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2003 Vol. 20, No. 5

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A New North Atlantic Oscillation Index and Its Variability
LI Jianping, Julian X.L.WANG
2003, 20(5): 661-676. doi: 10.1007/BF02915394
A new North Atlantic Oscillation (NAO) index, the NAOI, is defined as the differences of normalizedsea level pressures regionally zonal-averaged over a broad range of longitudes 80°W-30°E. A comprehensivecomparison of six NAO indices indicates that the new NAOI provides a more faithful representation ofthe spatial-temporal variability associated with the NAO on all timescales. A very high signal-to-noiseratio for the NAOI exists for all seasons, and the life cycle represented by the NAOI describes well theseasonal migration for action centers of the NAO. The NAOI captures a larger fraction of the variance ofsea level pressure over the North Atlantic sector (20°-90°N, 80°W-30°E), on average 10% more than anyother NAO index. There are quite different relationships between the NAOI and surface air temperatureduring winter and summer. A novel feature, however, is that the NAOI is significantly negative correlatedwith surface air temperature over the North Atlantic Ocean between 10°-25°N and 70°-30°W, whetherin winter or summer. From 1873, the NAOI exhibits strong interannual and decadal variability. Itsinterannual variability of the twelve calendar months is obviously phase-locked with the seasonal cycle.Moreover, the annual NAOI exhibits a clearer decadal variability in amplitude than the winter NAOI. Anupward trend is found in the annual NAOI between the 1870s and 1910s, while the other winter NAOindices fail to show this tendency. The annual NAOI exhibits a strongly positive epoch of 50 years between1896 and 1950. After 1950, the variability of the annual NAOI is very similar to that of the winter NAOindices.
Glacial-Interglacial Atmospheric CO2 Change--The Glacial Burial Hypothesis
2003, 20(5): 677-693. doi: 10.1007/BF02915395
Organic carbon buried under the great ice sheets of the Northern Hemisphere is suggested to bethe missing link in the atmospheric CO2 change over the glacial-interglacial cycles. At glaciation, theadvancement of continental ice sheets buries vegetation and soil carbon accumulated during warmer pe-riods. At deglaciation, this burial carbon is released back into the atmosphere. In a simulation over twoglacial-interglacial cycles using a synchronously coupled atmosphere-land-ocean carbon model forced byreconstructed climate change, it is found that there is a 547-Gt terrestrial carbon release from glacialmaximum to interglacial, resulting in a 60-Gt (about 30-ppmv) increase in the atmospheric CO2, with theremainder absorbed by the ocean in a scenario in which ocean acts as a passive buffer. This is in contrastto previous estimates of a land uptake at deglaciation. This carbon source originates from glacial burial,continental shelf, and other land areas in response to changes in ice cover, sea level, and climate. The inputof light isotope enriched terrestrial carbon causes atmospheric 513C to drop by about 0.3% at deglaciation,followed by a rapid rise towards a high interglacial value in response to oceanic warming and regrowthon land. Together with other ocean based mechanisms such as change in ocean temperature, the glacialburial hypothesis may offer a full explanation of the observed 80 100-ppmv atmospheric CO2 change.
Joint Propagating Patterns of SST and SLP Anomalies in the North Pacific on Bidecadal and Pentadecadal Timescales
ZHU Yimin, YANG Xiuqun
2003, 20(5): 694-710. doi: 10.1007/BF02915396
Wavelet analyses are applied to the Pacific Decadal Oscillation index and North Pacific index forthe period 1900 2000, which identifies two dominant interdecadal components, the bidecadal (15-25-yr)and pentadecadal (50-70-yr) modes. Joint propagating patterns of sea surface temperature (SST) andsea level pressure (SLP) anomalies in the North Pacific for the two modes are revealed by using thetechniques of multi-channel singular spectrum analysis (MSSA) and linear regression analysis with theglobal sea surface temperature (GISST) data and the northern hemispheric SLP data for the commonperiod 1903-1998. Significant differences in spatio-temporal structures are found between the two modes.For the bidecadal mode, SST anomalies originating from the Gulf of Alaska appear to slowly spreadsouthwestward, inducing a reversal of early SST anomalies in the central North Pacific. Due to furtherwestward spreading, the SST variation of the central North Pacific leads that of the Kuroshio-OyashioExtension (KOE) region by approximately 4 to 5 years. Concomitantly, SLP anomalies spread over mostparts of the North Pacific during the mature phase and then change into an NPO(North Pacific Oscillation)-like pattern during the transition phase. For the pentadecadal mode, SST anomalies develop in thesoutheast tropical Pacific and propagate along the North American coast to the mid-latitudes; meanwhile,SST anomalies with the same polarity in the western tropical Pacific expand northward to Kuroshio and itsextension region; both merge into the central North Pacific reversing the sign of early SST anomalies there.Accompanying SLP anomalies are characterized by an NPO-like pattern during the mature phase whilethey are dominant over the North Pacific during the transitional phase. The bidecadal and pentadecadalmodes have different propagating patterns, suggesting that the two interdecadal modes may arise fromdifferent physical mechanisms.
Dependence of Hurricane Intensity and Structures on Vertical Resolution and Time-Step Size
Da-Lin ZHANG, Xiaoxue WANG
2003, 20(5): 711-725. doi: 10.1007/BF02915397
In view of the growing interests in the explicit modeling of clouds and precipitation, the effects of varyingvertical resolution and time-step sizes on the 72-h explicit simulation of Hurricane Andrew (1992) arestudied using the Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR)mesoscale model (i.e., MMS) with the finest grid size of 6 km. It is shown that changing vertical resolutionand time-step size has significant effects on hurricane intensity and inner-core cloud/precipitation, butlittle impact on the hurricane track. In general, increasing vertical resolution tends to produce a deeperstorm with lower central pressure and stronger three-dimensional winds, and more precipitation. Similareffects, but to a less extent, occur when the time-step size is reduced. It is found that increasing thelow-level vertical resolution is more efficient in intensifying a hurricane, whereas changing the upper-levelvertical resolution has little impact on the hurricane intensity. Moreover, the use of a thicker surface layertends to produce higher maximum surface winds. It is concluded that the use of higher vertical resolution,a thin surface layer, and smaller time-step sizes, along with higher horizontal resolution, is desirable tomodel more realistically the intensity and inner-core structures and evolution of tropical storms as well asthe other convectively driven weather systems.
The Performance of Atmospheric Component Model R42L9 of GOALS/LASG
WU Tongwen, LIU Ping, WANG Zaizhi, LIU Yimin, YU Rucong, WU Guoxiong
2003, 20(5): 726-742. doi: 10.1007/BF02915398
This paper examines the performance of an atmospheric general circulation model (AGCM) de-veloped at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysi-cal Fluid Dynamics, Institute of Atmospheric Physics (LASG/IAP). It is a spectral model truncated atR42(2.8125°long× 1.66°lat) resolution and with nine vertical levels, and referred to as R42L9/LASG here-after. It is also the new version of atmospheric component model R15L9 of the global ocean-atmosphere-land system (GOALS/LASG). A 40-year simulation in which the model is forced with the climatologicalmonthly mean sea surface temperature is compared with the 40-year (1958 97) U.S. National Centerfor Environmental Prediction (NCEP) global reanalysis and the 22-year (1979-2000) Xie-Arkin monthlyprecipitation clinatology. The mean DJF and JJA geographical distributions of precipitation, sea levelpressure, 500-hPa geopotential height, 850-hPa and 200-hPa zonal wind, and other fields averaged for thelast 30-year integration of the R42L9 model are analyzed. Results show that the model reproduces well theobserved basic patterns, particularly precipitation over the East Asian region. Comparing the new modelwith R15L9/LASG, the old version with coarse resolution (nearly 7.5°long×4.5°lat), shows an obviousinprovement in the simulation of regional climate, especially precipitation. The weaknesses in simulationand future improvements of the model are also discussed.
Regime Shifts in the North Pacific Simulated by a COADS-driven Isopycnal Model
WANG Dongxiao, WANG Jia, Lixin WU, Zhengyu LIU
2003, 20(5): 743-754. doi: 10.1007/BF02915399
The Miami Isopycnal Coordinate Ocean Model (MICOM) is adopted to simulate the interdecadalvariability in the Pacific Ocean with most emphasis on regime shifts in the North Pacific. The compu-tational domain covers 60°N to 40°S with an enclosed boundary condition for momentum flux, whereasthere are thermohaline fluxes across the southern end as a restoring term. In addition, sea surface salinityof the model relaxes to the climatological season cycle, which results in climatological fresh water fluxes.Surface forcing functions from January 1945 through December 1993 are derived from the ComprehensiveOcean and Atmospheric Data Set (COADS). Such a numerical experiment reproduces the observed evo-lution of the interdecadal variability in the heat content over the upper 400-m layer by a two-year lag.Subduction that occurs at the ventilated thermocline in the central North Pacific is also been simulatedand the subducted signals propagate from 35°N to 25°N, taking about 8 to 10 years, in agreement with theeXpendable Bathy Thermograph observation over recent decades. Interdecadal signals take a southwest-ward and downward path rather than westward propagation, meaning they are less associated with thebaroclinic planetary waves. During travel, the signals appear to conserve potential vorticity. Therefore,the ventilated thermocline and related subduction are probably the fundamental physics for interdecadalvariability in the mid-latitude subtropics of the North Pacific.
The Change of North China Climate in Transient Simulations Using the IPCC SRES A2 and B2 Scenarios with a Coupled Atmosphere-Ocean General Circulation Model
BUHE Cholaw, Ulrich CUBASCH, LIN Yonghui, JI Liren
2003, 20(5): 755-766. doi: 10.1007/BF02915400
This paper applies the newest emission scenarios of the sulfur and greenhouse gases, namely IPCCSRES A2 and B2 scenarios, to investigate the change of the North China climate with an atmosphere-oceancoupled general circulation nodel. In the last three decades of the 21st century, the global warming enlargesthe land-sea thermal contrast, and hence, causes the East Asian summer (winter) monsoon circulation tobe strengthened (weakened). The rainfall seasonality strengthens and the summer precipitation increasessignificantly in North China. It is suggested that the East Asian rainy area would expand northward toNorth China in the last three decades of the 21st century. In addition, the North China precipitationwould increase significantly in September. In July, August, and September, the interannual variability ofthe precipitation enlarges evidently over North China, implying a risk of flooding in the future.
Establishing a Ultraviolet Radiation Observational Network and Enhancing the Study on Ultraviolet Radiation
BAI Jianhui, WANG Gengchen
2003, 20(5): 767-774. doi: 10.1007/BF02915401
On the basis of analyzing observational data on solar radiation, meteorological parameters, and totalozone amount for the period of January 1990 to December 1991 in the Beijing area, an empirical calculationmethod for ultraviolet radiation (UV) in clear sky is obtained. The results show that the calculated valuesagree well with the observed, with maximum relative bias of 6.2% and mean relative bias for 24 months of1.9%. Good results are also obtained when this method is applied in Guangzhou and Mohe districts. Thelong-term variation of UV radiation in clear sky over the Beijing area from 1979 to 1998 is calculated, andthe UV variation trends and causes are discussed: direct and indirect UV energy absorption by increasingpollutants in the troposphere may have caused the UV decrease in clear sky in the last 20 years. With theenhancement of people's quality of life and awareness of health, it will be valuable and practical to providUV forecasts for typical cities and rural areas. So, we should develop and enhance UV study in systematicmonitoring, forecasting, and developing a good and feasible method for UV radiation reporting in China,especially for big cities.
On a Simple Dynamics Model of Interaction between Oasis and Climate
WU Lingyun, CHAO Jiping, FU Congbin, PAN Xiaoling
2003, 20(5): 775-780. doi: 10.1007/BF02915402
This paper constructs a coupled system of oasis and atmosphere based on an oasis evolvement model byadding atmospheric motion to discuss the problem of oasis evolvement and its effects on regional climate.The results indicate that the range and scope of the negative temperature anomalies become larger whenthe oasis cover fraction increases. Correspondingly, the positive temperature anomalies becomes smaller inthe desert no matter in summer or spring. And the variability is more obvious in summer than in spring.So it may be concluded that the oasis not only maintains and develops itself but also develops partial airover the desert into an oasis climate.
30-60-day Oscillations of Convection and Circulation Associated with the Thermal State of the Western Pacific Warm Pool during Boreal Summer
REN Baohua, HUANG Ronghui
2003, 20(5): 781-793. doi: 10.1007/BF02915403
This study focuses on the characteristics of the 30 60-day oscillation (MJO) associated with theinterannual variability of the thermal state in the western Pacific warm pool. The composite resultsshow that the amplitude of MJO convection over the tropical western Pacific tends to intensify (reduce)in the WARM (COLD) case. The negative correlations between MJO convection in the WARM and inthe COLD cases are examined to be significant over most of the Asian-Pacific region. The evolutions of MJO convection and lower circulation, on the one hand, exhibit larger differences between the WARMand COLD cases, but on the other hand, display a unique feature in that a well-developed MJO cyclone(anticyclone) is anchored over the Asian-Western Pacific domain at the peak enhanced (suppressed) MJO convection phase over the western Pacific warm pool, either in the WARM or in the COLD case. Thisunique feature of MJO shows a Gill-type response of lower circulation to the convection and is inferred tobe an inherent appearance of MJO. The context in the paper suggests there may exist interactions between MJO and the interannual variability of the thermal state in the western Pacific warm pool.
The Influence of Convergence Movement on Turbulent Transportation in the Atmospheric Boundary Layer
HU Yinqiao, ZUO Hongchao
2003, 20(5): 794-798. doi: 10.1007/BF02915404
Classical turbulent K closure theory of the atmospheric boundary layer assumes that the verticalturbulent transport flux of any macroscopic quantity is equivalent to that quantity's vertical gradienttransport flux. But a cross coupling between the thermodynamic processes and the dynamic processesin the atmospheric system is demonstrated based on the Curier-Prigogine principle of cross coupling oflinear thermodynamics. The vertical turbulent transportation of energy and substance in the atmosphericboundary layer is related not only to their macroscopic gradient but also to the convergence and the di-vergence movement. The transportation of the convergence or divergence movement is important for theatmospheric boundary layer of the heterogeneous underlying surface and the convection boundary layer.Based on this, the turbulent transportatiou in the atmospheric boundary layer, the energy budget of theheterogeneous underlying surface and the convection boundary layer, and the boundary layer parameteri-zation of land surface processes over the heterogeneous underlying surface are studied. This research offersclues not only for establishing the atmospheric boundary layer theory about the heterogeneous underlyingsurface, but also for overcoming the difficulties encountered recently in the application of the atmosphericboundary layer theory.
Influence of the Mascarene High and Australian High on the Summer Monsoon in East Asia: Ensemble Simulation
XUE Feng, JIANG Dabang, LANG Xianmei, WANG Huijun
2003, 20(5): 799-809. doi: 10.1007/BF02915405
By using a nine-level atmospheric general circulation model developed at the Institute of AtmosphericPhysics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influenceof the Mascarene high (MH) and Australian high (AH) over the southern subtropics upon the East Asiansummer monsoon circulation and summer precipitation in East Asia. The use of ensemble statistics isadopted to reduce the simulation errors. The result shows that with the intensification of MH, the Somalilow-level jet is significantly enhanced together with the summer monsoon circulation in the tropical Asiaand western Pacific region. Furthermore, the anticyclonic anomaly in the tropical western Pacific to theeast of the Philippines may induce a weak East-Asia-Pacific teleconnection pattern. In the meantime,geopotential height in the Tropics is enhanced while it is reduced over most regions of mid-high latitudes,thus the northwestern Pacific subtropical high at 500 hPa extends southwestward, resulting in more rainfallin southern China and less rainfall in northern China. A similar anomaly pattern of the atmosphericcirculation systems is found in the experiment of the intensification of AH. On the other hand, because thecross-equatorial currents associated with AH are much weaker than the Somali jet, the anomaly magnitudecaused by tihe intensification of AH is generally weak, and the influence of AH on summer rainfall in Chinaseems to be localized in southern China. Comparison between the two sets of experiments indicates thatMH plays a crucial role in the interactions of general atmospheric circulation between the two hemispheres.
A Comparative Study of Conservative and Nonconservative Schemes
LIN Wantao, WANG Chunhua, CHEN Xingshu
2003, 20(5): 810-814. doi: 10.1007/BF02915406
For the conservative and non-conservative schemes of nonlinear evolution equations, by taking thetwo-dimensional shallow water wave equations as an example, a comparative analysis on computationalstability is carried out. The relationship between the nonlinear computational stability, the structure ofthe difference schemes, and the form of initial values is also discussed.
Analysis of Simulated Heavy Rain over the Yangtze River Valley During 11-30 June 1998 Using RIEMS
XIONG Zhe, WANG Shuyu, ZENG Zhaomei, FU Congbin
2003, 20(5): 815-824. doi: 10.1007/BF02915407
RIEMS' ability to simulate extreme monsoon rainfall is examined using the 18-month (April 1997September 1998) integrated results. Model-simulated heavy precipitation over the Yangtze River valleyduring 11-30 June 1998 is compared with the observation, and the relationships between this heavy rainfallprocess and the large-scale circulations, such as the westerly jet, low-level jet, and water vapor transport,are analyzed to further understand the mechanisms for simulating heavy monsoon rainfall. The analysisresults show that (1) RIEMS can reproduce the pattern of heavy precipitation over the Yangtze River valleyduring 11-30 June 1998, but it is shifted northwestwards. (2) The simulated West Pacific Subtropical High(WPSH) that controls the East Asia Monsoon evolution is stronger than the observation and is extendedwestwards, which possibly leads to the north westward shift of the heavy rain belt. (3) The Westerly jetat 200 hPa and the Low-level jet at 850 hPa, both of which are related to the heavy monsoon rainfall,are reasonably reproduced by RIEMS during 11-30 June 1998, although the intensities of the simulatedWesterly/Low-level jets are strong and the location of the Westerly jet leans to the southeast, which maybe the causes of RIEMS producing too much heavy rainfall in the north of the Yangtze River valley.
Up-Sliding Slantwise Vorticity Development and the Complete Vorticity Equation with Mass Forcing
CUI Xiaopeng, GAO Shouting, WU Guoxiong
2003, 20(5): 825-836. doi: 10.1007/BF02915408
The moist potential vorticity (MPV) equation is derived from complete atmospheric equations includingthe effect of mass forcing, with which the theory of Up-sliding Slantwise Vorticity Development (USVD)is proposed based on the theory of Slantwise Vorticity Development (SVD). When an air parcel slides upalong a slantwise isentropic surface, its vertical component of relative vorticity will develop, and the steeperthe isentropic surface is, the more violent the development will be. From the definition of MPV and theMPV equation produced here in, a complete vorticity equation is then put forward with mass forcing, whichexplicitly includes the effects of both internal forcings, such as variations of stability, baroclinicity, andvertical shear of horizontal wind, and external forcings, such as diabatic heating, friction, and mass forcing.When isentropic surfaces are flat, the complete vorticity equation matches its traditional counterpart. Thephysical interpretations of some of the items which are included in the complete vorticity equation butnot in the traditional one are studied with a simplified model of the Changjiang-Huaihe Meiyu front. A60-h simulation is then performed to reproduce a torrential rain event in the Changjiang-Huaihe regionand the output of the model is studied qualitatively based on the theory of USVD. The result shows thatthe conditions of the theory of USVD are easily satisfied immediately in front of mesoscale rainstorms inthe downwind direction, that is, the theory of USVD is important to the development and movement ofthese kinds of systems.
A New Way to Predict Forecast Skill
TAN Jiqing, XIE Zhenghui, JI Liren
2003, 20(5): 837-841. doi: 10.1007/BF02915409
Forecast skill (Anomaly Correlated Coefficient, ACC) is a quantity to show the forecast quality ofthe products of numerical weather forecasting models. Predicting forecast skill, which is the foundationof ensemble forecasting, means submitting products to predict their forecast quality before they are used.Checking the reason is to understand the predictability for the real cases. This kind of forecasting servicehas been put into operational use by statistical methods previously at the National Meteorological Center(NMC), USA (now called the National Center for Environmental Prediction (NCEP)) and European Centerfor Medium-range Weather Forecast (ECMWF). However, this kind of service is far from satisfactorybecause only a single variable is used with the statistical method. In this paper, a new way based onthe Grey Control Theory with multiple predictors to predict forecast skill of forecast products of theT42L9 of the NMC, China Meteorological Administration (CMA) is introduced. The results show: (1)The correlation coefficients between "forecasted" and real forecast skill range from 0.56 to 0.7 at differentseasons during the two-year period. (2) The grey forecasting model GM(1,8) forecasts successfully thehigh peaks, the increasing or decreasing tendency, and the turning points of the change of forecast skill ofcases from 5 January 1990 to 29 February 1992.
Quick Measurement of CH4, CO2 and N2O Emissions from a Short-Plant Ecosystem
WANG Yuesi, WANG Yinghong
2003, 20(5): 842-844. doi: 10.1007/BF02915410
Combining improved injector, gas line and valve-driving models, a gas chromatograph (GC) equippedwith Hydrogen Flame Ionization Detector (FID) and Electron Capture Detector (ECD), can measureCH4, CO2, and N2O simultaneously in an air sample in four minutes. Test results show that the systemhas high sensitivity, resolution, and precision; the linear response range of the system meets the requirementof flux measurements in situ. The system is suitable for monitoring fluxes of the main greenhouse gases ina short-plant field since it is easy to use, efficacious, and constant and reliable in collecting data.
A Case Study of the Improvement of Soil Moisture Initialization in IAP-PSSCA
GUO Weidong, WANG Huijun
2003, 20(5): 845-848. doi: 10.1007/BF02915411
A prediction system is employed to investigate the potential use of a soil moisture initialization schemein seasonal precipitation prediction through a case study of severe floods in 1998. The results show thatdriving the model with reasonable initial soil moisture distribution is helpful for precipitation prediction,and the initialization scheme is easy to use in operational prediction.