulent dispersion with r 0 will increase depth of Ekman layer, reduce wind velocity in Ekman layer and produce a more satisfactory Ekman spiral lines fit the observed wind hodograph. The wind profile in the surface layer including tur-bulent dispersion is still logarithmic but the von Karman constant k is replaced by k1 = 1 -2/k, the wind increasesa little more rapidly with height.
The Structure and Propagation of Stationary Planetary Wave Packet in the Barotropic Atmosphere
Lu Peisheng
1992, 9(2): 157-166. doi: 10.1007/BF02657506
Monthly or seasonally mean anomalies of large-scale atmospheric circulation are better represented by wave packets or their combination. Both qualitative and quantitative analyses of equations of wave packet dynamics, which are obtained by the use of WKB approximation, are very helpful for the understanding of structure, formation and propagation of stationary and quasi-stationary planetary wave packet patterns in the atmosphere. Indeed, these equations of wave packet dynamics can be directly solved by the method of characteristic lines, and the results can be simply and clearly interpreted by physical laws. In this paper, a quasi-geostrophic barotropic model is taken for simplicity, and the wave packets superimposed on several ideal profiles of the basic current and excited by some ideal forcings are investigated in order to make comparison of the accuracy of calculation with the analytical solution. It is revealed that (a) the rays of stationary planetary wave packet do not coincide with but go away from the great circle with significant difference if the shear of the basic zonal flow is not too small; (b) being superimposed on a westerly jet flow with positive shear (Uλ/y>0), the stationary wave packets excited by low-latitudinal forcing are first intensified during their northeastward propagation in the Northern Hemisphere, then reach their maximum of amplitude at some critical latitude, and after that weaken again; (c) the connected line of extremes (the positive and negative centres) of wave packet does not coincide with but crosses the ray by an angle, the larger the scale of external forcing, the larger the angle; and (d) the whole pattern of a trapped stationary wave packet is complicated by the interference between the incident and reflected waves.
The Theory Study of the Influence of the Topography on the Cold Frontal Motion
Gu Wei, Wu Rongsheng
1992, 9(2): 167-172. doi: 10.1007/BF02657507
In order to study the characteristics of cold frontal motion over the arbitrary topography, the velocity of cold frontal movement is derived by using the one layer shallow-water model. The results show that there exist the retardation in upwind side and rapid descent in the lee slope when the cold front crosses the topography.
Nonlinear Planetary Wave Instability and Blocking
Yong. L. McHall
1992, 9(2): 173-190. doi: 10.1007/BF02657508
The instability of geostrophic wave circulations related to the nonlinear processes involved in the zonal mean heat balance equations is studied. It is found that the planetary waves may be destabilized by thermal forcing in spe-cific baroclinic layers, called the breaking layers. The critical conditions of the instability will be given. In the troposphere, these conditions may be provided in blocking regions and the development of planetary perturbations is characterized distinctly by the unset, maintenance and decay of observed blocks. The whole blocking episode cannot be described as either the barotropic or baroclinic process only. The limitations on the study of wave-wave interaction using spectral models or spectrum analyses will be discussed also.
The Momentum Turbulent Counter-Gradient Transport in Jet-like Flows
V. N. Lykossov
1992, 9(2): 191-200. doi: 10.1007/BF02657509
A Numerical Study of Second-Order Turbulent Moments in the Stably Stratified Nocturnal Boundary Layer
Zhu Ping, Xu Xiaojin, Li Xingsheng
1992, 9(2): 201-212. doi: 10.1007/BF02657510
The structures and the vertical profiles of turbulent variance and covariance of the stably stratified boundary layer (SBL) are simulated with a second-order closure turbulence model. The results confirm that the vertical profiles of the dimensionless turbulence variance and covariance can be well represented by the form F = A(1 - Z / h)x. Here h is the height of SBL. and both exponent a and coefficient A are the functions of terrain, baroclinicity, radiation cooling and the state of temporal development of SBL. Comparing with Minnesota and Cabauw experiment data, we have analysed the value of a and expounded the main reasons that great difference in a exists among different literatures.
Transport of Water Vapor over North China during the Drought Period in Summer of 1980
Liu Yongqiang, Ding Yihui, Li Yuehong
1992, 9(2): 213-222. doi: 10.1007/BF02657511
The features of water vapor transport, such as temporal evolution, vertical structure and spatial pattern, over North China during the prolonged drought in the summer of 1980 have been analyzed through computation of water vapor flux based on the once daily ECMWF grid-point data at 12GMT. The results indicate that it is unlikely that the characteristics of the atmospheric mass divergence, ascending motion and stratification stability in North China were completely opposite to those in the Yangtze River Valley, where the heavy flood occurred in the summer of 1980. It is major differences that the strong ascending motion and significant water vapor convergence overlap fairly well each other in the vertical levels in the Yangtze River Valley, while the maximum ascending motion is accompa-nied by water vapor divergence or weak water vapor convergence in North China. This vertical structure in North China results in insufficient water vapor supply and, therefore, little condensation and precipitation in the middle and upper atmosphere were produced. Additionally, a mode of monthly-scale low frequency oscillation can be found in water vapor flux, which is in correspondence to the fluctuation period of rainfall.
Experiments in Forecasting Mesoscale Convective Weather over Changjiang Delta
Dang Renqing, Tang Xinzhang, Zhang Jiacheng
1992, 9(2): 223-230. doi: 10.1007/BF02657512
The real time operational severe convective weather forecast experiment carried out during May to July in 1990 over the Changjiang Delta is briefly described. The heavy rainfall and severe convective weather forecast worksheets for the Changjiang Delta have been proposed and used in the daily forecasting. Results show that the ability of 0-12h convective weather prediction has been improved significantly after the development of the forecast methods and the establishment of a mesoscale forecast base at Shanghai Meteorological Center during 1986 to 1990.Three cases of convective weather systems (meso-alpha, meso-beta, meso-gamma) during the experiment period are described and discussed.
A Numerical Research on the Influences of the Diurnal Variation of Solar Radiation on the Medium-Range Weather Processes
Huang Boyin, Zhao Gaoxiang, Ji Liren
1992, 9(2): 231-236. doi: 10.1007/BF02657513
In this paper, we use a spectral model for the medium-range numerical weather forecast to discuss the impact of the diurnal variation of solar radiation on the medium-range weather processes. Under the tests of two typical winter and summer cases, we find that the influences of the diurnal variation of solar radiation on summer weather are really important, especially on its rainfall, surface heat transport and 500 hPa height field. On winter weather, however, the influences are very weak.
Construction of Vertical Wind Profile from Satellite-Derived Winds for Objective Analysis of Wind Field
P. N. Mahajan, D. R. Talwalkar, S. Nair, S. Rajamani
1992, 9(2): 237-246. doi: 10.1007/BF02657514
During summer Monex-79, a variety of observing systems viz. research ships, research aircrafts, constant pres-sure balloons and geostationary satellite etc. were deployed, besides the regular conventional observations The pur-pose of these additional systems was to make the best possible data for the studies on various aspects of monsoon cir-culation. The present study is aimed at the construction of vertical wind profile using cloud motion vectors obtained from GOES (I-O) satellite and to examine whether the constructed wind profiles improves the representation of the monsoon system, flow pattern etc. in the objective analysis. For this purpose, climatological normals of the wind field are considered as the initial guess and the objective analyses of the wind field are made with, first using only data from conventional observations over land areas, subsequently including the constructed winds from cloud motion vectors. These analyses are then compared with the standard analyses of wind field obtained from Quick Look Atlas by T. N. Krishnamurti et al. (1979).It is inferred that satellite estimated mean wind profiles show good agreement with the mean wind profiles of the research ships with RMS errors less than 5 mps below 500 hPa and less than 8 mps above 500 hPa. It is further infer-red that the inclusion of constructed winds shows a positive impact on the objective analysis and improvement is seen to be more marked in the data-sparse region of the Arabian sea. Analyses which include the constructed winds show better agreement with the standard analysis, than the analyses obtained using only conventional winds. Thus, results of our study suggest that the wind profiles constructed using cloud motion vectors are of potential use in objective analysis to depict the major circulation features over the Indian region.
Preliminary Study on Vertical Velocity Caused by Katabatic Wind in Antarctica and Its Influence on Atmospheric Circulation
Ma Yimin
1992, 9(2): 247-250. doi: 10.1007/BF02657515
The vertical velocity at the top of Ekman layer caused by katabatic winds is proposed and deduced. By com-puting actual data we jet a distribution of the velocities over Antarctica. The distribution plays a positive role in maintaining the cyclone and anticyclone over Antarctica.
A Theoretical Test of the Geostrophic Momentum Approximation
T. S. Spassova
1992, 9(2): 251-255. doi: 10.1007/BF02657516
A previously developed model of a 2-dimensional air flow with constant horizontal shear is used to estimeate the accuracy of the geostrophic momentum approximation by comparison of exact solutions when exist with approxi-mate ones.