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空中人工引发雷电的正负先导特征研究 总被引:3,自引:3,他引:3
通过对 1998年 8月 2 2日空中引发雷电先导过程的光、电观测资料的综合分析发现 ,在空中引发雷电的先导系统中存在三个先导过程。①向下发展的负先导在起始阶段呈小阶梯特征 ,阶梯之间的时间间隔约为 2 0 μs ,阶梯的上升时间小于 1μs,随着负先导的下行发展 ,梯级增长。②金属导线上端向上发展的正先导在负先导接地之后 ,表现出明显的阶梯特性 ,阶梯之间的时间间隔平均为 15 μs。③从地面向上发展的连接正先导由多个振荡脉冲组成 ,脉冲之间的时间间隔约为 13μs,连接先导的发展也是梯级的。电场快变化中的高频分量随着距离的增加衰减很快。最强的发光是由向下的负先导接地时形成的小回击产生的 ,强光只集中在空气离化而形成的放电通道部分 ,光强则随着高度的增加很快衰减 ,其传播速度约为 2 .1× 10 8m·s-1。在小回击发生之前 ,向下发展的负先导在接地之前有较强的发光 ,而金属导线上端向上发展的正先导没有明显的发光。在小回击发生之后 ,金属导线上端向上正先导的发光强度被增强 ,其向上的传播速度约为 2 .4× 10 6m·s-1。金属导线部分在小回击发生之后约 2 2 0μs逐渐开始熔化发出强光 ,并向上发展而与前面向上发展的正先导的发光相并合 ,其传播速度约为 1× 10 6m·s-1 相似文献
45.
利用闪电宽带干涉仪系统对闪电的观测表明,地闪和云闪的云内闪电通道都存在双向发展的特征. 闪电在云中负电荷区域初始激发以后,在通道两端发生向不同方向同时发展的击穿过程. 这两种击穿过程均产生较强的辐射,且辐射频谱特征十分相似,表明云内闪电通道两端发生的击穿过程可能均为负击穿过程. 相应电场变化表明闪电通道双向发展期间伴随着负电荷的向上转移. 这一观测事实与Kasemir早期提出的闪电通道双向发展的概念有一定的差异. 相似文献
46.
利用2002年夏季青海野外观测慢天线电场变化仪资料,应用小波变换模极大方法对地闪首次回击辐射场的检测及多重分形谱特征进行了分析.发现小波分解在小尺度上的时间变异系数在回击主脉冲峰处(回击点)呈现明显的尖峰,据此可对回击点进行快速可靠的检测;地闪回击辐射场多重分形谱可用推广的多重分形二项倍增串级公式比较精确地拟合,最小标度指数及谱宽度平均分别为-011和15,是重要的回击特征参数,而小波及多重分形应是闪电信号处理的重要工具. 相似文献
47.
Correlations between gastropod shell dissolution and water chemical properties in a tropical estuary 总被引:1,自引:0,他引:1
Although poorly reported in the scientific literature, acidic waters characterize many South East Asian estuaries. The observation of shell dissolution in a typically marine gastropod whelk (Thais) prompted investigation into determining relationships between shell properties of this whelk and the water chemistry (including pH) of the Sungai Brunei estuary (Borneo) in which it occurs. Shell weight, shell length and topographical shell features were determined for populations of Thais gradata distributed along a gradient of pH and salinity ranging between 5.78 and 8.3 pH units, and 3.58 and 31.2psu. Shell weight varied independently of the co-varying acidity, salinity and calcium levels experienced. In contrast, shell length and a semi-quantitative variable based on shell sculpturing (shell erosion rank, SER) were significantly correlated with these water chemistry variables. This study brings attention to the potential use of estuarine organisms and systems in investigating current marine acidification questions. 相似文献
48.
Mussels were maintained for 4 weeks under different combinations of dissolved oxygen concentration (1.5, 3.0 and 6.0 mg O2 l(-1)) and salinity (15, 20, 25 and 30) in a 3×4 factorial design experiment. Clearance rate (CR), absorption efficiency (AE), respiration rate (RR) and scope for growth (SFG) decreased with decreasing salinity and dissolved oxygen concentration (DO), while excretion rate (ER) increased with decreasing salinity and increasing DO. The O:N ratio was <10 at salinities of 15 and 20, irrespective of DO levels. SFG was negative in most of the treatments, except for those under 6.0 mg O2 l(-1) or at a salinity of 30 when DO was lower. The results may help explain the distribution pattern of Perna viridis in Hong Kong waters and provide guidelines for mussel culture site selection. 相似文献
49.
50.
Green-lipped mussels (Perna viridis) were exposed to Aroclor 1254 (0.5, 5 and 50 microgl(-1)) and a mixture of benzo[a]pyrene (B[a]P) and Aroclor 1254 (0.3+0.5 and 3+5 microgl(-1)) for 12 days. On day 0, 1, 3, 6 and 12, the levels of DNA strand breaks in the mussel hepatopancreas were monitored using an alkaline unwinding assay. The results were compared to the findings of a previous study in which the levels of DNA strand breakage in the same species were measured following exposure to various concentrations of B[a]P (0.3, 3 and 30 microgl(-1)). The results indicated that Aroclor 1254 at a concentration =50 microgl(-1) did not cause any increase in DNA strand breaks while B[a]P at concentrations ranging from 0.3 to 3 microgl(-1) caused an increase in strand breaks after one day of exposure, followed by an apparent rapid recovery. In contrast, exposure to 30 microgl(-1) B[a]P caused no increase in DNA strand breaks over the exposure period. This was postulated to be due to an early elicitation of the DNA repair system by the relatively high exposure level of B[a]P. This hypothesis was tested in the present study, and the results suggest that exposure to the high B[a]P concentration might have elicited the defense mechanism within the mussels, resulting in no observed increase in DNA strand breaks. An increase in strand breaks was, however, evident when the mussels were exposed to lower B[a]P levels. The levels of DNA strand breaks were correlated with the body burden of B[a]P and Aroclor 1254 but no significant relationship was observed, possibly owing to the rapid metabolism of the toxicant and/or an effective DNA repair mechanism. As a result, DNA strand breakage in the hepatopancreas of green-lipped mussels may not be a suitable biomarker of exposure to the above toxicants in the marine environment. Our findings also suggest that it would be instructive to investigate (1) the role of DNA repair enzymes in the exposed mussels; and (2) the correlation between the activity of these enzymes and the body burden of specific toxicants. 相似文献