Vol.20, NO.3, 2009

Display Method:
Application of Doppler Radar Data to the Landfalling Typhoon Saomai Simulation
Shi Lijuan, Xu Xiaofeng, Li Bai, Yang Hongping, Xu Fengwen
2009, 20(3): 257-266.
The mesoscale model ARPS and its data analyzing system ARPS 3DVar developed by CAPS of Oklahoma university has a good potential to utilize in China. Using ARPS and its 3DVar assimilation system, the Doppler weather radar (CINRAD SA) reflectivity and radial velocity are assimilated. In order to test the effects of Doppler radar data on the initial field and on the forecast field, numeric study is carried out on super typhoon Saomai (0608) which lands at east China and causes a large damage. Comparison between experiments with and without radar data assimilation shows that Doppler radar assimilation can help obtain more realistic precipitation, wind and reflectivity structures within 6 hour initial time windows. The radar assimilation by ARPS 3DVar has the ability to improve the forecast on the mesoscale rain cell position and intensity. The improvement on typhoon track forecast is due to the effective adjustment of the typhoon vortex and eye structure by radar data assimilation. The result of precipitation forecast is improved significantly, mainly because of the physical quantities in assimilation test displaying typical characteristics of mesoscale system. However, there are some inadequate aspects still needing improvements in the stimulation of typhoon intensity.
A Strong Mesoscale Convective Process in Landfalling Typhoon
Xu Wenhui, Ni Yunqi
2009, 20(3): 267-275.
The fifth typhoon named Haitang landfalls in Fujian in 2005, and then moved northwestward. During this moving, there is a mesoscale convective cloud increasing markedly, within the periphery cloud cinctures of typhoon connecting with tropic convergence cinctures. Moreover, the mesoscale convective cloud passes the east and the north of Wenzhou, and causes heavy rainfalls in these places. This case indicates clearly that a strong mesoscale convective system can be developed under appropriate circumstance, even if the landing typhoon is abating. Severe weather can be resulted from the strong mesoscale convective system, even more dangerous than typhoon. Therefore, principles of strong mesoscale convective system in landing typhoon should be discussed on the structure and evolution of MCS to forecast rainstorm caused by the landfalling typhoon better in the future.The evolution of MCS in landfalling typhoon can be seen through the nephogram and radar reflecting data. Research on the structure of MCS by the NCEP data shows that the MCS along landing typhoon is gradient in maturation period.The synoptic situation, occurring two hours before MCS formed, could be analyzed by NCEP data. Then the formation of MCS is found attributing to two factors. One factor is the convective instability. The profound southeast current of typhoon transports the warm and wet air into the cold area in the north of Wenzhou. In this situation, the cold air is meeting the warm and wet air. So the convective instability is caused and increasing gradually. Meanwhile, the convergence of air is coming out in the influence of the special landform of the north of Wenzhou. However, the air will be moving upward vertically, which is caused by this convergence. So the vertical upward of air is the other factor.Using the theory of slantwise vorticity development and moist potential vorticity, the evaluative theory of this strong mesoscale convective system is obtained. The evolution of MCS could be shown by looking into the situation of MCS in maturation. MCS begins to develop from the area where the cold air pile meets the warm air. In this region, there is slantwise moist isentropic surface. The northwest cold pile forces warm air to climb up along the slantwise moist isentropic surface, so the cyclonic vorticity develops. Because of the interaction between the condition instability at low level and the condition-symmetric instability at middle layer, the convective-symmetric instability develops. In this circumstance, the stream slantwise and ascend at middle layer is widely formed by the vorticity caused by the slantwise isentropic surface. On the other hand, the increasing in vertical shear of horizontal wind or enhancing in moist baroclinity, because of the slantwise of moist isentropic surface, results in intensifying the development of vertical vorticity and stretching towards northwest of MCS.
Anomalous Features of Asian Summer Monsoon and Their Influence on the Continual Torrential Rain in South China in the Early Summer of 2005
Bao Yuanyuan, Jin Ronghua, Ju Jianhua, Kang Zhiming
2009, 20(3): 276-285.
Anomalous features of Asian summer monsoon and their influence on the continual torrential rain in South China in early summer of 2005 are analyzed. The results show that Southwest monsoon surges play a very important role in the rain band movement in Eastern China from the end of May to June. The South China Sea (SCS) summer monsoon doesn't start until the end of May (about three pentads later than normal) and leads to the obvious delay of the flood season in South China. From then on, Southwest monsoon over the Bay of Bengal moves mainly eastwards with smaller components towards the southeast part of Tibet Plateau than normal. At the same time, the western Pacific subtropical anticyclone (WPSA) is weaker and remains farther away from China mainland, and the cross-equatorial flow between 105°-115°E is weaker so that the northern component of the Southwest monsoon is also smaller. Meanwhile, East Asia trough is deeper and leads stronger cold air to China. All of these result in the Southwest monsoon main taining in south China and cause continual torrential rain there. Weaker Australia High is an important factor for the weaker cross-equatorial flow, and the weaker southward ITCZ and WPSA. Due to the stronger cold air over the large area from southern part of the Tibet to the northern India, the Indian monsoon breaks out late and marches slowly northwards so that the convection and the latent heat and the heat sources over southern part of Tibet Plateau and Bay of Bengal are obviously weaker than normal. The negative thermal feedback mechanism is conversely unfavorable for the northward marching of southwest monsoon. This is another important cause for the southwest monsoon and torrential rain's long-time staying in South China.
Distribution and Spatiotemporal Variations of Deep Convection over China and Its Vicinity During the Summer of 2007
Qi Xiuxiang, Zheng Yongguang
2009, 20(3): 286-294.
The large-scale persisting rainstorm, extremely heavy precipitation and severe convective events result in tremendous damage in economy and severe personnel casualty during the summer of 2007. Based on FY-2C hourly infrared TBB dataset from June to August in 2007, the distribution and spatiotemporal variations of deep convection over China and its vicinity during the summer of 2007 is analyzed and compared with the atmospheric circulation background based on the NCEP final analysis dataset and the climatological distribution of deep convection based on 10-year TBB dataset. The statistical characteristics of TBB less than -52℃ show that there are four active deep convection areas over China during the summer of 2007: South China seaside, the Tibetan Plateau, the Yunan-Guizhou Plateau, Sichuan Province together with Chongqing City and the Yangtze-Huaihe River Basin. The daily variations of deep convection over Central and East China show that the deep convection distribution is very different in different months, and the deep convection activity has an obviously fluctuating feature. The active deep convection areas are farther south and are located to the south of 30°N in June, and the active deep convection areas advance to the north of 40°N in July, however, the active deep convection areas retreat to the south of 25°N in August. The characteristics of the daily variations of deep convection are close associated with the evolution of the large-scale atmospheric circulation. The deep convection over the Tibetan Plateau and the Yunnan-Guizhou Plateau has one active peak and lasts longer time in the diurnal variations, but the deep convection over the Sichuan Basin and Chongqing City has a nocturnal characteristic and develops in the early morning. Comparing with the 10-year statistical results of TBB less than -52 ℃, there are some characteristics different from the 10-year results. First, the deep convection over South China occurrs more frequently in the afternoon than those in the 10-year statistical results. Second, the lifetime of the deep convection over Tibetan Plateau is much shorter than the climatological lifetime. Third, there are multiple active periods of the deep convection in a day over East Guizhou Province, the Northeastern Mountains in Sichuan Province, the Western mountains in Hubei Province, the Hills in Shandong Procince, the Yangtze-Huaihe River Basin, and the Plain of North China. Finally, there is feature of the deep convection over the Yangtze-Huaihe River Basin that the deep convection obviously propagates eastward during the summer of 2007.
A Jinan Heavy Rainfall on 18 July 2007
Wang Jin, Jiang Jianying, Jiang Jixi
2009, 20(3): 295-302.
Jinan is stricken suddenly by an extraordinary rainstorm on 18 July 2007. From 17:30 to 20:30, the maximum rainfall of the city exceeds 153.1 mm. An synthetic analysis of this heavy rain event is performed, using multiple data, including FY-2 double satellite data, NCEP 6-hour reanalysis data, routine observational data and automatic meteorological station data. The results show the heavy rainfall takes place under the favorable large-scale circumfluence, which includes the continental high pressure in west China developing eastward, and Jinan locates at the northeast of it. At the same time, coupling between a high level jet steam and a low level jet steam intensifies, and becomes strong divergence in the upper and strong convergence in the low over Jinan. The cold vortex in northeast China develops dramatically, and the cold air of its rear strengthens. The short wave trough at middle layer moves eastward, and lies over the shear-line in the low level. Both of them form the shape of forward trough. All of these lead together to atmospheric stratification around Jinan turning very unstable. This rainfall process is caused directly by strong meso-scale convective cloud, which is formed by the mergence of two deeply convective clusters at the tail of frontal clouds, and it shows a quasi-round shape structure of a horizontal scale of 200 km×200 km, and a time scale of no more than 5 hours. There is a meso-scale low pressure over the surface corresponding to the cloud. The heavy rain occurs during the rapid intensification stage of the meso-seale convective system. In addition, the transport of warm and moist southwest air current in the low-level leads heavy rain to develop strongly. This water channel extends northeastward and shows northeast-southwest orientation via Jinan, which provides plenty of water for rainfall.
Forecasting Experiments of CAM 3.1 Model Using Statistic Forecast SST Data
Han Xue, Wei Fengying, Dong Min, Dong Wenjie
2009, 20(3): 303-311.
Based on the "two-step method" in month/season forecast, a new statistic model is designed to predict the global SST field. The global SST during 1981-2000 are predicted using the model. Comparing with the NCEP SST field, the results indicate that the forecast global SST field from the statistic forecast SST model could reflect primary patterns of the global SST, and can predict the variability of SST anomaly in Niño3.4 which represents E1 Niño/La Niña event. The correlation coefficient between forecast SST and NCEP SST in Niño3.4 is 0.596. Furthermore, the numerical experiments based on the forecast global SST boundary conditions for forecasting the monthly anomalies of 500 hPa geopotential height over east-Asia (1981-2000) are performed using the NCAR CAM3.1 model. The first six eigenvectors which represent typical spatial patterns of CAM3.1 500 hPa and NCEP 500 hPa are decomposed from the CAM3.1 500 hPa and NCEP 500 hPa fields using EOF respectively. The results show that primary patterns of 500 hPa height anomalies in east Asia can be forecasted by driving CAM3.1 with the forecast global SST. However, the forecast ability of 500 hPa geopotential height over east Asia in summer is faulty and unstable in forecast experiments. A statistic revision method is provided to revise the forecast results of CAM3.1 model. The root mean square error and correlation coefficients of 500 hPa height anomalies between CAM3.1 forecast (revised before and after) and NCEP in summer over the east Asia are compared, the root mean square error between the two fields decreases every year, and the mean correlation coefficient during 1981-2000 increases. These results indicate that the forecasting skill of 500 hPa height anomalies over east Asia in summer is improved using the statistic revision method to a certain extent. The experiments show this statistical method can be used to improve the forecasting skill of the dynamic model CAM3.1.
The Spatial and Temporal Characteristics of China Continuous Cold Rainy Weather and South Cold Damage from February to May
Han Rongqing, Chen Lijuan, Li Weijing, Zhang Peiqun
2009, 20(3): 312-320.
Based on observed daily temperature and precipitation data of China 546 observation stations and daily sunlight hours of some representative stations in spring rice producing regions from 1951 to 2007, a uniform standard for continuous cold rainy weather all over China and cold damage of spring rice producing regions is defined. Temporal and spatial characteristics are also summarized using some statistical methods, for example, Empirical Orthogonal Function Decomposition (EOF) and Morlet wavelet analysis. The results show that usually more continuous cold rainy weather occur in the regions of Sichuan Basin, Guizhou Province, western parts in the south of the Yangtze and South China during the period of February to May. The maximum occurring in Sichuan Basin and Guizhou Province reaches up to 4-6 days per spring month averaged from 1951-2007. The scope of continuous cold rainy weather gradually expands northward and westward from the south of the Yangtze to the Yellow River Basin in spring, in which obviously continuous cold rain weather occurs in the southeastern parts of Northwest China and the southeastern Tibet since March and in Northeast China in May. The decadal changes of the continuous cold rainy days in spring denote that there are less days than climate average during the 1950s and from 1997 to present, and the temporal variations of the first EOF mode of the continuous cold rainy days of China show the characteristics of decade oscillations including inter-month seesaw during the period of 1963-1996.The spatial and temporal characteristics of cold damage for China spring rice producing regions during the period of 1951-2007 show that the frequency of cold damage occurring in Sichuan Basin and mid-lower Reaches of the Yangtze are once in every 1.5 years, more than that of the northern and southern parts of South China with once in every 2.5 years, where severe cold damage occurs frequently in Sichuan Basin and mid-lower Reaches of the Yangtze but the frequencies of moderate and severe cold damages are equivalent in the northern and southern parts of South China. The analyses also show that 3-4 years significant oscillation period of cold damage exists in the aforementioned 4 spring rice producing regions and moreover, a significant decadal oscillation of cold damage exists in Sichuan Basin. In 4 spring rice producing regions, there have been less cold damages since 2000. Moreover, cold damages are excessive and severe during the period of 1990s except for the northern of South China regions.
Radiative Characteristics of Convective Precipitating Cloud
Wang Xiaolan, Cheng Minghu, Zhou Fengxian
2009, 20(3): 321-328.
Radiative characteristics of convective precipitating cloud can be used for the classification of convective/stratiform precipitation and for the algorithm to retrieval the rain rate from brightness temperature observed by satellite remote sensors. The typical convective cloud system in Yichang area on 9 July 2003 is simulated with MM5 model and its upwelling radiative brightness temperature is simulated with Monte-Carlo 3D microwave radiative transfer model. The columnar precipitation simulated by MM5 model shows consilient with that observed by rain gauges. As for the cloud microphysical particles, it is found that except for the cloud ice, the contents of the cloud water, precipitable water and precipitable ice particles from the MM5 are nearly equivalent to that retrieved from TMI data. The simulated Tb85V from M-C model also indicates similar distribution with the observed by TMI. Tb85 is sensitive primarily to the precipitated ice and snow content in clouds. The weak correction between Tb85 and the surface rain rate is found. Given the rain rate less than about 5 mm per hour in this case, Tb19 rises since the rain rate increases. However it descends with the rain rate increasing while the rain rate is over 5 mm per hour. Because of the notable intercorrelation between Tb19 and graupel content, it can be regarded as the indicator of surface rain rate in the strong convective center, at least as the estimator of columnar precipitated water content at upper layers. The feeble correlation between Tb85 and graupel columnar content happens because the upwelling Tb85 is synthetically affected by the various hydrometers such as the emission from cloud water and the scattering from ice particles, in addition the shift caused by oblique FOV. Tb37 has obvious correlation with the surface rain rate when it is less than 20 mm per hour and is saturated when the rain rate is over 20 mm per hour. Cloud water and precipitated rain in the convective cloud play roles on Tb37. The Tb at each channel shows the synthetical results of tilted cloud cell or oblique FOV. The higher frequency, the lower Tb values show and the more replacement happens due to the oblique FOV. Tb85 observed at 52.8° angle is even 15 K less than that received at zenith, and the shift can reach 25 km as well as the title cloud cell.
The Automated Landmark Navigation of the Polar Meteorological Satellite
Yang Lei, Yang Zhongdong
2009, 20(3): 329-336.
The problem of automated landmark navigation for the polar meteorological satellite is addressed. Automated landmark navigation can correct the systematic image navigation errors due to orbit, attitude and alignment matrix disturbance. Traditional automated landmark navigation methods need selecting the base image from long time series satellite imagery; otherwise it can result in registration displacements. Previous methods have shown that having daytime and nighttime (including early morning) base images for each season can minimize the registration error. The processing of one year data would thus require a minimum of eight base images for each location, and it limits the method from being widely applied. There are great needs for an accurate, easily implemented navigation system capable of automated landmark navigation when long time series satellite imagery data are absent.First, cloud detection methods insure that contamination from cloudy pixels is minimized. Second, the base image is composed of content features and structural features. The content features are constructed from the energy distribution of the current satellite image's ocean, land, rivers and so on. By defining the landmark feature point, the landmark's structural features are constructed from the global template. The landmark content and structural features are combined together to form the full base image. Third, the maximum cross correlation (MCC) method produces displacement vectors, which are translated into satellite attitude corrections to be added to the orbital image navigation corrections. Each resulting displacement vector has a correlation coefficient, which quantifies how well a pattern is matched. Displacements with correlations lower than the 95% confidence value is the elimination of error matching. The image navigation accuracies are also closely related to the landmark spatial distribution. The image navigation corrections are more accurate when the landmarks are average distributed through the whole satellite image. Finally, FY-1D satellite data are used to assess the performance. The testing results shows that this method is automatic and is successful to rectify the image navigation errors due to attitude disturbance and the rectified errors are within one pixel. This method does not use long time cache files needed by early methods and thus extend the applicability. The proposed method has been applied in Chinese next generation polar meteorological satellite FY-3 and will be developed further in the next generation geostationary meteorological satellite FY-4.
Validation of GOME Ozone Profiles and Tropospheric Column Ozone with Ozone Sonde over China
Cai Zhaonan, Wang Yong, Liu Xiong, Zheng Xiangdong, Kelly Chance, Liu Yi
2009, 20(3): 337-345.
Global Ozone Monotoring Experiment (GOME) with the second Earth Remote Sencing (ERS-2) on board launched in 1995. To evaluate the performance of GOME's ozone data in China, ozone sonde observations at three stations in Lhasa (1998--1999), Xining (1996), and Beijing (2002--2003) are used to vali date ozone profiles and tropospheric column ozone retrieved from Global Ozone Monitoring Experiment (GOME). Ozone detecting systems are electrochemical concentration cell (ECC) sonde at Lhasa and Xining and GPSO3 sonde at Beijing; GOME data are retrieved by Liu et al. A comparison dataset consists of 51 matching pairs are obtained by applying a baseline criteria (±6 h, ±3° longitude, ±1.5° latitude). A statistical analysis of the differences between coincident O3 profiles obtained by GOME and those obtained by ozone sondes are conducted using the methodology suggested by von Clarmann. When comparing with measurements the ozone sondes vertical resolution are much better than satellite retrievals. Retrieval averaging kernels are applied to the high-resolution data so that these data are comparable. As the high-resolu tion sondes profiles do not cover the GOME retrieval altitude range, the high-resolution profile (ozone sonde only up to about 30 km) are augmented with monthly mean climatological profiles from TOMS V8. Statistical bias determination and precision validation show that in the lower and middle troposphere, the mean biases are significant within 5% at Lhasa and Xining and within 10% at Beijing. In the upper tropo-sphere and lower stratosphere, the mean biases are within 10% at Lbasa and Xining and within 20% at Beijing. In the middle and upper stratosphere, the mean biases are within 5% at all three locations. The larger bias in the troposphere and lower stratosphere at Beijing may result from a different type of ozone sonde and different time period (ozone profiles shows multiple peaks in Beijing area in the spring). The mean biases of the tropospheric column ozone are within 10 at all three sites, which are partly caused by different estimated tropopause heights between GOME and ozone sondes. The GOME monthly mean ozone concentration at 0—2.5 km correlates well with surface ozone measurements. basically capturing the termporal variations of surface ozone at Lhasa, Waliguan, and Linan. In conclusion, from lower troposphere to upper stratosphere, GOME data used here has strong ability to reflect ozone distribution and dynamic changes in China.
Variation Features of Atmospheric Precipitable Water Vapor Derived from Groud-based GPS in Beijing
Liu Dian, Liu Xiaoyang
2009, 20(3): 346-353.
Diurnal variations in pheric precipitable water atmospheric water vapor are studied (PW) for 2004--2007 derived from by analyzing 30 min averaged data of atmos Global Positioning System (GPS) observa tions at Peking university station (SA34). Comparing PW derived from GPS with that observed by radiosonde, the result shows that the root mean square error (RMSE) is less than 3 mm. On monthly mean, the curve of diurnal variations of PW is acquired, and composite diurnal variation of GPS PW, specific humidity, precipitation, temperature and wind vector are analyzed. The PW show a clear diurnal cyrcle with amplitude of about 3 mm in summer. A typical feature of the diurnal in Beijing is that the minimum value appears in the morning, and the maximum value appears in the midnight. There is some relations between the time of the maximum of PW and precipitation. The result of the wavelet analysis indicates that there is a 12-day cycle in most of the year. Precipitation occurs when the following two conditions are met. The instant PW is larger than the average PW of the past 12 days, and the other is the increment of PW in the last 16 hours is larger than the threshold. In summer, the most precipitation appears when the values of the minus value are high. Taking the above two conditions as the judging conditions, it could be prevented that the miscarriage of justice to precipitation when either the PW is high or the increment of the PW in 16-hour is larger than the threshold.
Subtropical High Forecast Model of Least Square Support Vector Machine
Liu Kefeng, Zhang Ren, Hong Mei, Yu Dandan, Wang Huizan
2009, 20(3): 354-359.
Based on the methods of empirical orthogonal decomposition (EOF), wavelet frequency decomposition and least square support vector machine, a summer 500 hPa potential height forecasting model is established to describe the form and change of the subtropical high situation. First, 500 hPa potential height fields sequences on NCEP/NCAR are separated into the time coefficients and corresponding eigenvectors which are orthogonal to each other with the method of empirical orthogonal decomposition. Then fifteen time coefficient series corresponding with major eigenvector (square contribution of 96.2%) are extracted and each time coefficient is decomposed to relatively simple signals with the method of wavelet analysis. Then, each signal prediction model is set up with the method of least square support vector machine. Finally, the forecasting simple signals are used to reconstruct the corresponding forecasting time series with the method of wavelet decomposition, then, the forecasting time series and corresponding major eigenvector are used to reconstruct 500 hPa potential fields with the methods of empirical orthogonal decomposition. The reconstructed potential fields are the fields which are forecasting results. Through experiments and analysis of contrast on the prediction model, the results show that the proposed algorithm model based on the above ideas can basically describe the distribution of 500 hPa potential situation and basically forecast the location and intensity of subtropical high within seven days. And the results also show that the 10-15 day forecasting results by the model can be used for reference for the medium and long-term activity of the subtropical high. The results also show that the model exhibits its properties of simplicity, stability, flexibility and good prospect of application.
Application of EOS/MODIS Data to Monitoring Sugarcane Cold Damage
Kuang Zhaomin, Li Qiang, Yao Yongmei, Ding Meihua
2009, 20(3): 360-364.
MODIS data with 250 meters resolution and the vegetation condition index are applied to set up a technological method of remote sensing to monitor and evaluate the sugarcane cold damage in Guangxi. Based upon MODIS data and the geo-data derived from sugarcane sample area determined by GPS, the sugarcane cold damage monitoring and evaluating model and the relevant work flow are constructed. According to the theory, value of normalized difference vegetation index is obviously lower than that of normal time after the cold damage. Through statistical analysis, the remote sensing monitoring and evaluating classification index of Guangxi sugarcane cold damage is attained by combination of the records of cold damage of Guangxi sugarcane during 2001--2007, overall analysis of the Guangxi sugarcane cold damage data from the agricultural department, the cold damage data of Guangxi sugarcane using remote sensing means and the field investigating data of some local sugarcane cold damage fields. Moreover, the spatial distribution and inflicted areas of sugarcane cold damage over Guangxi in the early of 2008 are monitored and evaluated and the result is consistent with that of field investigation. The monitoring result shows that the cold damage of sugarcane fields in northern Guangxi (Huanjiang county, Luzhai county, Liucheng county and Yizhou city) and central Guangxi (Xingbin district, Xiangzhou county and Wuxuan county) is more serious than that of sugarcane fields in southeast, littoral and Youjiang valley of Guangxi. In 62132 hm2 area of Guangxi sugarcane planting area the damage is rather severe, and in 364716 hm2 area the damage is light to moderate in extent (some areas are excluded due to cloud cover). In Xingbin sugarcane planting areas, the damaged areas are 4989 hm2, 44679 hm2, respectively. Cold damage area estimation error is no more than 5 percent. So, results indicate that this method can meet the requirements of operation to monitor and evaluate the spatial distribution and disastrous areas of sugarcane cold damage inflicted fields
Method to Evaluate Index of Water Bodies Density in Northeast China
Zhu Qinglin, Liu Li, Yin Wenyu, Wang Lina
2009, 20(3): 365-369.
Meteorological assessment of ecological qualities is proposed by China Meteorological Administration. The assessment is applied to evaluate ecological quality and its effect with appropriate indexes and proper methods. The trial evaluation scheme of ecological quality meteorology selects humidity, vegetation cover-age, water environment, land degeneration, and disaster occurrence indexes for evaluation, among which water environment is the most important one. However, there isn't a satisfactory way to evaluate index of water environment so far.Apractical method is proposed to evaluate the contribution of water body to ecological quality using MODIS data and ground observational data. Moderate resolution imaging spectroradiometer data is obtained from DVBS (Digital Video Broadcast by Satellite) by China Meteorological Administration. And the ground observational data is obtained from Water Affairs Bureau.First, several huge water bodies are chosen, as small area water bodies cannot be well monitored by MODIS. The area of these indicative water bodies has a preferable relationship with that of total water bodies. By analyzing water and other objects' spectral characteristics on EOS/MODIS images, the distinguished water compound bands are decided to get the method to recognize water area from remote sensing images. Then the threshold values of the channel reflectance and bright temperature of MODIS data are determined to distinguish water body from other objects. MODIS data of clear days in different seasons are adopted as much as possible to make statistical comparisons with ground observational data, thus a regression model can be set up between areas of indicator water bodies and total water area.Second, river length, lake and reservoir areas and length of coastline are chosen as indicators of water environment index. Each indicator has a weight to decide its contribution to water environment index, and the weight is calculated by normalization methods. So the water environment index is calculated by the summation of river length, lake and reservoir areas and length of coastline multiplied their weights respectively.Finally, the method is applied to evaluate water body indexes in Northeast China, and is proven feasible and practicable.
The Development of High Resolution Numerical Model System for Qingdao Olympic Sailing Competition
Miao Shiguang, Sun Guiping, Ma Yan, Xu Xiaoliang, Wang Xiaoyun, Lin Hang, Jiang Weimei, Liu Hongnian, Zhang Ning, Sun Lin, Wang Yaoting
2009, 20(3): 370-379.
In order to improve the skill of weather forecast and provide better meteorological service for Olympic Sailing Competition, high resolution numerical model system for Qingdao Olympic Sailing Competition (including forecast model and interpretation models) is developed.Based on Weather Research & Forecast (WRF) Model Version 3.0, a forecast model is set up with gird of 60×50×38 and horizontal resolution of 500 m. It takes about 1 hour and 20 minutes to produce 15-hour forecast on an IBM computer with 8 threads, which meets the requirement of operational forecast. Dynamic interpretations to the forecast results are carried out with the aid of a high resolution Planetary Boundary Layer Model (PBLM) and an Urban Neighborhood Scale Model (UNSM) (with the horizontal resolution of 100 m and 10 m respectively).This model system runs continuously during the summer of 2008, and the model products are used in Qingdao Branch of Beijing Olympic Meteorological Service Center. Results show that, the model system is robust and practical, and performs quite well on the simulation of urban heat island and local circulations (e.g., sea-land breeze and terrain/building effects). Analyses of numerical cases indicate that urbanization leads to urban heat island, increases sea-land temperature difference, and strengthens sea-breeze. Mean-while the drag effect of urban building decreases the wind speed, and slows down the advance of sea-breeze. The introducing of fine underlying surface data is critical to high resolution numerical simulation of local circulations (e.g., sea-breeze).The dynamic interpretation to the forecast results with the aid of a high resolution PBLM with the horizontal resolution of 100 m indicates that, generally PBLM could simulate the wind field and the effects of surrounding terrain very well. The PBLM results are consistent with the observations from buoys and automatic weather stations, and have similar charaeteristies with Lidar observations. Further fine-scale dnamic interpretation in terms of UNSM with the horizontal resolution of 10 meters shows that UNSM could well simulate the wind in urban blocks. So the dynamic interpretations based on the terrain-following coordinate PBLM and the build-aware UNSM are effective to simulate the effect of local terrain and buildings on the wind in interest venues.
The Subtle Weather Forecast of the Highway Traffic During 2008 Beijing Olympic Games
Zhang Deshan, Ding Deping, Mu Qizhan, Zhang Shuli
2009, 20(3): 380-384.
During 2008 Beijing Olympic Games, the short-term weather forecast and service for Beijing ring roads and highways is very important for people at home and abroad, and the task is undertaken by Beijing Weather Science and Technology Service Center.Statics analysis is done to check the correlation of observed weather factors of Beijing Observatory Station and 27 automatic weather stations at Beijing traffic section, 9 road surface automatic weather stations included. As a result, 97 simple linear equations are set up with correlation coefficients of each weather factors passing 0.01 level test. The highest air temperature, lowest air temperature, relative humidity correlation coefficients between automatic weather stations and Beijing Observatory Station are 0.9103--0.9884, 0.8777--0.9883, and 0.7499--0.9682. The correlation coefficient between the highest air temperature on freeway and the highest road surface temperature is 0.8502--0.9288. The correlation coefficient between the lowest air temperature and the lowest road surface temperature is 0.9171--0.9851.All linear equations are integrated into the Traffic Weather Forecast Platform, which could generate 5 short-term spatial subtle weather forecast products of the Second Ring Road, the Third Ring Road, the Fourth Ring Road, the Fifth Ring Road in 4 directions and 5 freeways as well. So the efficiency is greatly improved. These forecast products are published by newspaper, broadcast and 121 weather telephone service. During 2008 Beijing Olympic Games, based on short-term forecast products of Beijing Meteorological Observatory and the linear regression equation, objective weather forecast products of highway section are produced and applied in service.