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1988 Vol. 5, No. 4

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LARGE SIGNALS OF CLIMATIC VARIATION OVER THE OCEAN IN THE ASIAN MONSOON REGION
Fu Congbin, J. Fletcher
1988, 5(4): 389-404. doi: 10.1007/BF02656786
Abstract:
The aim of this paper is to identify and delineate large signals of climatic variation in the Asian monsoon region and try to understand the nature of transformation from one climate regime to another.It is found that the summer monsoon over the Indian and western Pacific oceans stows distinct climatic regimes with changes occurring in the years around 1875, 1900, 1940 and 1960. The change of about 1900 is the largest one, which occurs in step with the variation of global oceanic climate pointed out by Fletcher, et al. (1982).The main characteristics of the transformation from one regime to another is an alternation of meridio-nality of monsoon current. The transformation occurs most strongly in the western Pacific convergence zone, where monsoon has strong interaction with the trade wind systems.The variability of monsoon rainfall over India and East China also exhibits some large signals which are synchronous with those of wind field over the ocean: the monsoon rainfall increases (decreases) during the “meridional monsoon period” (zonal monsoon period) over the ocean.It should be noted that the apparent decreasing of plum rains in East China since 1958 which is well known in China would be linked mainly with the sudden increasing of U-component of SW monsoon over the South China Sea.Finally a kind of seesaw between Indian monsoon and East China monsoon with somewhat time-lag is discussed.
THE PROPAGATION CHARACTERISTICS OF INTERANNUAL LOW-FREQUENCY OSCILLATIONS IN THE TROPICAL AIR-SEA SYSTEM
Yan Jinghua, Chen Longxun, Wang Gu
1988, 5(4): 405-420. doi: 10.1007/BF02656787
Abstract:
The time series of sea surface temperature (SST), sea level pressure (SLP), zonal wind (U) and total cloudiness (CA), for the period of 1950-1979, over a 8o×8o grid-point latitudinal belt between 32oS and 32oN are made from COADS (Comprehensive Ocean-Atmosphere Data Set). The time harmonic analysis and power spectra analysis show that there exist quasi-biennial oscillation (QBO), three and half years oscillation (SO), five and half years oscillation (FYO) and eleven years oscillation (EYO) in these time series. The main propagation characteristics of these interannual low-frequency oscillations are as follows:(1) The variance analysis of SST shows that there is an active region of QBO and SO (with maximum variance), coming from the southwestern part of the subtropical Pacific, stretching eastward up to the west coast of South America, and then northward to the eastern equatorial Pacific. The QBO and SO disturbances of SST follow the same route and cause the anomaly of SST (El Nino and period of cold water) in the eastern equatorial Pacific.(2) Either the QBO or SO of SST can cause El Nino events, although it is easier when they are situated in the same phase of warm water at the eastern equatorial Pacific. The FYO of SST seems to be a standing oscillation. It plays an important role on the formation of strong El Nino events or strong cold water events.(3) The QBO and SO of U propagate eastward along the equator. The origin of QBO and SO may at least be traced as far as the western Indian Ocean. While they propagate along the equator, it strengthens two times at 90oE and the western Pacific, respectively. Like SST, the FYO of U is somehow a standing oscillation.(4) The Oscillations of U have a good coupling relationship with those of SST, while they propagate. When the QBO and SO of SST move to the east side of the eastern equatorial Pacific, it is the time for the QBO and SO of U to enter into the east part of the western Pacific.It is clear that, when we do research work on the formation of El Nino events, our consideration would not be confined to the tropics, it should cover the subtropical region in the southern Pacific. The features of the circulation and other oceanic states in this area are very important to the El Nino events.
TELECONNECTION OF THE DOMINANT SPATIAL PATTERNS OF THE SEASONAL 500 hPa GPH FIELD
Zhang Mingli
1988, 5(4): 421-436. doi: 10.1007/BF02656788
Abstract:
The dominant spatial patterns of the seasonal 500 hPa GPH field is induced by the EOF analysis. In winter, the first and fourth eigenvector show that the PEA and PNA-like anomalous flow pattern will prevail when the temporal coefficient is negative. Through the variation of the temporal coefficient of the eigen-vector, prevailing of these flow patterns is significantly related to the variation of SST in equatorial Pacific. These relationships are insignificant in other three seasons.
A PRELIMINARY STUDY ON THE CLIMATIC CHANGE OF THE HENGDUAN MOUNTAINS AREA SINCE 1600 A.D.
Wu Xiangding, Lin Zhenyao, Sun Li
1988, 5(4): 437-443. doi: 10.1007/BF02656789
Abstract:
Based on twelve tree-ring chronologies, two curves including the fluctuations of air temperature and the annual precipitation during last hundreds of years in the Hengduan Mountains area are drawn. Some significant cold/warm and dry/wet periods could be identified. A combined analysis between dendrochronologies and historical literature data of five classes helps us understand successive variations of each climatic pattern since 1600 A.D. In addition, the periodicities of some climatic features in the area have been studied in this paper.
ALGEBRAIC ROSSBY SOLITARY WAVE AND BLOCKING IN THE ATMOSPHERE
Luo Dehai, Ji Liren
1988, 5(4): 445-454. doi: 10.1007/BF02656790
Abstract:
In this paper, the atmosphere is divided into two regions which are governed by different equations. Furthermore, multiple-scale method is used to obtain the Benjamin-Ono equation satisfied by the nonlinear Rossby wave in weak shear zonal flow. The equation has algebraic solitary wave solution, and the sta-tionary streamfunction fields in the atmosphere are calculated by using numerical method, and the results demonstrate that the stationary solution is antisymmetric dipoles with the anticyclone north of the cyclone, and the structure is similar to the equivalent modon obtained by Mcwilliains (1980), Because the modon obtained here is an algebraic solitary wave, the modon may be called “algebraic modon”, and the stationary algebraic modon is consistent with observations of blocking pattern in the atmosphere.
A STEADY TWO-DIMENSIONAL CLIMATE MODEL WITH RESIDUAL CIRCULATION
Xun Zhu
1988, 5(4): 455-468. doi: 10.1007/BF02656791
Abstract:
Based on dynamical energy transport and thermodynamic energy balance in the earth’s atmosphere-ocean system a steady two-dimensional climate model with residual circulation is proposed. In the model, we include some important physical processes with feedbacks such as ice caps-albedo, water vapor-tempera-ture, etc. The simulated steady temperature field is very close to that of the real atmosphere. The numerical experiments show that doubling of the atmospheric carbon dioxide results in temperature increase of 1~2oC at the low latitude surface and 6~8oC at the high latitude surface. It is shown that a 6% decrease in the solar constant is required for the -10oC ice edge to move from its present latitude ~70o to~50o.
LONG-TERM VARIABILITY OF THE INDIAN SUMMER MON-SOON AND RELATED PARAMETERS
G. B. Pant, K. Rupa Kumar, B. Parthasarathy, H. P. Borgaonkar
1988, 5(4): 469-481. doi: 10.1007/BF02656792
Abstract:
The long-term variability of the Indian summer monsoon rain-fall and related regional and global param-eters are studied. The cubic spline is used as a digital filter to smooth the high frequency signals in the time series of the various parameters. The length of the data series varies from 95 to 115 years during the period 1871-1985. The parameters studied within the monsoon system are: (a) monsoon rainfall of the country as a whole; (b) number of break-monsoon days during July and August; (c) number of storms/ depressions in Bay of Bengal and Arabian Sea during summer monsoon season; and (d) dates of onset of summer monsoon over South Kerala Coast. The parameters studied outside the monsoon system are: (a) the Wright’s Southern Oscillation Index (June-July-August); (b) the January mean Northern Hemi-spheric surface air temperature anomaly; and (c) the East-equatorial Pacific sea surface temperature anomaly.In order to examine the variability under various degrees of the smoothing, the series are filtered with splines of 50% variance reduction frequency of one cycle per 10, 20 and 30 years. It is observed that the smoothed time series of the parameters within the monsoon system comprise a common slowly varying com-ponent in an episodic manner distinctly showing the excess and deficient rainfall epochs. The change of intercorrelations between the time series with increasing degree of smoothing throws some light on the time scales of the dominant interactions. The relation between Southern Oscillation and East equatorial Pacific sea surface temperature and the Indian summer monsoon seems to be dominant on the interannual scale. The low frequency variations are found to have significantly contributed to the instability of the correlations of monsoon rainfall with parameters outside the monsoon system.
THE WIND IN THE BAROCLINIC BOUNDARY LAYER WITH THREE SUBLAYERS INCORPORATING THE WEAK NON-LINEAR EFFECT
Xu Yinzi
1988, 5(4): 483-497. doi: 10.1007/BF02656793
Abstract:
In considering the weak non-linear effect, and using the small parameter expansion method, the analyt-ical expressions of the wind distribution within PBL (planetary boundary layer) and the vertical velocity at the top of the PBL are obtained when the PBL is divided into three layers and different eddy transfer coefficients K are adopted for the three layers. The conditions of barotropy and neutrality for the PBL are extended to that of baroclinity and non-neutral stratification. An example of a steady circular vortex is used to display the characteristics of the horizontal wind within the PBL and the vertical velocity at the top of the PBL. Some new results have been obtained, indicating that the magnitude of the speed in the lower height calculated by the present model is larger than that by the model in which k is a constant within the whole boundary layer, for example, in the classical Ekman boundary layer model and the model by Wu (1984). The angle between the wind at the top of the PBL and the wind near the surface calculated by the present model is less than that calculated by the single K model. These results are in agreement with the observations.
LARGE-SCALE FEATURES OF THE INDIAN SUMMER MON-SOON RAINFALL AND THEIR ASSOCIATION WITH SOME OCEANIC AND ATMOSPHERIC VARIABLES
K. D. Prasad, S. V. Singh
1988, 5(4): 499-513. doi: 10.1007/BF02678749
Abstract:
The summer monsoon rainfall totals for 31 meteorological subdivisions of India for the years 1901-1980 are analysed. The analysis reveals that four leading eigenvectors (EVs) are significant and account for 65 % of the total variance.The spatial pattern of the first EV exhibits in phase fluctuations over almost the whole India. The large coefficients of this vector can be considered as representative of the conditions of large-scale flood and drought over the country. The second pattern reveals the fluctuations mostly over the North Indian region (north of 20o latitude) probably in association with the Western Disturbances. The third pattern indicates fluctuations over the North-West and the North-East India in opposite phase and the fourth pattern exhibits the characteristic features of fluctuations associated with ‘break’. The spectral analysis of the coefficients of these EVs revealed quasi-periodicities of 2-5 years.On the basis of examination of the elements of these EVs the country has been divided into seven homogeneous regions. Rainfall indices of these regions and of the four EVs have been examined for seek-ing for association with some oceanic and atmospheric variables. The association is significant for the coefficients of the first EV and for the rainfall indices of central and South India. Among all the variables examined, Darwin pressure tendencies have the highest association and appear to be of special significance in prediction of the monsoon rainfall.
SEVERAL PROPERTIES OF METEOROLOGICAL KNOWLEDGE USED FOR EXPERT SYSTEM
Dai Honghua
1988, 5(4): 515-521. doi: 10.1007/BF02656795
Abstract:
This paper describes seven important, specific properties of meteorological knowledge from the view of KP (Knowledge Processing) and ES (Expert System). It also discusses the viewpoint of knowledge motion and the evolution-transition theory, These specific properties are very important for MKP (Me-teorological KP) and building MES (Meteorological ES).
A TWO-DIMENSIONAL AND STEADY-STATE NUMERICAL MODEL OF THE PLANETARY BOUNDARY LAYER
Hu Yinqiao, Su Congxian, Ge Zhengmo
1988, 5(4): 523-534. doi: 10.1007/BF02656796
Abstract:
In this paper, a two-dimensional and steady-state numerical model of the planetary boundary layer is developed. It includes the horizontal deformation of the eddy exchange coefficients and horizontal turbulence exchange. The difference between the structure of the heat island and cold island is analysed using this model.