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2000 Vol. 17, No. 1

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Wave-Mean Flow Interaction: the Role of Continuous-Spectrum Disturbances
Zeng Qingcun, Zhang Minghua
2000, 17(1): 1-17. doi: 10.1007/s00376-000-0039-0
Traditionally, “eddy feeds zonal flow” in the atmosphere is considered as a result of decaying unstable waves. We show that disturbances made of non-modal solutions-the continuous-spectrum disturbances-can also effectively transport zonal angular momentum and interact with the zonal basic flow. These disturbances, though stable, eventually decay, losing their energy to strengthen the westerly jets in the atmosphere.Calculations with observational data illustrate that the atmospheric zonal flow is maintained primarily by continuous-spectrum disturbances rather than by unstable waves. Angular momentum transport by continuous-spectrum disturbances is one order of magnitude larger than that by all kinds of normal modes (referred as discrete-spectrum disturbances) including unstable waves.
Interannual and Decadal Variations of Snow Cover over Qinghai-Xizang Plateau and Their Relationships to Summer Monsoon Rainfall in China
Chen Lieting, Wu Renguang
2000, 17(1): 18-30. doi: 10.1007/s00376-000-0040-7
Interannual and decadal variations of winter snow cover over the Qinghai-Xizang Plateau (QXP) are analyzed by using monthly mean snow depth data set of 60 stations over QXP for the period of 1958 through 1992. It is found that the winter snow cover over QXP bears a pronounced quasi-biennial oscillation, and it underwent an obvious decadal transition from a poor snow cover period to a rich snow cover period in the late 1970’s during the last 40 years.It is shown that the summer rainfall in the eastern China is closely associated with the winter snow cover over QXP not only in the interannual variation but also in the decadal variation. A clear relationship exists in the quasi-biennial oscillation between the summer rainfall in the northern part of North China and the southern China and the winter snow cover over QXP. Furthermore, the summer rainfall in the four climate divisions of Qinling-Daba Mountains, the Yangtze-Huaihe River Plain, the upper and lower reaches of the Yangtze River showed a remarkable transition from drought period to rainy period in the end of 1970’s, in good correspondence with the decadal transition of the winter snow cover over QXP.
The Interannual Variability of East Asian Monsoon and Its Relationship with SST in a Coupled Atmosphere-Ocean-Land Climate Model
Wang Huijun
2000, 17(1): 31-47. doi: 10.1007/s00376-000-0041-6
Based on a 200 year simulation and reanalysis data (1980-1996), the general characteristics of East Asian monsoon (EAM) were analyzed in the first part of the paper. It is clear from this research that the South Asian monsoon (SAM) defined by Webster and Yang (1992) is geographically and dynamically different from the East Asian monsoon (EAM). The region of the monsoon defined by Webster and Yang (1992) is located in the tropical region of Asia (40-110oE, 10-20oN), including the Indian monsoon and the Southeast Asian monsoon, while the EAM defined in this paper is located in the subtropical region of East Asia (110-125oE, 20-40oN). The components and the seasonal variations of the SAM and EAM are different and they characterize the tropical and subtropical Asian monsoon systems respectively. A suitable index (EAMI) for East Asian monsoon was then defined to describe the strength of EAM in this paper.In the second part of the paper, the interannual variability of EAM and its relationship with sea surface temperature (SST) in the 200 year simulation were studied by using the composite method, wavelet transformation, and the moving correlation coefficient method. The summer EAMI is negatively correlated with ENSO (El Nino and Southern Oscillation) cycle represented by the NINO3 sea surface temperature anomaly (SSTA) in the preceding April and January, while the winter EAM is closely correlated with the succeeding spring SST over the Pacific in the coupled model. The general differences of EAM between El Nino and La Nina cases were studied in the model through composite analysis. It was also revealed that the dominating time scales of EAM variability may change in the long-term variation and the strength may also change. The anomalous winter EAM may have some correlation with the succeeding summer EAM, but this relationship may disappear sometimes in the long-term climate variation. Such time-dependence was found in the relationship between EAM and SST in the long-term climate simulation as well.
The Interannual Variability of East Asian Winter Monsoon and Its Relation to the Summer Monsoon
Chen Wen, Hans-F. Graf, Huang Ronghui
2000, 17(1): 48-60. doi: 10.1007/s00376-000-0042-5
Based on the NCEP/NCAR reanalysis data the interannual variability of the East Asian winter monsoon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the tropical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropical Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly influenced by the processes associated with the SST anomaly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (El Ni?o), and it becomes strong when there is a negative SST anomaly (La Ni?a). Moreover, the SST anomaly in the South China Sea is found to be Closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possible reason for the recent 1998 summer flood in China is briefly discussed too.
Numerical and Dynamical Analyses of Heat Source Forcing and Restricting Subtropical High Activity
Zhang Ren, Yu Zhihao
2000, 17(1): 61-71. doi: 10.1007/s00376-000-0043-4
By using the numerical and dynamical methods, the influence and restriction of the heat source forcing on the subtropical geopotential fields and flow fields are studied and discussed in a model atmosphere. The main results show that the zonal symmetrical solar radiation heating chiefly induces the geopotential field changing gradually and leads the subtropical high moving slowly, but when the zonal asymmetric thermal difference between ocean and continent achieves its critical value, which usually causes the geopotential field a catastrophe, and consequently induces the subtropical high shake-up or jump. The abnormal activity of the subtropical high is possibly caused by the abnormality of the thermal factor.
Global Two-Dimensional Chemistry Model and Simulation of Atmospheric Chemical Composition
Zhang Renjian, Wang Mingxing, Zeng Qingcun
2000, 17(1): 72-82. doi: 10.1007/s00376-000-0044-3
A global two-dimensional zonally averaged chemistry model is developed to study the chemical composition of atmosphere. The region of the model is from 90oS to 90oN and from the ground to the altitude of 20 km with a resolution of 5o×1km. The wind field is residual circulation calculated from diabatic rate. 34 species and 104 chemical and photochemical reactions are considered in the model. The sources of CH4, CO and NOx, which are divided into seasonal sources and non-seasonal sources, are parameterized as a function of latitude and time. The chemical composition of atmosphere was simulated with emission level of CH4, CO and NOx in 1990. The results are compared with observations and other model results, showing that the model is successful to simulate the atmospheric chemical composition and distribution of CH4.
Mitigation Options for Methane, Nitrous Oxide and Nitric Oxide Emissions from Agricultural Ecosystems
Zheng Xunhua, Wang Mingxing, Wang Yuesi, Shen Renxing, Li Jing, J. Heyer, M. Koegge, H. Papen
2000, 17(1): 83-92. doi: 10.1007/s00376-000-0045-2
An experimental study on mitigation of greenhouse gas (CH4, N2O and NO) emission has been conducted in a typical cropping system of Southeast China for 4 years. By simultaneous measurement, the CH4, N2O and NO emission fluxes from rice-wheat rotation fields, effects of fertilization, water management, temperature and soil moisture were investigated. Temperature, fertilization and water status were found to be the key factors to regulate CH4, N2O and NO emissions. Based on the experimental results, some agricultural measures were recommended as technical options to mitigate greenhouse gas emissions from rice-wheat rotation ecosystems. These mitigation measures are reducing mineral N input, coupling organic manure with chemical fertilizers, applying fertilizers which release available N slowly during periods with intensive plant activity, and applying dry fermented organic manure and well management of water and fertilizer.
Study on Horizontal Relative Diffusion in the Troposphere and Lower Stratosphere
Zheng Yi
2000, 17(1): 93-102. doi: 10.1007/s00376-000-0046-1
The behaviour of relative diffusion theory and Gifford’s random-force theory for long-range atmospheric diffusion is examined. When a puff scale is smaller than the Lagrangian length scale, 2KTL, an accelerative relative diffusion region exists, i.e., σy∝t3/2. While the puff diffusion enters a two-dimensional turbulence region, in which the diffusion scale is larger than 500 km, or time scale is larger than 1 day, divergence and convergence are main cause of horizontal diffusion. Between the two above-mentioned regimes, diffusion deviation is given byσy=2KTL. The large-scale horizontal relative diffusion parameters were obtained by analyzing the data of radioactive cloud width collected in air nuclear tests.
A Numerical Study on Effects of Land-Surface Heterogeneity from “Combined Approach” on Atmospheric Process Part I: Principle and Method
Zeng Xinmin, Zhao Ming, Su Bingkai
2000, 17(1): 103-120. doi: 10.1007/s00376-000-0047-0
A method based on Giorgi (1997a, 1997b) and referred to as ‘combined approach’, which is a combination of mosaic approach and analytical-statistical-dynamical approach, is proposed. Compared with those of other approaches, the main advantage of the combined approach is that it not only can represent both interpatch and intrapatch variability, but also cost less computational time when the land surface heterogeneity is considered. Because the independent variable of probability density function (PDF) is extended to the single valued function of basic meteorological characteristic quantities, which is much more universal, the analytical expressions of the characteristic quantities, (e.g., drag coefficient, snow coverage, leaf surface aerodynamical resistance) affected by roughness length are derived, when the roughness length (and/ or the zero plane displacement) heterogeneity has been mainly taken into account with the approach. On the basis of the rule which the PDF parameters should follow, we choose a function y of the roughness length z0 as the PDF independent variable, and set different values of the two parameters width ratio αn and height ratio γ of PDF (here a linear, symmetric PDF is applied) for sensitivity experiments, from which some conclusions can be drawn, e.g., relevant characteristic terms show different sensitivities to the heterogeneous characteristic (i.e., roughness length), which suggests that we should consider the heterogeneities of the more sensitive terms in our model instead of the heterogeneities of the rest, and which also implies that when the land surface scheme is coupled into the global or regional atmospheric model, sensitivity tests against the distribution of the heterogeneous characteristic are very necessary; when the parameterαn is close to zero, little heterogeneity is represented, andαn differs with cases, which have an upper limit of about 0.6; in the reasonable range ofαn, a peak-like distribution of roughness length can be depicted by a small value ofγ, etc..
Tropical Convective Activities Related to Summer Rainfall Anomaly in China
Guo Pinwen, Tian Hong, Liu Xuanfei
2000, 17(1): 121-128. doi: 10.1007/s00376-000-0048-z
The paper presents the SVD-revealed relation of the tropical convection anomaly patterns to the summer rainfall counterparts of China, indicating that a) the ENSO-associated tropical convection anomaly is highly advantageous but the corresponding rainfall anomaly can only account for 10.3% of total variance, the rainfall anomaly related to tropical monsoon variation with the northern South China Sea as the center of convection abnormality for 18.8% and to the variation inside the tropical monsoon for 11.2%; b) the ENSO-related summer precipitation anomaly displays a pattern of excessive rainfall in the south and deficit in the north, the anomaly relative to the tropical monsoon variation a pattern of more precipitation in the Yangtze River valleys and less in North, Northeast and South China, and that in relation to the variation within the tropical monsoon a pattern of two rainbands, one in the Yangtze River valleys and the other in North China.
Conversion Characteristics between Barotropic and Baroclinic Circulations of the SAH in Its Seasonal Evolution
Liu Xuanfei, Zhu Qiangen, Guo Pinwen
2000, 17(1): 129-139. doi: 10.1007/s00376-000-0049-y
In the context of 1958-1997 NCEP/NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and baroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, where upon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter), the SAH is a thermal (dynamical) system, with dominant baroclinicity (barotropicity), either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the “thermal guidance” of its baroclinic component circulation, suggestion that the component circulation precedes the system itself in variation; iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the “dynamic steering” of its barotropic component circulation.
Calculation of Solar Albedo and Radiation Equilibrium over the Qinghai-Xizang Plateau and Analysis of Their Climatic Features
Zhao Ping, Chen Longxun
2000, 17(1): 140-156. doi: 10.1007/s00376-000-0050-5
Using radiation data from the Automatic Weather Stations (AWSs) for thermal balance observations, which were set up at Lhasa, Nagqu, Xigaze and Nyingchi by the Sino-Japanese Asian Monsoon Mechanism Co-operative Project in 1993-1996, and 1985-1989 Earth Radiation Balance Experiment (ERBE) measurements of Langley Research Center/NASA of US, and 1961-1996 monthly mean data from 148 surface stations over the Qinghai-Xizang Plateau (QXP) and its neighborhood, study is performed on empirical calculation methods of surface albedo, surface total radiation, planetary albedo and outgoing longwave radiation with the climatic features of radiation balance at the surface and the atmospheric top examined. Evidences suggest that the empirical formulae for surface albedo, planetary albedo, surface total radiation and outgoing longwave radiation from the atmospheric top are capable of describing their seasonal and interannual variations over the QXP. The surface albedo is marked by noticeable seasonal variation and yearly mean of 0.22 with the maximum of 0.29 in January and minimum of 0.17 in July and August; in winter the albedo has great horizontal difference, bigger in the mountains than in the river valleys, and small in summer. The planetary albedo shows a smaller range of its annual variation with the yearly mean of 0.37, the maximum (minimum) occurring in February and March (autumn). In winter its high-value regions are mainly at Gar (Shiquanhe) in the western QXP and from the southwestern Qinghai to the northeastern Tibet and the low-value area at the northern slope of the central Himalayas; in summer, however, the albedo distribution displays clearly a progressive decrease from southeast to northwest. As for the surface total radiation, its values and annual varying range are smaller in the east than in the southwest. Its high-value center is at the southern slope of the Himalayas in winter and makes a conspicuous westward migration in spring, remaining there for a long time, and it begins to retreat eastward in autumn, Monthly mean values of he surface net radiation are all positive and larger in summer than in winter. The net radiation is significantly intensified under the combined effect of surface total radiation and surface albedo from spring to early summer, resulting in the strongest sector in the mid plateau with its center staying nearly motionless from March to September, and is reduced in autumn dominantly by surface effective radiation. The earth-atmosphere system loses heat outward from October to next February and gains in other months. On an average, the plateau gains heat of 15 W m-2 on an annual basis.
Study on Ann-Based Multi-Step Prediction Model of Short-Term Climatic Variation
Jin Long, Ju Weimin, Miao Qilong
2000, 17(1): 157-164. doi: 10.1007/s00376-000-0051-4
In the context of 1905-1995 series from Nanjing and Hangzhou, study is undertaken of establishing a predictive model of annual mean temperature in 1996-2005 to come over the Changjiang (Yangtze River) delta region through mean generating function and artificial neural network in combination. Results show that the established model yields mean error of 0.45℃ for their absolute values of annual mean temperature from 10 yearly independent samples (1986-1995) and the difference between the mean predictions and related measurements is 0.156℃. The developed model is found superior to a mean generating function regression model both in historical data fitting and independent sample prediction.