Vol.14, NO.1, 2003

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Characteristics of Aerosol Optical Depth Distributions over Sichuan Basin Derived from MODIS Data
Li Cheng cai, Mao Jietai, Alexis Kai-Hon Lau
2003, 14(1): 1-7.
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Abstract:
The characteristics and seasonal changes of the aerosol optical depth (AOD) distribution of the Sichuan Basin from MODIS products are analyzed. In spring there is the biggest seasonal average due to the dusty weathers. Several regional large value centers in the basin are found. The first is in the west near Chengdu and had less seasonal change. The second is in the south between Yibin and Chongqing. The third is between Nanchong and Chongqing and has the biggest seasonal change and disappears in summer. The results provide the basic data for regional climate and air pollution research.
Flood Detection and Monitoring by Use of AMSU-A Microwave Data
Gu Songyan, Qiu Hong, Ran Maonong, Zhang Wenjian
2003, 14(1): 8-16.
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Abstract:
The Advanced Microwave Sounding Unit-A (AMSU-A) is a new advanced generation microwave-sounding unit, and has great potential in land characteristic analysis, especially on flood detection and monitoring. The wetness index analysis method of flood detection and monitoring by using AMSU-A microwave data was tested over Boyang and Tongting lake areas in China during the 1998 summer. To accomplish this, the characteristics of microwave radiance transfer about AMSU-A channels are analyzed first and the result indicates that the window channels of AMUS-A can give more information about the surface flooding. Then a set of wetness indexed by combining three channels out of four AMSU-A window channels (ch1, ch2, ch3, & ch15) is developed. Thereafter the best wetness index which is sensitive to the land surface wetness changes is chosen to conduct the detection and monitoring, and the flooding area is classified into four situations: flooding, mudding, over wet, and back ground dry area. In the Cal/Val Test, and the data from China L-SAR aboard on the plane and Canadian Radar-SAR aboard on the Radarsat are used, the Cal/Val results is up to 73%. The future work will focus on the possible improvements in the algorithm and extend testing of the algorithm to other regions.
Error Estimation in Wind Fields Derived from Dual-Doppler Radar and Data Quality Control
Liu Liping, Zhang Peiyuan, Liang Haihe, Niu Fang, Zhou Haiguang
2003, 14(1): 17-29.
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Abstract:
The method for quality control of dual-Doppler radar reflectivity, radial velocity and azimuthal location is introduced. The reflectivity correction approach with probability distribution method is presented. The two dual-Doppler radar systems in Hefei and Ma’anshan, Anhui Province, Yichang and Jiangzhou, Hubei Province, were used to observe the wind structure of the precipitation systems in the China Heavy Rainfall Experiment and Study in 2001. The reflectivities and radial velocities from the dual-Doppler radar are compared and the effect of azimuth location on dual-Doppler radar data is analyzed. The errors of wind derived from the two Doppler radar systems are estimated. The results show that the patterns of reflectivity and radial velocity measured by the Doppler radar systems are similar; but the values of reflectivity measured at Hefei and Ma’anshan are obviously different; the deviation of velocity measured by the two radars is 1-2 m/s. The error of wind derived from dual-Doppler radar is relative to wind direction, speed and position. The error is within 2 times of the measurement error of radial velocity in the area where the angle between the two radial velocities is in 40o-140 o. These results are valuable for the use of the dual-Doppler radar data and the observation by dual-Doppler radar.
Theoretical Analysis of Measurement Accurency of Dual Linear Polarization Doppler Radar
Ding Qinglan, Liu Liping, Ge Runsheng, Xu Bao xiang
2003, 14(1): 30-38.
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Abstract:
Measuring rainfall quantitatively is one of the main purposes of dual-linear polarization radar. The rain intensity can be derived from reflectivity ZH, differential reflectivity ZDR and specific differential phase KDP. The measurement accuracy of KDP is very important for deducing rainfall. The measurement accuracy of differential propagation phase shift ΦDP is calculated with various sample pairs M, range average intervals and spectrum widths σV by using theoretical formula. Then, the effect of those factors on the measurement errors of ΦDP is analyzed. Those results show that standard errors of ΦDP gradually decrease when the number of sample pairs M or range average interval increase, but standard errorsΦDP gradually increase withσV increasing (except in the case of σV=1 m/s). Moreover, three methods of obtaining KDP from ΦDP are summarized and the accuracy of those methods is compared. These results show that the errors of KDP produced by the second method are very large; the standard error of KDP can be less than 0.1o/km when using the first method and the third method on some conditions.
Quantitative Analyses of Several Q Vectors
Yue Caijun, Shou Shaowen, Dong Meiy ing
2003, 14(1): 39-48.
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Abstract:
Considering a typical Jiang-Huai Meiyu rainstorm event during 5-6 July, 1991 and the operational requirements, the differences of the capability of reflecting precipitation area among quasi-geostropic-, semi-geostrophic-, ageostrophic- and wet-Q vector divergence fields at 850 hPa, 700 hPa and 500 hPa are examined in detail; in the meanwhile, the capability of reflecting precipitation area for each Q vector itself in the divergence fields at the three layers is analyzed. On a quantitative comparison basis, the diagnostic features of the four Q vectors are obtained: (1) quasi-geostropic- and semi-geostrophic-Q vector divergence fields at the three layers respond less obviously to the synchronous rainfall, while ageostrophic- and wet-Q vector divergence fields are better than previous two; especially, the diagnostic capability of the wet-Q vector divergence field at each layer is greater than those of the others throughout the Meiyu-front rainstorm. (2) As far as each Q vector is concerned, the 700 hPa convergence field basically has good capability of reflecting precipitation area than those at the other two layers; in particular, the convergence of the wet-Q vector divergence at 700 hPa serves as a good indicator of precipitation intensity and fallout region. At last, the diagnostic property of each Q vector is documented on a theoretical basis, and not only the theoretical differences among four Q vectors are depicted in full but the results form the quantitative comparison are confirmed theoretically as well.
Contrast Study of Model Atmospheric Monthly-scale Predictability
Fan Xiaoqing, Li Weijing, Zhang Peiqun
2003, 14(1): 49-60.
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Abstract:
Based on the observed 500 hPa height, the monthly scale predictability of short-term climate variation by the method of Analysis of Variance (ANOVA) is studied, and the influences of the predictability of different scale movements on the whole predictability are also examined. The predictability of 500 hPa height simulated by the ECMWF T63 spectrum model and forecasted by the National Climate Center T63 spectrum model with the same method is researched. The results show that the atmospheric predictability of two models is much smaller than the actual atmospheric predictability, especially for the movements of wave number 0-3, which have the most important influence on the whole atmospheric movement. Therefore there is plenty of potential skill to improve the climate model if the forecasting of wave number 0-3 movements is improved.
Simulation of Daily Cycle of Boundary Layer Heat Island in Beijing
Yang Yuhua, Xu Xiangde, Weng Yonghui
2003, 14(1): 61-68.
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Abstract:
The non-hydrostatic mesoscale model MM5 is used to simulate the winter heat island of Beijing city with three-fold nesting and the finest mesh resolution of 3 km. With the observed building heights and landuse data of a 200 m×200 m resolution in Beijing interpolating into the model, and dividing the urban artificial heat of the underlying surface into two parts (constant and daily-changing parts), the simulation results show that the numerical model can successfully simulate the heat island effect and its circulation. The simulated daily cycle of the heat island is closer to the observation for the daily-changing anthropogenic heat than for constant heat. It indicates that using the heat conforming with the observation in the model can improve the numerical simulation of the heat island.
Experiment and Research of Short-range Ensemble Forecasting Techniques in Forecasting Meiyu Precipitation
Wang Chenxi, Duan Yihong
2003, 14(1): 69-78.
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Abstract:
Numerical weather prediction errors come from the initial conditions and model errors. Ensemble forecasting technique is an effective way to diminish the errors. Short-range ensemble forecasting experiments are made for three precipitation cases during the 1999 Meiyu period in the East China area. The MM5 model is used as the experimental model configuration. Eight ensemble members are created by choosing four kinds of cumulus parameterization schemes and two kinds of PBL parameterization schemes. The four kinds of cumulus parameterization schemes are Anthes-Kuo, Grell, Kain-Fritsch and Betts-Miller schemes. The two kinds of PBL parameterization schemes are MRF and Eta schemes.The resul ts indicate that different ensemble members have dif ferent forecasting result s . For the precipi tation fo recast ing results , the inf luence of cumulus parameterization scheme is larger than the influence of the PBL parameterization scheme .For the bias sco re , most ensemble members have a “wet” bias .The bias score is larger for large precipitation than that for small precipitation .The ef fects of ensemble averaging increase the bias score for small precipitation and reduce the bias sco re for large precipitation .Fo r different cases, the member w ho has the best precipitation forecasting results is not the same one .Af ter ensemble averaging , stable precipi tation fo recasting results can be got ten .Also the objective and quantitative precipitation probability fo recasts can be obtained f rom the ensemble forecasting .
Climatic Warming Process During 1980s—1990s in China
Wei Fengying, Cao Hongxing, Wang Liping
2003, 14(1): 79-86.
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Abstract:
The changes in annual, winter, spring, summer and autumn air temperatures over China in the last 50 years are analyzed through statistical diagnosis and the focus of the study is put on the difference of change and warming process between 1990s and 1980s. The results show that the annual temperature anomaly has an increasing trend in the last 50 years, but the inter-decadal change in annual temperature is not remarkable before 1990. The mean temperature from 1991 to 2000 is much higher than those in the other decades. Their 10-year means are – 0.12oC from 1951 to 1960, – 0.10oC from 1961 to 1970, – 0.04oC from 1971 to 1980, 0.14oC from 1981 to 1990, 0.57oC from 1991 to 2000, respectively. The difference between the mean from 1991 to 2000 and the mean from 1981 to 1990 is of statistical significance with a confidence level of α=0.05. The linear trend coefficient of the mean temperature over China is only 0.008oC per year before 1990, but 0.02oC per year from 1991 to 2000. The beginning of warning was at the end of the 1980s and the warming speeded up in the 1990s in China, during which period a transition from clod to warm occurred in the south of the Changjiang River Valley. The change trend of temperature and the warming processes is the 1980s and 1990s were very different for four seasons. In winter, the beginning of warming was the earliest with the strongest argument and the longest duration. The main contribution to the steep warming during the 1990s comes from the long-lasting higher temperature in winter and the temperature rising in spring, summer, autumn, especially the ever-increasing warming argument and the ever-expanding warming areas in spring and summer. Only 59% and 31% of stations over China have an increasing trend in spring and summer before 1990, but 83% and 50% from 1991 to 2000.
Estimate of Air-sea Fluxes During South China Sea Monsoon Experiment in 1998
Yao Huadong, Ren Xuejuan, Ma Kaiyu
2003, 14(1): 87-92.
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Abstract:
Based on the data of the South China Monsoon Experiment in 1998, the air-sea fluxes are estimated by using the bulk coefficient and multi-stratification formulas. The results of latent and the sensible heat fluxes by two methods are basically close. The latent heat flux is 1–3 W·m-2 larger and the sensible heat flux 0–1.5 W·m-2 smaller by the multi-stratification method than by the bulk coefficient method. Generally the latent heat flux increases gradually during the monsoon onset. The flux at night is larger before the monsoon onset than after. During the days, the flux is smaller in the beginning and middle of the monsoon onset period than the latter period. The sensible heat flux transports from the sea surface to atmosphere in the beginning of the monsoon onset and from the atmosphere to sea surface in the latter period of the monsoon onset. The momentum flux and friction velocity increase with speed.
Climatic-ecological Diagnoses on Seed Production of Two-line Hybrid Rice
Wang Kuojun, Shuai Xiqiang, Liu Jiaqing, Zeng Yulong
2003, 14(1): 93-100.
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Abstract:
Strict requirements for climatic-ecological conditions are needed for the two-line hybrid rice cultivation. While the seed production bases are concerning, full diagnosis and scientific assessment should be conducted on the local climatic-ecological adaptability. The special influences of climatic-ecological conditions on two-line hybrid rice are analyzed. It is pointed out that the two safety periods should be considered in seed production. A diagnosis method for analyzing the periods is given. The “Hunan Provincial Expert Service System for Climate Diagnose and Policy-making on Seed Production of Two-line Hybrid Rice” is developed and the system can be used to define the available zones and time-sections in Hunan for seed production. In the beginning of 2000, this proposal used by the system was adopted in Hunan Province and the management of the seed production is further promoted.
Analysis of Weather Factors Influencing Routing Design of North Pacific Ocean in Winter
Huang Bin, Liu Huanzhu, He Jinhai, Liu Tao
2003, 14(1): 101-108.
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Abstract:
Based on the fundamental tenets of weather-ocean routing and factors influencing routing design, the characteristics of explosive cyclones and extra-tropical cyclones in winter over the North Pacific Ocean are analysis, and the features of wind fields and sea waves are also taken into account. The results show that routing design should consider climate conditions, weather feature analyses and short/mid-range weather forecasts, so that ships can make use of favorable wind and sea waves and adverse weather (strong wind, high wave etc.) to secure and improve economical prof its.
Three Layer Structure Method and Its Application to Meteorology Information Processing System
Zhang Shunqian, Xio ng Zhiqiang
2003, 14(1): 109-118.
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Abstract:
A brief discussion is made on the conception, advantages, data flow of the three-layer structure, and the communication mode, based on the COM technology, between the application server and client programs. The application of the three-layer structure method to the meteorology information processing systems is described through the examples of rainfall editing and rainfall summing in a period of time to explain in detail the developing process of the three-layer structure system. Based on it, the general method, the related principles and skills for developing the application server and client programs using DELPHI 4 are presented.
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