Vol.19, NO.3, 2008

Display Method:
Meteorological and Hydrological Characteristics of Flood Related Torrential Rain over Huaihe River Basin in 2007
Jiao Meiyan, Jin Ronghua, Qi Dan
2008, 19(3): 257-264.
Based on the regular meteorological and hydrological data during the Huaihe River Basin torrential rain in 2007, the torrential rainfall process, the related large scale atmospheric circulation pattern and the evolvement of the flood as the meteorological and hydrological characteristics are analyzed. The conclusion hereby is drawn for the cause of flood happening by the torrential rainfall. The conclusion shows that the Huaihe River Basin flood is mainly related with seven torrential rainfalls. The later four torrential rainfalls are recognized as the significant factor to bring the Huaihe River Basin flood which happen during June 29 to July 10. Although the former three torrential rainfalls are not strong and not recognized as the main cause of flood, the water increase is still led to and becomes the hidden trouble of the whole valley heavy flooding, because the present of precipitation center is mainly in the northern Huaihe Basin where the anabranch of Huaihe is densely located. The large scale atmospheric circulation pattern shows that the torrential rain in Huaihe River Basin occurs under the quite typical Meiyu situation, and the stability of subtropical high has a great impact on the establishment of strong rain-belt. The hydrological data analysis reveals that the higher water line as well as the less water fluxes is on the upriver of Huaihe River Basin which is associated with the severe flood. The increase of the water level is directly led to by the heavy rainfall in the main Huaihe River Basin, and the variable of the water level is associated with the heavy rainfall especially in the upriver of Huaihe River. The rapid increase of the water level of Wangjia-dam is resultedin by the heavy rainfall in the upriver of Huaihe River Basin 2 days later, then the water level of Wangjia-dam exceeds the dangerous level after 2 phases rapidly increase. Based on the comparison and analysis with historical flood year of Huaihe River Basin, the result shows that the accumulated precipitation during the period of Meiyu in Huaihe River Basin in 2007 is the fourth heaviest in history, which is only less than the flood year of 1954, 1991 and 2003. Nevertheless, the water level in the main Huaihe River Basin is higher than that in 1991 and 2003, which is the second in historical record since 1954.The water level of Wangjia-dam is associated with the area rainfall of Wangjia-dam-Dapoling and Dabie-mountain valleys. The high water level of Wangjia-dam is caused by the heavy rainfall in the upriver of the Huaihe River Basin, which reflects the hydrological characteristics caused by the special geographical condition: The rainfall in the upriver is the main factor to bring the high water level in the main Huaihe River Basin.
Mesoscale and Microscale Analysis on a Local Torrential Rain Event in Fragrant Hills Area of Beijing on July 9, 2006
Guo Hu, Duan Li, Yang Bo, Bian Sufen, Li Jing
2008, 19(3): 265-275.
The local rainstorm in fragrant hills area of western Beijing at night on July 9, 2006 is an intense rainfall event, which covers only around 10 to 20 kilometers, and the severe rain lasts only 2 hours. Considering the temporal and spatial scale and the distribution of the rainfall, it is difficult to analyze and describe by regular meteorological data and synoptic-dynamic diagnosis methods even mesoscale dynamic models. Therefore, it is studied by intensified observation data including Doppler weather radar products, wind profile data, wind element of surface automatic weather stations and detection data of atmospheric water vapor by GPS, etc. It is found that development of the meso-γ scale heavy rain, even the disturbance in surface and boundary layer around the rainfall area, can be captured by the above mentioned data. Moreover, meso-scale convective system of the local heavy rain event and dynamic mechanism forming severe rain can also be explained by these data exactly.Fine research on the local heavy rain event by these observation data shows that topographic convergence line is proved to be the major system that causes the local torrential rainfall, and the formation and development of mesocyclone in the echo belt by topographic convergence line is the main factor causing the heavy rain. Convergence in atmospheric surface layer is very important in the local heavy rain event. Besides, the studies show that topographic convergence disturbance in surface layer in front of the mountain spreads upward giving rise to boundary layer disturbance which is the main dynamic factor of the heavy rain in fragrant hills zone. Sufficient water vapor and energy for the heavy rainstorm are provided by warm-moist advection of atmospheric surface layer from southeast.From the above analysis, it is concluded: Against the large scale background of warm-moist airflow ahead of long-wave trough in middle troposphere about 500 hPa in the daytime in summer and weak anti-cyclone wind in low layer in Beijing, topographic convergence echo belts can be formed by formation and development of southeast wind in surface layer at dusk on the plain. Meso-γ scale echoes with features of mesocyclone in the echo belts move and develop from southwest to northeast along southwest airflow ahead of 500 hPa long-wave trough. It is the major cause that brings the local rainstorm in fragrant hills area of Beijing at night on July 9, 2006. Convergence in atmospheric surface layer plays an important role in the local heavy rain event. There are three types of convergence simultaneously during the severe rain period of two hours: Wind shear convergence between the southeast wind from the plain and the north wind from the mountains, convergence and lifting of the southeast wind from the plain by mountains, and cyclonic convergence of meso-γ scale system in the center of rainfall region. Fine research on wind profile data around heavy rainfall region shows that there are disturbance in surface layer and it spreads upward, then boundary layer disturbance appears twice during the severe rain period during the two hours. Each propagation is about one hour and twenty minutes. It is one of the main dynamic mechanisms that cause the local heavy rain to occur. According to GPS water vapor data and Doppler radar velocity products, there warm-moist airflow in atmospheric surface layer from southeast to the core of the heavy rainstorm before and during the torrential rain.
Relationships Between Prediction Errors and Physical Predictors in Dynamical Seasonal Prediction
Ren Hongli
2008, 19(3): 276-286.
In order to better improve dynamical seasonal prediction by utilizing statistical experiences, the problem of capturing statistical experiences associated with climate model is discussed from the point of view of studying the impacts of physical predictors in climate system on model prediction errors. As model errors objectively exist in climate model and vary with the sate of climate system, the prediction errors of model change with state. Thus, deeply examining the characteristics that how the prediction errors of model are influenced by climate system state has important values to capture the statistical experiences associated with model and improve dynamical prediction in terms of the combination of dynamical and statistical methods. Problems and their meanings related with above characteristics are primarily proposed.Based on hindcast data of air-ocean coupled general circulation model in National Climate Center, China Meteorological Administration, the relationship between the prediction errors of summer mean circulation and total precipitation in dynamical seasonal prediction, and some primary physical predictors are comprehensively examined. These physical predictors selected include the sea surface temperature index in Niño3 region, the Pacific decadal oscillation index, the southern hemispheric annular mode index, the northern hemispheric annular mode index, and the North Atlantic oscillation index, which reflects the prevailing modes of interannual variability in climate system over tropics and extratropics.Results of correlation analyses show that there are some significant early or simultaneous relationships between the above-mentioned physical predictors and the model prediction errors of summer circulation and precipitation. In the five selected physical predictors, the sea surface temperature index in Niño3 region mainly correlates with the prediction errors of low-latitude circulation and precipitation. The correlationship between the Pacific decadal oscillation index and prediction errors is mostly characterized by simultaneous correlations and is significant not only over some low-latitude but also mid-and high-latitude areas. The southern and northern hemispheric annular mode indices standing for the leading modes over two extratropics are not corresponding to the evident early correlation with only some significant correlations over partial extratropics, whereas the simultaneous correlations are relatively evident and characterized by the distribution patterns similar to spatial modes of the two extratropical indices. The correlation situations between the North Atlantic oscillation index and circulation errors are very analogical to those corresponding to the northern hemispheric annular mode index, whereas the early and simultaneous correlations between it and precipitation errors are much better than those corresponding to circulation errors.By examining the physical processes that physical predictor influences the distribution of model prediction errors, investigating the relationship between predictor and prediction errors will not only help to evaluate the performance of model and provide reference for improving model, but also benefit the development of the new prediction strategy and methodology for correcting prediction errors. Thereby, physical basis and practical reference are provided to develop new method of predictor-based error correction, which will be studied and verified in further work.
An Accuracy Estimation of Global Solar Radiation Measurements at Meteorological Observatories in China
Qiu Jinhuan, Xu Xiaofeng, Yang Jingmei
2008, 19(3): 287-296.
When routine observations are performed by the pyranometer in the outside field, measurement errors will be caused by some factors, such as the polluted camera lens by which the measured value will be made less than the reality, as well as the temperature error, the cosine errorand the tilt error etc. Reliable accuracy estimation of the pyranometer-received global solar radiation (GSR) is significant to improve the use of the measurements. In the case of thin aerosol optical thickness (AOT) and small solar zenith angle, three characteristics of pyrheliometer-received GSR are presented. Compared with the diffuse solar radiation, the direct solar radiation contributes dominatingly to GSR; owing to the opposite shifts of direct and diffuse solar radiation with increasing AOT (the former decreases while the latter increases), GSR shows a weak sensitivity to AOT, molecular optical thickness, aerosol size distribution and refractive index; there is a small hemispherical reflectance and hence a weak sensitivity of GSR to the surface albedo. According to these properties, a method for accuracy estimation of GSR measurements at Chinese meteorological observatories is proposed. In the condition of cloud-free, thin AOT and small solar zenith angle, the solar constant (marked as E0, P) is retrieved from the GSR measurements and the broadband transmittance which is calculated using AOT retrieved from direct solar radiation. The deviation of the E0, P to the GRR (global radiation reference) is treated as an indicator of the uncertainty of GSR data. The simulations show that the uncertainties of the imaginary part of aerosol refractive index and the water vapor content are the two main error factors. Effects of random errors in input parameters such as aerosol optical properties, water vapor content and so on can be weakened by more statistical examples for the estimation, then more reasonable estimation results are produced. This method is applied to evaluating accuracies of GSR data at seven observatories which are Shenyang, Ejin Qi, Beijing, Urumqi, Golmud, Shanghai and Guangzhou in China. There are totally 1161 E0, P retrievals from GSR data in these seven observatories during 2000—2004, which are all measured in such conditions as clear (cloud-free) days; the solar zenith angle cosine (μ0) being larger than 0.7; τa(750 nm AOT) /μ0 < 0.3; the atmospheric column water vapor content being less than 2.0 cm. Among all these E0, P retrievals, the maximum deviation to GRR is 7.33 %, deviations of 97.78 %, E0, P retrievals are less than 5%, and the standard deviation is within 4.05% for every observatory. It is estimated that the uncertainty of GSR data in these observatories is usually better than 5% in the clear days and for μ0≥0.7.
An Introductory Study on the Calibration of CE318 Sunphotometer
Yang Zhifeng, Zhang Xiaoye, Che Huizheng, Zhang Xiaochun, Hu Xiuqing, Zhang Lijun
2008, 19(3): 297-306.
The indoor and field calibration methods of CE318 sunphotometer are mainly explored and the calibration results of the two methods are compared. Based on integrating sphere radiation calibration method, an experiment is carried out for the calibration of the sky scattering radiation channels at eight different wave bands of CE318 sunphotometer. Langley calibration method and standard instrument relative calibration method are used to calibrate sun direct radiation channels at different wave bands of CE318 sunphotometer. The results of this experiment show that the calibration results of sky scattering radiation channels at 670 nm, 870 nm, 1020 nm and the original calibration of the same instrument are fundamentally equal with the discrepancy less than 6%. It has high reliability. Unfortunately the result of the wave band of 440 nm is higher than the original calibration, and the departure range is about 18.9%. Based on the calibration results, it can be concluded that there are good feasibility and reliability in using integrating sphere for calibrating the sky scattering radiation channels. However, there is a little difference between the calibration results and theoriginal calibration. Considering the fact that aging filters might be led to by using conditions and measurement for long periods outdoors, some aerosol particles may fall on the filters which are inside the sensor head, even because the filters run very long time, so the filters are made broken. Generally speaking, the calibration results of the sun direct radiation channels are slightly larger than theoriginal calibration. The results show that the filters of some channels are aging, so it is necessary to replace them to ensure observation precision. In addition, the comparisons between the Langley method and standard instrument relative calibration method are made. It shows from the comparison results that good weather conditions on the day of calibration are required by the Langley method, which include clear sky, cloud-free and stable atmosphere, and very accurate standard instrument is required by the standard instrument relative calibration method. Because the standard instrument relative calibration method is more advantageous than the Langley method from the comparing results, the standard instrument relative calibration method is employed by the present study to calibrate the CE318 sunphotometer in the CARSNET (China Aerosol Robot Sunphotometer NETwork) of China Meteorological Administration to guarantee the precision of the observation data.
Test of the Synthetical Multilevel Analog Forecast Technology in Short-term Rainstorm Prediction
Li Bo, Zhao Sixiong, Lu Hancheng, Yang Guoxiang
2008, 19(3): 307-314.
A new synthetical multilevel analog forecast technology (SMAT) is developed to make the analog forecast trial of different pattern rainstorm process in a selected region, including cold front pattern, typhoon pattern, quasi-stationary front pattern, cyclonic pattern, inverted trough pattern etc. The new forecast system's research process, the study results and its application are introduced. "Synthetical" represents the combination of various meteorological elements, combination of large scale weather condition and meso-scale weather condition, combination of static simulation and dynamical process simulation. Multilevel indicates three level forecast flows by which different aspects are described and are embodied in a harmonious body. The basic element field is used to reflect macro-atmospheric circumstance (large scale) similitude, local physical elements are used to reflect local climate trait (meso-scale) similitude, numerical model integral products are used to reflect dynamical process similitude. "The reducing FAR (vacant-forecast rate) " technology and extremum check method are included in SMAT, which are useful in selecting analog terms and optimizing forecast conditions' combinations. Multi-meteorology terms and physical conditions' combination are also included in SMAT, which are useful in each analog level trail. This is a step forward than the former single element analog. The science problem analog criterion alters a lot with different analog elements and ranges and it is pointed out, the following method is used to resolve this problem. Analog degree in a more general view can be described by evaluating various good elements and their combination samples. The key analog range is selected from some possible ranges. In the 3rd level analog process, assimilation numeric products are imported. Moreover, based on double-times rolling forecast, losing-forecast events can be decreased. This is good to improve forecast capability in disastrous weather. The following conclusions can be drawn. The historical testing CSI (forecast successful index) of each pattern is more than 0.4 (some are even more than 0.6), model testing average CSI is 0.37, this is better than other work in the same field. Better indexes can be gotten in the 3rd level forecast than double levels forecast. The selection and operation way of critical analog deviation suggest the idea of "false alarm better than miss hit". This leads to the high false alarm index. The 3rd level forecast based on the model products can be used in reducing the false alarm index. After revising the model continuously, model average forecast ability can be improved. Comparing with other current forecast methods (CSI is about 0.35), a revised model testing average CSI (0.392) is obtained. SMAT is also good at COR (forecast precise rate) and POD (miss hit forecast rate) index. Results show that successful forecast in various rainstorm process is achieved. SMAT model has a stronger forecast capability.
Numerical Experiment of the Coupling of CAMS Complex Microphysical Scheme and GRAPES Model
Sun Jing, Lou Xiaofeng, Hu Zhijin, Shen Xueshun
2008, 19(3): 315-325.
The schemes describing the moist physical process in the meso-scale model include the microphysical scheme and the cumulus parameterization scheme. The rainfall calculated in cumulus parameterization scheme is in subgrid scale and the rainfall calculated in the microphysical scheme calculates is in grid scale. With the improvement of the model resolution, the microphysical scheme has become more and more important in the meso-scale model. More detailed microphysical processes are described in the mixed-phase microphysical scheme, so that it can be used in many researches such as microphysical mechanism of precipitation, the interaction between cloud and radiation, lighting activity of cloud and so on. Therefore, it is very necessary and significant to study and improve the mixed-phase scheme of the meso-scale model. GRAPES (short form of Global/Regional Assimilation and PrEdiction System) is the new generation numerical model system in China. In order to improve the physical processes in GRAPES model, CAMS (Chinese Academy of Meteorological Sciences) complex microphysical scheme is coupled with the meso-scale regional GRAPES system.CAMS complex microphysical scheme is a double-moment mixed-phase scheme. There are 5 kinds of hydrometeors in this scheme which are cloud water, rain water, ice, snow and graupel. The scheme includes 11 prognostic cloud variables. They are the mass content (Qv, Qc, Qr, Qi, Qs, Qg) and number concentration (Nr, Ni, Ns, Ng) and the extent of cloud droplet spectrum. There are 31 microphysical processes in the scheme. Not only the mass content can be predicted but also number concentration of hydrometeors. In this study, new microphysical variables and a new microphysical option are added into GRAPES. A numerical experiment is conducted using the new model. The case simulated is a heavy rainfall happening in North China during August 15—17, 2005. The model is integrated for 48 h with 60 s time step. Three other microphysical schemes are selected to simulate the same case to make a comparison.They are Thompson scheme, WSM6 scheme and NCEPcloud5 scheme. The simulated results of distribution of rainfall and hydrometeors are analyzed. Results are shown as follows. The distribution of rain band simulated by CAMS is similar to the observation and the development of rain band simulated by CAMS is consistent with those of other three microphysical schemes.The center of heavy rainfall simulated needs to be improved.The comparison of the regional average hydrometeors made between CAMS scheme and other three microphysical schemes shows the similar general characteristics. CAMS scheme is able to simulate the hydrometeors in reasonable distribution and value. Due to the different microphysical process in different scheme, the values of hydrometeors of four microphysical schemes are different. Results reveal the good capacity of CAMS scheme in describing cloud and precipitation processes in GRAPES model. The new scheme should be tested through numerical experiments and fine model design in the future.
Characteristics of Area Precipitation in Xinjiang Region with Its Variations
Shi Yuguang, Sun Zhaobo, Yang Qing
2008, 19(3): 326-332.
Using the data of precipitation including 144 meteorological and hydrological stations in Xinjiang from 1961 to 2005, annual and seasonal distributing features and its variations of area precipitation in Xinjiang are discussed by empirical orthogonal function (EOF), multiple regression analysis, maximum entropy analysis and so on, combining with 1 km×1 km gridding data of digital elevation model (DEM). Results show that mean annual area precipitation in Xinjiang region is 2724.6×108t and mean annual precipitation is 165.5 mm. For space distribution, area precipitation of Tianshan Mountains, Northern Xinjiang and Southern Xinjiang respectively occupy about 40.4%, 34.3% and 25.3% of all regions, and its mean annual precipitation are 409.1 mm, 277.3 mm and 66.2 mm, respectively. Area precipitation in summer is the most one about 54.4% of all year, 23.6% in spring, 16.5% in autumn, and the least 5.5% in winter. In the last 45 years area precipitation in Xinjiang presents clear annual variations and increasing trend, especially since 1987.
Climatic Characteristics of Disease by Colletotrichum gloeosporioides Penz on China Wolfberry in Yinchuan
Liu Jing, Zhang Zongshan, Zhang Lirong, Shen Ruiqing
2008, 19(3): 333-341.
The Colletotrichum gloeosporioides Penz is a fatal disease in Ningxia wolfberries, by which heavy economicloss is caused by deeply influencing its quality and yield. As an original habitat, it is very important to understand the biological characters of Colletotrichum gloeosporioides Penz, as well as its meteorological conditions and climate rules, so as to release the hazard of disease by decreasing the yield loss and the quality decline by means of effective and timely prevention and cure. After separating and breeding, effects of environmental conditions on the mycelia growth, sporulation, conidial germination of Collectotrichum gloeosporioides Penz are studied and its lethal temperature is detected by controllable climate boxes in 2004. The problems of the mycelia growth, number of sporulation and conidial germination in connection with different temperature, humidity, pH, carbon resource, nitrogen resource are obtained. The suitable and limited temperature and humidity index on every growth and sporulation stage is also set up.Based on meteorological conditions and its indexes on invaded Colletotrichum gloeosporioides Penz into branches of Lycium barbarum L, which are collected into laboratory and grow on the field during the growing season in 2004 and 2005, it is obtained that those meteorological conditions and indexes are the cause of the invasion and expansion by different amount of rainfall supply. According to perennial climatic data in the main planting areas, the status and time of disease of Lycium barbarum L caused by Colletotrichum gloeosporioides Penz have been simulated in each year from 1971 to 2000 in Ningxia.The results show that the suitable temperatures for mycelia growth are 22—31℃, the maximum and the minimum temperatures are 10℃ and 37℃ respectively. The same is for sporulation, but it is not for conidial germination whose suitable temperatures are 16—37℃ and extremum values are 10℃ and 40℃. The lethal temperature is 50℃, much different from the former researchers. The limit humidity for conidial germination is lower than 80% and the suitable one is upper 90%. The invasion of Colletotrichum gloeosporioides Penz to the leaf, flower and fruit is suitable under the temperatures of 28—32℃. The lower and the upper temperatures are 20℃ and 35℃ respectively. The injection experiments under different amount of precipitations in the field show that 5 mm, 10 mm, 20 mm and 40 mm are indexes that cause Lycium barbarum L anthracnose occurrence, diffuseness, popularity and expansion respectively.Suitable climatic condition for anthracnose occurrence of different degrees almost appears every year in growing season, mainly from middle July to early September.The frequency is over 70% that the conditions suitable for anthracnose occurrence are from the end of July to the end of August in the total 30 years, especially in the period of last three times of fruit gathering in the summer-fruit crown season. The climatic conditions in early June aren't suitable for the development of anthracnose and the highest incidence rate of disease is in August. The main cause that results in the lower and unstable yield in autumn may not be the inadequate of heat resource, but the destructive disease by Colletotrichum gloeosporioides Penz. The severe anthracnose occurs in the middle of 1970s, early and middle of 1990s in the 20th century. However, the relatively slight diseases appear in late 1980s and 1990s in the 20th century, but individual heavy diseases also happen in those period. By means of investigation, the results are true which indicates that meteorological indexes obtained through experiments are reliable.
Evaluating Aridity and Wetness of the Wheat with Palmer Moisture Anomaly Index in the East of Northwest China
Wang Yue, Jiang Zhihong, Zhang Qiang, Li Ke, Liu Mei, Xue Chunfang
2008, 19(3): 342-349.
Considering the lack of agriculture drought index in China, Palmer moisture anomaly index is introduced. Taking example for Yan'an, theoretical formula and physical meaning of Palmer moisture anomaly index is described. Using the method, the monthly Palmer moisture anomaly indexes of twenty wheat observation stations, such as Yan'an, Wuwei, Jingtai, Xining, Guide, Lanzhou etc, from 1961 to 2000 are calculated in the east of Northwest China, and the aridity and wetness of different period of growth for wheat are evaluated. The calculation of Palmer moisture anomaly index values is based on a supply and demand model of the soil moisture at a location. In addition to the current precipitation, air temperature, available water holding capacity (CWA), some factors derived from water balance equation are considered such as potential evapotranspiration, potential recharge, potential runoff, potential loss, surface soil moisture content, and underlying soil moisture content. Factors of several previous months are based on to establish each Palmer moisture anomaly index value. It shows that the method of Palmer moisture anomaly index is more reasonable to study the flood or drought of different period of wheat growth in the east of Northwest China. The extent of drought and flood event of different periods of wheat growth can't be objectively assessed by Z-index. The difference of years with same precipitation and different temperature and CWA can't be distinguished. Palmer moisture anomaly index in comparison with others is a good indication of the severity and extent of flood/drought event and of more objective classification of them, which is therefore quite applicable to an extended area. All these show that Palmer moisture anomaly index is more objective than Z-index for analysis on aridity and wetness in different period of wheat growth, and more accords with the results of analysis on aridity and wetness of the wheat in different period of growth. Analysis shows that Palmer moisture anomaly index can be the analysis tool of agriculture aridity and wetness in semiarid and semi-wetness regions in the east of Northwest China.
Simulation and Analysis on Light Environment of Greenhouse in Beijing Area
Liu Hong, Guo Wenli, Li Huijun
2008, 19(3): 350-355.
Daily light integral is determined by outside radiation and the light transmission rate of greenhouse. The greenhouse light environment is affected by factors like latitude, building location, surface material, skeleton structure and configuration density. Typical solar greenhouse is studied that is used to grow tomato and others vegetables in winter in Beijing. Based on the observed data of meteorological elements of radiation, temperature, humidity etc, both inside and outside solar greenhouse, using the mathematical method and computer simulation, the sun-light incidence rate of different surface radian curves of greenhouse is calculated. A mathematical model for solar radiation on the surface of a solar greenhouse is proposed and the heat transfer of a solar greenhouse with 8 m span is simulated.Five aspects are included in the model. Solar greenhouse mainly contains the surface, the back-wall, the roof and the gables, the gables' influence on solar radiation is not considered, assuming that the length of the solar greenhouse is unlimited. The direct radiation, sky radiation and the reflection radiation that the surface receives are calculated. The surface received solar radiation is divided into three parts. One part of the radiation is reflected by the surface, another part is absorbed by surface, the rest of the solar radiation goes into the greenhouse. The radiation distribution is calculated. The greenhouse direct radiation is not fully exposed on the ground. Direct radiation distribution and intensity in various parts of solar greenhouse under different times are calculated. In accordance with the direct radiation transmittance calculation algorithm, the sky radiations transmission rate is calculated. Then, according to the integral methods, sky radiations distribution and intensity in various parts of solar greenhouse under different times are simulate. The influences of crop growth on solar radiation are reflection and absorption. In accordance with crop growth dynamic change, the ground radiation changes. Radiation intensity on ground is calculated based on the law of diminishing index. Based on the experimental data and the literature, the simulating data of the ground radiation are analyzed and compared. The accuracy of simulation models is reasonable. The mean absolute difference is 9.41 W/m2, and the relative coefficient is 0.92. The model is valuable to simulate the relationship between environmental factors and crop growth, and it is significant to provide reference for optimization of greenhouse environment control.
Relative Humidity Error of L-band Electronic Radiosonde and Its Application
Yao Wen, Ma Ying, Xu Wenjing
2008, 19(3): 356-361.
The upper-air sounding data are one of the basic data applied in meteorology. The analysis and forecast of synoptic situation and weather system are directly affected by the accuracy of the data. Therefore, for the purpose of improving sounding accuracy, L-band electrical radiosonde has been employed broadly since January, 2002. Its data acquisition rate, accuracy and reliability, and the degree of automation have improved significantly since then. The new radiosonde has been implemented with carbon-film hygristor instead of Gold beaters skin hygristor to measure relative humidity. The measurement is made more accurately by the high sensitivity, short lag time, and fast response in low temperature of upper-air of carbon-film hygristor. In addition, the carbon-film has good consistency with device calibration line, which does not need to calibrate one by one. So the cost of production can be saved. The carbon-film hygristor, however, is significantly influenced by temperature. Data errors will be yielded by failure to calibrate it accurately. There are many researches on carbon-film hygristor performances but still without very encouraging results. Because of the complexity of upper-air observation, there is not a widely accepted standard to test sounding instruments' performances by the international community. Right now, the relative humidity data are corrected mainly by the radiosonde manufacturer. Whether the applied revising formula is reasonable or not, how is the corrected results, all need to be tested by objective analysis. However, a large number of the actual release record still shows a huge error in relative humidity sounding curve. Especially the unstable relative humidity data in the clouds which decrease strikingly with the increased altitude, and the decision of cloud location are affected directly. The accuracy of temperature detection and calculation of the geopotential height are thereby lowered. The process of correcting relative humidity data of the new L-band sounding system is described. Using the high-resolution humidity calibration equipment, many static-state testing experiments of the carbon-film hygristor are conducted at temperatures from-30 ℃ to 30 ℃, by which a substantial amount of data is acquired. Through the test results, the various properties of this element in detail are noticed. Also a mistake in correcting formula by the manufacturers is found because of their negligence to test the influence of paralleling 1 Megohm resistance in the circuit. Based on the analysis and calculation on these lab data, the correction equation of relative humidity is re-established. The comparison and analysis of correction on real upper-air sounding data of relative humidity indicate that not only the accuracy of relative humidity data is improved after correction, but also the detailed variations in relative humidity at the upper atmosphere during high humidity range can be clearly manifested. So the ability to judge vertical position of cloud layer is improved, so is the temperature measurement precision.
A Simulation Study on Raindrop Orientation Variation to Dual Linear Polarimetric Radar Observation with Different Transmitting and Receiving Model
Hu Zhiqun, Liu Liping, Xiao Yanjiao
2008, 19(3): 362-366.
On the basis of scattering and attenuation theory of raindrop, the coupling relation between vertical and horizontal polarimetric wave is analyzed with numerical simulation methods in the same transmission and receiving waves (STSR) and alternate transmission and receiving horizontal and vertical waves (ATAR) model. While radar beam passes through uniform rain area, the variety of horizontal reflectivity ZH and its error ΔZH, differential reflectivity ZDR and its error ΔZDR, the differential propagation phase shift ΦDP and specific differential propagation phase shift KDP and its difference ΔKDP brought by raindrop slant are compared respectively along with distance between the two polarimetric models. The results indicate that the ZH of STSR are bigger and ZDR are smaller than ATAR model while raindrop is slant, so the errors of ZH and ZDR in STSR model are bigger when attenuation are not considered. While attenuation is considered, the errors of ZH in STSR are small, the errors of ZDR of 3.2 cm are small too, and that of 5.7, 10.7 cm are big. However, the difference of ZH and ZDR between models is little because the raindrop slant is small in real air. Influenced by raindrop slant KDP is bigger in ATAR model than in STSR, it decreases less than in STSR model, so the difference of ΔKDP between models is more while the slant angle increases. The shorter the wave length, the bigger the KDP, and the larger the ΔKDP are impacted by slant. In addition, two real value definitions of ZH and ZDR are addressed, by which the scattering effect of raindrop slant is considered or not. The actual microphysical structure of raindrop can be better represented by the value of not considering slant, the influence of propagation effect is eliminated, and the full size is reflected accurately, which are better representatives on the application of radar data such as quantitative estimation precipitation. It is more reasonable that the none-slant-consideration ZH, ZDR values are regarded as the real definitions.
The Performance of TUVR Ultraviolet Radiometer
Tan Haobo, Deng Xuejiao, Wu Dui, Jiang Chenglin, Li Fei
2008, 19(3): 367-371.
An ultraviolet radiometer (TUVR) by the Eppley Lab of the United States is among the most popular instruments used for its reasonable design. Although not being able to detect the overall ultraviolet radiation, irradiance at the frequency section between 385 nm and 400 nm could be measured. After some time since the instrument is first put into use at the institution affiliated with the authors, the irradiance readings are found to attenuate a little. Under normal circumstances, it has to be sent back to the manufacturer for calibration, which is unpractical and costly. Under existing regulations in this regard, the instrument is probably discarded. When spectrometers are not an option as they are inconvenient for field operation, two new instruments are then introduced as reference to determine the cause of errors and ways of correcting data received. For this purpose, experiments are designed and conducted to analyze quantitatively the error source and contribution of measurement of surface UV radiation using the ultraviolet radiometer. The result shows that the degradation of sensors and pollution in the teflon diffusing disk are the main error sources. The decreasing rate (y) of sensors decreases linearly with its exposure time (t) and the fitting curve in Guangzhou is y=0.66t. The measuring error from the diffusing disk is mainly related to air pollution. Although the transmission of cleaned disk will be changed, it has linear relation with that of the original diffusing disk, and the adherence to Lambert cosine law is not affected. The value corrected by factors is very close to that of standard radiometer, and the correlation coefficient approaches 1.0.
Physical Meanings of "Cave Channel" in Strong Convective Storm with Its Application
Xu Huanbin, Tian Liqing
2008, 19(3): 372-379.
Since the "cave channel"(CC) or "zero region"(ZR) structure is suggested, several papers are published on this title. The understanding of the physical meanings of CC or ZR is deepened by these papers, but in principle and application there are questions to answer or clear up, such as the conditions of formation of CC or ZR in strong storm, the analogous CC in rain-storm, why previous studies do not indicate the existence of CC, how to find CC structure in practical application etc. These questions are answered and the meanings are further understood by observation facts and numerical simulations. It is shown explicitly as the following. The CC or ZR structure is the results of the interaction between cloud's macro-flow field and cloud's micro-particle terminal velocities in nature. Some special structure of radar echo is BWER (bounded weak echo region), WER (weak echo region) or OE (overhang echo), it is the product of the interaction too. The interaction can play very important role only when the terminal velocity of particles is equivalent to the velocity of airflow. If the terminal velocity of particles relatively is too small or too large the effects of this interaction are very weak. The study of this interaction can deepen the understanding of the dynamical and physical meanings of the radar products, it is much necessary to find the characteristic criteria for now-casting of high-impact weather and in weather modification.
Application of Geographic Information System to Decision-making Meteorological Service System
Wu Huanping, Luo Bing, Wang Weiguo, Duan Yan'e
2008, 19(3): 380-384.
Based on the component GIS technology, a framework of decision-making meteorological service system is proposed, which is composed of three layers. The lower layer is the data layer where meteorological data, geospatial data and socioeconomic data are mainly stored, and fundamental data for upper layers are provided. The middle layer is a general core meteorological component developed by GIS components, which is composed of many basic functions and interfaces to support the upper application such as interpolation algorithm and spatial measurements. The upper layer is the service platform including specific features for products building and decision-making. This multi-tiers architecture has greatly enhanced the reusing, sharing and scalability of the application. Six features of the system are introduced in brief as follows :Electronic map querying, meteorological mapping, historical and real time data retrieval, damage statistics and analysis, typhoon warning and damage assessment, and customize mapping automatically. Five key issues of GIS applying to meteorological service system are addressed. Firstly, to make current meteorological data share with GIS community, conversion method of meteorological data to the GIS format are discussed, complying with GIS concept data model, such as shape and GRID format. Secondly, spatial interpolation algorithm is focused on, and the potential and limitations of existing GIS interpolation functionality for specialization of meteorological and climate data are studied, and then a recommendation algorithm for specific application is set up. Thirdly, the meteorological element retrieval based on spatial technology is discussed. The fourth key issue is that plug-in software technology is adopted to build an assessment model about typhoon disaster evaluation, which can easily be added to and removed from the system since the model is changed constantly. Last, a surface model is introduced to implement three-dimensional visualization of meteorological data. In conclusion, it is found that the meteorological mapping capability can be greatly strengthened by GIS, the visualization effect of services produces can be improved, and spatial retrieval of meteorological elements can be implemented, disaster weather can be analyzed deeply for auxiliary decisionmaking.