Current Issue

• Numerical Simulation of Boundary Layer Structure in Desert-Oasis
• Lü Shi-hua;LUO Si-qiong
• 2005 Vol. 24 (4): 465-470. 
• Abstract ( ) PDF (286KB) ( )
• Using the NCAR nonhydrostatic mesoscale model MM5V3.6 and triple-nested simulation method, the circulation and boundary layer characteristic over desert and oasis were simulated. The results showed that the oasis-desert circulation and atmospheric boundary layer structure are symmetric without the influence of the background westerly air flow. The desert-oasis changes the circulation structure, temperature and humidity fields of original desert area. The vertical motion is downwards over oasis and upwards over desert, then the air is dry and cold over oasis; but warm and moist over desert. There is the wet air colume around oasis, which plays a key role in protecting the oasis. The oasis-desert circulation and atmospheric boundary layer structure are asymmetric due to the influence of the background westerly air flow. Because of the background westerly air flow, they can break the circulation structure of oasis system symmetry, which is unfavourable for the steady development of oasis system.

• Sensitivity Test of Oasis Boundary Layer Characteristic under Different Soil Moisture
• LUO Si-qiong;CHEN Shi-qiang;Lü Shi-hua
• 2005 Vol. 24 (4): 471-477. 
• Abstract ( ) PDF (1027KB) ( )
• The characteristics of boundary layer in Jinta oasis were simulated under the different soil moisture using the NCAR non-hydrostatic mesoscale model MM5V3.6. The results show that the rising rates of both the ground surface temperature and the surface air temperature are less than those of no irrigation. The higher the soil moisture is, the lower the oasis temperature is. The so-called "cold island effect" in oasis is more significant. Once irrigated, the surface sensible heat fluxes decrease, and the latent heat flux is higher. The characters of oasis would be seen when the soil moisture is 0.35. With the increasing of soil moisture, the height of oasis boundary layer will decrease. The oasis's energy and moisture will been kept in the lower part boundary layer, it will promote the oasis's maintenance and development.

• Numerical Simulation and Structure Analyses of the Local Circulation in Jinta Oasis Summer
• WEN Li-juan;Lü Shi-hua;ZHANG Yu;LI Suo-suo
• 2005 Vol. 24 (4): 478-486. 
• Abstract ( ) PDF (495KB) ( )
• The characteristics of Jinta Oasis on 5 July, 2004 was successfully simulated using the mesoscale model MM5 on the basis of replacing the landuse in the domain 3. The simulated results showed that in the day time, the oasis was a cold source, it maintains till 3000 m above the ground and the temperature-difference between the oasis and desert was the highest near the ground and the intensity of cold center weakened from low level to high level; the departure of the pressure field was positive on lower levels and negative on higher levels on the oasis, and the transition of them happened near 1300 m heights, and vice versa in desert; on lower levels the wind blew from the oasis, and the divergence weakened with the height. Above 750 hPa, the background wind dominated and there were some convergent; the anomaly wind field are divergent on lower levels and convergent on higher levels. The wind velocity was the smallest near the divergent/convergent center on the oasis and increased far from it. There was updraft on deserts and downdraft dominated the whole oasis. There were more than one downdraft center, and the height of it was not the same, which was the lowest on the center of oasis and higher on both sides of oasis. The strongest downdraft appeared on the edge of the oasis; Divergence distributed uniformly over lower levels of oasis and scattered convergence distributed on desert, 750 hPa convergence region began to appear over the oasis. On 700 hPa it dominated over the oasis, and convergence was the strongest on the edge of the oasis and desert. While over desert, there were almost the divergent and a little of convergent. Specific humidity and moist potential temperature have similar characteristics. Up a certain height and above it, their contours formed low trough and the centers of trough moved from high to low and from west to east under the influence of the downdraft and the background of west wind.

• Simulation of the Impact of Improvement of Land Surface Process Parameterization in Arid Region on Regional Climate in East Asia
• BAO Yan;ZHANG Yu;Lü Shi-hua;ZUO Hong-chao
• 2005 Vol. 24 (4): 487-496. 
• Abstract ( ) PDF (2035KB) ( )
• To further test the simulation performance of the new LSM bare soil parameterization scheme, we do some comparisons of numerical simulations among CCM3 and CCM3 with the validated land surface process parameters (LCCM3 for short)and observations from NCEP/NCAR and Xie global Precipitation data. Compared to the original CCM3, LCCM3 well represent the major feature of some large-scale system except subtropical high over Pacific Ocean, and have better performance in simulating system of Monsoon in East Asia, as well as surface air temperature. At the same time, LCCM3 partly modify the simulations the deviation of precipitation on the east side of Plateau in summer, and improve the simulation of winter snow over Plateau, sea level pressure of Northern Hemisphere in winter, which show it is a very important method to validate parameterizations of land Surface process and improve the land surface process scheme using observations to improve simulations of regional and global climate.

• Effect of Different Horizontal Resolutions on Simulation of Precipitation in Qilian Mountain
• LI Suo-suo;Lü Shi-hua;GAO Yan-hong;ZHANG Yu
• 2005 Vol. 24 (4): 497-502. 
• Abstract ( ) PDF (1224KB) ( )
• Using the mesoscale atmospheric model MM5V3.6, the precipitation in Qilian Mountain on July 14~17, 2002 is simulated by using different horizontal resolution. Then the simulated results are compared with observed precipitation. The results show that the precipitation center can be simulated well by using high horizontal resolution, but there are unreal precipitation centers, and its value is larger than that of the observation; the value of precipitation center can be simulated well by using low horizontal resolution, but the simulated precipitation center is not more than high horizontal resolution.

• Analyses of Cold-Wet Tongue and Boundary Layer Characteristic Inside and Outside of Jinta Oasis
• AO Yin-huan;Lü Shi-hua;CHEN Shi-qiang;ZHANG Yu
• 2005 Vol. 24 (4): 503-508. 
• Abstract ( ) PDF (1020KB) ( )
• Using the tethered balloon gradient data in Jinta during the intensive period of observation of oasis system energy and water cycle and numerical study in July 2004, the cold-wet tongue phenomena and boundary layer character on the edge of the Oasis are analyzed. The results demonstrated that there are cold-wet tongue phenomena inside and outside the edge of the Oasis. Cold-wet tongue was appeared from 09:00 to 18:00, its height is about from 0 to 600 m. Cold-wet tongue is not only affected by wind speed and direction and the intensity of sun heating up the surface, but also affected by the divergence wind over the Oasis in the afternoon. The finding is very important to study energy and hydro logic cycle, especially to exchanges of moisture and heat in Gobi and Oasis regions. This work provide a good basis for further study development and maintain of Jinta Oasis.

• Retrieval of Ground Surface Parameter over Jinta Oasis Using the Satellite Data
• MENG Xian-hong;L Shi-hua;CHEN Shi-qiang;ZHANG Yu
• 2005 Vol. 24 (4): 509-516. 
• Abstract ( ) PDF (1523KB) ( )
• TM image is the image obtained from Thematic Mapper(TM) scanner carried by Landsat. In this study, Landsat-5 TM data has been used to calculate the following land surface parameters in Jinta oasis:Normalized difference vegetation index(NDVI), modified soil adjusted vegetation index(MSAVI), fractional vegetation cover, surface albedo and surface temperature. Then we compared the retrievals of land surface reflectance and temperature with the observed. The results show the relative error of the surface temperature in Jinta area is less than 10%, and the relative error of the surface reflectance is less than 8%.

• Analysis on Microclimate Characteristic of Typical Clear Day in Ejina Oasis in Late Summer
• ZHANG Yan-wu;FENG Qi;Lü Shi-hua;HUANG Jing;SI Jian-hua;SU Yong-hong
• 2005 Vol. 24 (4): 517-521. 
• Abstract ( ) PDF (264KB) ( )
• The geographical characteristic of the oasis system has formed the special microclimate characteristic in oasis. Utilizing the observation data of Ejina oasis on 8~10 September 2003, the microclimate characteristic of oasis Tamar is Spp has been analyzed. In the Tamar is Spp, the ground surface temperature and surface layer temperatures have obvious daily change. At daytime, ground surface heats up the atmosphere and the atmospheric temperatures decreases with height in superadiabatic state; at night, the atmosphere heats up the ground surface, and the atmosphere is steady stratification layer. The daily change of air humidity in surface layer is contrary to that of temperature. The vertical distribution of air temperature in Tamar is Spp depends on mainly the absorbing solar radiation of ground surface and canopy layer. In canopy, it is mainly updraft at day time and downdraf at night. The desert circulation effect is not obvious. The atmospheric turbidity in oasis is small;the solar radiation is decreased less. So the oasis has good light resource background.

• Comparative Analyses on Ground Wind Field and Air Temperature-Humidity Characteristics Inside and Outside Jinta Oasis
• HU Ze-yong;Lü Shi-hua;GAO Hong-chun;ZHOU Xiu-yun
• 2005 Vol. 24 (4): 522-526. 
• Abstract ( ) PDF (223KB) ( )
• The ground wind field and air temperature-humidity characteristics in Jinta Oasis were analyzed by using the observational data derived from the Jinta Oasis Experiment (JTOEX) which was implemented from June to August of 2004 in Jinta County. The results show that the ground air temperature, specific humidity and wind speed are different obviously inside and outside the Oasis. The air is the cold, wet and quiet wind inside the Oasis, but the hot, dry and a little larger wind outside the Oasis. The air temperature and humidity field in the Oasis is an asymmetrical structure. The cold and wet centre is a little bit far east from the geometric centre of Oasis. But the wind speed field is a symmetrical structure contrastively. The weak wind centre keeps the same as geometry centre of the Oasis.The air specific humidity is different under the different wind directions.The geographic location of Oasis and wet or dry advection from environment may cause it.

• Characteristics of Energy Budget and Microclimate on the Edge of Oasis Summer
• ZHANG Yu;Lü Shi-hua;CHEN Shi-qiang;AO Yin-huang;HU Ze-yong;WEI Zhi-gang
• 2005 Vol. 24 (4): 527-533. 
• Abstract ( ) PDF (966KB) ( )
• The characteristics of the microclimate, radiation budget and energy transferring on the edge of oasis were analyzed. The data is got from "The Oasis System Energy and Water Cycle Field Experiment", which hold in the Jinta County on June 8 to July 12, 2004. It is found that, (1) at the daytime, the air vertical movement is downward, and the microclimate characteristics is influenced by the soil moisture; (2) the maximum value of solar radiation is around 1000 W·m^-2, and the net radiation can exceed 700 W·m^-2; (3) the sensible and ground heat fluxes are in same order of magnitude, the probability of negative sensible heat flux is about 70%; (4) the Bowen rate is in the order of ±10^-1, the residual of energy budget is about 28%.

• Preliminary Analyses on Ground Level Wind Field of Second Circulation in Jinta Oasis and Desert in Summer
• CHEN Shi-qiang;Lü Shi-hua;AO Yin-huan;HU Ze-yong;WEI Zhi-gang;ZHANG Yu
• 2005 Vol. 24 (4): 534-539. 
• Abstract ( ) PDF (305KB) ( )
• The experiment for energy and moisture transferring between oasis and desert was going from June to August 2004. Two different kinds of wind systems in Jinta oasis of Gansu province were analyzed using the observed wind data. The results showed that the second circulation was incited because of different temperature between the oasis and the desert. Winds blew away from the oasis in the day and converged around the desert from at nigh. The second circulation was not obvious when the background wind was strong and controlled the parallel direction of it. The second circulation controlled the vertical direction of the background wind. The west wind became weak and east wind didn't appear when the background wind changed. During that time, the second circulation appeared in the circle of the oasis.

• Characteristics of Heating (Cooling) Rate in Atmospheric Boundary Layer in Jiuquan Oasis Summer
• GU Liang-lei;HU Ze-yong;Lü Shi-hua;WEI Zhi-gang;ZHANG Yu;YAO Ji-min
• 2005 Vol. 24 (4): 540-544. 
• Abstract ( ) PDF (238KB) ( )
• Using the data of the study of observation experiment and numerical simulation on energy and moisture cycle of oasis system item and the information of Jiuquan observation station, heating and cooling rates of PBL in Jiuquan oasis are calculated, the daily variations in SL and PBL and the characteristics during some typical days are analyzed. It is found that the heating (cooling) rate in SL and PBL has an obvious changes; but the heating rates were equivalent to the cooling rates in SL and PBL, therefore, the atmospheric energy is conservative; moreover, sunshine duration, cloud cover and some special weather systems have important influences on the rates.

• A Primary Field Experiment of Land-Atmosphere Interaction over the Loess Plateau and Its Ground Surface Energy in Clear Day
• WEI Zhi-gang;WEN Jun;L Shi-hua;CHEN Shi-qiang;AO Yin-huan;LIANG Lin
• 2005 Vol. 24 (4): 545-555. 
• Abstract ( ) PDF (1723KB) ( )
• We introduce a primary field experiment of land-atmosphere interaction over the Loess Plateau in Pingliang, Gansu from 26 August to 11 September 2004. The data from different instruments are compared and calibrated. Using the data of this experiment, the characteristics of four components of net radiation, sensible heat, latent heat and soil heat flux on ground surface are analyzed. Comparing with the bare soil surface, the vegetation (corn) reduces the surface albedo and the upward short-wave radiation from ground surface; it also reduces the upward long-wave radiation from ground surface. As a result, the net radiation from the vegetation is higher than that from the bare soil surface. The latent heat flux from the vegetation is obvious larger than that from the bare soil surface. The downward soil heat at day and the upward soil heat at night from surface soil under the corn are smaller than the ones under the bare ground. Comparing with the one from the corn field over mesa, the downward short-wave radiation is little smaller and the upward short-wave radiation is obvious smaller from the flat ground cornfield. The upward long-wave radiation from the corn field over mesa is almost same as the one from the flat ground corn field beneath mesa. The net radiation is a little smaller at noon from the bottom flat ground corn field beneath mesa than the corn field over mesa. The soil heat flux is smaller in the morning and larger in the afternoon and same at night from the flat ground corn field beneath it than the corn field over mesa. There are not obvious differences of the sensible and latent heat fluxes between the flat ground beneath mesa and the corn field over mesa in daytime. There are obvious negative sensible heat fluxes in very early morning from the flat ground corn field beneath mesa.

• Analyses on Characters of Surface Radiation and Energy at Oasis-Desert Transition Zone in Dunhuang
• WANG Sheng;ZHANG Qiang;WEI Guo-an
• 2005 Vol. 24 (4): 556-562. 
• Abstract ( ) PDF (1150KB) ( )
• Using the data of land-atmosphere interaction over arid region in Intensive Observation Experiment Period in Dunhuang, Gansu Province in 2002, the characters of surface radiation and energy at the oasis-desert transition zone analyzed. The results show that the surface temperature and ground layer temperature at the oasis-desert transition zone are close to that of at Gobi at daytime. But nighttime of most of clear days, the oasis-desert transition zone is a cold source relative to the Gobi. The values of global radiation, upward shortwave radiation and upward long wave radiation at the oasis-desert transition zone are close to the values of the Gobi and the daily integral values are 24.48, 6.1, 41.42 MJ·m^-2·d, respectively. The daily integral values of sensible heat flux, latent heat flux and ground surface heat flux are 6.58, 1.60 and 0.38 MJ·m^-2·d, respectively. The quite large horizontal sensible heat flux may means the unbalance energy is quite large at the oasis-desert transition zone.

• Comparison of Atmospheric Data Scaling Transfer Scheme in Heihe River Basin
• GAO Yan-hong;CHENG Guo-dong;LI Xin;Lü Shi-hua
• 2005 Vol. 24 (4): 563-569. 
• Abstract ( ) PDF (996KB) ( )
• Scaling transfer is one of the available approaches in solving scale issues. In a large extended area, the reliability and validity of a statistic scaling model depend on dealing with of the observed data, especially in the area with inhomogeneous highland. Here, downscaling of the meteorological data in Heihe River Basin was studied, where the topography and underlying are extremely complex and heterogeneous. Results of interpolating from the global climate model output and statistical downscaling model, including objective analysis, were compared. The following conclusions were obtained: The finer grid atmospheric data by interpolating from coarse resolution global climate model output could get the local temperature and humidity characteristics of the plat area, while it could not be used in the high mountain area. Wind near surface did not match with the observation also. The 1 km resolution atmospheric grid data by statistical downscaling model through the objective analysis could well present the atmosphere elements condition in Heihe River Basin. It is proved that the objective analysis plays an important role in the scaling transfer process.

• Climatic Effects of 100 hPa Easterly Air Flow in Tropical (Ⅱ): Its Relationship with Summer Rainfall in North China
• XU Zhong-feng;QIAN Yong-fu
• 2005 Vol. 24 (4): 570-576. 
• Abstract ( ) PDF (934KB) ( )
• Based on the NCEP/NCAR reanalysis datasets from 1954 to 1998 and the monthly rainfall data of 160 stations in China at the same time, the relation between the intensity of the tropical easterly on 100 hPa and summer rainfall in North China has been studied. The results are as follows:(1) The easterly intensity has a sustainable positive relationship with summer rainfall over North China from spring to summer.(2) In the weak easterly year, the anomaly of the surface temperature of the Indian Ocean is symmetric to equator which the maximum anomaly locates in. Namely, the anomaly of the surface temperature at equatorial Indian Ocean is stronger than that at the North Indian Ocean and the India subcontinent. This kind of distribution of surface temperature weakens the easterly on 100 hPa, on the other hand, it also decreases the sea-land heating contrast which makes the south Asia summer monsoon weaken. Furthermore, water vapor transportation from the South Asia monsoon area to the North China decreases. As a result, the rainfall is less than ever over North China in weak easterly year.

• Characteristics of Bulk Transfer Coefficient in Precipitation Processes of Tibetan Plateau
• LI Guo-ping;TAO Hong-zhuan
• 2005 Vol. 24 (4): 577-584. 
• Abstract ( ) PDF (1615KB) ( )
• On the basis of original data from four stations of AWS installed in Tibet in the observational periods of six years(from July 1995 to June1999), according to PRC-Japan Asian Monsoon Cooperative Research Program,some typical processes of rainfall in the Eastern Tibetan Plateau in rainy season are chosen, the bulk transfer coefficients every 20 minutes in those processes are estimated by using the profile-flux method, and relationships in those rainfall processes between the bulk transfer coefficients and atmospheric stability in the surface layer, surface roughness length and rainfall amount are analyzed. The results show that the relations between bulk transfer coefficient and the atmospheric stability in the ground layer, surface roughness length are definite and close. The responses of bulk transfer coefficients to the processes of plateau rainfall are remarkable, but the correlations to peak and period of rainfall processes are not identical in each station.

• On the Forecasts and Result Tests of Natural Disasters in the Second Half-Year of 2003
• TANG Mao-cang;LIU Xiao-feng;LI Dong-liang;MEI Xiu-ping
• 2005 Vol. 24 (4): 585-589. 
• Abstract ( ) PDF (315KB) ( )
• There are 4 geothermal vortex arrays which induce natural disaster(drought/flood/earth-quake) activity in China. In this paper we firstly introduced characteristics of the 4 geothermal vortex arrays in the first half-year of 2003, then forecast the natural disaster which would happen in China in the second half-year of 2003 based on the evolvement of the geothermal vortex. The results showed that the forecasts of flood and drought were better, but the earthquake prediction was not so good. Finally, we made some suggestion to the earthquake prediction.

• Characteristic Zonal Wavenumber of Winter Circulation in Northern Hemisphere and Its Temporal and Spatial Evolutions
• YOU Wei-hong;ZHAO Ning-kun;Zhou Li-hua
• 2005 Vol. 24 (4): 590-597. 
• Abstract ( ) PDF (960KB) ( )
• Using the zonal spatial wavelet transform method for three-dimensional data, the characteristic zonal wavenumber of winter circulation in Northern Hemisphere and its temporal and spatial evolutions corresponding to the characteristic zonal wavenumber are investigated. The results show that there are three characteristic zonal wavenumbers of 500 hPa potential height in Northern Hemisphere winter, they are wave number 3, 2 and 1 respectively. For 500 hPa circulation in Northern Hemisphere winter, the main 3-wave activity are in the middle latitude regions, the main 2-wave activity are in the high latitude regions and the main 1-wave activity is in the low latitude regions. The orientations of the trough and ridge lines of the 3-wave circulations in the middle latitude regions are from northeast to southwest, the orientations of the trough and ridge lines of the 2-wave circulations in the high latitude regions are from northwest to southeast, and the orientations of the trough and ridge lines of the 1-wave circulation in the low latitude regions is from northeast to southwest. Corresponding to the characteristic zonal wavenumbers, the eastward migration features of winter circulation in Northern Hemisphere are very significant from 1949 to 1999. It has been estimated that the distance of the migration is about 5 longitudes in the past 50 years.

• Numerical Simulation of the Effect of Liquid Water Content and Ice Crystal Concentration on Lightning Flash Frequency
• XIE Yi-ran;QIE Xiu-shu;GUO Feng-xia;Marcia Baker
• 2005 Vol. 24 (4): 598-603. 
• Abstract ( ) PDF (269KB) ( )
• Assuming that collision between ice crystals and rimed graupel particles is the dominant mechanism for charge separation in thunderstorms, a numerical simulation has been used to study the effect of two ice glaciation mechanisms of crystal (Fletcher and Hallett-Mossop glaciation mechanism)and liquid water content on flash rate. The results show that there is a big disparity on ice crystal number concentration distribution with increasing of the pressure and the temperature in two glaciation mechanisms, this directly result in a difference of electrical activity of thundercloud. With liquid water content increasing, the time of the first lightning flash will be delayed, the location of breakdown process will be descended, and the lightning flash rate will be decreased.

• Aircraft Measurements of Sand Aerosol over Northwest China Desert Area in Late Spring
• NIU Sheng-jie;SUN Zhao-bo
• 2005 Vol. 24 (4): 604-609. 
• Abstract ( ) PDF (1526KB) ( )
• The sand aerosol number concentration is 1.0~10·cm^-3)generally, mean diameter is 1.6~4.6 μm, the maximum is 13.0~28.0 μm; TSP is 0.01~0.08 mg·m^-3; the ratios of PM_2.5 and PM₁₀ to TSP are 3.6%~13.8% and 50.3%~88.1%respectively in the upper air of desert. Sand aerosol number concentration is closely related to the surface conditions, it shows aerosol number concentration is higher over desert than that of land with growing vegetables. The size distribution of aerosol varies with height.

• Factors Affecting on Dust Emission by Wind Erosion and Their Variational Characteristics
• SHEN Yan-bo;SHEN Zhi-bao;DU Ming-yuan;WANG Wan-fu
• 2005 Vol. 24 (4): 611-616. 
• Abstract ( ) PDF (1180KB) ( )
• With the examples of Gobi and oasis in Dunhuang, the critical friction velocity of dust emission by wind erosion and the particle size distribution of surface soil during the wind erosion were analyzed in this paper. The results indicate that the u* t increased with soil moisture and vegetation cover, and the variation of u* t with diameter of particle is decreased firstly and is then increased, and there is a minimal u* t at some diameter, moreover, the land management practice also plays an important role. The particle size distribution of surface soil changes with time during the wind erosion. The instant particle size distribution is different from the average particle size distribution, and the vertical dust flux confirmed by the former is more sensitive with the variation of u* t, while the vertical dust flux confirmed u* t by the latter is bigger.

• Lanzhou Aerosol Optical Depth in Winter and Their Relation with Visibility
• ZHAO Xiu-juan;CHEN Chang-he;Yuan Tie;Zhang Wu;DONG Xiu-juan
• 2005 Vol. 24 (4): 617-620. 
• Abstract ( ) PDF (1569KB) ( )
• Utilizing the data monitored by sun photometer, the aerosol optical depth of Lanzhou in winter was calculated, and the turbidity coefficient β and the wavelength exponent α were further calculated using aerosol optical depth. The results show that the aerosol optical depth and turbidity coefficient are larger than the same historical period, and the most of aerosols are large particles. The aerosol optical depth and visibility were analyzed and fitted in the paper, both the change trend is just opposite, and the relation between them appears the trend of exponent decrease.

• Analyses on Variation Trends of Atmospheric Visibility and Its Effect Factor in Muilt-Cities in Central Liaoning
• MA Yan-jun;ZUO Hong-chao;ZHANG Yun-hai;HUI Xiao-ying
• 2005 Vol. 24 (4): 621-628. 
• Abstract ( ) PDF (1035KB) ( )
• Through analyzing the atmospheric visibility, meteorological factors influencing visibility, change features of pollutant, as well as the relation between the visibility and meteorological factors and pollutant concentration, the obtained results are as follows: (1) The visibilities in 5 cities have obvious the monthly, seasonal and yearly variation features. The monthly variation of visibility appears bi-peak patterns, the first peak value is in May, and second is in September or October. The value of visibility in winter is the lowest, and the hightest in spring or summer in a year. The visibility in Benxi became better in the past years, one in shenyang became better too from 1987 to 1997, but it is bad after 1997, one in other cities beccame worse in the same period. (2) The features of interannual change of meteorological factor influencing visibility in 5 cities are basically consistent with eath other, the yearly mean values of TSP, SO₂ in 5 cities all have the decreasing trend, the interannual change of NO_X is not obvious. (3) The correlation between visibility and humidity and fog is negative, and their correlation is very significant, the correlation between visibility and rainfall, wind and temperature is very complex, the correlation between visibility and the pollutant is negative.

• Relationship between Vegetation Variation and Precipitation in Northeast Gansu Region
• YANG Lan-fang;LI Zong-yi
• 2005 Vol. 24 (4): 629-634. 
• Abstract ( ) PDF (317KB) ( )
• Using the NOAA satellite data of AVHRR, the spatial distribution and annual changes of surface vegetation index in Northeast Gansu region from 1997 to 2001 was studied and the relationship between precipitation and vegetation index and the impact of precipitation on vegetation index in this region were analyzed as well. The results showed that the averaged vegetation has decreasing trend in the recent 5 years, but it has some increasing one in the north of this region. The precipitation played an important role in the monthly changes of surface vegetation and especially in the agricultural area. The vegetation in forest area, in which has the highest vegetation index, the impact of annual change of precipitation on surface vegetation was slight. The lowest vegetation index occurred in January~June 2000 and 2001, especially in 2001.

• Analyses on Regional Characters of Rainfall Change in Shaanxi Province
• BAI Ai-juan;SHI Neng;FANG Jian-gang
• 2005 Vol. 24 (4): 635-641. 
• Abstract ( ) PDF (507KB) ( )
• Based on the rainfall data of Shaanxi Province from 1950 to 2000, Using the method of REOF, winter, summer, and yearly precipitation fields can be divided into three subareas, they are the North Shaanxi, Guanzhong and west of South Shaanxi, the South Shaanxi. On the basis of this, the regional feature, the interdecadal change and the long-term trends of precipitation in Shaanxi are analysed. The results show that the rainfall in the past 50 years is scarce in the north, while plenty in the south. The decreasing trend of precipitation in North Shaanxi is more than Guanzhong and west of South Shaanxi, but the rainfall of South Shaanxi in summer and winter have increased slightly.

• Analyses on Cause of Sand Storm Weather Formation in Hebei Provice
• YOU Feng-chun;SHI Yin-shan;FU Gui-qin;AN Yue-gai
• 2005 Vol. 24 (4): 642-647. 
• Abstract ( ) PDF (773KB) ( )
• First, the evolution characteristic of sand storm occurring in Hebei Provice is analyzed, then the cause of formation of the sand storm is analyzed from the climate, the change of circulation situation and dynamic diagnosed and so on. The result are as follows: in recent years, the precipitation in springtime was continually less than the normal, and the air temperature in springtime was continually higher than the normal in this region, which provided the favourable conditions for sand storm occurring; the stronger cold air flow frequently move to the south is the main reason that the sandstorm is more than the normal.