Plateau Meteorology

Current Issue

28 April 2015, Volume 34 Issue 2   
  • Research about Radiosonde Stations Increase in Southeast Side of Qinghai-Xizang Plateau Based on Its Water Vapor Characteristics
  • DUAN Wei;DUAN Xu;YANG Jiakang;XU Kai
  • 2015 Vol. 34 (2): 307-317.  DOI:10.7522/j.issn.1000-0534.2014.00024
  • Abstract ( ) PDF (4940KB) ( )
  • Water vapor is one of the most concerned elements of atmospheric probing. Using NCEP reanalysis data and considering the terrain, the water vapor characteristics (e.g. distribution of water vapor, transport of water vapor, its convergence and divergence) in one sub-region of the Qinghai-Xizang Plateau(QXP), the southeast side of the QXP, are analyzed by the climate diagnostic methods. Based on its water vapor characteristics, the quantitative research of radiosonde stations Increase is developed. The results show that the water vapor transport and seasonal differences of atmospheric precipitable water show that the QXP in the southeast is the interaction region of East Asian monsoon and South Asian monsoon. The southeast side of the QXP is the most important water vapor channel in northeast hemisphere, especially in autumn, winter and spring. The atmospheric precipitable water in the southeast side of the QXP is significantly larger than the southwest side of QXP, the reason are directly related to the combination the southward convex curved terrain of the QXP and low latitude plateau terrain. For moisture convergence and divergence, terrain is a complex and special role in the southeast side of the QXP. Its role is not only exist level differences, but also exist longitudinal and latitudinal differences. Base on quantitative research about the key area of water vapor detection, the urgent area to increase radiosonde stations include northwestern of Yunnan-southeastern of Tibet-northern of Burma, eastern of Yunnan-western of Guizhou (near 25°N) and southwest of Yunnan.
  • Moisture Transport Features in Summer and Its Rainfall Effects over Key Region in Southern Margin of Qinghai-Xizang Plateau
  • XIE Chengying;LI Minjiao;ZHANG Xueqin;GUAN Xuefeng
  • 2015 Vol. 34 (2): 327-337.  DOI:10.7522/j.issn.1000-0534.2014.00034
  • Abstract ( ) PDF (7780KB) ( )
  • Regional water vapor convergence and divergence over the southern margin of the Qinghai-Xizang Plateau (QXP) can be regarded as a good factor for the formation of rainfall climate and extreme weather in the TP and its surroundings. In view of the key region in southern margin of the QXP (the key region for short), summer moisture transport and budget over the key region are analyzed based on the NCEP/NCAR reanalysis data from 1979 to 2010, combined with rainfall station data as well to explore its effects on the rainfall characteristics in the QXP and its surroundings. The main conclusions are summarized as follows. Influenced by the Indian low and the terrain of the QXP, three water vapor transport channels were transformed in the key region from the Bay of Bengal moisture flow, and those led to water vapor divergence over the key region where the southern boundary was the only input one. Meanwhile, different boundaries showed different monthly and interannual variations, especially for the contrary trend of the moisture budget intensity between the western and the eastern boundaries. The budget of input and output boundaries were affected by the activities of the Indian low and the South Asian monsoon, and the output boundaries moisture budget was directly connected with abnormal distribution of rainfall and the development of extreme drought and flood events in the QXP and even the monsoon region surroundings. In addition, the reliability of NCEP/NCAR and JRA-25 reanalysis data in qualitative research over the south margin of the QXP was confirmed by comparison of these tow datasets.
  • Variation Characteristics of Climatic Growing Season in the Middle Course of Yarlung Zangbo River during 1971-2010
  • YU Zhongshui;TANG Shuyi;Yundan Nima
  • 2015 Vol. 34 (2): 338-346.  DOI:10.7522/j.issn.1000-0534.2013.00175
  • Abstract ( ) PDF (2743KB) ( )
  • By using daily mean temperature and daily precipitation of Lasa, Rikaze, Zedang and Jiangzi in the middle course of Yarlung Zangbo River valley in 1971-2010, the variation of its climatic growing season was analyzed. The result shows: (1) The climatic growing season lengthened by 5~8 d·(10a)-1 obviously, the climatic growing season of limit temperature ≥ 0℃ and ≥10℃ had increased by 30 d, limit temperature ≥ 5℃ had increased by 20 d; with limit temperature ≥ 10℃ being considered, the winter season shortened while the summer season lengthened. (2) The trend was significant of beginning dates advanced, ending dates deferred, lasting days and active accumulated temperature increased of three critical temperature; precipitation and ≥5 mm precipitation days of limit temperature ≥ 10℃ was increasing by 19 mm·(10a)-1 and 1.5 d·(10a)-1, and confirmed a mutation in the end of 1980s, indicating the precipitation and temperature conditions of limit temperature ≥ 10℃ was changing to warm-humid significantly. (3) The interannual variability of ending dates was relatively stable, and other elements was unstable; The decadal variability of the beginning and ending dates, lasting days and all accumulated temperature keep step changes, but other elements presented fluctuation changes, the minimum appeared in 1980s. (4) The variation trend of ending date, lasting days and accumulated temperature of limit temperature ≥ 10℃, which can be considered mutation in the latter of 1990s, indicating the largest contribution to the extension of the summer season came from the significant delay trend of limit temperature ≥ 10℃.
  • Analysis on the Frontogenesis Mechanism of Dian-Qian Quasi-stationary Front Inducing Spring Rainstorm in Guizhou Province
  • DU Zhengjing;HE Yulong;XIONG Fang;DENG Xiaohong;SHI Kaiyin;PENG Qian
  • 2015 Vol. 34 (2): 357-367.  DOI:10.7522/j.issn.1000-0534.2013.00176
  • Abstract ( ) PDF (8039KB) ( )
  • Using satellite images, observational data and the 6-hour-inteval reanalysis data with 1°×1° resolution from NCEP, five spring rainstorm processes in Guizhou Province under the background of Dian-Qian quasi-stationary front from 2003 to 2006 are analysed. The results show: In the setting of quasi-stationary front, the spring rainstorm in Guizhou Province is impacted together with the upper and low jet stream, upper trough, cold air and the quasi-stationary front. The rich water vapor is transported from the Bay of Bengal and Beibu Gulf to Guizhou province by low level jet stream, and the convective available potential energy is accumulated continuously. The acceleration of high jet stream strengthens the large-scale ascending motion with divergence in high level and convergence in low level, and drives the cold air southward via the positive circulation below the jet stream, then makes the quasi-stationary front active and frontogenesis, which is the trigger mechanism of the rainstorm processes. The frontogenesis phenomenon shows that the acceleration of high level jet stream results in the frontogenesis in the polar front in the mid-upper troposphere and the formation of the positive circulation in the middle troposphere. The latter strengthens the horizontal deformation and vertical motion and then enhances the frontogenesis. The horizontal deformation and vertical motion impact the rainstorm directly: The range of the horizontal deformation is in proportion to the rainfall intensity, and the convective cloud generating near the quasi-stationary moves along the direction of the inclined item related to vertical motion. Quasi-stationary front is close to spring rainstorm in Guizhou province. The heavy rainfall area is distributed mainly southward one latitude zone from the quasi-stationary front. The acceleration of high jet stream, the intensity of the moisture convergence around the cold front and the region of high-energy tongue have an indicative function to the extent and intensity of heavy rainfall. Based on above frontogenesis mechanism, a physical model about spring rainstorm in Guizhou province induced by the quasi-stationary front is epurated.
  • Numerical Simulation Studies on a Rainstorm in Central Western Shaanxi Province
  • LIU Yanfei;LONG Xiao;WANG Hui
  • 2015 Vol. 34 (2): 378-388.  DOI:10.7522/j.issn.1000-0534.2013.00182
  • Abstract ( ) PDF (8451KB) ( )
  • The circulation feature of a mesoscale system and its dynamical and thermal characteristics in the phase of development are studied through analyzing and simulating for the rainstorm process which occurred in central Western Shaanxi province during 2829 July 2011 by observational data, NCEP final analysis data and high resolution output by mesoscale model WRF V3.4. Synoptic analyses indicate that upper troughs and low level shear are the main weather systems for this rainstorm. Diagnoses of the physics fields suggest that stronger upper divergence and week lower convergence associated with positive vorticity and strong vertical motions in the strong precipitation region during the developing phase of the rainstorm. At the initial phase of the rainstorm, Convective Available Potential Energy(CAPE) was accumulated and which was triggered and released rapidly (decrease 2200 J·kg-1 in 12 hours) by the strong vertical motions, which causes such a strong rainstorm. The strong precipitation in 3 hours occurred around the shear line on 850 hPa which was associated with high CAPE value. The analysis on the residual of Non-linear Balance Equation (NBE) features shows that the high residual of NBE appeared around the heavy precipitation area, which has close relationship with the adjustment between momentum and mass field.
  • Comparison of Simulations on Winter Sounding Profiles in PBL in East China between WRF and MM5
  • SHI Chun'e;LI Yaosun;YANG Jun;DENG Xueliang;YANG Yuanjian
  • 2015 Vol. 34 (2): 389-400.  DOI:10.7522/j.issn.1000-0534.2013.00206
  • Abstract ( ) PDF (11265KB) ( )
  • MM5 and WRF were run daily for December of 2006 and December of 2007 and the results at ground level and in PBL were assessed and compared by calculating a set of common used statistics measures using the ground-level observations of the China Meteorology Agency routine meteorological network, and the high resolution sounding data at observatories of Nanjing and Anqing. Generally, the simulated ground level temperature and humidity by both MM5 and WRF were reliable, but the simulated wind speed was a little worse. Both models performed better during daytime than during nighttime. In addition, the validation results showed evident regional distribution, e.g., the results changed worse from east to west for temperature, from southeast to northwest for humidity, from plain area to hill and mountain areas for wind speed. According to correlation coefficient (R) and mean absolute error (MAE), WRF performed better than MM5 for temperature and humidity at the ground level. Taking Nanjing and Anqing for examples, the modeled sounding in PBL at both 08:00 and 20:00 were acceptable, except for the wind speed below 150 m in Nanjing. The results at 20:00 were better than those at 08:00, and improved with increasing height for both models. In general, WRF performed better for temperature and humidity, while MM5 performed better for wind speed. Both models could reproduce the near surface temperature inversion, with overestimated the occurring frequency. For the near surface temperature inversion, MM5 outperformed WRF for the frequency, while WRF outperformed MM5 for the thickness and intensity.
  • Analysis of Equation for Convective Vorticity Vector during a Torrential Rainfall Process in Meiyu Season of 2011
  • QING Tao;SHEN Xinyong;HUANG Wenyan;HUANG Mingce
  • 2015 Vol. 34 (2): 401-412.  DOI:10.7522/j.issn.1000-0534.2013.00204
  • Abstract ( ) PDF (7363KB) ( )
  • Using NCEP FNL analysis data, black body temperature from FY-2E satellite, conventional and auto-metrological stations' observational precipitation data, and simulation output from high-resolution mesoscale model WRF V3.3 to analyze a precipitation process in Jiang-Huai valley in June 2011. Analysis results show that the simulation results are in good agreement with the observations when comparing the precipitation between simulations and observations and reproduce the precipitation process well. This precipitation process was controlled and influenced by the surface low and Meiyu front systems. Period from 14 to 15 June is the mature phase of whole precipitation process, and the most significant character of this period is that many mesoscale convective systems move and develop along the Meiyu front. To investigate how MCS impacts on Meiyu front and torrential rainfall, convective vorticity vector and its vertical component tendency equation were employed to analyze. The result shows that local variation for the vertical component was influenced by the diabatic term, and the relationships among diabatic heating, secondary circulation and Meiyu frontogenesis imply a CISK-like response between MCS and Meiyu frontogenesis. So as a good atmospheric variable, the convective vorticity vector, especially, the vertical component can be used to diagnose and reveal the relationship between MCS associated with diabatic heating and Meiyu frontogenesis.
  • Analysis of the Phenomenon of Lake-Land Breeze in Poyang Lake Area
  • CAO Jianhua;LIU Ximing;LI Guoping;ZOU Haibo
  • 2015 Vol. 34 (2): 426-435.  DOI:10.7522/j.issn.1000-0534.2013.00197
  • Abstract ( ) PDF (4800KB) ( )
  • Using the 20062010 conventional observed wind data from De'an, Poyang, Hukou, Jinxian and Xingzi, the lake-land breeze in Poyang Lake area was analyzed. These five observation stations are located within about 50 km radius of the Poyang Lake, which are respectively in the west, east, north, south and northwest parts of the Lake. The results show that lake-land breeze in Poyang Lake region occurs through the whole year, although it varies seasonally. Averagely, the strength of the zonal lake-land breeze is larger than the strength of the meridional lake-land breeze, with the values of 0.5~0.7 m·s-1 and 0.3 m·s-1 respectively. The transition of lake-land breeze in the west of Lake is about two hours earlier than that in the east of Poyang Lake, and the transition of lake-land breeze in the north of Poyang Lake is about five hours earlier than that in the south of Poyang Lake. Analyses of the wind and temperature data in August 2010 from the 153 automatic meteorological stations in the Poyang Lake region show that the lake-land breeze presents diurnal variation obviously due to the lake-land temperature difference. The shallow wave model is employed to study the cause of the lake-land breeze in Poyang Lake region by setting the heating term as the Poyang Lake, and the model can simulate the land breeze during the night and lake breeze during daytime.
  • Comparative Analysis of Sustained Drought Processes in Jiangsu during 1971-2011
  • ZHANG Pengbo;JIANG Youshan;LIU Lei;LI Yi;HU Shanshan
  • 2015 Vol. 34 (2): 444-454.  DOI:10.7522/j.issn.1000-0534.2013.00174
  • Abstract ( ) PDF (10299KB) ( )
  • By using the monthly precipitation data of Jiangsu province and the NCEP/NCAR monthly reanalysis data, combining with the abnormal precipitation mechanism analysis in Jiangsu province in recently 40 years, the differences between the Autumn-Winter-Spring Drought(AWSD) in 2010/2011 and other three sustained drought processes in recent 40 years in Jiangsu have been studied, respectively. The results show that the drought has maintained for the longest time in 1980/1981 and been most serious in 2010/2011. From the perspective of climatic factors, the drought grade of the troposphere and the intensity of sinking movement have been strong and sustained for a long time. In 1980/1981 and 2010/2011, potential height field presented high pressure in the west and low pressure in the east on 500 hPa, which is beneficial to East Asia trough enhancement and maintenance. Meanwhile, consistent with the blocking situation in the west Baikal Lake and the stronger winter monsoon, cold air moved southward frequently, which blocked the transmission of the south warm air, and made air more drier. SST anomaly distribution displayed as La Nina type. SST anomalies were negative in the east central Pacific around the equator and near the eastern coast in China, while positive in west central Pacific. Such abnormal distribution tended to form ‘east low and west high’ in potential height. Compared with the other two sustained drought processes, the drought intensity in 1998/1999 and 2008/2009 were slightly weaker, so there were also some differences in atmosphere background field and SST anomaly distribution.
  • Analysis of the Available Solar Energy Resources in Turpan
  • SHEN Yanbo;CHANG Rui;DU Jiang;CHENG Xinghong
  • 2015 Vol. 34 (2): 470-477.  DOI:10.7522/j.issn.1000-0534.2014.00003
  • Abstract ( ) PDF (3411KB) ( )
  • Using the measured data for a year of solar energy test station in Turpan combined with observation data of the weather station over the same period, from three aspects of solar radiation on inclined surface, direct normal irradiation and diffuse horizontal radiation to analyze the available solar energy resources and their variation characteristics and the possible causes in Turpan area. The results show: the annual irradiation on inclined plane with optimal angle is 1.4% higher than the inclined surface with latitude angle, and 23.16% higher than the horizontal plane. And the two groups of relative difference are diametrically opposed in seasonal changes, the relevant conclusions can be used for analyzing and evaluating the solar energy resources of the fixed photovoltaic power plant. The annual direct normal irradiation is 17% lower than the global horizontal irradiation, the relative difference in winter and spring is larger than that in summer and autumn, and the conclusions can be used for analyzing and evaluating the solar energy resource of thermal power generation. The annual diffuse horizontal radiation takes 49% of the global horizontal irradiation, the diffuse ratio and annual variation of the solar elevation angle are two major factors that influence the changes of two solar energy resources; in addition, the annual global horizontal irradiation might decrease 8% by the shelter of the buildings surrounding the weather station. Considering the climate average state, the measured annual global horizontal irradiation in this paper is 8% lower than the average value in recent 30 years. This research is trying to explain the connections and differences between the ‘available resources’ of solar power generation project and ‘radiation elements’ in the meteorological field, so as to provide references for the solar power plant to carry out scientific and reasonable resources measuring and evaluating works.
  • Analysis of the Long-Term Vibration of Jianghuai Meiyu in Response to Solar Activity Factor
  • CHENG Guosheng;CANG Zhongya;DU Yajun;ZHU Xiaolu
  • 2015 Vol. 34 (2): 478-485.  DOI:10.7522/j.issn.1000-0534.2013.00183
  • Abstract ( ) PDF (4684KB) ( )
  • Take the solar activity as the external forcing factor of the earth's climate, use wavelet analysis and cross wavelet analysis method, to research the relationship between the sunspot numbers and Meiyu in Changjiang-Huaihe River region, and the west Pacific subtropical high indices. The results show that the correlation between solar activity and Meiyu exists difference between the north, show positive correlation, and the south, show negative correlation. That is to say, during the high sunspot number years, the rainfall in the north area of Changjiang-Huaihe River region would markedly increase, meanwhile, the south area would decrease. Furthermore, the positive and negative correlation remains unchanged in time series. In the south part, Meiyu precipitation and the sunspot numbers has stable resonance cycle in 11 years, and Meiyu lag the sunspot numbers for about 0.5~1 year. The western Pacific subtropical high indices and the sunspot numbers also have good correlation. During the high sunspot number years, the subtropical high is shifted more southward and stronger, and the square is larger, or vice versa. That means the process chain of solar activity-western Pacific subtropical high-Meiyu in Changjiang-Huaihe River region may be exist in the influence of solar activity on the climate.
  • The Quasi-Biweekly Oscillation of Daily Precipitation and Low-Frequency Circulation Characteristics over North China Plain in Summer
  • HAO Lisheng;XIANG Liang;ZHOU Xuwen
  • 2015 Vol. 34 (2): 486-493.  DOI:10.7522/j.issn.1000-0534.2014.00004
  • Abstract ( ) PDF (6989KB) ( )
  • Based on daily precipitation data over North China in summer and the NCEP/NCAR reanalysis atmospheric circulation data, by using of power spectral analysis, Butterworth band-pass filter and other related methods, the low-frequency characteristics of daily precipitation over North China in summer and the features of atmospheric low-frequency circulation evolutions are investigated. The results indicated that low-frequency characteristics of summer rainfall in North China is mainly quasi-biweekly oscillation. In making extended-range forecasts, in addition to focusing on 30-60 day atmospheric oscillation signal, we also should pay attention to quasi-biweekly atmospheric oscillation signal. On 500 hPa height field, atmospheric low-frequency circulation are closed high and low pressure systems, simple and easy to identify. On 850 hPa, low frequency current field changes are a bit more complicated, but they regularly change along with the high level low-frequency systems moving. On 500 hPa height field, north of 35°N, the low-frequency system moves eastward, sometimes extended from Okhotsk Sea to the west. However those south of 35°N appears to be from the Northwestern Pacific to northwest, and then moved to west. In North China, the summer precipitation is mainly directly affected by the low-frequency system from high latitudes, and those from low latitudes is difficult to directly affect the North China, but through changes of the southerly or northerly airstream they can effects water vapor transport or cold air activities to North China, thereby increasing or decreasing precipitation intensity in North China. When the low-frequency low pressure on 500 hPa within 40°N-60°N moving from the west to the east near North China, it will induce cyclone or shear line build on 850 hPa flow field, so obvious precipitation appears in North China. When the low frequency low pressure on 500 hPa moves eastward out of North China, on 850 hPa the low level flow field will switch to divergence field or a consistent northerly wind, precipitation process is finished. Precipitation occurs, the low-frequency circulation of high level and low level has a good matching, these can be applied to extended-range forecasts of summer rainfall over North China.
  • Precipitation Days Number Reconstruction by Using Tree Ring Width at the Southwest Edge of Junggar Basin
  • SHANG Huaming;WEI Wenshou;YUAN Yujiang;YU Shulong;ZHANG Ruibo;CHEN Feng;ZHANG Tongwen;QIN Li;FAN Zi'ang
  • 2015 Vol. 34 (2): 494-502.  DOI:10.7522/j.issn.1000-0534.2013.00180
  • Abstract ( ) PDF (3752KB) ( )
  • Tree ring width data from the four sampling sites which are located at the southwest edge of Junggar Basin are used to established width chronologies here. Correlation analysis between tree ring width index and climatic factors indicates that the radical growth is dominated by moisture conditions. Tree ring width index is significantly positively correlated with precipitation and precipitation day's number and negatively with temperature, in which, the correlation coefficient between tree ring width standardized indexes of HXC and precipitation days number from February to August is 0.724. Because of the large slope and shallow soil of the sampling sites, the storage capacity of soil is weak. Heavy rain in growth season make a great contribution to precipitation amount, which result that the correlation coefficient between tree ring width index and precipitation days number is higher than that between tree ring width index and total precipitation. The linear regression method was applied to build the transfer function between tree ring width standardized chronology and precipitation days number, and the explain variance reaches 52.4%. Cross validation indicates the reliability and stability of the function. The drought history document in Yili, Tacheng and western part of northern slope of Tianshan Mountains was consistent with the reconstructed precipitation days. It also testified that reconstructed series could capture the drought events in the study area. Regional comparison between the reconstructed precipitation days at southwest edge of Junggar Basin and the precipitation history of Tianshan Mountains area and south slope of Tianshan Mountains reveals the reconstructed series in this study is more consistent with that in Tianshan Mountains.
  • Statistical Characteristics and Variations of Thunderstorm Frequency in South China from 1980 to 2010
  • LI Sang;GONG Daoyi
  • 2015 Vol. 34 (2): 503-514.  DOI:10.7522/j.issn.1000-0534.2013.00171
  • Abstract ( ) PDF (5619KB) ( )
  • By using the observed data from 20 weather stations in South China, the characteristics of diurnal, seasonal, multi-year variations and relative atmospheric physical parameters and circulation fields were demonstrated. The results showed that the thunderstorm frequency peak from afternoon to the evening(9% at 12:00(UTC, hereafter the same)), and least in the morning(2% at 03:00). The higher thunderstorm frequency occurred in July and August (>35%), and the lower thunderstorm frequency in December and January(<1%). The annual and summer thunderstorm frequency decreased with a rate of -1%·(10a)-1 and -3.5%·(10a)-1 from 1980s to 21th century, yet after 21th century, it has a weak increasing trend. On the whole year, the ratio of thunderstorm precipitation and total precipitation was 48%, but in summer, the value was 64%. The variation of annual(summer) thunderstorm precipitation were relatively similar with annual(summer) thunderstorm frequency, their correlation coefficient was 0.46(0.71). In summer, accompany with the variation of thunderstorm frequency, the atmospheric circulation exhibits large-scale abnormally in east Asia. During higher thunderstorm frequency month, the western Pacific subtropical high was abnormally weaker. Meanwhile, there was abnormally ascending flows in the upper-middle troposphere over the South China. In addition, from the view of thermal instability, the abnormally high total tolals index and abnormally high convective available potential energy index has significant relationship with thunderstorm frequency, their correlation coefficients were 0.58 and 0.76. The thunderstorm frequency has statistical relevance with the surface temperature, however, it requires substantial investigation to make sure that whether it is a response of thunderstorms thermal and dynamical factor to the global climate change.
  • Mechanisms of an Elevated Thunderstorm Process over Southern China in the Early Spring of 2009
  • BAO Yuanyuan;KANG Zhiming;LI Lun;HUANG Xiaoyu
  • 2015 Vol. 34 (2): 515-525.  DOI:10.7522/j.issn.1000-0534.2013.00187
  • Abstract ( ) PDF (13009KB) ( )
  • An elevated thunderstorm process in southern China on 3 March 2009 is analyzed by using conventional observation, 6.7 μm satellite vapor images and TBB, lighting location and NCEP/NCAR reanalysis. The main synoptic systems include trough at middle-low levels, vortex and shear line, low-level jet, upper-level southern and northern western jet. The storm is triggered by low-level jet warm water vapor transportation and invading of high-level cold air. The boundary is dynamically stable for the existence of a thick cold pad. Convection instability appears between low-level warm and humid southwest jet and the cold and dry air at middle and high levels, and strengthened by the descending motion of the upper jet. A strong baro-clinic frontal zone is formed by the meeting of southwest jet and the cold and dry air northward at low-middle levels. The confluence of the southwest air descending branch and the cold and dry air from northern area causes northeast backflow which couples with the southwest winds above the boundary and forms a secondary front circulation, the ascending air at middle-upper levels couples with descending air of northern westerly jet causes another secondary positive circulation, the two northward titling secondary circulations are very favorable for tilting ascending movement. The warm advection and water vapor flux convergence of low-level jet, the strong divergence at the right entrance of upper-level western jet and the convergence along the southern upper-level jet are also contributable for meso-scale ascending movement. Thunders and hails appear usually at the dense band of θse, low-level jet speeds, water vapor flux and 300 hPa divergence. In addition, the environmental conditions as the thin humid layer, strong wind shear, low-level temperature inversion, ascending motion at -20~0℃ super cooled water layer are very advantageous to thunderstorms.
  • Simulation of Three-Dimensional Fractal Structure of Lightning in a Thunderstorm Model
  • GUO Fengxia;WANG Haoliang;SUN Jing;WU Xin;LIANG Mengxue
  • 2015 Vol. 34 (2): 534-545.  DOI:10.7522/j.issn.1000-0534.2013.00193
  • Abstract ( ) PDF (4477KB) ( )
  • The lightning parameterization proposed by Mansell has been improved in threshold value for initiation and the redistribution of induced charge on channel, and then it is introduced into a three-dimensional dynamic-electrification coupled model in order to improve the simulation capacity to electrical activity of the cloud model. The simulation of a thunderstorm storm during Severe Thunderstorm Electrification and Precipitation Study (STEPS) and an ideal thunderstorm in mid-latitude region reveal the lightning simulated by the model, which includes a new lightning parameterization, is in good agreement with the observed result in development character and geometric construction of discharge. And the simulation result shows: the type and polarity of flash is depend on the charge structure and the position of initiation point, negative CG flashes occur only when a lower positive charge center exists below the main negative charge region, and the initiation points of negative CG flash are all with a high negative potential. The sedimentation of induced charge on lightning channel will change the charge of hydrometeors nearby the channel, and it plays an important role in the formation of complex charge distribution. The CG flash and the IC flash channels simulated from the lightning model have the fractal feature with fractal dimension of 1.47 and 1.69 respectively. Sensitivity analysis to threshold value for initiation shows that the effect of the increase of threshold value for initiation is to increase the time required to produce the first flash and to decrease the total number of flash. The first flash time is earliest when the breakeven threshold is used. The ratio of IC flash and CG flash is lesser when use uniform breakdown threshold (100 kV, 150 kV, 200 kV) than breakeven threshold and it best closes the observation result when breakeven threshold is used.
  • Analyzing a Heavy Rainfall Process Based on Dual-Doppler Radar and Lightning Data
  • YANG Lili;YANG Yi;ZHANG Tinglong;WANG Ying
  • 2015 Vol. 34 (2): 546-555.  DOI:10.7522/j.issn.1000-0534.2014.00006
  • Abstract ( ) PDF (5700KB) ( )
  • In order tofurther understand the application of Doppler radar data in mesoscale weather system as well as thedynamical structureof precipitationsystem, a large-scaledand more accurate inversion resultis aimed to get, basing on the newly-proposed fuzzy logical algorithm of cloud classification and the two-step variational method which is applied to dual-Doppler radar. The data come from Dual-Doppler Radar's (S-band) observation in Hefei and Fuyang, Anhui province. A heavy rainfall processoccurred in Anhui Province on 7~10 June in 2010 is analyzed by utilizing vertical accumulative total liquid water content(VIL), rainfalland distribution of lightning. The results show that this persistentrainfall is associated with the wind fieldswhichcantains a convergence in lower layers and a divergence in higher layers, a cyclonic wind rotation and a wind shear line. This rainfall process which is based on stratiformis shown to be a hybridcumuluscloudprecipitation. Besides, the stratiform lightning is few during this rainfall and mainly focuses on the negative ground flashes. The heavy rain occurred 20 minutes or so after lightning. The value of VIL in this heavy rainfall is small, which is less than 3 kg·m-2. There are strong relationships among cloudclassification, the area of rain, VIL and Radar's echo.
  • Radar Partial Shielding Region Identification Algorithm Based on the Probability Characteristics of Radar Echoes
  • GOU Yabin;LIU Liping;LI Ruiyi;DU Muyun;DUAN Yiping
  • 2015 Vol. 34 (2): 556-567.  DOI:10.7522/j.issn.1000-0534.2013.00192
  • Abstract ( ) PDF (11233KB) ( )
  • Partial blockage is one of the most important error sources of radar observation. A new shielding region identification algorithm without any dependence on the terrain information with high resolution is proposed. The algorithm first computes the probability of every grid's probability of emerging specified reflectivity exceeding a threshold which is defined as Z threshold only through checking the continuous operational radar observation data without using any sample database established manually, and then selects adequate probability threshold which is defined as C threshold to delineate the region with different shielding characters. Applying the algorithm with the continuous operational observation dataset during the period between May and October in 2012 at Jinahua Quhou and Shangrao, the completely shielding region, partially shielding region and no shielding region on 3 km CAPPI are derived separately. With the comparison of the observation data at April 29 in 2013 in the overlapping region on the 3 km CAPPI between Jinhua, Quzhou, Shangrao, Hangzhou and Huangshan, the validation of the identification results of the three radar sites are tested and the parameter sensibility of the Z and C threshold is analyzed, too. The multi-radar mosaic algorithm is optimized applying the partial shielding region results of the radar sites above to enhance the quality of multi-mosaic. The results show that the shielding region with different characters can be identified effectively by selecting adequate Z and C threshold; the selection of the Z and C threshold is the key and moderate Z threshold is beneficial to the further selection of the C threshold; the partial shielding effects can be easily eliminated based on the identification results and the data quality of multi-radar mosaic can be enhanced effectively based on the optimized multi-radar mosaic algorithm.
  • Construction and Application of Extreme Rainstorm Probability Prediction Based on Radar Echo Base Data
  • WANG Jianhong;HUANG Wei;WANG Qun;MIAO Chunsheng;ZHANG Zhigang;XU Liangmou
  • 2015 Vol. 34 (2): 575-585.  DOI:10.7522/j.issn.1000-0534.2014.00132
  • Abstract ( ) PDF (4960KB) ( )
  • Based on a statistical relation between local Radar echo intensity base data and local heavy rainfall, to find the upstream echo areas that will move to the local raining region in next hour by the regional Lucas-Kanade optical flow method. Meanwhile to analyze the echo features at every scan surface, so that to learn the raining system stretching altitude. By analysis of the temporal and spatial characteristics of dynamic echo areas in current hour with information at scan surfaces every 10 minutes, to build the relation between Radar echo intensity features and local rainfall, then applied it on a predicting method of improved rainfall extreme probability, thus to construct forecast and warning index of extreme rainfall return period in next hour. The results will provide the technique support and professional reference for emergency schemes and strategy and tactics. The whole scheme is based on the Doppler radar echo intensity base data at scanning surfaces and the hourly precipitation data of Jianhu weather station during June, July, August in 2006-2011. Jianhu station is within the scanning area of the radar located at Yancheng . The echo dynamic upstream of the local heavy rainfall system is determined by the regional Lucas-Kanade optical flow method. The statistical probability correlation is calculated between echo intensity classification and precipitation series in day and night by Peirson III and Generalized Pareto Distribution methods. The probability characteristics of return period of graded extreme rainfall and the local extreme rainfall under the echo types are also calculated, then the statistic index is constructed between the radar echo dynamic features including the trend of evolution and the probability of local extreme rainfall in next hour, the index correlation and its test all get to 70%. The index can predict the probabilities of different grade extreme rainfall in return period at local place. It is an optimization method of radar dynamic statistics for nowcasting and warning of the extreme rainstorm in next hour.
  • Statistical Characteristics and Automatic Detection of the Gust Front in Radar Reflectivity Data
  • XU Fen;YANG Ji;XIA Wenmei;ZHOU Honggen
  • 2015 Vol. 34 (2): 586-595.  DOI:10.7522/j.issn.1000-0534.2014.00005
  • Abstract ( ) PDF (6934KB) ( )
  • The variation features, the relationship between the moving speed and the arc length, and the overall and partial characteristics in the radar reflectivity data images of the gust front along the Yangtze River in Jiangsu are analyzed using Nanjing CINRAD data combined with the AWS wind data from 2009 to 2012. The radar reflectivity data distribution features of the three kinds of NBE are also analyzed in detail. An echo flatness calculation method is designed to analyze the similarities of the three NBEs in quantity. It is also found that the radial bands belong to the gust front echo can be identified by the wave width, the number of the wave peak,the peak threshold, and the bilateral gradient waveform from the radial wave characteristics in this article. The automatic detection of the gust front echo is achieved by combining the echo flatness testing method with the gust front radial waveform detection algorithm based on the radar reflectivity data preprocessing method. Finally, the effect results of the detection algorithm show that the detection accuracy rate is about 87% or more in the independent gust front whose average reflectivity data > 5 dBZ, and the detection accuracy rate is about 89% or more in the blended gust front whose average reflectivity data > 10 dBZ. The identification rate of the weak gust front is still low.

NewsDownloadMore+More+

DynamicsVideo InformationMore+More+

Links E-journal More+ More+

Official Wechat

QQ Group Chat

The system is designed and developed by Beijing magtec Technology Development Co., Ltd. with technical support: support@magtech.com.cn