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Current Issue  
 
2000 Vol. 14, No. 1
Published: 2000-03-30

 
    
       article
ADVANCE AND RETREAT OF THE SUMMER MONSOON IN CHINA
FONG Soi Kun,KU Chi Meng,HAO I Pan,WANG Anyu,WU Chisheng,LIN Wensh
2000, 14(1): 1-12 [Abstract]( 362 ) HTML PDF (895 KB)  ( 292
Abstract:By using the daily-14 year(1983-1996)NCEP/NCAR 2.5°×2.5° reanalysis data,wecarefully study in each pentad the advance and retreat of the summer monsoon in China and givento it a new definition.This definition considered the intensity of southwesterly winds at 850 h Patogether with its degree in temperature and moisture.The result revealed that:(1)The advance of the summer monsoon in China shows three abrupt northward shifts andfour relatively stationary stays.The four stable stages correspond to the peak of the pro-summerrainy period in South China,the"Meiyu"season in the Changjiang(Yangtze)-Huaihe RiverValleys.the rainy season in the downstream of the Huanghe (Yellow) Riyer Valleys and the rainyseason in northern China.The retreat of the summer monsoon is so fast that it totally retreatsfrom the mainland at about the mid-August.(2)The northward advance of summer monsoon in China is basically controlled by theseasonal variation latitudinally of the upper level planetary westerlies.It is in roughly accord withthe temporal variation in the position of 15 m s-1 isotaeh at 200 hPa.The fast retreat of thesummer monsoon is mainly due to the blocking effect of the Tibetan Plateau.(3)The advance of 500 hPa subtropical high of the western Pacific is also in aecordanee withthe advance of the summer monsoon in China.During the advancement of the summer monsoon,the eastward movement of the subtropical high shows great meaning that it creates the essentialcondition for the convergence of southward intrusion cold airs with the warm and humid southwesterly winds,which result in precipitation.There are three manifest eastward movementsof the subtropical high during its northward advancement.They coincide correspondingly to thebeginning of the peak of the pre-summer rainy period in South China,the"Meiyu"season in the Changjiang(Yangtze)-Huaihe River Valleys and finally the rainy season in northern China.Thewestern part of the subtropical high moves eastward to the region of Japan in late July and thebeginning of August.It then stays there for quite a long time which results in the straight movement of cold airs intruding from the north to the east of Tibetan Plateau,i.e.the easternregion of China.This provides good condition for the fast southward retreat of the summermonsoon.(4)The intensifieation and development of the Tibetan high at 200 hPa are closely related to the eastward movement of the subtropical high,they often occur simultaneously.
STUDY ON CLIMATIC FEATURES OF SURFACE TURBULENT HEAT EXCHANGE COEFFICIENTS AND SURFACE THERMAL SOURCES OVER THE QINGHAI-XIZANG PLATEAU
ZHAO Ping,CHEN Longxun
2000, 14(1): 13-29 [Abstract]( 314 ) HTML PDF (3143 KB)  ( 443
Abstract:Using monthly mean of surface turbulent heat exchange coefficients calculated based on datafrom four automatic weather stations(AWS)for thermal equilibrium observation in July 1993-September 1996 and of surface conventional measurements,an empirical expression is establishedfor such coefficients.With the expression,the heat exchange coefficients and the components ofsurface thermal source are computed in terms of 1961-1990 monthly mean conventional data from148 stations over the Qinghai-Xizang(Tibetan)Plateau(QXP)and its adjoining areas,and the1961-1990 climatic means are examined.Evidence suggests that the empirical expression is capable of showing the variation of the heatexchange coefficient in a climatic context.The monthly variation of the coefficients averaged overthe QXP is in a range of 4×10-3-5×10-3.The wintertime values are bigger in the mountainsthan in the valleys and reversal in summer.Surface effective radiation and sensible heat are thedominant factors of surface total heat.In spring surface sensible heat is enhanced quickly,resulting in two innegligible regions of sensible heat,one in the west QXP and the other innorthern Tibet.with their maximums emerging in different months.In spring and summersensible heat and surface effective radiation are higher in the west than in the east.The effectiveradiation peaks for the east in October-December and the whole QXP and in June and October forthe west.The surface total heat of the plateau maximizes in May.minimizes in December andJanuary,and shows seasonal variation more remarkable in the SW compared to the eastern part.Inthe SW plateau the total heat is much more intense than the eastern counterpart in all the seasonsexcept winter.Under the effect of the sensible heat,the total heat on the SW plateau starts toconsiderably intensify in February,which leads to a predominant heating region in the west,withits center experiencing a noticeable westward migration early in summer and twice pronouncedweakening in July and after October.However,the weakening courses are owing to differentcauses.The total heat over the north of QXP is greatly strengthened in March.thus generatinganother significant thermal region in the plateau.
AN IMPROVED LAND-SURFACE PROCESS MODEL AND ITS SIMULATION EXPERIMENT-PART II:COUPLING SIMULATION EXPERIMENT OF LAND-SURFACE PROCESS MODEL WITH REGIONAL CLIMATE MODEL
DING Yihui,ZHANG Jing,ZHAO Zongci
2000, 14(1): 30-45 [Abstract]( 335 ) HTML PDF (1964 KB)  ( 312
Abstract: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.
RESPONSES OF A GLOBAL CGCM TO CO2 INCREASE
LI Qingquan,Scott B. POWER
2000, 14(1): 46-60 [Abstract]( 241 ) HTML PDF (3450 KB)  ( 338
Abstract:The responses of the climate system to increase of atmospheric carbon dioxide(CO2)arestudied by using a new version of the Bureau of Meteorological Research Centre(BMRC)globalcoupled general circulation model(CGCM).Two simulations are run:one with atmospheric CO2concentration held constant at 330 ppm,the other with a tripling of atmospheric CO2(990 ppm).Results from the 41-year control coupled integration are applied to analyze the mean state,seasonal cycle and interannual variability in the model.Comparisons between the greenhouseexperiment and the control experiment then provide estimations of the influence of increased CO2on climate changes and climate variability.Especially discussed is the question on whether theclimate changes concerned with CO2 inerease will impact interannual variability in tropical Pacific,such as ENSO.
RETRIEVAL OF THE TROPICAL DIVERGENT WIND FROM OLR AND ITS APPLICATION IN ENSO DIAGNOSIS
ZHANG Yongsheng,JIANG Shangcheng
2000, 14(1): 61-81 [Abstract]( 285 ) HTML PDF (2406 KB)  ( 383
Abstract:In this paper,two schemes proposed by Julian(1984)and Krishnamauti(1986)are used toretrieve the tropical divergent wind at 200 hPa and 850 hPa from the satellite observational Outgoing Long-wave Radiation(OLR).The comparison study has been conducted among the OLR-derived divergent wind field and those directly from wind fields of ECMWF and CAC tropical analysis,and NCEP/NCAR reanalysis for examining their reliability.Then,the divergent windretrieved from OLR by using Julian's scheme is used to composite the diagrams of the Walker circulation and the local Hadley circulation during 1982-1983 ENSO event.The possible linkagebetween the anomalies of summer rainfall in East China during this period and the anomalous Walker and local Hadley circulations is discussed.It is shown that it is practically feasible to use the satellite observed OLR data in theestimation of the tropical divergent wind.It is aiso indicated that NCEP/NCAR reanalysis hasmade a progress for improving the reliability of the tropical divergent wind,though some biasesstill exist in the description of the intensity and position of the divergence (convergence) maximumcenters over Asian monsoon region.The application of Julian's method to a diagnosis on the evolutions of the anomalous Walker and Hadley circulations during 1982-1983 ENSO event showsthat the development of this ENSO event is not companied with the sudden reversal of the Walker circulation,but the propagation of the ascending branch over the western Pacific to the central-eastern Pacific and crossing through the date line,which results in a significant displacement of thevertical circulation over the West Pacific(WP)and the central-east Pacific(CEP).It is alsoindicated that there exists a close linkage between the change of local Hadley circulation in the WPand the Walker circulation in the CEP,implying that the Walker circulation possibly severs as abridge between the anomalies of the SST in the CEP and the change of local Hadley circulation inNorthwest Pacific.The latter is responsible for the climate anomaly over eastern China during thisperiod.
A PRELIMINARY STUDY OF FOURIER SERIES ANALYSIS ON CLOUD TRACKING WITH GOES HIGH TEMPORAL RESOLUTION IMAGES
WANG Zhenhui,ZHOU Jun
2000, 14(1): 82-94 [Abstract]( 279 ) HTML PDF (1121 KB)  ( 511
Abstract:Fourier series analysis is proposed as a new technique to address the problem of"sub-pixelmotion"in deriving cloud motion winds(CMW)from high temporal resolution images.Based on aconcept different from that of maximum correlation matching technique,the Fourier technique computes phase speed as an estimate of cloud motion.It is very effective for tracking small cellularclouds in 1-min interval images and more efficient for computation than the maximum correlation technique because only two templates in same size are involved in primary tracking procedure.Moreover it obtains not only CMW vectors but potentially also velocity spectrum and variance.Apractical example is given to show the cloud motion winds from 1-min interval images with the Fourier method versus those from traditional 30-min interval images with maximum correlation technique.Problems that require further investigation before the Fourier technique can be regardedas a viable technique,especially for cloud tracking with high temporal resolution images,are alsorevealed.
THREE-DIMENSIONAL NUMERICAL SIMULATION OF THE MESOSCALE WIND STRUCTURE OVER SHANDONG PENINSULA
SHENG Lifang,K. H. SCHLUNZEN,WU Zengmao
2000, 14(1): 98-107 [Abstract]( 273 ) HTML PDF (3120 KB)  ( 420
Abstract:General features of 3-dimensional mesoscale wind and temperature structure over Shandong Peninsula are described in this paper.Results are achieved by numerical simulation with the 3-dimensional non-hydrostatic mesoscale model METRAS.For the onset and cessation time of sea-land breezes,the simulation results agree well with the statistical analyses of observational dataavailable for the studied area.One interesting result is the 3 hour response time of wind field to thethermal change. Further statistic analysis based on the observational data is needed to make sure of this correlation.Important effects of coastal mountains on the wind structure are also exposed indetail by the model.Convergence and divergence centers resulting from the conjunction of sea-land breezes and complex terrain are clearly shown,which are not noticed before by conventional synoptic observation and theoretical analysis.
INVESTIGATIONS ON SHORT-TERM CLIMATE PREDICTION BY GCMs IN CHINA
ZHAO Zongci,GAO Xuejie,LUO Yong
2000, 14(1): 108-119 [Abstract]( 242 ) HTML PDF (1460 KB)  ( 362
Abstract:Investigations on the short-term climate predictions by general circulation models(GCMs)in China have been summarized and reviewed in this paper.The research shows that GCMs have thecapability to predict the seasonal and annual characteristics of atmospheric circulation in the Northern Hemisphere and the patterns of temperature and precipitation over China.It is inspiringto notice that the GCMs have the ability to predict the summer rainfall over China before twoseasons.Several issues for the short-term climate prediction by the GCMs have been discussed inthis paper.
AN URBAN SPECIALIZED METEOROLOGICAL SERVICE SYSTEM
FANG Qian,BIAN Guanghui,ZHENG Xinghua,YAN Mingliang,FENG Minxue
2000, 14(1): 120-128 [Abstract]( 219 ) HTML PDF (2557 KB)  ( 307
Abstract:In this paper,the design idea,working process and functional characteristics of Nanjing Urban Specialized Meteorological Service System are systematically described.Some advanced techniques,such as Internet/Intranet (WWW) technique,Active Server Pages(ASP)design andAutomatic Voice Composition etc.,are adopted here.By using Opening TCP/IP Agreement.thesystem realizes connecting the three networks of Novell,Windows NT and 9210 project (Meteorological Satellite Integrated Application Professional System) with ground meteorological special telephone line,thus the new process for collecting and processing data,making and disseminating specialized meteorological information,serving and managing users is established.
 
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