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1992 Vol. 9, No. 1

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The Structure of Low Frequency Phenomena in the Tropics and Its Interaction with the Extratropics
Peter J. Webster, Min Dong
1992, 9(1): 1-16. doi: 10.1007/BF02656925
The structure of planetary scale low frequency phenomena in the tropics is studied, and an attempt is made to de-termine its influence and interactions with phenomena at higher latitudes.In the tropics, it is found that the majority of the variance in the zonal wind structure is made up in wave num-bers 1 and 2. During warm events in the Pacific Ocean, when the Southern Oscillation Index is negative, almost all of the variance resides in the gravest mode which undergoes a 40o eastward phase shift. Meanwhile, the second logitudinal mode almost disappears. On the other hand, the meridional wind field possesses maximum amplitude at higher wave numbers. However, near the equator, the amplitude is small with extreme values occurring in the subtropics. The difference in scale and the location of extrema of the meridional and zonal wind components indicate that the tropical atmosphere is responding to two different driving mechanisms,Correlation analyses between variations of the zonal wind at reference points along the equator with variations of component elsewhere show that there are strong logitudinal connections. The strongest correlations between the tropics and higher latitudes exist in the region of the equatorial westerlies. In fact, stronger correlations occur between variations in U anywhere along the equator and the middle latitudes to the north and south of the equatorial wester-lies than to the latitudes immediately to the north and south of the reference points. We interpret this “remote” corre-lation pattern as indicating a two-stage teleconnection process which emphasizes the importance of the equatorial tropical westerlies of the Pacific Ocean as a “corridor” of communication between the low and high latitudes. The regionality of the correlations confirms, to some extent, recent theoretical development regarding trapped equatorial modes. Finally, time lagged correlations from plus and minus six months between variations of U and OLR indicate that the interactions between the extratropics and low latitudes possess an organized sequence. The extratropical in-fluence appears to propagate into the tropics followed by an eastward propagation along the equator. Finally, a propagation from the tropics to the extratropics in the upper troposphere occurs in the eastern Pacific Ocean. The time-lagged correlation sequence does not appear to be symmetric about the equator.
A Fluid Experiment of Large-Scale Topography Effect on Baroclinic Wave Flows
Guoqing Li, Robin Kung, Richard L. Pfeffer
1992, 9(1): 17-28. doi: 10.1007/BF02656926
The effects of topography on baroclinic wave flows are studied experimentally in a thermally driven rotating annulus of fluid.Fourier analysis and complex principal component (CPC) analysis of the experimental data show that, due to topographic forcing, the flow is bimodal rather than a single mode. Under suitable imposed experimental parameters, near thermal Rossby number ROT = 0.1 and Taylor number Ta = 2.2 × 107, the large-scale topography produces low-frequency oscillation in the flow and rather long-lived flow pattern resembling blocking in the atmospheric cir-culation. The ‘blocking’ phenomenon is caused by the resonance of travelling waves and the quasi-stationary waves forced by topography.The large-scale topography transforms wavenumber-homogeneous flows into wavenumber-dispersed flows, and the dispersed flows possess lower wavenumbers.
The Propagation of Inertia-Gravity Waves and Their Influence on Zonal Mean Flow Part Two: Wave Breaking and Critical Levels
Zheng Xingyu, Zeng Qingcun, Huang Ronghui
1992, 9(1): 29-36. doi: 10.1007/BF02656927
The gravity wave breaking is crucial to the large-scale circulation of middle atmosphere. In this paper, we follow Lindzen (1981) to draw out the parameterization of two-dimensional gravity wave breaking including inertial effect. Also we present some properties of critical levels and inertial critical levels.
Agroclimatic Study of Mountainous Regions and Its Progress in China
Zhang Yangcai
1992, 9(1): 37-45. doi: 10.1007/BF02656928
In recent years, the agroclimatic investigations have been made at various temporal and spatial scales in moun-tainous and hilly regions, and so have the adaptability tests on the crop ecoclimate. A large quantity of reliable and representative data are obtained. Through the synthetic studies on “bell”, “layer”, “topography” and “ecological-type” in mountainy and hilly regions, climate with agriculture and zonality with non-zonality are closely combined to show the similarities and differences of agroclimatic resources at various layers and with different topography types in mountainy and hilly regions. A general review is given in this paper.
Analytical Studies on the Variations of the Antarctic Ozone Layer
Qu Shaohou
1992, 9(1): 46-52. doi: 10.1007/BF02656929
The Antarctic ozone hole which was discovered in the mid 1980s has caused much attention from the scientists and politicians throughout the world.For the formation of the Antarctic ozone hole, most scientists believe that the man-made chemical materials such as CFCs etc. are main cause. On the other hand, the electrochemistry-dynamics theory presented by Wei (Guang Ming Daily Dec. 11, 1990) two years ago has also caused some attention.In the paper the data of ozone, solar activity meteorology over Antarctica have been used for statistical analyti-cal studies. Our results present some new evidence to support Wei's theory. However the influence of the human activ-ities can never be slighted.
A Numerical Study on Forecasting the Henan Extraordinarily Heavy Rainfall Event in August 1975
Cai Zeyi, Wang Zuoshu, Pan Zaitao
1992, 9(1): 53-62. doi: 10.1007/BF02656930
This study is essentially an experiment on the control experiment in the August 1975 catastrophe which was the heaviest rainfall in mainland China with a maximum 24-h rainfall of 1060.3 mm, and it significantly demonstrates that the limited area model can still skillfully give reasonable results even only the conventional data are available. For such a heavy rainfall event, a grid length of 90 km is too large while 45 km seems acceptable. Under these two grid sizes, the cumulus parameterization scheme is evidently superior to the explicit scheme since it restricts instabili-ties such as CISK to limited extent, The high resolution scheme for the boundary treatment does not improve fore-casts significantly.The experiments also revealed some interesting phenomena such as the forecast rainfall being too small while af-fecting synoptic system so deep as compared with observations. Another example is the severe deformation of synoptic systems both in initial conditions and forecast fields in the presence of complicated topography. Besides, the fixed boundary condition utilized in the experiments along with current domain coverage set some limitations to the model performances.
Comparison of Satellite and Ship Observations for Total Cloud Amount
Zhang Mingli, Garrett G. Campbell
1992, 9(1): 63-72. doi: 10.1007/BF02656931
The data series of monthly clouldiness over global ocean from COADS was compared with that of from satellite Nimbus-7 during April 1979 to March 1985. The correspondence between them is good. Both the two methods of observation can provide useful information of the distribution of cloudiness and the two data sets can be mutually complementary.
Atmospheric NO2 Concentration Measurements Using Differential Absorption Lidar Technique
P.C.S. Devara, P. Ernest Raj
1992, 9(1): 73-82. doi: 10.1007/BF02656932
Using the Differential Absorption Lidar (DIAL) technique, two types of approaches, namely, reflection from retroreflector/topographic target and backscatter from atmosphere, are available for studying remotely the atmos-pheric NO2 concentration. The Argon ion lidar system at the Indian Institute of Tropical Meteorology (IITM), Pune, India has been used for the measurements by following both the path-averaged and range-resolved ap-proaches. For the former, a topographic target (hill) is used for determining path-averaged surface concentration. In the latter, spectral properties of atmospheric attenuation is used for making range-resolved measurements in the sur-face layer. The results of the observations collected by following both approaches are presented. The average surface NO2 concentration was found to vary between 0.01 and 0.105 ppm and the range-resolved measurements exhibited higher values suggesting treatment of the lidar data for scattering and extinction effects due to atmospheric aerosols and air molecules, and atmospheric turbulence. Certain modifications that arc suggested to the experimental set-up, data acquisition and analysis to improve the measurements are briefly described.
Split-Explicit Integration of Primitive Equation Barotropic Model for the Prediction of Movement of Monsoon Depression
A. Bandyopadhyay
1992, 9(1): 83-92. doi: 10.1007/BF02656933
The split-explicit version of a limited area primitive equation barotropic model is formulated and tested for the prediction of movement of monsoon depressions. The model is integrated upto 48 hours with split-explicit time inte-gration scheme (Gadd, 1978a) using input of four synoptic cases. The model is also integrated explicitly. The forecast results obtained from both the versions are compared and discussed. The computational time in former version is less than half of the computational time needed in explicit version.
An Overview of the Madden-Julian Oscillation and Its Relation to Monsoon and Mid-Latitude Circulation
Bin Wang, Yihui Ding
1992, 9(1): 93-111. doi: 10.1007/BF02656934
In the past decade there has been extensive research into tropical intraseasonal variability, one of the major com-ponents of the low frequency variability of the general atmospheric circulation. This paper briefly reviews the state-of-the-art in this research area: the nature of the Madden-Julian Oscillation, its relation to monsoonal and extratropical circulations, and the current theoretical understandings.
Effects of the Qinghai-Xizang (Tibetan) Plateau on the Circulation Features over the Plateau and Its Surrounding Areas
Ding Yihui
1992, 9(1): 112-130. doi: 10.1007/BF02656935
Areview of the effects of the Tibetan Plateau on circulation features over the plateau and its surrounding areas has been made, with a special emphasis upon the monsoon circulations in South Asia and East Asia. This includes estimates of heat sources, dynamic and thermal effects of the plateau, and effects of the plateau on summer and winter monsoons. Major progresses made in this aspect by Chinese meteorologists have been specifically described and are compared with the achievements made by the meteorologists of other countries.