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.     

NONLINEAR WAVES IN BAROTROPIC MODEL

In this paper, from the system of equation describing a barotropic atmosphere using the method of Taylor expansion for the nonlinear terms, the periodic solutions of the nonlinear inertio-surface gravity waves and Rossby waves have been obtained.The finite-amplitude nonlinear inertio-surface gravity waves and Rossby waves with horizontal divergence satisfy all the KdV equation. The solutions are all the cnoidal function, i, e., the cnoidal waves which include the linear waves and form the solitary waves under certain conditions. For the finite-amplitude Rossby waves with horizontal divergence, we find the new dispersive relation including both the wave number and the amplitude parameter. In case of small amplitude it is reduced to the Yeh formula. It is shown that the larger the amplitude and width, the faster the finite-amplitude inertio-surface gravity waves and the slower the finite-amplitude Rossby waves with horizontal divergence propagate. The blocking or cut-off system in which the amplitude and width are large may be considered as Rossby solitary waves.     

AN IMPROVED LAND-SURFACE PROCESS MODEL AND ITS SIMULATION EXPERIMENT—PART II:COUPLING SIMULATION EXPERIMENT OF LAND-SURFACE PROCESS MODEL WITH REGIONAL CLIMATE MODEL

The Land-surface Process Model(LPM-ZD)has been successfully coupled with the regionalclimate model RegCM2 of NCAR.Then thus-obtained coupled model(CRegCM)has been appliedto simulate the climate characteristics of heavy rain in middle and East China for three months fromMay to July 1991.and compared with model output of NCAR-RegCM2 using BATS as land-surface process scheme,abbreviated as NRegCM.The results show that CRegCM has good abilityand performance.CRegCM successfully simulates the extreme precipitation event and thesimulations of CRegCM for surface temperature and some physical variables related to land surfaceprocess are more reasonable than those of NRegCM.     

INTERDECADAL VARIABILITY IN A MODEL ATMOSPHERE

By using the simulation results of an AGCM, which had been run from 1945 to 1993 forced by COADS SST, the interdecadal variability of the model atmosphere was investigated and compared with that of NCEP reanalysis data. It was found that, interdecadal variability exists significantly in both the tropical Pacific wind fields and the mid-high latitude atmospheric circulation of the model atmosphere. The tendency of time variation and spatial distributions of the interdecadal variability of the model atmosphere are basically consistent with observation. Relative to the mid-high latitude atmospheric circulation, the simulation of tropical Pacific wind is more satisfying, which suggests that anomalous variation of SST is still the main factor for the interdecadal variability of tropical Pacific wind. It might have more significant influence on the tropical wind than on the mid-high latitude atmosphere. However, there is still obvious difference between the simulation and observation. They could be attributed to both the simulation capability of the model and absence of other factors in the model which are important for the interdecadal climate variation.     

NUMERICAL SIMULATION EXPERIMENTS BY NESTING HYDROLOGY MODEL DHSVM WITH REGIONAL CLIMATE MODEL RegCM2/CHINA

Based on improvement of a distributed hydrology-soil-vegetation model (DHSVM for short)and its application to North China,a nested regional climatic-hydrologic model system is developedby connecting DHSVM with RegCM2/China.The simulated climate scenarios,including controland 2×CO_2 outputs,are downscaled to 8 stations in Luanhe River and Sanggan River Basins todrive the hydrology model.According to simulation results,under double CO_2 scenarios,annualmean temperature and evapotranspiration will increase 2.8C and 29 mm,respectively;precipitation also increase but with different value for each basin,6 mm for Luanhe River Basinwhile 46 mm for Sanggan River Basin;runoff change for the two basins is different too,27 mmdecrease for Luanhe River Basin while 26 mm increase for Sanggan River Basin.As a result,therunoff in future for Luanhe River Basin and Sanggan River Basin will be 74 mm and 71 mm,respectively,which is approximately a quarter of annual mean runoff(284 mm)of the wholecountry.Total streamflow for the two basins will decrease about 2.5×10~8m~3.All these indicatethat the warm and dry trend will continue in the two river basins under double CO_2 scenarios.Thenested model system,with both climatic and hydrologic prediction ability,could also be applied toother basins in China by parameter adjustment.     

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.     

A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PARTI:MODEL DESCRIPTION

A three-dimensional elastic nonhydrostatic mesoscale(β-γ)model with nested-grid is presented.It uses a set of fullequations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithmfor acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloudand free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloudmicrophysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future.     

A STEADY TWO-DIMENSIONAL CLIMATE MODEL WITH RESIDUAL CIRCULATION

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-temperature, 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 1-2℃ at the low latitude surface and 6-8℃ at the high latitude surface. It is shown that a 6% decrease in the solar constant is required for the - 10℃ ice edge to move from its present latitude -70° to-50°.     

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.     

A MODEL STUDY OF THE NOCTURNAL BOUNDARY LAYER

In this paper, a second-order model is proposed for the study of the evolution of the nocturnal boundary layer (NBL). The model is tested against the Wangara data on atmospheric boundary layer. The computer results show that the model can simulate some important characters observed in the NBL, and that a kind of sudden change may occur in the developing process of NBL.     

A THREE-DIMENSIONAL CLOUD-SCALE MODEL SUITABLE FOR COMPRESSIBLE ATMOSPHERE

A three-dimensional cloud-scale model has been designed.The governing equations of the model arecomposed of two groups of equations:one group includes compressible motion equations,continuity equation,pressure equation and thermodynamic equation,which are of Eulerian type,and the other consists of cloud-precipitation microphysics equations which are of Lagrangian type.Since the degree of influence of sound waveon the air motion is quite different from that on the temperature or hydrometeors,the time splitting procedureis used in solving governing equations.Both unstaggered and staggered meshes have been utilized.Integra-tion schemes adopted are the Eulerian backward difference method for the unstaggered mesh and semi-implicitmethod for staggered mesh.Several experiments of modelling have been conducted and a reasonable three-dimensional image of deep convection is obtained.With this model the horizontal and vertical vortex circula-tions are simulated.Furthermore,the effects of horizontal vortex on the formation and development ofdowndraft within cloud have also been studied.     

A STUDY OF 1.5-ORDER CLOSURE TURBULENCE MODEL

Based on turbulence theory,a 1.5-order closure turbulence model is established.The model incorporating with theground surface energy budget equation is constructed by means of a vertical one-dimensional(1-D)40-levelgrid-mesh.The numerical results reveal the 24-h evolution of the clear planetary boundary layer comparing with theWangara boundary layer data of days 33—34.The model also takes into account some physical processes of radiativetransfer and baroclinicity,revealing some important characteristics observed in the boundary layer,especially for theevolution of the mixed layer and low-level jet.The calculated results are in good agreement with the observational data.On the other hand,we also run the high-resolution model of the planetary boundary layer in the Mesoscale Model Ver-sion 4(MM4)with the same physical processes and initial conditions.The results show that the high-resolution modelcan not reveal those important characteristics as the 1.5-order closure model did.In general,it is shown that the 1.5-or-der closure turbulence model based on turbulence theory is better in rationality and reality.     

A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ) SCALE ATMOSPHERIC MODEL——PART Ⅱ:MODEL VALIDATION

By using the model developed in Part Ⅰ of the sister papers,simulations of severe storm,winter airflow and snowfall over a mountain,as well as mountain-valley winds and sea breeze are performed.Different functions of the model are verified through the computation and special emphasis is put on some important properties of the meso-(β-γ) systems frequently occurring.The simulation results of the cases are agreeable to field observations,conceptual models,and previous numerical studies.It is shown that the model is applicable for the researches and prediction of various local and/or regional weather processes,and capable of describing their macro-and micro-structures,influences of orographic and underlying-surface forcing,and interaction between meso-β and meso-γ scales.In addition,the evolutional characteristics and mechanisms of the modeled processes are also analyzed.     

A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PART Ⅰ:MODEL DESCRIPTION

A three-dimensional elastic nonhydrostatic mesoscale(β-γ) model with nested-grid is presented.It uses a set of full equations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithm for acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloud and free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloud microphysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future.     

THE MONTHLY PREDICTION EXPERIMENTS USING A COUPLED ANALOGY-DYNAMICAL MODEL

Considering from point of view of the dynamics,it is convenient to regard the field to be predictedas a small disturbance superposed on the historical analogous field,and thus the statistical technique can beused in combining with the dynamics.Along this line,a coupled atmosphere-earth surface analogy-dynamicalmodel is formulated and applied to making monthly prediction.This approach facilitated the utility of the useful information contained in both the historical data setand the initial field to improve the dynamic model based solo on the latter and show better skill in prediction.     

DESIGNATION AND APPLICATION OF A SPHERICAL LONG-WAVE SPECTRAL MODEL

A two-level,quasi-geostrophic long-wave model based on spherical coordinates was developed with theexplicit part belonging to a low-order model.However,it includes not only diabatic heating,Ekman fric-tion and mountain distribution,but also parameterized forcing effects of transfer properties of transienteddies.Experiment results showed that,due to the introduction of the parameterization of transfer propertiesof transient eddies,remarkable improvements on characters of low-order model had been obtained.Inaddition to its economization in calculation and conciseness in physics as in a low-order model,the long-wave model was shown to describe the energetics and angular momentum balance of the atmosphere much morereasonably,and to present the features of zonal mean westerlies and stationary waves much more correctlythan the corresponding low-order model.This kind of long-wave model was therefore regarded as suitablefor theoretical research and numerical modelling of some aspects of the general circulation of the atmosphere.     

THE SENSITIVITY TEST STUDY OF AIR-SEA SURFACE FLUX MODEL

In this article, a sensitivity test of air-sea surface flux model was carried out with the field observation data of Project “South China Sea Air-Sea Flux Measurement in 2000”. The results show that sensible heat fluxes are sensitive to observation errors, increasing the error of model calculation; In contrast, the latent heat flux and momentum flux are not as sensitive to observation errors as the sensible heat, and their calculated results are reliable. The test result also verifies…     

BMC LIMITED AREA MODEL GENERAL DESCRIPTION AND OPERATIONAL RESULTS

The limited area 5-level primitive equation model,as the first operational precipitation forecast model inChina,has been run at Beijing (National) Meteorological Center (BMC) for more than four years.The opera-tional results show that this model gives continuous services,and the forecast skill is satisfied for the forecastof some weather situations,such as extratropical cyclone,front and the precipitation associated with them.The forecast guides are widely used at the local weather services now.