The Development of a Nonhydrostatic Global Spectral Model

With the development of numerical weather prediction technology,the traditional global hydrostatic models used in many countries of the world for operational weather forecasting and numerical simulations of general circulation have become more and more unfit for high-impact weather prediction.To address this,it is important to invest in the development of global nonhydrostatic models.Few existing nonhydrostatic global models use consistently the grid finite difference scheme for the primitive equations of dynamical cores,which can subsequently degrade the accuracy of the calculations.A new nonhydrostatic global spectral model,which utilizes the Eulerian spectral method,is developed here from NCAR Community Atmosphere Model 3.0(CAM3.0).Using Janjic's hydrostatic/nonhydrostatic method,a global nonhydrostatic spectral method for the primitive equations has been formulated and developed.In order to retain the integrity of the nonhydrostatic equations,the atmospheric curvature correction and eccentricity correction are considered. In this paper,the Held-Suarez idealized test and an idealized baroclinic wave test are first carried out,which shows that the nonhydrostatic global spectral model has similar climate states to the results of many other global models for long-term idealized integration,as well as better simulation ability for short-term idealized integration.Then,a real case experiment is conducted using the new dynamical core with the full physical parameterizations of subgrid-scale physical processes.The 10-day numerical integration indicates a decrease in systematic error and a better simulation of zonal wind,temperature,and 500-hPa height.     

A Numerical World Ocean General Circulation Model

This paper describes a numerical model of the world ocean based on the fully primitive equations. A "Standard" ocean state is introduced into the equations of the model and the perturbed thermodynamic variables are used in the modlc's calculations. Both a free upper surface and a bottom topography are included in the model and a sigma coordinate is used to normalize the model's vertical component. The model has four unevenly-spaced layers and 4 × 5 horizontal resolution based on C-grid system. The finite-difference scheme of the model is designed to conserve the gross available energy in order to avoid fictitious energy generation or decay.The model has been tested in response to the annual mean surface wind stress, sea level air pressure and sea level air temperature as a preliminary step to its further improvement and its coupling with a global atmospheric general circulation model. Some of results, including currents, temperature and sea surface elevation simulated by the mode! arc presented.     

NUMERICAL STUDY OF SHORT TERM EFFECT OF SST ANOMALIES

Using a 5-layer P-o mixed coordinates primitive equations model, a process of heavy rain is simulated that occurred over the middle-and lower-reaches of the Changjiang River on July 1-2, 1991 and numerical experiments are done of the effects of sea surface temperature (SST) anomalies over different waters on the precipitation. The result has shown that the appearance of SST anomaly is followed in a short term (2 or 3 days) by. A change in the pattern of circulation as well as in precipitation to some extent.     

THE EFFECTS OF THE PLATEAU'S TOPOGRAPHIC GRADIENT ON ROSSBY WAVES AND ITS NUMERICAL SIMULATION

By using barotropic model equations, this article analyzed the characteristics of Rossby waves, the propagation features of wave energy and the influence of dynamic and thermal effects of the Tibetan Plateau on Rossby waves, and the focus is on discussing the plateau's topographic gradient effects on atmospheric Rossby waves. Then based on the WRF3.2 and the NCEP/NCAR FNL reanalysis data, we devised comparative tests of changing the plateau's topographic gradient and simulated a process of persistent heavy rain that happened in May 2010 in South China. The results are shown as follows. The Tibetan Plateau’s topography is conducive to the formation of atmospheric Rossby waves. while the plateau's terrain, its friction and heating effects can all make the atmospheric Rossby waves develop into the planetary waves; The effects of plateau's north and south slopes on the Rossby wave’ phase velocity is opposite, and when the slope reached a certain value can the quasi-steady normal fluctuations be generated; Simultaneously, due to the plateau's topographic gradient, descending motion appears at the west side of the plateau while ascending motion appears at the east side, and the vertical movement increased with the amplification of topographic gradients. The plateau's topographic gradient also obviously amplified the precipitation in South China, and the rainfall area increased with the amplification of topographic gradients and gradually moved from south to north and from west to east, which is conducive to the occurrence and development of convective activities in the downstream areas of the Tibetan Plateau; Moreover, for the plateau’s dynamic and thermal effects, the Rossby wave’ propagation shows upstream effects of energy dispersion, so the plateau can then affect the weather in downstream areas. Moreover, the wave group velocity increased with the degree of topographic slope.     

A NUMERICAL EXPERIMENTAL STUDY OF TROPICAL CYCLONE CROSSING SUBTROPICAL HIGH

The barotropic primitive equations model is used in a numerical study of a tropical cyclone crossing the Subtropical high. It is revealed that apart from its own characteristics, sensitive factors having immediate effects on the motion of the tropical cyclone also include its radial distance from the center of the subtropical high, the variation in latitudinal location and intensity. A complex mechanism for nonlinear interactions among the tropical,subtropical high and β effect is also shown in the experiment, and expected to serve for the diagnosis and prediction of abnormal motion.     

THE DESIGN OF A LIMITED AREA MESOSCALE MODEL AND PREDICTION EXPERIMENTS

Based on the dynamic frame of a 6-layer primitive equations model, a mesoscale primitive equations model is designed that includes larger range of physical processes. It is run in (x, y, σ) system with the model atmosphere topping at 10 hPa and availability of multiple conditions of horizontal boundaries, both horizontal and vertical resolution are adjustable; the precipitation scheme includes large scale and deep cumulus convective precipitation; the ground temperature is computed using surface heat budget equations; exchanges between land atmosphere and between ocean and atmosphere are considered, the Liouis format is used in the computation of vertical exchange budget; a scheme that combines the second and fourth order is employed in horizontal diffusion in which the coefficient is the function of the location of grid points and wind fields; the integration scheme is in the form of economic central difference.With the resolution that horizontal grids are spaced at intervals of 80 km and vertical length is unequally spaced into 16 layers, the model is experimented with 26 cases of forecast. The result has shown stable model computation, good prediction of major synoptic patterns and close reproduction of real precipitation. Statistics for a number of assessment indexes are given in this paper and comparisons are made to the original 6-layer model in respect of the forecasting ability and model properties.     

THE USE OF RADAR DATA IN THE NUMERICAL SIMULATION OF HEAVY RAINFALLS IN THE CHANGJIANG-HUAIHE RIVER BASIN

It is important for predictions of heavy rainfall to include radar data to provide better reflection of moisture. Numerical experiments were carried out with real cases of heavy rains in the Changjiang (Yangtze)-Huaihe River Basin using a PSU/NCAR mesoscale model that incorporated radar data. Processed radar data were added to the model to change the analysis of initial humidity field before 24-h numerical simulations were made and the results compared with a control experiment. It is suggested that the radar-data-incorporated numerical predictions could produce locations of precipitation areas and maximum rainfall that are closer to reality than the control, due to the fact that moisture and converging updraft are strengthened in the middle and lower levels of the troposphere in the area of heavy rains and areas nearby. The work is expected to improve numerical modeling and forecasts of heavy rains in middle and lower latitudes of China.     

THE SENSITIVITY OF NUMERICAL SIMULATION TO OROGRAPHY SPECIFICATION IN THE LOW RESOLUTION SPECTRAL MODEL－PART I: THE EFFECTS OF OROGRAPHY ON THE ATMOSPHERIC GENERAL CIRCULATION

In order to identify the sensitivity of the numerical simulation to the orography specification in a low resolution spectral model, two sets of numerical experiments for full-mountain and no-mountain cases are performed. By comparing the results, it is possible to determine the eflects of mountains on the atmospheric general circulation.This is a global, spectral model incorporating the primitive equations sugmented by physical parameterization and mountains, with five equally-spaced sigma levels in the vertical ang a triangular truncation at wavenum-ber 10 in the horizontal.Analysis of results supports earlier work by demonstrating that the low resolution global spectral model is capable of simulating the major features of global general circulation and indicates that it is necessary to consider the effects of mountains on stationary disturbances in the numerical simulation. The simulations show that topography plays an important role in intensifying heat sources for maintenance of disturbances.All the     

Retrospective Time Integration Scheme in Numerical Models

In view of the fact that the atmosphere is capable of memory, this research suggested and developed the viewpoint of atmospheric memorial dynamics. By introducing a memory function into the dynamic-thermodynamic equations of the atmosphere, these equations can be transformed into difference-integral equations. In this way, the numerical solution of the atmospheric motion can be obtained by using several initial fields rather than only one initial field. The retrospective time integration scheme is an original scheme based the system self-memorization principle, which differs greatly from other     

THE OSCILLATION OF CERTAIN ZONAL MEAN CHARACTERISTICS OF MOTION ON A SPHERIC EARTH'S ATMOSPHERE——PART 2:ANISOTROPIC QUASI-EDDY MOTION

This paper is an extension of the auther's works (1980,1982,1987).Simple anisotropic distribution of hori-zontal kinetic energy is assumed,i.e.,the zonal kinetic energy is twice that of the meridional kinetic energy.The large-scale atmospheric motion is considered as that consisting of quasi-horizontal eddies and regular flow.The techniques of quasi-eddy,quasi-steady,quasi-geostrophic and quasi-adiabatic approximations are usedin order to get the analytical solutions of the system of equations governing the variation of the zonal meancharacteristics.The results show that the zonal mean characteristics of the atmospheric motion are a combination of dif-ferent periods ranging from a few days to a few weeks depending on the components of Chebyshev polynomi-als of the sine of the latitude.When more general anisotropy of horizontal kinetic energy is assumed,Gegenbauer polynomials appearinstead of Chebyshev polynomials.When the distribution of horizontal kinetic energy is isotropic,the polyno-mials retrograde to Legendre polynomials.     

SENSITIVITY OF MESOSCALE CONVECTIVE SYSTEMS AND ASSOCIATED HEAVY RAINFALL TO SOIL MOISTURE OVER SOUTH CHINA

The impacts of soil moisture(SM) on heavy rainfall and the development of Mesoscale Convection Systems(MCSs) are investigated through 24-h numerical simulations of two heavy rainfall events that occurred respectively on28 March 2009(Case 1) and 6 May 2010(Case 2) over southern China. The numerical simulations were carried out with WRF and its coupled Noah LSM(Land Surface Model). First, comparative experiments were driven by two different SM data sources from NCEP-FNL and NASA-GLDAS. Secondary, with the run driven by NASA-GLDAS data as a control one, a series of sensitivity tests with different degree of(20%, 60%) increase or decrease in the initial SM were performed to examine the impact of SM on the simulations. Comparative experiment results show that the 24-h simulated cumulative rainfall distributions are not substantially affected by the application of the two different SM data,while the precipitation intensity is changed to some extent. Forecast skill scores show that simulation with NASA-GLDAS SM data can lead to some improvement, especially in the heavy rain(芏50 mm) forecast, where there is up to 5% increase in the TS score. Sensitivity test analysis found that a predominantly positive feedback of SM on precipitation existed in these two heavy rain events but not with completely the same features. Organization of the heavy rainfall-producing MCS seems to have an impact on the feedback process between SM and precipitation. For Case 1, the MCS was poorly organized and occurred locally in late afternoon, and the increase of SM only caused a slight enhancement of precipitation. Drier soil was found to result in an apparent decrease of rainfall intensity,indicating that precipitation is more sensitive to SM reduction. For Case 2, as the heavy rain was caused by a well-organized MCS with sustained precipitation, the rainfall is more sensitive to SM increase, which brings more rainfall. Additionally, distinctive feedback effects were identified from different stages and different organization of MCS, with strong feedback between SM and precipitation mainly appearing in the early stages of the poorly organized MCS and during the late period of the well-organized MCS.     

Impact of atmospheric and oceanic conditions on the frequency and genesis location of tropical cyclones over the western North Pacific in 2004 and 2010

This study examines the impact of atmospheric and oceanic conditions during May–August of 2004 and 2010 on the frequency and genesis location of tropical cyclones over the western North Pacific. Using the WRF model, four numerical experiments were carried out based on different atmospheric conditions and SST forcing. The numerical experiments indicated that changes in atmospheric and oceanic conditions greatly affect tropical cyclone activity, and the roles of atmospheric conditions are slightly greater than oceanic conditions. Specifically, the total number of tropical cyclones was found to be mostly affected by atmospheric conditions, while the distribution of tropical cyclone genesis locations was mainly related to oceanic conditions, especially the distribution of SST. In 2010, a warmer SST occurred west of 140°E, with a colder SST east of 140°E. On the one hand, the easterly flow was enhanced through the effect of the increase in the zonal SST gradient.The strengthened easterly flow led to an anomalous boundary layer divergence over the region to the east of 140°E, which suppressed the formation of tropical cyclones over this region. On the other hand, the colder SST over the region to the east of 140°E led to a colder low-level air temperature, which resulted in decreased CAPE and static instability energy. The decrease in thermodynamic energy restricted the generation of tropical cyclones over the same region.     

27.3-day and Average 13.6-day Periodic Oscillations in the Earth’s Rotation Rate and Atmospheric Pressure Fields Due to Celestial Gravitation Forcing

Variation in length of day of the Earth (LOD, equivalent to the Earth’s rotation rate) versus change in atmospheric geopotential height fields and astronomical parameters were analyzed for the years 1962-2006. This revealed that there is a 27.3-day and an average 13.6-day periodic oscillation in LOD and atmospheric pressure fields following lunar revolution around the Earth. Accompanying the alternating change in celestial gravitation forcing on the Earth and its atmosphere, the Earth’s LOD changes from minimum to maximum, then to minimum, and the atmospheric geopotential height fields in the tropics oscillate from low to high, then to low. The 27.3-day and average 13.6-day periodic atmospheric oscillation in the tropics is proposed to be a type of strong atmospheric tide, excited by celestial gravitation forcing. A formula for a Tidal Index was derived to estimate the strength of the celestial gravitation forcing, and a high degree of correlation was found between the Tidal Index determined by astronomical parameters, LOD, and atmospheric geopotential height. The reason for the atmospheric tide is periodic departure of the lunar orbit from the celestial equator during lunar revolution around the Earth. The alternating asymmetric change in celestial gravitation forcing on the Earth and its atmosphere produces a "modulation" to the change in the Earth’s LOD and atmospheric pressure fields.     

Mapping near-surface air temperature,pressure, relative humidity and wind speed over Mainland China with high spatiotemporal resolution

As part of a joint effort to construct an atmospheric forcing dataset for mainland China with high spatiotemporal reso- lution, a new approach is proposed to construct gridded near-surface temperature, relative humidity, wind speed and surface pressure with a resolution of 1 km× 1 km. The approach comprises two steps： （1） fit a partial thin-plate smoothing spline with orography and reanalysis data as explanatory variables to ground-based observations for estimating a trend surface; （2） apply a simple kriging procedure to the residual for trend surface correction. The proposed approach is applied to observations collected at approximately 700 stations over mainland China. The generated forcing fields are compared with the corresponding components of the National Centers for Environmental Predic- tion （NCEP） Climate Forecast System Reanalysis dataset and the Princeton meteorological forcing dataset. The comparison shows that, both within the station network and within the resolutions of the two gridded datasets, the interpolation errors of the proposed approach are markedly smaller than the two gridded datasets.     

A MODEL FOR QUANTITATIVELY ESTIMATING SHORT-RANGE PRECIPITATION BASED ON GMS DIGITALIZED CLOUD MAPS—PART I:ANALYSIS OF QUANTITATIVE CLOUD-PRECIPITATION RELATIONS AND MODEL DESIGN

Some typical samples are used to explore the quantitative correlation with their features between a convective cloud and its rainfall field,with which to develop two morphological functions for the correlation and by singling out their most suitable groups of parameters we propose a model for quantitatively estimating precipitation in the context of the in-advance recognition of meso-α convective system properties and its precipitating center.From the model fitting precision and forecasting accuracy we find that it is feasible to utilize geostationary meteorological satellite (GMS) digitalized imagery for estimating short-term rainfall in a quantitative manner.Also,evidence suggests that the model is supposed to be restricted in its applicability due to the fact that the employed samples are from rather typical rainfall events that are large-scale,slow-moving and have well-defined genesis and dissipative stages.     

SIMULATION OF SPATIO-TEMPORAL DISTRIBUTION CHARACTERISTICS AND RADIATIVE FORCING OF ORGANIC CARBON AEROSOLS IN CHINA

The International Centre for Theoretical Physics(ICTP,Italy) Regional Climate Model version 3.0(RegCM3) is used to simulate spatio-temporal distribution characteristics and radiative forcing(RF) of organic carbon(OC) aerosols in and around China.The preliminary simulation results show that OC aerosols are mostly concentrated in the area to the south of Yellow River and east of Tibetan Plateau.There is a decreasing trend of column burden of OC aerosols from south to north in China.The maximum value of column burden of OC aerosols is above 3 mg/m2 and located in the central and southern China,southeastern Tibet,and southwestern China’s Yunnan,Guizhou,Sichuan provinces.The simulation on the seasonal variation shows that the maximum value of column burden of OC aerosols appears in winter and the secondary value is in spring and the minimum in summer.The RF of OC aerosols which varies seasonally is negative at the top of the atmosphere(TOA) and surface.The spatio-temporal characteristics of the RF of OC aerosols are basically consistent with that of IPCC,implying the high accuracy of the parameterization scheme for OC aerosols in RegCM3.     

TROPICAL GRAVITY-ATMOSPHERIC LONG WAVE AND THE WALKER CIRCULATION

Orders of magnitude of terms related to earth's rotation in linearized vorticity and divergence equations governing tropical large-scale motion are analysed. It is discovered that βyD and βyζ are smaller by one order than βv and βu respectively and then may be neglected. On this basis, tropical wave motions are di s-cussed. It is found that there exists a kind of gravity-atmospheric long waves which is non-vorticit atmospheric long wave, whereas the Kelvin wave is essentially the gravity-atmospheric long wave with its velocity being much lower than that of gravity. Computation shows that there also exists a kind of large-scale slow waves whose moving speed is lower by one order of magnitude than that of Kelvin wave. Such slow wavs is likely to be the Walker Circulation.     

THE SECOND ORDER APPROXIMATION TO THE NONLINEAR WAVE IN BAROTROPIC ATMOSPHERE

A kind of technique of computer extension of perturbation series is presented and used in seeking for the second-order approximation to a large-scale travelling wave solution of the barotropic primitive equations. Numerical experiments show that the second-order approximation keeps major characters of the travelling wave solution and is indeed more exact than the zero-order and the first order approximations.     

Tropical gravity-atmospheric long wave and the walker circulation

Orders of magnitude of terms related to earth’s rotation in linearized vorticity and divergence equations governing tropical large-scale motion are analysed. It is discovered that βyD and βyξ are smaller by one order than βv and βu respectively and then may be neglected. On this basis, tropical wave motions are discussed. It is found that there exists a kind of gravity-atmospheiic long waves which is non-vorticit atmospheric long wave, whereas the Kelvin wave is essentially the gravity-atmospheric long wave with its velocity being much lower than that of gravity. Computation shows that there also exists a kind of large-scale slow waves whose moving speed is lower by one order of magnitude than that of Kelvin wave. Such slow wave is likely to be the Walker Circulation.     

THE FORMULATION OF FIDELITY SCHEMES OF PHYSICAL CONSERVATION LAWS AND IMPROVEMENTS ON A TRADITIONAL SPECTRAL MODEL OF BAROCLINIC PRIMITIVE EQUATIONS FOR NUMERICAL PREDICTION

In this paper,two formulation theorems of time-difference fidelity schemes for generalquadratic and cubic physical conservation laws are respectively constructed and proved,with earliermajor conserving time-discretized schemes given as special cases.These two theorems can providenew mathematical basis for solving basic formulation problems of more types of conservative time-discrete fidelity schemes,and even for formulating conservative temporal-spatial discrete fidelityschemes by combining existing instantly conserving space-discretized schemes.Besides.the twotheorems can also solve two large categories of problems about linear and nonlinear computationalinstability.The traditional global spectral-vertical finite-difference semi-implicit model for baroclinicprimitive equations is currently used in many countries in the world for operational weatherforecast and numerical simulations of general circulation.The present work,however,based onTheorem 2 formulated in this paper,develops and realizes a high-order total energy conservingsemi-implicit time-difference fidelity scheme for global spectral-vertical finite-difference model ofbaroclinic primitive equations.Prior to this,such a basic formulation problem remains unsolved forlong,whether in terms of theory or practice.The total energy conserving semi-implicit schemeformulated here is applicable to real data long-term numerical integration.The experiment of thirteen FGGE data 30-day numerical integration indicates that the newtype of total energy conserving semi-implicit fidelity scheme can surely modify the systematicdeviation of energy and mass conserving of the traditional scheme.It should be particularly notedthat,under the experiment conditions of the present work,the systematic errors induced by theviolation of physical laws of conservation in the time-discretized process regarding the traditionalscheme designs(called type Z errors for short)can contribute up to one-third of the totalsystematic root-mean-square(RMS)error at the end of second week of the integration and exceedone half of the total amount four weeks afterwards.In contrast,by realizing a total energyconserving semi-implicit fidelity scheme and thereby eliminating corresponding type Z errors,roughly an average of one-fourth of the RMS errors in the traditional forecast cases can be reducedat the end of second week of the integration,and averagely more than one-third reduced at integraltime of four weeks afterwards.In addition,experiment results also reveal that,in a sense,theeffects of type Z errors are no less great than that of the real topographic forcing of the model.The prospects of the new type of total energy conserving fidelity schemes are very encouraging.