MODIFIED MASS FLUX CUMULUS CONVECTIVE PARAMETERIZATION SCHEME AND ITS SIMULATION EXPERIMENT—PART Ⅰ:MASS FLUX SCHEME AND ITS SIMULATION OF THE 1991 FLOOD EVENT

Based on the existing cumulus convective parameterization schemes,a mass flux scheme(MFS)for cumulus convective parameterization has been successfully developed by reference to thework of Chen et al.(1996).The MFS is a comprehensive scheme.In MFS,not only theimportance of the large-scale moisture convergence is taken into account,but also it includes thecumulus updrafts and downdrafts,cumulus-induced subsidence in the environmental air.entrainment,detrainment and evaporation.The interaction between the cumulus and theenvironment is described by using a one-dimensional bulk model.At the same time the schemeincludes the penetrative and shallow convections.The MFS has been successfully incorporated into the regional climate model RegCM2developed by NCAR.The new model has been applied to simulate summer monsoon characteristicsand their variations of heavy rainfall process in the Changjiang-Huaihe River Basins for threemonths from May to July 1991.The results show that the new model can successfully simulate thisrainfall prolonged process.By comparising the model outputs of RegCM2.using the Kuo schemeand the MFS.it is found that the MFS is better in simulating the surface temperature,rainfallposition and amount,and rainfall duration.     

MODIFIED MASS FLUX CUMULUS CONVECTIVE PARAMETERIZATION SCHEME AND ITS SIMULATION EXPERIMENT—PARTⅡ:CUMULUS CONVECTION ACTIVITIES SIMULATED FROM THREE SCHEMES AND SENSITIVITY EXPERIMENTS BY USE OF MASS FLUX SCHEME*

By comparison of simulated cumulus convection processes in RegCM2,using the Kuo scheme,the Grell scheme and the mass flux scheme (MFS),it is found that the MFS can simulate the cumulus heating and moistening very well.A series of sensitivity tests show that the parameters for specifying the conversion coefficient from cloud droplets to raindrops,the turbulent entrainment and detrainment rates in updrafts anddowndrafts,and the intensity of the downdrafts have different degrees of influence upon the cumulus convection.Therefore.it is quite important for cumulus parameterization scheme to define these parameters as accurately as possible.     

MODIFIED MASS FLUX CUMULUS CONVECTIVE PARAMETERIZATION SCHEME AND ITS SIMULATION EXPERIMENT—PART II:CUMULUS CONVECTION ACTIVITIES SIMULATED FROM THREE SCHEMES AND SENSITIVITY EXPERIMENTS BY USE OF MASS FLUX SCHEME

By comparison of simulated cumulus convection processes in RegCM2,using the Kuo scheme,the Grell scheme and the mass flux scheme (MFS),it is found that the MFS can simulate thecumulus heating and moistening very well.A series of sensitivity tests show that the parametersfor specifying the conversion coefficient from cloud droplets to raindrops,the turbulententrainment and detrainment rates in updrafts anddowndrafts,and the intensity of thedowndraftshave different degrees of influence upon the cumulus convection.Therefore.it is quite importantfor cumulus parameterization scheme to define these parameters as accurately as possible.     

NUMERICAL MODELING OF CUMULUS CLOUD CHEMISTRY—PART Ⅰ.MODEL DEVELOPMENT*

A one-dimensional cumulus cloud chemistry model(ICCCM) is developed to simulate cloud physical processes and chemical processes during the evolution of a convective cloud.The cloud physical submodel includes a detailed microphysical parameterized scheme of 20 processes.The chemistry submodel is composed of three parts:gas phase chemistry,aqueous phase chemistry and scavenging of soluble gases.The gas phase reaction mechanism contains 85 reactions among 45 species including 13 organics.The aqueous phase reaction mechanism contains 54 reactions among 40 species and 12 ion equilibria.Mass of 19 gases is transported between the gas phase and the aqueous phase.With this model,studies may be made to analyze the interactions among processes during lifetime of a cumulus cloud.     

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.     

NUMERICAL EXPERIMENT ON THE SEASONAL VARIATION OF GLOBAL OCEAN AND THE EL NINO PROCESS——PART Ⅱ:NUMERICAL EXPERIMENT ON THE 1972-1973 EL NINO PROCESS*

In Part Ⅰ,the climatological state of the ocean has been simulated by integrating a 6-layer,4°×5°grid global ocean model up to 100 years.In this part,the forcing in 1971-1973 is calculated by COADS,and using the integrated result of the 100th year as the initial state,we simulated the El Nino process in 1972-1973.The results are as follows:(1)We have reproduced the 1972-1973 El Nino process and its cooling process in the equatorial eastern Pacific.The simulated distribution of SST and the intensity of El Nino are similar to the observations.(2)The results show that there are two kinds of processes in El Nino formation:(i)the warming occurs in the equatorial western Pacific,then propagates eastward to the central Pacific;(ii)the warm water forms near the coast of the South America and then,propagates westward along the equator.Observation indicates that the two processes were included in the El Nino in 1972.Our numerical experiment can simulate out both of them,although the first process is stronger than the second.In observation,the intensities of both processes are similar.(3)The El Nino process in 1972 can be simulated by running the model with the wind stress forcing,but its intensity is 1/2 the magnitude of observation.Only after adding the forcing of heat flux to run the model,its intensity can coincide with the observation.So the forcing effect of heat flux should not be ignored in the formation of El Nino,especially in the study of El Nino intensity.     

AN IMPROVED LAND-SURFACE PROCESS MODEL AND ITS SIMULATION EXPERIMENT——PART Ⅰ:LAND-SURFACE PROCESS MODEL AND ITS“OFF-LINE”TESTS AND PERFORMANCE ANALYSES

Based on the existing land-surface schemes and models,an improved Land-surface Process Model(LPM-ZD)has been developed.It has the following major characteristics:(1)The combination of physical equations and empirical analytical formulae are used to construct the governing equations of soil temperature and moisture.Higher resolution of model level and physical equations are adopted for the upper soil layers,and for the lower soil layers,lower resolution of model level is adopted and empirical analytical formulae are used.(2)In land surface hydrological process,the sub-grid distribution of rainfall and its effects are taken into account.(3)A simple snow cover submodel has been used,which includes effects of snow cover on soil thermodynamics and hydrology,as well as albedo.By use of this model and three groups of point observation data,a series of "off-line" tests have been carried out.The simulation results indicate that land-surface process model has good performance and can well simulate diurnal and seasonal variation of land surface processes for many kinds of land surface covers(forest,grass,crops and desert) in different climate zone.The results simulated by the model are consistent with the observations.Later,by use of one group of observation data and the model,a series of sensitivity experiments have been done.It is shown that the model is much sensitive to some parameters,such as initial soil moisture,vegetation physical parameters as well as the proportion of the grid covered with rain.Therefore it is much important for land-surface process model to define these parameters as accurately as possible.     

THE FORMATION MECHANISM OF CONCENTRIC DOUBLE EYE WALL TYPHOON—PART Ⅰ: DYNAMICAL ANALYSIS*

The strong vortex will mutually adjust the thermodynamic field and dynamic field to a state of gradient balance whilst forced by an external cold source,namely,the gradient adjustment process,in which a linearized two-layer model is dealt with in this paper.The analyses show that on account of the heterogeneous radial distribution of the cold source,the adjustment of the thermodynamic and dynamic fields results in the two-peak tangential wind feature,which is analogous to the character of concentric double eyewalls in the strong typhoon.Consequently,the gradient adjustment may be one possible mechanism for the formation of a concentric double-eye typhoon.     

NUMERICAL MODELING OF CUMULUS CLOUD CHEMISTRY-PART Ⅱ:THE IMPACT OF CUMULUS CLOUD PROCESSES ON OZONE CHEMISTRY*

Ozone chemistry processes are analyzed during a cumulus cloud process with the model（lCCCM）described in Part Ⅰ.The simulation results show that entire cumulus cloud process can be well described with the development of vertical velocities and liquid water content which are the two most outstanding features of cumulus clouds.Ozone chemistry is strongly influenced by cumulus clouds.NO_x can be transported upwards above 4 km in the first 20 minutes of the convection event and form a relative higher concentration area which enhances the production of ozone.Two areas appear during the convection event:area of net ozone production and area of net ozone depletion.The area of ozone depletion coincides with the area of liquid water within cloud.Results show that the aqueous phase（cloud water and rainwater）can alter gas ozone level through two ways:one is scavenging free radicals（HO₂）from the gas phase and thereby inhibiting the reactions of transformation to NO₂ from NO,which results in reduction of the gas source of ozone;the other is aqueous phase chemical reactions which consume ozone in the aqueous phase.Calculations reveal that the reaction O₃+OH→HO₂ is the main pathway of ozone depletion in gas phase during the process of cumulus clouds.     

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,     

ODD AND EVEN SYMMETRY OF ATMOSPHERIC CIRCULATION——PART Ⅱ:MEASUREMENT AND ANOMALY ANALYSIS*

First of all,for the odd and even symmetry components of both hemisphere circulations are given the absolute and relative measurements with which to examine the seasonal change and interannual abnormality of the components on the 1980-1986 monthly mean 500-hPa height charts.Results show a noticeable relationship between a major El Nino event and the component anomaly,with the even part anomaly almost-synchronizing with its culmination and that of the odd part about half a year prior to the event,a relation that is still more sharply manifested at the 200-hPa height field.     

DEVELOPMENT OF THE 2-D COUPLED STRATOSPHERIC-TROPOSPHERIC DYNAMICAL-RADIATIVE-CHEMICAL MODEL—PART Ⅰ:THE DESCRIPTION OF THE MODEL AND ITS PRELIMINARY RESULTS

In this paper,a two-dimensional(2-D)coupled stratospheric-tropospheric dynamical-radiative-chemical model has been developed,and some preliminary results have been given.From theseresults we can see that the latitude-height distribution characteristics and the seasonal variation ofthe dynamical fields such as atmospheric temperature,wind field,etc.can be effectively simulatedby using this model;and the modelled latitude-height distribution of trace gases gives theirdistribution characteristics and seasonal variation rather well.All of these are testimony to thestrong ability of the model.     

AN IMPROVED LAND-SURFACE PROCESS MODEL AND ITS SIMULATION EXPERIMENT——PART I:LAND-SURFACE PROCESS MODEL AND ITS“OFF-LINE”TESTS AND PERFORMANCE ANALYSES

Based on the existing land-surface schemes and models,an improved Land-surface ProcessModel(LPM-ZD)has been developed.It has the following major characteristics:(1)Thecombination of physical equations and empirical analytical formulae are used to construct thegoverning equations of soil temperature and moisture.Higher resolution of model level andphysical equations are adopted for the upper soil layers,and for the lower soil layers,lowerresolution of model level is adopted and empirical analytical formulae are used.(2)In land surfacehydrological process,the sub-grid distribution of rainfall and its effects are taken into account.(3)A simple snow cover submodel has been used,which includes effects of snow cover on soilthermodynamics and hydrology,as well as albedo.By use of this model and three groups of point observation data,a series of“off-line”testshave been carried out.The simulation results indicate that land-surface process model has goodperformance and can well simulate diurnal and seasonal variation of land surface processes for manykinds of land surface covers(forest,grass,crops and desert)in different climate zone.The resultssimulated by the model are consistent with the observations.Later,by use of one group ofobservation data and the model,a series of sensitivity experiments have been done.It is shownthat the model is much sensitive to some parameters,such as initial soil moisture,vegetationphysical parameters as well as the proportion of the grid covered with rain.Therefore it is muchimportant for land-surface process model to define these parameters as accurately as possible.     

NUMERICAL EXPERIMENT ON THE SEASONAL VARIATION OF GLOBAL OCEAN AND THE EL NINO PROCESS: ——PARTⅠ:CONTROL EXPERIMENT ON THE SEASONAL VARIATION OF GLOBAL OCEAN

A 6-layer,4°×5° horizontal resolution global ocean model has been designed and improved.After a 100-year integration,an equilibrium state has been reached from the upper to lower layers.By taking the mean state of last l0 model years as climatic state,we analyzed the characteristics of the seasonal variation in our model integration.The results show that the simulated seasonal variation is similar to the observed.So the design of our model is successful.Then,using the simulated climatic state of the seasonal variation as the initial state,and the observed stress and thermal state as the atmospheric forcing,we simulated the process of El Nino in 1972-1973 successfully.The simulated results of seasonal variation using our model will be presented in part Ⅰ.     

CHARACTERISTICS OF CONVECTIVE ACTIVITIES OVER ASIAN-AUSTRALIAN “LAND BRIDGE” REAS AND ITS POSSIBLE FACTORS*

Based on TBB data from GMS of Japan,NCEP/NCAR reanalysis data and precipitation data from CMAP(CPC Merged Analysis of Precipitation),an investigation is carried out of seasonal changes of precipitation and convection over Asian-Australian "land bridge" areas and its possible factors.The results show that the precipitation and convection over Sumatra take on clearly seasonal changes with abundant (less) rainfall in winter (summer).The convection over Sumatra moves northwestward rapidly along "land bridge" in the late-April and the early-May (the 25th pentad) and the rainfall shows similar variations.It is the accelerating of the convection moving that affects directly the subsequent enhancement of the convection over Indo-China Peninsula (ICP) area followed by the rupture of the subtropical high (SH) bands in this region leading to South China Sea (SCS) summer monsoon establishment.The zonal wind at lower troposphere in the equatorial Indian Ocean and the cross-equatorial flow in 105°E are the main factors associated with the accelerating of the convection moving northwestward along "land bridge".The further study suggests that the intensity of Sumatra convection has a close relation to the SST:when the central-east equatorial Pacific SST is warmer (colder),i.e.E1 Nino (La Nina) events,the SST in West Pacific warm pool is colder (warmer),Sumatra convection is weaker (stronger).     

NUMERICAL MODELING OF CUMULUS CLOUD CHEMISTRY—PART Ⅱ:THE IMPACT OF CUMULUS CLOUD PROCESSES ON OZONE CHEMISTRY

Ozone chemistry processes are analyzed during a cumulus cloud process with the model(1CCCM)described in Part Ⅰ.The simulation results show that entire cumulus cloud process can bewell described with the development of vertical velocities and liquid water content which are the twomost outstanding features of cumulus clouds.Ozone chemistry is strongly influenced by cumulusclouds.NO_x can be transported upwards above 4 km in the first 20 minutes of the convection eventand form a relative higher concentration area which enhances the production of ozone.Two areas ap-pear during the convection event:area of net ozone production and area of net ozone depletion.Thearea of ozone depletion coincides with the area of liquid water within cloud.Results show that theaqueous phase(cloud water and rainwater)can alter gas ozone level through two ways:one is scav-enging free radicals(HO_2)from the gas phase and thereby inhibiting the reactions of transformationto NO_2 from NO,which results in reduction of the gas source of ozone;the other is aqueous phasechemical reactions which consume ozone in the aqueous phase.Calculations reveal that the reaction O_3+OH→HO_2 is the main pathway of ozone depletion in gas phase during the process of cumulusclouds.     

THE FORMATION MECHANISM OF CONCENTRIC DOUBLE EYEWALL TYPHOON——PART Ⅱ:NUMERICAL SIMULATIONS*

In the context of a non-hydrostatic axisymmetric compressible numerical model,the concentric double eyewall structure of the typhoon was replicated well to discuss the formation mechanism of concentric eyewall with the aid of gradient wind adjustment.Evidence suggests that in the weakening phase of the typhoon,the heterogeneous radial distribution of the sensible and convective latent heating over the sea surface will induce the gradient wind unbalance accompanied by mutual gradient wind adjustment between the thermodynamic field and dynamic fields,which results in a two-peak tangential wind and concentric double eyewall structure.     

NONHYDROSTATIC NUMERICAL SIMULATION FOR THE “96.8” EXTRAORDINARY RAINSTORM AND THE DEVELOPING STRUCTURE OF MESOSCALE SYSTEM*

During the period of 3—5 August 1996(for short "96.8"),an extraordinary rainstorm event occurred in Henan,Hebei and Shanxi Provinces in China,resulting in severe flood catastrophe.Synoptic analyses indicated that the stable gross col field and the interaction between a northward moving typhoon(down into low pressure)and its east lateral Pacific subtropical high were the large-and meso-scale circulation conditions of the "96.8" extraordinary rainstorm.The mesoscale typhoon-low and its specific dynamical and thermodynamical structures were directly related to this rainstorm event.The nonhydrostatic version of mesoscale numerical model MM5 was used to conduct investigation of numerical simulation for this case.The simulation with the full physical processes of nonhydrostatic version MM5 was basically possessed of a capability to reproduce the genesis,development and evolution of the large-scale and meso-α scale synoptic systems.The simulative results using a two-way interactive nesting procedure revealed that the typhoon-low was possessed of an intensive coupled mechanism between the dynamical and thermodynamical fields,namely,the developing typhoon-low was possessed of a structure of the.cyclonic vorticity column with warm center and high humidity,the vorticity column on the lower levels was the moist convective instability and negative moist potential vorticity structure:the intensive ascending vertical motion and the intense divergence on upper levels and intensive convergence on the lower levels as well as the development of the convective cloud cluster were intercoupling:the intense southern wind jet companied by the typhoon-low was not only the interaccompanying and intercoupling condition of the development and maintenance of the typhoon-low and convective cloud cluster,but also was the transportable belt of the moisture source and heat energy of the "96.8" extraordinary rainstorm.The analysis of simulative results of precipitation indicated that the distribution of the rainfall belt and rainfall rate was basically consistent with that of the observation in spite of some rainfall centers less or larger than those of the observation for coarse or fine mesh domain,respectively.     

NUMERICAL EXPERIMENT ON THE SEASONAL VARIATION OF GLOBAL OCEAN AND THE EL NINO PROCESS——PART Ⅱ:NUMERICAL EXPERIMENT ON THE 1972—1973 EL NINO PROCESS

In Part Ⅰ,the climatological state of the ocean has been simulated by integrating a 6-layer,4°×5°grid global oceanmodel up to 100 years.In this part,the forcing in 1971—1973 is calculated by COADS,and using the integrated result ofthe 100th year as the initial state,we simulated the El Nino process in 1972—1973.The results are as follows:(1)We have reproduced the 1972—1973 El Nino process and its cooling process in the equatorial eastern Pacific.The simulated distribution of SST and the intensity of El Nino are similar to the observations.(2)The results show that there are two kinds of processes in El Nino formation:(i)the warming occurs in the equa-torial western Pacific,then propagates eastward to the central Pacific;(ii)the warm water forms near the coast of theSouth America and then,propagates westward along the equator.Observation indicates that the two processes were in-cluded in the El Nino in 1972.Our numerical experiment can simulate out both of them,although the first process isstronger than the second.In observation,the intensities of both processes are similar.(3)The El Nino process in 1972 can be simulated by running the model with the wind stress forcing,but its intensityis 1/2 the magnitude of observation.Only after adding the forcing of heat flux to run the model,its intensity can coin-cide with the observation.So the forcing effect of heat flux should not be ignored in the formation of El Nino,especiallyin the study of El Nino intensity.     

MAINTAINABLE MECHANISM OF MESO-β SCALE CONVECTIVE SYSTEM*

By means of the Penn State-NCAR Mesoscale Model Version 5(MM5)with a horizontal resolution of 20 km.the maintainable mechanism of Meso-β scale Convective System(MβCS)has been investigated on the basis of simulation of the temporal and spatial thermodynamics structure of the MβCS which occurred in Wuhan and its surroundings on 21 July 1998.The occurrence of the significant warm-core in the center of the MβCS happened in Changjiang River Basin between the Mufu Mountain and the Dabie Mountain.To the southern side of the MβCS,there exist the southwest low-level jet(LLJ)and the vertical secondary circulation in the low and middle troposphere respectively.In respect to the northern of the MβCS,the northwest jet emerges in the upper troposphere,accompanied with cold and dry atmosphere downdrafts,resulting in another secondary circulation.The foregoing mentioned vertical wind shear provides a favorable dynamical environment for the intensification and maintenance of the MβCS.Equally important,the latent heat release associated with the MβCS produces the warm center in the middle troposphere and the pressure falls.The pressure drop then accelerates air parcels toward the low leading to strong convergence as well as the intensified convection,establishing a positive feedback between the convection and the latent heat release,which is the thermodynamic mechanism of the development and maintenance of the MβCS.