应用气象学报

2014, 25(3)

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Abstract:

第3期封面及目次

Influences of the North Pacific Warming on Autumn Precipitation in Northwest China

Han Jinping

2014, 25(3): 257-264.

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Abstract:
Based on monthly precipitation data from 160 meteorological stations established by National Climate Center in China, NOAA reconstructed extended monthly SST and monthly atmospheric circulation data from NCEP-DOE Reanalysis datasets, the influence of North Pacific sea surface temperature (SST) on autumn precipitation from 1979 to 2012 in Northwest China is studied by using statistical analysis method. An inter-decadal change of the autumn precipitation is found around the year of 2000 by 11-year-running t test. It is in the dry period during 1986-1999 and wet period during 2000-2012 for the region in Northwest China. Further analysis shows that the inter-decadal change of autumn precipitation in Northwest China is connected with the warming SST in the North Pacific after 2000. When the SST in the North Pacific is in warm phase, the troposphere temperature over East Asia-Northwest Pacific is dramatically increased. The contrast of troposphere temperature between the north and the south over the East Asia-Northwest Pacific is directly associated with the strength of westerly jet and the geopotential high anomalies over the region. The warming of troposphere temperature over East Asia-Northwest Pacific weakens the atmospheric thermal contrast between the mid-low latitudes and the polar area in the East Asian region. Influenced by the decreased thermal contrast along East Asia region, the westerly jet over the East Asia-Northwest Pacific is reduced significantly. And the westerly jet center at middle latitudes near the East Asian coast shifts northward. The warming in troposphere circulation and the north shifting of weakened westerly jet tend to make the geopotential high along East Asian coast increase significantly. In other words, the trough at 500 hPa along the East Asian coast is weakened, which is characterized as an anomalous anticyclone at 500 hPa. The anomalous wind flows at 850 hPa in the south of the anticyclone are easterlies. As a result, the water vapor transported by anomalous easterlies from the Northwest Pacific into Northwest China along East Asian coast is increased. Both water vapor and convergence are enhanced, leading to increasing autumn precipitation in northwest China after 2000. Results suggest that autumn precipitation in Northwest China is in the wet phase after 2000 and has a rising chance to bring flood disaster. As the autumn precipitation is much different from summer rainfall, the prediction of the autumn precipitation in the Northwest China is a new challenge to short term climate forecast. The warming background in the North Pacific could be a factor to consider at the decadal timescale.

Evaluation on Surface Meteorological Element Forecast by Beijing Rapid Update Cycle System

Min Jingjing

2014, 25(3): 265-273.

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Abstract:
The rapid update cycle (RUC) based on the rapid update cycle data assimilation system and high resolution meso-scale numerical prediction system is widely applied at home and abroad. Using high frequency update cycle assimilation analysis based on dense meso-scale observations, RUC can provide high quality initial field for high resolution numerical model to produce refined numerical forecasts.Beijing rapid update cycle of assimilation forecast system (BJ-RUC) is established in 2007 and applied to operation in 2008 in China. The refined weather forecast products of BJ-RUC are important reference in daily weather forecast operation for forecasters. BJ-RUC is designed based on WRF model and WRF three-dimensional variational data assimilation system. Recent observations, including conventional observation from GTS global exchange, automatic weather station (AWS) observation and the high spatial and temporal resolution unconventional observations, are assimilated at intervals of three hours using WRF three-dimensional variational data assimilation system to produce a new estimation of the atmospheric state, which will be used as WRF model initial field. And then, the high-resolution WRF model outputs are used for short-range weather forecast.Using hourly surface observations of Beijing AWS from May to September during 2008-2010 the operational forecasts of BJ-RUC for the air temperature, relative humidity, 1 h rainfall, 6 h rainfall, the wind speed and direction are analyzed in details through objective verification methods. The operation performance is evaluated preliminarily based on the analysis.Results show that the surface meteorological elements of BJ-RUC system are well consistent with AWS measurements. The forecast results of 2 m temperature are too high, its error range is-1.5-1.5℃, and namely higher in the morning and night while lower at noon; results of 2 m relative humidity are too small, its error range is-25%-0, and bigger during the day while smaller during the night; forecast results of wind speed are too big, especially obvious in the afternoon, and the error range is 0.6-1.2 m·s^-1; the forecasting performance of the 6 h accumulated rainfall judgment is good, and the TS is 0.4; the stability of BJ-RUC is not good at the beginning of forecast time, and the forecasting performance is unstable with the increasing of the forecast range. In general, the forecasting surface information of BJ-RUC has a superior performance within 12 hours, which is very useful for short range weather forecast.

The Application of Radiosonde Observation Blacklisting Check to Variable Data Assimilation System

Zhuang Zhaorong, Xue Jishan, Han Wei, Liu Yan

2014, 25(3): 274-283.

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Abstract:
The radiosonde observations are very important for the numerical weather forecasting as they are more reliable data compared to other observations in the assimilation system. The radiosonde observation needs serious quality controlling before used in data assimilation, and the blacklisting check which uses monthly blacklist to delete the abnormal noise and bias data compared with background field is a significant step in observation quality monitoring. At present the radiosonde observations used in GRAPES (Global-Regional Assimilation and PrEdiction System) analysis system are scanned through preliminary checks such as climatological extreme check, consistency checks and background quality control in data assimilation system, but blacklisting check is not included. For the spurious high/low-pressure system structure of GRAPES analysis caused by the radiosonde observation in some region, the radiosonde observations are analyzed through comparing with NCEP analysis from June to August in 2007. Results show that the bias of radiosonde geopotential height observation and NCEP analysis is less than 50 gpm under 100 hPa. The bias is much bigger over 100 hPa and the radiosonde geopotential height is much smaller than NCEP analysis. Stations where the root mean square errors of the geopotential height between radiosonde observations and NCEP analysis for 500 hPa exceed 30 gpm are located in India, North Atlantic Ocean and Antarctic region. In those regions the unreliable observation ratios of some stations are above 20%, so they are listed in the blacklist. The geopotential height blacklist of radiosonde is provided by comparing observations with NCEP analysis and estimating the frequency of bad observation-quality station. The geopotential height blacklisting check of radiosonde is applied to GRAPES global 3D-var analysis system, and the cycle experiments of the analysis and forecast from 1 July to 21 July in 2009 are carried out. Two experiments are performed, Experiment 1 (control test) without blacklisting check and Experiment 2 with blacklisting check. The results indicate that the quality of geopotential height analysis of GRAPES is improved in India and Antarctic regions when considering geopotential height blacklist. The average root mean square errors of geopotential height GRAPES analysis and NCEP analysis for 500 hPa is reduced by 6 gpm in India Region and near 10 gpm in Antarctic Region after using blacklisting check in the 3D-var analysis system. In Antarctic region, the average biases and root mean square errors of geopotential height GRAPES analysis and NCEP analysis both decrease from 1000 hPa to high levels. The blacklisting check of radiosonde observation is a necessary step in the analysis system. The updated blacklist information will be used to assimilate the radiosonde observation more effectively.

Numerical Simulation of Maize Yield Variation in Northeast China Under B2 Climate Change Scenario

Yuan Dongmin, Yin Zhicong, Guo Jianping

2014, 25(3): 284-292.

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Abstract:
In order to assess the variation of maize growth due to climate change, the maize yield model is upgraded and coupled with a regional climate model named PRECIS. The maize growth period and yield in Northeast China are simulated both under baseline (1961-1990) and B2 climate change scenario (2011-2050). The variations over the next 40 years are predicted by considering and not considering CO₂ fertilizer efficiency (direct influence) separately. A direct influence module of CO₂ is added into the maize growth model to make concentration of CO₂ as an input variable. The upgraded model can simulate the yield and the increase of C4 crop, especially maize, with different concentration of CO₂. And results fit the field experiments well. Furthermore, this model could distinguish fertilizer efficiency of photosynthesis and transpiration. Under B2 scenario, the temperature rises continuously and is higher than the baseline (1961-1990). The precipitation is less on the whole, and the radiation is more than the baseline. What calls for special attention is that the precipitation is more in the 2020s, which is favorable to maize growth. Without considering CO₂ fertilizer efficiency, the production almost decreases, and the range of reduction closely relates to maturity. The reduction is biggest in parts of Songnen Plain, more than 20%. But in the 2020s, the production in most areas increases less than 20%. The variation is caused by weather condition, and the increasement of temperature and decreasement of precipitation should be the primary cause. As time goes on, the reduction is bigger and bigger. In the 2020s, the precipitation always is greater and beneficial to the maize growth. The CO₂ fertilizer efficiency is important, and its compensation effects on the maize yield is significant. The distribution of the yield variation is similar, but the range is less. As the concentration of CO₂ goes higher, the CO₂ fertilizer efficiency is more and more significant. So, the CO₂ fertilizer efficiency and weather condition must be considered. In the next 40 years, the variation of the maize growth period distributes relatively stable, and closely relates to the maturity. The growth period of mid-and early-maturation shorten obviously, but that of late-maturation elongate persistently. Changes of other three maturities are not obvious.The variation of yield and growth period has theoretical significance comparing with the average value of 1961-1990. But these results are based on the consideration of climate change barely, without social feedback and adaption to climate change, so the model needs improving in the future.

Forecast Method of Multi-model Air Temperature Consensus in Tianjin

Wu Zhenling, Pan Xuan, Dong Hao, Xu Shu, Wang Jing

2014, 25(3): 293-301.

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Abstract:
Based on genetic algorithm and particle swarm optimization, multi-model air temperature consensus forecast technology (MMATCFT) of hybrid evolutionary algorithm (HEG) is studied. The main technical thought of this method is that two integrated forecast models are set up respectively by using the genetic algorithm and particle swarm optimization, and then the final mixed forecasting model is established by the weight distribution scheme, which is founded through comparing forecast mean errors between the two models.In order to eliminate the impact of seasonal temperature characteristics of Tianjin, the daily rolling integrated forecast model based on 30-day data is adopted in practical operation applications with hybrid evolutionary algorithm. Using 2 m air temperature output data of four models of T639, GRAPES, TJWRF, BJ-RUC and observations of 35 automatic weather stations (AWS) in villages and towns of Tianjin from May to October in 2012, the forecast test of MMTCFT is carried out. Then the experimentation result is evaluated using the way of classification and station-separation, according to the meteorological standard that absolute error of temperature forecast is within 2℃. T639, GRAPES, TJWRF and BJ-RUC are separately run by China National Meteorological Center, Tianjin Meteorological Bureau and Beijing Meteorological Bureau. The analysis shows that the temperature consensus forecast model is effective and reliable. The technical scheme of the consensus forecast based on rolling model is more rational. The forecast errors are obviously smaller than any model mentioned above, and the forecast accuracy is higher. The average forecast accuracy of 6 h temperature, the daily maximum and minimum temperature in 35 AWS is 76.34%, 77.88% and 78.00% from May to October, respectively.

Correction Based on Distribution Scaling for Precipitation Simulated by Climate Model

Zhou Lin, Pan Jie, Zhang Lei, Xu Yinlong

2014, 25(3): 302-311.

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Abstract:
A statistical bias correction based on piecewise Γ distribution fitting to construct seasonal transfer function is applied to the precipitation simulated by a regional climate model PRECIS under the SRES-A1B emission scenario over China. The transfer function (TF) is derived from the control period of December 1962—November 1972, fitting the cumulative probability density function of both simulated and observed precipitation with Γ distribution. The 95th percentile precipitation is chosen to be the threshold and precipitation below and upon the threshold are fitted, respectively. When compared with wholesale fitting, this method can better fit the distributions of both small/medium precipitation and extreme precipitation. Then the TF is applied for the validation period of December 1991-November 2001. The correction strategy is based on the assumption that discrepancies between model and observation stay constant with time.Results show that PRECIS can reproduce the spatial distribution of mean and extreme precipitation, while the biases exist. The biases are larger if the topography is more complex. If the region is high or low in altitudes, the bias tends to be positive or negative, while Sichuan Basin is the exception, where large positive biases occur.The correction based on the piecewise Γ distribution fitting can well correct the spatial distribution of the mean precipitation over China, especially over the original large-bias regions, and the grids in which the bias percentages used to be larger than 100% are reduced from 23.5% down to 1.0%. Simulation of region-averaged monthly precipitation is significantly improved, especially over Southwest China and the Tibet Plateau regions. Precipitation in cold seasons is better corrected, while it has relatively larger biases in warm seasons especially in June due to a wide range of precipitation, which may bring difficulties during fitting. So, it's crucial to improve the fitting probability in warm seasons.The piecewise Γ distribution fitting correction also does a quite good job in correcting the extreme precipitation. The spatial distribution, probability density distribution and spatial correlation coefficient of consecutive dry days, the maximum 5-day precipitation amount and the contribution of extreme precipitation are corrected significantly, except for maximum 5-day preciptiation amount in East China, contribution of extreme precipitation in Northwest China and the Tibet Plateau are overcorrected. These show that the technique has the ability to correct the extreme precipitation.In general, the correction results are satisfying, which implies that the piecewise Γ distribution fitting correction is capable of improving the reproduction of both mean and extreme precipitation simulated by regional climate model PRECIS over China, which is useful for assessment research.

Sensitivity Study of WRF Parameterization Schemes for the Spring Sea Fog in the Yellow Sea

Lu Xue, Gao Shanhong, Rao Lijuan, Wang Yongming

2014, 25(3): 312-320.

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Abstract:
Sea fog is a water vapor condensation phenomenon, which happens in marine atmospheric boundary layer (MABL). Low atmospheric visibility caused by sea fog brings huge threat to maritime transportation, fishery and oil-drilling operations. Therefore, it is becoming increasingly important and being paid more and more attention. In recent years, meso-scale atmospheric numerical modeling has become a dominant way for the mechanism study and numerical modeling of sea fog.Previous studies on sea fog indicate that sea fog modeling is very sensitive to initial conditions, especially realistic representation of temperature and humidity profile in MABL. Besides initial conditions, turbulence process and cloud generating process are the other important aspects for sea fog modeling. In a meso-scale atmospheric numerical model, the turbulence process is described by planetary boundary layer (PBL) scheme, and the cloud generating process is determined by microphysics (MP) scheme. Due to the uncertainties of the modeling result and the complexities of turbulence and cloud microphysics processes, many options of PBL and MP schemes are available for choice focusing on different modeling purposes.Based on the Weather Research and Forecasting (WRF) model and cycling three-dimensional variational method, sensitivity study of WRF PBL and MP schemes for the Yellow Sea fog is conducted, focusing on 10 typical widely-spread sea fog cases. The result indicates that simulated sea fog area mostly depends on PBL scheme but little on MP scheme; density and depth of simulated sea fog are affected by MP scheme with cloud droplet number being predicted and how it is prescribed. The best combination of PBL and MP schemes is YSU and Lin, while the worst is Mellor-Yamada and WSM5. The Mellor-Yamada and QNSE scheme brings about much stronger turbulence simulation, resulting in much higher boundary layer, and therefore it's not favorable to the development and maintenance of sea fog, while turbulence intensity and boundary layer height produced by MYNN and YSU schemes benefit sea fog developing. MYNN scheme can match YSU scheme in general, however, the latter performs better in most cases while the former is better in certain ones. In depth investigation is needed to tell whether MYNN or YSU PBL scheme is better for a given sea fog case. These information can provide hints to choose and improve PBL and MP schemes of WRF for the Yellow Sea fog numerical prediction system in the near future.

Optimization of Nonlinear VAD Method in the Low-level Wind Retrieval

Ma Xiumei, Lee Wenchau, Zhao Kun, Tang Xiaowen, Yang Hongping

2014, 25(3): 321-329.

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Abstract:
The performance of nonlinear velocity azimuth display method in the vertical wind profile retrieval at low levels (below 2 km) is quantitatively examined by combing the theoretical analysis and cases observed by SoWMEX S-Pol radar and Yangjiang radar in Guangdong Province. Results show that the general structure and evolution of the low-level wind profile can be reasonably deduced by traditional nonlinear VAD method. The root mean square error can be used to evaluate orders of velocity azimuth display (VAD) fitting, but small error does not always mean the better performance especially with big continuous data absence, and a specific example is given. When setting the VAD fitting order to 3 instead of 2, coefficients which represent the horizontal wind u and v are closer to the wind derived from radial velocity image. However, when the fitting order comes to 4, coefficients lost their physical meaning. The wind direction differs a lot and the speed is much smaller than the value before. At the same time, the root mean square error decreases compared with the order of 3. Besides, data used in nonlinear VAD fitting come from the whole volume, which decreases quite a lot and leads to nonlinear VAD fitting error when the volume coverage pattern (VCP) only has some lower elevations (e.g., two elevations). Therefore, the retrieved wind could contain large error in certain situations, such as for a region with large continuous data absence or a volume scan with fewer elevations.After carefully evaluating the impact of the corresponding parameters on the nonlinear VAD retrievals by analyzing radar measurements, a modified nonlinear VAD method is proposed which takes account of the maximum fitting order in horizontal (VAD) and vertical adaptively according to the size of continuous data absence and the number of sweeps in a volume scan. VAD fitting is abandoned when the data absence is larger than 90°; the order is set to 3 when the data absence is between 60° and 90°; and the order is set to 4 when the data absence is smaller than 60°. The order of nonlinear VAD fitting is reduced when the VCP only has low elevations. Apply the method in two cases: One is a front case passing through Taiwan, China, the other is a typhoon case landfall in Guangdong Province, with both of them having nonlinearity in the low level wind profile. The wind profile after adjusted can significantly improve the wind retrieval, as compared with the traditional nonlinear VAD. Both wind speed and direction from modified nonlinear VAD agree with those from sounding observations, with the root mean square of the wind less than 2 m·s^-1, which is obviously better than nonlinear VAD before adjusted.

Characteristic Analysis of Continuing Current Process and M-component in Artificially Triggered Lightning

Zhou Fangcong, Zhang Yijun, Lü Weitao, Gao Yi, Zheng Dong, Zhang Yang, Chen Shaodong

2014, 25(3): 330-338.

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Abstract:
The continuing current (CC) process of cloud-to-ground lightning is a discharge process in which charges continuously transfer to ground along the lightning channel after return stroke. The magnitude of CC is small, but the duration of CC is commonly long, so CC often causes lightning disaster. It's very hard to get current data due to the randomness of lightning. Artificially triggered lightning, in which the time and location of triggered lightning can be controlled, is an effective way to measure current of lightning. Artificially trigged lightning is different from nature lightning which only has CC after return stroke, yet artificially trigged lightning has CC and initial continuous current (ICC) process both. Only the CC is analyzed using simultaneous observations of current, electric field change and chnnel luminosity by coaxial shunt, fast and slow antenna, and high-speed camera in Guangzhou Field Experiment Site for Lightning Research and Testing, Conghua, Guangdong, China. Then, photoelectric character and characteristic parameters of 14 CC and 43 M-components after return strokes of triggered lightning observed in summer in 2008 and 2011 are analyzed. The relationship between some characteristic parameters of CC and M-component is analyzed, too.The current waveforms of CC after return strokes are continuous and change slowly. Usually, there are current pulses ranging in size superimposed on CC waveforms. The slow electric field waveforms of CC are slowly changing, too. The lightning channel below the cloud is always luminescent during CC. The current waveforms, fast and slow electric field waveforms and channel luminosity variation waveforms of M-components are approximate symmetrical. The geometric mean of duration, charge transferred to ground, average current and action integral for CC are 22 ms, 6.0 C, 273 A, 4187 A²s, respectively. The geometric mean of magnitude, charge transferred, half peak width, rise time (10%-90%), duration, preceding CC level, inter-pulse interval, action integral for M-components are 409 A, 205 mC, 520 μs, 305 μs, 1.6 ms, 310 A, 6.5 ms, 465 A²s, respectively. There are very remarkable positive correlations between the duration of continuing current and number of M-components, and between the duration of continuing current and inter-pulse interval of M-components. The correlation coefficients are 0.83 and 0.75, and both pass the significant verification of 0.01 level.

Onset Corona Field Based on Isolated Metal Tip

Tan Yongbo, Zhu Junru, Li Xiangchao, Liang Zhongwu, Guo Xiufeng

2014, 25(3): 339-346.

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Abstract:
Corona discharges characterized by much lower current densities are often generated in a strong atmospheric electric field. What's more, corona discharges are very important because the corona charge layers can change the distribution of the electric field near the ground and affect conditions of the initiation and development of an upward leader near different tall objects. Therefore, corona discharges have attracted the attention of scholars at home and abroad, especially in the onset corona field. However, how to effectively show corona emission threshold is still a difficult problem in the study of atmospheric electricity.In order to obtain the electric field strength at the tip of metal in the case of corona discharge, the onset corona voltages must be obtained by laboratory test for different heights, shapes and materials of metal tips which are arranged on the middle of lower plate of two parallel metal plates. Dimensions of two horizontal plates are 1.2 m by 1.2 m and the distance between them is 1 m. Then environmental threshold electric fields are calculated for different heights, shapes and materials of metal tips. The two-dimensional Poisson equation is solved using finite element method and the corona emission thresholds at the tip of different types of metal tips are obtained.Effects on threshold electric fields by the height, material and shape are discussed, respectively. The following conclusions can be drawn from the experimental study. First, the environmental threshold fields are basically a linear decrease with heights of metal. The environmental threshold fields decrease first and then increase when metal tips are becoming sharp increasingly. Second, the height and shape of mental tips have no effects on corona emission threshold at the tip of metal tips. The corona threshold at the tip of mental tip is a constant. Finally, the corona triggering threshold is determined which is E_c=158.75 kV·m^-1 and the fitting function between corona emission threshold and spatial resolution is given. It will provide a reference for the judgment of starting moment of corona discharge for the future numerical simulation of corona discharge.

The Multi-scale Entropy Feature of the Chaotic Leader in the Cloud-ground Lightning

Li Chan, Zhang Yang, Lü Weitao, Zheng Dong, Tan Yongbo

2014, 25(3): 347-353.

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Abstract:
The chaotic leader is different from stepped leader and dart leader with distinctive features. It has many narrow pulses, causing strong high-frequency radiation. The pulse occurs right at the position of preceding stepped leader and dart leader, but its structure, width and interval all show significant irregularities. The chaotic leader is a new and special one with no exact definition of its pulse characterization so far.Multi-scale entropy is applied to the analysis of chaotic leader, and some key parameters applying in the lightning irregular pulse signal analysis are given after detailed analysis. Dart leader signal, stepped leader signal and the chaotic leader signal are analyzed with the given method and the results are compared, and case studies of the three-leader multi-scale entropy features prove the feasibility of this method. It's found out through statistical analysis that 3 leaders are different in entropy value especially when the scale is greater than 3, and thus they can be clearly distinguished by entropy values. Entropy value greater than 1.5 may indicate chaotic leader, and entropy value less than 1.5 is classified as stepped leader or dart leader. Furthermore chaotic leader and dart leader entropy value both increase with scales first and then stabilize but stepped leader entropy value doesn't change much. Characteristic entropy values for the chaotic leader are given: The average is about 2.0—2.1, the maximum is 2.6—2.8, and the minimum is 1.51—1.59. Based on the analysis of multi-scale entropy characteristics of 3 leaders, the physical meaning of the irregularity is also discussed. The irregularity degree of chaotic electric field pulse can be reflected by the entropy value: The greater the entropy value is, the greater the degree of irregularity. The characteristics of the electric field pulse in the waveform is directly related with the development of the discharge process. For the dart leader or stepped leader, the smaller entropy value illustrates that its discharge is regular. The chaotic leader in small scale with larger entropy directly demonstrates that in this range scale its discharge, polarity and intensity are irregular. It shows the electric discontinuity somewhere in the leader development channel during a certain period before the occurrence of subsequent stroke.

Tianjin Coastal Storm Surge Disaster Assessment Based on Urban Waterlogging Simulation Model

Duan Liyao, Xie Yiyang, Chen Jing, Zhao Yujie, Ren Yu

2014, 25(3): 354-359.

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Abstract:
Most waterlogging models for inland city use a single boundary condition, the boundary is usually set in a small or large river, with a single flow direction towards outside the region, or set on a highway or a large dam without water exchange alternatively. However, for coastal areas, the ebb and flow lead to changes in wet and dry. Adapting to the intertidal nature, the model should involve dealing with dynamic boundary.Based on urban waterlogging simulation model, the topography and geomorphology of Tianjin coastal areas, as well as the pipe network and drainage systems, are used to expand and improve Tianjin urban waterlogging simulation model. Dynamic water level is set at the coastal border, and the water level stands for the tidal level. When the tide level is higher than the coastal embankment, the tide floods into the city and causes waterlogging. Therefore, the model simulates not only rainfall waterlogging but also the submerging scenario due to storm surge invasion. The flooding scope and standing water depth are simulated using the redeveloped model for the historically typical storm tidal cases in the coastal areas of Tianjin. Referred with the collected records of disaster and actual survey, the developed model takes on skills to some extent in simulation of the submerged scenario due to storm surge invasion. Differences between the simulation and the historical records, however, are non-intentionally increased by using the latest ground elevation data. This approach is used in operational application for simulating the storm surge caused by Typhoon Damrey on 3 August 2012. The simulated flooding scope and site are closed to the actual scene, but the simulated standing water depth is larger. Much more detailed calibration should be done in future. Furthermore, the submerging scenarios caused by storm surge in several return periods are simulated. These simulations can be directly used in projecting and assessing the submerging scenario if there is a storm surge predicted to be an N-year return-level or if it has occurred. These simulations can also be directly reported to the government and business clients for early warning.

A Quantitative Method for Assessment of Regional Heavy Rainfall Intensity

Zou Yan, Ye Dianxiu, Lin Yi, Liu Aiming

2014, 25(3): 360-364.

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A quantitative method for assessment of regional heavy rainfall intensity is proposed, cases of Fujian Province are taken as examples. Based on the daily precipitation dataset of 66 stations in Fujian from 1961 to 2010, a definition of the regional heavy rainfall is first determined. Then four indices including maximum daily precipitation and maximum accumulated precipitation during the process are constructed as factors to evaluate an objective assessment model of composite intensity of regional rainfall.Using statistical methods such as percentile, the grade-level standards for the four indicating factors are studied. Finally, an assessment model of composite intensity of regional rainstorm is built. Compared with historical cases, the assessment model is reasonable and consistent with historical extreme cases.

Research and Implementation of Key Technology in MeteoGIS Web Platform

Hu Zhengguang, Zheng Weijiang, Gao Song, Luo Bing, Li Yuean

2014, 25(3): 365-374.

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Abstract:
In recent years, WebGIS plays an important role in meteorological data sharing, weather forecast and early-warning, public weather service and meteorological decision-making application. For instance, MICAPS integrated open source package SharpMap to display Web map services, and some branches develop meteorological Web service system based on commercial software such as ArcGIS and SuperMap. NINJO and MetView adopt Web Portal to integrate the WMS, WMF map services. However, there are some problems with the WebGIS application in current meteorology operational system. Generally, it is expensive and inconvenient to develop the WebGIS applications based on commercial GIS software. Open source GIS packages is also difficult for the developers to use and to ensure robustness. Besides, current WebGIS software hasn't taken meteorological data and meteorological analysis application characteristics into account.To solve the above problems, a new system named meteorology GIS (MeteoGIS) Web platform is developed with JAVA language by National Meteorological Center (NMC) for the developers and researchers. It could not only deliver kinds of heterogeneous meteorological data sources through Web efficiently, but also integrate meteorological analysis algorithms and models. The platform combines the WebGIS with meteorological operation characteristics, which could be used to develop kinds of meteorological applications systems. Besides, some current key technologies are used, such as intelligent cache, RIA, meteorological data monitoring and web map service mashup. This standard, flexible, easy and convenient meteorological WebGIS platform could be used by kinds of developers at national and in different province-level or county-level administrative regions.Based on MeteoGIS Web platform, NMC develops the national weather monitoring and warning system and some provinces develop weather forecast system and meteorological disaster response systems. These systems run stably in real-time weather operation, illustrating the key technique strong practicability and expansibility in massive data Web publishing, Web client rendering, data monitoring, and Web map service. There are still some problems to solve further, such as developing a html5 client and optimizing the load balance of the GIS server.

Technology and Implementation of Warning Information Distribution Based on Beidou Satellite

Wang Chunfang, Chen Yongtao, Li Chunlai, Jiang Kejian

2014, 25(3): 375-384.

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Abstract:
Warning information distribution (WID) is a key aspect in effective disaster risk reduction. All countries in the world are engaged in establishment and improvement of WID system over all kinds of transmission media. China has established an effective meteorological WID system based on radio, television, telephone, Internet, short message service, LED screen, village horn, etc. The system will be upgraded into a national level public emergencies WID system for all hazard events. But due to signal coverage, some areas of China are still uncovered and the time effect of WID still needs improving.Beidou satellite (BDS) is a navigation satellite system of China with short message communication capability. Its communication signal can cover all Chinese territory and surrounding areas. BDS has two communication methods, peer to peer and broadcast. The broadcast manner is of great value in improving the coverage and time effect of WID in China, especially in marine and distant land areas.However, WID based on BDS has some key problems such as low transmission rate, huge amount of redundant information (having no relevance to local area) and low reliability of long message distribution. To solve these problems, improved schemes are proposed on the system architecture, protocol stack and key issues of WID based on BDS. Feasible solutions including parallel transmission of uplink terminal, warning information encoding, affected area perception and unified message compensation are given. Based on those methods, a prototype system is established based on the protocol design including warning information network distribution, warning information BDS distribution and warning information BDS transmission.The prototype system is composed of integrated distribution platform, BDS distribution gateway, BDS command and control terminal, BDS, and BDS warning terminal. Integrated distribution platform is used for warning information input, revision, verification and distribution. BDS distribution gateway is used for protocol conversion from network distribution to BDS distribution. BDS warning terminal is used to receive warning information from BDS, filter out redundant information and give out severity discriminated warnings. Redundant information filtering is based on affected area encoding of warning message in three manners which are geocode, circle and polygon. Results can provide comprehensive analytical methods and practical experience to the establishment of WID system based on BDS or other satellite systems.

Vol.25, NO.3, 2014