Current Issue

28 October 2012, Volume 31 Issue 5   

articel

  • Possible Linkages among Anomalous Land Surface Condition, Surface Heating in Qinghai-Xizang Plateau in April and Summer Precipitation in China
  • YU Lin-Lin;CHEN Hai-Shan
  • 2012 Vol. 31 (5): 1173. 
  • Abstract ( ) PDF (1223KB) ( )
  • Based on GIMMS-NDVI data in 1981-2002, long-term snow depth dataset of China, rainfall data at 753 stations in China and ECMWF reanalysis data, the possible linkages among anomalous land surface conditions, surface heating in April in the Qinghai-Xizang  Plateau(QXP) and summer rainfall in China were explored using the statistical methods such as correlation analysis and composite analysis. The results show that the surface heating in the QXP is closely related to the land surface conditions. On the whole, the variation of vegetation index (NDVI) is consistent with that of the snow cover depth. Variation of vegetation (snow cover depth) can leads to anamolous surface heating by altering the surface sensible (latent) heating flux. It is found that the surface heating in the QXP is closely linked to summer precipitation in China. From the view of interannual anomaly, the anomalous surface heating in April bears significant negative correlations with precipitation anomalies in regions south to the Yangtze River in June, in North China and Northeast China in July, but in the middle-upper reaches of the Yangtze River and Huaihe River basin in August. Comparing with the interannual anomaly, the interannual increment anomaly shows even close relationship between the surface heating in April in the QXP and summer precipitation in China. Anomalous enchanced interannual increment of the surface heating in April tends to decrease the interannual increment of precipitation in June in the south of the Yangtze River and Southwest China, and increase (decrease) the interannual increment of precipitation in June in Southern (Northern) China in  July and August.
  • Analysis on Temporal and Spatial Variations for Cloud Radiation Forcing over Qinghai-Xizang Plateau Using CERES(SYN) Data
  • ZHANG Ding-Ling;HUANG Jian-Ping;LIU Yu-Zhi;CHEN Bin;ZHANG Lei
  • 2012 Vol. 31 (5): 1192. 
  • Abstract ( ) PDF (1112KB) ( )
  • The cloud and radiationdata, archived in CERES (Clouds and the Earth′s Radiant Energy System) SYN (Synoptic RadiationFluxes and Clouds) product, are applied to gain a better understanding of the temporal and spatial variations of cloud radiationforcing over the  Qinghai-Xizang Plateau(QXP) from November 2001 to October 2005. The results indicate four important points: Firstly, the whole QXP is the transition area of cloud radiationforcing, and this transition has significant seasonal and regional variations. The southeast of QXP makes a cooling effect, the western and northeastern QXP regions, an arid area, showed a weaker warming effect. Secondly, high cloud, upper-middle cloud and lower-middle clouds all contribute to the seasonal and regional differences of cloud shortwave radiationforcing, and the middle cloud is the main factor of regional differences; regional differences of longwave radiationforcing is not so obvious, but it has significant seasonal difference, which is mainly caused by the high cloud and upper-middle clouds, and cloud amount is a main factor of influence. Although the cloud amount of high cloud is small, but its impact is unnegligible. Thirdly, over  QXP, high cloud causes a net heating effect, upper-middle clouds have both heating effect and cooling effect, and low cloud cause a net cooling effect. Fourthly, for the diurnal variation of cloud radiationforcing, the shortwave plays a dominating role. The significant regional differences of diurnal variation are mainly caused by the cloud amount. During the daytime, the lower-middle clouds have the greatest contribution on the diurnal variation of shortwave radiation. At night, the high cloud plays an important role of diurnal variation of shortwave radiation, while the lower-middle clouds inhibit the for longwave radiationforcing.
  • Observational Analysis of Troposphere and Low Stratosphere at Minfeng Station on North Side of Qinghai-Xizang Plateau in July 2011
  • WANG Min-Zhong;WEI Wen-Shou;HE Qing;YANG Lian-Mei;CHENG Yu-Jing
  • 2012 Vol. 31 (5): 1203. 
  • Abstract ( ) PDF (1504KB) ( )
  • In order to meet the third Tibetan Plateau Experiment of Atmospheric Sciences, the Urumqi Institute of Desert Meteorology of China Meteorological Administration carried out an atmospheric scientific experiment on the detection of troposphere and low stratosphere using a radiosonde at Minfeng station on the north side the Qinghai-Xizang Plateau in July 2011. By analyzing the intensive radiosonde data obtained at Minfeng sounding station from 1 to 31 July 2011, the results show that: (1) Because of the thermal influence of plateau terrain, the height of troposphere may reach more than 16 000 m in summer at Minfeng station, its absolute height is approximately same with the absolute height of troposphere at Everest region. (2) Summer subtropical westerly jet on the north side of the Qinghai-Xizang Plateau behaves strongly, showing the east-west direction distribution, and thickness is about 12 000 m. With the maximum wind speed center located in  10 700 to 11 400 m heights, the maximum wind speed can reach 45 m·s-1. (3) Affected by the subtropical westerly jet in the bottom of the west and southwest winds, the water vapor over the northwest of the Qinghai-Xizang Plateau will be transported to the south of Tarim basin in summer. There have a high relative humidity value layer from 3 000 to 7 500 m heights at Ruoqiang, Minfeng and Hetian stations. The average relative humidity is about 60% to 70%, maximum humidity 85%, below the height of 3 000 m and a height of 8 000 m above the atmosphere with low humidity. (4) The convective boundary layer in daytime can be up to 3 200 m heights and the stable boundary layer in nighttime is about 1 200 heights, which is far higher than the observations of the Mount Everest region, but lower than the boundary layer height in Dunhuang region.
  • Application of Satellite-Based Rainfall Estimate on the Precipitation in Tibet Plateau
  • WANG Min;ZHOU Cai-Ping;WU Liang;ZHANG Ge-Li;欧Yang-Hua
  • 2012 Vol. 31 (5): 1215. 
  • Abstract ( ) PDF (1170KB) ( )
  • There have always been debates as to predict the precipitation in the TibetPlateau, where rugged terrain and the pool availability of sparse meteorological stations have presented hugechallenges for almost all existing models. The application of REF 2.0 (Rainfall Estimation Algorithm Version 2) in theTibet Plateauhad been described. At first, the suitability of the application was evaluated using the meteorological record at 39 stations in the Tibet Plateauat daily, monthly and annual levels, then the August precipitation pattern, and whole year of 2009 were estimated based on the correction of the coefficient of the model. The results showed a good tendency between the simulated and observed daily precipitation, with 46% sites which correlation coefficient isabove 0.40; but the simulation was very sensitive when the precipitation was small (close to 0 mm), and underestimated when the precipitation is large (>15 mm). As for month scale, the correlation coefficient in 62% sites isabove 0.80, but the simulation results were a little bit overestimated. The simulated precipitationresults in rainy season is significantly\|better than that in dry season, and the correction coefficient of 1.133 and 1.265could be applied respectively in rainy and dry seasons to improve the estimate. The correction coefficient of the annual simulation with the annual  precipitation from the 30 meteorological stations across the Plateau is 0.368 with the P\|value of 0.026. Overall, RFE 2.0 model shows good capabilities in estimating the precipitation inTibetPlateau, and can provide the reference for precipitation simulation in the Plateau.
  • Influence of Winter North Atlantic Oscillation on Spring Precipitation in China
  • SHAO Tai-Hua;ZHANG Yao-Cun
  • 2012 Vol. 31 (5): 1225. 
  • Abstract ( ) PDF (1147KB) ( )
  • Based on the precipitationdata at397 stations in China and the NCEP/NCAR monthly reanalysisdata, the relations between the winter North Atlantic Oscillation (NAO) and the spring precipitation in China using the correlation analysis and composite analysis are studied.  The resultsshow that the NAO significantly influence on the variations of spring precipitationin China. Associated with the positive (negative) NAO, the precipitation inSouth China will increase (decrease) and the precipitation inNorth China will decrease (increase). Further analysis indicates thatwinter NAO can exert notable influence on the atmospheric circulation over East Asia by propagation of wave train. In strong positive (negative) NAO year, the East Asian subtropical westerly jet enhanced (weakened) and the East Asia polar-front jet weakened (enhanced). The NAO-related atmospheric circulation resultedin the abnormalities of temperatures on500~200 hPa, cause corresponding variations in meridional gradients of temperature. Perhaps it is one of the reasons why NAO impacts on westerly jet stream over East Asia. The further analysis indicates thatupper-level cooling (warming) is closely related to anomalous sinking (rising) motion in 30°-40° N and rising (sinking) motion in 20°-30°N. These changes result in a drier (wetter) condition in the northern China and a wetter (drier) condition in the southern China.
  • Circulation Indices of South Asia High and Indian Low in Summer and Their Relation with Atmospheric Heat Source
  • HONG Fang-Ling;LI Li-Ping;WANG Pan-Xing;LUO Xuan
  • 2012 Vol. 31 (5): 1234. 
  • Abstract ( ) PDF (1321KB) ( )
  • Using NCEP/NCAR reanalysis data from 1950 to 2006, A set of seasonal and monthly circulation indices of South Asia High (SAH) and Indian Low (IL) in summer are calculated, including area index (s), intensity index (p) and center position index (λc, φc). The climatic and anomalous characteristics of SAH and IL and their contemporaneous correlation with atmospheric heat source in Asian monsoon area are investigated. The results show that, SAH is the weakest in June and the strongest in July and the center locates southeasterly by the normal in June, but northwesterly in July and August. IL is the strongest in July and the center locates westerly. There is notable correlation between the interannual anomaly of SAH, IL and the anomaly of atmospheric heat source in Asian monsoon area, respectively, but the correlation between IL and atmospheric heat source is higher. The primary effects of the Tibetan Plateau mainly display anomalous types of SAH, IL center position indices λc and atmospheric heat source over the Tibetan Plateau, Asian inland and the area between East Asia and Northeast  Asia at the same period; if SAH and IL centers locate easterly, the anomaly of atmospheric heat source  is positive in the west and negative in the east. There is no significant correlation between anomaly of atmospheric heat source over the Tibetan Plateau and its neighboring area and South Asia pressure intensity, but significantly positive correlation with IL intensity.
  • Design of Land Surface Model TBLSHAW and Its Simulation Analysis on Loess Plateau
  • YANG Qi-Dong;ZUO Hong-Chao;DONG Long-Xiang;ZHAO Jing;LI Qiang
  • 2012 Vol. 31 (5): 1243. 
  • Abstract ( ) PDF (1587KB) ( )
  • In order to improve the land surface model simulation in the semi-arid region, a new land surface model TBLSHAW (Two-Big-Leaf-SHAW) is developed based on the parameters of SHAW (Simultaneous Heat and Water Model) and CoLM (Common Land Surface Model) Model, and use the soil and near-surface boundary results obtained by SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) site on Loess Plateau. The model includes  a vegetation layer, several soil layers, and turbulent boundary layer. The vegetation layer use the two-big leaf model to calculate energy balance; soil layers used a coupled heat and moisture transport model to calculate soil temperature and soil moisture, and include the physical process such as the soil freezing and thawing, evaporation and precipitation infiltrate; turbulent boundary layer took use of the Monin-Obukhov theory to calculate turbulent heat fluxes. At last,  the data which is obtained by SACOL site are used to evaluate the TBLSHAW model. The simulated result indicate that the model can well simulate all the change tendency of the land surface characteristics at semi-arid region; the bias of the simulated soil temperature and moisture are small with the observed values, model efficiency and correlation coefficient are high; the model can well simulate net shortwave radiation and upward longwave radiation, but the bias of the simulated sensible and latent heat fluxes are large, that may be attributed to the low energy closure in this region, and need to investigate in the future.
  • Verification of Simulation Ability of BCC_CSM Climate Model in Regional Climate Change in China
  • SHI Yan-Jun;REN Yu-Long;WANG Shi-Gong;SHANG Ke-Zheng;LI Xu;ZHOU Gan-Lin
  • 2012 Vol. 31 (5): 1257. 
  • Abstract ( ) PDF (1347KB) ( )
  • In order to evaluate the simulation results of BCC_CSM climate model scientifically and provide the scientific evidence to improve and perfectthe model, using of standardized anomaly of Root Mean Square Error(RMSE), correlation coefficient methods, BCC_CSM climate model which developed by National Climate Center is validated against the NCEP/NCAR monthly reanalysis data in1948-2005 as observation field to verify the capability to simulate the regional climate change in China. Inspection elements include: Temperature field, wind field, relative humility fieldand surface heating field infour seasons on the upper, middle and lower troposphere etc. The results show that the standardized anomaly of RMSE in other three seasons between the simulatied and observed fields are smaller except for spring; The correlations of whole year are quite good, which have passed the significant test of significance level at α=0.05 in the most part of the country; RMSE of standardized anomaly and  correlations of  different meteorological element fields present with regional and seasonal characteristics;  the annual variation of everymeteorological element in different regional areas inChina is simulated by model,  the surface temperature simulated by BCC_CSM climate model is very well comparingwith the 13 modes of the IPCC AR4.
  • Case Study of the Impact of Mesoscale Topography on the Meiyu Frontal Rainstorm
  • ZHAO Yu-Chun;XU Xiao-Feng;CUI Chun-Guang
  • 2012 Vol. 31 (5): 1268. 
  • Abstract ( ) PDF (2413KB) ( )
  • Using the multiple observational data and NCEP reanalysis data, the synoptic background, environmental field features and activity characteristics of mesoscale convective systems (MCSs) producing an extremely rainstorm in the southern part of Anhui Province on 9-10 July 2007 areanalyzed. The effects of mesoscale topography like Dabie Mountain and Wannan mountainous areas on the MCSs activity and rainstorm formationare studied and investigated. Then the high resolution numerical simulation, topographical sensitivity experiments and comparisonanalysis are conducted to further deduce the role of mesocale topography in the activities of rainstorm-producing MCSs. The results are as follows: Two rainstorm centers are formed on the northeast side of Dabie Mountain and in the northern part of Wannan mountainous areas,respectively in the heavy pericipitation process, where four MCSs are formed. The extremely heavy  pericipitation  in Wannan region is produced by two quasi-stationary MCSs. The MCSs is of obvious diurnal variations and its diurnal peak is in the early morning. The Meiyu frontal lower-level convergence and high-level divergence are  main causes of the MCSs formation and development. In the southeast movement of the Meiyu front, the MCSs position relative to the mesoscale topography is variable and the predominant flow direction over the topography and the topographic Fwnumber is also changed continuously. The topographiesexert influences on the MCSs through different dynamic mechanisms. Under the high topographic Fwvalue, the impact of Dabie Mountain upon the downstream MCSs mainly is through mountain waves. Under low topographic Fwvalue, the flows around the topography and the mountain waves have a combined effect on the downstream MCSs. The Wannan mountainous areas arefavorable for the MCSs formation and maintenance when the MCSs move close to its north slope. The topographic blocking effect slows down the MCSs movement, which is beneficial to the formation of extremely  rainstorm in Wannan. The Dabie Mountain and Wannan mountainous areas have an obvious impact upon the intensity and distribution of the heavy  pericipitation, and their combined effect maybe the main and important cause of the extremely rainstorm in Wannan.
  • Diagnosis and Numerical Simulation of a Convective Rainstorm Process of Block Type Occurred in North China
  • JIANG Xue-Gong;LI Xia-Zi;LI Zhang-Jun;YUN Jing-Bo
  • 2012 Vol. 31 (5): 1283. 
  • Abstract ( ) PDF (2240KB) ( )
  • Using the routine and intensive observational data, the NCEP reanalysis data, the satellite images and the high resolution simulation result by MM5, a diagnosis and numerical simulation of a block type convective rainstorm process occurred in North China on July 23, 2006 were conducted. The result showed that the process happened in the low pressure circulation, in which the East Siberia Block was the main feature. The broad low pressure area and the vertical secondary circulation induced by the jet stream provided  the valuable environmental condition and dynamic forcing for the rainstorm. The water vapor transportation of synoptic scale on 700 hPa and 850 hPa, which was westerly direction to the  south of 40°N and easterly direction on the north side of the low, improved the environmental moisture conditions around Beijing. Just before the occurrence of rainstorm, the mesoscale moisture transportation with south-westerly direction on 850  hPa is  a key of forming rainstorm. MM5 model successfully reproduced the formation and evolution processes of the mesoscale convective systems (MCS), which was the directly weather system causing the rainstorm. The horizontally scale of MCS crossed 0.5 longitudes and from surface to 300  hPa vertically with a typical warm heart construction. The strong vertical secondary circulation, which was consistent with strong divergence on 400  hPa and convergence on 900  hPa, produced a favorable condition for the exploding of strong convection. Meanwhile, the instable energy transportation on the south side of the MCS, in which the intensive potential equivalent temperature gradient appeared, contributed to the rainstorm evidently.
  • Analyses on Rainstorm Characteristics in Middle and South of Shanxi Province during 18-19 August 2010
  • ZHAO Gui-Xiang;FAN Wei-Dong;LIU Zhi-Bin;HAN Long
  • 2012 Vol. 31 (5): 1309. 
  • Abstract ( ) PDF (1771KB) ( )
  • A  rainstorm occurred in Shanxi Province during 18-19 August 2010 are analyzed based on the encrypted data at automatic station, FY-2C product, and observational data. The results show that: (1) The rainstorm is affectedjointly by cutting low, trough and subtropical high. There are well consistency between the absolute value of TBB and precipitation at rainstorm stations. (2) In this process, the rainstorm area are very scattered. There are six centers which have typicalβ- and γ- mesoscale characteristics. The  rainstorm center have three patterns such as double, singleand isolate peak. (3) Analysis of automatic wind fielddata shows that there are three patterns such as vortex precipitation, shear precipitation and convergent precipitation. There are apparent differencewith intensity and duration of precipitation. The rainstorm area is related to its corresponding position with subtropical high. (4) Diagnosis of  index A shows that the rainstorm is caused by high humidity air and strong cold air from high latitude area. Under the background of unstable stratification, the high humidity air is constantly elevated height along the edge of subtropical high. In the upper-level of troposphere, the conversion is a main factor which made vorticity developed and vertical motion constantly strengthen.
  • Analyses on Mesoscale Characteristics Associated with Rainstorm in Liaodong Peninsula from 8 to 10 August 2010
  • LIANG Jun;ZHANG Sheng-Jun;SHI Xiao-Long;WANG Shu-Xiong;LIU Xiao-Chu
  • 2012 Vol. 31 (5): 1320. 
  • Abstract ( ) PDF (1986KB) ( )
  • Using the NCEP/NCAR reanalysis data, conventional observation data, satellite data, hourly rainfall observation data from nearly 100 automated weather stations and the sounding data from GTS1 digital radiosonde in Dalian, diagnostic analyses are made on characteristics of the mesoscale circulations associated with the threetorrential rain processes in Liaodong Peninsula from 8 to 10 August 2010. The synoptic background, mesoscale environment and triggering mechanism of the mesoscale convective system (MCS)  are focused. The results show that: (1) Northerly and stable position of Subtropical High Pressure provides the favorable large scale circulations for the rainstorm process. The direct raining system is the mesoscale convective complex (MCC), which is generated by the development of meso-β or meso-γ rain clusters along a shear line. (2)Link of the area of Liaodong Peninsulawith the channel of moisture transport by lower level jets and formation of moisture convergence arefavorable for occurrences of heavy precipitation in the area. (3)Before the heavy rainstorm  occurring, the increases of temperature and moisture in the lower troposphere, unsteady convective stratification, and significant decrease in the height of condensation and free convectionare the important conditions resulting in both the torrential rain occurrences in the rainstorm area. (4) Near the shear line, the coupling dynamical structure of positive vorticity region and the positive divergence forms, which causes strong upward motion in the lower troposphere, and has the convergent water vapor at the lower level lifted to the middle level, it is favorable for the genesis and development ofMCS. MCS  moving northeastward along the shear line  rapidly developand result in heavy precipitation occurrences. The heavy precipitation are located at the right forward position of the shear line and the position of the wind speed pulsation of the jet.
  • Discussion on the Spatial-Temporal Express Ways for Meteorological Drought
  • DUAN Xu;TAO Yun;ZHENG Jian-Meng;FAN Feng
  • 2012 Vol. 31 (5): 1332. 
  • Abstract ( ) PDF (886KB) ( )
  • The concept and the formula of time-area function of meteorological drought(MD) was proposed. Based on the daily precipitation and temperature data from 1 January 1951 to 31 May 2010, the CI and MD indexes are calculated and the MD temporal distribution is also analyzed. The results indicated that: (1) the MD index not only objectively but also exactly formulated the processes and intensities of meteorological drought in Yunnan Province in the last 60 years. Using the MD index the problem of subjectivity and uncertainty in defining the duration and  area of meteorological drought is well solved. The MD index not only offers possibility of completely descripted and compare historical drought events since the meteorological record, but also monitors the drought development process in real time. (2) according to the MD calculating results, the more serious meteorological drought years in Yunnan Province during 1952-2010  are 1959, 1963, 1966, 1969, 1974, 1979, 1984 and 2010, and the most serious drought year is 2010, which took place 90 days earlier than others so that it became a rare meteorological drought event of winter-spring-early summer continuous.
  • Change Characteristic of Low Cloud over North China Region and Its Relationship with Large Scale Circulation
  • NIU Xiao-Rui;WANG Shu-Yu
  • 2012 Vol. 31 (5): 1340. 
  • Abstract ( ) PDF (953KB) ( )
  • Using 43-year observationaldata in North China region, the temporal variations of the low cloud are examined. The relationship between low cloud in North China and large scale circulation indexes are analyzed with SVD method, and the effect of the western pacific subtropical high (WPSH) for low cloud over North China is studied. The analyzed result shows that the low cloud over North China region has remarkably decreased in the past 45 years, especially in autumn. On the decadal time scale, quasi-sixteen-year periodic oscillation is observed in seasonal low cloud amount over North China region, while 2~4-year periodic oscillations are found in summer. Among all the large scale factors, both coverage and intensity of the western Pacific subtropical high, the coverage of polar vortex region I, the intensity of region II and Northern Hemisphere polar vortex are strongly correlated with the autumn low cloud over North China region. With the anomalously large area of Western Pacific subtropical high, the geopotential heights over North China region is much higher with stronger ascending motion, correspond in lower atmosphere the south wind weak with less water vapor transport,which lead to decreasedlow cloud over the area.Polar vortex influences the low cloud through the south wind over North China region.
  • Analysis on Dynamic Diagnostic before and after Typhoon ‘Morakot’ Landing
  • WANG Yong;DING Zhi-Ying;LI Xun;SHEN Xin-Yong
  • 2012 Vol. 31 (5): 1356. 
  • Abstract ( ) PDF (1813KB) ( )
  • Using the GFS (Global Forecast System) analytical data with 0.5°×0.5° grid intervals, the NCEP reanalysis data with four times a day and the satellite cloud image data, the evolution characteristic   before and after the  typhoon  ‘Morakot’ landing with No. 8 are dynamically analyzed. Based on the diagnostic analysis of tendency equation of disturbed potential vorticity, the result  shows that: Firstly, there exists centers of tangential wind near typhoon center at mid- and low-levels which lead to the intensive area of the horizontal flux divergence of potential vorticity located on the inner side of the center of tangential wind. Secondly, the  negative and positive horizontal flux divergences of potential vorticity at low levels can be employed as a pointer for forecast the  typhoon moving on the sea. Thirdly, the intensive areas of negative vertical flux divergence of potential vorticity offer reference for forecast of  typhoon moving under the p coordinate. Finally, by using the vorticity equation, the principal determinants of the variation of the cyclone  vorticity at mid- and low-levels are discussed. Meanwhile, the important coupling effect of typhoon and southwest low-level jet in coastal region of the South China Sea and Southern China on the structure and routine of this typhoon are also investigated.
  • Analyese on Different and Common Points of Long Life Squall Line in Severe, Weak Convection Precipitation Processes
  • YAO Chen;ZHENG Yuan-Yuan;ZHANG Xue-Chen
  • 2012 Vol. 31 (5): 1366. 
  • Abstract ( ) PDF (1573KB) ( )
  • Based on the conventional observation data, automatic weather station data, NCEP 1°×1° reanalysis data and Doppler radar data, the physical mechanisms and mesoscale features of two long life squall lines under the different convection environments have been researched. The main conclusions are as follow: (1) Squall line has strong moisture convergence in surface layer; in severe convection precipitation process, squall line usually has deeper wet layer, stronger and more wider vapor convergence, and the lifting condensation level is lower. (2) One of the common features of squall line is that the strong cold advection in the upper level superpose on the warm advection in the low level, which  is of difference  in weak convection precipitation process, the establishment of unstable stratification mainly relates to the cold advection in the   upper level, the lapse rate of temperature is higher, these are some characteristics of weak precipitation supercell. But in severe convection precipitation process, strengthening of the warm advection in the low level also is the important reason of unstable stratification, θse has the humid neutral stratificationcharacteristic in the middle level and there is greater thermal unstable, which is of the typical characteristic of severe precipitation supercell. (3) Long life squall line all develop with the strong vertical wind shear; the vertical wind shear mainly cause by wind speed varying with height in severe convection precipitation process, and by wind direction varying with height in weak convection precipitation process. (4) Squall line all move along the direction of outflux boundary and leading flow. (5) The common points of squall line on the radar echo are that  they all have typical bow echo, the bow echo recedes when the gust front is away from the storm cell and the area of stratiform cloud echo increases. Squall line of Doppler radar radial velocity  associate with the development of the high area of meridional speed in the low level, MARC in middle level and the large range middle convergence  accompany with mesocyclone developping. The different ponit is the evolution of bow echo: In weak convection precipitation process the bow echo has the typical structure of supercell, but in severe convection precipitation process the bow echo develops with  severe precipitation supercell, the structure is markedly different from classical supercell or  weak precipitation supercell. (6) The high  area of meridional speed under 1 kmheight, MARCand mesocyclonescan be early-warning of disastrous winds on the surface.
  • Environment and Structure of Hail-Cloud at the end of North China Trough in Late Summer
  • SU Ai-Fang;YIN Yan;CAI Miao
  • 2012 Vol. 31 (5): 1376. 
  • Abstract ( ) PDF (2205KB) ( )
  • Effected by the hail-cloud at the end of North China though, the central and southern regions of Hebei Province occurred a sudden severe storm on 27 August2009, and the diameter of hail exceeds 40 mm, which led to serious disaster. The event was rare in the same period of history. Based on conventional observational data, Doppler radar and satellite detection information and retrieval products, Automatic station data, NCEP reanalysis data, the environment and structure of storm were analyzed. The result showed that the southward weak cold air triggered the severe convection and the boundary on the surface promoted the development of mesoscale convective systems. The hail cloud developed in the environment of up dry and low wet air levels. The latent heat of condensation might provide the energy    for the rapid development of hail cloud and the moderate deep layer vertical wind shear might provide the dynamic conditions. However, the thinner and lower moist air level, relatively high 0 ℃ layer (higher than the average height in history) at 08:00, higher TBB made it more difficult to forecast the severe convection. However, the relatively higher cloud optical thickness might give the forecast information before the severe convection developing. The hail cloud was of the  supercell-cluster characterized of linear arrangement  in radar reflectivity and right propagating of multi-cells made the strong storm to be sustaining.
  • Analysis on a Short-Time Snowstorm Weather in Wuhan Based on Variety of Monitor Data
  • LI De-Jun;TANG Ren-Mao;XIANG Yu-Chun;LIU Cao;CHEN Ying-Ying;XU Gui-Rong
  • 2012 Vol. 31 (5): 1386. 
  • Abstract ( ) PDF (849KB) ( )
  • A short-time  snowstorm event in Wuhan on 12 Feburary 2011 is analyzedusing Thies Clima laser precipitation monitor (TCLMP),  MP3000A microwave radiometer,  Doppler radar and artificial observation data. The results show that: (1)It has gone through three stagesin the heavy snowstorm process,  such as rain,  sleet and snow. At the rain stage, the TCLMP monitored a wide raindrop spectrum,  its maximum diameter is 4.5 mm,  the number concentration is small (only 2to 5 429 m-3·mm-1), which has a bimodal distribution,  and so on. (2) Dynamic exchange of vapor phase has beenobserved by using Microwave radiometer,  the specific humidity in the 1.5~3.5 km heights appears  a range of 14~16 g·kg-1large value area at 08:12-09:34(UTC),  and the sleet process is very short,  only 16 min, and it quickly switchedto the pure snowfall stage,  then snowfall in Wuhan reachs 5.035 mm within 65 min,  accounting for more than 80% of the entire snowfall. (3) The Doppler radar reflectivity correspondedwell to particle spectral width and number concentration,  the greater of the latter two is, corresponding to the greater strength of the radar echo is,  which closely relate to water vapor density of microwave radiometer and rainfall intensity of TCLPM. If combining them,  it will hasa very good monitoring capabilities of dynamic exchange for precipitation phase,  rainfall intensity,  magnitude and duration.
  • Research of Very Short-Term Heavy Precipitation Identification Method Combinated Multi-Radar Retired Parameters
  • WU Tao;WAN Yu-Fa;WANG Shan-Shan
  • 2012 Vol. 31 (5): 1393. 
  • Abstract ( ) PDF (1997KB) ( )
  • Based on the Severe Weather Automatic Nowcast System radar products, a very short-range heavy precipitation identification algorithm which inherits nowcasting method in NCAR Auto-Nowcast System  and  multi-radar parameters and fuzzy logic method is proposed. The research has been done on predictor chosen, error analysis and parameter threshold set. Identification factors such as quantity precipitationforecast, rain intensity, vertically integrated liquid water, echo top are chosen according to history data statistic analysis and the corresponding member functions are designed. Evaluation shows that the critical success index of very short-term heavy precipitation identification algorithm combined with multi predictors is 0\^18, and its performance is higher than that of QPF determination method and fuzzy logic method using the single predictor. Test of heavy rain indexthreshold shows that the appropriatethreshold is helpful to improve algorithm performance and it is assigned as 0.5~0.6 in this research. The main cause affecting the algorithm performanceis high false alarm rate which is caused by clutter echo, const-extrapolation prediction assumption, inappropriate Z-R relationship and not uniformityon heavy precipitation location. In general, more than one factor cause together false alarm due to rainfall complexity.
  • Error Correction in Three-Dimension Location System of Lightning VHF Radiation
  • WANG Yan-Hui;ZHANG Guang-Shu;ZHANG Tong;LI Ya-Jun;FAN Xiang-Peng;WU Bin
  • 2012 Vol. 31 (5): 1407. 
  • Abstract ( ) PDF (877KB) ( )
  • In order to improve the detection efficiency and location accuracy of three-dimension location system of lightning VHF radiation(LLR), basing the principle of LLR, the possible sources of error were analyzed. This study focuses on the error from GPS, A/D card and the position of station which were considered as sources for system error. The time signal from GPS showed a normal distribution which lead to the corresponding error of trigger time. The accumulated error in data was resulted from the unstable crystal oscillator, and it could affect the accuracy of location result greatly. The position error of station was resulted from GPS orientation system, and its correction would be depends on the long-term observation on fixed observation sites. Considering these errors, the difference value, between arriving time detected by receiver and arriving time calculated base on the location results, were fit to a straight line. The evolution rule of error was analyzed and corrected base on this line. And the detection efficiency of LLR was improved greatly and location results of LLR were more credible.
  • Researches of Weather Pattern and Boundary Layer Structure Characteristic on Serious Air Pollution Days in Urumqi
  • LI Xia;YANG Jing;MA Jun;WANG Jiang;ZHAO Ke-Ming;REN Quan;ZHAO Yong
  • 2012 Vol. 31 (5): 1414. 
  • Abstract ( ) PDF (1310KB) ( )
  • Using the real time meteorological observational data and daily air pollution index (API) from January 2004 to April 2009, the statistics were performed with regard to temperal distribution, 500 hPa circulation pattern, surface pressure pattern and corresponding boundary layer structure on serious air pollutiondays  with daily API above Ⅳ level. The results show that the occurrence frequencies of serious air pollution lasting for one, two, three and four days are 32.2%, 23.3%, 18.5% and 11.0%,respectively. The proportion of  500 hPa zonal circulation  is relatively high with value of 86.3%, but for the meridional circulation only below 9.6% on high air pollution days. According to the location of surface high pressure center (SHPC), the occurrence frequency reaches 86.3% when Urumqi is in the rear of the SHPC, and then  the frequency of 9.6% is for the location at the bottom of the SHPC. The frequencies of the other two patterns are relatively low. The vertical structures of the average profiles such as temperature, relatively humidity and wind of grade Ⅲ air quality days are almost in agreement with that of average  profiles in winter. Furthermore, the strong temperature inversion, lower wind speed and relatively deep easterly or southeasterly flows make great contributions to formation of serious air pollution. The relationship between serious air pollution and fog is significant with the  fog occurrence frequency of 81.3%. Moreover, the air quality tends to be poor under conditions of the vertical structure with wet at low level but dry at upper level and inversion at 20:00(Beijing  time) on the  day before that day.
  • Observational Studies on Characteristics of Aerosol Scattering and Absorption Coefficients over Semi-Arid Area of China
  • WANG Zhen-Hai;ZHANG Wu;SHI Jin-Sen;HUANG Jian-Ping;CHEN Yan;TIAN Lei;XIANG Tao
  • 2012 Vol. 31 (5): 1424. 
  • Abstract ( ) PDF (957KB) ( )
  • Based on the continuous observational data by AE-31 from 1 November 2007 to 31 October 2008 and M9003 from 1 August 2007 to 31 July 2008 at Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), the characteristics of aerosol scattering and absorption coefficients were studied over semi-arid area of China. The results showthat the annual average scattering coefficient is 158.86 M·m-1, the absorption coefficient is 14.11 M·m-1and the single scattering albedo at 520 nm is 0.83 over this region. The annual variations of scattering coefficient and the absorption coefficient are single-peak type. The peak values of scattering and absorption coefficients appear in December and  November, respectively. The diurnal variations of both coefficients aredouble-peak during the heating period but single-peak type in the non-heating period. Under the dust weather condition, both the coefficients increaseto 103.8% and 88.5%. Utilizing the data fromAPS-3321 at the same time, the correlation between  scattering and absorption coefficients PM2.5 concentration,    have beenstudied, the results show both the coefficients havegood relationship with PM2.5concentration and the correlation coefficients are more than 0.8.
  • Application Study of FY-3A/MWHS in Quantitative Precipitation Estimation
  • CUI Lin-Li;YANG Yin-Ming;YOU Ran;FANG Xiang
  • 2012 Vol. 31 (5): 1439. 
  • Abstract ( ) PDF (717KB) ( )
  • Based on the precipitation estimation mechanisms of FY-2C geostationary satellite, the satellite data from FY-3A microwave humidity sounder (FY-3A/MWHS) during the severe tropical storm ‘Linfa’ (0903), typhoon ‘Molave’ (0906) and typhoon ‘Morakot’ (0908) were used to estimate precipitation through the multiple linear stepwise regression method, and the precipitation estimation accuracy of FY-3A was validated using the observation data from automatic weather stations in MICAPS system and  TRMM and FY-2C satellites. The results indicate that there are some correlations between FY-3A/MWHS and the observed precipitation, and FY-3A/MWHS has some estimating capacity for different  rain amounts, especially for the moderate rain (3 mm≤precipitation<10 mm), it has higher accuracy both in the rainfall area and the amount. Comparing with FY-2C geostationary satellite, FY-3A has obvious advantages both in the estimation accuracy of different  precipitation amounts and the numbers of station with less error. It is a new attempt and a necessary complementary using FY-3A/MWHS to quantitative precipitation estimation.
  • Application of SWAT Model into the Reservior Runoff Simulation in Hewan Valley of Yellow River
  • SHI Lan;FENG Zhen;XU Li-Na;HAN Sheng
  • 2012 Vol. 31 (5): 1446. 
  • Abstract ( ) PDF (1173KB) ( )
  • The interval between Hekou town and Wanjiazhai reservoir of Wanjiazhai river basin of the Yellow River was chose as the study area, in which the space distribution of water cycle obtained by GIS/RS technology.The hydrological model based on SWAT (Soil and Water Assessment Tool) model was set up in the study area.Monthly runoff was simulated by SCS runoff method with the actual measurement data of day runoff on the hydrological stations of Toudaoguai and Wanjiazhai from 2000 to 2009, in which 2000 to 2006 was taken as the calibration period and 2007 to 2009 was taken as the validation.Not only the systematic simulation, the sensitive analysis and the parameter calibration in calibration period, but also error analysis, precipitation-runoff analysis and water balance analysis in validation period were taken. At the same time, the uncertainty of the incoming flow was considered.The results showed that the SWAT system on the structure was reasonable, the correlation coefficient reaches more than 0.97 and Nash-Sutcliffe model efficiency coefficient reaches more than 0.96 both in the calibration period and in the validation. In the general, the simulation system could reflect the inflow runoff process perfectly. Therefore, the simulation result could provide the positive reference for the comprehensive utilization of water resources and proper reservoir operation in the Hewan valley of the Yellow River.
  • Influence of Human Activity and Precipitation Change on Middle-Long Term Evolution of Landslide and Debris Flow Disasters
  • TAO Yun;TANG Chuan
  • 2012 Vol. 31 (5): 1454. 
  • Abstract ( ) PDF (860KB) ( )
  • Using the landslide and debris flow disaster data, reflecting human activity data (for example, the agricultural acreage data, highway mileage data, etc.) and precipitation data, based on the definition of the landslide and debris flow index in low-latitude plateau of China, human activity index and precipitation index, the influence of human activity and precipitation on mid-long term evolution of the landslide and debris flow in low-latitude plateau of China have been studied with the wavelet technique. The results indicate that the mid-long evolution of landslide and debris flow disaster trends to annually increase 0\^9 and has obvious stage feature. The abrupt point from rare  to frequent periods took place in 1993. There is significant in-phase resonance oscillation between the human activity and landslide and debris flow frequency on scale of 11~16 years, in which the variation of human activity occurs about 0.2~2.8 years before that of landslide and debris flow. So the increase of the landslide and debris flow frequency in low-latitude plateau of China may be mainly caused by the geo-environmental degradation having been induced by human activity. After the impact of human activity removed, there is significant in-phase resonance oscillation between the landslide and debris flow frequency and summer rainfall in low-latitude plateau of China in quasi-three-year and quasi-six-year scales, in which the variation of summer precipitation occurs about 0~0.8 years before that of landslide and debris flow. The summer  precipitation  is one of important external causes which impacts on the landslide and debris flow frequency in low-latitude Plateau of China. In the end, the middle-long term evolution predicting model of landslide and debris flow disasters frequency in low latitude plateau region with better fitting and predicting ability was built by considering human activity and summer rainfall.
  • Short-Term Wind Power Forecasting Experiment Based on WRF Model and Adapting Partial Least Square Regression Method
  • CHENG Xing-Hong;TAO Shu-Wang;WEI Lei;DUAN Wei;CHEN Jun-Ming;JIANG Ying
  • 2012 Vol. 31 (5): 1461. 
  • Abstract ( ) PDF (1116KB) ( )
  • Based on the Weather Research and Forecasting Model (WRF) with high temporal and spatial resolutions and the Adapting Partial Least Square Regression (APLSR) method, the short-term wind power forecast system coupled with the wind field and wind power forecasting models is developed in this paper. In order to assess the accuracy of wind field forecasts objectively, the wind speed and wind direction in the specified wind field in Gansu Province in January, April, July, and October 2009 were forecasted by WRF model, which were used to compare with the observed data at 50 m and 70 m heights on two wind masts closed to the wind field. Based on the relative accurate forecasts of wind field, the nonlinear statistic forecast models every 15 min for 200 wind turbines using APLSR method and single wind turbine technique were constructed based on the actual wind power recorded data and wind speed, wind direction, temperature, relative humidity and pressure forecasting values on the hub height from January 2008 to April 2009. So as to assess forecasting effects of wind power, forecast experiments from January to December 2008 were carried out. The  results showed that: (1) The probability distributions of wind direction forecasts are consistent with the observed values in January, April, July, and October 2009, and the forecasting effects of   static wind is also good. (2) The correlation coefficients between the wind speed forecasts and observed values at 50 m and 70 m heights on two masts in January, April, July, and October 2009 are 0\^6~0.8. Root mean square error (RMSE) of forecasting error of wind speed is between 1.5~2.6 m·s-1. And WRF model can well forecast the diurnal variation characteristic of wind speed. (3) The correlation between total wind power forecasts and actual wind power recorded values for the wind field every 15 min from January to December 2008 are remarkable. Correlation coefficients are 0.58~0.90 and have passed the confident level of 99.9%. (4) The forecasting errors of total wind power every 15 min from January to December 2008 which compared with the total rated installed capacity are relatively small and RMSE of forecasting errors of total wind power are 2.76%~12.89%.