综合治理是地震前兆台站防雷保护的必由之路

雷电灾害是气象自然灾害的一个组成部分。地震前兆台站的防雷问题是一个十分重要的问题,然而防雷技术目前在国际上尚未过关。经过多年的研究与实践,该文作者及其同事认为,综合治理是地震前兆台站防雷保护的必由之路。     

Water table control on rill initiation and implications for erosional response

On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.     

人工引发雷电的静态摄影及特性分析

展示和分析了人工引发雷电的近距离静态摄影照片,从中可以获取雷电某些宏观特征的有用信息。     

空中触发闪电的下行先导及其接地行为

１９９６年夏季在江西南昌附进行的人工触发闪电野外实验中,用新开发的不接地的火箭－导线技术成功地在雷暴云下的负环境电场中触发了云对地产偿电。我们用一套成像率为１０００幅／秒的高速数字化摄像系统对下行负先导进行了观测。     

冷涡雹暴闪电特征分析

分析１９９６－１９９７年４次冷涡雹暴过程中获取的闪电定位７１３雷达回波资料。其结果表明：在降雹前１５分钟,闪电次数存在一个酝酿和跃增过程,到隐雹出现时,闪电次数达到最大值;降雹过后,闪电次数缓慢下降。其中云内闪电和总闪电频数分布与这一现象对应较好。通过对闪电闪击区域与地面和雹位置进行叠加和比较,发现两者吻合较好,应用闪电位置和强度资料与雷达回波图象相叠加,发现闪电出现频繁的区域,正好对应于雷达强回     

中国区域闪电分布和闪电气候的特点

利用1998年1月1日到2003年12月31日TRMM卫星探测到18～38°N、74～123°E闪电资料,对中国区域年、季、日发生闪电频数和随经纬度变化,闪电密度分布和闪电气候特征进行了计算分析。结果表明:中国陆地区年均日发生总闪电数约54600次,白天占到54.47%,夜间占到45.53%,昼夜比为1.2。日闪电频数的年变化是双峰值,闪电主要发生在4～9月,占年总闪电的92%。4月中到5月中旬为次峰值,主峰值在7月中到8月中旬,占年总闪电的43.4%,夏季6～8月占到60%,11月到次年2月发生闪电很少,仅占年总闪电的0.4%以下。日变化以单峰值为主,峰值范围宽,年均每小时达到2275次左右,傍晚18时达到最高峰值,占到日出现闪电的9.1%,上午9～11时达到日变化的最低谷,仅占日出现闪电总的3%,闪电峰值是低谷的12倍,说明中国区域闪电高发时间主要在傍晚。中国区域年均发生闪电频数随纬度的变化要比随经度的变化大,沿海的陆地区出现闪电频数比内陆区高,内陆区比海区高,东部比西部高的特点。4个季节发生闪电峰值的日变化时间表明,不同季节出现闪电峰值的日时段不同,冬季主要在中午,秋季主要在下午,春季主要在晚间,夏季主要在傍晚。中国区域年均白天、夜间和昼夜不同闪电密度分布表明,东部比西部高,闪电高密度区相对较集中。区域对比说明,白天发生闪电     

The physics of thundercloud and lightning discharge. Comment on the note by Earle Williams and Sharon Stanfill The physical origin of the land–ocean contrast in lightning activity

The arguments and conclusions of the commented Williams and Stanfill article in relation to the validity of the thermal and aerosol hypotheses advanced in order to explain the land–ocean contrast in lightning activity are critically re-examined. This re-examination reveals that the analysis presented by these authors is incomplete, thus weakening the corresponding conclusions. To cite this article: C. Pontikis et al., C. R. Geoscience 336 (2004).     

重庆市地形对雷电灾害主要致灾因子影响分析

利用2007—2016年重庆市闪电监测资料及该区域数字高程模型,使用GIS空间分析、数理统计等方法,研究了雷电灾害两种主要致灾因子(闪电密度、强度)与3类地形因素(海拔高度、坡度、坡向)之间的关系。结果表明海拔高度、坡向对地闪密度具有影响,坡度与地闪密度呈负相关关系;不同坡向分类之间的地闪强度分布具有明显差异,海拔高度、坡度与地闪强度不相关。     

2007—2018年金衢盆地地闪气候特征大数据分析

本文选取2007—2018年金华地区地闪资料，研究分析金衢盆地地闪大数据的气候特征，及地闪资料与地形、海拔高度的对应关系.结果显示：1）2007—2018年金华地区地闪年均次数为45 481次，年均地闪密度为4.3次·km^-2·a^-1，地闪密度变化范围为2.64~5.92次·km^-2·a^-1；2）2007—2018年金华地区逐年地闪空间分布差异大，各年的空间分布不均匀，地闪主要分布在西南角的仙霞岭及其至会稽山沿线，以及兰溪市、婺城区及金东区交界的金华山，而东南角海拔较高的大盘山和北面的龙门山的总地闪密度高值面积较小；3）将总地闪密度分段与地形、海拔高度对比显示，80次·km^-2以上总地闪密度与高海拔山区有较好的一致性，强地闪（电流强度100 kA以上）密度为5~7次·km^-2的25个点中有23个点分布在海拔208~989 m山区；4）下垫面电阻率较低的三江流域地区地闪密度为金衢盆地内最大的"洼地"，杭长铁路及附近的地闪密度仅接近平均值，这与其他相关研究结论不一致；5）2007—2018年中有41.7％年份的地闪次数和总地闪次数随海拔高度增加，其他年份的地闪强度均值和总地闪强度均值随海拔高度增长，且均通过了显著性检验.     

Urban hailstorms: a view from Alberta

Urban hailstorms are rarely studied in detail. This work documents five urban storms in Alberta where damage has, on three occasions, set the record for Canada's most costly natural disaster. Information from newspapers, insurance companies, and disaster assistance programs was utilized to supplement meteorological records and information obtained from public surveys.The record-breaking hail swath which accompanied the 1987 Edmonton tornado was mapped using over 800 responses to an unprecedented newspaper survey. Tennis ball sized hail struck 125 km² of the city. Record-sized hailstones for Alberta were collected. Citizens' measurements of giant hailstones were compared to laboratory measurements. The rural storms were tracked using lightning detector information and damage was mapped using crop insurance and disaster assistance claims. The tornado-bearing storm was found to have a unique track.A late-season hailstorm which struck Calgary in 1991 was mapped using homeowner insurance claims organized by postal areas. Nine out of thirty areas had claims rates exceeding 50%, mainly for shingle replacement. Experiences of claims adjustors and an informal public survey were also utilized. Rural storms were mapped using weather radar and crop losses. The radar beam was strongly attenuated when it passed through hail-bearing storms and, thus, its ability to detect large hail was compromised.Weather conditions, urban and rural damaged areas, and insurance payments were compared for all five local hailstorms. These storms were discussed within the context of the long history of Alberta hail research and current trends in technology implementation. Forecasting of these hailstorms using conventional severe weather indicators was difficult in Calgary because of that city's proximity to the mountains. Hailstorms that struck Munich, Denver, and Toowoomba (Australia) were also discussed, and the hailstones collected from the great Munich storm were compared to those collected from the Edmonton storms.