TWO-DIMENSIONAL NUMERICAL HAILCLOUD MODEL

This paper describes a two-dimensional slab-symmetric hailcloud model,of which dynamics almost con-tains all the dynamic factors.The model with the improved precipitation process included can show the bipara-meter change of particle size-distribution.A new suspending lateral boundary condition is proposed whichmay improve the influence of boundary on the airflow within computing domain.The subroutines designedfor studying the change in outline of precipitating particle region can describe the interaction between airflowand precipitation particles.With this model the structure of weak ccho region in hailcloud is simulatedand the airflow patterns under different thermal disturbances and wind shear are studied.     

NUMERICAL SIMULATION STUDY OF HAIL CLOUD—PART Ⅰ:THE NUMERICAL MODEL

In order to study mechanisms of hailstone formation and hail suppression with seeding and toobtain optimum seeding technique for hail cloud,a 3-D compressive numerical seeding model forhail cloud is developed.The water substance in hail cloud is divided into 8 categories,i.e.,watervapor,cloud droplet,raindrop,ice crystal,snow.graupel,frozen drop and hail,and the detailedmicrophysical processes are described in a spectrum with two variable parameters and morereasonable particle number/size distributions.Then,the model is able to predict concentration andwater content of various particles.Especially.it can calculate the number of hailstones whosecores are graupel or frozen drop and apply to study mechanism of hailstone formation.Additionally,a conservative equation of AgI as seeding or glacigenous agent is found andnucleation by condensation of artificial nucleus,and nucleation by freezing of cloud droplet or raindrop which contact with AgI particle are considered.The dynamic energy flux of hail shooting onground is used to verify seeding effect.Therefore the model is also used to study mechanism of hailsuppression with seeding and the seeding technique,     

NUMERICAL STUDY OF TROPICS-EXTRATROPICS INTERACTION

A nonlinear steady-state baroclinic primitive-equation numerical model of atmospheric forced stationarywaves is used to investigate the tropics-extratropics interactions.Newtonian cooling,Rayleigh friction andbiharmonic horizontal diffusion are included in the model.The Eliassen-Palm (EP) cross-section and three-dimensional wave activity flux,which was derived by Plumb (1985) for linear quasi-geostrophic stationarywaves on a zonal flow,are used as diagnostics for the vertical and horizontal propagation of the waves.Results of the numerical experiments and diagnostics analyses suggest that the extratropical influenceon the tropical large-scale motion is important.The mid-latitude orographic forcing,especially of the Qing-hai-Xizang Plateau,and the extratropical thermal forcing make substantial contribution to the main-tenance of the cyclonic circulation over the eastern tropical and subtropical Pacific as well as the inversecirculation over the western Pacific in the upper troposphere.In addition,the longitudinal variation ofdiabatic heating in tropics has a significant influence on the wintertime stationary waves at higher latitudes.     

THE NUMERICAL MODELING OF RADIATION FOG

The formation and development of radiation fog are studied by using a one-dimensional model.Theresults are as follows:(1)The fog can change the ambient wind and temperature fields,on the contrary,theambient fields may also influence the fog;(2)The modeling fog forms initially at a certain level above thesurface,which is detailedly explained in the paper;(3)Turbulence delays the formation of fog but promotesits development;(4)Whether fog liquid water content exchange coefficient equals momentum exchangecoefficient has no influence on the numerical results.In addition,wind,temperature,exchange coefficient,and net radiative flux before and after the formation of radiation fog,are also studied.     

A NUMERICAL SIMULATION OF TYPHOON GENERATION

By using a two-dimensional axisymmetrical PEM in which two physical processes (the Ekman pumping and the vertical transportation of cumulus momentum) are included, the genesis and development of typhoons have been simulated. The results of numerical simulation show that the generation and structure of the typhoon simulated by the model involving both the physical processes are much close to a real one in the atmosphere as compared with that involving either the Ekman pumping or the cumulus momentum transport. Therefore, it can be suggested that the cumulus momentum transport and Ekman pumping together play an important role in the genesis and development of typhoons through the CISK mechanism.     

NUMERICAL SIMULATION ON ACIDIFICATION OF CLOUD WATER

The numerical simulation on the acidification of cloud water has been carried out withthe assumption that the cloud droplets forming on the sulfuric acid, sulfate and nitrate nucleidissolve acidic and alkaline gases and achieve a gas-liquid equilibrium in a very short time. The resultshows that the acidification of cloud water is not only related to the initial concentration ofacidic, alkaline gases and aerosol of cloud air, but also to the cloud water content.     

A NUMERICAL MODEL FOR HILLY-LAND GLOBAL RADIATION

Based on the simulations of the hilly-land topographic parameters,i.e.,average orientation and slope,and topographic screen angle,a theoretical model is detailed to greater extent for global radiation overhilly countries in terms of the experimental data.Three main aspects are examined:the model construction;numerical run with the model parameters;discussion of simulations obtained locally in the model run for thesouthern Dabie Mountains.Results show that the significant effect of the topography on global radiation.The present model applies inprinciple to the numerical simulation of global radiation for any form of topography of various regions.     

NUMERICAL EXPERIMENT OF SIX-LEVEL IMPLICIT PRIMITIVE MODEL

In this paper, a numerical test is carried out by using a six-level implicit primitive equation model defined in a πcoordinate. The model equations are solved with nonlinear iterated method, yielding fairly good results.However, it is time-consuming to solve the model with iterated method. Thus, this model is restored to the advective scheme and solved by means of a split method. Several actual examples are forecasted, which have yielded good results.     

A NUMERICAL MODEL OF MIXED CONVECTIVESTRATIFORM CLOUD

A 2-D slab-symmetric model of mixed convective-stratiform cloud is developed bysuperimposing convective cloud-size field on the convergence field,in order to simulate and studythe mixed clouds consisting of stratiform cloud and convective cloud.A deep convective,anelasticand conservative system of equations with basic variables(V,θ,π')is solved by a new method tocalculate dynamic field.The water substance in the cloud is divided into 6 categories and themicrophysical processes are described in spectrum with two variable parameters and morereasonable particle number/size distributions.To compare with measured radar echo intensity andstructure,the model may calculate echo intensity of the model cloud observed by radar.     

NUMERICAL SIMULATION STUDIES ON SHORT-RANGE CLIMATIC VARIATION

Several global and regional climatic models(including atmosphere models, ocean models and coupledatmosphere-ocean models)are improved and developed to simulate the predictability of short-range(i.e.monthly,sea-sonal,interannual)climate variability,based on the understanding of global and regional climatic characteristics andprocesses,and according to the theorem of climatological dynamics.The results of numerical experiment show that someare very encouraging,some others reveal problems existed.However,the model and data are being more and more ad-vanced.     

NUMERICAL EXPERIMENTS ON DYNAMIC MECHANISM OF BLOCKING

By using a two-level quasi-geostrophic spectral model, the numerical experiments on blocking process affected by thermal forcing are conducted. The dynamic mechanisms of blocking, including the resonance between wave and forcing, the control effects of thermal forcing on the position and intensity of the highs and the instabilities of two kinds of equilibrium states are studied by controlled experiments.     

ERROR GROWTH IN NUMERICAL PREDICTION AND ATMOSPHERIC PREDICTABILITY

The article is to report some results of numerical experiments on the error growth and the atmosphericpredictability Experiments with two-level global baroclinic primitive equation spectral model have mainresults as follows.The magnitude of initial errors directly affects the error growth,but its distributionform has little effect on the growth.The loss of predictability resulting from small-scale error is much greaterthan that from large-scale error.The small-scale error rapidly grows and is transferred to the large-scaleerror by interaction between different scale waves,which stimulates the growth of error for the whole systemOrographic forcing restrains planetary-scale error(wavenumbers 0—3)but enhances the small-scale error(wavenumbers 8 or greater).Hence,orographic effects on the error growth closely depend on the characteris-tic scale of initial errors,and there may be a critical wavenumber between 4 and 7.The error growth is great-er in Northern Hemisphere than in Southern Hemisphere if initial errors are the same.In the end we givesome discussions about model,initialization scheme,etc.,to improve model prediction.     

SIMPLIFIED DYNAMICAL ANOMALY MODEL FOR LONG-RANGE NUMERICAL FORECASTS

In this atmosphere-ocean-land coupled model, two basic ideas are developed, One is that the observational climate field is utilized and only the anomalous components are predicted. The other is that the transient Rossby wave is treated as the meteorological "noise" on the long-term variation that must be predicted in a climate forecasting. According to the latter, the transient Rossby wave can be filtered by omitting the partial derivative with respect to time in the atmospheric vorticity equation. But the time derivative term is still kept in the thermal equation for underlying ocean and land. With this assumption, the vorticity equation becomes time-independent, i.e. it is only a balance relationship between the anomaly geopotential height field and earth's surface heating field. This model is different from the usual GCM, so it may be called as the filtered anomaly model (FAM).A dozen examples of one month prediction are summarized in this report.     

NUMERICAL EXPERIMENTS ON THE TROPICAL AIR-SEA INTERACTION WAVES

By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that whenthe Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in theocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of theeastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,thelarger the eastward propagating components of the air-sea interaction waves.The results of the numerical experimentsare in good agreement with those of the theoretical analysis(Chao and Zhang,1988).     

NUMERICAL SIMULATIONS OF β-GYRES IN TROPICAL CYCLONES

1INTRODUCTIONEversincethe1940抯,thetropicalcyclone(TC)hasbeenviewedasapointvortexorrigidvortex.Thepredictionissummedupasoneforairflowintheambientfield.Themethodusuallysucceeds.Thesteeringtheoryfortheairflowbecomesitstheoreticalfoundation.Thoughwithsomesuccess,theactualtrackofTCmovementcanbemuchdeviatedfromthesteeringcurrent,asseeninroutineforecastpractice.Withoutmuchchangesintheambientsteeringcurrent,theTCcanhaveunexpectedchangesinthedirection,speedofmotionorintensity.Atypicalexamplewo…     

NUMERICAL STUDY OF QUASI-BIWEEKLY OSCILLATION IN TROPICAL ATMOSPHERE

By using a P-σ incorporated coordinate five-layer primitive equation spherical band model with surfacetemperature controlled by the heat balance equation,a simulation is done of disturbance formation in ananomalously warm SST area and of the quasi-biweekly oscillation(QBWO)of the disturbance,and associatedrainfall and SST with SST being 1/3 period of oscillational phase ahead of rainfall.The study shows that theoscillation is produced by cloud-radiation interaction.Initial anomalously warm SST in the mid-western Pa-cific causes stronger oscillation than in the eastern.Hence the oscillation gets attenuated during the eastwardmovement of the disturbance.     

NUMERICAL SIMULATION OF ACIDIFICATION PROCESSES IN COLD CUMULUS CLOUDS

In this paper, a 1-D time dependent cold cumulus chemistry model is presented. In the coldcumulus model, 4 categories of hydrometeors: cloud drops, raindrops, cloud ice crystals, graupelparticles, and 18 microphysical interactions are considered, In the chemical model, the source andsink terms for pollutants include: the complicated interactions between pollutants (gases andaerosol particles) and the hydrometeors (especially ice crystals and graupel particles), the ex-changes of chemical compounds between two hydrometeors accompanying microphysical processesand the aqueous oxidations of S (IV) to S (VI). The two models are combined to study the acidifi-cation processes in cold cumulus clouds.     

A NUMERICAL ANALYSIS ON TYPHOON ASYMMETRIC STRUCTURE AND MOTION

Five prediction experiments are carried out with two typhoons in 1992 using a limitedarca primitiveequations and two-way interactive model in a movable,nested mesh. The result indicates good agreementin terms of motion between the prediction and observation. Studying the asymmetric structure in the cases selected, a close link is uncovered between the temporal evolutions of the structure and the track of motion in a tropical cyclone. Understanding of real asymmetric structure will help to improve the skill offorecasting tropical cyclones.     

NUMERICAL STUDY OF OROGRAPHIC INFLUENCE ON LOW FREQUENCY OSCILLATION

Orographic effects on monthly-and seasonal-scale low frequency oscillation are investiged in terms of a five-level global spectral model with a triangle truncation at wavenumber 10 that contains relatively full physical parameterization, followed by analysis and comparison of the lowpass filtered data separately obtained from models with and without orography. Results show that remarkable seasonal characteristics are displayed in the orographic forcing-generated low frequency wavetrain on monthly and seasonal scales. It is found that the Northern Hemisphere summer orography-produced tropical heating acts as source of the low-frequency wavetrain for both hemispheres. Besides, the simulations indicate that the orographic wavetrain perturbation can give rise to the anomaly in the equatorial zonal flow, whose transient forcing will cause a new wavetrain in the Southern Hemisphere, thus completing the cross-equatorial propagation of the northern wave in interhemispheric action.     

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.