Vol.20, NO.4, 2009

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Display Method:
Establishment and Assessment of the Grid Air Temperature Data Sets in China for the Past 57 Years
Zhang Qiang, Ruan Xin, Xiong Anyuan
2009, 20(4): 385-393.
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Temperature data from meteorological stations in China for the past 57 years are interpolated by introducing digital elevation model(DEM) and taking the edge effect of interpolations into consideration on the basis of the ordinary Kriging method. Using this method, the daily, monthly and annual mean data sets of the grid-based temperature in China with the resolution of 1°latitude by 1°longitude are obtained. The results of the grid data sets quality assessment show that DEM has an apparent effect on the spatial structure of temperatures and plays an important role on interpolations. Great improvements on the spatial interpolation in alpine spots are achieved after exploiting DEM. Compared with station data, grid data sets are more plausible to depict the annual and seasonal mean temperature distribution. The grid data sets can well simulate the spatial difference of the annual mean temperature trends in China. The grid data sets can also well demonstrate the change of annual mean temperature in China which as a whole rises by about 1.6 ℃ for 1951—2007, with a warming rate of about 0.28 ℃/10 a. The warming in the later half 20th century is more rapid than the average values of the world and the Northern Hemisphere. The most evident warming occurs in the past over 20 years. The grid data sets also indicate that: Period from 1998 to 2007 is a decade when the annual mean temperature is the highest since 1951, amongst which the annual mean temperature anomaly in 2006 is close to that in 1998 with the highest value before 2000, and the annual mean temperature anomaly in 2007 with a value of 1.3 ℃ beyond that in 1998, is the highest since 1951.
Characteristics of Atmospheric Electric Field near the Earth' s Surface Under Different Weather Conditions in Beijing
Wu Ting, Lü Weitao, Liu Xiaoyang, Dong Wansheng, Zhang Yijun, Li Chengcai, Wang Meihua, Yang Jing, Li Changhe
2009, 20(4): 394-401.
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Abstract:
Based on the measurements of atmospheric electric field and various meteorological elements from the rooftop of a building (about 15 m high), the characteristics of atmospheric electric field in different weather conditions are analyzed. Criteria to select fair-weather days are set according to the data of solar radiation, height of cloud base, precipitation amount and wind speed. As a result, 173 days out of nearly fifteen months are determined as fair-weather days. Data of electric field as well as visibility, concentration of PM10 and absolute humidity of these days are averaged respectively to describe their mean diurnal variations and correlations between electric field and various factors. The result indicates that the diurnal variation of electric field in fair-weather exhibits a double oscillation with trough at 05:00 and 12:00 and peak at 07:00 and 23:00 (Beijing time). The seasonal variation of electric field is also obvious. Variation of fair-weather atmospheric electric field is closely related to the variation of aerosol concentrations. Aerosols can absorb small ions, which dominate the conductivity of air. As the concentration of aerosol increases, the concentration of small ions decreases, and the conductivity decreases as well. Finally, the electric field increases. As a result, the fair-weather atmospheric electric field is positively correlated with the aerosol concentrations. Mean diurnal variation waveshape of absolute humidity in fair weather is similar with that of atmospheric electric field. Under some conditions absolute humidity and electric field also exhibit almost simultaneous fluctuations lasting for several hours. These characteristics show the influence of water vapor on atmospheric electric field. In dusty weather, electric field measured at the observatory remains highly negative and changes rapidly. Various quantities in several strong dust events are turbulent to study relationships between different elements. Result shows that there is a strong correlation between electric field and PM10 which reflects the concentrations of sand particles. However, in most cases, there is no obvious correlation between electric field and wind speed. Theoretically, atmospheric electric field in dusty weather is simultaneously determined by quantity of sand particles and wind speed. But the result indicates that the quantity of sand particles plays more important role in the change of atmospheric electric field.
Error Analyses and Network Optimization for Time-of-arrival Lightning Locating System
Zhang Wenjuan, Meng Qing, Lǜ Weitao, Yao Wen, Zhang Yijun
2009, 20(4): 402-410.
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Time of arrival (TOA) measurements in lightning studies is pioneered by Proctor D E in South Africa. With the high accuracy and large detection range, TOA lightning locating system are widely used all over the world. A variety of studies are made on the retrieval of lightning locations and analysis of location errors. Results show that network geometry, number of antennas, differencing scheme, timing error are important factors affecting retrieval accuracy. Location errors of TOA lightning locating system are analyzed, and effects of station amount, network geometry and baseline length on location accuracy are investigated too. A linear algebraic algorithm is introduced for retrieving the location and time of occurrence of lightning ground strikes from a TOA network. Based on the algorithm, Monte Carlo computer simulation method is used to estimate the locating error, assuming that the system has an overall timing root mean square error of 1 μs , neglecting all other possible errors (e.g., anomalous noise). The detailed spatial distributions of retrieval errors are provided. Results of this research provide scientific basis for design and optimize a lightning network in practical work. The results indicate, in a lightning locating system, location errors do not simply decrease with the amount of stations. They are closely related with network geometry. As for geometry of rectangle, diamond, star and triangle shape, rectangle network with a central station have better location accuracy. In a lightning locating system, sources outside the network have lager location errors than that inside the network. Range errors outside the network increase with distance away from center of the network. With a certain network geometry, location errors decrease with station amount. Regional lightning locating system requires a minimum of four stations. A good network requires three or more widely spaced stations transverse to waves approaching from any direction. A square network of four stations has blind regions near the symmetry axes. This problem can be solved by adding a central station in the square. Within the effective detection range of the network, coverage area and location accuracy both increase with the length of the baseline. On determination of baseline length, factors such as antenna's detection efficiency, timing errors, terrain are all important variables that should be considered.
Total Cloud Amount Difference Between ISCCP Product and Ground Observation over China
Wang Minyan, Wang Bomin
2009, 20(4): 411-418.
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ISCCP (International Satellite Cloud Climatology Project) is an international authorized objective climatology project on cloud study. It has provided valuable data to studying the budget of global cloud and radiation, the distribution of cloud and water since 1983. The spatial and temporal total cloud amount differences are investigated using ISCCP D2 product and cloud dataset of ground observation over China during 1984—2006, based upon the analysis on the differences of cloud amount observation between the satellite platform and the ground observation. Due to the difference between the detection method and ability, observation coverage and time, inconstancy of cloud top/base, cloud height, cloud thickness, and cloud vertical distribution, the total cloud amount from satellite platform are different from that of surface dataset value. The quantitative analysis results show, although the two datasets show the consistent characteristics of total cloud amount distribution and climatology variation, regional differences are still remarkable. Based on the total cloud amount data from 568 surface stations, a new total cloud amount gird data series is formed with the reference of ISCCP D2 girds. Total cloud amount from satellite data is 8.46% higher than that given by surface data in the comparable 145 satellite-surface grids over China on average. The total cloud amount difference is smaller in the southern region, and larger in the northeastern region. It is closely related with the difference of detection method, cloud properties in different regions and the natural geography factors. With the 172 ISCCP D2 grids and 568 ground stations, the climate change trend is compared and analyzed. The annual variation of total cloud amount derived from the ISCCP D2 product and ground observation is accordant in the 5 regions (the northwest region, Tibetan Plateau region, the northeast region, the north of China and the south of China) during the period of 1984—2006. The total cloud amount decreases over China in the recent 23 years, the trend from ISCCP D2 product 0.015% per year is less than that from the ground observation, 0.063%per year. The total cloud amount increases slowly in the northeastern region, while decreases in Tibetan Plateau region and the northwestern region. With integral anomaly method, it shows the total cloud amount decreases in 1984—2001 and increases rapidly in 2002—2006 using satellite and surface data. The causes that total cloud amount from the two datasets (ISCCP D2 product and ground observation) over China have difference, and the quantitative results on spatial-distribution difference of total cloud amount and the trend of climate change, are helpful to further study on the cloud amount, radiation balance, and the promotion of climate models' performances.
Effect of Summer Heat Source Low-frequency Oscillation over the Tibetan Plateau on Precipitation in Eastern China
Wang Yuenan, Chen Longx un, He Jinhai, Zhang Bo
2009, 20(4): 419-427.
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The relation between the atmospheric heat source (AHS) over the eastern Tibetan Plateau (TP) and rainfall intraseasonal oscillation is investigated using daily NCEP/NCAR reanalysis and observed rainfall data of the middle and lower reaches of the Yangtze River during the year 1978 of drought and 1999 of flood. The propagation of low-frequency oscillation AHS over the eastern TP are studied too. The results show that the 10—20 day oscillations have important contributions to AHS over the eastern TP in summer of 1978, and 30—60 day oscillations play an important role in AHS over the eastern TP in summer of 1999. AHS over eastern TP takes on a form of intraseasonal oscillation not only in 1978 but also in 1999. And a remarkable correlation is found between AHS over the eastern TP and rainfall in the Yangtze River valley at intraseasonal oscillation period of time by cross spectrum analysis. In addition, based on 10—20 days and 30—60 days filter curves of AHS over the eastern TP in summer of 1978 and 1999, low-frequency AHS at period of 10—20 days over the eastern TP appears standing wave in zonal direction in 1978, but low-frequency AHS at period of 30—60 days over the eastern TP moves eastward to middle and lower reaches of the Yangtze River.
Detection and Analysis on Deep Convective Clouds in a Frontal Cyclone Using Multispectral Remote Sensing Data
Zhu Yaping, Cheng Zhoujie, Liu Jianwen
2009, 20(4): 428-436.
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Detection and analysis on deep convective clouds in a frontal cyclone using NOAA-16/AMSU-B and GOES-9 data are investigated. A series of detection algorithms and discrimination are adopted, including the microwave brightness temperatures detection from the two window channels, water vapor channel microwave brightness differences identification based on the NOAA-16/AM SU-B data, infrared brightness thresholds detection of cloud top temperatures, the water vapor and infrared window temperature differences determination, and the classification of cumulonimbus clouds correlating with deep convective clouds applying with infrared/water vapor spectral features. These methods are validated by overlaying surface conventional data on the results and comparing them. The results show that microwave brightness temperatures from window channels can discriminate deep convective clouds effectively, while the brightness temperatures of 89 GHz are affected by surface features and the cold water surfaces are mistaken to convective clouds. The brightness temperatures of 150 GHz are just slightly influenced by surface characteristics, so the detection areas are coincident with those from water vapor channel microwave brightness differences identification, which can identify the deep convective clouds well and depend on the thresholds less. As to GOES-9, different infrared brightness thresholds bring about significant detection differences. Single thresholds are applicable to the local areas and the thresholds applicable to global regions should vary in spatial and temporal scales. The water vapor and infrared window temperature differences can detect convective regions well, while the determination areas are smaller. The stepwise cluster can identify cumulonimbus clouds correlating with deep convective clouds by means of infrared/water vapor spectral features, which can classify clouds objectively by combining image and pattern recognition. The detection areas are coincident with NOAA-16/AM SU-B detection areas, and the surface conventional data can validate the results, including hazards weather and cumulonimbus clouds.
Speed Distribution of 100-year Extreme Winds in Lower-reaches of the Yangtze
Huang Shicheng, Zhou Jialing, Ren Jian, Chen Bing, Cheng Ting
2009, 20(4): 437-442.
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In engineering meteorological application the basic wind speed of 100-year return period is commonly confirmed according to the recommend value of national regulation or China basic wind speed distribute map by the method of interpolation. In order to avoid both the potential hazard in engineering design and the higher cost in construction, which may be caused by the low re solution of the basic wind speed distribute map in low er-reaches of the Yangtze and the lacking of actual wind speed data along the river, eight short-term wind observation points are selected along low er-reaches of the Yangtze, and the observation runs synchronously with their neighboring meteorological stations from 2000 to 2006. So the observation pro gram is set up to meet the demand of engineering constructions along low er-reaches of the Yangtze. The observation points are built by on-side investigation to eliminate the extreme terrain effects and can represent the actual wind of the low er-reaches to the largest extent. At every observation point, it is assured that more than one year of simultaneous observation with its adjacent weather station is carried out, although the observational time for each point is not always homology. Based on the short-term synchronous wind data and the annual maximum wind speeds of 40 weather stations of lower-reaches of the Yangtze from 1971 to 2006, the 99% confidence level logistic reconfiguration scheme and extreme value Ⅰ type calculation procedure are referred also a new wind speed distributive status over lower-reaches of the Yangtze is described in detail. Results indicate that along low er-reaches of the Yangtze the 100-year return period maximum wind speed is 25 to 38 m· s-1 which is 3 m ·s-1 larger than upper limit and 2 m · s-1 smaller than lower limit of the result by the general method. lower-reaches of the Yangtze, two gale regions exist both in the Nanjing-Zhenjiang segment and in the Nantong-Chongming segment, where the 100-year return period maximum wind speed is greater than 29 m ·s-1 and even above 34 m · s-1 near the entrance. It is also found that on both sides of Changzhou-Jiangyin river segment two lower extreme wind speed regions are symmetrical distribution, where the 100-year return period maximum wind speed is about 23 to 24 m· s-1. Fully considering the wind data of weather stations and the local wind speed observation, the results are important supplement for the concerned meteorological application works.
Pentad Average Temperature Changes of Inner Mongolia During Recent 40 Years
Pei Hao, Alex Cannon, Paul Whitfield, Hao Lu
2009, 20(4): 443-450.
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In order to understand characteristics of the pentad average temperature changes from 1964 to 2003 in Inner Mongolia, daily temperature records of 47 meteorological stations are analyzed. According to the results of the jump point tests, this 40 years are divided into two 20-year periods, the first 20-year period is from 1964 to 1983, and the second is from 1984 to 2003. From these daily temperature data, the pentad (5 days) average temperature is calculated, and then the pentad average temperature of the second 20-year period is compared with that of the first 20-year period at 5-day interval (pentad). Then the cluster analysis is done. First, the stations are classified into 5 clusters using 4 optimal determining indices. Based on kmeans method and the pentad average temperature differences between the two periods, clustering analysis is conducted, so the spatial pattern of the pentad average temperature differences clusters are obtained. By analyzing the polar plots of the pentad average temperatures, it is clear that the patterns of the pentad average tem perature changes are different in different regions and seasons. The warming in north is more obvious than in south, and it happens more frequent in winter, late summer to early fall than in other seasons. The pentad average temperature in most of the stations rises most of the time, and the spatial distribution of the pentad temperature changes clusters shows that there is a zonation along the latitude. Significant warming most frequently appears in winter. Meanwhile, there are a few pentads that show cooling, but not quite significant. Both the maximum and minimum pentad temperature rise, but the differences betw een them decrease. The timings of the minim um temperature pentads are earlier in the second 20-year period, and the timings of the maximum temperature pentads are earlier or later, while the timings of the minim um and maximum temperature pentads are more synchronic, so the temporal and spatial evenness of the minimum and maximum temperature pentads enhances. In addition, most of the stations show that the durations between the maximum and minimum temperature pentads are longer in the second 20-year period than that in the first 20-year period. From these results, it can be concluded that the global warming may reduce the seasonal and regional temperature differences. The medians of the annual average temperatures of the first 20-year period and the second 20-year period are compared, indicating that the annual average temperatures rise all over Inner Mongolia, and no temperature decrease is found.
An Evaluation Method of Heatstroke Grade with Meteorological Approaches
Chen Hui, Huang Zhuo, Tian Hua, Wu Hao
2009, 20(4): 451-457.
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An increase in the frequency of heat wave accompanies the global climatic change, and causes the continuous occurrence of grouped heatstroke. In order to reduce the impact of heat wave on human health, an index method for heatstroke meteorological forecast is established based on full research about the method of heatstroke both at home and abroad. The methods on heatstroke weather forecasting include index method, statistical analysis method and weather classification method. The method of statistical analysis is the most widely used now, but needs long-time series observation data. The statistical model is based on correlative analysis between case data and meteorological factors. The daily surface observation data of 358 cities from 1996 to 2005 are used, including daily maximum air temperature and daily average relative humidity. Daily numbers of heatstroke sufferers in Wuhan from June to August in 1994 and 1995 are adopted too. Then the correlation between meteorological factors and heatstroke cases is analyzed, and the heat index is chosen as meteorological index to grade with the method of quartile division considering the climatic background of different regions. Four grades of heatstroke are determined by the daily maximum air temperature and the duration of different high temperature weather condition. The correlations between grades of heatstroke forecast and daily numbers of heatstroke sufferers in Wuhan during July to August of 1994 and 1995 are analyzed, and the grades are also compared with daily maximum temperature. Moreover, days of each grade of heatstroke are statistical analyzed from 1996 to 2005. The results suggest that the grades reflect the influence of weather conditions upon heatstroke reasonably. The method on grading prediction of heatstroke can be applied to the actual operation. Many domestic provincial meteorological bureaus have started heatstroke forecasting research and service these days. However, it is hard to form a national uniform standard due to the vast territory and regional differences of climatic background. The method of quartile division takes different climatic background into consideration, so the standard of heatstroke forecast is graded all over the country. The error is reduced through this method to a certain extent and it provides technique foundation for developing national operational heatstroke forecast method.
Case Study of LST Distribution in Nanjing Based on ASTER Data
Shen Shuanghe, Zhao Xiaoyan, Yang Shenbin, Zhou Qiang
2009, 20(4): 458-464.
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Urban Environment has attracted ever more attention at present. Nanjing is a densely-populated city in lower-reaches of the Yangtze River. Knowledge of land surface temperature distribution in Nanjing can help people understand urban climatic condition, especially urban thermal environment, improve the habitat and make scientific layout for urban development. In order to understand the land surface temperature distribution of the city, with the aid of ASTER thermal infrared data and split-window algorithm, its land surface temperature (LST) is retrieved under the support of ENVI software and then land surface temperature field is established. Comparing ASTER LST with ETM+ LST, the results are very accordant. Comparison between ASTER LST and actual measurement data in meteorological station results in a difference of 0.9℃, it is within the range of permissible error, indicating that LST from ASTER is reliable. Results show that there is obvious heat island effect on Nanjing city, the land surface temperature in urban is higher than in suburbs, and there are many cold islands in the urban parks with the larger water bodies and thick plants. The land surface temperature of different space has great discrepancies: The maximal temperature is 56 ℃, the minimum temperature is 23 ℃, with a difference of 33 ℃. There is notable difference in surface temperature among different land uses: The surface temperature is the highest in the regions of asphalt concrete surface in the sun; it is higher in sparse vegetation regions than in dense vegetation cover regions; it is higher in sparse human regions than in dense human regions; the minimum temperature is found over the Yangtze River. On the whole, the surface temperature is higher in the south of Yangtze River, Dachang and Qiaobei than other regions, where it is generally more than 40 ℃. LST exceed 45 ℃ in some districts, including Dachang, Nangang, Qiaobei, Zhongyangmen, east bus station, Xinjiekou, Fuzimiao, Zhonghuamen, the west of Qinhuai River and Yuhuatai, showing characteristics of fleck. The regions where LST exceed 48 ℃ concentrate in Zhongyangmen, Xinjiekou, east bus station, and west of Qinhuai River. The temperatureis lower than 35 ℃ in Zijin Mountain, Xuanwu Lake, Qinhuai River and some urban parks with the larger water bodies and thick plants and LST of Yangtze River is under 30 ℃. With the expansion of city, the heat island effect is even more remarkable in the newly urbanized regions, but the water and the highly dense vegetation in urban help mitigate the thermal effect.
Preliminary Study on Precipitation Process Detection Using Wind Profiler Radar
He Ping, Zhu Xiaoyan, Ruan Zheng, Wu Lei, Yang Xinrui, Ma Shuqing
2009, 20(4): 465-470.
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In order to investigate precipitation process using wind profiler radar (WPR), an observation case is analyzed. WPR is very sensitive to precipitation process and can be used to detect many indicative phenomena before the rain. In this case, horizontal wind shear is recognized 10 hours before the precipitation, and the maximum observation-height increases by at least 2 km than usual. As the rainfall draws near, the height of downward speed gradually decreases.Data analysis shows that domestic WPR is applicable to work in precipitation weather. It provides various instructive data for studying precipitation such as horizontal wind, vertical wind and signal to noise ratio data. Further, WPR can provide data of wind speed, falling speed of rain-drops and their vertical distribution simultaneously, so it' s fairly useful for investigating precipitation process in depth.
The Drought Monitoring in Hexi Area Using the Runoff-denoted Z Index and the Palmer Index
Wang Jinsong, Huang Yuxia, Feng Jianying, Wang Baojian
2009, 20(4): 471-477.
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Hexi is a typical irrigation agricultural area, it is impossible to grow crops based on the natural precipitation, which is only 100-150 mm every year on average. The runoff of inland river is the main water resource for agriculture. That means the high/low runoff is the main determination of dry/wet condition in the target area. Therefore, runoff is considered as the variable to define a Z-index in order to monitor the drought in Hexi irrigation area. Being the Palmer drought severity index-PDSI has been widely applied in the world since the 1960s. In addition, the PDSI is also widely used in drought assessment, comparison and its spatial/temporal distributions analysis. So PDSI is selected to compare with the runoff-denoted Z index in the drought monitoring in Hexi area.The monthly runoff data from hydrological representative station, the tilth area and the meteorological data from representative station of inland river in Hexi area are utilized. A runoff-denoted drought index, the runoff-denoted Z index is established by processing runoff normally. Dry and wet grades are also divided using this index. Considering the relationship between the dry/wet grades and the actual situation of agricultural irrigation, the irrigation grades of Z index are obtained. The precipitation is derived from runoff to revise the Palmer drought severity index. In addition, Penman method is adopted replacing the Thornthwaite method to improve the potential evaporation calculating scheme. Results show that drought monitoring is improved when the runoff is calculated in Palmer drought severity index and the calculation method of potential evaporation is changed. Based on the drought events in Hexi area, the monitoring effect of the Z index is better than the Palmer drought severity index. So it can be concluded that the drought monitored by the runoff-denoted Z index is closer to the actual status in Hexi irrigation area.
The Climatic Variety and Anomaly of the Winter Mean Air Temperature of the East Monsoon Area in China
Chen Shaoyong, Guo Zhongxiang, Gao Rong, Han Tong
2009, 20(4): 478-485.
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Spatial anomaly features and time evolution rule of the winter mean air temperature in China' s east monsoon area are analyzed using data from 375 stations over the years of 1961-2006, adopting the methods of linear regression analysis, multinomial fitting, EOF, REOF, Mann-Kendall, Glide t-examination, Wavelet analysis and power spectrum analysis etc.The incalescence rate is 0.39 ℃/10 a in the recent 46 years, and the annual maxim incalescence occurs in February. The air temperature has taken on an increment trend since 1971. There is a remarkable mutation in 1987 and from then the air temperature reached to a more remarkable warmer period, then the temperature slightly dropped at the beginning of this century. The stability of winter temperature to the north of yellow river is higher than the south. The change of air temperature in most of the regions takes on an obvious uptrend. The incalescence rate increased from south to north. The areas where the getting-warmer trend is inconspicuous are mainly to the south of monsoon area. Using the EOF method analysis, the abnormity of winter mean air temperature in monsoon area of east of China is divided into two common distributive modes: The all area unanimous model and the quasi north and south difference model. Using the REOF method analysis, the area can be divided into 3 sub-areas: The south, the middle and the north monsoon areas. Temperature of the monsoon area is mainly of the all area unanimous model. In the whole areas, 80% of the top-ten warmer years are later than 1990. The exceptional change of air temperature is periodical with a cycle of about 5 years and a cycle of 22 years. Air temperature has turned in to rise in the early years of 1970s in each area, and there is a generally remarkable mutation during 1986-1987.
Computation of Showalter Index by an Iterative Method
Wang Xuezhong, Hu Banghui, Lv Mei, Zou Li, Ni Donghong
2009, 20(4): 486-491.
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In order to improve computational accuracy of Showalter Index, a bisection iterative method (BIM) is introduced to the calculating scheme in two parts: One part is the computation of atmospheric properties of lifted condensation level (LCL), which are requisite to potential pseudo-equivalent temperature (PET) calculation. The other is computation of 500 hPa temperature of the parcel lifted pseudo-adiabatically from LCL keeping PET conservation. Comparing BIM with schemes of Zhang shows that Showalter Index computed by BIM reaches an acceptable accuracy level. Furthermore, the BIM is evaluated by contrasting it to table interpolating method (TIM) of Shou through their 500 hPa parcel temperature difference analysis. Result shows that BIM temperatures are less than those of TIM uniformly with the maximal absolute error of 1.36 ℃. Statistically, the average (-0.68 ℃) and average absolute errors (0.69 ℃) are quite close in magnitude, which shows that the differences are systematic ones. The possible cause is that to the BIM, pseudo-adiabatic parcel ascent is considered, in which all condensed water is instantly removed from the parcel. While the 500 hPa parcel temperature of TIM might be obtained by adiabatic process with entrainment of all condensed water, which can be regarded as the inner heat source of the parcel system consisting of saturated air parcel and condensed water of the adiabatic ascent. The physics difference means that the nearer to saturate the air parcel at initial position of 850 hPa is, the larger negative difference in magnitude between BIM and TIM parcel temperature on 500 hPa there is. In the lower section between -5 and 10 ℃ of 850 hPa air parcel temperature, the 500 hPa parcel temperature difference distribution is consistent with the above mechanism. While in the left interval from 11 to 30 ℃ upper section, the magnitude of 500 hPa temperature difference decreases following an increasing process with 850 hPa dew point depression increasing, which can be only partly interpreted through the mechanism. Computational algorithm and adopted experiential formula difference might be the other cause of 500 hPa parcel temperature difference distribution. The BIM is introduced to compute the parcel temperature at given pressure level lifted adiabatically from initial level with known atmospheric properties, which is essential for stability analysis through parcel method. As a result BIM can also be used in the computation of many stability indexes such as modified Showalter Index, lift index, CAPE (convective available potential energy) and CIN (convective inhibition energy). The great computational efficiency and application convenience makes BIM useful for weather diagnostics.
The Relationship Between Summer Rainfall over China and Spring NDVI Variability in Tibetan Plateau
Fan Guangzhou, Zhou Dingwen, Huang Ronghui, Hua Wei, Wang Yongli
2009, 20(4): 492-496.
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The influences of spring NDVI variability over Tibetan Plateau on China summer rainfall and its mechanism are investigated through the correlation analysis and composite analysis using normalized difference vegetation index (NDVI), the monthly mean rainfall and the NCEP/NCAR reanalysis datasets for the period of 1982-2001. Overall, the correlation coefficient between spring NDVI and summer rainfall takes on a spatial distribution pattern " + - +" from northwest to southeast. An obvious annual rainfall difference is also observed in high and low spring NDVI over Tibetan Plateau by composite analysis. The cause for the different regions in rainfall maybe is general circulation variability over China and other related regions, which is attributed to heat source variability in Tibetan Plateau that originated from spring NDVI variability.
The Preliminary Analysis and Optimization of Meteorological Data Delivery Operation Flow
Xiao Wenming, Feng Wei, Yang Genlu
2009, 20(4): 497-503.
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Radar products, AWS data, T213 model products and the satellite product data are taken as cases, and the operation process flows for them are drawn using standard flow analysis method. Several critical time points are defined (for instance, data zero time, time of data arrival in provincial meteorological bureau, time of data sent to National Meteorological Information Center, time of data broadcast and so on), then several KPIs (key performance indicators) are identified. During the process of experiments, critical time points are recorded, then quantitative analysis and statistics are performed for time consumed in each leg of data delivery. On this basis, the critical factor that influences timeliness of data delivery is analyzed. Analysis suggest that the critical factors that influences timeliness of radar product data and AWS data are T1(the internal of data zero time and time of data arrival in provincial meteorological bureau) and T2(the time internal of data arrival in provincial meteorological bureau and data sent to National Meteorological Information Center); the cause is that there is no standard data delivery service flow in the two leg of data delivery. The critical factor that influences timeliness of T213 is the DVB-S broadcast, which consumes 5852s, taking 99% of the end to end data delivery time. The amount of T213 files is so large that the bandwidth of broadcast is overloading. In addition, during the experiments it's also found that some log data of delivery is absent. So standard data delivery service flow for the whole operation system should be established. Then the optimization solution is proposed and implemented. The result of optimization shows that the timeliness of data delivery is increased significantly and better operation effect is obtained. The optimization has practical significance in establishing standard data delivery service flow and increasing the timeliness of data delivery.
The Statistic of Automatic Weather Station's Efficiency
Li Yan, Liang Haihe, Meng Zhaolin, Pei Chong, Shi Cheng
2009, 20(4): 504-509.
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Over 2100 state automatic weather stations (AWS) can be monitored by the Atmospheric Observing System Operations and Monitoring (ASOM) platform of CMA Meteorological Observation Center at present. They are divided into six groups by areas, which are north, northeast, east, south central, southwest, northwest China. The efficiencies of the AWS are statically analyzed in the respect of data arrival rate, equipment availability and reliability. Influencing factors on the data format errors of datagram and the qualities of data element errors are also analyzed. The results indicate that the data arrival rate, equipment availability and the reliability of all the 2100 state AWS maintain over 80%, with a generally consistent trend. The AWS operation efficiencies of the northeast region are the highest and those of the southwest are the lowest. The data arrival rate is the precondition of the equipment availability and reliability. With the data arrival rate fixed, the format error of datagram has more influence on the equipment availability and reliability comparing to the data elements errors. The 1st line data format errors have more influence on AWS operation efficiencies than the 2nd line data format errors. The ground temperature is the main elements affecting AWS operation efficiencies. Among the ground temperature factors, the different levels of ground temperature have different impacts on AWS efficiencies; 320 cm ground temperature has the most significant influence, while the 5 cm ground temperature's influence is relatively lower. It shows a trend that deeper layers of the geothermal elements have greater influences on AWS efficiencies.
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