Search

This paper reveals the dynamic movement characteristics of thunderstorms using total lightning data obtained from very low- and low-frequency (VLF/LF) location measurements. Eight thunderstorms, which were evenly distributed in the morning, midday, afternoon and evening, are selected to compare the different kinematic features over the Pearl River Delta (PRD) region in the south of China from 17 to 23 May 2014. The connected-neighbourhood labelling method is used to identify lightning clusters and obtain the centroids. Significant characterisation parameters are put forward as metrics to reveal the kinematic features of thunderstorms, including the duration time, valid area (VA), movement velocity, movement direction and farthest distance in longitude and latitude during the life cycle of the storm. A common trend is that the storms initiate in the west of the PRD region, moving to the east and disappearing after the thunderstorm travels around 106.5 km in longitude. There are two kinds of distributions to depict the property of the valid area, which are one-peak distribution with the maximum in the mature stage and two-peak distribution with a relatively smaller peak in the early time of the storm. The velocity does not show the same trend as the variation in VA which shows a steady increase or decrease during the lifetime of thunderstorms. The biggest VA and highest velocity are 891 km 2 occurring on the evening of 17 May and 204.8 km h -1 occurring on the morning of 20 May. The 19 May evening storm was the weakest, with the maximum VA and velocity being 253 km 2 and 115.3 km h -1 , respectively. The motion of eight storms shows a distinct pattern as the spread of direction distributes tightly in the range of 0–180 ∘. The movement characteristics of thunderstorms and the associated parameters may help to improve the nowcasting and forecasting system of thunderstorms in the warm season. [ABSTRACT FROM AUTHOR]

Mapping the thunderstorm electrical structure could provide an effective way for lightning-sensitive facilities protection, such as aircraft and maritime assets. However, the weather radar that is normally used to forecast storms and rainfall mainly detects precipitation in the atmosphere and indicates the existence of liquid raindrops and ice particles by reflectivity. Here, we use intra-cloud events of eight thunderstorm days in the warm season, which are detected by VLF/LF Total Lightning monitoring system, to reveal the thunderstorm electrical structures in the 300 × 300 km area of the Pearl River Delta (PRD) region. The differences in height range in four types of time intervals and three types of intro-cloud events proportions are compared on 16 May. With the proportion between 20% and 80% in the time interval of 15 min, the height distribution and the electrical structure of eight thunderstorm days are clearly exhibited. The positive IC events lie in the average height between 7.5 and 12.4 km, while the negative IC events are located between 5.3 and 11.7 km. The electrical structures show the variations during the evolution process, with a dipole structure in most circumstances, while temporary reversions are identified in the initial and the dissipating stage of thunderstorms, presenting the inverted dipole and the tripole structures. [ABSTRACT FROM AUTHOR]

To understand the distribution and seasonal changes of macrobenthos in Zhoushan sea area, two cruise surveys were carried out in the summer and winter. A total of 219 species were recorded in the sampling sediment during the two seasons. Two-way ANOVA results showed that the differences were not significant among sections in all the community parameters (species number, biomass and density) and species diversity (Shannon-Weiner index and Pielou's evenness index), but significant between seasons in species number, density and Shannon-Weiner index. This might be influenced by two factors as follows: (1) water currents' differences between seasons; (2) considerable differences in temperature between seasons. [ABSTRACT FROM AUTHOR]

• 3/10 reduced-scale shaking table experiments on CAP1400 were performed. • Rack's number, experimental scales and vertical excitation were studied. • The sliding displacement results were influenced greatly by scale effect. • The fluid pressure was greatly affected by vertical excitation. The seismic study of the spent fuel storage rack (SFSR) is of great significance for ensuring the safety of spent fuel. But it is a challenging topic for the complex nonlinear behaviors such as fluid–structure interaction (FSI), friction and impact. At present, owing to the lack of the understanding of these nonlinear behaviors, in engineering design process, the seismic analysis of SFSRs is usually conducted with a conservative method. To reduce the excessive margin in the seismic design of CAP1400 (a new reactor type developed by China) rack, we have performed a 1/10 scale shaking table experimental study in the previous work. As an extension of the previous study, a series of 3/10 reduced-scale seismic experiments considering the effect of FSI were carried out to study the scale effects in this paper. The experiments obtained friction coefficient between the rack and the tank (spent fuel pool model), the maximum sliding displacement of the rack and the fluid pressure distribution of the tank wall. Furthermore, the seismic responses of the rack under different experimental variables such as the number of racks, experimental scales and vertical excitation were derived. The results showed that the relative uncertainty of the sliding displacement response is very large. Moreover, the large sliding displacement differences between single-rack case and double-rack case indicated that fluid–structure interaction has a strong influence on sliding of rack. We adopted a generally used similarity criterion for seismic experiment of rack, and the experimental results showed the scaling analysis of fluid pressure satisfies the similarity relationship, however, the displacement results were influenced greatly by scale effect. These results can be the benchmarks for the seismic analysis of CAP1400 spent fuel storage rack under dynamic seismic loading. [ABSTRACT FROM AUTHOR]