Current Issue

• TRANSmISSION LINE mODEL AND CURRENT VELOCITY OF CLOUD-TO-GROUND LIGHTNING RETURN STROKES
• Chen mingli;Liu Xinsheng
• 1995 Vol. 14 (4): 385-395. 
• Abstract ( ) PDF (373KB) ( )
• Based on the maxwell's equations and the spectral ch aracteristics of lightning radiation field produced by return stroke, an expression of vertical electric field produced by a cloud-to-ground lightning has been developed, provided that the channel of return stroke is vertical and stands on an imperfect conductive surface Thus, the troubles due to using unsuitable image method can be overcome Considering that the optical measured return stroke velocity and the velocity of current propagation are two different concepts, we assumed that the current velocity inside a return stroke channel equals the light propagation velocity(c) approximately A return stroke front is just the front of stronger ionization due to ions accelerated by current It should be after the current front Based on the above two points, the transmission line model has been improved This new model can reasonably explain the simultaneous measurements of electric field and current of cloud-to-ground lightning flashes.

• THE CORRELATION ANALYSIS OF ELECTRIC ACTIVITY,CONVECTION AND PRECIPITATION IN CONVECTIVE CLOUD AND STRATUS
• Zhang Yijun;Hua Guiyi;Yan muhong;An Xuemin
• 1995 Vol. 14 (4): 396-405. 
• Abstract ( ) PDF (352KB) ( )
• In this paper,electric and echo characteristics,convection and precipitation were analysed and correlation between them were investigated in 6 different cloud systems The results indicated that except instability energy,-10 ℃ and 0 ℃ temperature levels,altitude difference between them,altitude difference between 0℃ temperature level and the top of cloud were important parameters that represented dynamics and electric characteristics in thunderstorm The electrification processes in thunderstorm strongly depended on ice phase of cloud The relationship between electric activity and convective activity was positive correlation most of lightning are occured during height for 30dBz echo was higher than -10℃ temperature level The intense electric activity corresponded to heavy precipitation and didn't correspond to weak precipitation The lightning may be influence on characteristics of thunderstorm during dissipating stage.

• ARTIFICIALLY TRIGGERED LIGHTNING AND THE RAIN GUSH
• Zhang Yijun;Yan muhong;Dong Wansheng
• 1995 Vol. 14 (4): 406-414. 
• Abstract ( ) PDF (313KB) ( )
• In this paper,based on the measurement results of precipitation increasing abruptly after a artificially triggered lightning,gravitational collision efficiency of raindrop near the channel of lightning was calculated by using a simple electrostatic model The results indicate that lightning can produce the rain gush under certain condition Higher ion density(>10 ¹⁴/m ³) is needed meanwhile,it depends on the electric field change caused by lightning and electric field intensity near the channel of lightning before triggered lightning.

• PRELImINARY EXPERImENTS OF A LAND- SURFACE PROCESS mODEL WITH SImPLE PARAmETERIZATION OF SNOW-COVER
• Yan Zhongwei;Ji Jinjun
• 1995 Vol. 14 (4): 415-424. 
• Abstract ( ) PDF (351KB) ( )
• Having considered the snow-cover process,we developed a new version of the land-surface process model from the existing soil-vegetation-atmosphere model The new model describes additionally two major effects of snow-cover:the large reflectivity of solar radiation due to the high albedo of snow-surface and the lagged soil hydrological impact due to snow-melting A few experiments were designed against the meteorological and the surface radiation data observed during the HEIFE project,which was carried out at the Heihe region,in Northwestern China The modeled processes forced by atmospheric precipitation (both rainfall and snowfall) seem quite reasonable Some modeling elements such as the surface soil temperature and the surface net radiation coincide well with the observations.

• NUMERICAL EXPERIMENTS FOR THE EFFECTS OF THE RISING OF THE TIBETAN PLATEAU ON THE FORMATION OF ASIAN SUMMER MONSOON
• Wu Chisheng;Wang Anyu
• 1995 Vol. 14 (4): 425-433. 
• Abstract ( ) PDF (331KB) ( )
• Five sets of numerical experiments were performed by using a five-layer limited area primitive equation model Among them,one is for real topagraphy with mean height of 4000 m;and the others are for the heights of 1000 m,2000 m, 3000 m, 3500 m,respectively Their results were compared each other It was shown that: (1) The atmospheric heat source over the Tibetan Plateau and its southeast neighbourhood strengthened with the rising of the Plateau Especially,when the mean height of Plateau was rised from 3000 m to 3500 m,the intensity of the heat source increased significantly and correspondently,the Asian summer monsoon circulations were changed obviously (2) When the mean height of Plateau was rised to 3 500m,the South Asian high in the upper troposphere appears,and the tropical easterly to the south of the high center was strengthened considerably Meanwhile,the low-level thermal low over the Asian continent moved westward to over the Plateau rapidly If the Plateau rised higher than 3 500m,the monsoon meridional cell,with the ascending branch over the Plateau and the two descending branches to the north and south sides of Plateau respectively,was seted up completely As a result of adding of the Plateau monsoon to the monsoon caused by the thermal difference between sea and continent,the Asian summer monsoon was strengthened considerably (3) In response to the rising of Tibetan Plateau,the distribution of rainfall was also changed The positive (increasing) and negative(decreasing) rainfall centers were located in the southeast side of the Plateau and the east coast of the Bay of Bengal,respectively.

• THE COMPARATIVE EXPERIMENT OF INFLUENCES ABOUT SURFACE DRAG COEFFICIENTS IN BOUNDARY PROCESS ON NUMERICAL WEATHER FORECASTING FOR HEAVY RAIN
• Chen Yuchun;Qian Zhengan;Zhang Lisheng;Wang Xiaoli
• 1995 Vol. 14 (4): 434-442. 
• Abstract ( ) PDF (355KB) ( )
• In this paper,the limite-area numerical weather forecasting model suitable for complex topography and the observation data over Tibetan Plateau and part area of its north-side are used to study the influences of surface dray coefficients in boundary process on numerical weather forecasting (especially precipitation forecasting) Firstly,dray coefficients of different underlying surface are altered and combined Secondly,4 groups of different numerical experiment schemes are designed At last,24 96h numerical forecasting experiments about a typical Jianghuai Meiyu heavy rain weather process during 11 15 June,1991 have been carried out The results show: (1) Surface dray coefficients has some influences on short-range forecasting of center intensity of rainfall (2) Among 4 schemes,scheme 2,in which the drag coefficients over Tibetan Plateau and part area of its north-side are modified,has a better result (3) With integration time prolonging,the influences about boundary process on rainfall and weather situation are more notable.

• NUMERICAL STUDY FOR FOHN IN EAST SLOPE OF TAIHANG MOUNTAIN
• Chen ming;Fu Baopu
• 1995 Vol. 14 (4): 443-450. 
• Abstract ( ) PDF (290KB) ( )
• In this article,we use many years of climatic statistic data to analyse the fohn characters in Taihang mountain areas,and set up a two-dimensional numerical model to simulate the influence of topographic thermal-dynamic effects on the formation and development of the fohn The modelling results clearly show the climatic characters of foen in Taihang mountain and reveal its governing factors as well as modification affect caused by surface thermal effect,point out that the steep stepped terrain in east slope of Taihang mountain is the basic reason to cause fohn in this area It forces airflow to change from sub-critical to supercritical condition and thus cause strong downslope wind Surface heating weakens the fohn strength,while,cooling makes it strong.

• CHARACTERISTICS OF LONGWAVE RADIATION OVER THE QINGHAI-XIZANG PLATEAU
• Ji Guoliang;Jiang Hao;Lu Lanzhi
• 1995 Vol. 14 (4): 451-458. 
• Abstract ( ) PDF (273KB) ( )
• In this paper, characteristics of the upward, downward longwave radiation and surface effective radiation over the Qinghai-Xizang Plateau are analysed by using the upward and downward longwave radiation data observed at Wudaoliang in the northern Qinghai-Xizang Plateau from September 1993 to August 1994, the longwave radiation data observed at Lhasa, Nagqu, Gerze and Garze stations in the Qinghai-Xizang Plateau from August 1982 to July 1983, the longwave radiation data in Qinghai-Xizang Plateau Meterorological Experiment (QXPMEX)from May to August 1979 and radiation data in HEIFE of 1991.The result s show that over the Qinghai-Xizang Plateau, the surface effective radiation is larger than that over the plain because the downward longwave radiation is small.The annual variation of surface effective radiation is large in summer and small in w inter over the western Plateau, large in w inter and small in summer over the eastern Plateau, large in spring and autumn and small in w inter and summer over the northern Plateau.The role of surface effective radiation in the surface radiation balance is larger than the surface abledo over the Qinghai-Xizang Plateau.

• SOLAR RADIATION AND ATMOSPHERIC TURBIDITY OVER XIGU DISTRICT OF LANZHOU IN WINTER
• Tian Wenshou;Huang Jianguo;Chen Changhe
• 1995 Vol. 14 (4): 459-466. 
• Abstract ( ) PDF (277KB) ( )
• By means of thermoelectric actinometer mounted with eight kinds of the light filter,the spectral intensities of the solar direct radiation were measured over the Xigu district of Lanzhou city in winter Based on these observation data,aerosol's optical depth and atmospheric turbidity were calculated by using simple radiation transfer equation and Angstrom formula, and the characteristics of the atmospheric turbidity and solar radiation as well as the interaction between them were analysed further At the same time, we discussed some problems in the turbidity calculation by using Angstrom formula Last,the effects of the air mass, atmospheric trubidity and water vapor on the relative fluxes of the solar spectral radiation were also discussed.

• THE LAND USE CLASSIFICATION USING NOAA METEOROLOGICAL SATELLITE DATA FOR THE HEDONG REGION OF GANSU PROVINCE
• Guo Ni;Chen Tianyu;Chen Qian
• 1995 Vol. 14 (4): 467-475. 
• Abstract ( ) PDF (311KB) ( )
• In this paper,the land use in the region of 32.5° 38.0 ° N,100.5 ° 109.0 ° E is classified according to the vegetation index difference in time and space of various vegetations by using NOAA/AVHRR data from 1992 to 1993 The annual variation characteristics of vegetation index of different land use are discussed according to classified results.

• THE BUDGETS OF THE MOIST AVAILABLE ENERGY FOR A CASE OF MESOSCALE CLOUD CLUSTER
• Wu Baojun;Xu Chenhai;Liu Yanying;Fan Genyan
• 1995 Vol. 14 (4): 476-485. 
• Abstract ( ) PDF (349KB) ( )
• In this paper,budgets of the moist available energy for a case of mesoscale cloud cluster accompanied by heavy rainfall influencing Beijing area during 09:22 14:00 UTC August 1, 1990 had been diagnostically studied by the use of operational data The results show that (a) During the developed period (12:00 UTC) of the cloud cluster,a lot of the moist available energy was released In other words,the conversion term was a dominant energy sink (b) Because of both the vertical transport term and the latent heat release supplied the moist available energy to the cloud cluster,it is persisted for a long time In other words, both the terms were dominant energy source (c) The order of surface pressure change term was too small,it almost had not influence on whole situation (d) The orders of both the horizontal transport term and the effective factor change term were larger,they had in some degree influence on whole situation.

• A DIAGNOSTIC ANALYSIS OF FLASH HEAVY RAIN IN NORTHEAST CHINA
• Sun Li;Lian Yi;Bai Lesheng
• 1995 Vol. 14 (4): 486-494. 
• Abstract ( ) PDF (330KB) ( )
• In this paper,a diagnostic analysis on a case of flash heavy rain occurred in the south part of Changchun on 20 July 1991 is conducted Results show (1) Before the occurrence of this flash heavy rain,the existence of θ _se-gradient reinforcement area,convective instability area and its tendency, Q-vector convergence area and greatly increasing of vapour content provide advantageous environmental conditions for the occurrence of the heavy rain (2) The energy transformation between the large-scale and meso-scale motions by non-linear interactions processes was a main physical mechanism for the formation of the flash heavy rain.

• THE DISCUSSION ON THE OPERATION OF OZONE SONDE OF OZ-IA-S
• Zhang Wenyu;Feng Guanghong
• 1995 Vol. 14 (4): 495-498. 
• Abstract ( ) PDF (141KB) ( )
• Based on the data precision obtained by the ozone-sonde of OZ-IA-S in the field observation,this paper discusses its measuring methods The results show that the instrument is of high sensitivity In order to obtain precise data,the bubbler should be cleaned and filtrated with dry solid filter before use.

• FAN-SHAPED SCANNING TECHNOLOGY OF DUAL-LINEAR POLARIZATION RADAR
• Wang Zhijun;Song Xinmin
• 1995 Vol. 14 (4): 499-504. 
• Abstract ( ) PDF (216KB) ( )
• This paper introduces the fan-shaped scanning technology of dual-linear polarization radar It not only satisfy to be need of applied research of dual-linear polarization radar,but also is as reference for designing antenna motion pattern of digital weather radar.

• STUDIES ON THE EFFECT OF SNOW COVER OVER THE QINGHAI-XIZANG PLATEAU IN WINTER AND SPRING ON GENERAL CIRCULATION OVER EAST ASIA IN SUMMER
• Luo Yong
• 1995 Vol. 14 (4): 505-512. 
• Abstract ( ) PDF (304KB) ( )
• The temporal and spatial characteristics of snow cover over the Qinghai-Xizang Plateau are analysed and the important influences of snow cover over the Plateau in winter and spring on the climate formation and anomaly in East Asia in summer are revealed The advances of diagnosis and numerical experiment on the effects of snow cover over the Plateau in winter and spring on general circulation in East Asia in summer are summarized,respectively The possible effective mechanism of the snow cover over the Plateau in winter and spring is proposed.