Plateau Meteorology

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28 August 2007, Volume 26 Issue 4   
  • Characteristics of Surface Radiation and Energy Budget over Afforestation Area and Bare Soil over the Gaolan Mountain of Lanzhou City in Winter
  • AO Yin-huan;CHEN Yu-chun;YANG Sheng-peng
  • 2007 Vol. 26 (4): 693-700. 
  • Abstract ( ) PDF (993KB) ( )
  • Using the land-atmosphere interaction data observed at the Gaolan mountain of Lanzhou city from 9 to 29 December 2005,the daily variation characteristics of surface radiation,energy budget,soil temperature and moisture were compared and analyzed over afforestation area and bare soil at typical clear day and average condition in winter.The global radiation and downward atmospheric radiation in afforestation area are similar to that in bare soil,while the reflected solar radiation and ground surface long wave up-ward radiation are quite different between these two kinds of ground surface because of the difference of surface characteristics.In winter,the sensible heat flux played a leading role,and soil heat flux and latent heat flux were very small,especially the latent heat flux,which peak value was often under 10 W·m-2.It was very interesting to note that the sensible heat flux was higher over the afforestation area than the ones at the bare soil during observation,which deserved further study.In winter the characteristics of the averaged daily variation was very close to the ones under a typical clear day,from which we concluded that the influence of cloud and snow was very limited.The daily mean albedo in both of the afforestation area and bare soil are relative stability,it varies between 0.20~0.28 in afforestation area and 0.25~0.31 in bare soil,averaged of 0.21 and 0.29,respectively.
  • Analysis on Climate Characteristics in Naqu in Recent 40 Years
  • MAO Fei;LU Zhi-guang;ZHANG Jia-hua;ZHENG Ling-yun
  • 2007 Vol. 26 (4): 708-715. 
  • Abstract ( ) PDF (581KB) ( )
  • Using the daily meteorological data of 6 stations in Naqu from 1961 to 2000,the potential evapotranspiration was estimated with the UNFAO Penman-Monteith model;the distribution and the annual and interannual variations of temperature,precipitation,potential evapotranspiration in recent 40 years were analyzed based on the general statistic methods and Mexican Hat wavelet.The main results show that the mean temperature in spring,summer,autumn,winter,growing season(from May to September) and a year all increased in recent 40 years.The precipitation in summer increased and that in other 5 periods all decreased.The potential evapotranspiration in autumn,and winter decreased and that in other 4 periods all increased in recent 40 years.The potential evapotranspiration in 6 periods all decreased in recent 30 years.The climate change in Naqu is not obvious,but it generally changed towards warm and wet from 1961 to 2000,which would maintain change towards warm and wet after 2000.The climate changes are favoured for agriculture and grazing and improving entironment.
  • Basic Climate Characteristic and Evolution of Drought and Flood in the Hetao and Its Vicinity Area for Recent 530 Years
  • LI Qian;LI Dong-liang
  • 2007 Vol. 26 (4): 716-723. 
  • Abstract ( ) PDF (1004KB) ( )
  • Based on the drought and flood grades of 21 meteorology stations in the Hetao and its vicinity area from 1470 to 2005,recent 536-year drought and flood evolution characteristics and tendencies were analyzed.Results show that average drought and flood grades to be bigger than 3,the whole is dry,west for the stable drought and eastern alternates with for the drought and flood in the Hetao and its vicinity area in recent 530 years.The drought and flood of this area may be divided 4 typical kinds of structures in the spatial anomaly: The entire area consistent is drought(flood);Southeast drought(flood)-northwest flood(drought);Southwest drought(flood)-northeast flood(drought) and middle drought(flood) and east-west flood(drought) are reverse.The average drought and flood grades of 19 ages anomalous spatial structures in 53 ages and the above 4 kinds of types are similar from in 1570's.The linear trend analysis indicated that,this area has not displayed the obvious drought tendency in recent 536-year time scales,but arid degree obviously aggravates in 50 years,like drought and flood grades Yinchuan,Xi'an in half century raise the nearly 1 grade.The drought and flood grades overall have significant periods of quasi 23 years,quasi 26 years,quasi 73 years and quasi 100 years.
  • The Impacts of Climate Change on the Natural Pasture Grass in Qinghai Province
  • ZHANG Tai-ren;YAN Liang-dong;ZHANG Feng;LI Chao-sheng;DONG Zhang-hang;CHAI Xiu-mei;LI Zi-zhen
  • 2007 Vol. 26 (4): 724-731. 
  • Abstract ( ) PDF (796KB) ( )
  • The impacts of climate change on the growth,height and output of the natural pasture grass is discussed,and an analysis has been made in it on the changes of the pasture grass in terms of its height and output in relation to the meteorological conditions,based on both natural grass data from 5 typical livestock-oriented meteorological stations in the Qinghai Province and the climate data from 1971 to 2002.It is concluded that,on the one hand,the climate warming has a greater positive effects on the growth of the pasture grass than its negative impacts,thus giving rise to a higher output and greater grazing capacity in the moist pasturelands across the province.On the other hand,climate warming tend to accelerate evaporation in the arid and semi-arid pasturelands,which in return hinders the growth of the grass,hence decreasing its output.Meanwhile,the proportion of high-quality grass declines while the inferior weeds seemingly gain ground.Furthermore,the total coverage of the natural pasturage is shrinking and areas dominated by desert plants are expanding,consequently the productivity of the natural pasturelands declines significantly with the pasturelands evolving toward negative degradation.The findings of this paper are intended to provide a scientific basis for making a long-term plan of livestock production in the Qinghai Province and in the country as a whole,as well as for the policy-making in implementing the China's Grand West Development Strategy.
  • Distribution and Variation Trend of Cloud over Northwestern China
  • CHEN Yong-hang;CHEN Yan;HUANG Jian-ping;ZHENG Zhi-hai;SU Jing;HUANG He
  • 2007 Vol. 26 (4): 741-748. 
  • Abstract ( ) PDF (1046KB) ( )
  • Using the monthly mean data of ISCCP D2 and NCEP/NCAR from July 1983 to September 2001,the distribution of 15 different cloud types in three climatic subregions in Northwestern China were analyzed.Also the trend of cloud amount and their possible formation process were discussed.The results show that the optical thickness and water path of liquid stratus,ice stratus,liquid nimbostratus,ice nimbostratus and deep convective clouds are the highest.Liquid stratus mainly occurs over Tianshan Mountains,Northern Xinjiang and Southern Shanxi and ice stratus mostly occurs over Northern Xinjiang.Liquid nimbostratus,ice nimbostratus and deep convective cloud,and also liquid altostratus,ice altostratus and cirrostratus,with values of optical thickness and water path at the second highest level,have a similar distribution.Their high value areas are over Tianshan Mountains,Kunlun Mountains,Qilian Mountains,Southern Shanxi and Southern Gansu.Therefore,those regions have advantage for artificially enhanced precipitation.During the nearly 20 year periods,the trend of the high-level cloud amount significantly decreased while low-middle-level cloud amounts increased in all of the three climatic regions.Such a process probably exists between the cloud and earth-atmospheric system in northwestern China that the increase of surface temperature enhances evaporation,thus causing the increase of the low-middle-level cloud amounts and leading to precipitation to increase and the high-level cloud amount to decrease.
  • The Lightning Characteristics of Thunderstorm over Tibetan Plateau and Its Origin Discussion
  • ZHANG Ting-long;QIE Xiu-shu;YAN Mu-hong
  • 2007 Vol. 26 (4): 774-782. 
  • Abstract ( ) PDF (672KB) ( )
  • Ground-based observation of thunderstorm and lightning flash was carried out over central Tibetan Plateau in the summer of 2003 and 2004.30 cases of thunderstorm were analyzed in this article.The results showed that the thunderstorm over Tibetan Plateau has a triple charge structure.Among them 73% have a large-than-usual lower positive charge center(LPCC),and 27% have a normal triple charge structure,i.e.,the LPCC is weaker than the former.The flash frequency of thunderstorm over Tibetan Plateau is tens times smaller than other lower altitude regions with similar latitude,and the average value is usually about 1 fl·min-1.Due to the different characteristics of lightning flash,the thunderstorm with a large-than-usual LPCC can be classified into three types and defined them IC-dominated type,-CG-dominated type,+CG-dominated type,respectively.Finally,after investigating of meteorological parameters of the three type thunderstorms,we found that there is a high difference between surface and air temperature and a low relative humidity just before IC-dominated type thunderstorms,while the difference between surface and air temperature is small for the +CG-dominated type thunderstorm because they occurred in the evenfall time.
  • Study on the Growth Mechanism and Microstructure of a Heavy Hail in the Eastern Part of Qinghai Province
  • ZHANG Guo-qing;SUN An-ping
  • 2007 Vol. 26 (4): 783-790. 
  • Abstract ( ) PDF (1298KB) ( )
  • Using the Doppler radar data to analyse a heavy hail process which appeared in Datong and Huzhu in the northeastern part of Qinghai Province on August 8,2004,and the observed hail spectrum and collected hailstone,the isotope,bubble structure and ice crystal are analyzed.The results show that the hail spectrum have two peaks and the hailstone appear conical(a few of them show ellipsoidal).In the hailstone,the main part of hail embryo is the graupel.The hailstone can be divided into four layers according to its growth mode and the two middle ice crystal layers which are the hail main growth areas are the longest and its thickness are relatively bigger and the growth altitudes of two middle ice crystal layers are lower,temperature are higher and the thickness are bigger.The main texture distribution of conical hail bubble is radial and similar ellipsoidal hail is longitudinal.The distribution of bubble concentration shows single peak in hail and the spectrum width of bubble is less than 100 μm.The bubble concentration of clear or unclear layers in hail is different with small fluctuation.The observation result for each layer isotope shows that the growth temperature of hail lies at 10~-30℃ and the growth height lies at 4.0~9.0 km.According to up and down mode the hail grow up in the humid atmosphere.It is consistent with the analytic result of ice crystal.
  • Application of Some Simulated Energy Index to Thunderstorm Forecast at Zhongchuan Airport
  • LIU Wei;GAO Yan-hong
  • 2007 Vol. 26 (4): 791-797. 
  • Abstract ( ) PDF (1044KB) ( )
  • The sounding observation net in China is not sufficient for mesoscale convection system activity study.Nemerical simulation results could provide the souding data at some extent for the places where there are no souding observations and the times when it not the souding time.Here,nonhydrostatic mecoscale MM5 model products were used to model the thunderstorms activities at Lanzhou Zhongchuan airport during 10~11 and 24~25 June 2005.The simulated results show that the Convective Available Potential Energy(CAPE) and Convective Inhibition(CIN) is more indicative than other indexes.It will be possible for dry thunderstorm occurring when CAPE is larger than 20 J·kg-1.Precipitation take place in thunderstorm when CAPE is larger than 100 J·kg-1.Due to the bias of air temperature and humidity at lower atmosphere,the calculation of CAPE and CIN is amended.The simulated air temperature and humidity in the lower atmosphere are replaced by the observations at Zhongchuan airport and the simulated souding data is used.It is found that CAPE after amending could predict the timing of thunderstorm happening and could describe the energy accumulation and releasing process than the simulation results.It is pointed out that the simulation result is not so good as within it when the integrat time longer than 36 hours for thunderstorm prediction.
  • The Improvement of Artificial Ice Crystal Parameterization of IAP Three Dimensional Convective Storm Model and Its Application to Case Study
  • CUI Ya-qin;XIAO Hui;WANG Zhen-hui;ZHOU Li-na
  • 2007 Vol. 26 (4): 798-811. 
  • Abstract ( ) PDF (2066KB) ( )
  • On the base of IAP-CSM3D(Three-Dimensional Convective Storm Model) which was set up by the Institute of Atmospheric Physics(IAP),Chinese Academy of Sciences,its parameterization of artificial seeding was improved.The parameterization equations of microphysical processes that contact with artificial ice crystals were deduced.In the ameliorated model,the artificial ice crystals induced by cloud seeding were treated as a separate predictand.Natural ice crystals and artificial ice crystals were discretely considered in the ameliorated model comparing with its former.The size distribution of artificial ice crystals was considered as a double-moment parameterization to more accord with fact.Then a hailstorm event occurred in Chifeng City in North China on 8 July 2005 was simulated by the ameliorated model to analyze the influence of artificial ice crystals on hailfall and the microphysical processes of artificial ice crystals.The results show that the model simulation is very consistent with observation,indicating the improved IAP-CSM3D model has more credible ability in seeding simulation than its former.The results of the simulation of natural cloud show that frozen drop is the main hail embryo in the simulated hailstorm.The simulations also indicate that seeding AgI in the hailstorm may markedly decrease the hailfall amount,especially in the earlier stage of hailstone formation in the seeding cloud,seeding cloud may have the best effect of reducing hail shooting,which can obtain a maximal effectiveness of reducing hail shooting,under a condition that the seeding can keep a minimal reduction in its rainfall amount.The primary cause of reducing hailfall is that seeding can remarkably abate the transformation amount of frozen drops into hail embryos in the hailstorm.There are different contributions of artificial ice crystals to ice-phase precipitation particles at different stages of cloud development.Simulations illustrate that the artificial ice crystals have little contribution to snow but more to frozen drop and graupel.The simulated result also shows characteristics that artificial ice crystals have a narrower size distribution with a smaller average size and a larger concentration.
  • Statistic and Case Studies on Radar Three Body Scattering of Severe Hailstorm
  • LIAO Yu-fang;YU Xiao-ding;WU Lin-lin;HE Cai-fen;YIN Zhong-hai
  • 2007 Vol. 26 (4): 812-820. 
  • Abstract ( ) PDF (1041KB) ( )
  • 23 hailstorms that produced three body scattering spike(TBSS) during 11 severe convection events in China were selected to establish 499 TBSS samples,and a statistical study on characteristics of the TBSS based on these samples was conducted.A case study on an outstanding TBSS case was also completed.The result show:(1) for the minimum display threshold of 5 dBz,the minimum reflectivity to produce TBSS is around 60 dBz,86% TBSS cases occur under the condition that the maximum reflectivity is larger than 63 dBz;(2) The length of TBSS has closed correlation with intensity of reflectivity core and the volume of the reflectivity core,the stronger reflectivity core,the larger volume of the reflectivity core,the longer TBSS;(3) the highest and lowest mirror point height of TBSS are 12.5 km and 1.1 km,respectively,with 61% TBSS mirror points between 3~6 km;(4) TBSS mainly occur in the west part of the radar umbrella,that is,the upstream region of the dominant storm-bearing layer average wind;(5) hailstorms can produce TBSS under different underlying surfaces;(6) nearly all TBSS last more than 30 minutes,with the majority lasting 30~60 minutes,some last more than 90 minutes;(7) when TBSS occur,nearly all storms produce hail lager than 2 cm,while 80% of large hail producing storms have TBSS,therefore,the TBSS can be used to aid severe hail warning;(8) among the 23 severe hail storms,about half are supercell storms.
  • A Study on Doppler Radar Velocity Pattern Recognition Technique and Divergence Extraction Approach
  • HU Zhi-qun;XIA Wen-mei;TANG Da-zhang;XU Fen;WANG Li-rong
  • 2007 Vol. 26 (4): 821-829. 
  • Abstract ( ) PDF (826KB) ( )
  • Large-scale wind fields always are a result of large convergence or divergence hybridized with cold or warm advection,so four sorts of mixed wind fields are abstracted:(1) warm advection combined with large scale convergence;(2) cold,with convergence;(3)warm,with divergence;(4)cold,with divergence.Different fields lead to unlike zero velocity lines characteristics,which have indicated effect to estimate divergence of large-scale wind fields.By means of the curve degree and the inter-angle between zero points in a distance ring and radar center,a quantificational arithmetic to calculate air divergence is deduced by mathematics approach at firstly,and then a method of one by one adjustment is introduced to identity zero velocity points.United with zero identified,a principle of pattern recognition and its approach are documented,whereby,air average divergences can be extracted from Doppler radar base data,the divergences of different levels are quantificationally received,and furthermore,an idea of divergence plan position indicator(div PPI) is advanced.On basis of two cases,the effect of picture identification is analyzed by contrasting div PPI with velocity PPI,divergences extracted by identification are compared with EVAD.
  • The Preliminary Application of Ensemble Prediction in Flash Flood Forecasting
  • LI Jun;LIAO Yi-shan;ZHANG Bing;SHEN Tie-yuan
  • 2007 Vol. 26 (4): 854-861. 
  • Abstract ( ) PDF (914KB) ( )
  • Four flood cases were selected to compare the effect between different model resolutions,an experiment has been implemented to study the flood prevention using ensemble forecast approach,which constructed by various physical processes of mesoscale model.The results indicate that it is not a beneficial selection under the actual operational conditions,to improve the forecast capability of heavy rain which caused mostly flash flood events only by heightening the model resolution,moreover,there are uncertainties in the results of single determinate forecasting.Thus the ensemble approach was introduced in the fields of flood prevention,compared with the single forecasting of determinate model,a series of quantitative results were offered by ensemble prediction.The different precipitation grand of ensemble average and ensemble extremum can lead to classify the measures.Additionally,the ensemble prediction can not only offer the distribution of precipitation but also offer the quantitative reliability with the result,combine the Probabilistic Quantitative Precipitation Forecasts(PQPF) with hydrological model,a probabilistic hydrological forecasting system can be built.
  • Comparison between the Monthly-Scale and Seasonal-Scale Regional Climate Simulation
  • HU Yi-jia;ZHONG Zhong;MIN Jin-zhong
  • 2007 Vol. 26 (4): 862-873. 
  • Abstract ( ) PDF (2020KB) ( )
  • The Regional Climate Model(RegCM3) has been used to conduct the monthly-scale and the seasonal-scale simulation for the abnormal climate event of China in the summer of 1998,and the comparative study has been performed between the two time-scale simulations.The results show that,different initial conditions and time scales can cause some uncertainties to the simulated precipitation amount,but precipitation scenario is independent with the simulation time scale.Instead,it lies on the ability of the model to represent the weather and climate system associated with precipitation processes in the atmosphere.Due to the effect of large scale boundary force,the simulated circulation patterns of two time scale experiments are almost the same.As the simulation time scale extends longer,the difference of simulated month-average circulation pattern,temperature and humidity between two time scale simulations is not significant,only increases a little in the inner region.However,there are no essential distinctions between monthly-scale and seasonal-scale simulations.And the bias between them will not increase unlimitedly with the time scale extends,instead,it only fluctuates in a range.The difference between two time scale simulations for the precipitation over the Huaihe river valley in July is not so obvious,whereas it becomes a little more significant for the precipitation over Northeast China in August,especially for the low level jet.
  • Analysis on Drought Variation over 10 Hydrological Regions in China during 1951-2005
  • WANG Zhi-wei;ZHAI Pan-mao;WU Yong-li
  • 2007 Vol. 26 (4): 874-880. 
  • Abstract ( ) PDF (745KB) ( )
  • Based on the monthly precipitation data of 629 stations during 1951 to 2005,drought variations over China's 10 main hydrological regions were analyzed using Z index calculations.The results revealed that evident expanding trends in drought area were detected in the Songhuajiang River,the Huaihe River,and the Haihe River basins.However,the areas of drought showed no significant increasing or decreasing trends in the region of the Yangtze River,the Zhujiang River,the Southwest Rivers,and the Southeast Rivers basins,and decreasing trend was found in Northwest Rivers basin.Interdecadal and decadal variations were distinct for all the 10 hydrological regions.Interannual variations were large for the Huaihe River,Haihe River and the Liaohe River basins,and it was small for the Southwest Rivers and the Yangtze River basins.Since 1990's,drought areas rapidly increased in the Songhuajiang River,Liaohe River,Haihe River and the Huaihe River,but began to decrease since the early 2000's.According to the analyses of linear trends and secular variations,it was predicted that drought areas would likely to decrease in early 2000's for the Haihe River,the Liaohe River,the Songhuajiang River,the Huaihe River,the Northwest Rivers and the Yellow River basins due to the increases of precipitation.In contrast,the Southeast Rivers and the Zhujiang River would likely to face increases of drought coverage because of less rainfall amounts.And there are no obvious changes in drought for the Yangtze River and the Southwest Rivers basins.
  • Analyses on Boundary Layer Structure of a Frontal Heavy Fog Process in Nanling Mountain Area
  • DENG Xue-jiao;WU Dui;TANG Hao-hua;FAN Shao-jia;HUANG Hao-hui;MAO Wei-kang;YE Yan-xiang
  • 2007 Vol. 26 (4): 881-889. 
  • Abstract ( ) PDF (1008KB) ( )
  • Using the field observational data in Nanling mountain area in the first nine-day periods of March 2001,the structural characteristics of wind,temperature and humidity and weather pattern in the periods of fog-free and heavy fog have been analysed.The analyses of sounding reveal that the surface fog is essential the saturation area extending into the surface during the cold air outbreak,and the fog form when the cloud base reach the surface ground.The dissipation process of surface fog is virtual a process of the lifting cloud base from the surface ground.The construction of boundary layer is controlled by the influencing weather systems.The construction of frontal inversion play a major role in the sustaining of cloud system or fog,the mono-layer strong inversion construction is favourable to the development of fog,while the multi-or dual-layer weak inversion constructions may lead to the dissipation of fog.The occurrence of fog closely relate to strong south wind at low-level,southwest or west southwest wind at upper air and the warming before the occurrence of fog,resulting in the high humidity of the whole layer.The observation also show that when there is light to moderate precipitation during the fog process,the visibility get better with the phase of the peak precipitation rate,the oscillations of weak and strong rain result in the oscillations of bad and better visibility,showing the close relationship between microphysics processes and visibility inside the body of fog.

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