VLF Imaging of Lightning-Induced Disturbances of the Lower Ionosphere

提出了一项为期三年的甚低频（VLF）观测计划，该计划在美国多个地点进行，目的是“成像”与闪电放电有关的电离层扰动。第一年的实验包括测量波多黎各、亨茨维尔、学院公园、休斯顿和斯坦福的VLF发射机信号的振幅和相位，提供一个覆盖整个大陆的大圆路径网格。瞬态电离层扰动的位置是通过在交叉和共线VLF路径上同时发生来确定的。闪电引起的电离层扰动事件是根据其特征特征来识别的，其发生是由于(i)闪电引起的辐射带高能粒子的降水，以及（ii）闪电辐射与下部电离层的直接向上耦合产生强烈的加热和电离。第二年的项目包括在阿拉巴马州亨茨维尔附近的五个紧密间隔的地点进行测量，目的是在一个紧密（但不规则）的路径网格上进行层析成像。拟议的测量计划协同受益于斯坦福大学在南极洲帕尔默的观测和最近开发的VLF在地球电离层波导中的三维传播模型。第三年的观测计划强调测量美国西南部和中南部已知高雷暴活动地区的事件发生情况。

A three year program of very low frequency (VLF) observations at multiple sites across United States is proposed for the purpose of 'imaging' ionospheric disturbances that occur in association with lightning discharges. The first year experiment involves measurement of amplitude and phase of VLF transmitter signals at Puerto Rico, Huntsville, College Park, Houston and Stanford, providing a grid of great circle paths over the continent. The location of transient ionospheric disturbancesare determined by means of simultaneous occurrences on crossing and collinear VLF paths. The lightning-induced ionospheric disturbance events are recognized on the basis of their characteristic signatures and occur due to (i) lightning-induced precipitation of energetic particles from the radiation belts, and (ii) direct upward coupling of lightning radiation to the lower ionosphere producing intense heating and ionization. The second year program involves measurements at five closely spaced sites in the vicinity of Huntsville, Alabama for the purpose of tomographic imaging on a tight (but irregular) grid of paths. The proposed measurement program synergistically benefits from Stanford observations at Palmer, Antarctica and a recently developed three dimensional model of VLF propagation in the earth-ionospherewaveguide. The third year observation program emphasizes measurement of event occurence in the south western and south-cenbtral United States region of known high thunderstorm activity.