DIAGNOSIS ON LOW FREQUENCY COMPONENT OF ENSO VARIABILITY-PART Ⅱ:ORIGIN OF THE COMPONENT

Diagnosis is undertaken on the origin for the low-frequency component(LFC) of ENSO variability in the context of 1979-1990 OLR and u-wind datasets.Evidence suggests that ① a power spectrum-yielded maximum,significant statistically,is derived from the OLR monthly anomalies in a 3-5-year period range over the tropical central/western Pacific;②compositean alysis of the signals of the monthly anomaly low frequency component(period>3 years) confirms further the dynamic features of the component as documented in Part Ⅰ:③serving as forcing on ENSO,the related monsoon region represents the source area of the component;④the one-point correlation maps of unfiltered OLR monthly anomalies with zonal wind on a lagged,a simultaneous and a leading basis show clearly the close relation between the u wind-associated eastward travelling low-frequency wave and the low-frequency oscillation of low-latitude central/western Pacific large-scale convection and the east-moving mode is likely to be excited by the oscillation at a 3-5-year period range.It follows that the large-scale convection oscillation shows up as the origin of the eastward waves,i.e.,ENSO LFC.     

DIAGNOSIS ON LOW FREQUENCY COMPONENT OF ENSO VARIABILITY—PART Ⅱ:ORIGIN OF THE COMPONENT

Diagnosis is undertaken on the origin for the low-frequency component (LFC) of ENSOvariability in the context of 1979—1990 OLR and u-wind datasets.Evidence suggests that ① apower spectrum-yielded maximum,significant statistically,is derived from the OLR monthlyanomalies in a 3—5-year period range over the tropical central/western Pacific;②compositeanalysis of the signals of the monthly anomaly low frequency component (period>3 years)confirms further the dynamic features of the component as documented in Part Ⅰ:③serving asforcing on ENSO,the related monsoon region represents the source area of the component;④theone-point correlation maps of unfiltered OLR monthly anomalies with zonal wind on a lagged,asimultaneous and a leading basis show clearly the close relation between the u wind-associatedeastward travelling low-frequency wave and the low-frequency oscillation of low-latitude central/western Pacific large-scale convection and the east-moving mode is likely to be excited by theoscillation at a 3—5-year period range.It follows that the large-scale convection oscillation showsup as the origin of the eastward waves,i.e.,ENSO LFC.     

DIAGNOSIS OF LOW FREQUENCY COMPONENT OF ENSO VARIABILITY—PART Ⅰ:GLOBAL-SCALE DYNAMIC CHARACTERISTICS OF THE COMPONENT

Composite investigation is performed of global dynamic characteristics of >3—4-year period low-frequency oscillation in ENSO variability of air-sea coupling in the context of monthly mean wind andSSTA.Evidence suggests that the horizontal(vertical)anomaly circulation at tropical latitudes(equatorial)exhibits their evolution to be,in substance,a kind of low-frequency wave slowly travel-ling eastward,featured by wave number 2 moving along the equator and zonal wind swiftly decayingoff the equator in relation to divergence/convergence:the time that the low-frequency wave takes tomove around the equator in its halfway is precisely the period of the ENSO low-frequency component(LFC)(approximately 4 years);the ocean also displays corresponding response to the component.     

AN ANALYSIS OF THE CAUSES OF MEANDERING TRACKS OF TYPHOONS

Criteria of the free meandering tracks of typhoons are derived from the genera! solutions of typhoon motion equations. It is suggested that the meandering motion of a typhoon is caused by the combination of the internal force, the initial speed of the typhoon and the average pressure gradient force of the typhoon volume affected by the environmental pressure field. It is also revealed that under specified circumstances, the meandering may be caused only by the typhoon's internal force. Finally two examples of fitting calculation are given for illustration.     

ELEMENTARY VIEW OF GREENHOUSE EFFECT OF THE ATMOSPHERES OF VARIOUS PLANETS

The global mean temperatures of the atmosphere and the surface of various planets of the solar system are deter-mined by taking the system as in radiative equilibrium,with the atmosphere taken as transparent to solar radiation butwith an albedo α,and composed of N layers each of which absorbs all infrared radiation that falls on it,and a top layerof partial absorptivity a,while the surface is taken as black.It is found that,for the earth's atmosphere with α=0.33,N=0,a=0.83,it gives the current observed mean surface temperature T_s=15℃ and the effective mean radiative temper-ature of the atmosphere T_a=242.6K.On the other hand;the atmosphere of Venus is characterized by α=0.70 andN=70,which yields a surface temperature of about 700K.It is also found that surface evaporation and absorption of solar radiation by the atmosphere tend to lower the sur-face temperature.     

ON DIAGNOSTIC ANALYSIS OF ENERGY FIELDS OF EXPLOSIVE ENHANCEMENT OF TYPHOON OFFSHORE

The energetics process of offehore typhoon in three kinds of explosive enhancement (T_EE) are ana lyzed using ECMWF data. The results are as follows: (a) During the explosive development process,the enhancement of the rotational kinetic enersy (K_W) is mainly in the lower troposphere while that ofthe potential energy (PE) is in the upper troposphere. The magnitude of rotational kinetic energy islargely bigger than that of divergent enersy (K_Χ). (b) The environmental energy advected into the typhoon was about 30% of the internal increment of typhoon energy. The magnitude of energy was an order larger than increment of typhoon energy. (c) Among those three kinds of explosively developed typhoon, the enersy transformation mechanisms are different. (d) The influence of environment fields onabrupt intensification of typhoons couldn't be overestimated.     

ANALYSIS OF AMBIENT FIELDS AND SATELLITE IMAGERY CHARACTERISTICS OF EFFECT OF BAY OF BENGAL STORMS ON LOW- LATITUDE PLATEAU

Based on the composite analysis method, 12 rainstorms triggered by Bay of Bengal storms(shortened as B-storms hereafter) across the whole province of Yunnan were studied, and some interesting results of rain and circulation characteristics influenced by the storms were obtained for low-latitude plateau.Usually, when a rainstorm weather occurs in low-latitude plateau, the B-storm center locates in the central,east or north parts of the Bay of Bengal. At the same time, the subtropical high ridge moves to 15°N - 20°Nand the west ridge point moves to the Indo-china Peninsula from the South China Sea and the low-latitude plateau is controlled by southwest air streams coming from the front of the trough and the periphery of the subtropical high. The southwest low-level jet stream from the east side of the bay storm has great effect on heavy rains. On the one hand, the southwest low-level jet stream is playing the role of transporting water vapor and energy. On the other hand, the southwest low-level jet stream is helpful to keep essential dynamical condition. From the analysis of the satellite cloud imagery, it is found that mesoscale convection cloud clusters will keep growing and moving into the low-latitude plateau to cause heavy rains when a storm forms in the Bay of Bengal.     

AN IMPROVEMENT OF STATISTICAL PREDICTION OF TYPHOON TRACKS

In this paper, a statistical interpretation composite forecast model for typhoon track is set up by using numerical forecast products and several forecast schemes. Tested in 1994 typhoon season, its forecastperformance is much better than that of a previous statistical forecast model. The test shows that it is aneffective method that sufficiently Anproves objective forecast of typhoon track using the numerical forecast output products obtained in forecast and adopting several schemes in composition.     

AGROCLIMATIC BASIS OF OPTIMUM SEEDING TIME OF CROPS

In this article the theoretical method to determine the optimum seeding time of wheat and maize isestablished.For wheat,it is based on the close relationship between accumulated temperature and numberof leaves on the main stalk as well as number of stalks per plant of wheat,and for maize,based on theclimatic potential productivity model of maize.Using these models,we found that the optimum seeding time should be,for winter wheat,decided byaccumulated temperature from seeding date to the beginning of dormancy,and for maize,postponed forabout 30 days for medium variety and about 50 days for early variety in contrast with traditional seedingtime.Besides,through analysing climatic data the agroclimatic pattern of optimum seeding time for bothcrops in Beijing area has been found as well.     

GROUND-BASED MEASUREMENTS OF COLUMN ABUNDANCE OF OZONE AN

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AN ANALYSIS OF THE CHARACTERISTICS OF EQUATORIAL WESTERLIES

The real-time data of the high level atmosphere obtained by the R/V Xiangyanghong No.5 involved in the international TOGA-COARE project at 2°S, 155°E and at fixed real time of 05, 11, 19 and 23 h GMT each day from Nov. 5, 1992 to Feb. 18, 1993 are used to analyze diagnostically the vertical structure of wind and humidity over the central area of the warm pool. The results show that (1) the lowfrequency oscillation of the equatorial westerlies (i. e. reconstruction-development-decline) is closely related to the vigour and interruption of the Asian-Australian monsoon (including air flow across the equator caused by East Asia cold wave), (2) the variabilities of the vertical structure of wind and humidity, and the processes of precipitation and gale weather in the troposphere of the warm pool area are closely related to the intensity of the equatorial westerlies, and (3) there are strong wind belts over the high and low level atmosphere in the western equatorial Pacific at the inception of the ENSO event, and jet flow at the high and low level atmosphere during the equatorial westerly burst.     

A THEORETICAL STUDY OF MULTI-WAVELENGTH LIDAR EXPLORATION OF OPTICAL PROPERTIES OF ATMOSPHERIC AEROSOLS

Feasibility is investigated of multi-wavelength lidar exploration of size distribution patterns (SDP) and -complex refractive indices (CRI) of aerosols in different layers of a stratified atmosphere, and an improved observational scheme is worked out for the optical parameters (extinction coefficients, angular scattering coefficients and their ratios) of the substance in layers homogeneous horizontally in optical depth obtained by a bi-static lidar system. Variations are examined of these parameters versus CRI (whose real part is 1.33-1.63 and imaginary 0.00-0.1) and working wavelengths (0.3472, 0.53, 0.6943 and 1.06 μm) in such SDP as Junge-3, 4 and 5. The Deirmendjian Haze M and L. A method is thereupon developed for retrieval of aerosols' SDP and CRI from these parameters and tested by suitable numerical experiments.     

INFLUENCES OF DIURNAL CHANGE OF SOLAR RADIATION ON SIMULATED PROPERTIES OF SUMMER MONSOON

Comparative experiments with and without the diurnal change of solar radiation are made inthis paper by use of an air-sea coupled 7-layer primitive equation modeling system in a zonal domainbetween 60°S and 60°N.The results show that the quasi-stationary patterns of the mean monsooncirculations are not evidently affected by the diurnal change of solar radiation.The main influencesmay come from the land-sea distribution and the orography.However,the inclusion of the diurnalchange of solar radiation into the model system may improve the intensities of the simulatedmonsoon circulations both at the high and the low levels.It can influence the distributive patternof precipitation to a larger extent.Without the diurnal change,precipitation in the interior of landwould decrease and in the coastal regions it would increase.The changes of the soil temperatureand the soil moisture are fairly correspondent to that of precipitation.The areas with increasingprecipitation and the areas with decreasing precipitation are distributed in the wave form.As to theinfluences on the monsoon development,the results indicate that the diurnal change of solarradiation can speed up the development of the monsoon in the early stage.Therefore,the inclusionof the diurnal change of solar radiation can make the model equilibrium state to reach earlier.     

A NUMERICAL SIMULATION OF THE DISTRIBUTION OF ACID PRECIPITATION IN CHONGQING AREA OF CHINA

A numerical model for the study of the regional acid precipitation is developed. The model consists of five parts: the distribution patterns of SO2 concentration, the mesoscale flow fields, the parameterization of SO2 transformation into SO4-, the parameterization of precipitation scavenging process, and the relationship between SO2 content in precipitation and ground level concentration of SO2 in the air. The distribution of SO2, SO2- and pH for all precipitations in Chongqing area during the period of July to October 1982 are simulated with the model. A comparison of the simulated results with experimental data shows that high SO2 concentration centres correspond to low pH centres. The source of the acid rain in Chongqing area is local air pollution which is due to the lower effective stack height, low wind velocity in the area, basin topography, and the use of coal with high sulphur content. The mechanism for the formation of the acid precipitation here may be different from that in the United States     

THE JUMP OF CLIMATE CHANGE OF TYPHOON ACTIVITIES

Based on data of typhoon over the West Pacific and the South China Sea for the last 40 years, theshort-term climate oscillation of typhoon activities was revealed. The result indicated that the climaticvariation of typhoon activities has a tendency of climatic jump in changes in early 1970's. It showed thatbefore the jump of change the number of typhoon was increased and the intensity of typhoon was intensified after which the tendency of variation went contrary. In addition, the increase of typhoon numberduring recent years suggested again the jump of climatic change in the late 1980's, but the intensity oftyphoon did not have the same change. The analysis indicated that the short-term climatic oscillation andthe jump of climatic change have certain physical background. Such climate change tendency of typhoonwas shown to be related to the climatic oscillation of general circulation and SST, especially to the WestPacific subtropical high.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

MEASUREMENT OF pH AND CHEMICAL ANALYSIS OF RAIN WATER IN RURAL AREA OF INDIA

Large number of rain water samples, at 7 rural locations in the semi-arid region of the DeccanPlateau were collected during 4 consecutive monsoon seasons (1979-1982).pH, conductivityand the major ionic components (C1~-, SO_4~= , NO_3~- , NH_4~+ , Na~+, K~+, Ca~(++), Mg~(++) of the abovesamples were determined. The pH of rain water was found to be highly alkaline and the valuesvaried from 6.4 to 7.8. Soil-oriented elements showed good correltioan (r~0.6) with pH valuesof rain water. The high concentration of soil-oriented elements, specially Ca~(++), is found to play animportant role in neutralizing the acidity of rain water and maintaining high alkaline pH. The studysuggested that the contribution of atmospheric aerosol of natural sources (sea and soil) to thechemical composition of rain water is more than that of anthropogenic origin.     

FURTHER STUDY ON THE PROPERTIES OF OPERATORS OF ATMOSPHERIC EQUATIONS AND THE EXISTENCE OF ATTRACTOR

The equivalent operator equation is derived from the full primitive nonlinear equations of theatmospheric motion and the properties and physical senses of the operators are studied.In theinfinite dimensional Hilbert space,the global asymptotic behavior of the atmosphere system withthe non-stationary external forcing is studied under the assumption of the bounded externalforcing.The existence theorems of the global absorbing set and the global attractor are obtained.Thus,the conclusions deduced from the large-scale atmosphere(Li and Chou 1996 a;1996 b)areextended to the general atmosphere.     

ARTIFICIAL NEURAL NETWORK CORRECTION OF ROUGH ERRORS OF OBSERVATIONS

In the context of tower measured radiation datasets.following the correction principle meetinga diagnostic equation in data quality control and in terms of a technique for model construction ondata and ANN(artificial neural network)retrieval for BP correction of radiation measurementswith rough errors available,a BP model is presented.Evidence suggests that the developed modelworks well and is superior to a convenient multivariate linear regression model,indicating its wideapplications.     

NUMERICAL STUDY OF THE ABNORMAL TRACK OF TYPHOON MAGGIE

Typhoon Maggie (1999) interacted with another tropical depression system and moved along a west-southwest track that is somewhat abnormal during its pre-landing stage. Two numerical experiments are carried out in this paper to study the effect of the interaction on the track of typhoon Maggie using the mesoscale numerical weather prediction model system with a tropical cyclone bogusing scheme developed by Center for Coastal and Atmospheric Research, the Hong Kong University of Science and Technology. Results show that the cyclone system interacting with Maggie is the main factor for the abnormal track of Maggie.