Current Issue

• A Study on the Algorithm Making Attenuation Correction to Observations of Radar Reflectivity Factor(Ⅱ):Numerical Simulations and a Case Study
• WANG Zhen-hui;ZHANG Pei-chang
• 2001 Vol. 20 (2): 115-120. 
• Abstract ( ) PDF (245KB) ( )
• Uniformly distributed radar reflectivity is assumed for numerical simulation to study the effectiveness of the attenuation correction algorithms and criteria for computational stability, and the influence of the errors in radar observation and attenuation coefficient and the bin resolution on the effectiveness. Radar observations are also used in a case study of attenuation correction. The results have been compared with those from Hitschfeld-Bordan algorithm and those from Meneghini's iteration. The results have shown that correctable thickness in radial direction decreases as radar reflectivity factor and attenuation increase, that high resolution of data bin is beneficial to improve the stability during correction computation and correctable thickness can be increased, and that the random error in discrete radar data and the error in attenuation coefficient make the correction more difficult to carry out. The bin-by-bin algorithm is as good as HB when attenuation is weak and errors negligible. Otherwise the approximated bin-by-bin algorithm can be used to obtain a computing efficiency higher than the iterative scheme. The criteria determined by the coefficients in k-Z relationship and bin resolution can be used to avoid efficiently the computation overflow caused by unstable over correction.

• Primary Forecast for Precipitation Trend in Rainy Season in North China
• ZHANG Qi long;WENG Xue chuan;CHENG Ming hua
• 2001 Vol. 20 (2): 121-126. 
• Abstract ( ) PDF (255KB) ( )
• Based on the monthly rainfall data of 18 stations in North China from 1951 to 1999, the long term variation of the precipitation in the rainy season in North China are simply analyzed by using regress analysis method. On the view of the influence of the ocean on the climate, the primary forecast for long term trends of the precipitation in the region are carried out by using the empirical orthogonal function(EOF) model based mean generating function. The results show that the rainfall reduced by nearly 64 mm in Region I and 119 mm in Region Ⅱ during 49 years(from 1951 to 1999). The transition period from the more(or less) rainfall to the less(or more) is about 17 years in Region I and 20 years in Region Ⅱ. The preliminary forecast results show that during the next 10 years(1999-2008), summer rainfall in North China is basically in its multi year mean state, that is, no obvious drought phenomena.

• Study on Cloudwater and Rainwater Chemical Characteristics under Different Weather System over China
• LEI Heng chi;WU Yu xia;XIAO Hui;SHEN Zhi lai
• 2001 Vol. 20 (2): 127-131. 
• Abstract ( ) PDF (204KB) ( )
• The cloudwater chemistry was analyzed over nearly 10 provinces and cities in China from 1985 to 1993. The results indicate that the cloudwater is acidic at South but non acidic at North China. The chemical species of cloudwater is affected by precipitation weather system. In North China, when it was influenced by Mongolia low eddy, the cation of Ca ²⁺ increased to very high which demonstrate the yellow sand pollution process. In South China, when it influenced by stationary front precipitation system, the cloudwater is acidic and concentration of ion is also high.

• Numerical Simulation of Surface Energy Fluxes over Heterogeneous Land Surfaces in HEIFE Area
• YAN Yu ping;WANG Jie min;M. Menenti;SU Zhong bo
• 2001 Vol. 20 (2): 132-139. 
• Abstract ( ) PDF (325KB) ( )
• Surface energy fluxes are simulated using 3D nonhydrostatistical RAMS over heterogeneous land surfaces in HEIE area. It is showed that the net radiation over oasis is larger than that over desert/Gobi. The Bowen ratios are 0.4 and 4.0 over oasis and desert respectively. Evaporation can last in the whole night and there is negative sensible heat flux over oasis. At the same time, simulations are compared with observations andsatellite remote sensing retrieval. The simulated surface latent heat fluxes are more consistent with observations than that of sensible heat fluxes over oasis. The simulated sensible heat fluxes are more consistent with observationsthan that of latent heat fluxes over desert/Gobi. In general, the simulated and satellite retrieved net radiation are both in agreement with the observations. On oasis, the error of surface sensible heat fluxes retrieved from satellite is smaller than the simulations, but the simulated latent heat fluxes are more consistent with observations than those retrieved. However, on desert/Gobi, the simulated sensible heat fluxes are more consistent with observations than those of satellite retrievd.

• On the Numerical Simulation of Flow Field and Turbulent Diffusion over the Mountain and Valley Terrain
• WU Jian;JIANG Wei mei;WANG Wei guo
• 2001 Vol. 20 (2): 140-147. 
• Abstract ( ) PDF (348KB) ( )
• By using the numerical modelwith the E-ε closure the air stream, the motion of turbulence and the diffusion of three lowersources in different position has been simulated. It has been shown that the thermodynamicitem in the TKE equation is not important anywhere, but the item of shear energy production is more important than the thermodynamic item in the valley when the wind speed is higher. It has been found also that the concentration at the bottom of valley is not so high, when the source is located on the top of mountain or before the mountain.The valley will be polluted seriously under any stratification if the source is located in the valley. When the source is located inthe valley, the pollutant canbe transferred with the backflow, if the wind speed is hight; also the pollutant can be transferred with the coming flow, if the wind speed is lower.

• Experiments on Computing Pressure Gradient Force of Error Subtraction Scheme in Yunnan Mesoscale Numerical Model
• QIANG Xue min;JU Jian hua
• 2001 Vol. 20 (2): 148-157. 
• Abstract ( ) PDF (421KB) ( )
• A new method, named as error subtraction scheme, is introduced into Yunnan mesoscale numerical forecasting experimental model to compute the pressure gradient force for high and steep topographic areas. The modelling results of the five schemes with and without the error subtraction scheme are compared with one another. It is found that the modelling results are not perfect enough when they are directly used in three examples. However, when five formulas are used with the error subtraction scheme, the results are all remarkable improved to different extent, and the one using the revised classical scheme is more successful.

• An Analysis on Characteristic of Autumn Rainfall Anomaly in Northwest China
• LI Yao hui;LI Dong liang;ZHAO Qing yun
• 2001 Vol. 20 (2): 158-164. 
• Abstract ( ) PDF (279KB) ( )
• With EOF, REOF, period analysis and Morlet wavelet analysis, the spatial anomaly features, time evolution rules and period variations for autumn rainfall anomaly in northwest China and the reiationships between the rainfall anomaly and the middl east Pacific SSTA are studied in detail by using the autumn pricipitation data for the period of 1960~1997 from 63 observational stations and the SSTA in the area of NINOC. Some significant results are obtained.

• Singular Value Decomposition Analysis of Air Temperature in Spring in Sichuan Province and Chongqing City and 500 hPa Geopotential Height
• LI Yue qing;LI Chong yin
• 2001 Vol. 20 (2): 165-172. 
• Abstract ( ) PDF (312KB) ( )
• Using Singular Value Decomposition(SVD) technique, the relationship between 500 hPa heigt over the Northern Hemisphere and spring air temperature in Sichuan Province and Chongqing City(SPCC) is studied.The result shows that two fields have closely correlations in both synchror and asynchronous time space. The first mods derived from SVD indicate the key coupled features of the height and temperature fields. When 500 hPa height is negative(positive) anomalies in the(150°~180°E, 60°~70°N) region in previous October and is positive(negative) from Qinghai Xizang Plateau to East China in the same spring, the spring air temperature in SPCC will be positive(negative) anomalies. The change of general circulation, by influencing the regional weather and climate, is one of the important reasons for the anomalies and cooling of the air temperature in SPCC in spring. And the variations of 500 hPa height field in previous October is a forecast signal for the anomalies of spring air temperature in SPCC.

• Simulation of Influence of Climate Change on Water Resource over Luanhe River Valley Using a Hydrological Model(I):Introduction of Precipitation-Runoff Modeling System(PRMS) and Its Replant over Luanhe River Valley
• FAN Guang zhou;Lü Shi hua;CHENG Guo dong
• 2001 Vol. 20 (2): 173-179. 
• Abstract ( ) PDF (281KB) ( )
• We briefly introduce theprecipitation runoff modelingsystem(PRMS) of U.S. Geological Survey. The model is a better hydrological modelin current world.It includes many physical processesand can be used to simulate several hydrological processes. The PRMS is replanted to Luanhe river valley, and primarily test its modeling capability. The results show that the replant of the model is successfulover the Luanhe river valley. The model can truly reproduce the annual and seasonal variationof the channel runoff and the other variables of water resource over Luanhe river valley. We can use the model to study the influence of the climate change on the water resource over Luanhe river valley.

• Analyses on Severe Dust Storm Process During April 14 and 15, 1998
• ZHENG Xin jiang;XU Jian fen;LUO Jing ning;SUN Lan dong;YE Hui ming;XU Dong pei
• 2001 Vol. 20 (2): 180-185. 
• Abstract ( ) PDF (334KB) ( )
• Using satellite cloud images, numerical forecasting products and regular meteorological data, the dust storm weather occurred in western China during April 14 and 15, 1998. It found that this process occurred in the atmospheric circulation situation adjusting process and it caused baroclince trough and cold frond. And we mainly analysed the cause of formation of two severe dust storm centers, found that the first severe dust storm area caused by strengthened cold frond cloud band, while the second one was by 3 cloud bands together. The severe dust storm area was in the right side of upper air jet stream exit area, and in the downwind of 500 hPa positive vortex center and the ascending area of secondary counter circulation. Also we take a primary discussing by dynamical meteorology principle, and provide new evidence for forecasting.

• Effects of Urbanization on Radiation Fog in Xishuangbanna Area
• HUANG Yu ren;SHEN Ying;HUANG Yu sheng;TAN Ying zhong
• 2001 Vol. 20 (2): 186-190. 
• Abstract ( ) PDF (206KB) ( )
• Using the data from Jinghong and Damenglong weather station, we analyzed the reasons of radiation fog reducing in XishuangBanna, Yunnan province. The results show that the climatic features of annual foggy day, mean annual temperature, mean annual humidity, mean annual maximum temperature and mean annual minimum temperature etc of Jinghong and Damenglong were very similar from 1960 to 1984. However. after 1985, the variations of foggy day and mean annual humidity in Jinghong and Damenglong were different due to urban construction and natural climatic variation. The urbanization plays the very important role on radiation fog reducing in the area.

• Analyses of Microphysical Features for Spring Precipitation Cloud Layers in East of Qinghai
• LI Lun-ge;DE ligeer
• 2001 Vol. 20 (2): 191-196. 
• Abstract ( ) PDF (253KB) ( )
• Based on artificial rain enhancement airplane and Particle Measuring System(PMS) the precipitation cloud microphysical features have been largely studied during the spring artificial rain enhancement in Qinghai. According to airplane sounding data about 15 times in 1995 and 1997, we analyzed the lower atmosphere aerosol particles distribution features in east of plateau and its relationship with atmospheric sounding vertical distribution, and mainly discussed the preliminary distribution features of cloud drop, precipitation particles, as well as ice crystal and super cooled liquid water content.

• Recognition Model of Hail Cloud Based on Matter Elements and Extension Sets and Its Results Verification
• LI Zuo yong;LIN Lei;DENG Xin min
• 2001 Vol. 20 (2): 197-201. 
• Abstract ( ) PDF (197KB) ( )
• Hail cloud recognition is a pattern recognition problem of multi-parameter. The recognition result of hail cloud based on single parameter is always non-compatible. The basic thinking of matter clements and extension set was used for changing the non-compatible problem into compatible problem. On the basis of designing the classical matter elements matrixes and the extensional matter element matrixexes of hail clouds and thunderstorm clouds, the recognition model of hail cloud is presented according to the magnitude of correlation degrees calculated between the clouds to be recognized and the two kinds of sample clouds. The accuracy of hail cloud recognition in Chengdu by this method is over 85%.

• Analyses of Doppler Features of a Heavy Storm
• WU Zhi-fang;ZHANG Chun-liang;ZHANG Pei-yuan
• 2001 Vol. 20 (2): 202-207. 
• Abstract ( ) PDF (241KB) ( )
• The atomospheric circulution background, echo evolution, wind field structure and Doppler feature of a heavy strom were analysed with weather map, satellite cloud photograph and the 5 cm Doppler radar data. It was discussed preminarily that the occurance of the heavy strom was closed related to the geographical features of underlying surface. The research on the detective method was conducted initially for a heavy strom by means of Doppler radar. The conditions are described which is useful to hailstorm development and hail growing according to the radial divergence and wind field derived by radial velocity. The result shows that the heavy hailstorm is frequently occur in the overlapping area of the largest radial velocity and intensity.

• Perfect Q-Vector and Its Diagnoses
• YAO Xiu ping;YU Yu bin
• 2001 Vol. 20 (2): 208-213. 
• Abstract ( ) PDF (269KB) ( )
• Referring to quasi geostrophic Q-vector, taking account of the main heating forcing factor-diabatic heating of the development of synoptic systems, the concept of perfect Q-vector was proposed, an expression of the perfect Q-vector and the perfect ω equation, in which the divergence of perfect Q-vector was taken as an only forcing term, was derived in this paper. And the perfect Q-vector was applied to diagnose a heary rain process for August 3~5, 1996. The results showed that there were more advantageous using the perfect Q-vector, and suggested that the perfect Q-vector could clearly reveal the system development of the heary rain; the divergence center or line, the divergence field and the frontogenesis function field of the perfect Q-vector could be used to locate the heary rain area; the center magnitudes of the perfect Q-vector divergence field and the frontogenesis function field could be signified the intensity of the heary rain. So, the perfect Q-vector divergence and the frontogenesis function are two important parameters in the process of diagnosing and forecasting the heary rain.

• The Singular Spectrum Analysis of Snow Damage in Eastern Qinghai-Xizang Plateau
• DONG An xiang;JU Zhang;YIN Xian zhi;ZHOU Lu sheng
• 2001 Vol. 20 (2): 214-219. 
• Abstract ( ) PDF (245KB) ( )
• Usingsingular spectrum analysis, the climatic feature of snow damage in the east Qinghai Xizang Plateau have been analysed during the winter half years of 1967-1996. The results show that general tendency of snow damage increases, specially in the late winter. This may respond to global warming. Its quasi periods are main 2.0~3.1 and 5.4~7.5 years. There is an abrupt change of snow damage from below to above normal about 1985/1986. The snow damage anomaly has the trends for two year in winter half year and one year in the late winter by means of SSA-MEM technique predicting.

• EOF Iteration Scheme with Multitime Historical Data and Its Application to Summer Climatic Prediction over Yunnan Province
• DUAN Xu;YOU Wei-hong;LI Yue-qing
• 2001 Vol. 20 (2): 220-224. 
• Abstract ( ) PDF (194KB) ( )
• EOF iteration scheme with multitime historical data can make better use of the information in historical data. The forecast method will be improved well and used widely when it introduce the empirical law, the observational fact and the climatic law etc into actual short range climatic prediction, especially when we have a better understanding of the physical process and factors which affect the climate changes. By using the monthly mean sea surface temperature data in 4 regions, a forecast model based on EOF iteration scheme for the summer climatic prediction over Yunnan province is established. The verifications of the summer precipitation and temperature forecasts for Yunnan province show that the operational forecast average scores of this model can reach 79.6% and 87.0% in 1995-1999, respectively. These scores show that the physical statistical forecast method with multitime historical data based on EOF iteration scheme is an effective path of short range climatic prediction.