Vol.19, NO.1, 2008

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Transport Condition of Surface Layer Under Haze Weather over the Pearl River Delta
Wu Dui, Liao Guoliang, Deng Xuejiao, Bi Xueyan, Tan Haobo, Li Fei, Jiang Chenglin, Xia Dong, Fan Shaojia
2008, 19(1): 1-9.
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In recent years, the aerosol pollution over the Pearl River Delta (PRD) region is getting worse, resulting in haze weather with visibility decreasing and air quality deterioration. The surface layer transport condition such as airflow is closely related to the dilution and diffusion of atmospheric pollutants. By using statistic method under a set standard based on dataset from 466 Guangdong provincial surface automatic weather stations, Guangzhou operational weather stations, visibility data of PRD's atmospheric component observational network, and PM10 data of PRD's urban environmental observational network, typical haze weather and cleaning weather processes are analyzed in 2004 and 2005. The surface wind and its effect on heavy haze and cleaning weather processes are analyzed using Vector Sum Technique. The zonal circulation over Eastern Asia in favorite haze season in 2004 is stronger than that in 2005. The year with weak zonal circulation has marked exchange between the north and the south, allowing much cold air to cross Nanling Mountain to reach PRD, the accompanying strong wind is favor for the diffusion of the pollutants. In the year with strong zonal circulation cold air has little chance to cross Nanling Mountain to reach PRD so that the pollutants accumulate much easily. The haze weather over PRD has the regional features with the most likely occurrences in dry season and the least in rainy season. The haze processes often happen from October to next April, while cleaning processes often occur in the seasons when typhoon or cold air is prone to occurrence. Compared to 2004, the frequency of still wind is lower and the wind speed in dry season is larger in 2005, those factors are not favor for the form of haze weather. Analysis using Vector Sum Technique shows that regional haze process is closely related to the regional still wind process by which formation of airflow stagnation area is led to, while cleaning process is related to strong advection transport.
An Effective Method to Solve the Streamfunction and Velocity Potential from a Wind Field in a Limited Area
Zhu Zongshen, Zhu Guofu
2008, 19(1): 10-18.
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The streamfunction and the velocity potential are variables commonly used in the scheme design for atmospheric data assimilation and initial field analysis of numeric weather prediction.They can be obtained in partitioning a wind field by solving the Poisson equations of the vorticity and the divergence of the horizontal components of the wind field. Difference method is usually adopted in a limited area; nevertheless, an obvious departure exits between the original wind field and the reconstructed one from the sum of the streamfunction and velocity potential components in the vicinity of the boundary of the limited area.An effective scheme is designed to solve by difference method the streamfunction and velocity potential of a wind field in an Arakawa-A grid limited area, based on analyzing detailedly the approach and characteristics in the process of the solution. The key techniques in the scheme include the following. Firstly, the solution domain is expanded by two rings by extrapolating linearly the wind field to improve a calculation of boundary values. Secondly, consistent difference schemes are introduced in the solution procedure to enhance the solution precision. And finally only two to three iterations are imposed on incremental corrections to get a satisfactorily accurate result. Experiments are carried out with real wind data and their results indicate that the streamfunction and velocity potential of a wind field can be acquired by the scheme and the reconstructed wind field is reproduced with a very high precision.
Comparative Investigation on Meiyu Parameters in Different Subregions of the Changjiang-Huaihe Valley
Min Shen, Qian Yongfu
2008, 19(1): 19-27.
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Using the rotated empirical orthogonal function (REOF) analysis of the averaged June to July rainfall field, the Meiyu amount and the Meiyu onset data (MOD) during the years from 1957 to 2003, the Changjiang-Huaihe Valley is divided objectively into three subregions, namely, the center (CEN), the southeast (SE) and the northwest (NW). The time sequence of the Meiyu onset and ending dates is SE, CEN and NW. It is consistent with the temporal change of geographical location of the rain band.The periodic variations of Meiyu parameters are analyzed using the binomial coefficient weighted average method and the Morlet wave analysis.Result shows that different subregions have different periodic variations. The long-term trend of the Meiyu parameters in the NW is obviously different from that in the CEN and the SE. The Meiyu duration and the Meiyu amount in the CEN and the SE are both increasing, the Meiyu ending dates of the above two regions are delaying. The opposite case is found in the NW. The MOD in the SE is advancing, while there is no apparent trend in the CEN and the SE. The atmospheric circulation patterns related to the Meiyu abnormalities of the three subregions are analyzed by using the NCEP monthly data of height fields during the years from 1957 to 2003. The results point out that the composite differences of the 500 hPa height field in the Northern Hemisphere between the more and the less Meiyu years of the three subregions are all of the wavelike structures with positive and negative values in alternation. The distribution of the positive and negative difference centers in the SE subregion is similar to that of the CEN, but with a more eastward and southward shift than the CEN. The wavelike distribution pattern in the NW subregion is opposite to that in the CEN, and it is also opposite to that in the SE at low latitudes and in the regions along the North Pacific, the North America and the North Atlantic.The distribution patterns of the positive and negative composite difference centers in the years with the earlier and the later MOD in the SE and the NW are both similar to that in the CEN. However, the position in the SE has an eastward deflection and that in the NW has a westward shift. The distribution pattern of NW is opposite to that of the SE.
Turbulent Characteristic Parameter of Different Strong Wind Samples
Li Yachun, Wu Jingang, Xie Zhiqing, Jiao Shengming, Liu Cong
2008, 19(1): 28-34.
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Abstract:

In structure wind engineering, the accuracy of wind turbulent characteristic parameter is extremely important to the calculation of wind load of large structures. In the actual wind observation and analysis, the gale data are generally used to analyze the turbulent parameter characteristics, and more attentions are caught by the strong wind such as typhoon in coastal area. The calculation of wind turbulent characteristic parameter may be disturbed by an excessive attention given to the strong wind data. Moreover, the precision in the calculation of wind load may decline. In order to comprehend the impact of different strong wind samples upon the calculation of turbulent characteristic parameter values, an analysis and a comparison between two groups of wind speed samples are made. In the experiment, the CSAT3D three dimensional supersonic anemometer is used to observe the instantaneous wind speed from June to September in 2005 on the no rthern coast of Jiaozhou Gulf. About 605 hours effective wind observation data or 3631 subsamples are obtained in the experiment and divided into 10-min time step. The subsamples are divided into two groups according to different wind speed. One is called continual strong wind sample, in which the average wind speed during 10 minutes of each subsample is more than 8 m/s and the duration is more than 30 minutes. The other is called relative strong wind sample, in which the average wind speed of the subsamples is not always more than 8 m/s. The turbulent characteristic parameters of the two wind sample groups are calculated and a comparison between the two groups is made accordingly. It shows that though the average wind speed of continual strong breeze samples is about 37.6% more than that of relative strong wind samples, the average turbulent intensity of the relative strong breeze is 18%—23.5% smaller than that of the comparative strong wind samples, and the former average gust factor is more than 10%smaller than the latter, where as the former average friction velocity is 50% more than the latter. These results show that the value of wind turbulent characteristic parameter doesn't match the wind velocity well. Sometimes the wind velocity is small but its turbulent characteristic parameter value is big and vice versa. So, different wind velocity sample or different statistical methods may affect the calculation results of wind turbulent characteristic parameter.The calculation of wind turbulent characteristic parameter may be affected by an excessive attention given to the strong wind data. Moreover, the precision in the calculation of wind load may decline.
Vulnerability Analysis, Evaluation and Vulnerability Zoning of Lightning Disaster in Beijing
Guo Hu, Xiong Yajun
2008, 19(1): 35-40.
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Abstract:
Based on the lightning disasters, thunderstorm days, economic and population data of eighteen counties in Beijing during 1995—2005, vulnerability analysis, evaluation and vulnerability zoning of lightning disaster are made. The analysis on spatial distribution of annual mean thunderstorm days in Beijing shows that there are more thunderstorms in the north than those in the south, and more thunderstorms in the west than those in the east. The thunderstorm activities in Miyun district are the most, whose annual thunderstorm are more than thirty-five days. The least thunderstorm activities exit in Tongzhou district, whose thunderstorm days are less than twenty-five.The study on spatial distribution of lightning disaster frequency indicates that more lightning disasters occur in the city zone and near the suburb than in the remote suburb.There are more dwellers in the city zone and near the suburb than in the remote suburb, and regarding GDP (gross domestic product) the former is more than the latter. It suggests that the thunderstorm activity is not the only cause for lightning disaster in Beijing. The lightning disaster might also relate with the population density and the economy in the disaster area.The vulnerability of lightning disaster might include two factors at least :the criticality of the disaster and the frangibility of the disaster area. Therefore, four indices are selected to evaluate the vulnerability of lightning disaster in Beijing. They are annual mean thunderstorm days (M), lightning disaster frequency (P), economic vulnerability module (D) and vital vulnerability module (L).M is used as a measurement of nature thunderstorm activity in Beijing. P is historical lightning disaster frequency.D and L are used to scale the economic and population characters of disaster areas respectively. Firstly, the four indices are classified into four degrees with a given value as follows:the extreme high degree is 1.0, the high degree is 0.8, the intermediate degree is 0.5, and the low degree is 0.2. Secondly, the comprehensive vulnerability evaluation index of lightning disaster is obtained by adding the degree values of the four indices. Then the comprehensive vulnerability evaluation index for the eighteen counties is also graded as four degrees, which are defined as the maximal damageable area, the high damageable area, the medium damageable area and the low damageable area. Finally, vulnerability zoning of the lightning disaster is obtained based on the vulnerability degree values of the eighteen counties in Beijing. The result shows that the city zone and Fengtai district belong to the maximal damageable area. Haidian district, Chaoyang district, Changping district and Shijinshan district belong to the high damageable area. Yanqing district, Daxing district, Mentougou district and Pinggu district belong to the low damageable area.The rest districts belong to the medium damageable area. Scientific basis might be provided for the planning of regional prevention and reduction of lightning disaster in Beijing.
Climatological Characteristics of Summertime Moisture Budget over the Southeast Part of Tibetan Plateau with Their Impacts
Shi Xiaoying, Shi Xiaohui
2008, 19(1): 41-46.
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Climatological characteristics of water vapor budget over the southeast part of Tibetan Plateau and their impacts on ambient areas in summer are investigated based on NCEP/NCAR reanalysis data for the period from 1961 to 2005. The result shows that the southeast part of Tibetan Plateau is a moisture sink, under the seasonal average of summer condition, the water vapor net budget is 39.9×106 kg/s. The establishment and advance of Asian summer monsoon play an important role in the incoming water vapor of the southeast part of Tibetan Plateau, and the outgoing moisture is closely associated with the advance and retreat of rain belt of East China. The southeast part of Tibetan Plateau, as the moisture transport channel to the east of Northwest China and mid-lower reaches of the Yangtze River, plays a great role in the moisture budget around it. The southeast part of Tibetan Plateau, as a transferring station, is one of the key factors to the flooding anom alies of precipitation in mid-lower reaches of the Yangtze River and the drought anomalies in North China. By power spectrum analysis, it is found that there is quasi-biennial oscillation in the interannual variations of moisture budgets at east/north boundary over the southeast part of Tibetan Plateau and summer precipitation of mid-lower reaches of the Yang tze River/eastern part of Northwest China. An in-phase inter-annual variation are shown by the moisture budgets at east boundary over the southeast part of Tibetan Plateau and the summer precipitation of mid-lower reaches of the Yangtze River, and the same to moisture budgets at north boundary and the summer precipitation of eastern part of Northwest China.It shows that the quasi-biennial oscillation of moisture budgets at east boundary is closely association with that of precipitation in mid-lower reaches of the Yangtze River, and the quasi-biennial oscillation of moisture budgets at north boundary is closely association with that of precipitation of the eastern part of Northwest China.
The Checking and Removing of the Autocorrelation in Climatic Time Series
Tao Jie, Zhang Xueqin, Tao Jianqiang, Shen Qiangming
2008, 19(1): 47-52.
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It is well known that global climate is warming over the past decades. And there are great uncertainties for the assessment of warming magnitude caused by meteorological data itself, different methods adopted, hypothesis of future emission scenario, and other factors as well. Ordinary least squares (OLS) is usually used to analyze the trend of climate change by fitting linear regression to the time series of meteorological observation. And the hypothesis of independence should be met by the random error of the time series, otherwise autocorrelation exists in the time series and uncertainties will appear in the results.Unfortunately research on the autocorrelation of climate change is weak. So taking the temperature observation (including mean temperature, maximum temperature and minimum temperature) of Pinghu meteorological station in Zhejiang Province during 1954—2004 as an example, the autocorrelation possibly existing in time series and its influence on the trend analysis of climate change are studied. And the method of Durbin-Watson test is introduced to check whether the autocorrelation exists or not in the time series during the utilization of OLS in the trend analysis of temperature change. And if so, the method of Cochrane-Orcutt is adopted to remove the autocorrelation. Analysis indicates that the warming trend is magnified by the existence of autocorrelation in Pinghu temperature time series, and the confidence level of warming trend is improperly increased, by which uncertainties of clim ate change is added. In a word, it is indispensable to check and remove the autocorrelation of climatic time series, and much more work should be done further to test the autocorrelation and its possible impacts on the uncertainties of warming forecasting at regional and global scale.
Observation Study on the Temperature and Wind Profiles over the Pearl River Delta in Autumn
Li Minghua, Fan Shaojia, Wang Baomin, Wu Dui, Zhu Wei, Liu Ji, Yu Guanming, Bao Ruoyu, Fan Qi
2008, 19(1): 53-60.
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Abstract:
For the purpose of study on the characteristics of the boundary layer and its effects on air pollution in the Pearl River Delta, the comparison observation based on balloon sounding is conducted by Sun Yat-Sen University in Qingyuan, Panyu and Xinken of the Pearl River Delta in October, 2004. The temperature and wind profiles of the boundary layer over the Pearl River Delta in autumn are studied on the observation data.It is found that the temperature lapse rate is small while the occurrence frequency of the temperature inversion is high and the intensity is low over the Pearl River Delta in October, 2004. The surface temperature inversion occurs earlier over the city cluster than over the Pearl River estuary and the average intensity over the city cluster doubles that over the Pearl River estuary while the low-lever temperature inversion frequency over the city cluster is lower than that over the Pearl River estuary. The relatively low temperature and the high-speed sea breeze postpone the occurrence time of the surface temperature inversion and increase the occurrence frequency of the low-lever temperature inversion over the Pearl River estuary.It is also found that the Pearl River Delta is influenced by several kinds of local circulations and the wind profiles of the boundary layer are complex in October, 2004. The prevailing wind direction is northeast, and in the daytime the wind directions of the three sites are consistently in the northeast while in the nighttime there are obvious differences in wind direction between the city cluster and the non-city cluster, which is that the wind direction of the non-city cluster (Qinyuan and Xinken) is in the northeast and that of the city cluster is in the northwest. The city cluster is markedly characterized by local circulations and heat island circulation is frequently observed at night; the Pearl River estuary is markedly characterized by gradient wind and sea breeze circulation is frequently observed at night, and the occurrence frequency of 20-hour sea breeze is 51.8%; the local circulations of both the city cluster and the Pearl River estuary are observed under the same meteorological background of low-speed system wind and basically on the same dates.
Visibility Variations in the Pearl River Delta of China During the Period of 1954—2004
Huang Jian, Wu Dui, Huang Minhui, Li Fei, Bi Xueyan, Tan Haobo, Deng Xuejiao
2008, 19(1): 61-70.
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Atmospheric visibility is one of the good indicators of atmospheric fine particle pollution.To well understand the evolvement course of atmospheric environment of the Pearl River Delta (PRD), the temporal variation of visibility is examined by using three statistical methods, namely, cumulative percentiles, Ridit analysis and frequency of smoke/haze days, based on the historical visibility data of five geographically dispersed cities (Shenzhen, Gaoyao, Guangzhou, Taishan and Huiyang) from 1954 to 2004. The characteristics of visibility variation and its possible cause are investigated preliminarily.The temporal variation shows that there is a remarkable decline in visibility for all cities of PRD in the 51 years studied. At the end of 1950s visibility in some cities, e.g., Guangzhou and Gaoyao, evolves from low to high. The increasing consumption of coal and decreasing usage of trees seems to be responsible for this trend. In 1960s, visibility is generally high and experienced very good air quality in PRD.The visibility degradation for PRD is at early 1970s, which is prior to that of some other areas in China. Between the early 1980s and early 1990s, a stage of high-speed economic growth, the visibility gets worse. After the middle of 1990s the decline trends of visibility eventually become moderate. In the course of visibility variation of PRD, it should be pointed out that the visibility trend for PRD in the 51 years studied actually descends all the same even though the visibility declining rate slows down after the middle of 1990s. From 1960s to the period of 2001—2004, the declines of the average visibility are about 62.1%, 55.7%, 50.4%, 50.3% and 47.2%, in Shenzhen, Gaoyao, Guangzhou, Taishan and Huiyang, respectively, and the average extinction coefficient of atmosphere for the period of 2001—2004 is about 2.6, 2.3, 2.0, 2.0 and 1.9 times of that of 1960s. In recent years, Shenzhen has the lowest visibility in PRD, followed in turn by Gaoyao, Guangzhou, Taishan and Huiyang. The trend of visibility in PRD is mostly in accordance with local economic development and population growth in this period. It is also found that Gaoyao, a city located at the western part of PRD, has a lower visibility in comparison with the eastern city of PRD. It shows that the regional transport of atmospheric pollutants has a significant effect on the visibility over the down wind area. Furthermore, the relationship of visibility trends with atmospheric pollutant emissions in recent years is also discussed. It is found that visibility in PRD has not been improved substantively while the direct emission of particles has markedly decreased in the past few years since a series of prevention and control projects of atmospheric pollutants are implemented. The likely cause is that gas-phase aerosol precursor species, especially SO2 and NOx, have not been under control.
Assessment of Meteorologic Condition Effects and Dynamic Yield Forecasting Based on Rice Growth Model
Shuai Xiqiang, Wang Shili, Ma Yuping, Li Yingchun
2008, 19(1): 71-81.
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Using daily meteorological data and observation on rice phenology and biomass for the thirty-one agrometeorological stations of the double cropping rice region in the middle Yangtze River Valley from 1981 to 2004, based on adjusting, adaptation and validating for rice growth Model ORYZA2000, the double cropping rice region in the middle Yangtze River Valley is divided into seven areas for the phenological parameters in the model according to the phenological development rate, combined with climate, landform and genetic characteristics of rice. The application of ORYZA2000 in the middle Yangtze River Valley is implemented. Using the regionalized parameter of the crop, the simulation effect of rice phenology and biomass in early rice and late rice is simulated and tested in the growth model. The average errors of samples of fitting verification of anthesis and autumn of early rice and late rice are 3—6 days. And the ones of extrapolated samples are 3—5 days. The average relative errors of samples of fitting verification of the total aboveground biomass and weights of storage organs of autumn of early rice are 12.8% and 20.1% respectively. And ones of extrapolated samples are 10.1% and 19.9%. The average relative errors of samples of fitting verification of the total aboveground biomass and weights of storage organs of autumn of late rice are 8.5% and 6.0%. And ones of extrapolated samples are 2.9% and 3.5%. Test of assessment of meteorological condition effects in different years is carried out using the regionalization of the crop growth model. Using the relative value of annual change of the advance of development and biomass comparing with average ones in the recent three years and the previous year, evaluation of the agrometeorological condition is made (e.g., the phenology is retardation or quickens, and the biomass increases or decreases). The changes of the development stage and influence on biomass and yield of early rice in low temperature in 2002 and late rice in high temperature in 2003 are simulated by the model. The simulation results and assessments are consistent with actual conditions. Several correlation models between simulated dry matter weight of rice at various development stages (panicle initiation, flowering, kernel milky maturity, maturity) and relatively climatic yield for each station are developed, and then rice yield could be forecasted combining the prediction of yield trend. To calculate correlation coefficient significance test of the area models by t test, 23% early rice and 27% late rice yield forecasting by the models at various development stages pass significance level of 0.10, others pass significance level of 0.05, 0.01 or 0.001. With the advance development, significance level of some models raises 0.10 to 0.05. The average relative errors of rice yield forecasting at various development stages for all stations based on rice growth model are 4.8%—6.1%, the results are satisfied.
MCS Census and Modification of MCS Definition Based on Geostationary Satellite Infrared Imagery
Fei Zengping, Zheng Yongguang, Zhang Yan, Wang Hongqing
2008, 19(1): 82-90.
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MCSs (mesoscale convective systems) are significant weather systems causing heavy rain and other severe weather events during the warm season, which are very difficult to forecast in operation. Geostationary satellite infrared imagery with higher spatial and temporal resolution can provide much available information for MCS surveillance and forecasting. Since Maddox defined the MCCs (mesoscale convective complexes) based on enhanced satellite IR imagery, there are many detailed studies on the MCSs, but these studies revealed that Maddox's MCC definition is too strict. Then the MCS definition based on satellite imagery is always modified. In recent years, some studies classified MCS to MαCS (meso-α convective system) and MβCS (meso-β convective system). But because the definition of MCS based on satellite imagery is not uniform, it is very hard to compare various results of MCS census. First, the progress of MCS census research is reviewed, and the smallest horizontal scale of MβCS (meso-β convective system) is modified as that the diameter of cold cloud continuous area of TBB value≤-32 ℃ is more than 20 km. Secondly, based on the new definition of MβCS, the mesoscale convective systems are investigated over the Huaihe River Basin utilizing GOES-9 satellite IR imagery during June 21—July 22 2003, the results reveal that there are 10 MαCSs and 24 MβCSs. Comparing the definition of MβCS with that in the study of Ma et al, there are 7 MβCSs which can not satisfy the MβCS definition of Ma et al, and 6 of them lead to heavy rain over Huaihe River Basin. It shows that the new MβCS definition can better reveal the relationship between heavy rain and MCSs over the Huaihe River Basion. Finally, the other three typical MβCSs which produced heavy rainfall over Beijing are analyzed, Shalan Town of Heilongjiang Province, and Shanghai. The diameter of these three MβCSs is about 20—150 km, so they satisfy the new MβCS definition, but do not satisfy the MβCS definition of Ma et al. The results reveal that the new MβCS definition is very helpful to investigate and forecast the MCSs producing severe weather events in China.
Observation Study on Properties of Cloud and Fog in Ice Accretion Areas
Luo Ning, Wen Jifen, Zhao Cai, Tang Lei
2008, 19(1): 91-95.
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Ice accretion on conductors from freezing rain or glaze is a common meteorological disaster in Guizhou mountainous areas, causing serious damages with the warped wire, the collapsed pole and/or tower and broken circuit. For example, the severe ice accretion in 1984 in Guizhou brings the blackout in the local electricity transport network. The security of electricity transport is threatened by ice accretion on conductors. The glaze forms from freezing rain on conductors near surface with the air temperature between 0 ℃ and 6 ℃ in Guizhou. It is found in experiment that ice frozen between 0 ℃ and 6 ℃ is difficult to fall off with its great density, which is a main cause for Guizhou's ice accretion with the extreme danger. In Liupanshui of western Guizhou the site especially for observation of ice accretion on conductors is built by national power company. In this site and two other ice accretion areas in northern and central Guizhou the field observations are conducted with the elevations of 2128 m, 1780 m and 1659 m respectively. The growth rate of conductor ice accretion is closely associated with the cloud-and fog-conditions. The major observation factors include cloud droplet size distribution, water content in cloud and fog, air temperature, wind direction, wind speed, long and short diameters of ice accretion on conductors. The cloud droplets and water content in cloud and fog are colleted with the method of integration suction. The ice accretion is measured in the specific stands in both east-west and north-south directions. In three observation areas there are no significant differences for cloud droplets on both the concentration of 140—312 droplets/cm3 and the average diameters with arithmetic mean diameter of 7.5 μm, cube root diameter of 11.3 μm and median volume diameter of 20 μm; although the number concentration of cloud droplets with the diameter bigger than 14 μg are 12.5% of the total concentration, water content contributed by them is as high as 78% due to the dominant contribution to water content considering the high collision efficient of these large cloud droplets on conductors, the distribution of large droplets is a key factor involving ice accretion; the water content with the average value of 0.20 g·m-3 in cloud and fog decreases with air temperature from 0 ℃ to -6 ℃; more ice accretes on conductors of north-south than east-west direction caused by prevailing northeast wind in the surface levels during the stationary front period in winter; the growth rate of ice accretion is proportional to the water content in cloud and fog and the wind speed, especially of more obvious direct ratio with the wind speed over 3 m·s-1.
Variations Trend of Soil Temperature at Deep Layers in Lhasa from 1961 to 2005
Du Jun, Hu Jun, Yang Yong, La Ba, Lu Hongya
2008, 19(1): 96-100.
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Abstract:
Using the data of monthly mean soil temperatures at 0.8 m, 1.6 m and 3.2 m in Lhasa from 1961 to 2005, the linear trend, climatic anomalous and climate abrupt of deep soil temperature during recent 45 years are analyzed by using of linear trend analysis, accumulated variance and signal noise ratio methods.In terms of linear trend, the annual mean soil temperatures at 0.8 m and 1.6 m display a significant increasing trend in Lhasa in the past 45 years, and an increase of (0.54—0.62 ℃)/10a, especially at 0.8 m is indicated. During recent 35 years (1971—2005), the maximum rising range of mean soil temperature at 0.8 m and 1.6 m is in spring, the rate of rising is (0.84—0.69 ℃)/10a, its minimum is in autumn. But the maximum rising range of mean soil temperature at 3.2 m is in summer, the rate of rising is 0.71 ℃/10a, and its minimum is in winter. Comparing to the air temperature, the rising range of soil temperature is bigger in the same period. In addition, the rising range of the mean soil temperature at deep layer increases, specifically at 0.8 m and 1.6 m.There is an obvious increase tendency of inter-decadal variations of the annual mean soil temperatures at 0.8 m and 1.6 m from the 1960s to the 1990s. The seasonal mean soil temperatures at 0.8 m and 1.6 m are low from the 1960s to the 1970s, obviously in spring, and they are still low slightly in the most seasons of the 1980s. But there is positive anomaly of the mean soil temperature in all the seasons of the 1990s, specifically in spring and summer.The inter-decadal variations of the seasonal mean soil temperature at 3.2 m show an obvious increase trend from the 1970s to the 1990s. There is negative anomaly of the mean soil temperature at 3.2 m in all the seasons of the 1970s, especially in summer. To the contrary in the 1990s, there is positive anomaly of mean soil temperature in all seasons. It is also much evident in summer.The annual mean soil temperatures at 0.8 m, 1.6 m and 3.2 m are anomalous warm in 1999, whereas anomalous cold year occurs only in 1963 at 1.6 m.In summer, the anomalous warm of the mean soil temperature at deep layer takes place in 1999. In winter, the soil temperatures at 0.8 m and 1.6 m are anomalous cold in years in 1960s, and the mean soil temperatures at 3.2 m are anomalous warm in 1999, 2002—2005.Except for no abrupt change at 3.2 m in winter, the seasonal and annual mean soil temperatures at deep layer have abrupt changes, and it occurs in the 1980s. In summer and autumn there is a sudden change in 1986, in spring and winter there is a climate abrupt in 1983.
Convective Storm Life Cycle Parameters Derived from Radar Reflectivity Data
Zhang Jiaguo, Wan Yufa, Wang Jue
2008, 19(1): 101-105.
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Weather radar is one of the important tools of severe storm warning. It is important to depict the density and evolution of whole storm using weather radar reflectivity data for storm identification and tracking. Therefore, based on 3-demension CHINRAD/SA radar reflectivity, cell gravity potential energy (CEPE), a new physical parameter, is defined, which is relevant to storm life cycle. Its expression is derived and characteristic is studied. In addition, the vertical reflectivity profile of the cell is built and analyzed. The results show that the density of whole storm cell can be compactly and objectively described by the CEPE, and the cell evolvement trend is reflected by its change. If using CEPE to describe cell life cycle, there are two basic processes during the entire life cycle of the cell, namely developing process and weakening process. In spite of the overview single-peak distribution pattern, sometimes there is a little pulse in the pattern which occurs mostly at developing phase. At mature phase, the value of the CEPE is marked different among different cell types. The largest is for supper cell, the second is for multi cell, and the least is for ordinary cell. Accordingly, cell type can be distinguished by CEPE to some extent. The characteristics of vertical reflectivity profile (VPR) of the storm cell are different from initiative to dissipated phases, which help to identify the evolution of the storm cell. But these differences can not be opened out to 150 km and in 30 km, as the effects of the earth curvature and radar blind area respectively. Comparing these two methods, it is obvious that the VPR is not as concise and objective as the CEPE.
Ice Runs of the Yellow River and Its Defense in Inner Mongolia
Pan Jinjun, Bai Meilan
2008, 19(1): 106-110.
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Ice run is a kind of nature disaster mainly induced by meteorological factors. The regions along the Yellow River bank in Inner Mongolia are frequently influenced by the disaster and it may result in losses of properties and menace to human safety. The disaster's characters, forming mechanism, occurrence prone period, tendency prediction as well as hazard estimation are studied and analyzed. Based on these analyses, some conclusions are obtained as follow. The ice run is a kind of special natural disasters resulted from both the climatic and geographical factors in specific area; the ice run occurs only in ice river's opening and closing periods which are about one month long respectively in spring and autumn season; with the global warming trend, the ice river opening time is becoming earlier and the closing time is being postponed gradually, so the disaster's hazards will increase; according to both the disaster particularity and its present defending situation, some countermeasures are proposed to be taken such as strengthening the infrastructure project construction, and the disaster forecasting and monitoring system construction as well as paying attention to enhance the public prevention awareness etc.
Intra-seasonal Inhomogeneity of Summer Extreme Precipitation in the East Part of Northwest China
Yang Jinhu, Jiang Zhihong, Wang Pengxiang, Bai Huzhi
2008, 19(1): 111-115.
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Abstract:
Based on 33 weather stations daily precipitation datasets in the east of Northwest China from 1960 to 2004, the extreme precipitation threshold of different stations are defined by centesimal value method, by introducing extreme precipitation concentration degree and period which reflects time distribution feature. Intra-seasonal inhomogeneity characteristics of extreme precipitation are analyzed by the new parameter in the east of Northwest China. The result show that the summer extreme precipitation shows increasing trend in the east of Northwest China. From long term tendency, it is found that the summer extreme precipitation displays clear inter-annual variability since 1980s. Moreover, it shows distinct inter-decadal change in the recent 45 years. It is proved that inconspicuous spatial difference is reflected by extreme precipitation concentration degree and period. It is also found that there is high relativity between summer extreme precipitation concentration degree and concentration period and summer extreme precipitation in the east of Northwest China. If the summer extreme precipitation concentration degree leans to high and concentration period leans to early date, the extreme precipitation leans to more amount, vice versa. It is proved that summer extreme precipitation concentration degree and period exhibit remarkable inter-decadal period vibration in recent 45 years. Despite summer total precipitation showing decreasing trend in the east of Northwest China, the summer extreme precipitation displays increasing trend, therefore it shows that there exist negative correlation between summer extreme precipitation, summer extreme precipitation concentration period and east Asian summer monsoon, but there is positive correlation between summer extreme precipitation concentration degree and east Asian summer monsoon, moreover its relativity is more remarkable between extreme precipitation.
Meteorological Information Display and Query System Based on WebGIS
Liu Xulin, Zhao Wenfang, Liu Guohong
2008, 19(1): 116-122.
[FullText HTML] (3826) [PDF 1481KB](5181)
Abstract:
With the rapid development of detection technique in meteorology, more and more real-time detection data are obtained in Beijing Municipal Meteorological Bureau, but the integrated display system for all kinds of detection data is relatively left behind. Considering the situation, a meteorological information display and query system is developed, free software Mapserver and PostgreSQL are used in the system.Mapserver is an open source development platform which multi-format geographic data are supported on Internet. MapServer is not a full-featured WebGIS system. Instead, MapServer is good at rendering geographic data like maps, images, and vector data on the web. Beyond browsing GIS data, MapServer allows you to create "geographic image maps" that are, maps that can direct users to the content. Many kinds of geographic format data are supported, interface for second development in many language is provided, and it can be used in many operation systems. MapFile is a kind of file format, in which the color and style of map elements are defined. Map elements are managed and organized by MapFile in Mapserver. What users need to do is just to setup up Mapserver and configure Web server correctly and create their own MapFile, then their WebGIS system is built successfully. PostgreSQL is also an open source Database software. Usually, PostgreSQL is used to manage their data, such as GIS database.It is very easy to build a WebGIS system by using Mapserver and PostgreSQL. In Beijing Municipal Meteorological Bureau, Linux system is chosen as WebGIS operation system. First, Mapserver and PostgreSQL need to be installed under Linux system. In addition, some configurations need be done to make sure they can work together. Second, detection data database has to be built. Database is used to store meteorological observation data and at the same time makes query more efficient. The third step is to handle station data which is very important. Station data are converted into geographic format data, which are points displayed on maps. Last is to create MapFile according to the file format of MapFile. In the system, real-time data including temperature, precipitation, humidity and other observation data are showed on maps directly, and the dynamic search and query for data are realized. For example, different time is input by users, different observation data of different time are displayed on maps. Especially the temperature and precipitation contours can also be displayed in the system. In addition, wind vector is displayed on map as map symbol which is created by wind observation data. In conclusion, multi-data integrated display is realized in the system. Multi-data information can be known for forecasters directly from it, with which immediate, efficient and scientific assistant decision support are supplied.
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