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2003 Vol. 20, No. 1

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Amplitude-Phase Characteristics of the Annual Cycle of Surface Air Temperature in the Northern Hemisphere
2003, 20(1): 1-16. doi: 10.1007/BF03342045
The amplitude-phase characteristics (APC) of surface air temperature (SAT) annual cycle (AC)in the Northern Hemisphere are analyzed. From meteorological observations for the 20th century andmeteorological reanalyses for its second half, it is found that over land negative correlation of SAT ACamplitude with annual mean SAT dominates. Nevertheless, some exceptions exist. The positive correlationbetween these two variables is found over the two desert regions: in northern Africa and in Central America.Areas of positive correlations are also found for the northern Pacific and for the tropical Indian and PacificOceans. Southward of the characteristic annual mean snow-ice boundary (SIB) position, the shape ofthe SAT AC becomes more sinusoidal under climate warming. In contrast, northward of it, this shapebecomes less sinusoidal. The latter is also found for the above-mentioned two desert regions. In theFar East (southward of about 50N), the SAT AC shifts as a whole: here its spring and autumn phasesoccur earlier if the annual mean SAT increases. From energy-balance climate considerations, those trendsfor SAT AC APC in the middle and high latitudes are associated with the influence of the albedo-SATfeedback due to the SIB movement. In the Far East the trends are attributed to the interannual cloudinessvariability, and in the desert regions, to the influence of a further desertification and/or scattering aerosolloading into the atmosphere. In the north Pacific, the exhibited trends could only be explained as aresult of the influence of the greenhouse-gases loading on atmospheric opacity. The trends for SAT ACAPC related to the SIB movement are simulated reasonably well by the climate model of intermediatecomplexity (IAP RAS CM) in the experiment with greenhouse gases atmospheric loading. In contrast,the tendencies resulting from the cloudiness variability are not reproduced by this model. The model alsopartly simulates the tendencies related to the desertification processes.
Systematic Errors of Zonal-Mean Flow in Dynamical Monthly Prediction and Its Improvement
CHEN Bomin, JI Liren, YANG Peicai, ZHANG Daomin
2003, 20(1): 17-27. doi: 10.1007/BF03342046
An analysis of a large number of cases of 500 hPa height monthly prediction shows that systematicerrors exist in the zonal mean components which account for a large portion of the total forecast errors, andsuch errors are commonly seen in other prediction models. To overcome the difficulties of the numericalmodel, the authors attempt a hybrid approach to improving the dynamical extended-range (monthly)prediction. The monthly pentad-mean nonlinear dynamical regional prediction model of the zonal-meangeopotential height (wave number 0) based on a large amount of data is constituted by employing thereconstruction of phase-space theory and the spatio-temporal series predictive method. The dynamicalprediction of the numerical model is then combined with that of the nonlinear model, i.e., the pentad-mean zonal-mean height produced by the nonlinear model is transformed to its counterpart in the numericalmodel by nudging during the time integration. The forecast experiment results show that the above hybridapproach not only reduces the systematic error in zonal mean height by the numerical model, but alsomakes an improvement in the non-axisymmetric components due to the wave-flow interaction.
Spatial and Time Structure of a Gravity Wave in Horizontal Atmosphere of Heterogeneous Stratification
ZHANG Lifeng, WANG Xingbao, ZHANG Ming
2003, 20(1): 29-36. doi: 10.1007/BF03342047
By the use of the WKBJ method combined with the characteristic line method, the asymptotic solutionof a gravity wave envelope in the atmosphere of horizontal heterogeneous stratification and time-varyingstratification is obtained. The solution shows that not only the variation of amplitude of the gravitywave but also the variation of wavelength and the width of the envelope are affected by the horizontalheterogeneity. As the wave envelope moves from a region of strong stratification to a weak one, thehorizontal wavelength will become shorter, the width of the envelope will narrow and its amplitude willincrease. The variation of stratification with time cannot lead to the variation of wavelength and envelopewidth, but the amplitude of the wave envelope will increase while the amplitude of the wave decreases in time.
Diagnosis of the Heavy Rain near a Meiyu Front Using the Wet Q Vector Partitioning Method
YUE Caijun, SHOU Shaowen, LIN Kaiping, YAO Xiuping
2003, 20(1): 37-44. doi: 10.1007/BF03342048
A heavy rain process of the Changjiang-Huaihe Meiyu front (MYF) is diagnosed by the agency ofthe traditional Q vector partitioning (QVP) method to decompose the wet Q vector (Q) in a naturalcoordinate system that follows the isoentropes and by using the numerical simulation results of the revisedMM4 meso-scale model. The technique shows that the partitioned wet Q vectors can lead to a significantscale separation of vertical motion related to the torrential rain. The results not only verify the existingconclusion that different scales interact throughout the rainstorm but also indicate the largely differentroles of these scales during differing phases of the heavy rainfall on a quantitative basis. Specifically, duringthe developing stage, the large-scale plays a predominant role in forcing vertical motion, while frontal-scaleforcing is secondary; during the intense stage, the frontal-scale evolves into the primary factor of forcingvertical motion, whereas the large-scale forcing is minor and plays a diminishing role and can even beignored; and during the decaying stage, the large-scale once again serves as the main forcing of verticalmotion in such a way that the forcing of the frontal-scale decays quickly and is of secondary importance.Furthermore, the partitioned wet Q vectors are suggested to be more suitable than the total wet Q vectorfor evaluating the potential physical mechanism of rainstorm genesis. The first step is that the forcingof large-scale 27 @ Q*s gives rise to the genesis of meso-scale 2 @ Q*n forcing; and then, accordingly as27 @ Q*n forcing increases, whereby the secondary circulation is reinforced, the intensity of the rainfall isstrengthened; and at last, the secondary circulation caused by 2 @ Q*n forcing is directly responsible forgeneration of the MYF heavy rainfall.
The Regional Climate Effects of Replacing Farmland and Re-greening the Desertification Lands with Forest or Grass in West China
SHI Weilai, WANG Hanjie
2003, 20(1): 45-54. doi: 10.1007/BF03342049
The West Development Policy being implemented in China causes significant land use and land cover(LULC) changes in West China, of which the two most important types of LULC change are replacingfarmland and re-greening the desertification land with forest or grass. This paper modifies the prevailingregional climate model (RCM) by updating its lower boundary conditions with the up-to-date satellitedatabase of the Global Land Cover Characteristics Database (GLCCD) created by the United StatesGeological Survey and the University of Nebraska-Lincoln. The modified RCM is used to simulate thepossible regional climate changes due to the LULC variations. The preliminary results can be summarizedas that the two main types of LULC variation, replacing farmland and greening the desertification landswith forest or grass in west China, will affect the regional climate mostly in northwest and north China,where the surface temperature will decrease and the precipitation will increase. The regional climateadjustments in South, Southwest China and on the Tibet Plateau are uncertain.
The Progresses of Recent Studies on the Variabilities of the East Asian Monsoon and Their Causes
HUANG Ronghui, ZHOU Liantong, CHEN Wen
2003, 20(1): 55-69. doi: 10.1007/BF03342050
The variabilities of the East Asian summer monsoon are an important research issue in China, Japan,and Korea. In this paper, progresses of recent studies on the intraseasonal, interannual, and interdecadalvariations of the East Asian monsoon, especially the East Asian summer monsoon, and their causes arereviewed. Particularly, studies on the effects of the ENSO cycle, the western Pacific warm pool, the TibetanPlateau and land surface processes on the variations of the East Asian summer monsoon are systematically reviewed.
On the Determination and Characteristics of Effective Roughness Length for Heterogeneous Terrain
ZHONG Zhong, ZHAO Ming, SU Bingkai, TANG Jianping
2003, 20(1): 71-76. doi: 10.1007/BF03342051
A new method is proposed for the effective roughness length (ERL) in heterogeneous terrain basedon the principle of equalization of momentum or heat fluxes calculated by the drag coefficient parameter-ization scheme used in the ECMWF numerical model. Compared with the area-weighted logarithmicallyaveraged ERL (drag coefficient), the newly calculated ERL (drag coefficient) is about 40% (16%) largerwith a roughness step of 2.3. These differences reach their maximum values when the ratio of smooth torough surface is 60% to 40%. Since the determination by this method is not sensitive to the atmosphericstratification, it is suitable for use in climate models.
Observation and Numerical Simulation of Cloud Physical Processes Associated with Torrential Rain of the Meiyu Front
WANG Pengyun, YANG Jing
2003, 20(1): 77-96. doi: 10.1007/BF03342052
Cloud micro-physical structures in a precipitation system associated with the Meiyu front are observedusing the balloon-borne Precipitation Particle Image Sensor at Baoshan observatory station, Shanghaiduring June and July 1999. The vertical distributions of various cloud particle size, number density, andmass density are retrieved from the observations. Analyses of observations show that ice-phase particles(ice crystals, graupel, snowflakes, and frozen drops) often exist in the cloud of torrential rain associatedwith the Meiyu front. Among the various particles, ice crystals and graupel are the most numerous, butgraupel and snow have the highest mass density. Ice-phase particles coexist with liquid water dropletsnear the 0℃ level. The graupel is similarly distributed with height as the ice crystals. Raindrops belowthe 0℃ level are mainly from melted grauple, snowflakes and frozen drops. They may further grow largerby coalescence with smaller ones as they fall from the cloud base. Numerical simulations using the non-hydrostatic meso-scale model MM5 with the Reisner graupel explicit moisture scheme confirm the mainobservational results. Rain water at the lower level is mainly generated from the melting of snow andgraupel falling from the upper level where snow and graupel are generated and grown from collection withcloud and rain water. Thus the mixed-phase cloud process, in which ice phase coexists and interacts withliquid phase (cloud and rain drops), plays the most important role in the formation and development ofheavy convective rainfall in the Meiyu frontal system.
Influence of Interannual Variability of Antarctic Sea-Ice on Summer Rainfall in Eastern China
XUE Feng, GUO Pinwen, YU Zhihao
2003, 20(1): 97-102. doi: 10.1007/BF03342053
Based on the Antarctic sea-ice coverage reanalysis data from the Hadley Center and other observationaldata during the 30-year period from 1969 to 1998, it is shown that Antarctic sea-ice coverage exhibitsconsiderable interannual variability with a complex relation to El Nino and the South Oscillation (ENSO).Besides this, the ice maintains the seasonal persistence of the atmospheric circulation in high latitudesof the Southern Hemisphere. Thus it can be used as a predictor in short-term climate prediction. Bothcorrelation and time series analyses demonstrate that summer rainfall in eastern China is closely relatedto Antarctic sea-ice coverage. When it is extended during boreal spring through summer, there is morerainfall in the lower reaches of the Yellow River of North China, and in contrast, less rainfall is found in theZhujiang River basin of South China and Northeast China. A further analysis indicates that this rainfallpattern is related to the intensity of the East Asian summer monsoon caused by interannual variability ofAntarctic sea-ice coverage.
Mechanism of Formation of the Ozone Valley over the Tibetan Plateau in Summer Transport and Chemical Process of Ozone
LIU Yu, LI Weiliang, ZHOU Xiuji, HE Jinhai
2003, 20(1): 103-109. doi: 10.1007/BF03342054
With the 3D chemical transport model OSLO CTM2, the valley of total column ozone over the TibetanPlateau in summer is reproduced. The results show that when the ozone valley occurs and develops, thetransport process plays the main part in the ozone reduction, but the chemical process partly compensatesfor the transport process. In the dynamic transport process of ozone, the horizontal transport process playsthe main part in the ozone reduction in May, but brings about the ozone increase in June and July. Thevertical advective process gradually takes the main role in the ozone reduction in June and July. The effectof convective activities rises gradually so that this effect cannot be overlooked in July, as its magnitudeis comparable to that of the net changes. The effect of the gaseous chemical process brings about ozoneincreases which are more than the net changes sometimes, so the chemical effect is also important.
A Parameterization Scheme of Surface Turbulent Momentum and Sensible Heat over the Gobi Underlying Surface
ZHANG Qiang, HUANG Ronghui, TIAN Hui
2003, 20(1): 111-118. doi: 10.1007/BF03342055
The parameterization of surface turbulent fluxes over the Gobi Desert in arid regions is studied by usingrationally screened observational data. First, the characteristics of Monin-Obukhov similarity functionsare analyzed and their empirical formulae are fitted. The results show that fitted curves of changes ofsimilarity functions of wind speed and temperature with stability parameter differ little from the typicalempirical curves and are within the ranges of scatter of the empirical curves, but their values in the neutralcondition are different from the typical values to some extent. Furthermore, average values of momentumand scalar (sensible heat) roughness lengths as well as changes of scalar roughness length with frictionvelocity are determined by utilizing the data. It is found that the average values of scalar roughness lengthare about one order smaller than that of the momentum roughness length and decrease with increasingfriction velocity, but they are evidently larger than their theoretically forecasted values.
An Investigation on the Relationship Between Emission/Uptake of Greenhouse Gases and Environmental Factors in Semiarid Grassland
WANG Yuesi, HU Yuqiong, JI Baoming, LIU Guangren, XUE Min
2003, 20(1): 119-127. doi: 10.1007/BF03342056
Measurements of greenhouse gases CO2, CH4, and N2O were made by static chamber-gas chromato-graph in Inner Mongolia. Results indicate that with growing seasons, the daily variation patterns ofemission/uptake of greenhouse gases differ greatly in the prairie ecosystem. The peak of seasonal emis-sion/uptake of three greenhouse gases occurs at the melting period in spring when soil moisture is highand rainfall is rich. The daily emissions of CO2 from steppe vegetation in growing seasons are low duringthe daytime and high at night. Higher temperatures are advantageous to emission of CO2, as abovegroundbiomass determines the amount of CO2 photosynthetic uptake. The key factors that influence the dailyvariation patterns of CH4 uptake and N2O emission in semiarid grassland are soil moisture and the oxygensupplying condition, while the changes in daily temperature mainly affect the range of daily variations.The seasonal changes of N2O emission are positively related to seasonal change in soil moisture. Freegrazing reduces the daily mean deviation of exchange rates of CO2, N2O, and CH4, but it decreases theamount of annual emission/uptake of N2O and CH4 yet it increases the annual emission of CO2.
Numerical Simulations of a Heavy Rainfall Case in South China
LOU Xiaofeng, HU Zhijin, SHI Yueqin, WANG Pengyun, ZHOU Xiuji
2003, 20(1): 128-138. doi: 10.1007/BF03342057
Using a double-parameter non-hydrostatic elastic three-dimensional model with detailed microphysicalprocesses, the authors simulate the heavy rainfall event in South China which occurred on 9 June 1998 andlasted for more than 3 hours. This case is a supercell, and the upward and downward drafts interact witheach other, which transfers rich water vapor at the converging position to upper levels, and the two draftstogether maintain the convective course. The vertical heating profiles and contributions to water matterof five kinds of micro-phase processes are revealed quantitatively in the results. Condensation releases themost heat, which is more than that of the absorption by evaporation and melting. The rain particles firstcome from the autoconversion of cloud particles, the warm-rain process; later from the cold-rain process,the melting of grauple particles. The precipitation intensity reaches 75 mm h-1 while its efficiency remainshigh. The total amount of rain is 32 mm, a value close to the observations of nearby stations.
Research on Atmospheric Motion in Horizontal Discrete Grids
LIU Yudi, WANG Bin, JI Zhongzhen
2003, 20(1): 139-148. doi: 10.1007/BF03342058
Starting from the linear shallow-water equations and using Arakawa A-E and Z grids, a study is madeof inertia-gravitational and Rossby waves in the six grids from the perspectives of frequency and groupvelocity. Results indicate that grids C, Z, and E thereof give smaller distortion compared to the others.
A Comparative Study of the Numerical Simulation of the 1998 Summer Flood in China by Two Kinds of Cumulus Convective Parameterized Methods
PING Fan, GAO Shouting, WANG Huijun
2003, 20(1): 149-157. doi: 10.1007/BF03342059
The NCC T63L20 model of the National Climate Center, China Meteorological Administration isemployed to simulate the 1998 summer flood, which mainly occurred in the region of the Yangtze River andNortheast China. For this study, two kinds of cumulus convection parameterized schemes are employed inthis model respectively. The simulations show that the Gregory parameterized scheme, which is still usedin the United Kingdom Meteorological Office routine model, simulates more reasonable rainfall amountand distribution compared to the Kuo-type scheme. Moreover, the Gregory scheme better simulates thetendency of general circulation than the Kuo-type scheme. On the whole, the Gregory scheme providesa good simulation of the main features of the seasonal precipitation and general circulation in China,although the simulated result still exhibits some departures from the observations.
Distributed Parallelization of a Global Atmospheric Data Objective Analysis System
ZHAO Jun, SONG Junqiang, LI Zhenjun
2003, 20(1): 159-163. doi: 10.1007/BF03342060
It is difficult to parallelize a subsistent sequential algorithm. Through analyzing the sequentialalgorithm of a Global Atmospheric Data Objective Analysis System, this article puts forward a distributedparallel algorithm that statically distributes data on a massively parallel processing (MPP) computer.The algorithm realizes distributed parallelization by extracting the analysis boxes and model grid pointlatitude rows with leaped steps, and by distributing the data to different processors. The parallel algorithmachieves good load balancing, high parallel efficiency, and low parallel cost. Performance experiments ona MPP computer are also presented.