Current Issue

• A Study on Algorithm to Make Attenuation Correction to Radar Observations of Radar Reflectivity Factor(Ⅰ):Theoretical Analysis
• ZHANG Peichang;WANG Zhenhui
• 2001 Vol. 20 (1): 1-5. 
• Abstract ( ) PDF (265KB) ( )
• From radar meteorological equation and the relationship between radar reflectivity factor and attenuation coefficient, an algorithm named bin-by-bin and its approximations and the over correction detecting criteria have been derived for attenuation correction to discrete radar observations. The algorithm has taken into account the spatially discrete, integrate sampling feature of radar observations and the criteria are determined by the coefficients in k-Z relationship and bin resolution. It is expected that the algorithm behaves as good as Hitschfeld Bordan approach when attenuation is weak and the approximations to the algorithm would be more efficient for computation than the iterative method. The criteria can be used to avoid efficiently the compntation overflow caused by unstable over correction even though the unstability feature inherent in attenuation correction can not be solved. It has been shown that high resolution of data bin is beneficial to improve the stability during correction computation.

• Study on the Characteristics of Positive and Negative Leader in Triggered Lightning in Altitude
• ZHANG Yi-jun;LIU Xin-sheng;WANG Cai-wei;XIAO Qing-fu;ZHANG Guang-shu;DONG Wan-sheng;ZHOU Liang-cai;ZHONG Ding-zhu;FAN Ling-meng;CHEN Ming-li;WANG Dao-hong
• 2001 Vol. 20 (1): 6-13. 
• Abstract ( ) PDF (386KB) ( )
• The optical and electrical data of triggered lightning in altitude on 22 August 1998 were analyzed. The results indicated that there were three leader processes in triggered lightning in altitude. A negative leader propagated downward from bottom end of wire in a discontinuous pulses pattern with intervals of about 20 μs and rise time of less 1 μs. A positive leader starting from the top end of wire showed a pulses pattern with the intervals of 15 μs after the negative leader reached the ground. Meanwhile, a positive leader was initiated from the ground and propagated upward in discontinuous pulses pattern with intervals of 13 μs when the negative leader approached the ground. Following this was a mini-return stroke which emit intense light only in the channel section between ground and bottom end of wire and had an upward speed of 2.1×10 ⁸m·s ^-1. The negative leader emit more intense light than the positive leader initiated from the top end of wire before mini-return stroke. The light emit by the positive leader initiated from the top end of wire was intensified and propagated upward in speed of 2.4×10 ⁶m·s ^-1 after mini-return stroke. The wire was melted after 220 μs of mini-return stroke and had intense light which propagated upward in speed of 1.0×10 ⁴m·s ^-1.

• Numerical Study of the Effects of Dynamic and Thermodynamic of Qinghai-Xizang Plateau on Tropical Atmospheric Circulation in Summer
• ZHENG Qinglin;WANG Sanshan;ZHANG Chaolin;SONG Qingli
• 2001 Vol. 20 (1): 14-21. 
• Abstract ( ) PDF (508KB) ( )
• By employing the CCM3(R15L9) long range spectral model developed on the basis of CCM3 climate model, the seasonal simulations have been carried out to investigate the dynamic and thermodynamic effects of Qinghai-Xizang Plateau on the tropical atmosphere circulation in June, 1996. The results show that the dynamic and thermodynamic effects of the Plateau in early summer are obviously favorable for increasing the air mass temperature over the belts near 30°N and 30°S, and contribute to the northward shift of the Northern Hemisphere subtropical westerly jet, the enhanced tropical upper-layer easterlies and help to enhance the equatorial western flow at lower-and middle-layers. All these roles are helpful of accelerating of the season transition. The Plateau's influences contribute to the genesis and enhancement of the cross-equatorial air flow, and play profound impacts on the mass exchanging between the Northern and Southern Hemisphere. Fourthly, the effects of the Plateau are beneficial to the development of the easterly wave motion over tropical Pacific lying east of 140°E, which also suggests that its effects help to reinforce tropical cyclones over South China Sea and about 2 000 km to east of Philippine.

• The Principal Feature of Qinghai-Xizang Plateau Monsoon Variation in 40 Years
• BAI Hu-zhi;XIE Jin-nan;LI Dong-liang
• 2001 Vol. 20 (1): 22-27. 
• Abstract ( ) PDF (325KB) ( )
• The daily monsoon index of Qinghai-Xizang Plateau during 1961-1995 is calculated, the start and end time of summer monsoon of Qinghai-Xizang Plateau are preliminarily determined. Based upon that, we investigate the interannual variation features of the monsoon index and its relationship with the 500 hPa geopotential height fields and monsoon of East Asia. The results are as follows:The anticorrelation exists in the start and the end time of summer monsoon; The interannual and interdecadal variation of Plateau monsoon is obvious; The strong(weak) winter Plateau monsoon is contemporarily related to the high(low) 500 hPa geopotential height fields over Qinghai-Xizang Plateau and the Ural mountains and to the strong(weak) winter monsoon of East Asia; The strong(weak) summer Plateau monsoon is contemporarily related to the low(high) 500 hPa geopotential height fields over the Baykal lake and south of Qinghai-Xizang Plateau and to the high(low) 500 hPa potential height fields over West Asia and East China and also to the strong(weak) summer monsoon of East Asia.

• The Effects of Vertical Resolution of P-σ Coordinate Regional Climate Model on Simulated Results
• WANG Shi-yu;QIAN Yong-fu
• 2001 Vol. 20 (1): 28-35. 
• Abstract ( ) PDF (524KB) ( )
• A nine level 1°×1° P-σ corrdinate regional climate model is developed on the basis of a five level P-σ model and inter comparisons the simulated results of the nine level model and the five-level model are carried out by using the NCEP reanalysis monthly mean data. It is found that the improved nine level model has a better simulations of the geopotential field, the temperature field and the precipitation field in winter and summer. For the simulation of wind fields, the nine-level model performs better than the five-level model in the lower layers in winter, however, a little worse in summer. In the whole, the increase of vertical resolution results in large improvements of the P-σ model simulation and it is a fair preparation for the further developing of the regional ocean-atmospheric coupled model.

• A New Idea to Improve China Summer Precipitation Forecasting
• DONG Wenjie;WEI Zhigang;CHOU Jifan
• 2001 Vol. 20 (1): 36-40. 
• Abstract ( ) PDF (231KB) ( )
• At present, the dynamic model method and the statistical climatic method are used at flood season precipitation forecasting. The difficulty of the dynamic method is that it is too far a way to fit an operational prediction's requirement and the limit of the statistical method is that it has no power facing the case that the multi factors are simultaneously abnormal. By the examples to predict the precipitation of summer in 1998 in China, a new idea of the dynamical statistical forecasting combination is found out.In the case that two or more factors are simultaneously abnormal, use the dynamical model to separate and diagnose the dependent contribution of each abnormal factor and the combing contribution of multiple abnormal factors. The EOF analysis is applied to the numerical experiment to predict summer precipitation anomalies. The main forecasting result accords with the real distribution of summer precipitation anomalies in 1998 in China.

• A Study of the Rain Scavenging Coefficient of SO ₂ in Guiyang
• ZHAO Cai;LI Qitai
• 2001 Vol. 20 (1): 41-45. 
• Abstract ( ) PDF (222KB) ( )
• Using the SO ₂ data collected from the air and earth's surface, meteorological data and cloud physical data, a calculating method of the rain scavenging coefficient of SO ₂ was advanced. The rain scavenging coefficient of SO ₂( k _w) was calculated for different rain strengths and seasons. This coefficient k _w has been used in the numerical calculation for the SO ₂ concentration in Guiyang, the obtained results consisted with the practically detacted data.

• Research of Dust Depositions of 930505 Extremely Severe Sandstorm in Gansu
• ZHANG Ning;QING Ji-zu;NI Tong;ZHAO Hong;LIU Weng-jun
• 2001 Vol. 20 (1): 46-51. 
• Abstract ( ) PDF (330KB) ( )
• Research and analysis were carried out of the deposition distribution and amount of the 930505 extremely severe sandstorm occured at Jinchang, east Gansu corridor. The main results are as follows:(1) The dust deposition of the sandstorm corers 80.7 percentage of the tatal area of Gansu Province. The totaly amount of dust deposition in Gansu Province is estimated to reached 1 245.3×10 ⁴ t·mon ^-1 with the maximum value of 699.4×10 ⁴ t·mon ^-1 in Jinchang area.(2) The active duststorm weather region is about 7.0×10 ⁴ km ², but the area in which the atmospheric environment was severely degraded is much more larger and reach 35.5×10 ⁴ km ².

• A Numerical Study on the Forcing Field of Midsummer Drought Circulation on the Northeast Side of Qinghai Xizang Plateau
• JIA Xiaozhong;CAO Xiaoxia;LI Dongliang
• 2001 Vol. 20 (1): 52-57. 
• Abstract ( ) PDF (337KB) ( )
• The previous results show that the midsummer drought on the northeast side of Qinghai Xizang Plateau is a drought controled by the subtropical latitude high, and the structure of drought circulation displayes a barotropic state. In order to study the maintaining mechanism of the drought circulation, the resultant circulation of 5 typical midsummer drought cases and its forcing field were calculated, and the numerical experiment utilizing a spherical, nondivergent, quasi-geostrophic, barotropic vorticity equation spectral model with forcing and dissipation termes was made. The results show that the mean duration of maintenance of drought circulation is about a week or so, the existence of drougt flow forcing source regions is critical for the maintenance of the drought circulation. The main forcing source region is in the North of Qinghai Xizang Plateau.

• Numerical Simulation of Oasis-Induced Mesoscale Atmospheric Flow and Its Sensitivity Test of Key Factors
• ZHANG Qiang;YU Xue-quan
• 2001 Vol. 20 (1): 58-65. 
• Abstract ( ) PDF (409KB) ( )
• Using a non-hydrostatic, highresolutional and two dimensional mesoscale atmospheric numerical model, to take account of the condition of a simple land surface process, oasis-induced mesoscale atmospheric flow is simulated. The sensitivities of the mesoscale atmospheric flow to oasis horizontal spatial scale, thermodynamical difference between oasis and near desert, large-scale horizontal wind speed, large-scale surface sensible heat flux are studied. It is found that the oasis induced mesoscale atmospheric flow becomes strong with an increase of thermodynamical difference between oasis and near desert, and it becomes weak with an increase of large scale horizontal wind speed and large scale surface sensible heat flux, but change of intensity of the mesoscale atmospheric flowwith horizontal spatial scale of oasis isn't a monotonous function. The mesoscale atmospheric flowshall be the strongest when horizontal spatial scale of oasis is about 20 km, and it shall become weak when oasis horizontal spatial scale is smaller or larger. At the same time, the distribution of horizontal spatial scales of the oases in Hexi region is analysed, and it is found that the scale in which oases come in great numbers is 15~25 km. This scale is mainly identical with the scale in which oasis can induce the strongest mesoscale atmospheric flow.

• A Statistical Inference from Probability of the Worst Drought Year to Occur in the Northwest China
• LI Ke;GAO Ju;ZHAO Dong;YANG Bixuan;GUO Hongwu
• 2001 Vol. 20 (1): 66-70. 
• Abstract ( ) PDF (213KB) ( )
• Based on the data of the classes of flood/drought about five hundred years in northwest China, using the theoretical model of Bernoulli test and others, the character of probability was studied for the worst drought to occur, the statistical rule of the worst drought year to was occurred to be obtained. In the background of the climate getting warm over the world, the result of the statistical inference of probability of the worst drought year will occur to be given in the 21th century in northwest China.

• Analyses of Climatic Trend and Jump over Middle Reaches of Yarlung Zangbo River in Tibetan Plateau in Recent 42 Years
• ZHOU Shunwu;JIA La;DU Jun
• 2001 Vol. 20 (1): 71-75. 
• Abstract ( ) PDF (237KB) ( )
• The climatic variation tendencies and interdecadal variations over middle reaches of Yarlung Zangbo River in Tibetan Plateau are analyzed by using the observed data of summer mean temperature/precipitation at 4 stations(Lasha, Xigaze, Zedang and Jiangzi) from 1957 to 1998. The main results are as follows:There exists respectively significant ascent and descent trends for summer temperature and rainfall over this region in recent 42 years. An obvious climatic jump of summer temperature occurs in late 1970's through early 1980's. From the middle of 1960's to 1980's the summer rainfall was obviously below the normal in this area. However, there was an increasing trend of rainfall after 1990. Summer temperature and precipitation have the oscillation period of 2~3 years.

• The Stable Energy in Lanzhou City and the Relations between Air Pollution and It
• SHANG Kezheng;DA Cunying;FU Youzhi;WANG Shigong;YANG Debao
• 2001 Vol. 20 (1): 76-81. 
• Abstract ( ) PDF (299KB) ( )
• According to the view of energy, we put forward a new parameter-stable energy, which describe the stability from surface to the given altitude and its calculating method. By using the sounding data of Lanzhou meteorological station and the concentrations of air pollution of Lanzhou environmental station during 1988-1992, we have worked out 15 layers the stable energy from 300~1000 m and the correlation coefficients between stable energy and concentration of SO ₂, CO, NO _X. The results are as follows:To describe the stability of lower air, stable energy is better than thickness and intensity of inversion layer. The annual change regular pattern of stable energy is the same as concentrations of air pollutant. Except for July, the correlation between stable energy and concentration of air pollutant have pass the significant level test at the α=0.01.

• Observation and Analysis of Mass Concentration of Dust and Sand Aerosol in Spring in Helanshan Area
• NIU Shengjie;SUN Jimin;CHEN Yao;LIU Hongjie
• 2001 Vol. 20 (1): 82-87. 
• Abstract ( ) PDF (300KB) ( )
• Aerosol mass concentrations were obtained under different weather conditions including atmospheric background, dust, sand blowing and dust storm, and there are largelg differences for averaged aerosd mass concentraions under above four kinds of different dust and sand weather conditions. On the average, the aerosol mass concentrations of dust weather is 3.54 times larger than that of atmospheric background; of sand blowing, 2.95 times larger than that of dust; of dust storm, 2.68 times larger than that of sand blowing. The sand aerosol mass concentrations of background in the Helan Mountain vary from 76.0 to 142.4 μg·m ^-3 in spring, and also the average value in desert area is more than the value in Yinchuan 20%. Furthermore, the mass concentrations between Anderson and KB-120E are different.

• A Phase Space EOF Method and Its Application to Climate Diagnosis
• LI Yueqing
• 2001 Vol. 20 (1): 88-93. 
• Abstract ( ) PDF (311KB) ( )
• According to the phase space technique and Empirical Orthogonal Function(EOF) analysis, a new method of phase space EOF analysis was presented and it is used. the variation of precipitation and temperature was investigated in Sichuan. The results show that the jump is the most important characteristic for climate change and the periodicity is secondary. There is obvious jump at higher climatic hierarchy and lower climatic hierarchy can feeds back to the climatic jump. The positive(negative) feedback highlight(conceal) the climatic jump. In climatic diagnosis and analysis, this is a distinctive method.

• Relationship between the Surface Heating Fields over Qinghai-Xizang Plateau and Precipitation of Southwest China in Autumn
• CHEN Zhongming;LIU Fuming;ZHAO Ping;MA Zhengfeng
• 2001 Vol. 20 (1): 94-99. 
• Abstract ( ) PDF (314KB) ( )
• Surface heating fields over the Qinghai-Xizang plateau were estimated using the 35 years(1961-1995) data set of 148 observation stastions in the Qinghai-Xizang plateau and near area, the relationship between the surface heating fields over the plateau and precipitation in the southwest China in autumn is anlysed. The results are as follows:(1) There are negative correlations between the surface heating over eastern part of Qinghai-Xizang plateau and precipitation in southwestern China in autumn.(2) Anomaly of 500 hPa atmospheric circulation over the Asia-Europe forced by abnormal of surface heating over the Plateau is able to restrict amount of precipitation in the southwestern part of China in autumn.

• Period and Jump Analyses of Climatic Variation in Ningxia in Recent Hundred Years
• LI Yan-chun;LI Yan-fang
• 2001 Vol. 20 (1): 100-104. 
• Abstract ( ) PDF (275KB) ( )
• Using Mann-Kendall jump test and moving t test, the periods and jump character of climatic variation in Ningxia in recent century are analysed based on the data of annual rainfall and temperature departure during recent hundred years in north of Ningxia and the data of temperature and precipitation obtained from 19 meterological stations of Ningxia since using apparatus. The results show that the climate in Ningxia during recent century can be divided into 5 main periods. Before 1930's, it was a dry and cold period; from 1930's to the middle 1950's, a warm and humid period; from the middle 1950's to the late 1960's, a cold and humid period; from the late 1960's to the middle 1980's, a cold and dry period, and from the middle 1980's to now, a warm and dry period. The annual mean temperature as well as autumn and winter temperature became jump in the middle 1980's. About 1960's, the annual precipitation became jump and in the middle and late 1970's, the autumn precipitation of Ningxia became jump.

• Temperature Variations over Qinghai Xizang Plateau in the Past 600 Years
• FENG Song;YAO T;ong;JIANG Hao;KANG Xingcheng
• 2001 Vol. 20 (1): 105-108. 
• Abstract ( ) PDF (198KB) ( )
• Three subregions are compartmentalized for temperature over Qinghai Xizang Plateau based on the ISCCP surface temperature data during July 1983～December 1990. Ice core and/or tree ring data in the past 600 years are chosen in each subregion and then the data are computed into the air temperature index with the method of standardization and area proportioned. Variations of air temperature index show that three times of cold and warm periods appeared in the past 600 years. It is the coldest in the middle of 17th century.

• Relationship of Winter Disturb Source Vortex over West and Summer Rain Belt over East China
• LIU Yanxiang;TANG Maocang
• 2001 Vol. 20 (1): 109-112. 
• Abstract ( ) PDF (206KB) ( )
• In summer, the distribution of rain belt over East was controlled by the last winter position of Disturb source vortex over West China, during 85°E to 105°E latitude. The vortex is to the north of 35°N longitude, the belt is occurred in Yellow River reaches and to the north(first rainfall pattern-Ⅰ) in summer; between 32°N and 35°N longitude, the belt is appeared in Huaihe River basin(second pattern-Ⅱ); and the vortex is down to the south of 35°N, the belt is in Yangtze River basin and/or Jiangnan area(third pattern-Ⅲ). In the hotspot region over south east of Tibet, the stronger geothermal pulse in winter has more important influence for climate disaster in next summer over Yangtze River, Huaihe River reaches and Sichuan, Guizhou area of China.