应用气象学报

Interannual and Interdecadal Variations of Winter Water Budgets in the East Asian Monsoon Humid Region

Liao Rongwei, Zhao Ping

2011, 22(6): 641-653.

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Abstract:
Using monthly means of NCAR/NCEP reanalysis datasets and rainfall data from 160 surface stations in China, a water budgets sequence over the East Asian Monsoon Humid Region is calculated by a water vapor transport method for the period from 1958 to 2007, referring to changes in water budgets associated with the anomalous atmospheric circulations and precipitation in the East Asia Monsoon Humid Region. Relationships between the water budget index and the variability of the atmospheric circulation and rainfall in China are examined. Results show that the established water budgets sequence displays the variability on the interannual and interdecadal scales. The higher-index values mainly occur in the 1960s and the 1980s and the low-index values mainly occur in the 1970s and the 1990s. The index reflects the variations of the meridional winds anomalies and indicates an intensity of winter monsoon and an anomaly of rainfall along the valleys in the East Asian Monsoon Humid Region. Corresponding to the higher-index values, the high pressure centering in Mongolia and the low pressure centering in the Aleutian Islands are weaker. Meanwhile, the southerly wind anomalies are prevailing in the lower troposphere in the East Asia and cyclonic circulation anomaly appears in the vertical troposphere over the mainland of China. This anomaly intensifies the convergence and upward motion to the south area of 30°N, driving the warm water vapor transport coming from the Bay of Bengal and the South China Sea, and increases the water budgets and precipitation, with the difference of rainfall above 40 mm. The anomalous water vapor transport mainly appears between 600 hPa and 900 hPa, where the western and southern boundaries are the major input regions, the eastern and northern boundaries are the major output regions. The anomalous water budget is larger in meridional than in zonal direction, accounting for 91.3% for the changes of net incoming and expenditure while the anomalous zonal water budget is smaller. So the main cause for the difference and significant anomaly for rainfall is the changes of the incoming and expenditure water budgets in meridional. The differences for water budgets and rainfall in north and south parts are significantly different, which contribute greatly to the changes of zonal income and expenditure. The inter-decadal variability of water budgets reflects the strength of the water vapor transport and the amount of water vapor from the ocean, and also indicates an anomaly of the interdecadal rainfall variation in the East Asian Monsoon Humid Region with a rainfall anomaly above 30 mm.

alidation of Atmospheric Radiative Transfer Model with Field Experiments Using Tethered-balloon-borne Facilities

Zhang Wenxing, Lü Daren, Huo Juan, Wang Yong, Sun Baolai, Li Liqun

2011, 22(6): 654-662.

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Abstract:
Atmospheric radiative transfer and its algorithms are the theoretical basis and effective tools in the field of remote sensing and inversion algorithm in the earth system, and also the key tools for the space,ground target recognition and quantitative assessment of background radiation. During recent decades, a series of radiative transfer(RT) model have been proposed to support a large variety of quantitative remote sensing as well as target,background discrimination research and applications. Owing to respective approximations and simplifications inherent in those RT models, their accuracy, uncertainty and adaptability are of critical significance to different researchers and end users. Validation of the RT model for its different wave band, in particular by using field experiments is necessary, especially for those applications with higher accuracy demands. Among the RT codes currently used, a considerable part of them are MODTRAN and its evolution versions. In China, MODTRAN has also been applied to the study of remote sensing, atmospheric correction of satellite images, and a wide range of applications in the atmospheric sciences, hence, the validation mainly focuses on MODTRAN model and the thermal infrared window 8—14 μm (714~1250 cm^-1) band first of all. Due to little atmospheric absorption in the infrared window band and very low radiance, this band is a range of wavelengths to which the Earth's atmosphere is relatively transparent, and is an important band used for space,ground target recognition, and ground/satellite-based remote sensing as well. Because the spectral composition of radiation transfer varies greatly with varying local environmental conditions, such as aerosol characteristics, water vapor content, surface temperature, greenhouse gases and so on, the accuracy that MODTRAN demonstrates should be attained by making the comparisons between observed radiances and the radiances computed from coincident in situ profile data. For field experiment validation, a scheme is proposed, using a special patented tethered balloon as platform and a combined sensor system consisting of both meteorological (GPS radiosonde, aerosol particle spectrometer, ozonesonde) and radiation observation instruments (visible and broadband thermal infrared imager), as well as wireless receiver,transmitter. Field experiments are conducted in August 2006 at IAP's Xianghe Observatory. During the process the tethered balloon going up and down in the atmosphere of boundary layer, measurements of both meteorological and radiation instruments at different height are carried out simultaneously. Using the observed meteorological parameters as input to RT model (MODTRAN 4.0), comparisons between observed radiances and radiances output from the model are used to validate the accuracy of the RT algorithm. The balloon is launched and drawn back for 16 times to do the validation. Analysis on the experiment results show that in thermal infrared wave band, the statistical results of the root-mean-square error of relative error between model output (with real-time meteorological parameters as input) and simultaneous radiance measurements is less than ±3%

An Improved Retrieval Algorithm of Aerosol Optical Depth

He Tao, Zhao Fengsheng

2011, 22(6): 663-672.

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Abstract:
The algorithm to retrieve the aerosol optical depth over land has been completely restructured to produce the collection 005 products based on the algorithm by Levy et al. But the accuracy of the MODIS aerosol optical depth (AOD) products still has very large differences for different seasons and geographic locations in China. In order to improve the accuracy of aerosol retrieval products, an easier and faster algorithm for retrieval of aerosol optical depth over land with MODIS 1B data is introduced. This algorithm deals with the surface reflectance relationships is the same way as MODIS V5.2 algorithm.In order to better represent aerosol properties in China, the size distribution and refractive index of aerosol have been improved. Considering the fine structure of the aerosol size distribution has a little effect on satellite remote sensing of aerosol optical depth, this algorithm use the Junge aerosol size distribution to approximate the aerosol size distribution in an actual atmosphere. The real and imaginary index of refractive is 1.5 and 0.005, respectively.The complex refractive index is assumed for all wavelengths (0.47, 0.55, 0.66 μm and 2.1 μm). In order to verify the accuracy and regional applicability of this algorithm, aerosol optical depth is derived with this algorithm using the MODIS 1B data at Taihu and Xianghe, and this retrieval result is compared with equivalent measurements from AERONET (AErosol RObotic NETwork) site (Level 2.0 data). The MODIS/AOD product and 1B data from September 2006 to June 2008 at Taihu (MODISI/AOD product and 1B data from May 2008 to July 2009 at Xianghe) has been matched with L2.0 AOD product from AERONET stations during the same period. Data from the AERONET are averaged within 30 min before and after the satellite's passing, and the MODIS data are averaged over a 10 km (15 km at Xianghe) area centered at the ground stations. The comparison results show that the standard deviation of the new algorithm inversion results and L2.0 AOD product at Taihu is 0.429. The standard deviation of the MODIS/AOD product and L2.0 AOD product at Taihu is 0.693. Accordingly, the standard deviations of two comparison experiment at Xianghe are 0.493 and 0.542, respectively. These results show that this algorithm retrieval results have good consistency with the sun photometer observational results at Taihu and Xianghe. The retrieval algorithm is more accurate than the current MODIS aerosol algorithm and its inversion results are reasonable. In addition, the settings for aerosol model and optical properties are simple and convenient in the new algorithm, which can effectively reduce the computational time for looking-up table and the iteration time for solving equations.

An Ensemble Ocean Wave Forecast System and Preliminary Experiment

Sun Minghua

2011, 22(6): 673-680.

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Abstract:
The basic methods of ensemble wave prediction at home and abroad and an ensemble wave numerical forecast system are introduced. The system is established by running the operational wave model WAVEWATCH Ⅲ using wind data from the 15 members' ensemble weather forecast system, which is based on the T213L31 model and operational running in China National Meteorological Center. The ensemble model calculates 15 members wave field, including one control forecast and 14 perturbation members forecast. The model computes the waves over all the oceans up to 10 days at 12:00 with 1° by 1° resolution. Based on hot initialization, the model uses the 12 h wave hindcast as its initial field. Through the information extraction and processing from the 15 member's wave fields, the system produces the ensemble wave products such as ensemble mean and spread, spaghetti charts and probability charts. Forecast experiment for the period from 1 Sep to 31 Oct in 2007 is done using the system and buoys data in the Pacific and Atlantic at the same period. The main verifying indexes are bias and root mean square error. For the mean monthly bias of 10 m wind speed and significant wave height, the performance of the ensemble mean is better than the control forecast, however both of them have a relatively low system deviation and one cause is that the spin up time of the system may not be long enough. For the monthly root mean square error, the ensemble mean of 10 m wind speed is lower than the control forecast by 3—12 percentage for the different forecast periods, meanwhile the ensemble mean of significant wave height is lower than the control forecast by 3—17 percentage with consistent variation trend. Comparing 15 ensemble members' forecast to the Buoy_46006 data, it shows that the ensemble members can follow the changes of the observation well and cover the variation range of the observation other than the deterministic forecast. In summary, the verification results show that the ensemble technique can provide a successful method of extending the standard deterministic forecasts to the probabilistic domain and the prediction skill of the ensemble mean is better than that of one single deterministic forecast. The ensemble method could provide additional information that could not be gleaned from a purely deterministic approach and has a good prospect of application in the field of wave forecast.

Height Assignment Error of FY-2E Atmospheric Motion Vectors and Its Application to Data Assimilation

Xue Chenbin, Gong Jiandong, Xue Jishan, Tao Shiwei, Zhang Hua

2011, 22(6): 681-690.

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Abstract:
Atmospheric motion vectors (AMVs) can provide plenty of useful information for synoptic analysis and numerical weather prediction, because of their excellent temporal and spatial coverage. It is of great value to apply FY-2E AMVs efficiently with the purpose of improving the initial fields and numerical forecasts. The existing assimilation systems in China are in lack of systematic guidance on the quality of FY-2E AMVs, and therefore call for research on optimizing the parameters in data assimilation system, which is very important and foundational to numerical weather prediction.The error characteristics of FY-2E AMVs are investigated on the basis of quality indicator attached. Statistical results demonstrate that the quality indicator of FY-2E AMVs has relatively weak implication of quality, because speed biases and root mean square errors with high quality indicator are still very large. With the study of inversion theory of AMVs, it is found that the inaccuracy of height assignment is the main problem that causes large observation error. According to this problem, the one-dimensional variational method is employed to adjust the height of AMVs. At the same time, the improvement is compared before and after height adjustment by means of radiosonde observations. As a result, it shows that the quality of FY-2E AMVs can be improved greatly after height adjustment. The absolute error of wind speed at every level in the northern hemisphere extra-tropics is reduced from 4 m·s^-1 to 2 m·s^-1 or less, while root mean square error from 10 m·s^-1 to 6 m·s^-1 or below. And the situation improved in the Southern Hemisphere extra-tropics is even more apparent. Height bias has been controlled within 20 hPa at every level below 150 hPa after height adjustment, and the characteristic of single-level wind field is evident. These facts reflect that the height of AMVs designated is systemically high in the Northern and Southern Hemispheres extra-tropics.Furthermore, the method of innovation vector and zero-order Bessel fitting function which is based on the theory of least square method are adopted together to partition background and observation error variances in the observation space, and thus the observation error of AMVs and the quality control coefficient can be estimated according to the statistical distribution of the innovation vectors. In order to validate the assumption on uncorrelated observation errors required in 3DVAR method, observation errors are inflated to avoid the influence caused by correlated errors. Finally, the predictability and impact of FY-2E AMVs data assimilation schemes is assessed in GRAPES global numerical prediction system. The results confirm that short-range forecast ability for the global numerical weather prediction system can be improved in the Northern Hemisphere, by introducing new observation error schemes with height adjustment. The improvement above high levels appears better than those of middle and low levels.

Interpretation of Cloud Classification Using the Color Image Composed by Three-channel Data

Chen Yingying, Tang Renmao, Zhou Yuquan, Yuan Zhengteng, Xiang Yuchun, Li Dejun

2011, 22(6): 691-697.

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Abstract:
Clouds are the result of atmosphere dynamical and thermo-dynamical process. Different cloud types reflect different weather situations and cloud microphysical structure features. Satellite image offers large-area and all-day information of the cloud formation, gathering or disperse. Cloud classification is one of the most important objectives of the satellite image research.At present, only one single channel can be used to identify cloud category at one time. A quick, direct and accurate method of the interpretation of cloud classification has not yet been developed. It becomes particularly important to get the composed information of cloud optical thickness, effective particle radius and cloud top height information quickly.In order to better use the multiple spectral data of Medium Resolution Spectral Imager (MERSI) on FY-3A meteorological satellite to carefully analyze the macro and micro physical parameters of cloud system, according to the fact that the 0.65, 1.6 μm and 11.25 μm channel on MERSI is respectively sensitive to cloud optical thickness, effective particle radius and cloud top height based on the Santa Barbara DISORT Atmospheric Radiative Transfer, SBDART, which is that larger 0.65 μm reflectance means larger optical thickness, larger 1.6 μm reflectance means smaller effective particle radius, larger black body temperature of cloud top means lower cloud top height or warmer surface under clear air, the method of three color compositions is used to the explanation and interpretation of the cloud classification by FY-3A meteorological satellite data on 20 June 2009. The color is composed of red for visible reflectance, green for near infrared reflectance, and blue for the infrared brightness temperature. Redder means larger optical thickness, greener represents the smaller cloud top particles, and bluer means lower cloud tops or warmer surface under clear air.The technology makes different cloud types show in different colors, which is beneficial to directly distinguish cloud pixel from clear sky area, and the land boundary also can be recognized. In this case, cloud located at typhoon eye mainly shows orange-red, while spiral clouds band shows orange-yellow, indicating the reduced optical thickness compared with the typhoon eye. Mixed cloud system covering the Yangtze River Basin shows clear multiple-layer features, low layer cloud is yellow-green, middle layer cloud is dark-red, and high layer cloud shows orange-red. Over the sea, thin dark-yellow cirrus covers the marine stratiform cloud, which is white. Blue means clear air, but there is difference between sea and land because of the different temperature and reflectance.Besides the advantage of multiple spectrums, the 1000 m even 250 m resolution of FY-3A meteorological satellite makes the cloud detailed structure more clearly. The two advantages have greatly improved the accuracy of cloud classification.Meanwhile, the characteristic values for typical cloud, providing empirical values for the initial clustering center of fuzzy clustering method.

The Modification of Meteorological Drought Composite Index and Its Application in Southwest China

Zhao Haiyan, Gao Ge, Zhang Peiqun, Yan Xiaodong

2011, 22(6): 698-705.

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Abstract:
The meteorological drought composite index (I_C) is recommended as an effective operational drought monitoring index from National Standard and has been applied by National Climate Center to monitor drought conditions across the whole country in recent years. However, uncontinurous enhancement of drought is frequently observed in the development of drought process at many stations, where uncontinurous enhancement of drought means that daily change is greater than or equal to one drought degree (-0.6) and the I_C value is equal to or less than 0.6 a day before. In order to optimize I_C, modified standard precipitation index (Z₆₅) by weighted average precipitation (W_AP) is introduced. Due to different weighted coefficients of daily precipitation, modified I_C(I_CW) can decrease uncontinurous enhancement of drought to the most extent. Taking Southwest China as an example, daily I_C and I_CW(modified I_C) from 1 January 1961 to 10 May 2010 is calculated, and the differences between I_C and I_CW in frequency of every drought degree and monthly variability of drought frequency are analyzed. Since formula and value range of I_CW are both similar to I_C, the same drought degree is adopted. It indicates that there is no significant difference between I_CW and I_C in frequency of drought. Moreover, the annual intensity of drought from 1961 to 2009 is also analyzed. The results indicate I_CW is also similar to I_C very much and there is no significant trend of annual intensity. Furthermore, as stable index of drought, uncontinurous enhancement of drought of I_C and I_CW are counted. It shows that I_CW has less uncontinurous enhancement of drought than I_C at all four stations, so I_CW has improved the stability of drought according to different weighted coefficients of daily precipitation. Take soil moisture observed on 8, 18 and 28 as representative, the correlation between I_C, I_CW and soil moisture is analyzed from January 1993 to May 2010. The results show that I_CW has greater correlation coefficients with soil moisture of 10 cm at all stations than I_C, and I_CW has greater correlation coefficients with soil moisture of 20 cm at three stations than I_C, showing that I_CW is more consistent with soil moisture.Above all, the analysis shows that I_CW is close to the characteristics of actual drought and suitable for daily drought monitoring in Southwest China. However, there is still some uncontinurous enhancement of drought existing in I_CW due to great uncontinuous change of M₃₀.

Evaluating the Quality of Temperature Measured at Automatic Weather Stations in Beijing

Yang Ping, Liu Weidong, Zhong Jiqin, Yang Jie

2011, 22(6): 706-715.

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Abstract:
Data quality is a basic assurance for meteorological researches and data applications. Considering data integrality, veracity and confidence, the standard for AWS (automatic weather station) data quality assessment is defined band a set of index is established for AWS data quality assessment and a feasible observation data quality control flow is designed. Following the definition and principia, AWS data can be categorized as correct, mistake and dubious data. The spatial and temporal consistent detections are employed in the data quality control flow. Based on the quality control flow and assessment index, hourly data measured by 187 AWS in Beijing from 1998 to 2009 is evaluated. The results show that the AWS net of Beijing is set up following a fine layout. Although the distribution of AWS is uneven, most AWS is located in urban area such as Haidian and Chaoyang districts, especially in early time of the AWS construction process, some AWS are set up in mountainous area according to the need of different region representative. It is beneficial for urban and rural climate comparing, data sequence reconstruction and regional climate research. The severe missing data is rare, and discrete and slight continuous missing data is just found in concentrated regions and with regional consistent characteristic. The highest error rate of AWS temperature data is 3.8% and it is below 1% in most years. The amount of dubious data is much more than the mistaking data. But more than half of dubious data can be got back after space consistency check. It means that the AWS data in Beijing is reliable. The rates of mistaken data are above 20% after 2004. It shows that the amount of dubious data is not related with the rate of mistake data and on the other hand the uncertainty of AWS data set is reduced after 2004. In conclusion, the assessment result reveals that the AWS data in Beijing are accurate, reliable and show great potential in the future application.

Effect of Meteorological Factors on PM_2.5 in Late Summer and Early Autumn of Beijing

Pu Weiwei, Zhao Xiujuan, Zhang Xiaoling

2011, 22(6): 716-723.

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Abstract:
The characteristics of PM_2.5 concentration of Beijing and the relationship with meteorological factors are investigated, using the PM_2.5 data of Baolian, Shangdianzi stations, sounding data, wind profiling radar data and precipitation data during July, August and September from 2006 to 2008. The results show that the average PM_2.5 concentration of late summer and early autumn at urban station (Baolian) are significantly higher than that of rural station (Shangdianzi). The prevailing southerly air flow of July to September of Beijing can transport the pollutants that generated in Tianjin, Hebei and Shanxi to Beijing. Due to the mountains blocking in the north, the pollutants are very likely to accumulate and form particle pollution. So the wind direction at 1500 m level has significant influence on PM_2.5 concentration. The transport of pollutants by the southerly flow not only enhances the pollution level of urban, but also contributes to the fine particle pollution in regional background areas. The northerly flow is clean, and plays the important role of effective dilution and diffusion of PM_2.5 in Beijing area. The ground wind speed plays different roles in urban and rural areas. The southerly and northerly wind could diffuse PM_2.5 in urban area when the wind speed exceeds 2 m·s^-1 and 3.5 m·s^-1, respectively. In rural area, the northerly wind could dilute and diffuse PM_2.5 effectively, but the southerly wind has no effect of diffusion. The variation of PM_2.5 concentration has positive correlation with precipitation amount and PM_2.5 initial concentration. The precipitation amount and PM_2.5 initial concentration in the process of below-cloud scavenging in urban and rural areas are different. As the most critical factor in the below-cloud scavenging process, the capture coefficient depends on the raindrop size, particle size and the raindrop falling speed. Owing to high PM_2.5 concentrations in urban area, the capture efficiency of PM_2.5 per unit time is greater than that of rural area under the same precipitation condition. In rural area where PM_2.5 concentration is lower, the scavenging process depends on the increase of precipitation amount. The PM_2.5 concentration decreases with the increase of mixing layer when it exceeds 1000 m. Vertical diffusion of PM_2.5 is more effective when the mixing height breakthrough 1500 m.

The Role of Boundary Layer Convergence Line in Initiation of Severe Weather Events

Wang Yan, Yu Lili, Li Yanwei, Zhu Nannan, Gao Liuxi

2011, 22(6): 724-731.

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Abstract:
CINRAD/SA Doppler Weather Radar can always detect weak and narrow echoes. Generally, those echoes can be closely associated with boundary layer convergence line, the feature and evolution of which may indicate the initiation of severe weather events. The data detected by Doppler radar from June to September of 2008 and 2009 in Tianjin areas, and the data on the events of sea breeze fronts from 2002 to 2007 are statistically analyzed. It shows that radar echo of boundary layer convergence line is also weak and thin, the intensity of echoes is 15—25 dBZ, and the width of echoes is 3—10 km. Boundary layer convergence line may be divided into three types, including sea breeze front, gust front and thin line due to special weather conditions. Single boundary layer convergence line may form isolated thunderstorm with favorable situation with moderate impact. The collision between boundary layer convergence lines can trigger thunderstorms or enhance the existing thunderstorms to be more severe.56 and 44 sea breeze front cases are observed by radar in 2008 and 2009 respectively. The total number of 25 events of the initiation of severe weather events is closely associated with sea breeze front, including 17 events in 2008 and 8 events in 2009. The formation times of sea breeze front are different, the earliest time is 09:30, while the latest is 16:00. The sea breeze front's maintenance time is also of different length, the longest maintenance time is 6.5 hours, and the shortest is only 1 hour. The general distance that sea breeze front extends to the interior is 70—80 km, and the farthest distance reaches 120 km, with the height of 1.5 km in general. Those provide important information on the initiation of thunderstorms for nowcasts.11 and 9 gust front cases are observed by radar during the observation period in 2008 and 2009 respectively. The maintenance time of gust fronts are inhomogeneous, with the longest maintenance time of 4.0 hours. Collision between sea breeze front and gust front can trigger thunderstorms. The boundary layer convergence lines due to local conditions will be discussed in future research. Analysis on the AWS data in Tianjin area combined with the data of Beijing sounding above 850 hPa indicates that thunderstorms are more likely to occur in the region with large temperature gradient, the temperature difference between 850 hPa and 500 hPa may reach 28℃.

Spatial and Temporal Variations of Hazes in Guangxi from 1960 to 2009

Liao Guolian, Zeng Peng, Zheng Fengqin, Wei Yujie

2011, 22(6): 732-739.

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Abstract:
With the development of Guangxi economy and accelerating urbanization, human activities have discharged various pollutants into the atmosphere, which cause increasing atmospheric haze phenomenon in recent years. The toxic and harmful substances of hazes affect human health and environment a lot, becoming a new kind of severe weather. So it is very important to analyze the spatial-temporal variation characteristics of haze, which provide scientific bases for effective forecasting and controlling haze weather. Based on the data provided by 80 surface observation stations from 1960 to 2009, the haze days in Guangxi are calculated, and the characteristics of spatial-temporal variations of haze in Guangxi and its relationship with climate elements are analyzed by using EOF, linear trend estimation and other analytical methods. The average annual haze days in Guangxi are found to rise gradually over the past 50 years, which is closely related to the human activity and the increase in emissions by economic development. The haze happens more frequently in major cities and their surrounding areas than in remote areas and coastal areas. Comparing the periods of 1960—1979 and 1980—2009, and the remote areas and coastal areas, the haze days increase by different degrees in most parts of Guangxi, especially in Wuzhou, Liuzhou and other industrial cities. Haze in Guangxi occurs mainly in autumn and winter rather than in spring and summer, which may be the results of less precipitation. Compared to the 1960—1979 stage, the average monthly haze days increase significantly in 1980—2009 stage, especially in flood season. Haze days increase most significantly in December by 3.5 d, while in July increasing only 0.2 d. The average annual haze day in Guangxi over the past 50 years is 30.0 d, and the maximum is 61.7 d, which occurs in 2006. When haze weather occurs, the visibility distance mostly ranges from 5 km to 10 km, and the relative humidity mostly ranges from 70% to 90%. The change of haze days in Guangxi is proportional to temperature, and inversely proportional to wind. So, in addition to air pollution, the long-term decrease trend of wind speed in the last 50 years may have caused more hazy days.

The Effect of Meso-scale Environment on Temperature in Huang-Huai-Hai Plain Area

Li Xin, Guo Jianxia, Jin Lianji

2011, 22(6): 740-746.

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Abstract:
With the rapid development of urbanization, the environments of weather stations have suffered to varying degrees. The representativeness and accuracy of observational data are affected at some urban stations because the surrounding environment outside the observation field is very complex, and the impact on meteorological factors cannot be ignored. Using these observed data may lead to partial or even wrong conclusions. To solve this problem, population-based methods are proposed to determine the type of stations, without fully considering the meso-scale environment. Therefore a new method is introduced to determine the type of stations by analyzing the land use within 20km.Previous studies usually focus on geographical area or all stations of country, but in order to investigate urbanization effects, it suggests choosing weather stations within the same climatic zone. The flat topographic and booming industry in Huang-Huai-Hai Plain provide favorable conditions for studying meso-scale impacts on temperature measurement. Using a temperature dataset of 199 stations during 2005—2007 and corresponding 20 km environmental survey data in 2007, the meso-scale environmental impacts on surface temperature are investigated. The data is revised based on latitude, longitude and altitude. The original observations without homogenization can reflect the impact of environment on the temperature because no station moved in this area during those yeares. This stations in the residential areas and farmland stations are compared by the average total annual value of the anomaly, the yearly value, the monthly value and the hourly value.The average observed temperature in residential area stations is 0.662℃ higher than that in farmland stations. The buildings around the weather stations have much effect on the minimum temperature measurements, while affect little on the maximum temperature measurement. The environmental impact in descending order is caused in winter, spring, autumn and summer. The temperature measurements at different times are affected by the surrounding buildings to varying degree. The impact on descending order is 02:00, 20:00, 08:00 and 14:00.In addition, the difference between two-type stations has also been analyzed when the residential and farmland environment within 20km range account for 60%, 70%, 80% of the whole area. It's found that with the typical underlying surface ratio grows, the temperature difference between the two-type stations becomes larger.

Establishment of Meteorological Model for Estimating Standard Ice Thickness in Anhui Province

Wen Huayang, Tian Hong, Tang Weian, Lu Jun

2011, 22(6): 747-752.

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Abstract:
An extreme frozen ice and snow disaster brings severe losses in Anhui Province during early 2008. Some overhead transmission lines are destroyed seriously during this event. It is important to investigate the characteristics of ice accumulation and develop appropriate models to estimate the disaster, but the research doesn't go smoothly due to the lack of data. If a quantitative relationship can be built between the meteorological elements and the ice thickness by the wire icing observation data of fewer stations, the ice-covered mechanism can be understood better, which can also lay the foundation for disaster risk regionalization.Based on the long-term wire icing observation data and climate data of 16 meteorological stations in recent 50 years, several models are built by stepwise multiple linear regression and artificial neural networks, to calculate standard ice thickness of wire icing in Anhui Province.Through coordinated experiment, the optimal models built by stepwise multiple linear regression are confirmed which handle temperature, humidity, wind speed of the icing day, one day before and two days before. The models by artificial neural network perform better in simulating comparatively, but in the prediction they are very unstable, and less effective. The model driven by 26 meteorological factors (data from 1987 to 2008) perform better than the model driven by 24 factors (data of from 1960 to 2008). The best models are picked out by the results of simulating and predicting. And the absolute deviation is 1.1 mm to the north of the Huaihe River, 1.3 mm to the south of the Huaihe River, 6.6 mm in the area of high mountains, and the relative deviation rates of the three models are about 60%—70%. The result is better than other references. For the mechanism of icing, temperature, humidity and wind are key factors, among which temperature is the most influential one. The ice thickness of the plains and hilly areas are mainly affected by weather conditions of the day, while that of mountain areas are also affected by the weather conditions of a few days before. Finally, the ice-wire thickness at the meteorological stations without wire icing observation is calculated by the optimal model, which proves this method feasible.

Torrential Rain Events Assessment Model for the Upstream of the Huaihe River Basin

Zheng Guo, Xue Jianjun, Fan Guangzhou, Li Zechun

2011, 22(6): 753-759.

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Abstract:
Torrential rain disaster is one of the most serious meteorological disasters in China, the assessment of which has important practical and theoretical significance. On the basis of precipitation data, statistics analysis is carried out to establish the torrential rain events assessment model, and the torrential rain events which happen in the upstream of the Huaihe River Basin is assessed with this model. Four indicators are selected to describe torrential rain events in this assessment model, which are averaged area daily rainfall, maximum area daily rainfall in area daily, rainfall coverage range and rainfall duration. Through the statistical analysis of historical torrential rain events data, several grades are defined for the four indicators according to the probability distribution, and then the grade standards assessment matrix is established. The degree of the torrential rain events is calculated by the method of the Euclidean distance, through Euclidean distance between the torrential rain events indicator vector and each column vector of the assessment matrix, the degree of this torrential rain event can be determined. Through the assessment of historical and live torrential rain events which happen in the upstream of the Huaihe River Basin, the assessment results correspond well with the actual impact of the torrential rain disaster, which indicates that the degrees of torrential rain events assessed by this torrential rain events assessment model is reasonable. The pre-assessment can be made by this torrential rain events assessment model to publish warning information when the forecast data are used, and the assessment accuracy has a positive effect on the forecast accuracy.Through the assessment of historical torrential rain events by this model, the results show that in 226 historical torrential rain events, there are 47 times belonging to level 1, 86 times belonging to level 2, 55 times belonging to level 3, 25 times belonging to level 4, 9 times belonging to level 5, 3 times belonging to level 6, and just 1 time belonging to level 7, which are consistent with the theoretical analysis. According to the assessment results, the most serious torrential rain events happen in 2007, which is consistent with the historical facts.The correlation between the assessment levels of torrential rain events and the Wangjiaba water levels passes the test of 0.005 level, inferring that the selection of the assessment region and the assessment results of the torrential rain events of this research are rational.The analysis of the assessment results shows that the torrential rain events happen 2 days before the peak of Wangjiaba water level, which has important significance to guide the disaster prevention and mitigation. However, the assessments of the influences of torrential rain events are insufficient, which need further research.

Beijing Electric Power Load and Its Relation with Meteorological Factors in Summer

Zhang Ziyin, Ma Jingjin, Lei Yangna

2011, 22(6): 760-765.

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Abstract:
Power security with stability is essential for normal operations of modern cities which guarantee industrial productions, communication, transportations, daily lives and so on. For the specificities of modern grid (electric power system), a local accident can spread to the entire electric grid instantaneously, and usually results in huge economic losses. The abnormal increase of power load can often cause an accident for the power grid. The power grid of Beijing is a typical receiving end grid, obtaining about two thirds of its demand from North China Power Grid. So an accurate prediction for the electricity load Beijing is very important for power dispatching and safety operation of the entire grid. However, the electricity load may be influenced by a combined effect of many complex factors, such as the industrial and agricultural productions, transportations, daily lives, weather and climate. The different factors may take different effects on the power load variability on various timescales. Major achievements are made through previous research, but it is still a challenge today to predict accurately the power load variability, especially in the daily time scales. A further and quantitative study on the daily power load variability and its main factors would be helpful for the precise prediction.Based on the daily electric power load and meteorological data of Beijing during the period from January 2006 to September 2010, an analysis is implemented with statistical method aiming for better understanding electric power load of Beijing and its main affecting factors in summer. The results indicate that temperature, wind speed and relative humidity are the major factors which are significantly correlated with the maximum electric power load in summer. Among these factors, the daily minimum temperature is the most influencing factor with a correlation coefficient of 0.65 and significance at 0.001 level. Considering the 1℃ effect for energy consumption, the daily maximum electric power load would increase 39.7×10⁷W with temperature rising 1℃ when the daily maximum temperature is higher than 26℃, or when the daily minimum temperature is higher than 18℃. Using the statistical regression model can roughly predict the maximum power load fluctuations. It can provide some reference for the power allocation decision in advance. Moreover, the effects of temperature humidity index (I_TH) on the variability of electric power load are also checked, where I_TH are expected to quantify the degree of human body comfort. The outcomes suggest that the I_TH can improve the explained variance of the daily maximum electric power load than a single temperature factor.

The Application of Relative Humidity Index to Agricultural Drought Monitoring

Feng Jianshe, Wang Jianyuan, Wang Xintang, Xue Xiaoping, Chen Yanchun, Li Hongyi, Fan Liju

2011, 22(6): 766-772.

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Abstract:
Relative humidity index and corresponding methods are introduced to deal with daily agricultural drought monitoring. The method recommended by FAO is used to calculate the potential evapotranspiration and rectify the crop coefficient.When rectifying the crop coefficient under soil water stress condition, the absorbable total available soil water in the root zone is used to replace the total available soil water in the root zone. Because the latter causes higher results, which means water stress seldom occurs. Actually, most of the roots are located in shallow layer, only a small part of major roots extends to deep layer. For example, the roots of winter wheat can be 1.0 m deep before winter, but 80%—85% of the roots are in the soil shallower than 0.4 m. Therefore, if water stress occurs in the upper soil, the winter wheat's growing will be limited despite enough water in the deeper soil, because 15%—20% of the roots in deeper soil can't absorb enough water for transpiration. So it's necessary to consider the water absorbing capacity of the crop root, that's why the absorbable total available soil water in the root zone is used.When calculating the relative humidity index, steady rule can't be reflected reasonably in any individual period, because the former field water balance affects the current soil water condition. By summing up the weighted relative humidity index during different period of time, the combined relative humidity index is evolved, and it can well reflect the cumulative affection of former field water balance.The relative humidity index of single crop reflects the soil water condition on one kind of crop, regional combined relative humidity index is evolved by summing up the combined relative humidity index of single crop weighted on its planting area. With this method, agricultural drought monitoring can step over single crop growing season, so and agricultural drought can be monitored throughout the whole year.There are 114 stations for soil moisture manual observation in Shandong Province. From 28 Feb 2008 to 8 Dec 2008, manual observation is carried out every ten days, and 3048 groups of data are available. The comparison shows that for 2012 groups of data, drought degree calculated from relative humidity index is coincident with observation, reaching 66%. The accuracy is lower than 50% in most of west-north area of Shandong, the irrigation district of the Yellow River, the Dongping Lake, and the Weishan Lake. On the other hand, the accuracy is mostly greater than 70% in east-central of Shandong and some other districts. Among the whole period, the degree of coincident is lower in spring than that in summer.

Vol.22, NO.6, 2011