Vol.23, NO.5, 2012

Display Method:
Comprehensive Observation Experiments and Application Study of Artificially Triggered Lightning During 2006—2011
Zhang Yijun, Yang Shaojie, Lü Weitao, Zheng Dong, Dong Wansheng, Li Bin, Chen Shaodong, Zhang Yang, Chen Lüwen
2012, 23(5): 513-522.
The Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD) has been conducted in Guangzhou Field Experiment Site for Lightning Research and Testing, Conghua, Guangdong, China from 2006 to 2010. In the experiments, the acoustics, optics, electricity and magneticelements of the discharge process in triggered lightning are observed synthetically. The characteristics of induced voltages produced by triggered lightning on power lines and signal lines of an automatic weather station are measured and analyzed. The triggered lightning technique is also used to test the detection efficiency and precision of lightning location system in Guangdong Province. The peak current of return stoke (RS), the transferred charge within 1 ms after the RS beginning, the half-peak width and the 10%—90% risetime for RS waveform are recorded and analyzed. The relationship between the luminosity of the lightning channel and the continuous current intensity during the initial stage and interval of the return strokes for triggered lightning flashes is analyzed. The results reveal that, on the whole, luminosity of the air-ionized part of lightning channel shows obvious positive correlation with current. Linear correlation exists between square root of integrated luminosity and current when the luminosity of lightning channel doesn't reach saturation in the high-speed images. However, the parameters in the fitting equation are slightly distinct for different processes. The 2D propagation speed of upward positive leader for the triggered lightning is about 104—105 m·s-1. The speed of downward negative leader involved in altitude triggered lightning is about 105 m·s-1. The information on the shape and velocity of the leader channel provided by the high-speed camera records and the synchronous electrical field change data are used to calculate the charge densities and current of upward positive leader for the triggered lightning. The results indicate that, prior to disintegration of the wire, the charge densities of the upward positive leaders range from several micro-coulombs to hundreds of micro-coulombs per meter, and the distribution of charge densityis strongly skewed toward the upward positive leader tips.The calculated current in the upward positive leaders ranges from less than one to dozens of amperes, and increases with the ongoing propagation of the leader. The induced voltage pulse caused by the RS on the overhead power line appears as a positive peak initially and then declines sharply, followed by a negative peak, with a period of several microseconds between the positive and negative peaks. The maximum negative and positive peaks of the bipolar induced voltages on the power line are-10.31 kV and 4.47 kV, respectively. The voltage associated with the fast-changing pulses superposed on the continuous current following the return strokes can exceed 1 kV. The waveform of voltage on the signal for wind speed shows the peak pulses resembled a "V" shape. The results of the lightning location system in Guangdong report that the flash and stroke detection efficiency are 92% and 45% for rocket-triggered lightning, respectively. The space location error ranges from 111 to 5250 m with a mean space location error of 759 m. The relative error between peak current estimated by LLS and the direct measured current from the channel bottom of artificial triggered lightning is 16.3%.
The Evaluation of Wind Measurement Accuracy by Wind Profile Radar
Deng Chuang, Ruan Zheng, Wei Ming, Ge Runsheng
2012, 23(5): 523-533.
As a new type of detection instrument, wind profile radar (WPR) can detect meteorological factors such as wind profiles. The special detecting ability of WPR decides its broad application in atmospheric science research, climate research, meteorological operation application, aviation security and many other areas. Data quality control and accuracy of WPR for application of comprehensive developing meteorological operation has the vital significance.Based on basic data of WPR and meteorological background information, a new method of evaluating wind measurement precision of WPR is proposed. Combined with PB-type Ⅱ troposphere WPR detection data from Yanqing Meteorological Observatory of Beijing, the feature of WPR data is analyzed, processing all continuous observation data of four months (March, June, September and December) of 2010, except for some missing measurements. According to rain gauge data hour by hour, all data are divided into two categories: Clear sky and rainfall, rainfall data are extended to five hours before and after the precipitation. Yanqing is located in the north mountain areas of Beijing, few days of precipitation are observed by WPR site, only 15 times in all. A total of 34380 individual observation cycle data of clear sky and 2580 individual observation cycle data of rainfall are statistically analyzed, respectively.Results show that the maximum height is 8 km in June and September, 6 km in March and December when the velocity error is less than 1.5 m·s-1, and the wind direction error is less than 10°, which basically meets the design requirements of the radar detection height. Quality of radar return signal and inhomogeneity of atmosphere are the two influencing issues for wind measurement accuracy of radar.Signal quality directly affects the detection height, and the SNR (signal to noise ratio) of radar return signal has influences on wind measurement precision on the upper air, where -15.0 dB of SNR can be judged as the threshold of maximum detection height of radar wind measurement reliability. Inhomogeneity of atmosphere underclear air conditions affects the precision of wind measurement slightly.Larger errors of horizontal wind direction and speed appear when it rains, making the wind accuracy unacceptable especially. 1 or 2 hours before the convective precipitation, horizontal wind direction and speed of the variance increase rapidly, which could be a sign of strong precipitation.This new method and the evaluating approaches have the following advantages: Four groups of three-beam detected pattern are used to evaluate effective detected height and accuracy of wind measurement under clear sky conditions.The wind levels are determined through the threshold value combined horizontal speed and direction.The thresholds are based on different months and different heights under clear air conditions.The influences of wind measurement precision are given by analyzing two different types of precipitation.Inhomogeneity of atmosphere is found obviously before rainfall, which can be seen as a warning indicator before strong precipitation.
Geolocation Approach for FY-3A MERSI Remote Sensing Image
Guan Min, Wu Ronghua
2012, 23(5): 534-542.
Fengyun 3 series are second generation polar-orbiting meteorological satellites in China. The first satellite of Fengyun 3 series, FY-3A, is a research and development satellite and is launched successfully at 1100 BT 27 May 2008. The Medium Resolution Spectral Imager (MERSI) is a main payload of FY-3A spacecraft and since June 2008, it has been acquiring daily global data in 20 spectral bands from the visible to the thermal infrared-15 with 1 km and 5 channels with 250 m spatial resolution at nadir. In order to satisfy the requirements of quantitative application, MERSI data need to be geolocated, which can provide accurate latitude and longitude information for follow-up remote sensing productions. The geolocation algorithm of MERSI data, which is adapted by National Satellite Meteorological Center (NSMC), is introduced in details, as well as the error analysis.MERSI rotates a 45° mirror to get 360° views across the orbit direction. MERSI is a paddle broom electro-optical instrument that uses the forward motion of the satellite to provide the along-track direction of scanning. MERSI simultaneously senses, in each band, 10 rows of 1 km detector pixels and 40 rows of 250 m detector pixels. The MERSI detectors are grouped on four focal planes. Detectors for each band are laid on the focal planes in the along-scan direction. MERSI swath is about 2000 km, and generates about 140 GB data per day.According to the characteristics above, parameter method is used for MERSI remote sensing data geolocation. This approach creates the spatial relationship model between the sensed data and the earth based coordinate system, according to MERSI scanning mode, sensing geometry, satellite/sensor's attitude and position. There are 10 coordinate systems and 9 rotated relationships involved in the model. Since 45° mirror brings image rotation, there is a module removing the rotation in the model.When processing data, the line-of-sight vector from each detector of a band is calculated in the instrument coordinate system first. Then the line-of-sight and satellite position are rotated to the earth centered rotating coordinates. The intersection of the line-of-sight with the WGS-84 ellipsoid is calculated. An iterative search process is used to follow the line-of-sight from the instrument to the intersection of the terrain surface represented by a DEM. This geolocation approach for MERSI has been applied to FY-3A data preprocessing system.Five factors that influence the accuracy of results are analyzed. These factors include satellite position/velocity error, satellite attitude error, satellite-instrument installation error, instrument-inner geometry error and instrument thermal distortion.Compared geolocation results with the true remote sensing image using the land-water mask, it shows that the error alone the orbit direction is about 0.167 km and the error along the scanning direction is about 0.058 km. This geolocation approach for MERSI (250 m) achieves accuracy up to 1 pixel.
Pentad Precipitation Changes During Recent 40 Years in Inner Mongolia
Pei Hao, Hao Lu, Han Jingwei
2012, 23(5): 543-550.
In order to study the characteristics of the pentad precipitation median changes in Inner Mongolia, the daily precipitation records of 44 meteorological stations from 1964 to 2003 in this area are analyzed. These 40 years are divided into two 20-year periods, one is from 1964 to 1983, and the other is from 1984 to 2003. From these daily precipitation data, the pentad (5 d) precipitations in each period are calculated and compared at 5-day interval (pentad), and then the clustering analysis is conducted.First, the optimal clustering number of the pentad precipitation change between the first period and the second period is determined by 4 determining indices, classifying the stations into 4 clusters. Then, based on the pentad precipitation differences between two periods, and k-means method, clustering analysis is conducted, so the spatial pattern of the clustered pentad precipitation differences are obtained. The lower temporal resolution data may mask some of the more subtle changes. Use of different time-resolution data can sometimes lead to different conclusions.The spatial uniformity of 11-day precipitation changes clustering is better than the 5-day result. This is most likely due to the different duration of the temperature and the precipitation process. Therefore, analyzing different climatic factors calls for different time-resolution data.By analyzing the polar plots of the pentad precipitations, it is clear that the patterns of the pentad precipitation change are different in different regions and seasons, and the spatial distribution of pentad precipitation change clusters shows that there is a zonation along the longitude. Meanwhile, medians of annual precipitations of the first period and the second period are compared, indicating that the annual precipitation has increased in the most parts of Inner Mongolia. It can be concluded that the seasonal and regional precipitation difference has increased.These changes reflects the correlation of the distribution and trends of precipitation with the intensity and trends of the East Asian monsoon, as well as the complexity of precipitation characteristics in the different climatic zones in Inner Mongolia.
Application of Cloud Analysis System to Typhoon Molave Simulation
Qu Youming, Cai Ronghui, Zhu Lijuan, Wang Guijuan, Wang Hongyan
2012, 23(5): 551-561.
The moist physical processes (mutual transformation of water substance), cloud and rain formation, and corresponding dynamic and thermal effect on precipitation forecast is important for the meso-scale and micro-scale numerical weather prediction model. In order to improve the cloud microphysical parameterization of GRAPES_Meso model, the surface cloud observation data, satellite image and Doppler radar reflectivity are analyzed, and the GRAPES Cloud Analysis System is developed referring to ARPS model and ARPS Data Analysis System (ADAS).The progress and principle of cloud analysis in meso-scale numerical weather prediction model is described at first, and then the technical feasibility of leading cloud analysis into GRAPES_Meso model is analyzed, based on which the cloud analysis module is designed. There are several monomial sub-modules in the GCAS (GRAPES Cloud Analysis System) such as the observation pre-treatment sub-module, 3D cloud cover analysis sub-module, humidity and moisture contents filed analysis sub-module. The special pre-treatment process has been designed for domestic observation data. The GRAPES Cloud Analysis System is developed for the first time which is based on LAPS (Local Analysis and Prediction System) cloud analysis program and referring to ARPS model and ADAS. The adjustment of the 3D cloud cover and initial field and cloud water and hydrometeors is analyzed when surface cloud observation data, satellite image and Doppler radar reflectivity is assimilated in the GRAPES_Meso. The performance of the GRAPES Cloud Analysis System is inspected by the simulation of the landing Typhoon Molave (0906). First, the distribution of 3D cloud cover is retrieved from the cloud analysis system. Second, the cloud water and hydrometeors is produced quickly based on the 3D cloud cover and the height of cloud top and bottom, also, the initial field is adjusted. Third, the forecast of typhoon track in the simulation has a little error, however, the cloud analysis system has displayed positive effects on typhoon landing sites and typhoon track and intensity forecasting compared to the controlled experiment. Finally, the feasibility and correctness of cloud analysis is verified by analysing the radar reflectivity derived from cloud analysis system, indicating the performance of total precipitation forecast is improved obviously.The feasibility of Cloud Analysis System and the assimilating capability are discussed. The System is suitable for operational run for its low computation cost and hot-swap support. Further more, there are some questions which deserve to be more widely debated, for example, Cloud Analysis System should match with the model, region and resolution. The quality control of Doppler radar reflectivity factor data, coordination between initial moist thermal and dynamic field are also very important.
Prediction of Meteorological Elements Based on Nonlinear Support Vector Machine Regression Method
Wang Zaiwen, Zheng Zuofang, Chen Min, Gao Hua
2012, 23(5): 562-570.
Nonlinear regression method based on basic support vector machine is introduced, which is able to solve nonlinear problems. The cross validation in this method makes it able to optimize the kernel function parameters.Therefore, in numerical weather prediction interpretation, nonlinear support vector machine regression technique is better than multi-variant MOS regression method when the linear relationship between the predictor and certain elements, such as wind and specific humidity, is not clear. The numerical prediction products of operational meso-scale model (MM5V3) in Beijing Meteorological Service and observations are used to make 6—48 h interpretation products with 3-hour interval of meteorological elements of 15 venues stations in Beijing. The comparison of interpretation products and MM5V3 forecast indicates that the root mean square error for 2 m temperature, 10 m wind u component, 10 m wind v component and 2 m specific humidity reduces by 12.1%, 43.3%, 53.4% and 38.2%. Compared with the prediction results of MOS, 2 m temperature, 10 m wind u compoent, v component prediction results of SVM are slightly better than those of MOS, and 2 m specific humidity prediction result of SVM is better than that of MOS.Defining the forecast with deviations no more than 2℃ as accurate for 2 m temperature, the forecast accuracy of SVM-release, MOS-release, MM5V3 model and T213 model are 66.5%, 62.2%, 58.8% and 2.5%, respectively. Forecast accuracy of 10 m wind u, v components are defined as the percentage of forecast with absolute deviations within 1 m/s, thus the forecast accuracy of SVM-release are 77.6% and 76.7%, forecast accuracy of MOS-release are 75.8% and 73.7%, forecast accuracy of MM5V3 model are 54.5% and 41.1%, and forecast accuracy of T213 model are 46.9% and 34.9%.Forecast accuracy of 2 m specific humidity is defined as the percentage of forecast with absolute deviations within 2 g·kg-1, thus the forecast accuracy of SVM-release, MOS-release and MM5V3 model are 84.9%, 67.8% and 61.7%, respectively. It shows that nonlinear support vector machine regression method is good at solving nonlinear dependence between meteorological elements and predictors, and performs better than MOS.
Possible Impacts of Future Climate Change on Irrigated Winter Wheat and Adaptive Strategies in Henan Province
Cheng Lin, Liu Ronghua, Wang Xinli
2012, 23(5): 571-577.
Henan Province is one of the most important growing areas for winter wheat in China, and irrigation is the main planting and managing mode for winter wheat. Traditionally, winter wheat is watered three times during the whole growing season, namely, irrigating before overwintering, at green turning stage and jointing to grain filling stage respectively. As to the impact of climate warming, how the irrigated wheat would be influenced in the future has been concerned.DSSAT-CERES Wheat Model is widely used in China and has been proved feasible in future influence simulating. Based on parameters debugging and regional validation of the DSSAT-CERES Wheat Model, two different climatic scenarios data which is outputted by regional climate model PRECIS is combined to study the possible yield variation of winter wheat in the future 30 years of 2021—2050 in Henan Province. The reduction rate of yield and the reduction distribution as well as the changing of water use efficient (WUE) are shown.By drawing quartile graph, the fluctuation of the yield in the future is analyzed.In case of two kinds of greenhouse gas emission scenarios A2 and B2, on the assumption that the traditional irrigation mode doesn't change, the average rate of yield reduction is 5% approximately, and the reduction in A2 scenario is more obvious than B2. Generally speaking, the final yield reduction on the east and southwest plain is relatively less, and the largest reduction rate appears in different decade for different scenarios. With the yield reduction, the variability of yield decreases a little, but 25%—75% interval which means stable yield also shrinks.Extreme low yield is more likely to occur in B2 scenario than A2. During 2021—2050, with the decrease of final yield and increase of water consumption, the WUE for irrigated winter wheat will decrease by 9% averagely for two scenarios. Taking the advantage of crop model experiment, sowing date, planting density and irrigating method are adjusted, respectively. Results show that postponing the planting date has an effect on increasing yield and yield stability, subtracting the planting density to some extent achieves more yield than increasing the density, and changing the watering method from ditch irrigation to trickle could save water resource and enhance final yield.
Meteorological Conditions of Road Surface Icing on Beijing Expressway
Li Xun, Yin Zhicong, Ding Deping, Xie Zhuang
2012, 23(5): 578-584.
Based on the datasets monitored by Vaisala ROSA stations from 2007 to 2009 (preliminary quality controlled) and diagnostic analysis, the characteristic and meteorological condition of Beijing expressway road surface icing is discussed on outside and inside lane separately. The results are as follows: The road surface icing almost occurs on the northwest and City Link of Beijing expressway, and the road surface icing in Juyongguan Station is the worst. Compared with inside lane, the outside lane is easier to ice because of lower road surface temperature, less traffic volume, and more stable road surface environment. According to the statistic results, the road surface icing may occur from November to the next March in Beijing. The annual variation of the icing is also significant, and the frequency of freezing has a close relationship with precipitation and atmospheric temperature. Furthermore, the diurnal variation of the icing-moment is significantly both on the inside and outside lane, with more than 80% of the icing events occurs between 2000 BT and the next 0800 BT, mainly after midnight. The duration of icing before midnight is markedly longer than that of after midnight and could last 23 hours.Ponding and snow on road are necessary for icing, and the icing caused by snow accounts for more than 75%, followed by freezing rain and sleet. Snow has several characteristics such as high albedo rate, solid and low surrounding temperature, making it easier to ice. The meteorological conditions of road surface icing are investigated. When the icing caused by snowfall occurs, the surrounding wind speed is mostly below 4 m·s-1 in favor of keeping stable and radiation cooling. And the road surface and atmospheric temperature are both below 0℃, and the former is often slightly higher than the latter, which account for more than 80% of the situations. The cause may be that the road surface is heated up by release of heat when icing. The differences are also obvious: The road surface temperature and atmospheric temperature is always between-5℃ and 0℃ when icing during snowfall, but below-5℃ after snowfall. The conditions of icing caused by other phenomena are similar, but the temperature is almost below-2℃. It should be pointed out that the time span of datasets is short and the datasets directly monitored by road weather station are used to study the road surface icing for the first time inland, so the results are preliminary. With the observation samples increasing, some new characteristics may be revealed, and added to the conclusions.
Thermal Offset Correction Methods for Sensitivity of PSP Pyranometer
Yang Yun, Ding Lei, Cheng Xinghong, Quan Jimei, Peng Jida
2012, 23(5): 585-592.
The PSP pyranometer is used as a reference pyranometer and a reliable in strument in China. Before 2006 it is once used as national diffused reference to measure the reference diffused irradiance, the value of which is used in the sum composition method to calculate the reference global irradiance. The probability distribution of the nighttime thermal offsets within the pyranometers demonstrates near normal distribution. The offset of PSP type pyranometers is larger than that of 8-48 and CMP22 type. Finding the characteristics of the offset within different types of pyranometers and doing the calibration will improve the accuracy of diffused irradiance. The pyranometer calibration is done underclear sky. The negative thermal offset of the pyranometer causes that the sensitivity is underestimated. By the experiment and study on the thermal offset correction method for different type pyranometer, five correction methods are compared. The net longwave sensitivity method: Calculating the net longwave sensitivity of the pyranometer using longwave blackbody radiation, which is used in the sum composition method outdoors to correct the thermal offset of the pyranometer to reduce the offset effects. The differential algorithm with the reference global irradiance: Comparing it with the reference value derived from the sum composition method using the absolute cavity radiometer and CMP22 type secondary standard pyranometer with shading. The net longwave equation method: Analyzing the data of pyranometers and PIR type pyrgeometers measured at night to correct thermal offset. The cover method: Covering the dome of pyranometers in daytime to measure the offset of pyranometer directly. Using the voltage output of pyranometer in the nighttime as the thermal offset: Calculating the average voltage (night) when solar is 7° lower than horizon and transform it to irradiance as the thermal offset. When using the sum composition method to calibrate PSP pyranometer, the correction results of the net longwave sensitivity method is better than other methods. The result of the cover method is more close to the net longwave sensitivity method, the correction effects using the night voltage output method is not good. Drawing the daytime offset curves separately using the five offset correction methods, the net longwave equation method and the net longwave sensitivity method is more close to the reference value. But these methods are only confined to the shaded pyranometers, because shading makes pyranometer performs more like in the night. For unshading pyranometers, because of the effects of direct irradiance, the five correction methods are distinctly different with the true value. When using CMP22 and 8-48 pyranometers with shading in the sum composition method to test the reference diffused irradiance, the thermal offset could be ignored. But the CMP22 or 8-48 pyranometer should be calibrated by "shade/unshade" method to reduce the effects of offset for sensitivity.When the net longwave sensitivity method or the cover method is used in the sum composition method, the accuracy of PSP's sensitivity could be improved 1%.
The Development of Urban Climatic Map and Its Current Application Situation
Ren Chao, Wu Enrong, Katzschner Lutz, Feng Zhixiong
2012, 23(5): 593-603.
More than half of the world population now lives in urban areas. According to UN report in 2008, by 2030, nearly 60% of the humanity will be urban dwellers. The rapid urbanization in the past half a century has not only brought new immigrants into the urban areas, but also has gradually changed the physical urban environment. There has been a worldwide vision to design cities which are sustainable, healthy, comfortable, and even enjoyable. Thus, it is necessary to bridge the gap between urban climatology and town planning and urban design, and to transfer the climatic knowledge into planning languages. Facing the global issue of climate change, it is also necessary to include the changing climatic considerations holistically and strategically in the planning process, and to update city plans. Recently urban climatology and its application studies have gained world-wide public concern from a series of international conferences and published official reports, e.g., the white paper on "Climate and More Sustainable Cities" published by World Climate Conference-3, United Nations Conference on Climate Change in Copenhagen in 2009, training workshop on urban climate by World Meteorological Organization, Climate Change and Cities-First Assessment Report of the Urban Climate Change Research Network in 2011, etc. Among them, the study of urban climatic map (UCMap) has been popular. It is first developed by German in the 1970s. Now over 40 years development, there are about 20 countries having their own UCMap studies and relevant application projects for improving urban climatic condition and providing information reference for the design of human living environment.Facing the global issue of climate change, it is also necessary to include the changing climatic considerations holistically and strategically in the planning process, and to update city plans. The historical development of UCMap study is reviewed, introducing the key concepts, methodologies, framework and procedures of developing UCMap. The current application situation in Germany, Japan and Hong Kong of China are selected to conduct case studies for exploring their advantages and existing problems. The key lessons of each case study are also provided. Furthermore, according the current situation of China, the urgent need to carry out such study is also pointed out to deal with the environmental problems caused by the recent fast urbanization and solve the conflict among social need, economic benefits, landscape and ecological environment. Due to the poor quality of meteorological data and the urgency of application, a simplified method is expected to apply for development of middle-mage cities and new rural construction of China. Also, the future trend of UCMap study is discussed, which should develop a quantitive method of defining and validating climatope, make the feasibility of application into urban planning, and adopt the climate change into consideration.
The Moving Tendency of Holdridge Life Zone with Its Dry and Wet Climate Changes of Gannan Meadow in Recent 40 Years
Wang Jianbing
2012, 23(5): 604-608.
Gannan meadow lies in the south-west of Gansu Province, on the northeast border region of Tibet Plateau. Gannan meadow is the core region of the important water source supply area of the Yellow River, which provides a natural defense for the upper reaches, playing a unique role in the water source and eco-environmental security of the Yellow River Basin.Owing to the climate change and the artificial sabotage, the production performance and ecology function of Gannan meadow shows an obvious declining trend in recent years, the grassland degeneration and deserting trend are accelerated, and the phenological of herbage shows an obvious earlier trend. The ecology and environment of Gannan meadow has obviously changed. The Holdridge life zone system is a common used method to study the relation of the vegetative cover and climate, which has an obvious significance of physics and biology. It is widely used in the study of ecology environment, the dry and wet climate changes, the climate regionalization and so on.Most of the meadows in Gannan Plateau are distributed in Hezuo, Xiahe, Luqu and Maqu, so 4 places are selected as representative area to study the moving tendency of Holdridge life zone and dry and wet climate changes of Gannan meadow. Based on the meteorological data, the method of Holdridge life zone is used to analyze the moving tendency of Holdridge life zone and the dry and wet climate changes of Gannan meadow during 1971—2010. The results show that life zone of Gannan meadow still belongs to the subalpine meadow of Tibet Plateau alpine vegetation system. But impacted by the global climate change, the temperature of Gannan meadow increases obviously with the tendency ratio of 0.44—0.46℃ every decade, meanwhile the bio-temperature has increased by 0.23—0.27℃ every decade, too. The variety of precipitation shows a different trend between the northern and southern in Gannan meadow, the moving tendency of Holdridge life zone is diverging from the mean center, and the stability of the Gannan meadow ecosystem is attenuating.The Holdridge REPof Gannan meadow shows an obvious ascending tendency in the rate of 0.02—0.03 per decade. After the 1990s, the climate of Gannan meadow shows a warm-drying trend, which is more obvious in the southern of Gannan meadow. The humidity degree of Luqu has changed to humid from the perhumid, and Maqu is in the same transition, too. The most important climatic factor for the Holdridge REPincreasing is the temperature, and then is the precipitation and the air humidity.The temperature rising plays a very important role in the warm-drying trend of Gannan meadow.Considering the complexity of the environment and the fragility of the ecology system in the border area of Tibet Plateau, the impact of this change on ecology and environment of Gannan meadow still needs further study.
Application of Cloud Phase Retrieval to Snowstorm in Akzo Using MODIS Data
Hu Liequn, Huang Zhen, Huang Weijun, Xiong Ling
2012, 23(5): 609-613.
Using satellite remote sensing information, the distribution of cloud-top particle can be retrieved and the physical mechanism of certain weather phenomenon can be explained. Nowadays, cloud phase inversion method based on passive remote sensing instruments on 8 μm, 11 μm and 12 μm spectral bands (corresponding to three MODIS infrared spectral channels: Ch29, Ch31 and Ch32) are relatively practical, which is called tri-spectral cloud phase inversion method. EOS/MODIS satellite data in Akzo Prefecture of Xinjiang and observations from relevant weather station are analyzed to study a snowstorm. The change of cloud phase is revealed by tri-spectral brightness and temperature difference scatter diagram, which clearly shows the whole process of cloud clustering from water cloud to hybrid cloud, and finally to ice cloud. It also reveals the physical mechanism how this weather system occurs and finally develops to blizzard. It can be seen that the result from tri-spectral cloud phase inversion method is completely according with actual circumstance. Therefore, it can be concluded that tri-spectral cloud phase inversion method has a theoretical advantage and a wide application foreground in practice. Meanwhile, this method of MODIS data cloud phase recognition can be applied to analysis of blizzard clouds by FY-3 satellite.
Privilege Management Model Based on RBAC for Meteorological Data Resource Service
Li Dequan, Ruan Yuzhi, Yang Runzhi, Ma Tinghuai
2012, 23(5): 614-623.
In recent years, Role-Based Access Control (RBAC) is apopular privilege management model at home and abroad, which has a distinct advantage than the other traditional access control technologies such as MAC and DAC.The basic principle of RBAC introduces the concept of role endued with authority between user and privilege, and user is also endued with role.However, RBAC still has its limitations when it comes to applications in meteorological department of CMA with fine-grained data access control, and distinct definition.To meet the growing demand for data sharing, a novel access control management model must be built.According to the requirements and characteristics of meteorological data sharing, a model is proposed for a general solution of data-sharing privilege management and multi-dimensional data-sharing privilege management, which is improved from RBAC model.As a shared data resource, meteorological data have a large number of classifications, with a complex hierarchical structure, and very fine particle size of retrieving. In consideration of these comprehensive characteristics, this model introduces the concept of targeted object dimensions in RBAC on the basis of more flexible rights management mechanisms and calculation formula, which improves the security and flexibility of the data sharing services to meet the needs.This model decomposes the fine-grained access privilege of sources by object dimension, and realizes access control of different levels from coarse-grained to fine-grained. The model can authorize directly not only the role but also the user, which greatly improves the flexibility and scalability.The model has been developed as re-pilot study in China Integrated Meteorological Information Sharing System (CIMISS), which is the key project and the practical application of operational systems involved in the meteorological department. A prototype system is built to verify this model. Its deployment is helpful to manage the data retrieving and information access, and simplifies data authorization, maintenance management process, and improves data security. The model supports general security framework of the meteorological database information services, which prevents unauthorized user to access data. As a result, high stability and good security of the simple privilege management model are achieved, and security management information systems based on this model will play an important role in the meteorological data service in the future operations.
Design and Implementation of Special Data Service System for Climate Monitoring
He Wenchun, Gao Feng, Xu Yan, Feng Mingnong, Sun Chao, Zhao Chunyan
2012, 23(5): 624-630.
Currently, the national meteorological data service systems have basically met the demand of operational systems and scientific research. But, as the deep development of the meteorological operations, it's urgent to develop special data services to meet the specific requirements. For instance, the special data service system for climate monitoring is designed and implemented.The system is made up of one supporting database and four modules: Data-update monitoring, special dataset producing, data serving and task scheduling modules. The supporting database is in charge of fetching meteorological data from basic databases and storing information for the system operation. The data-update monitoring module detects the status of data updating with the strategies designed for each dataset, and triggers the special dataset producing module. The special dataset producing module produces datasets with scientific and practical methods, including analyzing, filtering, arranging, making statistics and standardizing of original data. The data serving module provides two ways for service: Data pushing and downloading via FTP. The task scheduling module dispatches the other modules according to business rules, realizes a complete operational flow perfectly by implementing three scheduling modes: Real-time scheduling, exception handling, and manual calling.The system is developed based on SSH architecture, DWR technology and configuration management. SSH involves three open-source products: Struts, Spring and Hibernate, which separately implement three layers of the system: Web representation layer, business logic layer and data access layer. The web representation layer provides a web platform for data manager submitting manual calling of producing datasets with the method of synchronous and asynchronous interaction, realized by using Struts and DWR. The business logical layer is based on Spring product, which implements all of the four operational modules, and implements the calling interface for the web representation layer. The data access layer provides data fetching interface by creating views of data in basic databases and encapsulating data access objects with Hibernate. In addition, the skills of configuration management, including the business configuring and the third-party software configuring, enhance the flexibility and scalability of the system.The system is a successful attempt on special meteorological data service. After being put into operation, it produces thirteen real-time updating special datasets, and serves climate monitoring systems very well. The specific dataset producing method, complete strategy of task scheduling, management skills of configuration, and the technical framework of the system provide a widely reference and promotional value for other special meteorological data service systems' design and implementation.
The Platform for Meteorological Information Retrieving and Visualized Product Producing in MESIS
Lü Zhongliang, Luo Bing, Wu Huanping, Zheng Weijiang, Tang Wei, Bai Xinping
2012, 23(5): 631-637.
MESIS (MEteorological Service Information System) is a new generation system with GIS, database, visualization, multimedia and Web technology integrated to produce and share comprehensive weather service products in National Meteorological Center and provincial meteorological departments.The purpose of the system is to further improving the means and the quality of meteorological services, to establish a meteorological service platform providing rolling, continuous and customized products that can satisfy the needs of government decision making and social developing. The completion of this system will accelerate meteorological service of China to catch up with the international level.The MESIS has four main advantages: The rich geographical information, high quality graphics and outputs, powerful meteorological information statistics and analysis ability, and the open system architecture. It includes four kernel modules, the meteorological information management module, the data processing module, data statistic and analyzing module, and the service products producing module. So far, the MESIS has been widely applied in national and provincial meteorological departments, achieving satisfying results.The platform architecture, design of functions, and key technique, e.g., the GIS application are introduced. The implementation of meteorological information retrieving and visualized product producing are figured out. The problems during the construction of this system are also discussed in details, and the proper solutions are also given in the consideration of various factors. The key technique of this system has also been described in depth.