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1998 Vol. 15, No. 4

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Seasonal Prediction Experiments of the Summer Droughts and Floods during the Early 1990’s in East Asia with Numerical Models
Huang Ronghui, Li Xu, Yuan Chongguang, Lu Riyu, Moon Sung-Euii, Kim Ung-Jun
1998, 15(4): 433-446. doi: 10.1007/s00376-998-0025-5
It has been shown by the observed data that during the early 1990’s, the severe disastrous climate occurred in East Asia. In the summer of 1991, severe flood occurred in the Yangtze River and the Huaihe River basin of China and in South Korea, and it also appeared in South Korea in the summer of 1993. However, in the summer of 1994, a dry and hot summer was caused in the Huaihe River basin of China and in R. O. K.. In order to investigate the seasonal predictability of the summer droughts and floods during the early l990’s in East Asia, the seasonal prediction experiments of the summer droughts and floods in the summers of 1991-1994 in East Asia have been made by using the Institute of Atmospheric Physics-Two-Level General Circulation Model (IAP-L2 AGCM), the IAP-Atmosphere/Ocean Coupled Model (IAP-CGCM) and the IAP-L2 AGCM in?cluding a filtering scheme, respectively. Compared with the observational facts, it is shown that the IAP-L2 AGCM or IAP-CGCM has some predictability for the summer droughts and floods during the early 1990’s in East Asia, es?pecially for the severe droughts and floods in China and R. O, K.. In this study, a filtering scheme is used to improve the seasonal prediction experiments of the summer droughts and floods during the early 1990’s in East Asia. The predicted results show that the filtering scheme to remain the planetary-scale disturbances is an effective method for the improvement of the seasonal prediction of the summer droughts and floods in East Asia.
The Role of Diabatic Heating, Torques and Stabilities in Forcing the Radial-Vertical Circulation within Cyclones Part II: Case Study of Extratropical and Tropical Cyclones
Zhuojian Yuan, Donald R. Johnson
1998, 15(4): 447-488. doi: 10.1007/s00376-998-0026-4
Utilizing Eliassen’s concepts, the forcing of the isentropic azimuthally-averaged mass-weighted radial-vertical circulation by diabatic heating and torques within an extratropical cyclone and a typhoon was studied through nu-merical simulations based on the linear diagnostic equation derived previously. The structure of the forcing associated with diabatic heating and torques was determined from quasi-Lagrangian diagnostic analyses of actual case studies. The two cyclones studied were the Ohio extratropical cyclone of 25-27 January 1978 and typhoon Nancy of 18-23 September 1979. The Ohio cyclone, which formed over the Gulf Coast and moved through Ohio and eastern Michigan, was one of the most intense storms with blizzard conditions to ever occur in this region. Typhoon Nancy which occurred over the South China Sea during the FGGE year was selected since relatively high quality assimilated data were available. Within the Ohio cyclone, the dominant internal processes forcing the mean circulation with em-bedded relatively strong hydrodynamic stability were the pressure torque associated with baroclinic (asymmetric) structure and the horizontal eddy angular momentum transport associated with the typical S-shaped thermal and wind structures of self-development. Within typhoon Nancy, the dominant internal process forcing the mean circula-tion with embedded weak hydrodynamic stability was the latent heat release. This analysis shows that the simulated azimuthally-averaged mass-weighted radial motions within these two cy?clones agree quite well with the “observed” azimuthally-averaged mass-weighted radial motions. This isentropic nu?merical study also provides insight into the relatively important internal forcing processes and the trade off between forcing and stability within both extratropical and tropical cyclones.
A Regional Climate Model Simulation of Summer Monsoon over East Asia: A Case Study of 1991 Flood in Yangtze-Huai River Valley
Wei Helin, Wang Wei-Chyung
1998, 15(4): 489-509. doi: 10.1007/s00376-998-0027-3
The evolution of summer monsoon over East Asia is the result of multi-scale interactions, including the large-scale subtropical high, upper level jet and regional-scale Meiyu front, vortex, and thermal heating. Regional Climate Models should be a better way to simulate the summer monsoon evolution, because not only they can reflect the large-scale forcing through boundary condition, theirs high resolution can also catch regional-scale forcing in de-tail. To evaluate the ability of SUNYA-ReCM to simulate the evolution of the summer monsoon over East Asia es-pecially in the extreme climate, a simulation of the East Asian flood that occurred during 1991 summer was per-formed. This simulation was driven by large-scale atmospheric background derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Tropic Ocean Global Atmospheric (TOGA) analysis. The model is capable of reproducing the major features of the monthly mean monsoon circulation, anomalous rainfall in the Yangtze-Huai River Valley and the two northward jumps of rainfall belt as well as the other large-scale components of the monsoon. The changes of the large-scale circulation during the evolution of summer monsoon are also well simulated, which include: (1) the wind direction changes from southeasterly to southwesterly in the South China Sea. (2) The northward shift of the upper westerly over East China and the Tibetan Plateau. (3) The northward shift of the western Pacific subtropic high at 500 hPa. The model also has a good simulation on the evolution of the regional-scale components of the monsoon, including Meiyu front and southwest (SW) vortex in Sichuan Basin.
Decadal Variation of Summer Rainfall in the Yangtze-Huaihe River Valley and Its Relationship to Atmospheric Circulation Anomalies over East Asia and Western North Pacific
Wu Renguang, Chen Lieting
1998, 15(4): 510-522. doi: 10.1007/s00376-998-0028-2
Decadal variations of summer rainfall during 1951 through 1990 are analyzed by using summer rainfall data of 160 stations in China. Four major patterns of decadal variations are identified. The decadal variations of summer rainfall showed northward shift in the eastern China from South China through the Yangtze-Huaihe River to North China. Summer rainfall in the Yangtze-Huaihe River valley underwent two obvious decadal transitions during the 40 years: one from rainy period to drought period in the end of the 1950’s, the other from drought period to rainy period in the late 1970’s. Correspondingly, the atmospheric circulation over East Asia through the western North Pacific showed two similar obvious transitions. The East Asian/ Pacific (EAP) pattern switched from high index to low index in the end of the 1950’s and from low index to high index in the late 1970’s, respectively. Hence, summer rainfall in the Yangtze-Huaihe River valley is closely associated with the EAP pattern not only in the interannual variation but also in the decadal variation.
Study on Conventional Atmospheric Dispersion Models in China, America and Canada
Wang Tijian, Li Zongkai, Sun Zhaobo
1998, 15(4): 523-530. doi: 10.1007/s00376-998-0029-1
The conventional atmospheric dispersion models used in China (CRADM), America (HPDM) and Canada (AMS) are investigated. The main differences between the three models are described, and the various aspects of CRADM, HPDM and AMS for same input are compared and discussed. Some problems in application of atmos-pheric dispersion models lo environmental impact assessment are analyzed and suggestions for rivision are proposed. Results show that the Briggs plume rise formula in neutral condition overestimates the real rise due to the fact that the accumulative effect of ambient turbulence on plume is not considered in his model.
Modification of Sea-salt Aerosols over the Coastal Area in China
Li Fang, Duan Minzheng, Lu Daren, Kikuo Okada
1998, 15(4): 531-540. doi: 10.1007/s00376-998-0030-8
Aerosol panicles over the coasial area are subject to the modification of their chemical composition during their transport and diffusion. For examining the modification, the marine aerosol panicles are collected at an island, East China Sea. Comparison of elemental composition of the marine aerosols with that of the samples collected at a coast-al site, e.g. in Shanghai, was made. The results of chemical analysis show that the loss of chlorine component in aerosol particles is one of the main characteristics in the course of diffusion of marine aerosols into the coastal contin-ent. Sulphur is a dominant component for fine particles in both marine and coastal aerosols. The relation of particle number concentration and particle size distribution to the meteorological conditions was discussed briefly. These results can be used as a reference in the estimation of equivalent refractive index of the aerosols for radiation transfer.
Theoretical Relationship between SSA and MESA with Both Application
Ding Yuguo, Jiang Zhihong
1998, 15(4): 541-552. doi: 10.1007/s00376-998-0031-7
It is theoretically demonstrated that singular spectrum analysis (SSA) is an equivalent form or Maximum Entropy Spectrum Analysis (MESA) which is essentially a nonlinear estimation of the classical power spectrum. Both methods have respectively some different features in application as a result of the difference of description of manners. The numerical experiments show that SSA possesses some special advantage in climatic diagnosis and pre diction, e.g., to steadily and accurately identify periods and investigate on domain of time in combination with frequency, which cannot be replaced by MESA. Thus SSA has extensive application in the near future.
Retrieval Single-Doppler Radar Wind with Variational Assimilation Method-Part I: Objective Selection of Functional Weighting Factors
Wei Ming, Dang Renqing, Ge Wenzhong, Takao Takeda
1998, 15(4): 553-568. doi: 10.1007/s00376-998-0032-6
In variational problem, the selection of functional weighting factors (FWF) is one of the key points for discussing many relevant studies. To overcome arbitrariness and subjectivity of the empirical selecting methods used widely at present, this paper tries to put forward in optimal objective selecting method of FWF. The focus of the study is on the weighting factors optimal selection in the variation retrieval single-Doppler radar wind field with the simple adjoint models. Weighting factors in the meaning of minimal variance are calculated out with the matrix theory and the finite difference method of partial differential equation. Experiments show that the result is more objective comparing with the factors obtained with the empirical method.
Comparison of Manual and Automatic Methods for Measurement of Methane Emission from Rice Paddy Fields
Zheng Xunhua, Wang Mingxing, Wang Yuesi, Shen Renxing, Li Jing, J. Heyer M. Kogge, Li Laotu, Jin Jisheng
1998, 15(4): 569-579. doi: 10.1007/s00376-998-0033-5
The methane emission flux from rice paddies was simultaneously measured with automatic and manual methods in the suburban of Suzhou. Both methods were based on the static chamber/ GC-FID techniques. Detail analysis of the experimental results indicates: a) The data of methane emission measured with the automatic method is reliable. b) About 11 or 19 o’clock of local time is recommended as the optimum sampling time for the manual spot measurement of methane emission from rice paddies. The methane emission fluxes measured by manual sampling at local time other than the optimum time have to be corrected. The correction coefficient may be determined by automatic and continuous measurement. c) In order to get a more accurate result, an empirical correction factor, such as 18%, is recommended to correct the seasonally total amount of measured methane emission by enlarging the au-tomatically measured data or reducing the manually measured ones.
A High-Order Compact Scheme with Square-Conservativity
Ji Zhongzhen, Li Jing
1998, 15(4): 580-584. doi: 10.1007/s00376-998-0034-4
In order to improve the accuracy of forecasts of atmospheric and oceanic phenomena which possess a wide range of space and time scales, it is crucial to design the high-order and stable schemes. On the basis of the explicit square-conservative scheme, a high-order compact explicit square-conservative scheme is proposed in this paper. This scheme not only keeps the square-conservative characteristics, but also is of high accuracy. The numerical ex-ample shows that this scheme has less computing errors and better computational stability, and it could be considered to be tested and used in many atmospheric and oceanic problems.