Vol.26, NO.3, 2015

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Correcting Geopotential Height Errors of Some Mandatory Levels of Chinese Historic Radiosonde Observations
Ruan Xin, Xiong Anyuan, Hu Kaixi, Liang Xiuhui, Wang Zhiwen, Yang Yanru, Zou Fengling
2015, 26(3): 257-267. DOI: 10.11898/1001-7313.20150301
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Abstract:
Radiosonde observations are crucial in weather forecast and upper-air climate research. Due to their high vertical resolution, they are also important for calibration and validation of satellite temperature and water vapor retrievals. Quality control of Chinese radiosonde observations of 1951-2012 is conducted with hydrostatic check, and the result reveals that ratios of erroneous geopotential height (GPH) of 900 hPa, 800 hPa, 80 hPa and 60 hPa before 1963 are 2%-11%, which are much higher than other levels. The ratios of erroneous GPH of 250 hPa and 70 hPa in mid of the 1970s of a few stations in Yunnan Province are also much higher than other levels. Changes with observation code and practice in Chinese radiosonde observations are thoroughly investigated. Then the possible cause of the phenomenon is analyzed and validated with observations.The height of each pressure level in sounding is calculated by accumulating the thickness of layers between each pressure levels below on the base of station elevation. And the thickness is determined by hydrostatic equation automatically nowadays, but due to the limitation of calculation capacity before the 1980s, they are available in ready-made GPH-table. However, 900 hPa, 800 hPa, 80 hPa and 60 hPa are not included in the GPH-table possibly because they are not directly used in weather charts then. So GPHs of levels in question are obtained through interpolation on time-GPH chart after GPH of other levels are available on the chart through looking up the GPH-table. This practice makes GPH of levels in question vulnerable to human mistakes, thus many records contain errors. The explanation to the cause of the problem is validated with observations.Furthermore, the method to correct the erroneous GPH record is proposed, which is to recalculate it based on hydrostatic equation with correct observations of other levels from the same sounding. The correcting method is validated since the originally correct GPH records are reproduced accurately. For 900 hPa and 800 hPa of Ganzhou Station, differences between reproduced GPHs and original ones are less than 5 gpm, and about 50% of reproduced GPHs are exactly the same as original ones. Differences for 250 hPa of Kunming Station are all less than 5 gpm either, but differences are slightly larger for 70 hPa, possibly because the layer between 70-100 hPa is as large as 2300 gpm approximately, and significant levels are not enough to reveal all the details of temperature profile. Besides, the correcting method is validated from another aspect, since after the erroneous GPH are corrected, the relevant hydrostatic residue series become consistent.
A Risk Forecast Method for Southwest Road Damages Based on Precipitation
Di Jingyue, Wang Zhi, Tian Hua, Xie Kai, Yang Xiaodan, Chen Hui, Xu Fengwen
2015, 26(3): 268-279. DOI: 10.11898/1001-7313.20150302
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Abstract:
Landslides, debris-flows and other disasters along roads caused by precipitation occur frequently, becoming one of the most important factors of roads damages. Yunnan, Guizhou, Sichuan and Chongqing are especially prone to road damages. Based on the information of road damages, the corresponding precipitation data from January 2007 to July 2013 and 24 h precipitation forecast data from July 2012 to July 2013, probability forecast models are adopted to describe probabilistic relations between precipitation and road damages. First, precipitation factors of the day and over the past two, three, four, five, six, seven days and effective precipitation over the past 15 days are analyzed by the method of Kendall correlation, and precipitation of the day and the past effective precipitation are identified because of small correlation. Second, after the normality process to two factors, polynomial fitting, Fourier fitting and Gaussian fitting are applied to the frequency distribution of the disaster and two kinds of precipitation factor. According to the analysis of fitting correlation and the fitting error, Gaussian fitting method is selected to apply to the scattering distribution of precipitation and road damages. Finally, universal probability forecast models of road damages based on effective precipitation (Model Ⅰ) and comprehensive of the day and effective precipitation (Model Ⅱ) are established, and the fitting adjustable coefficients are 0.9108 and 0.8333, respectively. According to critical precipitation thresholds of two models, combining the grade of hazards risk and precipitation risk to road damages, two kinds of warning classification scheme based on precipitation are proposed. Two risk forecast models for road damages are developed. Risks of road damages are divided into five levels by probability of damage occurrence: Very small, small, medium, large and very large. Two risk forecast methods are tested, showing they are both applicable to describe the relation between precipitation and road damages, and have a high forecasting accuracy and strong reference value in disaster forecast. In comparison, two models have the same trend and results of Model Ⅱ are generally greater than Model Ⅰ in number. In the flood season and disaster-prone period, Model Ⅱ is more sensitive to subjective forecasts than Model Ⅰ.The risk forecasting systems of road damages are created for Southwest China based on two methods, and used in risk operation since the end of 2012 achieving good effects.
Increased Mixing Ratio of Surface Ozone by Nighttime Convection Process over the North China Plain
Xu Shihui, Xu Xiaobin, Lin Weili, Wang Ying, He Xinhe, Zhang Hualong
2015, 26(3): 280-290. DOI: 10.11898/1001-7313.20150303
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Abstract:
Surface ozone and other reactive gases are observed at Gucheng (39°08′57″N, 115°44′02″E) in Hebei Province of China from June to September in 2013. There are 10 cases with rapid increases of the mixing ratio of surface ozone, and sharp decreases of the mixing ratios of nitric oxides and carbon monoxide when convection processes occurs at night. The mixing ratio of surface ozone mostly increases from less than 30×10-9 to 60×10-9-80×10-9 within less than 1 hour and stays at a higher level during the night and the next morning than that on undisturbed days. Such phenomenon cannot be explained by photochemical production. The increase rate of surface ozone level is not correlated with wind speed. Therefore, the change in ozone cannot be attributed to horizontal transport of polluted airmass.To understand the phenomenon, meteorological data from Gucheng and from ECMWF reanalysis are analyzed. Surface pseudo-equivalent potential temperature (θse) for each case is calculated from the simultaneously measured meteorological data. In all nighttime cases of convection process, the surface θse values decrease dramatically within a short time, coinciding with the steep increases of the ozone level and the wind speed. This suggests that the mixing ratio of surface ozone is enhanced by descending air from aloft. The convective process occurs in the warm area ahead of the front in most cases except for once near the cold front. These clearly indicate that convective downdrafts transport air with higher ozone and lower θse from upper atmosphere to the surface layer. With the vertical profiles of θse values calculated from ECMWF reanalysis data, levels of origins of downdrafts are estimated as from around 500-800 hPa. Vertical profiles of ozone observed using an unmanned aircraft near the station show that ozone mixing ratio over the boundary layer at dusk is higher than 60×10-9, supporting the view that the increased mixing ratio of surface ozone during and after the nighttime convection process is caused by air descending from the lower to mid free-troposphere. The phenomena with ozone enhancement is also observed at an urban station in Bejiing. In most cases when Gucheng and Beijing urban are impacted by the same convective systems, and ozone and θse at both sites show similar trends. All above implies that ozone mixing ratio maintains around 60×10-9-80×10-9 in the mid and lower free-troposphere over the North China Plain in summer and early autumn, and ozone increase by convective downdrafts is able to impact a large area of the North China Plain. Compared with other places, convection process causes larger ozone increase, which may exert stronger impact on the atmospheric environment.
Daily Total Radiation Model Based on Air Pollution Index
Yu Li, Shen Shuanghe, Tao Sulin, Li Meng, Ding Conghui
2015, 26(3): 291-299. DOI: 10.11898/1001-7313.20150304
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Abstract:
Solar radiation is the primary energy source of various physical processes in the natural environment, the basic force of driving formation and evolution of weather and climate. It's one of the most important natural factors in many scientific fields. However, compared with temperature and precipitation, solar radiation data are rather deficient in China, and thus it is necessary to seek a new way to calculate it by using the routine meteorological variables. With the rapid development of the national economy and the continuous expansion of cities, the air quality of some large and medium-sized cities has been gradually worsening. However, these effects are often neglected in radiation model, which may cause great errors in the solar radiation calculation. Therefore, a more precise solar radiation model which regards air pollution index as a dominant factor is built to improve model simulation accuracy. By analyzing the statistical analyses about observations of 23 nationwide sites from 2001 to 2012, the model is established for assessment of daily radiation with nonlinear regression method, which is called DSRM-Y. The model includes three independent variables: Daily temperature range, astronomical percentage of sunshine and air pollution index. Meanwhile, to check the simulation effect, results of DSRM-Y are compared with those of a previous model called DSRM-C. Results show a significant negative correlation between two essential factors of air pollution index and daily solar radiation. In addition, a good fitting effect is expressed in scattering diagram, mean bias error, root mean square error and error analysis of daily total radiation between calculated and measured values. The application result of DSRM-Y at Xining, Shanghai and Kunming indicates, as the air pollution index rises, the daily solar radiation weakens in all three sites. In terms of model comparison, the root mean square error of DSRM-Y is less than that of DSRM-C for all sites, indicating DSRM-Y performs better.
Estimation of Climate Change Effects on Water Use Efficiency of Rain-fed Winter Wheat
Cheng Lin, Fang Wensong
2015, 26(3): 300-310. DOI: 10.11898/1001-7313.20150305
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Abstract:
Investigating the influencing rule of climate change on water use efficiency (WUE) of rain-fed winter wheat can offer scientific reference for agriculture adapting to climate change. Based on yield information and observed soil water data at representative stations, the historical trend of WUE is analyzed. Simulation models for meteorological yield and soil water variation quantity are established, and four different kinds of climate change scenarios, which are outputs by regional climate models of PRECIS and REGCM4.0 are combined to estimate the probable variation trend of WUE in the future years of 2021-2050 for rain-fed wheat. It is validated that in the basic scenario years, simulated yields by the combination of two regional climate models with meteorological yield simulation model are close to actual values, so methods for estimating future yield of wheat is proved feasible. Results by data analyzing shows that the average yield for representative stations varies as a cubic curve during the last 30 years of 1981-2010, and grows faster before the year of 2000. Water consumption of wheat also increases with fluctuating. The average WUE value of rain-fed wheat for representative stations in Gansu, Shanxi and Henan are 13.19 kg·mm-1·hm-2, 12.86 kg·mm-1·hm-2 and 11.28 kg·mm-1·hm-2, respectively. The varying trend of WUE is similar to a quadratic curve, and the maximum value appears in the year of 2003. Estimation results under four different climate change scenarios shows that in 2021-2050, water consumption of winter wheat would increase dramatically, and the increasing amount could reach to 6.2% for all the representative stations and all scenarios averagely. Yields in the future would decrease and some increase, and the variation rate would be 1.4% on average. The value of WUE would decrease 3.8% on average, meanwhile, the variability rate would also decrease. The increase of water consumption would be the main cause for WUE decreasing in the future. From the inter-annual variation during 2021-2050, WUE would show a non-significant trend of increasing under the simulation of PRECIS model, and comparing to the average value of 1981-2010, the decreasing rate of WUE would be more significant under A2 scenario than B2. However, there would be a significant decline trend for WUE simulated by REGCM4.0 model, and under the scenario of RCP8.5, the reduced value of WUE would be higher than that of RCP4.5. Generally speaking, the climate scenario of RCP has even more negative effects on WUE of rain-fed wheat.
Characteristics of Downward Cloud-to-ground Lightning Return Strokes Occurring on Tall Structures with Different Heights
Chen Lüwen, Lü Weitao, Zhang Yijun, Zhang Yang
2015, 26(3): 311-318. DOI: 10.11898/1001-7313.20150306
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Abstract:
To study the difference between characteristics of lightning return strokes occurring on tall structures with different heights, comprehensive observations for 58 natural downward negative cloud-to-ground lightning flashes with confirmed grounding points are analyzed. When heights of grounding points are below 200 m, the arithmetic mean and geometric mean values for the number of strokes per flash, inter-stroke intervals, peak currents of the first strokes, peak currents of the subsequent strokes, 10%-90% rise times of the first stroke optical pulses, widths from 10% wave front to 50% wave tail of the first stroke optical pulses, 10%-90% rise times of the subsequent stroke optical pulses, and widths from the 10% wave front to the 50% wave tail of the subsequent stroke optical pulses are estimated to be about 3.7 and 1 (33 samples), 95 ms and 66 ms (15 flashes containing 95 strokes), -57.9 kA and-43.8 kA (30 samples), -34.1 kA and-30.8 kA (68 samples), 3.8 μs and 3.1 μs (17 samples), 38.1 μs and 32.5 μs (17 samples), 2.2 μs and 2.0 μs (19 samples), 52.9 μs and 35.0 μs (19 samples), while values are estimated to be about 2.6 and 1 (22 samples), 94 ms and 57 ms (10 flashes containing 41 strokes), -104.3 kA and-92.9 kA (24 samples), -50.1 kA and-42.6 kA (32 samples), 28.3 μs and 22.7 μs (13 samples), 119.8 μs and 110.5 μs (13 samples), 10.1 μs and 8.8 μs (4 samples), 126.5 μs and 124.8 μs (4 samples) when heights of grounding points are greater than 200 m. On the whole, the number of strokes per flash and inter-stroke intervals of flashes occurring on structures taller than 200 m and those lower than 200 m are close. But peak currents of the first strokes, peak currents of the subsequent strokes, 10%-90% rise times of the first stroke optical pulses, widths from 10% wave front to 50% wave tail of the first stroke optical pulses, 10%-90% rise times of the subsequent stroke optical pulses, widths from the 10% wave front to 50% wave tail of the subsequent stroke optical pulses for the flashes occurring on structures taller than 200 m are greater than those occurring on structures lower than 200 m, and arithmetic mean (geometric mean) values of the former are 1.8 (2.1), 1.5 (1.4), 7.4 (7.4), 3.1 (3.4), 4.6 (4.3), 2.4 (3.6) times of the latter.
Features of Radiosonde Balloon Drifting with Impacts on Divergence Calculated by Triangle Method
Wang Xuezhong, Hu Banghui, Wang Ju, Huang Hong, Zou Xun
2015, 27(3): 319-327. DOI: 10.11898/1001-7313.20150307
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Abstract:
Traditional radiosonde balloon can float a long distance from its releasing place especially when reaching a high level above ground, while special radiosondes consisting of wind profiler and satellite remote sensing information are snapshots of atmospheric status and have no spatial drifts of particular location. The spatial derivatives (such as divergence) calculated through triangle method are closely related to the triangle's three-culminations position. The balloon floating and inhomogeneity introduced by the mixed use of data from traditional and special radiosondes can dramatically change the relative position of those culminations. The balloon floating feature and its impact on the divergence calculated through triangle method is a subject of potential application. Based on traditional radiosonde data of three stations in Eastern China, namely Nanjing, Anqing and Hangzhou with time coverage from 2006 to 2013, statistical features of balloon drift are investigated. And three experiments are designed to investigate how the balloon drifting impact the divergence computed through triangle method. The first experiment does not take the balloon drift into account, representing the traditional case which regards the radiosonde is right above the releasing point. The second experiment regards three balloons floating freely controlled by the atmospheric circumstance, which reflects the true physical processes of balloon motion. The third experiment is to simulate the inhomogeneity of traditional and special radiosondes: The balloon from Nanjing is assumed to have no horizontal motion as an analogue of special radiosonde and balloons from other two stations are freely floating as representatives of traditional radiosondes. Result shows that the balloon floats eastward all year round except in July and August. The float distance is larger in winter contrast with other seasons, with its maximum of about 120 km. In July and August, the balloon floats eastward within the low level and change its direction to westward at higher level. In meridional direction, the balloon floats in the manner of monsoon. In tropospheres, it floats northward in summer and southward in winter. Above 100 hPa in stratosphere it floats oppositely, southward in summer and northward in winter. The whole layer maximum mean drift distance is about 30 km in July and August, and the distance is larger than 100 km in winter above 100 hPa. Divergence differences between the second and third experiments to the first experiment are researched. The absolute difference increases with the height and reaches its maximum between 200-100 hPa in each month. The second experiment's relative differences are larger from June to September, with the extreme value about 7%. Relative differences of the third experiment are larger than those of the second experiment. In July and August, the relative difference of the whole layer is slightly less than 9%. In winter months, they are larger contrast to other months, when the relative difference of the third experiment is 25% at 200 hPa and greater than 50% at 50 hPa in January. It indicates that when the divergence of high level is calculated through triangle method, the balloon drift should be taken into account. When both traditional and special radiosonde data are used, for the inhomogeneity of measurement causes large differences, the balloon drift must be considered.
Short-term Climate Prediction for Summer Rainfall Based on Time-scale Decomposition
Liu Na, Li Shuanglin
2015, 26(3): 328-337. DOI: 10.11898/1001-7313.20150308
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By using one set of hindcasted integration of NCEP Climate Forecast System Version 2.0 (CFSv2) beginning from April during 1982-2008, for summer seasonal forecast, along with observations and reanalysis datasets, a downscaling scheme with time-scale decomposition is developed for summer rainfall prediction of the Yangtze-Huai Basins and North China. First, both the predictand and selected predictors are decomposed into inter-annual and decadal scales through Fast Flourier Transformation filtering. And then two downscaling models are separately built, predicted results for two timescales are combined to represent the total prediction. By using the scheme, the summer rainfall of 1982-2008 is hindcasted and compared with CFSv2 raw prediction first. A cross validation shows that skills in the present scheme are significantly improved with increased spatial and temporal correlation coefficients and decreased root mean square error, in comparison with the raw prediction. The spatial correlations with observations for both the Yangtze-Huai Basins and North China have the maximum exceeding 0.8 and a long-term average of 0.53, 0.51, greater than the original-0.06, -0.01 for two regions. The predicted rainfall temporal correlation at each station is also improved, with the regional mean increased from-0.2 to 0.2 in raw model prediction to about 0.5 after downscaling, significant at 0.01 level. The root mean square error exhibits a decrease with the rate of exceeding 10% at most of stations. Then a five-year hindcast from 2009 to 2013 is performed and used for validation as independent samples. Results suggest that spatial correlations of the predicted rainfall with the observed in five samples are significantly higher than the raw prediction, with the mean increased from 0.24, 0.08 to 0.37, 0.44 for two regions. Spatial patterns of rainfall anomaly percentage in two of these independent samples are reasonably closer to observations. Also, the predicted rainfall strength is much closer to the observation, comparing to the raw prediction. Finally, the scheme is applied for the real-time prediction of summer rainfall in 2014. The prediction result displays more rainfall over the mid-lower Reaches of the Yangtze and over the north region of the Yellow River valley, with an anomaly percentage of 20%, along with rainfall anomaly percentage of-10%. Compared with observations, the rainfall anomaly pattern can be predicted to some extent through the downscaling method, especially over the southern region of Yellow River.
Effects of Slope and Altitude on the Precipitation During the Flood Season in Beijiang River Basins of Guangdong Province
Liang Shenghua, Zhang Ling, Qian Huaisui, Li Mingxia, Zou Xiaoshuo
2015, 26(3): 338-345. DOI: 10.11898/1001-7313.20150309
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Abstract:
To study the spatial differentiation phenomena of precipitation in composite-mountain system, the relationship between the mountain slope, altitude and the precipitation of Beijiang River Basins during the flood season is analyzed with the method of multi-factor separation, using monthly precipitation data from 1959 to 2000 collected from 40 hydrologic stations. In order to eliminate effects of macro geographical factors, the data heterogeneity caused by different locations of hydrologic stations is resolved by using the geographically weighted regressing (GWR) method. The correlation diagram of the multi-year mean precipitation and the altitude is constructed according to the evaluation from GWR, and it is divided into four sub-areas based on the point scattering. On the basis of the division, the correlation between the precipitation change and altitude is researched. According to the changing rate of precipitation with the altitude, Beijiang River Basins are partitioned, and effects of warm air through the upstream and downstream on precipitation change with altitude are studied.The result shows that the distribution of the multi-year mean precipitation during the flood season in Beijiang River Basins is perpendicular to parallel and it decreases from the south to the north. The rainy area is in the southeast of the basin and the mainstream from Yingde to Qingyuan is a stable rainy center. With the change of altitude, precipitation curve shape of the composite-mountain system can be summarized as the parabolic type. The variation of precipitation with the change of altitude in composite-mountain system is related to the precipitation interception effect of warm air through the upstream and downstream of the ridge. Varying characteristics of the average precipitation during the flood season in Beijiang River Basins demonstrate the obvious regional differentiation, it can be divided into four sub-regions, and there are different maximal precipitation in different sub-areas. From the south to the north, altitudes are 77.3 m, 408.4 m, 353.6 m, 376.9 m and the maximum precipitation are 1566.2 mm, 1467.5 mm, 1295.9 mm, 1151.5 mm, respectively. The precipitation during the flood season in Beijiang River Basins gradually increases from south to north, which means that the annual variation of precipitation presents spatial distribution regularities, bigger in north and smaller in south. This is associated with interception effect of mountains to the airflow and warm air strength. When the warm air is stronger, the interception effect on airflow upstream mountain water is relatively small. When the warm air flow is weak, the interception effect of upstream mountains is relatively strong.
The Accuracy Test of Retrieved Precipitation Water Vapor Based on Beidou Observations
Guo Wei, Yin Qiu, Du Mingbin, Liu Min, Zhu Xuesong
2015, 26(3): 346-353. DOI: 10.11898/1001-7313.20150310
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Abstract:
The Beidou Navigation Satellite System is an independent system under construction in China. Observations of Beidou can be used to retrieve atmospheric precipitation water vapor (PWV) and provide information of water vapor with high precise and high real time. Beidou meteorological observation network is built by Shanghai Meteorological Bureau with PANDA (position and navigation data analysist) and M300C_GNSS, UNICORE-UB240 Beidou receivers, and the atmospheric precipitation water vapor is acquired. First, satellite data is received by Beidou meteorological observations and satellite orbit files are downloaded synchronously, and then zenith total delay (ZTD) is calculated by PANDA modules, and at last the PWV is retrieved based on surface meteorological parameters observed by automatic weather stations.Results of PWV retrieved by Beidou data (WBD) are compared with both PWV retrieved by GPS data (WGPS) and radiosonde data (WRadio), as the technology of them are mature. WGPS is retrieved by two methods: One is GAMIT (GPS at MIT) with the method of double difference phase observation, the other is PANDA with the method of precise point positioning. WRadio is retrieved by the method of water vapor integration from different pressure levels. The horizontal distance difference between corresponding observations is no more than 10 km, the elevation difference between GPS and Beidou observations is no more than 5 m, and the elevation difference between radiosonde and Beidou observations is about 30 m. Results show that the root mean square error (RMSE) between WBD and WGPS is no more than 3.5 mm, the correlation coefficient between them is over 0.95, and the RMSE between WBD and WGPS-P is smaller than that between WBD and WGPS-G, which means that the retrieve method has certain influence on results of PWV. The RMSE between WBD and WGPS-Radio is about 3.6 mm, the correlation coefficient between them is over 0.96, and WBD is on the high side compared with WGPS-Radio. WBD can well reflect the temporal changing characteristics of water vapor in the atmosphere and has corresponding relations with precipitation, which plays an important role in short-term weather forecast and climate analysis. The accuracy of WBD relies much on the precise ephemeris of Beidou.With the development of the Beidou Navigation Satellite System, the accuracy of PWV based on Beidou observations can surpass that based on GPS observations. Therefore, making the best of the Beidou Navigation Statellite System and improving meteorological service with WBD is important for the modernization of meteorology.
Comparative Analysis of the Cloud-to-ground Lightning Data Between Two Lightning Location Systems
Zhao Wei, Jiang Yujun, Tong Hangwei, Zhang Bin
2015, 26(3): 354-363. DOI: 10.11898/1001-7313.20150311
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Abstract:
Comparative analysis of the lightning location data from 2009 to 2013 is conducted by temporal and spatial distribution and detection efficiency, to explore the difference of data collected from two lightning location systems (LLS) of Zhejiang meteorological department and Zhejiang electric power department. Results show that the inter-annual cloud-to-ground (CG) lightning frequency observed by the LLS of Zhejiang meteorological department is stably lower than that observed by the LLS of Zhejiang electric power department. The number of positive CG lightning occupies 3.5% of total CG lightning observed by the LLS of Zhejiang meteorological department, which is also 2% less than that observed by the LLS of Zhejiang electric power department, and both of them are in a reasonable interval. From the viewpoint of spatial distribution, the CG lightning density of two datasets is nearly equal in coastal plain and the Jinhua-Quzhou Basin, but the CG lightning density obtained by Zhejiang electric power department is stably more than that of Zhejiang meteorological department in the other areas except in Chun'an which is located in the border of Hangzhou and Quzhou. It is also found that the occurrence of high CG lightning density region in Chun'an observed by LLS of Zhejiang meteorological department is abnormal. Further analysis of the number of monthly mean thunderstorm days obtained by these two LLSs and manual observation indicates that the monthly mean thunderstorm days observed by the LLS of Zhejiang meteorological department is not more than that of manual observations except in summer, when the monthly mean thunderstorm days observed by LLS of Zhejiang electric power department is almost more than that of manual observations every month. It suggests that the LLS of Zhejiang meteorological department does well in detecting strong thunderstorms while the weaker thunderstorms could be missed. Hence, the LLS detective ability of Zhejiang electric power department is better than that of Zhejiang meteorological department. On the other hand, comparative analysis of detection efficiency is made based on the data of accidents of lightning trip-out on Zhejiang Power Grid. It is concluded that the detection efficiency of the LLS of Zhejiang electric power department is around 6% higher than that of Zhejiang meteorological department.
Disturbance of Moon to FY-2E Full Disk Images
Chen Boyang, Feng Xiaohu
2015, 26(3): 364-368. DOI: 10.11898/1001-7313.20150312
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Abstract:
There are obvious white exceptional bands in all 4 infrared (IR) full disk images of FY-2E, which have adverse effects on using images. By analyzing the time when exceptional band appears, the fact that bands in different IR images are in the same place, the matter in the white band, and the fact that the full disk images are all right after exceptional band, it's concluded that the satellite is all right but the moon's disturbing is the cause why exceptional band appears. Based on the FY-2E characteristics, it's identified that the process of moon leads to the white band in the image via direct-current restoration of FY-2E. Using satellite orbit parameters, the moon orbit and libration data, it can be confirmed the stochastic error in the circuit and libration are two important causes for the uncertainty in calculation. However, only 4 times are found during operation period from Mar 2012 to Jan 2013 though it seems to be 12 times according to the calculation. Both the analysis and the calculation are useful in practice for better using of FY-2E satellite.
Research and Implementation of Ensemble Forecast Product Analysis and Display Platform
Yu Lianqing, Li Yuean, Gao Song, Luo Bing
2015, 26(3): 369-377. DOI: 10.11898/1001-7313.20150313
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Abstract:
In response to the impendent requirement of ensemble forecast applications in modern weather forecast operations, an ensemble forecast product analysis and display platform named NUMBERS (NUmerical Model Blending and Ensemble foRecast System) is developed. The application background, requirement analysis, design of system architecture and function implementation are discussed in details. In addition, some key technologies such as dynamic page layout rendering and data pooling, are also described.First of all, the ensemble forecast platform is designed using the client-server architecture. On the server side, there is a data processing program that converts large amounts of ensemble numerical model output into product data to ensure the performance of client data visualization program. On the client side, there is a data visualization program and a management console program. The data visualization program provides features including ensemble product data analysis, blending of multiple deterministic models, customized geographic information service, layer-based graphics rendering, interactive configuration of graphics layers, and exporting of weather maps. The management console program provides a unified user interface to help users manage all settings of the platform.As there is a large difference in computing resource throughout the meteorology department, the ensemble forecast platform is designed to be cross-platform by employing a modular and stratified design approach with C++ is programming language.In order to enhance graphics rendering quality of weather maps, an innovative page layout rendering technique is proposed, allowing a flexible configuration of graphics elements like layers, titles and legends and creation of professionally-looking weather maps.As an effective abstraction of ensemble data may significantly improve working efficiency of forecasters, advanced ensemble prediction algorithms and graphics rendering technologies are incorporated into the platform, which support nearly all popular products including statistics quantities, probability forecast, stamps, spaghetti, plume and box-whiskers.Since September 2013, the platform has been put into operation in central meteorological observatory and nearly all observatories of province capitals. Ever since, the platform is further improved by adding new features and fixing bugs based on user feedbacks. In the future, the platform will be improved by incorporating the latest algorithms in ensemble prediction, enhancing support for professional forecast such as typhoon track prediction and short-term strong weather prediction, introducing ensemble prediction validation and improving interactive performance. Furthermore, all the features of the platform will be incorporated into the fourth edition MICAPS, which will play an important role in flourishing China ensemble forecast applications and improving operational capability.
Improved Implementation of Meteorological Integrated Display System Based on WebGIS
Zhao Wenfang, Liu Xulin, Nie Kai
2015, 26(3): 378-384. DOI: 10.11898/1001-7313.20150314
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Abstract:
In order to overcome shortcomings of traditional WebGIS implementation method, an application framework of WebGIS based on Ajax is introduced and real-time meteorological data integrated displaying system is established, which can provide quick displaying and querying of meteorological data.pMapper is a MapServer application framework based on PHP/MapScript, composed of a series of PHP, JavaScript, CSS and XML files. It offers broad functionality and multiple configurations to facilitate the setup of WebGIS based on Ajax, including map operation, spatial analysis, and attribution query functions. Meanwhile, custom plugins can be supported to extend the framework. There are two advantages to develop WebGIS based on Ajax by using this framework: Developer-friendly and open source.On the basis of its characteristics and advantages, the main development method under this framework is also discussed. In order to provide a user-center GUI, some new CSS templates and custom plugins are embedded into the framework. In addition, some source codes are modified to present better query result table and charts on the Web. The real-time meteorological data integrated displaying system provides friendly map operation, quick querying and displaying of different meteorological data, and the visualization of statistics charts for observation elements, e.g., temperature, precipitation and wind. Meanwhile, it also provides analysis of rainfall contour overlaid on the map. The system consists of four layers: Data layer, data interface layer, business logic layer and client layer. The data layer on the bottom mainly stores and provides fundamental data for data interface layer which consists of various data access services. The business logic layer provides specific business logic processing and WebGIS services, responding to requests from the client layer, which provides all kinds of meteorological information dynamically and instantly through a friendly browser interface. At present, this system is on trial for more than one year in the Beijing Meteorological Bureau, providing high performance and better data sharing services. The system brings high performance and better user experience, shortening the average response time of most Web pages to less than 3 seconds, and it can support 100-150 concurrent users. The peak access time is 0800 BT and 1600 BT every day, but the total Web traffic will suddenly increase when high impact weather happens. The top three visited pages are automatic weather station page, radar products page, and nowcast products page, and visitors mainly come from Beijing Meteorological Center.
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