Plateau Meteorology

Current Issue

28 August 2014, Volume 33 Issue 4   
  • Connections between the Dominant Modes of Westerly over the Upstream Region of Qinghai-Xizang Plateau and the Regional Precipitation of China and NAO in Winter
  • YU Jingjing;LIU Yimin;LI Xiaofeng
  • 2014 Vol. 33 (4): 877-886.  DOI:10.7522/j.issn.1000-0534.2013.00108
  • Abstract ( ) PDF (9317KB) ( )
  • Based on the ERA40 reanalysis dataset and the observed precipitation data from Chinese stations, two major modes of wintertime westerly from Northern Atlantic to the upstream region of Qinghai-Xizang Plateau (QXP) were investigated through empirical orthogonal function (EOF) and their connections with the wintertime regional precipitation of China and the Northern Atlantic Oscillation (NAO). It reveals that the associated time series of the first two major modes of wintertime westerly (EOF1 and EOF2) over the upstream area of QXP are significantly correlated with the NAO, while their connections with the regional wintertime precipitation of China are totally different. The EOF1 is evidently correlated with the precipitation over the south-west of the QXP as well as the precipitation over the middle and lower reaches of Yangtze River. However, the EOF2 delineates no significant correlation with the wintertime precipitation over China. Further analysis suggests that the anomalous westerly in the low altitudes associated with EOF1 can reach to the upstream of QXP in the mid-south Asia-Europe continent, increases the creeping flow over the south-west of the QXP, enhances the precipitation over the south-west of the QXP, and vice versa. Due to the topography blocking, the detouring flow around the south side of QXP becomes stronger, converges with the anomalous south-easterly from the south side of anomalous west-Pacific subtropical high over the middle-lower reaches of Yangtze River, enhances the ascending movement, increases the anomalous precipitation over the middle and lower reaches of Yangtze River, and vice versa. While, the relationship between the EOF2 and the wintertime precipitation over China is not significant due to the anomalous zonal wind component in the low latitudes associated with EOF2 does not extend eastward. From this study, the extension of the westerly over the upstream region of QXP plays an important role in affecting the wintertime precipitation over China, and the westerly wave train associated with EOF1 in westerly is an important medium for NAO to influence the wintertime precipitation over China.
  • Transport of Dust Aerosols from Troposphere to Stratosphere over Qinghai-Xizang Plateau
  • YANG Qin;TIAN Wenshou;LONG Xiao;CHEN Lei;ZHANG Jie;HUANG Qian;TIAN Hongying
  • 2014 Vol. 33 (4): 887-899.  DOI:10.7522/j.issn.1000-0534.2013.00095
  • Abstract ( ) PDF (10860KB) ( )
  • Using the mesoscale model WRF coupled with a dust module together with the NCEP reanalysis data and satellite observations, the characteristics of the vertical transport of dust aerosols from the near surface to the upper troposphere and the lower stratosphere are investigated through a case study and the effect of the Qinghai-Xizang Plateau on the stratosphere and troposphere mass exchanges is also discussed. The analysis reveals that deep convection can inject dust aerosols into the stratosphere. However, the aerosol concentrations in the lower stratosphere are largely affected by locations of dust sources and convection intensity as well as the precipitation. When there is no overshooting convection, vertical motions can not transport aerosols directly into the lower stratosphere. However, small scale diffusion and mixing processes can slowly transport aerosols in the upper troposphere into the lower stratosphere using a few hours of time. Under conditions of no system precipitation, the strong convective activities in summer over the Qinghai-Xizang Plateau make it a favorable location for aerosols in the troposphere entering into the lower stratosphere. The stratospheric air intrusion has a large impact on time variation and spatial distribution of aerosol concentration in the upper troposphere when there are no strong dust emissions near the surface.
  • Composite Characteristics of the Abnormal Circulation in May between Extreme Drought Years and Rainy Years of Yunnan
  • ZHENG Jianmeng;ZHANG Wancheng;MA Tao;ZHOU Jianqin
  • 2014 Vol. 33 (4): 916-924.  DOI:10.7522/j.issn.1000-0534.2013.00029
  • Abstract ( ) PDF (5615KB) ( )
  • Using the NCEP/NCAR reanalysis data from 1961 to 2010, the discrepancies of atmospheric circulation between the extreme-drought years and above-normal rainfall years in May of Yunnan are analyzed. The results show that the characteristics of atmospheric circulation in May of above-normal rainfall years are different from those of extreme-drought years in both low and high latitude. The extreme-drought-year circulation shows two-trough-one-ridge pattern in mid-high latitude on 500 hPa, with the corresponding anomaly field of geopotential height presenting ‘-+-’ pattern and the westerlies moving northward are later than normal years; rather straight flows cover mid-low latitude and large-scale negative anomalies of sea-level pressure cover Asia; cold air activities that might influent Yunnan are weak. On the contrary, it exhibits two-ridge-one-trough pattern in above-normal rainfall years, with the ‘-+-’ pattern of the anomaly field over the mid- and high-latitude and the westerlies moving northern are earlier. The trough over the Ural maintain and Caspian Sea tends to lead cold air intruding China, positive anomaly center of sea-level pressure locating at the eastern part of the Qinghai-Xizang Plateau, which makes cold air activities strong. At the low latitude, the west Pacific Subtropical High (WPSH) is strong and shifts westward, so that the northward and eastward advancement of the tropical westerlies is inhibited and the onset of summer monsoon over the Bay of Bengal and Indo-China peninsula is late and weak, vice versa. The south Asian High in above-normal years is strong and big and locates westward compared to that in extreme-drought years. There is anomaly large-scale and deep subsidence flow at low-latitude in the northern hemisphere(including Yunnan) in extreme-drought years, which is contrary to that in above-normal years. In above-normal rainfall years, the southwest water vapor transport is dominant over Yunnan province and the water vapor converge is comparatively strong than normal, with moisture content above normal and and the shift between dry season and wet season is early, the WPSH shifting eastwards. In extreme-drought years, the WPSH locates westward and southward, the west water vapor transport and water vapor divergence covers Yunnan, with moisture content below normal, and the shift between dry season and wet season is later. The correlation coefficient of Asian summer monsoon index WYI and the precipitation in May is significant positive, especially it is related to the extreme rainfall events.
  • Impact of SST in Northern Pacific Ocean on Flood Season Precipitation in Guizhou
  • WANG Fen;CAO Jie;TANG Haopeng;GU Xiaoping;YANG Ruowen
  • 2014 Vol. 33 (4): 925-936.  DOI:10.7522/j.issn.1000-0534.2013.00090
  • Abstract ( ) PDF (9958KB) ( )
  • Based on the precipitation of summer at 83 stations in Guizhou from 1979 to 2011 and the mean monthly reanalysis SST data,the relationship between summer precipitation and the SST in the Pacific Ocean are investigated in terms of SVD. The results are as follows:(1) The key SST region which influencing precipitation in Guizhou from California cold current to Kuroshio from previous summer to spring,the relationship between SST in spring and precipitation in Guizou is not close,the relationship between the previous SST and precipitation in the middle-east of Guizhou is closer. (2) Composite analysis results are as follows: In flood year,the distribution of Northern Pacific Ocean SST from west-north to east-south is ‘-+-’,but in drought year the distribution of Northern Pacific Ocean SST from west-north to east-south is ‘-+-’,the relationship between rainfall rich and El Nino events isn't close,but the relationship between rainfall deficit and La Nina event is close. (3) The possible mechanism that the influence of previous Northern Pacific Ocean SST on precipitation in Guizhou:Northern Pacific Ocean SST rising can cause wave train spreading to the middle Western Pacific Ocean,which making the Western Pacific subtropical high moving to west,benefiting to rainfall；the influence of Northern Pacific Ocean SST dropping was not as good as those caused by SST rising,it can cause Western Pacific subtropical high moving to east,not benefiting to rainfall.
  • Validation of Summer Surface Air Temperature and Precipitation Simulation over Heihe River Basin
  • XU Jianwei;GAO Yanhong
  • 2014 Vol. 33 (4): 937-946.  DOI:10.7522/j.issn.1000-0534.2013.00149
  • Abstract ( ) PDF (4403KB) ( )
  • The 10-year simulation (1999-2008) from June to August is conducted using the regional climate model WRFV3.0 driven by the NCEP/DOE reanalysis data. The model results are validated over the Heihe River Baisn and its surroundings. The assessment of advantages and disadvantages are objectively given for reginal climate simulation in the surface air temperature and precipitation over the complex terrain. The results show that, compared to the coarser resolution reanalysis data, the high resolution regional climate simulation more precisely presents the distribution characteristics of the surface air temperature and precipitation in complex terrain area, which shows a dominant impact of complex topography on the spatial distribution of the surface air temperature and precipitation. Quantitative assessments by BSS indicator show an obvious improvement of the surface air temperature simulation at almost all of observation stations, which provides data support for the spatial distribution and quantity of the surface air temperature for complex mountain area with no observations. The improvements in the precipitation simulation is not as high as the surface air temperature, only at half of all stations are closer to the observation than the reanalysis. An overestimation in the precipitation exists in the southestern Qilian Mountain. It might be related to too strong orographic lifting on windward slope in the high resolution or the representation of observation location in a regional grid cell.
  • Enhanced Cold-Season Warming in Arid and Semi-Arid Regions of China
  • RAN Jinjiang;JI Mingxia;HUANG Jianping;GUAN Xiaodan;QI Yulei;HE Yongli
  • 2014 Vol. 33 (4): 947-956.  DOI:10.7522/j.issn.1000-0534.2013.00065
  • Abstract ( ) PDF (4301KB) ( )
  • Using 55-year monthly homogenization surface air temperature at 713 stations from the National Climate Center of China, the seasonal and regional characteristics of warming in China have been investigated. In particular, the atmospheric circulation before and after cold-season warming over arid and semi-arid region have been analyzed. The interannual variation shows that warming began in the mid 1980s, and increased fast in the 1990s, then gradually slowed down in the early 21st century. The annual average warming trend in semi-arid and arid areas is 1.7 times that in humid and semi-humid areas. As for seasonal characteristics, the warming trend during cold-season is 1.9 times that of warm-season. The warming trend is comparatively fast in arid and semi-arid areas with more than 0.3℃·(10a)-1 and particularly notable over the Qinghai-Xizang Plateau, middle inner Mongolia, northeast and north China. However, the warming trend in humid and semi-humid areas is relatively slow, in which the central and west regions is slower than east coast. The cold season temperature in arid and semi-arid areas experienced a significantly abrupt change from cold to warm in 1986. A composite analysis is used here to investigate the response of the atmospheric circulation. The weakening of arctic polar vortex, eastern Asia trough, shallow trough in Europe and Siberian High, and anomaly cyclonic circulation as well as abnormal southeast wind in eastern China all could induce the warming in semi-arid and arid areas.
  • Analysis of Atmospheric Turbulence Characteristics on the Upper and Lower Levels in Urban Canopy Layer
  • CHEN Jiwei;ZUO Hongchao;MA Kaiming
  • 2014 Vol. 33 (4): 967-976.  DOI:10.7522/j.issn.1000-0534.2013.00059
  • Abstract ( ) PDF (4345KB) ( )
  • Using observational data of atmospheric turbulence by three eddy covariance systems (EC) which were installed on the upper and lower levels in urban canopy layer at Yuzhong town in Lanzhou city, the turbulent fluxes of difference land surfaces and the turbulent kinetic energy characteristics of different wind direction were analyzed. After that, the spectra of velocity of the minimum turbulent kinetic energy in minimum turbulent kinetic energy at range of wind directions and the maximum turbulent kinetic energy in maximum turbulent kinetic energy at range of wind directions were studied on the upper and lower levels in urban canopy layer. Finally, the applicability of local similarity theory on the upper and lower levels in urban canopy layer was tested. The results show that: (1) Observational sensible heat flux and friction velocity on urban underlying surface which is constituted by cement, masonry on the upper level in urban canopy layer and urban lawn underlying surface on the lower level in urban canopy layer are relatively close, the differences of observational latent heat flux and CO2 flux are significant in the daytime. (2) Generally speaking, turbulent kinetic energy on the upper level in urban canopy layer is greater than the lower level in urban canopy layer. On the upper level in urban canopy layer, turbulent kinetic energy is greater with a more open upwind, but turbulent kinetic energy is greater with a street mouth on the lower level in urban canopy layer. (3) The eddy scale on the upper level in urban canopy layer is greater than the lower level in urban canopy layer. Spectra of velocity for small scale eddies in the inertial subrange fundamentally accord the -2/3 power relationship, and they are approximate isotropic. However, spectra of velocity for large scale eddies do not accord the -2/3 power relationship, and they are anisotropy. (4) For unstable stratification, the dimensionless variance of velocity change with stability on the upper and lower levels in urban canopy layer approximate accord the 1/3 power relationship of local similarity, while stable stratification are not. The dimensionless variance of temperature, humidity and CO2 concentration on the upper and lower levels in urban canopy layer do not accord the -1/3 power relationship of local similarity under whatsoever stratification. (5) Nearly neutral stratification, the dimensionless variance of velocity on the upper and lower levels in urban canopy layer at u, v, w direction are 3.52, 3.03, 1.49 and 2.62, 2.22, 1.50.
  • Analysis of Cloud Vertical Structure over Western China Based on Active Satellite Data
  • YE Peilong;WANG Tianhe;SHANG Kezheng;Lü Qiaoyi;WANG Shigong;LI Jingxin
  • 2014 Vol. 33 (4): 977-987.  DOI:10.7522/j.issn.1000-0534.2013.00158
  • Abstract ( ) PDF (818KB) ( )
  • Cloud vertical structure over western China and its neighborhood was analyzed using the 2B-CLDCLASS-LIDAR data of CloudSat/CALIPSO during the period from March 2007 to February 2008. The results show that the occurrence frequency of single-layer cloud is greater than multi-layer cloud over the whole region, multi-layer cloud occurrence frequency for Tianshan Mountains and the middle-west of Qilian Mountains is higher than the surrounding area throughout the year. Cloud top and base heights of all clouds change apparently with the seasons and regions, and the seasonal variation of cloud top height is more significant than cloud base height. The cloud height of each layer has no remarkable seasonal variation in Northwest region, however, the significantly distinct in Qinghai-Xizang Plateau. The average of cloud thickness is greater than 2 km for single-layer cloud and ranges from 1 km to 2 km for double-layer and three-layer clouds. The vertical distance of double-layer clouds is greater than other consecutive layers, and the seasonal variation of consecutive layers in Qinghai-Xizang Plateau is more significant than Northwest region. The occurrence frequency of ice phase cloud in summer over the south slope of Qinghai-Xizang Plateau is greater than other seasons. However, more ice clouds over other regions are present in winter and spring. Apart from the south slope of Qinghai-Xizang Plateau, the occurrence frequency of ice cloud in winter is greater than 80% for other regions.
  • Study of Multiple Perturb Tropical Cyclone Ensemble Forecast
  • TAN Yan;CHEN Baode
  • 2014 Vol. 33 (4): 1012-1021.  DOI:10.7522/j.issn.1000-0534.2013.00068
  • Abstract ( ) PDF (3210KB) ( )
  • The tropical cyclone ensemble forecast experiments are based on the GRAPES-TCM model, the Lagged Average Forecasting(LAF) and the Breeding Growth Mode(BGM) methods are combined to used for making the initial perturbations, which have been devided into three part to considered: the introduction of initial perturbation, the scaling down of environment region and the vortex region respecctively. The verification technique has been applied on the real time forecsts of 16 tropcial cyclones in 2008, including the ensemble mean, foreacast error, spread analysis and the relative skill score. The results indicate that: The average errors of ensemble mean track forecast are 231.48 km(24 h), 386.4 km(48 h) and 632.05 km(72 h). Both the error of ensemble mean and the ensemble spread are incresed with the forecast leading time. On the contrary, the ratio of these two part is decresed. Most of the samples are well good obey the correlationship between the forecast error and ensemble spread, but there is still a little sample indicate the small spread with large error situation and the large spread with small error situation. The percentage of realative skill score which ensemble forecast performed better or the same is 66.2%, especailly in the later time of model forecas. Futhermore, more attention should be paid on the situation when the ensemble system has different senarios, forecaster or user should aware of the uncertainty of the forecast and the likehood of the occurence, as well as the resluts for the event with small probability.
  • Analysis of Heavy Rain to Rainstorm Event on the West of the Gansu Corridor
  • LI Jianglin;YU Ye;WANG Baojian;RONG Yuliang
  • 2014 Vol. 33 (4): 1034-1044.  DOI:10.7522/j.issn.1000-0534.2013.00070
  • Abstract ( ) PDF (6617KB) ( )
  • A heavy rain to rainstorm event on the west of Gansu Corridor in 2011 was analyzed, using observated precipitation data, NCEP/NCAR reanalysis data and simulated results. The results show that: The cause of heavy rain was geopotential height which be high in north and low in south, and the convergence of airflow of warm and moist from south and cold air from north on the west of Gansu Corridor. So much water vapor was provided by three vapor sources for this heavy rain process. Before the rainstorm, the atmospheric energy is accumulated, then the energy began to release when heavy rain occurred, and finally to the end of the rainstorm, the energy release over. The entire layer was updraft over the precipitation area when the heavy rain occurred. The strong updraft not only made the warm and moist air convergence and uplift but also released potential heat and heated atmosphere during the ascent, then formed positive feedback and made the vertical movement enhance. The Q-vector was analyzed. It is showed that distribution of Q-vector was in accordance with the precipitation area. There was no good correlation between the intensity of the Q-vector convergence and the intensity of rainstorm, but center value of Q-vector convergence less than -3×10-15 hPa-1·s-3 if only there is precipitation. So Q-vector convergence zone can be better forecast rainstorm and large rainfall districts, but not able to forecast rainstorm intensity. Finally, through numerical simulation, the actual precipitation value center was coincidence with simulated precipitation center. The movement and development of atmosphere circulation was analyzed by high space and time resolution numerical model results. Simulation of the MCAPE and radar reflectivity factor and other physic index has good instruction significance to this precipitation process.
  • Study of Different Methods for Simulating the Impact of Urban Surface on Meteorological Elements in Beijing in Winter
  • CHENG Chen;WANG Xiaoyun;MIAO Shiguang;WANG Ying
  • 2014 Vol. 33 (4): 1045-1056.  DOI:10.7522/j.issn.1000-0534.2013.00062
  • Abstract ( ) PDF (5190KB) ( )
  • This paper focuses on two different methods for simulating the impact of urban surface development on monthly averaged meteorological elements in Beijing winter. After analyzing the major weather process and distribution characteristics of month mean meteorological elements in Beijing in January 2012, using WRF/BEP modeling system, the month mean 10 m wind speed, 2 m air temperature and 2 m humidity were simulated by the cases-averaged method and the mean-field method. Then the results of two methods under new and old land use conditions are evaluated against the observation. At last, the analysis of affect caused by urban development and the comparison of two different methods for reflecting this affect are carried out. The results show that: Both methods have good simulation results. Hite rate of air temperature and specific humidity is higher than 70% and the wind speed is more than 60%. The spatial distribution of the characteristics of month-averaged meteorological elements and diurnal variation simulated by two methods are consistent. Urbanization slightly decreases the specific humidity and wind speed in Beijing but increases the air temperature. And the impact of urbanization simulated by two approaches also have the same trend. The cases-averaged method not only reflects the average impact of urban development but also gets the extreme impact of a month. The mean-field method may not get the extreme impact conditions and precipitation simulation.
  • Research of Synoptic Model and Physical Quantity Parameter of Thunder-Gust Winds Impact Area
  • YANG Xiaoxia;HU Shunqi;JIANG Peng;WAN Mingbo;WANG Wenqing;LIU Guicai;GAO Huijun;PU Zhangxu;HUA Wenli
  • 2014 Vol. 33 (4): 1057-1068.  DOI:10.7522/j.issn.1000-0534.2013.00057
  • Abstract ( ) PDF (4582KB) ( )
  • The thunder-gust winds in Shandong Province from 1971 to 2008 were statistical analysed and the climate feature was studied. The circulation system and the occurring areas of 93 times regional thunder-gust winds from 2000 to 2008 were researched. The results show that: Four kinds of thunder-gust winds synoptic models were built mainly by 500 hPa influence system: the southerly air flow in the front of trough model, the northerly air flow in the rear of trough model, the west edge of subtropical high model and the front of the lateral trough for revolving to south model. The physical quantity parameters in 93 times thunder-gust wind processed were ferreted out and analyzed. The thunder-gust winds from June to August accounts 63.1% and most in July. The northwesterly winds were the most wind direction in winds directions of thunder-gust winds. But the southwesterly winds were the most in July. The 8~9 scale wind power of thunder-gust winds take 80.8%. In the spring and autumn the thunder-gust winds produced mostly in southerly air flow in the front of trough. The thunder-gust winds in the northerly air flow in the rear of trough model occurred mainly in June and August. The thunder-gust winds in west edge of subtropical high were mainly in July. In the subtropical high west edge model, the convection available potential energy (CAPE) was most high and the 0~6 km wind vertical shear was the minimum. In the trough rear model, wind vertical shear was the maximum and CAPE was higher. In the trough front model, CAPE and wind vertical shear was all larger. In the lateral trough model CAPE and wind vertical shear were all small. The trough front model was the most in northwest and middle part of Shandong. The trough rear model was the most in south of Shandong. The lateral trough model influence mainly north and peninsula of Shandong and the subtropical high west edge model influence mainly northwest and middle part of Shandong. In the inland in spring atmosphere humidity and CAPE was small, the difference in temperature between high and low level, 0~6 km wind vertical shear and gale index were all large. In summer, low levels in atmosphere are warm and wet and CAPE was high, but 0~6 km wind vertical shear and gale index was all smaller. The temperature and humidity condition in south of Shandong was higher than in northwest and middle part of Shandong. In the coast area of peninsula in Shandong, the low level atmosphere was wet and cold and CAPE was lower and gale index smaller. But K index, the θse difference between high and low level and 0~6 km wind vertical shear were large. The month change of temperature and wet in low level atmosphere was small.
  • Analysis of Jet Stream Characteristic during the Snowstorm Process in North China
  • CHEN Xuezhen;MU Jianli;ZHAO Guixiang;YANG Dong
  • 2014 Vol. 33 (4): 1069-1075.  DOI:10.7522/j.issn.1000-0534.2013.00205
  • Abstract ( ) PDF (5093KB) ( )
  • The wide snowstorm in the middle and south of north China on 10-11 November 2009 was analyzed using the NCEP reanalysis data and the general automatic meteorological observing stations data. The results indicate that: (1)The snowstorm occurred in the weather system of upper trough on 500 hPa, low vortex and shear line, and Hetao front occlusion on 700 hPa. (2)The snowstorm located in the right back of the entrance of polar front jet stream and the front left of the subtropical jet stream on 200 hPa, the front left of Southwest jet stream on 700 hPa, and the front right of the easterly jet stream on 925 hPa and 850 hPa. (3)The snowstorm was caused by the jet streams at different altitudes. The low-level jet was formed and developed under the coupling of upper-level jet. The easy-coupling area is where positive vorticity advection is increasing when the altitude increases, in the right of the entrance area of the upper-level jet or the left of the exit area of upper-level jet. (4)Southwest jet stream has provided adequate water vapor for the snowstorm and formed the high-humidity area, which made and maintained the convection instability layer in the snowstorm area. (5)Southwest jet stream and Northerly jet stream formed convergence zone over the snowstorm area, which set up the raising movement of the weather scale for the snowstorm. (6)The secondary circulation caused by the coupling of upper-level and low-level jet increased the raising movement, triggered the release of unstable energy, and increased the intensity and duration of the snowstorm. (7)Easterlies on 925 hPa formed dry and cold mattress in the boundary layer of the snowstorm area, which helped the southerly warm and humid air to climb and strengthen dynamic lifting effect.
  • Formation Mechanism and Analysis of Radar Observation of a Heavy Rainstorm Accompanied by Hail that Back of Trough
  • ZHANG Yiping;YU Xiaoding;SUN Jinglan;LIANG Junping;LI Zhou
  • 2014 Vol. 33 (4): 1093-1104.  DOI:10.7522/j.issn.1000-0534.2012.00200
  • Abstract ( ) PDF (13329KB) ( )
  • Using the conventional observation, new generation weather radar, AWS, NCEP data, the weather formation mechanism of a local heavy rainstorm accompanied by repeatedly hail under the northwest flow situation and the structure of mesoscale convective system were detailed analysed. The results showed that: (1)The local heavy rainstorm accompanied by hail occurred in the situation of northwest airflow and atmospheric stratification was very unstable. The value of CAPE at 14:00(Beijing time, hereafter the same) was significantly increased compared to that at 08:00,which provided instability energy for heavy rainstorm and hail; The large value center of water vapor content in the lower-troposphere provided adequate moisture conditions for newborn monomers that generated continued by forward propagation and backword propagation. Local heating of the ground was uneven, the ground temperature reached to the threshold of the convective temperature in the afternoon which made the ground warm air mass free up, and resulted in the initial convective echoes, when it reached thermal convection conditions, the ground mesoscale convergence line and dew-point front for local heavy rainstorm and accompanied by many times hail weather had strengthening and triggering effect. Mesoscale low pressure on the ground was the important reason for convergence maintained and water vapor concentration. (2)On the chart of radar, in the process of the initial echo generated in Zhoukou nearby, strengthened and moved to south-east direction, γ-scale convective cells constantly generated at the rear and right rear of that, the new generated cells experienced the phase of cumulus clouds formed and strengthened, matured and merged, weaked and dissipated. Its direction of propagation and movement closed to opposite, which made the strong echoes near Zhoukou were the state of quasi-stationary dynamic equilibrium and constantly persistent. Subsequently, new meso-γ-scale convective cells were constantly generated in the front side of the band echo that nearly east-west from Xuchang to Taikang, And it linked to the convective cells of backward spread near Zhoukou, and arrayed into northwest-southeast linear multi-cells echo bands. Forward propagation and backword propagation respectively experienced back weakened and front weakened stages. And the middle echo near Zhoukou developed the most productive. The meso-γ-scale convective cells in the multi-cell structure of two forms of forward propagation and back propagation formed a remarkable ‘train effect’, which made local heavy rainstorm with repeatedly hail weather happened in Zhoukou and Xihua. The charts of average radial velocity contained mesoscale vortex, and the northwest-southeast linear convection echo bands had the structural features of convergence, divergence and convergence alternated in the middle and lower layers. The upper layer was opposite with the middle and lower layers. The formation and evolution of linear thunderstorm system were larger related with that downdraft uplifted warm and humid air of severe thunderstorm. The convective cells were generated in the low-level that appearred convergence, and the upper level that appearred divergence.
  • Analysis on Global Distribution Characteristics of Cloud Microphysical and Optical Properties Based on the CloudSat Data
  • YANG Bingyun;ZHANG Hua;PENG Jie;WANG Zhili;JING Xianwen
  • 2014 Vol. 33 (4): 1105-1118.  DOI:10.7522/j.issn.1000-0534.2013.00026
  • Abstract ( ) PDF (8339KB) ( )
  • The global distribution and seasonal variation of the cloud physical characteristics (including the cloud liquid and ice water content, liquid and ice water path, the effective radius, etc.) and cloud optical parameters(the cloud optical depth, etc.) were analyzed by the CloudSat data from January 2007 to December 2010. The results show that: The distribution of ice water path is mainly over the North America, South America, Africa, Australia and the South Asia, as well as the Pacific, Atlantic and Indian Ocean, with the highest values reaching 600 g·m-2 or more. In the vertical direction, the high values of ice water content are located near the height of 8 km over the equatorial regions and from 4 to 8 km over the middle latitude regions. The high values of liquid water path are located over the Pacific Ocean, the Indian Ocean and the middle and low latitudes of Atlantic. In the vertical direction, the value of liquid water content decreases with height. The ice effective radius reaches its maximum of over 200 μm near the surface at high latitudes, while having a maximum of over 80 μm at 4~8 km in the equatorial region and at 2~4 km in the mid-latitude. The liquid effective radius maximizes under 1 km, with a value of over 12 μm. The total cloud optical depth is below 40 around the globe, with largest values located in the vast middle and high latitudes as well as the oceans off the west coasts of low-latitude continents. Large cloud optical depths are concentrated below the boundary layer. The distribution of the cloud optical depth is closely linked to cloud amount, which is in good spatial accordance with the former, and also to cloud water content, and cloud effective radius. The latest analysis of satellite observation data for the climate models, and improvement of the cloud optical parameterizations and cloud microphysical schemes of the models are provided.
  • Effect Evaluation of Precipitation Enhancement and Hail Suppression Programs in Beijing Region
  • LI Hongyu;JI Lei;ZHOU Wei;LUO Bu
  • 2014 Vol. 33 (4): 1119-1130.  DOI:10.7522/j.issn.1000-0534.2013.00027
  • Abstract ( ) PDF (5188KB) ( )
  • Seeding effects investigation or evaluation is one of the most important parts of weather modification. It also acts as a crucial standard of assessing the scientific and technological level of weather modification activities, and plays an extremely important role in promoting the development of the subject. Combining the weather modification activities in Beijing region in recent years, the seeding effects of precipitation enhancement and the economic benefits of hail suppression from 2004 to 2010 was assessed, based on the classical method of historical regional regression and the agricultural disaster data collected around the whole region. The results show that: (1) In the assessment period from May to September, the average ratio of precipitation enhancement efficiency tends to maintains about 20% following with the sample numbers accumulated year by year. In the target area selected, cloud seeding totally increased the precipitation amount by 417.8 mm during the 7 years. The statistical seeding effect is very manifest in a high significance level. (2) The estimated average annual economy benefit of hail suppression is nearly 248 million yuan. The average cost-benefit ratio is about 1:16. The highest and the lowest economy benefit appeared in 2009 and 2005, with a corresponding cost-benefit ratio of 1:27 and 1:6, respectively. The methods studied for seeding effects evaluation and the results help to strengthen the scientific and technological base of the exploitation and utilization of cloud water resource in Beijing and its neighboring region, and firmly supporting the construction of local disaster prevention and mitigation projects as well.
  • Numerical Calculation of Lightning Return Stroke Electromagnetic Field Coupling Voltages on Overhead Line
  • LIU Xiaodong;ZHANG Qilin;FENG Xuyu;YANG Xinpei;LIU Jiao;LI Chen
  • 2014 Vol. 33 (4): 1146-1153.  DOI:10.7522/j.issn.1000-0534.2013.00089
  • Abstract ( ) PDF (2572KB) ( )
  • In order to simulate the surrounding electromagnetic field of lightning return stroke channel on overhead line, firstly, the characteristics of the surrounding electromagnetic field of lightning return stroke channel were analyzed by using the modified transmission line model with exponential current decay with height. And then the lightning induced over-voltage of the overhead line was calculated by using the procedure based on Agrawal field line coupling model. Moreover, the accuracy of the program was verified by comparison between its calculation results and the practical experimental results, the calculation results were close to the experimental data. The calculation results showed that, the vertical and horizontal components of the electric field were both to be taken into account in the coupling mechanism. The peak value and the maximum front steepness of the induced voltages were affected by the peak value and the maximum time derivative of the channel-base current, while the amplitude of the induced overvoltage was only affected by the current amplitude. At close distance from the lightning channel (as 50 m), the lightning induced over-voltage of the overhead line was inversely related to the return stroke velocity. With the increase of the observation distance, the maximum time derivative of the lightning induced over-voltage was increased, but the peak value decreased. In addition, the induced voltage would increase with increasing height of the overhead line and also increase with increasing the grounding impedance, and the induced voltage was unrelated to the cable length and diameter changes.
  • Mesoscale Structure of Torrential Rain Tropical Cyclone Over Liaodong Peninsula and the Effect of Complicated Topography
  • LIANG Jun;LI Ying;ZHANG Shengjun;ZHANG Caifeng;LIU Xiaochu
  • 2014 Vol. 33 (4): 1154-1163.  DOI:10.7522/j.issn.1000-0534.2012.00202
  • Abstract ( ) PDF (11329KB) ( )
  • Using the NCAR nonhydrostatic mesoscale model MM5, the precipitation associated with typhoon Winnie(9711) turning to Bohai Sea after landfall and topography forcing was simulated and its meso-scale structures was analyzed based on temperature of Block Body (TBB), disturbed streamline field and vertical velocity. The distributions of TBB display a clear mesoscale structure of convective cloud. The storm rainfall over Liaodong peninsula is closely related to mesoscale convec- tive system and topographic effect. The sensitivity experiments of topographic effect on the changes of precipitation and structure of typhoon Winnie show that: (1)The local vertical circulations in north and east of Liaodong peninsula are favorable for formation and development of mesoscale convective cloud masses. (2) Topography plays important roles in precipitation increment. The rainfall over the upwind slopes of the mountains and the precipitation cell intensity are increased with the topographic effect. Contrarily, the precipitation cell intensity is decreased without topographic effect. Heavy rainfall areas are corresponding to convergence zone. (3) There exists significant increase of easterly wind velocity in the lower layer. Mesoscale cyclonic vortex systems are continuously generated and transported to the south of Liaodong peninsula which is favorable to sustain tropical cyclone (TC) intensity and induce heavy precipitation. (4) The circulation of typhoon Winnie can be partly changed as the result of topography forcing. The local circulation of typhoon will be enhanced when cyclonic circulation initiated by topography forcing, and the rainfall will be increased accordingly, and vice versa.

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