Current Issue

• MODELLING TESTS OF THE ERRORSUBTRACTION SCHEME FOR THE PRESSURE GRADIENT FORCE IN MODELS WITH TOPOGRAPHY
• Qian Yongfu;Zhou Tianjun
• 1995 Vol. 14 (1): 1-9. 
• Abstract ( ) PDF (577KB) ( )
• In the present numerical models with topography, there is a common problem of computation of the pressure gradient force in the steep mountainous areas. That is, the, computational formats with high accuracy are complex and time-consuming and those which are simple and time-saving arc not precise and stable. In order to solve the problem, the authurs recently developed a scheme called the error subtraction method of the pressure gradient force which assumes that the computational errors of the pressure gradient force are mainly resulted from the topog-rapby and have less relations to the pressure patterns. The tests made by use of ideal fields show that the method is successful. Modelling tests are made in this paper to check the error subtraction scheme of the pressure gradient force in models with topography developed by the authors. Four computational formats are selected, the modelling results of the four formates with and without the subtraction scheme are compared with one another. It is found that the modelling results are not very much different between the schemes with and without sub- tractions when formats with higher accuracy are used. However, the formats with error subtractions can still improve the modelling results to some extent. For formats with low accuracy the error subtraction method can fundamentally improve the accuracy and stabillty of computation. and get satisfactory efficiency of modellings.

• A VARIATIONAL ASSIMILATION SCHEME WITH ADJUSTING PARAMETERS OF THE MODEL EQUATION——STUDY BASED ON LORENTZ MODEL
• Gao Jidong;Chou Jifan;Shen Jun
• 1995 Vol. 14 (1): 10-18. 
• Abstract ( ) PDF (533KB) ( )
• Some variational assimilation experiments with conjugate method are carried out by using the Lorentz system in this paper. The results show that with the increasing errors of model parameter, the effect of assimilation becomes the more poor the more poor until the results have no meanings. We retrieve both the initial values and the parameters of the model simultaneously, i. e., the optimal initial values and the optimal parameters are gotten at the same time. The forecasting results based on Lorentz system are improved large.

• THE CHARACTERISTICS OF THE TEMPORAL VARIATION OFFLOW-OFF ATTANG NAIHAI AND GE ZHOUBA
• Ma Zhuguo
• 1995 Vol. 14 (1): 19-27. 
• Abstract ( ) PDF (541KB) ( )
• Based on monthly mean flow-off data at Tang Naihai and Ge Zhouba . the characteristics of the temporal variations of flow off are analysed. The results indicate that there are periodic variations of high flow and low flow, and there are different characteristics in different places. At Tang Naihai, there are the dominant periods of 7.4 and 18.5 years, and there are the dominant periods of 15. 14 and 7.07 years at Ge Zhouba. The duration of flow-off departure (the signs of departure are same) at Tang Naibai is longer than that at Ge Zhouba, the monthly variability of the flow-off atTang Naibai is larger than that at Ge Zhouba.The monthly variations of multi-years mean flow-off are a single peak characteristic at Ge Zhouba, but at Tang Naihai, the monthly variations of multi-years mean Dow-off are double peaks, the double peak characteristic at Tang Naihai is related to the movement of the West Pacific Subtropical High. At last, the relationship between the flow-off at Tang Naihai and the departure of sod temperature of the area are also analysed, it is found that high flow years correspond to high Soil temperature, and low now years correspond to low soil temperature.

• EFFECT OF CLOUD SHADOW ON SHORTWAVERADIATION PARAMETERS OF REGULARCLOUD ARRAY
• Bian Huisheng;Liu Changsheng
• 1995 Vol. 14 (1): 28-38. 
• Abstract ( ) PDF (608KB) ( )
• An analytic model is developed by using solar radiation transfer equation to study shortwave radiation parameters of regular cloud array. The model includes many factors such as the limited view of the ground due to nearest clouds, the shade on the earth casted by clouds, the scattering and absorbing between cloud sides, cloud and earth surface, etc. The main feature of this model is the reduction of direct solar input due to shadowing by a neighboring cloud and this, due to its complexity,is neglected by precious researchers. Compared with the results of Bradley's model which doesn't consider the shadow effect., the shortwave radiation parameters of this model have great improvement at large solar zenith angle. This shows that the effect of shadow must be considered to simulate shortwave radiation parameters. In addition, the shortwave radiation parameters of regular cloud array are compared with those of plane-parallel cloud at same optical depth. The relations between radiation parameters of regular cloud array and other factors such as μ ₀(cosine of solar zenith angle) . R _s(albedo of earth surface) are also discussed.

• SOME CHARACTERISTICS OF C-G LIGHTNING IN SEVERE WEATHER
• Ge Zhengmo;Guo Changming;Yan Muhong;Meng Qing
• 1995 Vol. 14 (1): 39-46. 
• Abstract ( ) PDF (502KB) ( )
• Altogether, the Beijing LLS(Lightning Location System) recorded 71858 negative C-G lightnings and 12961 positive or 15.28% of the tatol, C-G lightning in 1989 and 1990 summers . However in 1991, the percentage of positive C-G lightning, 26.16%, is much higher than previous years. By analysing data, the results indicate that the hourly distribution of lightning in 1991 was unusual. It reached maximum at 18:00(BT), minimum at 08:00 and another maximum at 04:00, which is similar to that in Gansu region. There were also some differences for other parameters.A case study for a hailstorm on July 11, 1991 is also presented. The C-G lightning was not inside, but in the vicinity of the strongest echo area of hail cloud. The C-G lightnings gradually moved toward the anvil with the dissipation of the storm. Their locations clustered in cloud. The number of positive C-G lightning was more than that of negative C-G lightning at the vigorous stage of the storm. During the entire developing stage the distribution of C-G lightning of hailstorm was different from that of a mesoscale system without hail fall. The average positive C-G lightning intensity reached maximum during hailing.

• STATISTICAL ANALYSIS OF MEASURING ACCURACY FOR THE DUAL LINEAR POLARIZATION RADAR AND RAINFALL ESTIMATE
• Chu Rongzhong;Xu Baoxiang;Jia Wei;Li Xiaoping
• 1995 Vol. 14 (1): 47-54. 
• Abstract ( ) PDF (511KB) ( )
• Based on the statistical analysis of the partial data measured by a dual linear polarization radar during 1988-1990,it is found that the space correlation coefficient ρ _V , the time correlation coefficient ρ _T , the differential reflectivity Z _DR and its mean square deviation σ _DR follows different statistical distribution rules, respectively. An approximate nagtive linear correlation between σ _DR(dB) and ρ _T is also found. When ρ _T> 0.95 and mean pretreatment sampling number K=32, σ _DR can be cut down to be less than 0.2 dB. The best sampling method is 32 pairs of radial sampling-mean. These conclusions provide a basis for improving the hardware of the radar and exploring its meteorological applications of this new system. When selected best sampling method, measuring accuracy isn't important source for the area rainfall estimate error.

• STUDIES OF DYNAMIC INFLUENCE OF QINGHAI-XIZANG PLATEAU ON THE EASTWARD MOVING TROUGH IN WINTER PART Ⅲ THE ANALYSES OF SIMULATIONS EXPERIMENTS RESULTS
• Qian Zhengan;Jiao Yanjun
• 1995 Vol. 14 (1): 55-66. 
• Abstract ( ) PDF (868KB) ( )
• In this paper, the simulations results of the second part of the series papers are analysed concretely. The results show the experiments reproduce clearly the influence of Qinghai-Xizang Plateau on the westerly flow. The influences of different orogaphy, intensity and location of Jet, intensity of the eastward moving trough (EMT) itself and the baroclinic intensity of the basic westerly on the EMT are showed as well. Some of these results reproduce clearly the well-known facts of the terrain impacts in the past, some of them are new,and some of them can provide reference in the EMT prediction.

• DISTRIBUTION OF SNOW COVER ON THE QINGHAI-XIZANG PLATEAU AND ITS INFLUENCE ON SURFACE ALBEDO
• Wei Zhigang;Lü Shihua
• 1995 Vol. 14 (1): 67-73. 
• Abstract ( ) PDF (506KB) ( )
• The data set of snow cover in 58 grid points on the Qinghai-Xizang Pla-teau for the period from July 1983 to June 1990 are analyed by using EOF method.Theresults show the main of snow cover on the Qinghai-Xizang Plateau is in the west and south of the Plateau. There is a opposite variation of snow cover between the western. southern parts and the middle, northern, eastern parts of the Qinghai-Xizang Plateau. The distribution and monthly variation of the surface albedo in clear day is the same as the snow cover on the Qinghai-Xizang Plateau.

• MEASUREMENT OF ARTIFICIALLY TRIGGERED LIGHTNING DISCHARGE CURRENT AND ITS CHARACTERISTIC ANALYSIS
• Zhang Yijun;Liu Xinsheng;Chen Mingli;Wang Caiwei
• 1995 Vol. 14 (1): 74-79. 
• Abstract ( ) PDF (403KB) ( )
• Artificially triggered lightning discharge current and step voltage were measured on July 27, 1993. The results show that artificially triggered "slow" discharge process consisted of continuous current and current pulses when the positive electric field dominated on the ground. The current pulses were bipolar. The lightning discharge characteristic was relative to the electric characteristic of thunderstorm. The maximum of lightning current was 1.2 kA. The duration of the lightning was 25 ms. The electric charge neutralized by the triggered lightning was 8.9 C. Measurement result of step voltage was consistent with that of current. It is a indirect measurement method of lightning current.

• A IMPROVED THERMAL-DYNAMICAL MODEL FOR THE FORECASTING OF PRECIPITATION IN FLOOD SEASON
• Chen Zeyu;Tang Maocang
• 1995 Vol. 14 (1): 80-89. 
• Abstract ( ) PDF (632KB) ( )
• Based upon three equations, which are parameterization equation of equivalent infrared radiation temperature of planetary atmosphere, thermal balance equation in earth-atmosphere system, thermal conductivity equation of soil, the author built a numerical model for the forecasting of Precipitation Anomly in Flood Season (PAFS) (from April to Sept.). It effectively revises some disadvantages in that of aA Thermal-dynamical Model for Long-Range Precipitation Prediction deduced by Tang Maocang et al., makes the forecasting more objective .The distribution of the coefficients are calculated by using least square method, confirmed the reasonableness of option of the precipitation distinction in the summer of China, which have been advanced by Tang Maocang.By using optimum interpolation, the objective analysis fittes the real distribution very well. The model has some predicting ability for characterizing the distribution of the extreme value axes of precipitation system.According to sensitivity test, the model is sensitive to the thermal state of deeper soil. It means that it is necessary to induct equations, that can dipict describe the thermal conductivity in the deeper layer of sub-surface, when deducing numerical model for the forecasting of long range climate change.By the model, we calculate the PAFS from 1981 to 1990 . The averaged probability of the same symbol is 50% in the ten years.

• SPATIAL AND TEMPORAL VARIATION OF ANNUAL RAINFALL IN THE NORTHWEST ARID AREAS OF CHINA
• Tian Rongxiang;Gao Lin;Gao Youxi
• 1995 Vol. 14 (1): 90-95. 
• Abstract ( ) PDF (379KB) ( )
• In this paper, six independent rainfall regions are divided in West China through analysis of annual rainfall during 1958-1987 for 68 stations. Eight types of different spatial distribution of rainfall are divided by analysis for 3 areas in NW China. The results show that the control weather system in arid area of NW China is mainly westerly system. In 1958-1987, climate change was different in different areas.

• CHARACTERISTICS OF ENVIRONMENTAL FIELD AND VORTICITY BALANCE IN SUMMER PRECIPITATION PROCESSES OVER TIANSHAN MOUNTAIN AREA AND SURROUNDING AREAS
• Li Li
• 1995 Vol. 14 (1): 96-101. 
• Abstract ( ) PDF (405KB) ( )
• In this paper,diagnosis was carried out for characteristics of environmental field, heat and moisture budgets and vorticity balance in summer precipitation processes over Tiansban Mountain area and surrounding areas. The results show that characteristics of environmental field before precipitation occered is benefited of development of influencing system of precipitation. There are some differences of Q ₁, Q ₂ and vorticity balance during precipitation and before precipitation occered. Horizontal advection play the main part in heat and moisture budgets during precipitation. Heating of latent heat was balanced enssentially by cold advection. Water vapour that precipitation required was transported mainly by horizontal advection. Positive vorticity accumulated by horizontal advection was balanced with negative vorticity made by divergence term in vorticity balance. Nonline advection which is connected with jet of subtropical frontal zone occupies a main place in heat and moisture budgets and vorticity balance.

• ALBEDO OF ULTRAVIOLET RADIATION ON SEVERAIL UNDERLYING SURFACE
• Chen Wanlong
• 1995 Vol. 14 (1): 102-106. 
• Abstract ( ) PDF (333KB) ( )
• This study makes use of EPPLEY's ultraviolet radiometer to measure the albedos of ultraviolet radiation(UV) on six kinds of underlying surface . The primary results are presented as follows: (1) The albedo of UV-radiation is 2.4% for bare soil, 6.7% concrete, 2.1% grassland, 4.2% sands, 6.6% black soil and 83.5% new snow surface, respectively. (2) The UV-albedos are smaller than those of total solar short-wave radiation, especialy for previous five kinds of underlying surface, namely,except for snow. (3) The daily curve of UV-albedo is similar to albedo of total solar short-wave radiation.

• A DIAGNOSTIC ANALYSIS OF THE REGIONAL STORM RAINFALL OF TWO LOW N-E JETS OVER LOESS PLATEAU
• Liu Zichen;Zhang Jianhong
• 1995 Vol. 14 (1): 107-113. 
• Abstract ( ) PDF (460KB) ( )
• In this paper, two regional storms that no South West(SW) jet occured over the Loess Plateau were analysed, the results show that the low North-East (NE) jet plays an important role in this kind of storm. So this kind of storm was called NE jet storm. Compared with SW jet, NE jet has own properties. Then three flow model of low NE jet storms were given.

• STUDY ON THE WATER DROP SIZE DISTRIBUTION (WDSD)IN PRECIPITUS STRATIFORM CLOUDS
• Niu Shengjie;He Zhenzhen
• 1995 Vol. 14 (1): 114-120. 
• Abstract ( ) PDF (395KB) ( )
• The cloud and the rain drop size distributions in stratiform clouds which are in the region of Mount Tai and Xinan River are calculated . The cloud droplet and drop ( d≥80μm) and the raindrop size distributions are fitted by using N= AN ₀exp(- ad+ bd ²- cd ³). The observational and calculated results are well matched. The correlation coefficients are bigger than 0.93 and the significance level is 0.001. The calculated mean diameter, mean cube-root diameter, liquid water content and total concentration are all well matched with observational results. It has been proved that the water drop size distribution is representative.

• CORONA CURRENT MEASUREMIENT AND THEORETICAL ANALYSIS OF "Lightning ELIMINATOR"
• Yan Muhong;Zhang Yijun;Hua Guiyi
• 1995 Vol. 14 (1): 121-128. 
• Abstract ( ) PDF (547KB) ( )
• Until now,the corona current produced by "Lightning eliminator" and the eliminating principle of the "lightning eliminator" have being unknown question.In this paper, based on the measurement of corona current and electric field produced by "lightning eliminator", corona current density during recovery of electric field was evaluated on the theoretical from recovery characteristic of electric field on the ground after the lightning. The results show that even if the electric field reached to stable stage,measured value is an order larger than theoretical value.However, theoretical value is as same order of magnitude as corona current caused by natural point on the ground. The corona current caused by "lightning eliminator" is not stronger than that of the natural point. In addition, the structure of "lightning eliminator" (stronger local surface eletric field and bigger corona effective area) can amplify the smaller change of electric field in the air. Therefore,the displacement current was increased. So the function of corona current on eliminating principle is not evident.