Vol.23, NO.6, 2012

Display Method:
The Regionalization and Temporal Characteristic of Rainfall Anomalies in North China During Summer
Zhao Cuiguang, Li Zechun
2012, 23(6): 641-649.
North China is one of the three rainfall areas in eastern China. Precipitation over North China shows the characteristics of burstiness and locality. According to the statistics, 80%—90% precipitation occurs from June to August. Sometimes daily precipitation of a rainstorm can be up to 50% precipitation amount of that month. So it is important to forecast precipitation correctly especially to forecast larger magnitude precipitation correctly.Objective precipitation forecast is a difficult problem in NWP products interpretation at present in which models are always established station by station. Precipitation especially larger magnitude precipitation is small probability event for individual station, so establishing an effective forecast equation is difficult. Precipitation intensity, spatial and temporal distribution over North China has its own particularity. Due to the regionality characteristic, it is difficult to summarize in one weather mode. Objective partitioning can be used in establishment of precipitation forecast mode. Similar samples in the weather region are combined together. Regional forecast mode is more stable than single-station forecast mode, because the number of large-class precipitation samples is increased. In addition, sample data time selection is important for objective precipitation forecast modeling process.Based on the data of daily precipitation at 703 weather stations over North China from 1981 to 2007, which covers the domain of 32°—42°N, 110°—124°E, the temporal and spatial distribution characteristics are analyzed with Rotated Empirical Orthogonal Function (REOF) method. REOF analysis manifests that precipitation fields may be divided into 7 divisions. Mann-Kendall test and running t-test are used to analyze about the temporal change characteristics of different regions over North China during summer, in order to investigate the beginning and ending dates of rainy season specifically. The 7 divisions are different in precipitation beginning and ending dates. The initial date and final date of rainy season over North China are set up, and their dates are further identified, showing obvious regional features. Rainy season begins the earliest and ends the latest in the mountainous areas of the northeast of North China. It begins the latest in the central part of North China, and it ends the earliest in the southeast of North China. The concentration of precipitation time is different from the natural seasons. The long-term variation trend of precipitation anomalies in various regions and their stage are studied.
Meridional Variation of South Asian High and Its Relationship with the Summer Precipitation over China
Wei Wei, Zhang Renhe, Wen Min
2012, 23(6): 650-659.
South Asian High (SAH) is the most intense and stable upper level anticyclone in boreal summer. As a member of the East Asian Summer Monsoon system, SAH plays an important role in the regional climate anomaly over China.The meridional variation of SAH is analyzed by using the monthly mean data derived from the European Center for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA-40) from 1958 to 2002. An index of SAH (SAHI) is defined to measure its meridional variation in summer and to analyze its relationship with the summer precipitation over China. The results show a significant correlation between the meridional position of SAH and the summer rainfall over China for both the interannual timescale variability and the long-term linear tendency. The correlation coefficients between SAHI and the summer rainfall in North China and in the Yangtze River Valleys are 0.577 and-0.604, respectively, both of which exceeds 0.01 level. When SAH locates further northward (southward), North China and South China are wetter (drier) than normal, while the Yangtze River Valleys is drier (wetter) than normal. And the southward linear trend of SAH corresponds with the decreasing trend of rainfall in North China and the increasing trend of rainfall in the Yangtze River Valleys.Linear regression analysis of the circulation reveals that when SAH locates further northward, an anomalous anticyclone controls eastern China with its center tilted southward from 200 hPa to 850 hPa. In the upper atmosphere, the anomalous anticyclone forms a divergence zone over North China. In the lower atmosphere, it results in flows diverging over the Yangtze River valley, and converging over North China. Besides, the northward movement of SAH would cause the upper-level westerly jet and the Western Pacific Subtropical High move northward, with the rainbelt locating in North China.The meridional anomalous variation of SAH is closely related to the sea surface temperature anomalies (SSTA) of the Tropical Indian Ocean (TIO), the Central and Eastern Equatorial Pacific, and the northern Pacific. And the TIO SSTA might modulate its meridional position directly. Positive TIO SSTA might lead to a southward expansion of SAH.Due to strong correlation with the summer rainfall over China and being modulated by the TIO SSTA, the meridional variation of SAHI could be considered as an important indicator used to predict the regional climate anomaly.
Interaction Between Landfalling Tropical Cyclone and Summer Monsoon with Influences on Torrential Rain
Cheng Zhengquan, Chen Lianshou, Li Ying
2012, 23(6): 660-671.
Based on Tropical Cyclone Yearbooks, NCEP/NCAR reanalysis data and dynamic composite analysis, the relationship between the torrential rain associated with landfalling tropical cyclones and summer monsoon jets is studied. Several sets of numerical experiments are carried out to analyze influences on heavy rain of interaction between the landfalling tropical cyclone Bilis (2006) and the summer monsoon. Composite analysis show that tropical cyclones resulting in a large range of torrential rain always link with a low-level jet for a long time even after landfall, which makes them obtain sufficient water vapor flux. While for the weak rainfall tropical cyclones, the linking might break before landfall, which cuts off the water vapor transport from the low level jet. Numerical experiments reveal that water vapor transport from the low-level jet of summer monsoon is favorable to the maintenance of the tropical cyclone structure of warm core. Cutoff of the water vapor transport will lead to the stretch of a dry tongue into the cyclonic circulation from the boundary, destruct the tropical cyclone structure, and make the mesoscale and microscale synoptic systems weakened, which results in the obvious weakness of the rainfall intensity and the reduction of heavy rain coverage. Water vapor transport from the southern boundary is much more important than any other boundary. In the sensibility numerical experiment, the wave spectrum method is applied to alter the mesoscale and microscale winds to strengthen and weaken the monsoon jet speed. Results show that moderate change of wind speed in low level jet only change the distribution and coverage of heavy rain a little, but the grid number of extremely strong rainfall (more than 200 mm) varies notably. Under the background of summer monsoon, a tropical cyclone moving into the monsoon channel will strengthen wind speed of the low level jet, which strengths the transport of water vapor at low level. Furthermore, the movement of tropical cyclone over land changes the distribution of water vapor, instability energy and the relevant heavy rain, and the unique dynamic structure of tropical cyclone, and strong convergence at low level and strong divergence at upper level, could strengthen the rain intensity.
Wind and Rainfall Features and Risk Assessment of Tropical Cyclone in Fujian
Zhang Rongyan, Xu Zonghuan, You Lijun, Gao Jianyun, Bao Ruijuan
2012, 23(6): 672-682.
Tropical cyclone (TC) influences Fujian Province frequently and often makes severe damages. The damages aroused by TC depend on undertaker, disaster defense abilities and the factors such as environment, weather and so on.The weather factor is a trigger and the essential term of the damage. TCs from 1961 to 2010 which affect Fujian Province are divided into 11 types according to their landing sites and moving paths. Then spatial features of rainfall and wind speed of each TC type are given, and then spatial features of damage potential are given based on them. Evidence shows that TCs landing Fujian Province mostly land Taiwan first and often result in rainfall and strong wind speed, meanwhile TCs landing south to the Pearl River estuary only result in strong wind speed in Fujian Province. The most serious damages aroused by rainfall located in north of Ningde and Jinjiang, while the strongest wind speed occurs in south coastal area of the Province. TCs landing Taiwan and then landing north of the Province again cause the heaviest rainfall, the strongest wind speed aroused by TCs landing Taiwan and then landing south of the Province, TCs landing Taiwan and landing south of the Province again, then landing south of the Province directly cause the broadest area of strong wind speed. Using objective correlation coefficient weighting, an assessment model of damage potential of rainfall and strong wind speed is established. The model reveals some facts: The highest damage potential area is often near the landing site and north to it. When TCs move westward into inland, it often produces a secondly highest area. TCs landing Taiwan, then landing north or middle of the Province again produce the highest damage potential, and landing south of the Province directly or landing south to the Pearl River estuary. High damage potential areas mostly appear in coastal area, west or north of the Province, while low potential areas appear in the river basin.
Influences of the Deflection of Stratospheric Polar Vortex on Winter Precipitation of China
Xiong Guangming, Chen Quanliang, Wei Linxiao, Hu Deqiang
2012, 23(6): 683-690.
Using NCEP/NCAR reanalysis data and monthly precipitation data of 160 stations in China from 1970 to 2010 provided by National Climate Center, the deflection intensity variation of the stratospheric polar vortex, which moves toward the Eurasia, is analyzed and the relationship between the deflection intensity indexes in winter and the precipitation in the corresponding and later period is also studied by means of wavelet analysis, correlation analysis, composite analysis and so on. Results show that there is a dominant interannual oscillation period of about 6—8 years for the deflection intensity indexes. The interannual oscillation period is roughly 8 years from the 1970s to the mid and late 1980s, but it shortens to 6 years from the late 1980s to the early 2000s. Positive phase oscillation occurred mainly in the late 1980s, 1990s and recent years.The deflection of the stratospheric polar vortex, which moves toward the Eurasia in January, has a very important impact on precipitation in the same period and later in February. The same period of significant positive correlation between the deflection intensity index in January and precipitation in January mainly occurs in central China and southwest Xinjiang, but significant negative correlation is also found in central Xinjiang. The later period of significant positive correlation between the deflection intensity index in January and precipitation in February is also mainly located in central China, but extends northwestward, making precipitation in north of central China and south of North China relatively reduced, while precipitation in west of North China and east of Northwest China relatively increased.From the analysis of circulation situation background, it can be summarized that strong Eurasian polar vortex in January may lead to reduced East Asian trough and East Asian winter monsoon. The departure of the southeast wind is remarkable in central and eastern China, which is easy for warm and humid air moving toward the northwest of China. The northerly anomaly is remarkable in north Lake Baikal region, which makes cold air and warm air meet to the north of normal situation. Also, lower humid air transmit upward obviously increases, and significant strong convergence center appears in central China. It is found that there is a significant negative correlation between the index of the Eurasian polar vortex intensity and the index of East Asian winter monsoon in January, which passes the test of 0.05 level.
Statistical Characteristics of Short-time Heavy Precipitation in Shan-Gan-Ning Region from May to September in Recent 6 Years
Han Ning, Miao Chunsheng
2012, 23(6): 691-701.
The statistical characteristics of short-time heavy precipitation vary in different areas. Based on thehourly automatic weather station precipitation data and NCEP reanalysis data with the resolution of 1°× 1° in Shaanxi, Gansu, Ningxia from May to September during 2005—2010, the statistical analysis are conducted to explore the spatial-temporal distribution of short-time heavy precipitation in different class, synoptic conceptual models and their features of physical parameter. The results indicate there are 4 active and 3 inactive areas of short-time heavy precipitation in Shan-Gan-Ning Region.Hourly precipitation above 80 mm could occur in both areas. Short-time heavy precipitation (over 30 mm per hour) is closely associated with special terrain such as wind ward slop of mountain and trumpet-shaped terrain. Short-time heavy precipitation is active in July and August, followed by June and September. The severe rainfall occurs mostly in late June and mid-August, and the cumulative frequency is slightly smaller in early August because of droughts season. Diurnal variation presents the bimodal distribution. Short-time heavy precipitation (over 30 mm per hour) shows the characteristic that severe precipitation tends to occur in the evening (2000—0800 BT). With the increase of precipitation intensity, that feature becomes more obvious. Spatial-temporal distribution features above are closely associated with the large-scale atmospheric circulation. All 3 kinds of synoptic conceptual model have common features in physical quantities filed: Ample of vapor, convective unstablestratification, instable energy, high 0℃ isotherm height, thick warm cloud layer, and weak wind shear. Despite common features, each model has its unique features.Trough and subtropical high pattern is the most typical type in Shan-Gan-Ning Region. This pattern has the highest value of LCL and lowest of Δθse(500 hPa minus 850 hPa), LI, K and CAPE, so the short-time heavy precipitation happens most frequently and the hourly precipitation is seldom more than 25 mm. Low vortex and typhoon far away pattern has the most favorable vapor condition and its deep wet area, sub-synoptic scale Ω system, lowest LCL results in broad precipitation areas and stronger precipitation. Shear between two high pressure pattern has the highest contribution of Δθse, LI, K, CAPE and strongest vertical wind shear (0—3 km), which leads to the most sever precipitation. Short-time heavy precipitation of this pattern occurs more suddenly and doesn't last long, when the SWEAT reaches near 300. It can also be found that the occurrence of short-time heavy precipitation is often accompanied by thunderstorm.
Application of Vertical Component of Convective Vorticity Vector to the Diagnosis of a Rainstorm Brought by Southwest Vortex
Tao Li, Li Guoping
2012, 23(6): 702-709.
Convective vorticity vector (CVV) is employed to analyze the rainstorm caused by the shallow system of southwest vortex during 16—18 July 2010, using convective vorticity vector vertical component (Cz). The relationship between every component of the CVV and the 6-hour accumulated precipitation is investigated, particularly the meaning of vertical component in rainstorms caused by southwest vortex. It shows that the vertical component of CVV is a good indicator of the rainstorm caused by southwest vortex. The occurring time of strong precipitation and the peak value of vertical component of CVV are consistent. If [Cz] reaches an extreme value, the precipitation will change significantly, probably leading to heavy rain phenomenon.Thus the peak time of [Cz] can be an indicator of the heavy rain forecast. When the rainstorm begins, the precipitation region shows consistently positive values of Cz, with the heavy rain to strengthen. When the positive values of Cz expand larger, the contours become intensive, and the gradient increases. The scope of positive values of Cz and the rain belt are largely the same. In the distribution of lower troposphere 850 hPa level, the rainstorm area locates near the center of the positive values of Cz and tend to the larger gradient of Cz. The main cause is the positive vorticity advection in front of the westerly trough, so that the vorticity in southern Sichuan and eastern Sichuan enhance, and the wet isentropic surface becomes steeply. The rising movement and the water vapor deliver strengthens, which is beneficial to the formation of heavy rain. Along the vertical distribution of Cz in the storm center, the storm intensity increases significantly when vertical components from lower to higher troposphere show consistent positive values. This rainstorm case confirms that the convective vorticity vector can be used for analyzing the shallow meso-scale system like southwest vortex. However, there are very limited cases, so further validation and improvements are needed.
Quality Control of Differential Propagation Phase Shift for Dual Linear Polarization Radar
Du Muyun, Liu Liping, Hu Zhiqun, Yu Rong
2012, 23(6): 710-720.
Data processing and quality control is the foundation of the application of dual-linear polarization Doppler radar. Based on the observation in field experiments by a C-band Polarization Doppler Radar on Wheel (CPDRW), the difference of differential propagation phase shift ΦDP between precipitation and ground clutter and its relationship with signal-to-noise ratio SNR are analyzed and a new data analyzing and processing methodology is suggested. According to this new method, the useless ΦDP data can be given up and the KDP data with higher accuracy can be acquired. Analysis indicates that ΦDP data are vulnerable to the influence of the non-meteorological target like ground clutter and usually appears large fluctuations. ΦDP data are also sensitive to the variability of SNR and cross-correlation coefficient ρHV(0), especially the latter. It appears abnormal fluctuations with the quality of related SNR and ρHV(0) becomes poor and that will affect the quality of the estimation of KDP data if no appropriate quality control scheme is adopted. Using this kind of KDP data, obvious errors in the quantitative application of precipitation estimation and precipitation particle morphology recognition can be obtained. In this new method, the abnormal volatility of ΦDP data combining with reflectivity factor ZH and radial velocity Vr information is used to isolate the ground clutter, and then improper data are eliminated in the quantitative application such as quantitative precipitation estimation or attenuation correction. According to SNR and ρHV(0), the meteorological data is divided into good, poor and bad categories. For the good data, the fluctuation is smaller, the increasing trend with distances which accords with theoretical expectations is evident, so the preprocessing algorithms and estimate KDP data can be used directly; for the poor data, although the fluctuation is more pronounced than the good data, the data continuity begins to become poor and there are some ΦDP data "pile" and "depression", however, much weather information remains and the variation trend is also obvious, so the data correction algorithm are applied so as not to affect the estimated KDP data; and for the bad data, it not only has the large fluctuation, the overall variation trend is also difficult to identify, sometimes even negative growth phenomenon appears which is contrary to the theory, so they are eliminated to ensure the overall quality of ΦDP data. After a large number of actual data validation, it reveals that the suggested method can keep the meteorological information to the greatest extent and ensure the overall quality of ΦDP data at the same time, and it can also estimate the high quality of KDP data.
Ground-based Visible Cloud Image Classification Method Based on KNN Algorithm
Zhu Biao, Yang Jun, Lü Weitao, Chen Liying, Ma Ying, Yao Wen, Zhang Yijun
2012, 23(6): 721-728.
Cloud plays an important role in the meteorological research, and it is one of the most important factors of earth's energy balance and hydrological cycle. In order to actualize the automatic ground-based observation of clouds, automatic classification of cloud image is a difficult problem.A cloud classification scheme which classifies the cloud images into cumulus, stratus and cirrus is discussed. The clear sky is considered as a separate category in the scheme. Three kinds of image features, texture, color and shape are analyzed. The texture features describe the local information of image by using gray information normally, which have the characteristics for translation invariance. The color features consider the color of the image and focus on description of the overall image information, which have the characteristics for translation, rotation and scale invariability. The shape features describe the outline or region feature of the specific objectives and focus on description of single target. By analyzing the cloud image features of four different sky conditions, extraction algorithms are introduced in details. Using gray-level co-occurrence matrix and Tamura texture, color moment, and moment invariants, 21 characteristic parameters are extracted. Because of its high performance in solving complex issues, simplicity of implementation and low computational complexity, the K-Nearest Neighbor (KNN) classification algorithm is selected to process 21 characteristic parameters. 8 different K values and different features combination are used to recognize the 4 types of sky conditions. Classification experiments are conducted using single feature, combination of each two features, and all of these features together. The 7 experimental results demonstrate that the new scheme is feasible. And using texture features, color features and shape features together can get better performance than using these features alone or any two of them combined. When the parameter K is set to 7 and all 21 characteristic parameters are considered, the identification accuracy of cumulus, stratus, cirrus and clear sky are 91.1%, 74.4%, 70.0% and 100.0%, respectively, with the average accuracy up to 83.9%.
Comparison of Surface Solar Radiation Reanalysis Data and Observations over China
Wang Dan, Sheng Lifang, Shi Guangyu, Che Huizheng
2012, 23(6): 729-738.
Comparison of surface solar radiation data of NCEP/NCAR, NCEP/CFSR reanalysis data and data from stations and marine observations are conducted to check whether reanalysis data can reflect the characteristics of surface solar radiation over China. The results show that NCEP/NCAR reanalysis data are less reliable before 1979, but both NCEP/NCAR and NCEP/CFSR reanalysis data are high reliable after 1979, and the reliability is higher in east and low latitude areas than that in west and high latitude areas over China. Because the daily mean data calculated by six-hour reanalysis data is lower than real data over China, it is reasonable to calculate the daily data by excluding the case of zero observation to minish the deviation.Long-term average errors between NCEP/NCAR, NCEP/CFSR and station observations of surface solar radiation are 10.37 W·m-2 and-42.68 W·m-2 in Chinese Mainland from 1979 to 2009, with standard deviation of absolute errors being 12.31 W·m-2 and 4.19 W·m-2. Average errors between NCEP/NCAR, NCEP/CFSR and marine observations of surface solar radiation are-161.19 W·m-2 and-179.66 W·m-2 over the sea during marine observing, with standard deviation of absolute errors being 37.07 W·m-2 and 35.36 W·m-2. The surface solar radiation from both NCEP/NCAR and NCEP/CFSR reanalysis data are bigger than station observations along the Yangtze River Valleys around Chongqing, where the biggest deviation appears.This maybe due to the fact that cloudiness data from reanalysis are smaller than observations here. Since the NCEP mode doesn't consider aerosols, it has also induced the bigger deviation of surface solar radiation between reanalysis data and observations.Besides, Chongqing is a mountainous region, whose terrain shelter influences surface solar radiation. It should increase surface solar radiation from 18% to 63%, when reanalysis data are used on the Yangtze River Valleys. There is some false phenomenonin long-term variation of surface solar radiation from reanalysis data. For example, a false upward trend exists notably in NCEP/NCAR reanalysis data before 1979 and the false extreme value of NCEP/CFSR reanalysis data appear in 1998. To some extent, the reanalysis data can be used for study of the surface solar radiation in Chinese Mainland. And the temporal and spatial distribution characteristics of surface solar radiation can also be reflected over the sea. For the deviation and false phenomenon of reanalysis data, more attention should be paid when using them in long-term climatological diagnosis. Compared with surface solar radiation from land station observation, there is a big deviation between the marine observations and the reanalysis data. This may due to the lack of marine observations, which will confine the evaluation and development of NCEP mode. Besides, the sea data used are constructed from marine observations from 2006 to 2007. For its insufficient sample, the data quality of surface solar radiation from NCEP/NCAR and NCEP/CFSR reanalysis data need to be studied further over the sea.
Quality Detection of Surface Historical Basic Meteorological Data
Ren Zhihua, Yu Yu, Zou Fengling, Xu Yan
2012, 23(6): 739-747.
Surface basic meteorological data are observational values from surface stations, including hourly values, daily extreme and cumulative values. Chinese surface historical basic meteorological data consists of observations from more than 2400 national stations since as early as 1951, including 20 kinds of elements, such as air temperature, air pressure, humidity, wind, precipitation, evaporation and so on. These data are the basis of regional and global climate change researches and predictions, synoptic dynamic analysis and public meteorological services. The digitization of these data is started by China Meteorological Adminiatration in 1979. High quality digital data should be faithfulness to the paper reports. But incorrect data and data missing problems caused by digitization and restoring have been found, besides those caused by error observations. Resolving these problems will contribute to the improvement of operational application accuracy, scientific researches and data processing.In order to identify quality problems of Chinese surface basic meteorological data and improve the data quality, several methods are applied to detect the data quality of air temperature, pressure, humility, wind and precipitation observed by 2474 national surface stations in China from 1951 to 2009. The above data are collected based on National Meteorological Information Center (NMIC) and provincial archived electronic data files. Results show that a large number of error data different from actual measurements are stored in both NMIC and provincial archived data files, which are caused by incorrect digitization. For example, some electronic data files are replaced by other station measurements, some meteorological elements aren't observed for a period, and some data are miss-typed. Some flaws between NMIC and provincial archived data files also shows, including the data file differences in time span and various data source (automatic or manual observation), and data difference induced by asynchronous correction of wrong data. It is impossible to detect all the above data problems using conventional data quality control methods, so some special methods are proposed for each kind of problem. The proportion of incorrect measurements of the whole data is low, though its number is huge. For example, for more than 2400 national stations, only 0.06 percent of data are wrong copied, and for more than 700 baseline stations, only 0.34 percent of precipitation data are missing. The data quality detecting method mainly focuses on temperature, pressure, humidity, wind and precipitation data from about 700 baseline stations, and data problems are verified by checking the monthly paper reports but not corrected. With this work experience, thorough data problem detections and corrections on the whole elements from historical electronic data files are carried out by China Meteorological Administration. A review of this program and the results will be published soon.
Data Evaluation and the Advantage of the Double Automatic Weather Stations
Wen Huayang, Xu Guanqing, Zhang Hu, Hua Liansheng, Tan Changchun, Zhou Yao
2012, 23(6): 748-754.
Anhui Provincial Meteorological Service starts pilot run of double automatic weather stations at national weather stations in 2010. The stations are deployed in Xiuning, Anqing, Kuche and other districts, and they have been put into test run one after another since October of 2010. A detailed assessment is carried out to evaluate the hourly data of temperature, air pressure, relative humidity, 2 min average wind speed, 5 cm ground temperature and grass temperature of the double automatic weather stations in Xiuning, Anqing and Qimen from January to August of 2011. At the same time, the advantages and disadvantages of the double automatic weather stations are discussed.The data integrity of the double automatic weather stations is analyzed by calculating missing rate. The missing rate of air pressure of Station A is 0.38%, and Station B is 0.15% in Xiuning, but rate of Station A and B both missing at the same time is only 0.07%. So it is considered that the double automatic weather stations can reduce missing rate, and ensuring the integrity of data. The difference of the double sets of data is discussed by the statistical features, consistent rate, rate of gross errorand out-of-tolerance rates. Through the detailed analysis, it shows that most elements (such as temperature, air pressure and relative humidity) of the double automatic weather stations have stable and smaller difference.For example, the average air pressure of station A is lower than station B in Anqing, with the difference of 0.01 hPa. In 5812 effective samples of difference data, there are 1659 samples with difference of 0.0 hPa, and for 99.2% of all the samples, differences are within ±0.1 hPa. The standard deviation of difference is 0.08 hPa.The difference has higher concordance rate, lower out-of-tolerance rates and lower gross error. For example, the consistency rate of temperature is 96.6% in Qimen, the out-of-tolerance rates of humidity is 0.0% in Xiuning, the gross error rate of air pressure is 0.0% in Anqing. However, some elements of the double automatic weather stations have lager difference, such as the grass surface temperature and ground temperature. For example, the gross error of grass surface temperature is 12.7% in Xiuning, and the out-of-tolerance rate of ground temperature is 29.7% in Anqing.The data evaluation shows that the abnormal data, instrument systematic error can be found through monitoring the difference and the moving average of difference data, and whether the instruments have significant changes in performance can be determined by the daily change characteristic difference data of the double data. Thus, the double automatic weather stations have the potential advantages of ensuring the quality of data, and resolve the deficiency of current automatic stations in some degree in operation.
An Icing Conductor Meteorological Model Based on Estimating the Visibility in Fog Condition
Wu Xi, Sun Pengjie, Liu Yu, Jin Xiping
2012, 23(6): 755-762.
By using the daily icing data of Erlangshan Mountains in Sichuan Province during three winter seasons provided by Southwest Electric Power Design Institute and related meteorological data, methods of correlation analysis, regression analysis are used to study the meteorological factors and icing index associated with the icing over Erlangshan Mountains. From the view of physical concept, the main meteorological factors influencing the strength of icing conductor and the microscopic process of conductor icing are analyzed by the fluid mechanics and thermodynamic principles. The theoretical framework of the rime icing conductor model and the glaze icing conductor model are built. By analyzing icing data and conventional meteorological data, it is found that the icing density is not well correlated with other meteorological elements except for temperature. An icing density model is established by the method of nonlinear regression analysis whose fitting correlation ratio is 0.5652. This density model can reflect the real icing density. According to the relationship between the visibility, extinction coefficient and liquid water, the liquid water content and its transportation can be estimated by the visibility.To choose the most proper scheme for Sichuan mountain climate characteristics, liquid water content estimated by different model is compared using observed data. Combined with the observed icing data, Kunkel scheme is selected for fitting test. As a result, it is found there is a good correlation between the growth of icing thickness and the liquid water content. The conductor icing thickness is decomposed into the rime icing which is formed by horizontal droplet and the glaze icing formed by precipitation. An icing process efficiency index is defined for further transformation of the theoretical models of conductor icing.From physical significance analysis, temperature and wind are main influencing factors of the icing process efficiency index. But the icing process efficiency index is not significantly correlated with temperature and it is related to the wind speed with exponential relationship. Based on these results, an icing conductor model is established to achieve the purpose of engineering application. From the analysis of the model fitting results, this icing conductor model can reflect the actual icing conductor on the whole, especially reflecting the trend well. The correlation coefficient between the icing thickness and fitting thickness is 0.8340, and the mean square error of icing thickness is 28.61 mm.
Atmospheric Vapor Content over China and Its Climatological Evaluation Method
Wang Bingzhong, Shen Yanbo
2012, 23(6): 763-768.
Water vapor content in atmosphere is important for the calculation of surface solar radiation, so it is a necessary parameter. At the same time, water vapor is a kind of climate resources which plays an important role in climatology. In order to evaluate water vapor properly, the integrated water vapor of each station is calculated based on the aerological climate standard data of the whole 124 aerological meteorological stations in China from 1971 to 2000. The distribution of annual value indicates that water vapor content in China increases with latitude except Tibetan Plateau. Using the data from China Surface Climate Standard Monthly Database (1971—2000), the surface vapor pressure is revised by corresponding surface air pressure, and then a consistent or monthly empirical formula which can be used throughout the country is obtained. Root mean square error (RMSE) of fitting value from the empirical formula and observational value is 0.25 cm. The affection of polynomial power on fitting value is discussed in depth and it can be seen that the high power polynomial which makes good fitting correlation doesn't mean the lowest RMSE. The optimal fitting formula of revised surface vapor pressure (x) by surface air pressure and integrated water vapor content (y) is: y=0.185x+0.093. The greatest advantage of this formula is that it can be used all over the country, no matter highland or lowland, in the north or in the south. Therefore, it can be considered much more close to the practical situation.