应用气象学报

2018, 29(3)

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Abstract:

The Upgrade of GRAPE_TYM in 2016 and Its Impacts on Tropical Cyclone Prediction

Ma Suhong, Zhang Jin, Shen Xueshun, Wang Yuqing

2018, 29(3): 257-269. DOI: 10.11898/1001-7313.20180301

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Abstract:
The model reference profile and the vortex initialization scheme in GRAPES_TYM of China National Meteorological Center are modified in 2016 to improve the ability of tropical cyclone (TC) track and intensity prediction.The reference atmosphere profile is often applied in numerical weather prediction model to guarantee model integration stability and the accuracy. The reference atmosphere profile of isothermal temperature is replaced by a profile based on the horizontal mean of the model initial condition in GRAPES_TYM. It could decrease the amplitude of the perturbation of potential temperature and pressure and increase the accuracy and stability of model integration.The TC vortex initialization is a key factor to TC track and intensity numerical prediction. The TC vortex initialization scheme in GRAPES_TYM includes two parts:Vortex relocation (the vortex in the analyzed field is moved to the location analyzed by forecasters) and intensity correction. The modification of vortex initialization scheme includes two aspects:The relocation of vortex is removed, the radius of correction of the intensity is reduced to 4° from 12° in order to weaken the influence on the outer circulation of TC, which is assumed well analyzed by global model with higher resolution that provides the initial and boundary conditions for regional model.Experiments are carried out twice a day using 2014-2016 main TCs which last more than 72 h. Results show that upgrade of reference atmosphere profile could reduce the northward bias and the mean track errors especially for the mid-turning typhoon around 140°E. The modification of the radius of the intensity correction from 12° to 4° could improve TC track prediction especially for 0-72 h. GRAPES_TYM with the upgrade of reference profile and vortex initialization scheme could reduce the mean track errors by 10%(24 h), 12%(48 h), 16%(72 h), 14(96 h), and 15%(120 h) compared with the operational system.Results from 2014-2016 are also compared with results of NCEP global forecast system (NCEP-GFS). Mean track errors of GRAPES_TYM are larger than those. The track error differences are 9.2 km(24 h), 17.2 km(48 h), 18.4 km(72 h), 41.1 km(96 h) and 60.3 km(120 h), which are generally within 50 km except for 120 h prediction. GRAPES_TYM performs better than NCEP-GFS for TCs moving westward or northwestward and landing at the coast of China. The mean TC intensity errors of GRAPES_TYM within 72 h are smaller than those of NCEP-GFS.It can be found from the above results that the regional model improvements are more important for TC track prediction compared with improvements of model initial conditions which come from the global model, especially when the resolution of global model get higher and more data are assimilated. Therefore, more efforts should be put into the regional model optimization and improvement in the future.

Coverage Capacity of Hail Detection for Yunnan Doppler Weather Radar Network

Shi Baoling, Wang Hongyan, Liu Liping

2018, 29(3): 270-281. DOI: 10.11898/1001-7313.20180302

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Abstract:
Weather radar is a powerful tool for hail detecting, but the detection ability of Doppler weather radar network is influenced not only by weather radar volume coverage pattern (VCP) strategy, but also radar beam blockage due to the complex terrain in mountainous areas. Hail storm cells emerge on the low-level area far from the radar and near the cone of silence is often underestimated. In addition, meteorological scatter objects are distorted at less terrain blockage areas or even can't be detected completely at severe blockage area. Radar beam blockage by various terrain shape in mountainous region is very common, resulting in some of storm cells difficult to identify by weather radar network. Therefore, an assessment method of hail observation ability for Doppler weather radar network is proposed, based on the average height of 0℃, -20℃ level and the height of the core of storm cells. The multiple layer grid data of three-dimensional coverage for Yunnan C-band Doppler weather radar network is built up by combining the radar beam hybrid scanning method with the high-resolution Shuttle Radar Topography Mission (STRM) terrain data. According to characteristics of the hail cell stretching level, the coverage scope above 0℃ level of weather radar network is considered as an assessment method to evaluate hail detecting capabilities of weather radar network. Based on C band Doppler weather radar network in Yunnan Province, 607 hail ground report samples are collected during 2014-2016 to analyze capabilities and limitations of hail detection in the low-latitude plateau, and the detection area classification is summed up. Results show that it is reasonable for judging effects of the hailstorm detection with the height of 0℃ level and several height differences. The suitable detecting area account for roughly 75% throughout the province. Areas located in the northeast part of Zhaotong prefecture and the northeast part of Lincang prefecture are evaluated as hail detecting disadvantaged zone because of severe terrain blockage. Theoretically, with weather radars, based on the hailstorm probability during 2014-2016, over 90% hailstorm in Yunnan can be monitored and recognized effectively. About 3% hailstorm cell can be recognized when higher than 8 km, and about 6% hailstorm falls around radars that only cover below 8 km, and these may cause underestimation. 8.5% area of Yunnan is still beyond coverage, and 9 radars will be put into operational observation network. The proposed method can be used for assessing the ability of hailstorm detecting with the Doppler weather radar network quantitatively.

Comparison Analysis on Detection Performance of Ground-based Microwave Radiometers Under Different Weather Conditions

Zhang Xuefen, Mao Jiajia, Wang Zhicheng

2018, 29(3): 282-295. DOI: 10.11898/1001-7313.20180303

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Abstract:
Ground-based microwave radiometer (MWR) detects atmospheric temperature and humidity by receiving atmospheric microwave radiation, which can conduct 24-hour unattended, high-resolution observation. It can detect short-time variation of atmospheric elements. MWR is an important supplement to routine sounding. However, it has different observation accuracy at different times, seasons and weather conditions. Observation accuracy and influencing factors analyses are essential in scientific experiments and operation processes.In order to minimize error effects of radiosonde migration, results from three types of remote sensing devices under two weather conditions are compared. By analyzing differences of temperature and relative humidity between sounding and three MWRs at home and abroad of different technology systems in no-cloud and cloud samples, performances of these MWRs are evaluated.In the aspect of temperature, the correlation coefficient for MWRs and sounding is above 0.98. In no-cloud condition, errors of MWR-G and MWR-A are less than ±1℃ (the former is negative and the latter is positive). MWR-A has -1.8℃ deviation. Root mean square errors (RMSEs) of three types of MWRs increase with height. RMSEs of MWR-G, MWR-A and MWR-C are 2.2℃, 3.0℃ and 3.8℃. In cloud condition, vertical distributions of temperature error of three microwave radiometers have no significant changes in comparison with no-cloud condition. The RMSEs of three microwave radiometers in cloud condition are 0.5℃ higher than those in no-cloud condition. Microwave radiometer can identify the near surface radiation inversion layer accurately. But it's hard to identify the high-altitude inversion layer. In the aspect of relative humidity, the error of cloud samples is higher than the error of no-cloud samples, and the error of middle-high cloud samples is higher than that of low cloud samples. In no-cloud condition, RMSEs of MWR-A and MWR-C are 15% and 18%, less than the RMSE of MWR-G. In cloud condition, RMSEs of MWR-G, MWR-A and MWR-C (about 26%) are larger than those in no-cloud condition. The existence of cloud has a major influence on the detection of microwave radiometer relative humidity:No matter which height level, errors of low-middle cloud samples are bigger than those of no-cloud samples. Errors of high cloud samples are bigger than those of no-cloud samples, and the amplification of RMSE is about 10%-20%. This comparison analysis will provide some reference basis for the further improvement of the accuracy of MWR atmospheric profiles and the scientific research, promotion and operation processes of MWRs.

Consistent Correction to Ground-based Radars in the Lower Reachers of the Yangtze Based on TRMM/PR Observations

Chu Zhigang, Xu Dan, Wang Zhenhui, Han Jing, Fei Haiyan

2018, 29(3): 296-306. DOI: 10.11898/1001-7313.20180304

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Abstract:
There are almost 200 ground-based operational Doppler weather radars in China's new generation weather radar network, accumulating a large amount of radar data continuously for nearly 20 years. These historical data from weather radars are essential for researches related to China's radar climatology. However, reflectivity factors of two adjacent radars are often found inconsistent in observation overlap area, which is similar to the WSR-88D (Weather Surveillance Radar-1988 Doppler) in US. Some reflectivity differences are reported more than 3 dB. The fundamental cause for this problem is that different radar has different calibration error which will cause a reflectivity factor bias. Reflectivity differences of two adjacent radars will certainly reduce accuracy and precision of multiple radars joint Quantitative Precipitation Estimation and Nowcasting. Therefore, a ground-based radar correction method based on TRMM/PR (Tropical Rainfall Measuring Mission/Precipitation Radar) observations is proposed, which is named as Selective Comparison Method. Ground-based radar and TRMM/PR data are spatially matched and the abnormal values are gradually eliminated to extract an Optimal Matchup Datasets with relatively high correlation coefficient in the new method. Then the ground-based radar bias is calculated and corrected with the Optimal Matchup Datasets. The Selective Comparison Method is applied for consistency correction to seven S-band radars in the lower reaches of the Yangtze from May to September in 2013. Results show that annual reflectivity factor biases of three radars are greater than 1.5 dB among seven ground-based radars in the research area. These biases lead to some differences in adjacent radar observations and bring about a significant spatial discontinuity in multiple radar reflectivity fields. After correction, the average reflectivity differences of seven radars significantly decrease from 1.8 dB to 0.5 dB. Furthermore, all reflectivity differences between two adjacent radars are less than 1.0 dB. The reflectivity factor consistency and spatial continuity of multiple radars are greatly improved. Comparing to the traditional Geometric Matchup Method, the Selective Comparison Method performs better, and it overcomes the problem that some radars may be over-corrected. This correction method is only suitable for the quality control of historical ground-based radar data because TRMM/PR stopped its observations in 2014. Further improvements are still needed to extend this method to GPM/DPR to achieve real-time radar data processing in the future.

Simulation of Basin Topography Impacts on Rainstorm in Sichuan

Duan Jingxin, Zhao Tianliang, Xu Xiangde, Lu Chunsong, Li Yueqing, Chen Zhilong, Guo Xiaohao, Cheng Xiaolong, Zhao Yang, Meng Lu

2018, 29(3): 307-320. DOI: 10.11898/1001-7313.20180305

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Abstract:
Topography, especially the height and shape conditions have significant effects on precipitation. Previous studies focus on effects of mountain topography upon precipitation, while influencing mechanisms of the basin topography are not widely discussed. The Weather Research and Forecasting (WRF) with Chemistry model is used to simulate a heavy rain event which occurs on 20 July 2012, over Sichuan Basin. A sensitive test is designed in which the topography of Sichuan Basin is uplifted, with other conditions the same as the control test. The topography in the sensitivity test shows a trend of slow decline from west to east, eliminating the role of basin topography, but keeping the influence of the Tibetan Plateau around the Basin.From the atmospheric dynamics, thermal and cloud micro-physics standpoints, diagnostic analysis is used to analyze results of these two tests, and differences between two experiments are discussed. Results show that the time of heavy rainstorm in the control test is later than that in the sensitivity test, and the rainfall intensity in control test is strongly enhanced. From the point of atmospheric dynamics, when southwesterly airflow through the basin from south, a stronger positive vorticity center forms in the south of the Basin in the lower layer of troposphere in the control test, and southern wind is weakened. Therefore, the water vapor and energy reach the northern part of the Basin later, leading to the precipitation delaying. At the same time, with the southward wind transport, the positive relative vorticity of the lower layer in the northern part of the Basin is continuously strengthened. Favorable dynamic structure strengthens the vertical motion and thus increases the precipitation intensity. From the thermodynamic view, there is more heat and water vapor in control test due to its lower height. Besides, these variables accumulate subjected to topographic dynamics, and are less likely to diffuse, providing sufficient water vapor for the rainstorm. In addition, the high temperature and high humidity condition makes the low level of the control test accumulates moist static energy. When airflow carrying moist static energy reaches the northwest of the Basin, strong upward is stimulated under the influence of topography and the positive relative vorticity in the lower troposphere. From the opinion of micro-physics, the stronger vertical motion provides advantage for the vertical development of the cloud system, and more water vapor provides greater supersaturation for precipitation particles in the control test. Under these conditions, precipitation particles, especially rain water, snow crystals and graupel, are generated and transformed in large quantities, enhancing the precipitation intensity to heavy rainstorm.

The Inconsistency of Forecasting in Operational Numerical Prediction Products

Guo Dafeng, Duan Mingkeng, Xia Minhui, Chen Xiangxiang

2018, 29(3): 321-332. DOI: 10.11898/1001-7313.20180306

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Abstract:
The inconsistency of the forecast reflects evolution characteristics with time of the prediction error of continuous multiple prediction at a fixed time in the future. In order to explore the inconsistency of forecasting products in operational numerical forecasting applications, 12 h precipitation and 2 m ground temperature, which are predicted by three numerical models GQEC, T639 and GQJP from November 2015 to October 2016 are analyzed. Quantitative calculation method of Jumpiness index is adopted by considering the sensitivity of the index to the target region.The inconsistency of the numerical model in three different regions is studied by means of statistical analysis and typical case study. Results show that for statistical average, the inconsistency of the numerical models increases with the extension of the forecast time. Long time prediction inconsistency is greater. Jumpiness index of precipitation and temperature is related to the magnitude of the change, and Jumpiness index of precipitation is larger than that of temperature. It also shows that results of two consecutive temperature forecast are more consistent. The temperature prediction ability of the model is better than that of precipitation forecast. The comparison of different numerical models shows that GQEC has obvious advantages in many aspects. Although Jumpiness index of GQJP is less than T639, its jumping frequency is greater, indicating its prediction consistency is inferior to T639. There are seasonal differences in jumping frequency of model products. Both the jump frequency of precipitation and temperature is the highest in summer and the lowest in winter. The inconsistency test of two typical cases of rainstorm and cold air cooling process further corroborates statistical analysis results. Results also show that the forecast inconsistency of the numerical model is not only related to the geographical position, but also to the selected area size. The larger the region is, the smaller Jumpiness index becomes, and vice versa. In addition, the spatial distribution of Jumpiness index in the region is related to geographical location and topography. In general, where elements change bigger, Jumpiness index becomes greater there. The regional distribution of Jumpiness index of different meteorological elements is different. The index value of Jumpiness index of 12 h precipitation forecast increases gradually from north to south in region Ⅰ. While 2 m ground temperature prediction, Jumpiness index from north to south in region Ⅰ gradually decreases.

Simulations of Aerosol Influences on the East Asian Winter Monsoon

Ma Xiaolin, Gao Xining, Liu Yu, Guo Zengyuan

2018, 29(3): 333-343. DOI: 10.11898/1001-7313.20180307

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Abstract:
As the most active circulation system in the northern hemisphere in winter, the east Asian winter monsoon has an important influence on weather and climate in east Asia. In recent years, the concentration of aerosol keeps increasing, and the east Asian winter monsoon is influenced by its change. Numerical simulation experiments are carried out to study the influence using NCAR/UCAR CAM5.1 model, adopting the aerosol emission source of years of 2000 and 1850 each, and models are run from 1991 to 2010 for 20 years. Results from 2001 to 2010 in winter are analyzed.It is found that the increase of aerosols reduces the winter monsoon in the southeastern China and northeastern Asia (35°-55°N, 115°-150°E). At the same time, causing precipitation to reduce and temperature to drop in the southeastern region of China. The increase of aerosols changes the distribution of atmospheric heat sources, resulting in the heat source on the southeastern region of China weakened, and heat sinks strengthened; heat sinks in the northeastern China are weakened and heat sources on Japan Islands are strengthened. The production of potential energy is weakened, and the consumption is enhanced. Another result is that the change of heat source and heat sink is mainly caused by the change of latent heat of condensation, and the change of latent heat generated by large scale process plays a key role. Besides, in the southeastern and northeastern regions of China, the conversion from the divergent wind kinetic energy into the full potential energy increases, resulting in the divergent wind weakening. At the same time, the conversion from the divergent wind into the non-divergent wind in this area is weakened, causing the weakening of the non-divergent wind, and finally resulting in the weakening of east Asian winter monsoon. Through direct and indirect climate effects, aerosol affects heat balance and precipitation, changes the distribution of atmospheric heat sources and thermal structures, leading to changes in the full potential energy and kinetic energy as well as the transformation between them, and ultimately causing the weakening of the east Asian winter monsoon. The impact of aerosol increase on east Asian winter monsoon cannot be ignored.

Application of ECMWF Ensemble Forecast Products to Rainstorm Forecast in Guangxi

Zhao Huasheng, Huang Xiaoyan, Huang Ying

2018, 29(3): 344-353. DOI: 10.11898/1001-7313.20180308

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Abstract:
Using the maximal correlation minimum redundancy algorithm and random forest regression algorithm, a rainstorm interpretation forecasting method with numerical prediction products is proposed based on the ensemble prediction system of European Center for Medium-Range Weather Forecasts (ECMWF). The precipitation forecast of 51 members in ECMWF ensemble prediction system are interpolated to weather stations, and then, the maximum related minimum redundancy algorithm is used to filter ensemble members. Finally, several member interpolations that have the highest correlation with the predictand and the least redundancy with each other are selected as input factors of the random forest regression algorithm. Furthemore, in order to make modeling samples of the forecast model more pertinence, the modeling samples are classified using the mean rainfall value of ECMWF ensemble prediction products of 51 members. That is, when the mean precipitation using ECMWF ensemble prediction products at a certain station is relatively large and there is a possibility of precipitation above the storm level, only historical samples containing a large amount of precipitation are selected as modeling samples of the forecasting model. Therefore, the forecasting model reduces the influence of the sunny and wet weather samples on the noise of the forecasting model, so that forecasting model focuses on the training of large precipitation samples. When the mean value of the predicted ECMWF ensemble precipitation at a certain weather station is small, all samples of the weather station (including samples of sunny days and heavy precipitation) are modeled so that the training of the forecasting model can reconcile the heavy rain samples and thus as far as possible to avoid the rainstorm of weather station omissions reported. This method is applied to 89 stations in Guangxi, and a 4-year cross-independent sample test forecast for 2012-2015 is carried out. The business test forecast is carried out in 2016. In the 4-year cross-independent sample test results, rainstorm TS and ETS scores of this method are all improved by 0.04-0.09 and 0.04-0.07, respectively, compared with the average value after interpolation using the precipitation forecast of 51 members in ECMWF ensemble prediction products. Results of the business trial in 2016 show that TS and ETS scores of the method for interpretation rainstorms TS and ETS scores are improved by 0.07 and 0.05, respectively, compared with average values of pre-interpolation methods for the precipitation forecast of 51 members in ECMWF ensemble prediction products. It shows that the proposed rainstorm precipitation method of ECMWF ensemble prediction products has advantageous effects on forecasting and practical application forecast.

Meteorological Model of Wire Icing Caused by Rime and Glaze Based on the Process Judgment

Chen Bailian, Hu Xinxin, Wu Xi, Cheng Zhigang

2018, 29(3): 354-363. DOI: 10.11898/1001-7313.20180309

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Abstract:
Due to lack of detail observations of wire icing processes under natural environment, evolution characteristics of wire icing processes isn't very clear and the modeling is difficult. To solve this problem, under the support of the National Research Funds for Public Welfare, a special equipment for automatic monitoring the mass of ice accretion on wires is successfully trial-manufactured and employed in field observation experiments carried out in Guizhou. During the field observation experiments from January 2011 to March 2013, plenty of detail observations of wire icing process are obtained, including minutely evolution of ice mass and relative meteorological elements, which provide conditions for subsequent research. Using the experiment data, evolution characteristics of wire icing processes and relative meteorological conditions are investigated. Results show that there are five different evolution phases in the whole icing process, including beginning, growth, persistence, fading and dispelling of the ice-coat, and the judgment criteria of meteorological conditions are found out. A numerical model describing wire icing processes caused by rime and glaze is developed and applied to simulate observed wire icing processes.Based on the theoretical model frame for wire icing which is universally accepted, and combined with the judgment criteria of meteorological conditions, a numerical model of wire icing caused by rime and glaze based on the process judgment is presented. The model adopts improved parameterization schemes and algorithms, including respective procedures for rime and glaze icing, and takes the mass loss due to sublimation and surface evaporation into account. With the in-situ meteorological data combined with the judgment criteria of meteorological conditions, the numerical model is validated by applying to simulate observed wire icing processes. Modeling results show it is able to describe correctly the whole icing process, including growth, persistence, fading and dispelling of the ice-coat, with the maximum difference of ice-coat quality between modeling and observation less than 20%. Modeling errors come from two aspects, including calculation errors of the model itself and errors of meteorological data input. The icing model with common meteorological elements input can be used to calculate and hourly variation of mass, thickness and density of the ice-coat, and is of practical value for application. Under the condition of inputting with microphysics observations of real weather processes, the modeling result can be further improved. Furthermore, taking advantage of products from a refined local numerical weather forecast model, this icing model can be applied in predicting the evolution of the ice accretion on the real power transmission lines, and has wide application prospect.

Initial Stage of Lightning Discharges Initiated by NBE and IBP

Zhang Xiao, Zhang Yang, Zhang Yijun, Zheng Dong, Lü Weitao

2018, 29(3): 364-373. DOI: 10.11898/1001-7313.20180310

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Abstract:
Lightning initial stage is an important and fundamental physical process. How lightning initiates is a hot topics in the research of lightning physics. Initial breakdown is observed by many researchers, and the first pulse of IBP is regarded as the starting marker of intracloud lightning or cloud-to-ground lighting. Lightning discharge characteristics and laws during initial stage in a thunderstorm progress are researched based on Low-frequency E-field Detection Array (LFEDA). In 212 intracloud lightnings and cloud-to-ground lightnings of short range, 32 lightnings are initiated by NBE, accounting for 15%, and 180 lightnings are initiated by IBP, accounting for 85%. As an initial NBE (INBE), it is more isolated and larger than the first pulse of initial IBP (FIBP). The average time interval from INBE to subsequent first pulse is 7 ms, with a mid-value of 3.9 ms. The amplitude ratio between INBE and the subsequent pulse is 3.5. The above values are larger than those of FIBP with the corresponding values of 0.6 ms, 0.2 ms and 0.8. Most of the positive INBE and FIBP corresponds to an upward discharge in the initial stage while negative correspond to a downward one. The average height of INBE is 9.9 km, which is less than isolated NBE of 13.6 km. There is also a sensible difference in discharge height between isolated positive NBE and the negative one. The isolated negative NBE is much higher than the positive one. It may occur between upper positive charge region and shielding layer, which is related to the middle and upper atmosphere discharge. The average height of FIBP is 8.1 km. There are no obvious differences in discharge height between INBE and FIBP. The average speed during the first 15 ms of the lightning initiated by NBE is 3.1×10⁵ m·s^-1, with a mid-value of 3.0×10⁵ m·s^-1, which decreases with the initial altitude. The maximum and minimum average speed is 7×10⁵ m·s^-1 and 1.2×10⁵ m·s^-1, respectively. To better reveal the difference in INBE and FIBP, an estimated velocity is calculated based on the hypothesis of low-frequency pulse corresponding to a channel extending. The estimated speed of INBE is 4.7×10⁷ m·s^-1, which is faster than FIBP with a velocity of 1.5×10⁷ m·s^-1. The shorter rising time for INBE also indicates a faster velocity. There are no apparent differences in rising time, half-peak width and pulse width for INBE, NBE in process and isolated NBE. It is difficult to distinguish INBE from other NBE by pulse property.

Effects of Horizontal Charge Distribution in Thunderstorm Clouds on Lightning Discharge

Lin Hui, Tan Yongbo, Ma Yuxiang, Du Sai, Zhou Jiechen, Qiu Mengyang

2018, 29(3): 374-384. DOI: 10.11898/1001-7313.20180311

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Abstract:
The charge structure of thunderstorm and its internal charge distribution is an important subject in the field of atmospheric electricity research, because it has a direct impact on characteristics of lightning discharge. Influences of different charge structures in thunderstorm on lightning discharge are studied in many aspects, such as lightning types, polarity, and scales, however, but there are few quantitative investigations on effects of the horizontal distribution. Therefore, based on the existing stochastic lightning parameterization scheme, a thundercloud model is set up based upon the work of Stolzenburg et al.(1998) revealing charge structure with four charge regions within convective updrafts in thunderstorms and a negative screening layer usually exists at the top of storms. Parameters that control the horizontal distribution of charge is introduced, and then 2-dimensional fine-resolution lighting discharge simulations are performed. Results show that horizontal distribution forms of charge in upper positive region play a key role in lightning discharge, and with forms of charge changes from dense unevenness into single uniform, lightning type changes from positive cloud-to-ground flashes to positive intra-cloud flashes, then into negative cloud-to-ground flashes, and finally into positive intra-cloud flashes in limited cases. When the distribution of charge levels in the main negative charge region tends to be uniform, the type of lightning changes from negative cloud-to-ground flashes to positive intra-cloud flashes, then to positive cloud-to-ground flashes and finally to positive intra-cloud flashes in limited cases. The horizontal distribution of space charge has a significant effect on the propagation of lightning leader. If it is dense uneven, the leader propagates in the center of the charge density, otherwise, the leader can extend more than 10 to 20 km in the horizontal direction. As the horizontal distribution of charge in the charge region tends to be uniform, potential lines between two charge regions are concentrated towards the charge density center, and the potential well extends horizontally, causing the different initial potential values of the lightning trigger points, which result in the generation of different types of lightning and far-spreading lighting leader in the horizontal direction.

Vol.29, NO.3, 2018