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2001 Vol. 18, No. 3

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Influence of Inhomogeneity on the Estimation of Mean and Extreme Temperature Trends in Beijing and Shanghai
Yan Zhongwei, Yang Chi, Phil Jones
2001, 18(3): 309-322. doi: 10.1007/BF02919312
Inhomogeneities in the temperature series from Beijing and Shanghai are analyzed, using the detailed histories of both sets of observations. The major corrections for different periods range from -0.33 to 0.6?for Beijing and -0.33 to 0.3? for Shanghai. Annual mean and extreme temperature series are deduced from the daily observations and trends in the adjusted and unadjusted series are compared. The adjusted yearly mean temperatures show a warming trend of 0.5? / century since the turn of this century and an enhanced one of 2.0?/century since the 1960s. In contrast, the unadjusted data show a twice this value trend for Shanghai but little trend for Beijing at the long-term scale and overestimate the recent warming by 50%-130%. Beijing experienced a decrease of frequency of the extremes together with a cooling during the 1940s-1970s and an increase of frequency of extremes together with a warming since then. The trends of frequency of extremes at Shanghai were more or less opposite. It is implied that the regional trends of strong weather variations may be different even when the regional mean temperatures coherently change.
Mechanism of Balanced Flow and Frontogenesis
Wu Rongsheng, Fang Juan
2001, 18(3): 323-334. doi: 10.1007/BF02919313
The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise,discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the multi-value problem.
Implementing a New Snow Scheme in Simplified Simple Biosphere Model
Sun Shufen, Xue Yongkang
2001, 18(3): 335-354. doi: 10.1007/BF02919314
This paper describes a modified version of SSIB through implementing a new snow model (SAST) in Simplified Simple Biosphere Model SSIB for climate study and presents the evaluation results by testing the scheme based on the field data from Russia and France. The relevant equations in the scheme are given,which describe complicated interactive processes among air-vegetation-snow-soil continuum through mass and heat exchange. An efficient numerical scheme is developed to solve the nonlinear equations successfully.By using the field data from Russia and France, the function of the new scheme is evaluated. The numerical results from the scheme show good agreement with field data. It indicates that the scheme developed here is workable and can be extended for climate study.
Evaluation of Haney-Type Surface Thermal Boundary Conditions Using a Coupled Atmosphere and Ocean Model
Peter C. Chu, Chen Yuchun, Lu Shihua
2001, 18(3): 355-375. doi: 10.1007/BF02919315
A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition, which linearly connects net downward surface heat flux Q to air / sea temperature difference △T by a relaxation coefficient k. The model was initiated from the National Centers for Environmental Prediction (NCEP) atmospheric observations for 1 December 1977, and from the National Ocean Data Center (NODC) global climatological mean December temperature and salinity fields at 1° ×1° resolution. The time step is 7.5 minutes. We integrated the model for 450 days and obtained a complete model-generated global data set of daily mean downward net surface flux Q, surface air temperature TA,and sea surface temperature To. Then, we calculated the cross-correlation coefficients (CCC) between Q and △T. The ensemble mean CCC fields show (a) no correlation between Q and △T in the equatorial regions, and (b) evident correlation (CCC≥ 0.7) between Q and △T in the middle and high latitudes.Additionally, we did the variance analysis and found that when k= 120 W m-2K-1, the two standard deviations, σQ and σk△T, are quite close in the middle and high latitudes. These results agree quite well with a previous research (Chu et al., 1998) on analyzing the NCEP re-analyzed surface data, except that a smaller value of k (80 W m-2K-1) was found in the previous study.
The Weakening of the Asian Monsoon Circulation after the End of 1970's
Wang Huijun
2001, 18(3): 376-386. doi: 10.1007/BF02919316
The transition of the global atmospheric circulation in the end of 1970's can clearly be detected in the atmospheric temperature, wind velocity, and so on. Wavelet analysis reveals that the temporal scale of this change is larger than 20 years. Studies in this work indicate that the trend of the transition over the mid-latitude Asia is opposite to that of global average for some variables at the middle troposphere. Another finding of this research is that the African-Asian monsoon circulation is weaker and the trade wind over the tropical eastern Pacific is weaker as well after this transition. Such a signal may be found in the summer precipitation over China as well.
Study of 1998 Heavy Rainfall over the Yangtze River Basin Using TRMM Data
Cheng Minghu, He Huizhong, Mao Dongyan, Qi Yanjun, Cui Zhehu, Zhou Fengxian
2001, 18(3): 387-396. doi: 10.1007/BF02919317
TRMM (Tropical Rainfall Measuring Mission) data have been made available to the public users since June 1998. In this paper, some preliminary research is reported for the case study of heavy rainfall over the Yangtze River Basin using TRMM data at 2140 UTC 20 July 1998. TRMM derived precipitation products are also compared with rain gauge observation, ground radar data and numerical model simulation results.It is shown that TRMM data can be easily used to monitor the heavy rainfall and have many applications.
Problems of Nonlinear Computational Instability in Evolution Equations
Ji Zhongzhen, Lin Wantao, Yang Xiaozhong
2001, 18(3): 397-403. doi: 10.1007/BF02919318
Some problems of nonlinear computational instability are discussed in this article, which are shown as follows: 1) Three types of representative evolution equations are analyzed, and the close relationship between the nonlinear computational stability or instability in their corresponding difference equations and the properties of their solution is revealed. 2) The problem of nonlinear computational instability in conservative differencing equations with the periodic boundary condition is further discussed, and some effective ways to avoid nonlinear computational instability are proposed. 3) The problem of nonlinear computational instability in non-conservative difference equations with the aperiodic boundary condition is focused on by using nonlinear advection equations as examples, and "snynthetic analysis method"is given to judge their computational stability.
Modelling the Global Monsoon System by IAP 9L AGCM
Xue Feng, Bi Xunqiang, Lin Yihua
2001, 18(3): 404-412. doi: 10.1007/BF02919319
The global monsoon system is simulated by IAP 9L AGCM. The result indicates that the model successfully simulates the monsoon system in the lower troposphere including the classic tropical monsoon,the subtropical monsoon and the temperate-frigid monsoon. Besides, the planetary monsoon in the upper troposphere is also realistically reproduced. On the other hand, the stratospheric monsoon is poorly simulated, a further analysis reveals that this is caused by the systematic overestimation of the westerly in the model.
Computational Stability of the Explicit Difference Schemes of the Forced Dissipative Nonlinear Evolution Equations
Lin Wantao, Ji Zhongzhen, Wang Bin
2001, 18(3): 413-417. doi: 10.1007/BF02919320
The computational stability of the explicit difference schemes of the forced dissipative nonlinear evolution equations is analyzed and the computational quasi-stability criterion of explicit difference schemes of the forced dissipative nonlinear atmospheric equations is obtained on account of the concept of computational quasi-stability, Therefore, it provides the new train of thought and theoretical basis for designing computational stable difference scheme of the forced dissipative nonlinear atmospheric equations.
Equatorial Envelope Rossby Solitons in a Shear Flow
Zhao Qiang, Fu Zuntao, Liu Shikuo
2001, 18(3): 418-428. doi: 10.1007/BF02919321
A simple shallow-water model on an equatorialβ-plane is employed to investigate the nonlinear equatorial Rossby solitons in a mean zonal flow with meridional shear by the asymptotic method of multiple scales. The cubic nonlinear Schrodinger (NLS, for short) equation, satisfied for large amplitude equatorial envelope Rossby solitons in shear basic flow, is derived. The effects of basic flow shear on the nonlinear equatorial Rossby solitons are also analyzed.
Impacts of Sea Surface Temperature in the Tropical Pacific on Interannual Variability of Madden-Julian Oscillation in Precipitation
Li Wei, Yu Rucong, Zhang Xuehong
2001, 18(3): 429-444. doi: 10.1007/BF02919322
The Madden-Julian Oscillation (M JO) is investigated in two sets of 11-year records of observed precipitation, the daily mean Microwave Sounding Units (MSU) oceanic rainfall (Spencer, 1993) data and the pentad Climate Prediction Center Merged Analysis of Precipitation (CMAP) data (Xie and Arkin, 1997).Obvious interannual variability is found in the M JO in the tropical Pacific. M JO is limited to the west of dateline in normal years while extends more east during the year of warm sea surface temperature (SST) appeared in the eastern Pacific (i.e., El Nino years of 1982-1983, 1986-1988, 1991-1992) and manifested in the central-eastern Pacific for several months. The most significant correlation between interannual variability of M JO in the central-eastern Pacific and SST was found in the vicinity of the Nino3 region. Forced by observed SST, CCM3 presents a realistic trend of interannual variability to M JO in the 11 years, with a smaller magnitude than that from the observation. Comparison between the two realizations of the CCM3 simulation, which are forced by weekly and monthly mean SST respectively, showed that the M JO activities resemble each other in central-eastern Pacific while there is discrepancy in the western Pacific. It is suggested that the interannual variability of M JO is controlled, to certain extent by the powerful interannual variability of SST in the central-eastern Pacific. In the western Pacific, however, there were remarkable impacts of the intraseasonal oscillation of SST on the M JO, where there was active M JO around the year. The notable disagreement between simulated and observed M JO in the western Pacific may come from the lack of high frequency variation of SST force, or from the shortage of air-sea interaction for the intraseasonal time scale. It might be of importance to the M JO which is unable to be represented in the atmospheric model.
Intraseasonal Oscillation: the Global Coincidence and Its Relationship with ENSO Cycle
Chen Xingyue, Wang Huijun, Xue Feng, Zeng Qingcun
2001, 18(3): 445-453. doi: 10.1007/BF02919323
Based on the atmospheric reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), the interannual variability of the atmospheric intraseasonal oscillation (ISO) and its relationships with the El Nino/Southern Oscillation (ENSO) cycle have been investigated. This work reveals that there exists global coincidence in the interannual variation of ISO among different latitude bands and that relationships between the interannual variation of ISO and the global sea surface temperature (SST) or the outgoing longwave radiation (OLR)are very complicated. We also find that the correlation coefficient between ISO and Niiio3 SST anomaly has apparent decadal scale variability, which means that the inter-relationship is stronger in some periods and weaker in other periods.
The Scandinavia Ozone Loss and Surface Heating
Zhou Libo, Zou Han, Ji Chongping, Wang Wei, Jian Yongxiao
2001, 18(3): 454-466. doi: 10.1007/BF02919324
Analysis on NASA Total Ozone Mapping Spectrometer (TOMS) ozone shows a clear ozone loss, -50 DU (15% of the total ozone), over Scandinavia. Correlation analysis between the ozone loss and the east-to-west sea surface temperature (SST) contrast in the North Atlantic shows correlation coefficients -0.96 for seasonal variation and -0.70 for monthly mean (168 months) in 1979-1992. Correlation coefficients between the ozone loss and the surface-to-atmosphere heat fluxes are higher than -0.87. Therefore the authors suggest that the warm Atlantic current carries energy northward to Scandinavia and causes ozone loss there via the surface-to-atmosphere heating processes.