EFFECT OF THE THERMAL FORCING ON THE SECONDARY CIRCULATION OF TYPHOONS

A non-dimensional secondary circulation equation for typhoons has been derived and then 11-yr com-positing typhoon data were used to estimate the thermally forced secondary circulation.The main resultshave been obtained as follows:(1)The diabatic heating and Cu vertical heat mixing are major thermal forcing factors.They have thesame magnitude of order.(2)The effects of eddy flux and Cu horizontal mixing of heat are of minor im-portance.(3)Ekman pumping and Cu vertical heat mixing cooperatively work.This feedback process isfavorable for the enhancement of the secondary circulation of typhoons.     

THE ROLE OF THE MERIDIONAL CIRCULATION IN STATIONARY WAVE PROPAGATION

In a general baroclinic atmosphere,when the basic state includes meridional circulation,the sta-tionary waves might not only pass through the equatorial easterlies,but also strengthen significantly.The orographic forcing in the Northern Hemisphere mid-latitude might cause marked responses in thelow latitude atmosphere.This suggests that the meridional circulation plays an important role in theconnection of stationary responses in mid and low latitudes,and so does the heating forcing in theNorthern Hemisphere mid-latitude.Forced by the heating forcing in the Northern Hemisphere mid-latitude,the features similar to the Northern Hemisphere summer monsoon circulation can be ob-tained.It appears that the meridional circulation plays certain role in the formation of summer mon-soon circulation.The heating anomaly forcing located at the eastern equatorial Pacific makes the sta-tionary waves present PNA(Pacific-North America)pattern in the winter hemisphere,but it doesnot in the summer hemisphere.It suggests that the meridional circulation has a marked influence onthe route of stationary wave propagation both in the winter and summer hemispheres.     

PERIOD-DOUBLING BIFURCATIONS OF THE ATMOSPHERIC CIRCULATION AND APERIODIC VARIATIONS OF THE FLOW PATTERNS

An eighth-order set of ordinary differential equations, which governs the dynamics of aquasi-geostrophic flow of the baroclinic atmosphere, is used to investigate bifurcational and chaoticforms of the atmospheric circulation. Numerical integrations of the set exhibit period-doublingbifurcations of the flow patterns. It would seem that the Feigenbaum relation (r_n-r_(n-1))/(r_(n+1)-r_n)=4.6692 is satisfied approximately. Above a limit point the solutions are aperiodic and chaotic, anda strange attractor having four inter-linked chaotic fragments appears. A window of period-6emerges also in the chaotic region.     

THE EFFECTS OF MECHANICAL FORCING ON THE MEAN MERIDIONAL CIRCULATION AND TRANSFER PROPERTIES OF THE ATMOSPHERE

Experiments using a quasi-geostrophic model and the ECMWF T21 spectral model with and without orography are performed to investigate the effects of mechanical forcing on the mean meridional circulation. Results show that mechanical forcing intensifies the horizontal poleward heat flux and redistributes the eddy angular momentum in the vertical, and that this changes significantly the intensity and location of the mean meridional circulation centres.It is shown how the mean meridional circulation is set up in such a way to satisfy both the dynamical and thermodynamical transport requirements of the model atmosphere. Whenever external forcing changes the eddy fluxes, the Coriolis torques from the upper horizontal branches of the mean meridional circulations change to balance the extra divergence of eddy momentum flux, and additional adiabatic heating is produced by the vertical branches of the toroids to balance the extra divergence of eddy heat flux. The mean meridional circulation is, therefore, confirm     

THE EFFECTS OF GENERAL CIRCULATION ANOMALIES ON PRECIPITATION IN THE RAINING SEASON OF SHANDONG

1 INTRODUCTION Locating in mid-latitude East Asia monsoon region, the Shandong province is marked by significant monsoon climate. Precipitation in summer (from June to August) takes up about 60% of the annual total[1] and drought and flood damages take place frequently. The province is in a zone where the northern and southern climates change into each other for it is between two plains, the North China Plain and Chang Jiang R (the Yangtze).-Huai He R. Plain. Droughts and floods in …     

THE ROLE OF THE QINGHAI-XIZANG PLATEAU IN FEEDBACK MECHANISMS AFFECTING THE PLANETARY CIRCULATION

3. Observational Evidence. Figure 7 shows the Line Island precipitation index from 1910 to 1975. This indexwas computed and combined for the precipitation stations of Fanning Island, Washing-ton Island and Christmas Island. It is defined by assigning the value of 100 to thewattest in a long series of months, say January, and the value 0 to the driest month inthe same series. The interval between the wettest and driest month of January is thus     

THE EFFECTS OF THE ARCTIC SEA ICE ON THE VARIATIONS OF ATMOSPHERIC GENERAL CIRCULATION AND CLIMATE

The SST anomaly of the central-eastern equatorial Pacific and the arctic sea ice anomalies of the four districts lo-cated respectively in 160°E—110°W,110°W—20°W,70°E—160°E and 20°W—70°E are taken as five separate factors.And the relationship between each factor and the atmospheric general circulation and the climate is investigated byobservational analysis and numerical experiments.It is shown that the effects of the arctic sea ice anomalies on the varia-tions of atmospheric circulation and climate are comparable to or even in some cases greater than that of EI Ninoevents.So one should pay much attention to the study of polar sea ice anomalies in climate research.     

NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION

A time-dependent linear model on the equatorial beta plane is developed in this paper.Its verticalstructure consists of two active layers with equal density and temperature above the thermocline and aquasi-stationary layer with constant density below the thermocline.The results of nurnericat experiments show that the direct influence of heat on the equatorial ocean ismuch smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction,the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibriumand anomalous development of the ocean-almosphere circulation.     

THE NONLINEAR INTERACTION BETWEEN DIFFERENT WAVE COMPONENTS AND THE PROCESS OF CYCLE OF GENERAL CIRCULATION

By using a two-level quasi-geostrophic truncated spectral model taking account of the nonlinear interaction between different wave components (i. e. basic current, ultra-long waves and long waves), the index cycle of general circulation is investigated. The calculated results show that the circulation index has a, quasi-periodic vacillation with a period of 8 to 16 days, which can be created by the nonlinear interaction and that the nonlinear interaction between different wave components may cause the tilted-trough vacillation, amplitude vacillation of wave pattern and quasi-periodic change of wave number of flow pattern.     

THE DYNAMIC EFFECT OF THE TIBETAN PLATEAU ON THE FORMATION OF ZONAL TYPE CIRCULATION OVER EAST ASIA

From a statistical study of the atmospheric circulation types over the Northern Hemisphere it is found that the zonal type circulation predominates in East Asia. From a three-layer primitive equation model in σ-coordinate, the orographic effect on a westerly current over the Northern Hemisphere is studied. A distinguished deepening trough is observed in the lee-side slope of the Rocky Mountains. But a pronounced trough is over the East Asia coast far from the Tibetan Plateau. In a case of 48 h numerical forecast, it is found that the effect of the Tibetan Plateau tends to build up a rather zonal type circulation, which is con-sistent with the observations. These may be partly explained by the topographic effect of the north slope of the Tibetan Plateau in a simple geostrophic theory.     

THE EFFECTS OF THE QINGHAI-XIZANG PLATEAU ON THE MEAN SUMMER CIRCULATION OVER EAST ASIA

Four numerical experiments of simulation have been conducted in this paper by the use of a five-layer primitive equation numerical model with incorporated pressure-sigma vertical coordinate system. The initial fields are taken from the July zonal mean data of many years, while the heat sources and sinks are ideally specified according to the mean heating field over the East Asia calculated from the real data of July, 1979. On the basis of simulated results of temperature and geopctential height patterns we emphatically discuss the effects of the topography and the heating of the Qinghai-Xizang Plateau. From the analyses in this paper, it appears that the heating over the Bengal region makes a larger contribution to the middle and the south branches of the monsoon cell and is also the main cause for the existence of the southerly channel to the east of the Plateau, for the break of the subtropical anticyclcne belt below the 500 hPa level and for the formation of the summer Asian anticyclone at the 300 hP     

LAGRANGIAN METHOD USED IN THE RESEARCH OF ATMOSPHERIC CIRCULATION

Based on the conservation of entropy and potential vorticity in adiabatic atmospheric motion without theconsideration of friction,calculation is made of the trajectory of a particle on an isentropic surface by use ofthe data of FGGE III-b.Results of several calculation schemes of the trajectory discussed show that thelocal data interpolation and Runge-Kutta time-integral scheme is the best.The calculated trajectory reflectsthe large-scale atmospheric motion only and the small-scale motion emerges as a deviation term of thecalculated trajectory.And then the outbreak and propagation of planetary wave are studied by means ofthe deformation of a material line,with the result showing that the material line can be tracked in the trop-osphere only in a few days,beyond which the interaction between the small-scale waves and large-scale motionleads to its dramatical twisting and deformation.Therefore,the Lagrangian method is assumed to be an effectivemeans of diagnostic research in the nonlinear interaction in atmospheric circulation,in addition to the generalstudy of the atmospheric circulation.     

THE NUMERICAL SIMULATION OF THE THREE-DIMEN-SIONAL TELECONNECTIONS IN THE SUMMER CIRCULATION OVER THE NORTHERN HEMISPHERE

In this paper, a quasi-geostrophic, 34-level spherical coordinate model with Rayleigh friction, Newtonian cooling and the horizontal eddy thermal diffusivity is used to simulate the three-dimensional telecon nection in the summer circulation over the Northern Hemisphere.The computed results show that the change of the heat source over the Tibetan Plateau may cause the change of the atmospheric circulation over the middle and high latitudes in the Northern Hemisphere. When the heal source over the Tibetan Plateau is enhanced, it may cause the Tibetan high to enhance over South Asia and cause the change of the atmospheric circulation over East Asia and North America, i. e., Northeast China and North Japan will be controlled by a trough, which brings about a cold summer in this area. In the same way, an anticyclone will be enhanced over the Okhotsk sea. Moreover, another trough will be formed over Alaska, while another ridge will develop to the northeast of North America. Besides, the Pacific subtropical high will be weakened. These results are in good agreement with those obtained from the observed data.     

THE INFLUENCE OF EDDY VISCOSITY ON THE SUBTROPICAL PLANETARY-SCALE CIRCULATION IN SUMMER

The influence of eddy viscosity on the distribution of subtropical quasi-stationary planetary waves in summeris analysed theoretically.It is found that since the basic flow is very weak,the eddy viscosity may play an impor-tant role for the subtropical planetary-scale motion in summer.A linear,quasi-geostrophic,34-level spherical coordinate model is also utilized to calculate the differencesof quasi-stationary planetary waves and of quasi-stationary disturbance pattern responding to forcing bytopography and heat sources under the different eddy viscosities.The computed results show that thecoefficient of eddy viscosity considerably influences the strength of the subtropical planetary-scale circulationin summer.     

THE MEDIUM-RANGE VARIATIONS OF THE SUMMER MONSOON CIRCULATION SYSTEM OVER EAST ASIA

The Asian monsoon circulation system can be divided into two subsystems, i.e., the East Asian monsoon system(EA MS) and the Indian monsoon system (IMS). In this paper the main elements including the Indian monsoon trough, the South Asian high. the upper easterly jet etc. and the interactions between EAMS and IMS arc dealt with. The basic emphasis is put on the medium-range variations of the EAMS. Some significant results arc obtained.     

THE EARLY SUMMER FLOOD PERIODS OF SOUTHERN CHINA AND THE SUMMER MONSOON CIRCULATION OF EAST ASIA

Based on the thermodynamic characteristics of the summer monsoon and foe change of the lower layer wind fields, the relation between the early summer flood periods of southern China, Including the first flood period of South China and the plum rains period of the middle-lower reaches of the Yangtze River and the activities of the summer monsoon is analysed.The establishment processes of the summer monsoon circulation of East Asia are investigated.It is shown that the beginning and ending of the flood periods are exactly in accordance with the arrival and departure of the fore boundary of the summer monsoon.The establishment process of the circulation from the very beginning of the arrival of the monsoon to the time of great prosperity of development are not the same for each year.They can be classified into four categories.Each category may have four or three stages.Besides, the structure of the summer monsoon regime of East Asia is not unitary.There exist four types of structure model of the monsoon regime of East Asia.     

INFLUENCE OF 200 hPa DIVERGENCE CIRCULATION ON THE TRACKS OF TROPICAL CYCLONES

The characteristics of 200 hPa divergent wind and velocity potential have been analysed for four kinds of tropical cyclone tracks having impact on the SOuth China Sea.It is found that the difference of monsoon circulation in 200 hPa divergence wind field may affect the medium-range movement characteristics of tropical cyclone tracks.Corresponding to the west Pacific subtropical high,the orientation of 200 hPa secondary convergence line and its extension to the west may indicate the variability of track types.The direction of tropical cyclone movement is 2 longitudes west of and parallel to the 200 hPa secondary divergence line.     

ANOMALIES OF THE BACKGROUND CIRCULATION OF THE IAP GCM MODEL ATMOSPHERE IN AN EL NINO YEAR

Analysis is performed of the May-September mean circulation,referred to as the background circulationhereinafter,in the IAP(Institute of Atmospheric Physics,Academia Sinica)GCM model atmosphere,It is foundthat in an El Nino year there occur anomalies in a set of major systems,e.g.,Southetm Oscillation,Walker andHadley circulations,the western Pacific subtropical high and ITCZ,2nd in large-scale precipitation,with theirhappening dominantly in the Northern Hemisphere tropical and subtropical latitudes in the western Pacific.These results that are in rough agreement with the analyz(?)d actual observations demonstrate the applicabilities ofthe model to the study of low-latitude circulations.     

RESPONSE OF THE ATMOSPHERIC GENERAL CIRCULATION TO WINTER SNOW COVER ANOMALY

In this paper,the response of the atmospheric general circulation to winter anomalous snowcover was investigated through observations studies and model simulation.Results from the observations show that:(1)the anomalous winter snow cover in theextratropics of Eurasian Continent bears an intimate relation to the contemporary atmosphericgeneral circulation.The positive anomaly of winter snow cover is usually accompanied by positiveatmospheric EUP teleconnection pattern and stronger East Asian winter monsoon:or vice versa.(2)The linkage between them suggests that the abnormal winter snow cover has an importantimpact on winter atmospheric general circulation.The anomalous snow cover pattern can lead tothe anomaly of winter atmospheric EUP teleconnection pattern and thus influence East AsianWinter monsoon.With NCAR CCM2 including BATS land surface scheme,three groups of experiments wereperformed to examine the atmospheric response to the anomalous snow cover pattern and explorethe relevant mechanism.Simulated results agree well with the observations,which testify thesignificant response of the atmosphere to snow cover anomaly.It is found that the radiative coolinginduced by anomalous snow cover plays an important role in above processes,and the feedback oflong-wave radiation can not be neglected.     

EFFECTS OF THREE-DIMENSIONAL STRUCTURE OF HEATING FIELD ON THE SUMMER MONSOON CIRCULATION IN ASIA

In this paper,a primitive equation linear wave model is used to examine the effects of three-dimen-sional structure of heating field on the behavior of stationary planetary waves in summer and to comparethe roles of different heating functions for the formation and maintenance of summer monsoon circulationin Asia.It is shown that the aloft heating connected with the latent heating,especially the deep condensationheating associated with the cumulus convection in low latitudes,plays a crucial part in the Asian summer mon-soon and the structures of planetary wave responses are quite sensitive to the vertical distribution of heating.